Final Report Summary - DEPLOYTECH (Large Deployable Technologies for Space)
Executive Summary:
DEPLOYTECH is a three part project whose primary focus is the increase in Technology Readiness Level (TRL) of promising deployable space technologies. The three technologies concerned are:
• Inflatable structural components for satellites in the micro-nano satellite categories;
• Bistable Reeled Composite (BRC) deployable booms (with special reference to solar array applications) for mid-large sized satellites;
• Closed-section lenticular carbon fibre deployable booms for solar sails.
Project Context and Objectives:
The overall objective of this project was to develop three innovative large space deployable technologies.
InflateSail Development
The test platform for the inflatable structure is a 3U CubeSat called InflateSail. It is earmarked for launch with QB50 (a multi-CubeSat mission) to an altitude of approximately 320 km. InflateSail is a technology demonstration mission and consists of a 10 m2 gossamer drag sail connected to the satellite body by a 1 m long inflatable-rigidisable mast. The large surface area of the deployed sail increases the aerodynamic drag on the satellite, and thereby causes it to rapidly deorbit. The complete system (deployable mast and deployable gossamer sail) is a technology demonstrator for an end-of-life satellite deorbiting system, aimed at mitigating the issue of space debris.
InflateSail will first inflate and rigidise the deployable mast, before deploying its gossamer sail. The purpose of the inflatable mast is to separate the sail from the host satellite body, reducing the likelihood of any interaction between the sail and the host satellite’s appendages, and also increasing the aerodynamic stability of the combined system. Placing the drag sail sufficiently far aft of the system centre of mass allows the system to align itself with the incoming air flow, much like the feathers of an arrow stabilise it during flight. This ensures that a maximum drag area is presented, and the satellite is therefore removed from orbit as rapidly as possible.
Cool Gas Generator Development
In support of the InflateSail development of an inflatable-deployable structure, TNO and CGGT focused on developing the inflation subsystem. A Cool Gas Generator (CGG) was developed that is able to deliver the gas required for the inflation of the structure. This document summarizes the work that has been carried out during the three years of the project. It will reference towards the design and test documents that have been produced during the project.
This report is based on the final presentation given to the EU in Brussels on February 2nd 2015. The different slides are expanded in text and where possible reference is made to the different official documents that have been made.
DLR Booms & Deployment Unit for GOSSAMER 2
The third part of the DEPLOYTECH project focuses on closed-section lenticular carbon fibre deployable booms for solar sails of DLR, their deployment mechanisms and specifically their scalability. The developed booms and mechanisms are designed for a 20 m x 20 m solar sail demonstrator featuring a full attitude and limited orbit control. This demonstrator, called Gossamer-2, is a scaled up successor of a smaller deployment demonstrator for solar sail technology, Gossamer-1. Gossamer-2 being the second step of 3 steps is part of the DLR/ESA´s “Gossamer Roadmap”, aiming to scale deployable technology in order to mature them and increase TRL, in a top-down manner regarding system size and complexity.
Cool Gas Generator (CGG)
In the first section, the start of Deploytech will be discussed, including the set-up of the requirements. In the second section, the design process of the Small Modular CGG will be discussed and in the third section, the production and testing of the SMCGG’s is described. In the final section, the design, test and verification documentation is given.
Proposal phase
In the proposal for Deploytech, the CGG was identified as an interesting option to inflate small inflatable structures. Before Deploytech two options were available:
1) A pressurized gas system with a tank, valves and a regulator. Used in most inflatable structures that have flown in space. Advantage: proven and qualified technology, gas at ambient temperature. Disadvantage: complex, may leak, high pressure, expensive, not easy to miniaturize, limited life time
2) Hot gas generator as used in the American Mars landers. Advantage: proven technology, simple and rugged, long life time. Disadvantage: only for short duration inflation, hot gas cause several thermal problems, not available in Europe (although basic gas generator technologies do exist in Europe)
Deploytech wanted to explore a new European technology, the Cool Gas Generator, developed by TNO in the Netherlands. It is similar to a hot gas generator, except that it produces a pure gas at ambient temperature instead of a mixture of hot gasses. The CGG allows for a simple and rugged system with a long life time, and gas at ambient temperature.
However the CGG had never been demonstrated with an inflatable system and in fact no suitable CGG existed. Therefore a new CGG design was conceived, the Small Modular CGG, short SMCGG. The idea was to design a small CGG that could be easily modified to provide different amounts of inflation gas for different applications.
The work would start at the start of Deploytech and was planned to be finished in two years with the delivery of QM CGG’s for testing at the Surrey Space Centre. The development followed a traditional approach with first an Engineering Model to be built and tested and then to progress to a Qualification Model. Spare Qualification Models might be used by SSC for flight units.
Introduction to CGG’s
Cool Gas Generators are solid propellant motors with a solid propellant charge in which the gas is chemically stored. When started, a chemical reaction is started in which the gas is formed. The reaction is designed in such a way that the residuals (chemicals that or not part of the gas that is formed) of the decomposition stay in the generator as a slack material. The generator is designed in such a way that the output gas has ambient temperature when it leaves the generator. The gas composition can be an almost pure gas. This combination extends the applicability of cool gas generators far beyond that of conventional solid propellant gas generators. Up to this moment, CGG’s for nitrogen and Oxygen have been extensively tested and are being commercialized. Furthermore CO2 and hydrogen generators are in development.
Project Results:
InflateSail
InflateSail is a technology demonstration mission for a drag deorbiting system. Two gossamer structures are deployed from a 3U CubeSat: a 1m long inflatable-rigidisable mast, and a 10 m2 drag sail supported by bi-stable CFRP deployable booms. The InflateSail satellite will be launched as part of the European QB50 mission in 2016.
The objectives of the InflateSail mission are to demonstrate the potential of a sail-mast system as an end-of-life deorbiting solution for larger satellites. The deployable sail would increase a host satellite's aerodynamic drag, thus reducing its orbital decay time. The inflatable mast provides an offset between the centre-of-mass of the host satellite and the centre-of-pressure of the gossamer sail, which facilitates passive attitude stabilisation and thereby maximises the presented drag area. Additionally, InflateSail will demonstrate the use of an aluminium-polymer laminate inflatable cylinder as a lightweight deployable structural member, and use a Cool Gas Generator (CGG) for storage and release of the inflation gas.
In the course of this project, the complete InflateSail satellite was designed, constructed, and tested. The primary engineering challenge was to design the large deployable structures to fit within the limited space available in a 3U CubeSat (10 x 10 x 34 cm) and reliably deploy to their full dimensions. The experimental payloads (the inflatable mast and deployable sail) were developed and their functionality verified through a qualification campaign.
Inflatable-Rigidisable Mast
In its deployed configuration the inflatable mast assumes a length of 1 m and diameter of 90 mm, and for launch it is folded down to a height of 63 mm using an origami pattern. The skin material consists of an aluminium-polymer laminate; after deployment the residual creases in the membrane are removed through plastic deformation of the aluminium-laminate material. This step ensures long-term structural performance of the inflatable boom, without the need to keep the boom pressurised.
The Cool Gas Generator (CGG) inflation system was custom-developed for this mission by TNO and CGG Safety and Systems. Two CGGs are installed immediately below the folded cylinder. A single CGG is sufficient to perform the inflatable deployment and rigidisation, with the second included for redundancy.
In the development of the inflatable mast, key results include:
• Development of the origami packaging technique, enabling the 1 m long boom to fold down to a height of less than 65 mm, while still being able to deploy rapidly. A key challenge was the limited dimensions of the inflatable mast, and a novel manufacturing technique was required.
• Demonstrating the efficacy of strain-rigidisation in ensuring long-term structural performance of the inflatable mast, by removing the residual creases in the Aluminium-laminate skin material. Characterising the stiffness and strength of the deployed boom was further complicated by difficulties in accurately measuring the material properties of the laminate material.
• Environmental testing of the deployable mast, including deployments in vacuum conditions using Cool Gas Generators. Under vacuum the gas release of the CGGs is very fast, requiring the inflatable mast to be able to deploy rapidly. Ascent vent tests demonstrated the ability of the inflatable to release any residual air inside the folded boom; this is required to avoid self-deployment of the boom during launch of the satellite.
Sail Deployment System
The sail deployment module consists of two components: the boom deployment system, which stores and deploys the four co-coiled CFRP booms, and the sail storage spindle, around which the four sail quadrants are wrapped. The system is an updated version of a design previously qualified at SSC, with as notable improvements a low-friction sail deployment spindle to reduce deployment loads on the booms, and a smaller boom coil to mitigate blossoming. The sail deployment system went through vibration testing and was successfully deployed at thermal extremes.
Gossamer Deorbiting System
The outcome of the InflateSail development was a 3U CubeSat with full avionics stack (antennas, radios, power system, attitude determination and control system) and two large deployable structures as payloads.
The decision to both move away from an inflatable sail structure, and to reduce the size of the sail to 10m2 was made in the first year of the project. A thorough discussion of the scale of InflateSail is given in deliverable D2.1 section 2.3: Geometry and Sizing. A quote from this section:
“Astrium performed a more thorough analysis using their thicker Kapton-aluminium laminate (see Section 2.2.7) and fixing the boom diameter at 20 mm. They assumed the maximum quantity of inflation gas is 4.5 g.
The results are given in Tab. 2.14 and Tab. 2.15. Astrium’s results indicate that the maximum attainable sail area using an inflatable sail structure is about 0.45 m2. This result was one of the main motivators in moving away from the completely inflation deployed and supported sail structure designs. This, together with the scaling arguments presented in Section 2.3.2 is largely what led to focus being placed on the two designs presented in Section 2.3.3.”
The change was discussed with reviewers at the M18 project review in Brussels. From the minutes of the meeting: “Deployed geometry discussion and further justification for InflateSail design change based on scaling laws governing inflatable boom strength (leading to delay in InflateSail design schedule)”
The proposal for DeployTech was writing by the end of 2010. At that time, the commercialization of the CGG was starting up and CGG Technologies was being planned, but was not yet founded. Therefore it was decided that CGG Technologies would be brought into the project if DeployTech should be awarded by the EU. This happened at the end of 2011 and at that time CGG technology was a functioning company. The activities were split among CGG Technologies and TNO in the following way. CGGT: lead, system design and interfaces, documentation, casing design and manufacturing, pressure and leak testing. TNO: grain design and testing, igniter design and testing, CGG testing, classification testing
System Definition Phase of Deploytech
After the project start early 2012, the system definition phase started in which the InflateSail system was defined. The start-up of this phase was slow as it took a long time to get the definition of InflateSail to a level that meaningful design work could be started on the CGG. In the second half of 2012 the first designs appeared and the first specifications were drawn up. By the end of 2012 the design work had begun.
SMCGG design
The system design activities for InflateSail continued in 2013 and the CGG design effort continued to feed the system design and analysis on InflateSail level with the best data on the CGG. In the summer of 2013, during a meeting at TNO, the design was frozen on its main requirements like the gas volume of 3 nl was finally selected. The requirements document [1] was adapted to include the decisions taken in these meetings. The first major issue of the design description [2] was completed soon after this meeting. I the second half of 2013, the design of the SMCGG was worked out in detail, especially the fluid and mechanical interfaces. In the production drawings for the grains were completed and they were already produced in third quarter of 2013 and put into storage.
During this phase, the planned test phases were re-organised to cope with the delay in the definition of the InflateSail structure and the SMCGG requirements. To compensate for the delay, the EM and QM test phases were merged into one larger test phase where first an instrumented re-usable CGG housing would be used for initial testing and if they went well, directly the QM types would be tested. The instrumented re-usable CGG was dubbed the “DM”, or Demonstration Model.
In the first quarter of 2014 the design was worked out in construction drawings for the machining company. Several sessions were held with TNO and the machining company were held to optimize the design in both mass as well as production costs. In May 2014 the drawings went to the machining company and production started.
During the test phase several small problems came up and the design was changed several times to solve them. Different types of O-ring were tried before a leak tight design was found. Besides the design of the SMCGG itself, the design phase also included the design of additional equipment. These include: moulds to produce the CGG grains, a transport box including mounting brackets and small transfer pieces to allow standard measurement equipment to be mounted on the small ports available in the DM. The results of the tests and the subsequent design changes were included in the final design description [3] which was produced at the end of the project.
Production and testing of the SMCGG
The first items that were produced for Deploytech were the moulds that were produced in September 2013 for the production of the grains. After production, the moulds had to be re-worked as the tolerances were not good enough. Valuable lessons were learned from this.
In April 2014 the main production phase started with the production of the DM and QM casings. At the same time the purchase of the smaller parts (O-rings, grates etc.) were started. Also additional equipment (transfer pieces, mounting brackets and the transport boxes were manufactured. The first test were conducted with the DM in April and May 2014. These tests involved testing of the rupturing foil system, designed to isolate the SMCGG grain from the environment. This foil was designed to rupture at a pre-determined pressure using a breaker to introduce a stress point in the foil.
With the results of these tests some changes were made in the design and the already manufactured CGG’s were returned to the machining shop for reworking. Early June the tests resumed with the Physical properties test of the DM and QM hardware. The results of these test can be found in the detailed test report [4]. All hardware passed these tests. The next tests involved pressure and leak testing of the CGG’s without propellant. During these tests, it was found that the O-ring design was leaking and a redesign was necessary. After the redesign, the CGG’s were again tested for leak and all but one passed. The CGG’s also passed the leak tests.
After these tests, the CGG were assembled with the already produced grains to form complete units. At TNO the firing test campaign started on the 9th of June 2014 and lasted for a week. First DM tests were conducted without grain and were used to confirm the breaker test results, later on different firing test were conducted. For the tests and conclusions, the reader is referenced to the test reports [4] and [5]. An important test was the classification test [6]. The results of this test showed that the CGG could be transported as a non-hazardous item.
After the tests the first CGG’s were shipped to the Surrey Space Centre for further testing with the other Deploytech hardware. These tests included three firings with Deploytech hardware in which the Inflatesail structure was inflated. [7] When the first tests were completed at Surrey, the remaining CGG’s were assembled and send to Surrey in September 2014.
Verification, documentation and other deliveries of the SMCGG
With the test results gathered with the tests at SSC a verification document [8] was established in which all requirements were checked against the test data. Most requirements were verified and those who could not be fully verified were discussed. Together with the SSC it was established that the CGG’s were fit for flying on the Inflatesail mission.
The following documents have been produced during Deploytech and have been provided to the SSC as input for formal Deploytech documentation
– Requirements document (CGGTTN-2012-09 v7)
– Detailed Design Description (CGGTTN-2013-01 v4)
– Test and verification plan (DPL-CGT-PL-01)
– Drawings of the CGG (both DM and QM versions)
– Assembly and test procedures (DPL-CGT-PR 1 to 4)
– Verification document (DPL-CGT-RP-02)
– Non formal: action lists, presentations etc.
Furthermore seven QM CGG’s have been delivered to SSC. One QM remain in the Netherlands as a mass dummy and the DM has been used for testing at TNO. The DM also remains in the Netherlands to be used in future tests.
Gossamer-2 concept – scaling up Gossamer-1 technology
As the second step in the DLR/ESA´s “Gossamer Roadmap” Gossamer-2 will be a 20 m x 20 m, 3-axis stabilized, squared solar sail deployment system featuring limited orbit and full attitude control. This is planned to be demonstrated in a 500 km altitude orbit. Furthermore deployment itself, monitored by several cameras and power generation using thin film photovoltaics will be demonstrated. It is obvious that such an ambitious system needs the suitable hardware components such as booms and deployment mechanisms.
Aiming for an ultra-light weight deployable technology that is scalable in size and complexity, system components are scaled up from the prior step in the “Gossamer Roadmap” Gossamer-1, a 5 m x 5 m in-orbit squared solar sail technology demonstrator. Like Gossamer-1, Gossamer-2 is utilizing the same basic design with two crossing CFRP booms mounted on the main satellite structure, which are deployed by four autonomously acting mechanisms, that hold the stowed sails as well as the flattened and coiled booms. The basic design is given in Figure 1, as the left image shows the Gossamer-1 solar sail and the right image the previous study leading to the “Gossamer Roadmap”, the ODISSEE 20 m x 20 m ground demonstrator of DLR and ESA. The typical deployment sequence of Gossamer-1 and Gossamer-2 is illustrated in Figure 2: Starting with a stowed spacecraft, four deployment units deploy the thin shell CFRP booms and sail quadrants simultaneously. Once the full size is achieved the deployment units jettison themselves off leaving a lighter sailcraft ready for function demonstration.
Within DEPLOYTECH booms as well as the deployment mechanisms are scaled up and designed to work for the 20 m x 20 m in-orbit sail demonstrator Gossamer-2. Figure 3 illustrates the scaling from Gossamer-1 sail size to the Gossamer-2 sail size. Here the booms are not only scaled up in length, furthermore they are scaled up in cross section, while the cross sectional geometry is adjusted to larger geometric dimensions.
Dealing with larger booms and larger sails, the deployment units as well are scaled and adapted to fit Gossamer-2, as part of the DEPLOYTECH project.
Boom Design and Manufacturing
The thin-shell CFRP booms used for Gossamer-2 and investigated within DEPLOYTECH are made of a 0.14 mm thin, 0/90 plain-weave prepreg (pre-impregnated CFRP material). The booms feature a double-Ω shaped cross section (sometimes referred to as lenticular). Each of the two crossing booms are joined from two 14 m long boom segments to a total length of about 28 m, thus using four 14 m boom segments. Gossamer-2 booms are scaled up from the Gossamer-1 booms as explained. In Figure 4 a size comparison of a Gossamer-2 boom and a Gossamer-1 boom manufactured at DLR is illustrating the size and material appearance.
To stow these large boom structures the boom are flattened in cross section and rolled up on a cylindrical hub that is part of the deployment unit. A partially flattened and rolled up boom in stowed configuration is depicted in Figure 5 a), while in Figure 5 b) the cross sectional dimensions in a fully deployed configuration and in stowed configuration is given. Although the booms possess intrinsic stresses when stowed, the booms alone do not deliver sufficient deployment force to deploy themselves and the sails. Thus, the deployment units are needed providing the deployment force and a controlled process of deployment.
The booms are manufactured from half-shells with a thickness of 0.14 mm, made of 0/90 plain weave CFRP prepreg cut to stripes. The CFRP raw material (prepreg) has an aerial weight of 94 g/m², resulting in the specific mass of the booms of about 60 to 70 g/m. After cutting the prepreg stripes roughly to size, they are formed into the 14 m long tools and cured under vacuum and high temperatures between 80 and 200 °C. Then each half shell is trimmed along the edges to the final size. The produced half shells (see Figure 6 a) are then bonded to another at their flanges using an adhesive, as shown in Figure 5 b). Followed by another curing cycle (tempering) to increase the adhesive´s strength, the finished boom can be unformed, as shown in Figure 6 b). For mechanical boom testing and deployment tests the produced 14 m boom was cut into shorter boom specimens (see Figure 7) in order to fit into the test stand and to be able to test different load regimes with undamaged booms.
Deployment Unit Design
Concept
As the interfaces of potential launch vehicles for GOS-2 are unknown the BDU should be used universally. In this regard upper and lower interface sections can be designed and attached later to the BDU. These interface sections shall also be used for accommodating the sail spools. For realizing a boom deployment in two planes like GOS-1 the BDU is based on a flip-over design.
BDU Design and Functionality
In Figure 9 the core components of the BDU design, which include the CFRP boom, the Belt Winding Mechanism, the Battery and Electronic Box, the Boom Guidance System as well as the Coiling Hub are shown. All structural components are machined out of aluminium. Only the boom guidance half shells are made out of CFRP.
The boom deployment is controlled by an electric gear motor, which is directly coupled to a winding mechanism for a steel belt. Beginning from the belt spool the steel belt is guided around a deflection pulley through the CFRP guidance half shells towards the boom spool. On one end it is attached to the belt spool and on the other end it is fixed to the boom spool. Furthermore the steel belt is co-coiled with the boom on the boom spool. The deployment of the boom is driven by the up reeling process of the steel belt by which the boom is pulled out of the coiled boom package.
Scaling and BDU dimensions
In the up-scaling process of the BDU from GOS-1 to GOS-2 size the principles of the mechanisms could be taken over but almost all geometrical dimensions must be adapted. So the boom spool width has to be adjusted to the bigger GOS-2 boom. Also the diameter of the boom spool must be changed from 100 mm to 200 mm to ensure an adequate boom coiling for reducing local buckling.
The outer dimensions of the BDU are driven by the boom spool width and diameter, the minimal necessary boom supporting length and the offset between the two deployment planes. Considering these parameters the outer dimensions follow to a length of 650 mm, a width of 300 mm and a height of 450 mm.
BDU Evolvement
A preliminary design study for a potential boom and sail deployment mechanism for GOS-2 size was performed by M. Richter during his diploma thesis. Within this study three different concepts are designed and evaluated. In the end the most suitable concept bases on a shell design, which shall entirely be made out of sandwich plates. As mentioned before the interfaces for possible space vehicles are unknown. That is why the concept for the deployment mechanism has changed toward a development of an universally useable BDU design. In Figure 10 the shell design of the preliminary design study (left) and the current prototype of the boom deployment mechanism (right) are shown.
Testing and Analysis of the Deployment Unit and Booms
BDU Thermal-Vacuum Tests
A thermal-vacuum test was performed with the prototype of the BDU at the test facilities of DLR Bremen. The main objective of this test was to demonstrate the functionality of the mechanisms and the deployment motor under thermal loading and after thermal cycling. Also an estimation of the increase in motor current for low temperature deployment should be done.
The test included 6 cycles from about +60°C to -40°C. After the last cycle a partial deployment test in the TV-chamber at a temperature of -40°C was successfully performed. During this test the motor current was measured. In comparison to room temperature the motor current was approximately doubled for thermal-vacuum conditions at -40°C. In Figure 11 a) a snapshot from the boom deployment unit in front of the thermal-vacuum chamber and from the partial deployment inside the thermal-vacuum chamber (Figure 11 b) are shown. After the thermal-vacuum test a full deployment test under ambient conditions at room temperature was done at the test facilities of DLR Braunschweig and TU Braunschweig. This test was also successfully performed without any anomalies. In conclusion the TVAC test was considered successful as all test goals have been demonstrated.
BDU Vibration Tests
Sine and random vibration tests of the deployment unit were performed in all 3 axes, followed by deployment tests to confirm functionality.
The main objectives were to: Confirm structural stability, suitability of motor for sine and random vibration loading and the approve functionality of mechanism after vibration testing.
The tested hardware was the before described qualification model of the deployment unit (BDU) comprised of the surrounding structure, a boom spool with a 6 m coiled boom, the belt mechanism with its motor as well as mass dummies resembling batteries and the electronic box. Additionally the model was equipped with several accelerometers for measurements. The CFRP boom was completely coiled up while the boom spool was locked with launch locks. In Figure 13 a) the tested BDU configuration fixed on the shaker system is shown for one tested axis. The test procedure started with a resonance survey, followed by sine vibrations, another resonance survey, random vibrations and a last resonance survey.
The applied load levels are based on a launch envelope of the Gossamer-1 project, taking different launch vehicles into account. These load levels were increased according to ECSS standard for Testing, but had to be adjusted for some test runs to comply with the maximum loads the shaker system is capable of. In the random vibration test very high loads were measured at the motor in the out of plane z-direction, while smaller loads at the boom spool end plate and at the side plate near the boom spool axle were detected. Overall the tests were very successful and the dynamic behavior of the BDU was consistent throughout the tests. This led to the conclusion that the structure was not damaged and no parts were loosened during these tests. Visual inspections after each test confirmed this, since no visible damages or cracks could be observed. A final deployment test under ambient conditions was successful (see Figure 13 b), and the functionality after vibrations tests was confirmed while no anomalies were observed.
BDU Test Analysis
Finite element (FE) analyses for simulating the vibration tests are performed with the FE program ANSYS R15.0. The main objective of these simulations is the validation of the FE model by comparison of measurement and simulation.
For meshing the model for all thin walled structures shell elements are used. The other parts of the model are meshed with solids. The mesh of the entire FE model consists of almost 600,000 nodes. This is shown in Figure 14. For simulating all three tested axes three different simulations are required as the boundary conditions must be adapted. The first fundamental natural frequency belongs to the longitudinal movement of the boom spool. Regarding this natural frequency a very good agreement between measurement and simulation could be observed (see Figure 15a)). Further comparisons showed that the simulated acceleration signal values differ slightly from some and strongly from other measured values. One reason for these deviations could be the non-linear dynamic behaviour of the structure caused by different effects (for example: longitudinal movement of the boom package on the spool and movement of the boom layers against each other, clearance between friction bearings and boom spool axle and more).
Mechanical Boom Testing
Mechanical testing of the considered CFRP booms for Gossamer-2 were performed within DEPLOYTECH with the objectives to determine and quantify bending, torsional and axial compression behaviour under realistic loading.
Boom bending occurs in the considered solar sail concept when loads are applied in an asymmetric fashion during deployment or in operation, when spanning the sails. This can be the case when for example one boom or sail needs higher forces to be deployed then others, due to friction or folding effects, or in the case one sail quadrant is tensioned more than an adjacent one. Here the maximum bearable bending loads in each cross sectional direction of a boom and the bending stiffness (simplified as spring rate) are important and were determined. The mechanical torsional behaviour has been investigated since combined load cases of flexural-torsional buckling and lateral-torsional buckling may occur. These are originated in asymmetric load introduction into the booms due to necessary interfaces (connections) to the sail quadrants or asymmetries in the cross sectional geometry or material of the boom. The determined torsional stiffness (torsional spring rate) gives important information about the torsional load capacity of the boom regarding the design of a sailcraft, and indicates when the boom might fail due to torsional loads. As third load type axial compression was regarded. Ideal load applications into the booms would be done in a symmetric fashion, leading to the axial compression. This is ideally for the booms since they can bear the highest loads for this type of loading. It is also the nominal load case as Gossamer-2 has a symmetric load distribution on each boom and sail. The maximum bearable load in axial direction was therefore determined. Figure 16 gives an overview of the applied loads in a cross sectional view of the boom.
The mechanical characterization and tests were performed in a vertical multi-load test stand, simulating realistic sailcraft loads on the booms, reaching over 2 floors of the building, and without the use of any gravity compensation. Booms are mounted hanging vertically with their root fixed in a massive aluminium clamping device, while its tip is freely hanging in a sensor equipped rack. The boom is positioned according to the tested specimen size with about 4.5 m in length each. The load (force) is applied under an angle of attack, utilizing a motor-pulley-system, with strings attached to an adapter at the boom tip. Furthermore to load introduction, the boom-tip-adapter holds target points for optical measurement. Forces were measured with force sensors integrated into the rack while the boom tip deflections were tracked with a photogrammetry system and additional laser sensors. The lower part of the test stand, with its rack containing the sensors and loading system as well as the photogrammetry system and the necessary computer and data acquisition system, is depicted in Figure 17 a). In Figure 17 b) the upper part of the test stand at the floor above, holding the fixed boom in its clamping device is shown.
For each load type one boom specimen with a length of 4.5 m, adding up to 3 specimens and 28 test runs in total were tested. Many test data were generated, but the bending tests show the most typical behaviour of the tested thin shell booms. When following the graph in Figure 18 a) showing the boom tip deflection versus applied loads (forces), the slope starts with a linear section in the beginning. Then, when the deflection is increased a non-linear buckling behaviour can be observed. Each drop in force in the graph indicates an occurring buckling. This continues until the largest drop in force values occurs and the boom globally buckles (column buckling) and snaps. This point of failure does not necessary have to be the same as the maximum force value as one can see in the graph.
A typical buckling pattern, when buckling failure occurs with the buckled flange and convex sides, is shown Figure 18 b). In all test runs exceeding the maximum bearable loads leading to failure, cracks and creases accompanied by breaking fibres on the CFRP boom shells were observed. This indicates local material failure.
Boom analysis – Buckling and Coiling Simulations
The packing ability of coilable booms is realized by elastic deformation of the thin boom shell material. Depending on the material properties and the geometry of the shell more or less stress states arise.
Therefore, simulation of the stowing and deploying process have been made using with ANSYS/LS-Dyna explicit FE-Software. The used boom and coiling cylinder geometries are related to the expected Gossamer-2 dimensions. Moreover a guiding shell was implemented that supports the coiling of the boom around one of the two cylinders. It is therefore a substitute for the otherwise used metallic belt. The main outcomes are the observed maximum strain values that are used to make statements on potential shell damages.
Concluding the findings one can state, that the combination of LS-Dyna and ANSYS FE-Software is able to show the qualitative means of the boom stowing and deployment processes. For generating reliable values on material strains and potential failure locations, one need to invest more calculation time for fine meshes.
Roll-Up Solar Array
The Roll-Up Solar Array development was adversely affected by procurement issues, and the poor health of one of the key members of the RolaTube organisation (see letter attached at end). Despite this, the solar array concept was taken through the design phase, and a functional Engineering Model was produced.
Potential Impact:
Potential Impact
InflateSail
A primary objective for InflateSail was the development of a technology demonstrator for a gossamer deorbiting system for larger host satellites. A 3U CubeSat was designed, built and tested, which contained two large deployable structures: a 1m long inflatable rigidisable mast and a 10m2 deployable drag sail. The system will be tested on the QB50 launch scheduled for 2016, and forms the basis of further development of European solutions for space debris mitigation.
The scientific results of InflateSail have been published in academic journals and conferences, including:
• Viquerat, A.D. Schenk, M. & Lappas, V.J (2013), "DEPLOYTECH : nano-satellite testbeds for gossamer technologies" AIAA/ASME/ASCE/AHS/ASC Structures, Structural Dynamics and Materials Conference 2013, 8–11th April 2013, Boston, Massachusetts. Paper number AIAA 2013-1805.
• Lappas, V.J. Fernandez, J.M. Stohlman, O., Viquerat, A., Prassinos, G., Theodorou, T., Schenk, M. (2013), "Demonstrator Flight Missions at the Surrey Space Centre involving Gossamer Sails. The Third International Symposium on Solar Sailing, 11–13th June 2013, Glasgow.
• Schenk, M., Kerr, S., Smyth, A.M. & Guest, S.D. (2013), "Inflatable Cylinders for Deployable Space Structures" Proceedings of the First Conference Transformables 2013, 18—20th September 2013, Seville, Spain.
• Viquerat, A, Schenk, M., Sanders, B. & Lappas, V. J. (2014), "Inflatable Rigidisable Mast For End-Of-Life Deorbiting System" European Conference on Spacecraft Structures, Materials and Environmental Testing (SSMET) 2014, April 1–4, Braunschweig, Germany.
• Schenk, M., Viquerat, A.D Seffen, K.A. & Guest, S.D. (2014), "Review of Inflatable Booms for Deployable Space Structures: Packing and Rigidisation"; Journal of Spacecraft and Rockets, Volume 51, Issue 3, pp. 762-778.
• Viquerat, A., Schenk, M., Lappas, V.J. & Sanders, B. (2015), "Functional and Qualification Testing of the InflateSail Technology Demonstrator"; 2nd AIAA Spacecraft Structures Conference, SciTech 2015, 5–9 January 2015, Kissimmee, FL.
A number of MEng/MSc theses were written on components of InflateSail:
• Andrew Smyth, "Inflatable Structures for the De-orbiting of Satellites", MEng thesis, University of Cambridge, 2013
• Stephen Kerr, "Inflatable Structures for the De-orbiting of Satellites", MEng thesis, University of Cambridge, 2013
• Charly Knight, "Characterisation of Metal-Laminate Foils for Inflatable Space Structures", MSc thesis, University of Surrey, 2014
• Thileepaan Sivamathavalingam, "Manufacturing and Testing of Inflatable Origami Booms", MSc thesis, University of Surrey, 2014
Cool Gas Generators
The SMCGG development has created a number of Economical, Scientific and Societal results that are listed here.
The CGG developed for the Deploytech project was commercialised by CGG technologies as the companies aim is to create turnover from the production and sales of Cool Gas Generators. Two channels were developed for this up till now:
Cubesat webshop:
The CGG developed for Deploytech are being marketed via the cubesatshop of ISIS BV in the Netherlands (www.Cubesatshop.com) since beginning of 2015. This marketing has given several leads but no sales yet.
Aircraft application:
The Deploytech CGG is the basis for a CGG offered to Aero Fluid Products in the US that will use it as a pneumatic emergency drive for an aircraft actuator. The product is presently in development and production and sales of several hundreds of units is expected to start in 2016. Aero Fluid products has purchased 8 CGG in 2014 for trails with their system. These trails were very successful.
Space applications:
At this moment, Airbus Defence and Space and the Surrey Space Centre have each purchased 5 shortened CGG’s of the Deploytech type for the Inflatesail mission.
Due to the Deploytech project a new innovative CGG could be developed that has good commercial potential. The Deploytech project gave the possibility to developed but also qualify the CGG and provide a first space demonstration on the Inflatesail mission. This was a great help for our company as it provided heritage and an additional product that we can market and sell.
The new IP that was generated is in the form of drawings, procedures, production and assembly plans and test results. These have been recorded. No new patentable IP has been generated by CGG technologies. The IP is protected by keeping them as company confidential records. Thy will only be shared with other organisations on a need to know basis and signing of a NDA
The test results are part of the CGG test records and are used to confirm the reliability of the CGG’s.
Economic results
• A 3 nl CGG has been developed and flight H/W has been delivered to SSC for the Inflatesail technology demonstration mission. This has been the first in-house development for CGG technologies, and DeployTech is the first “heritage” hardware project for the company
• Based on the DeployTech experience, CGGT has been asked to deliver 1.7 nl CGG units to SSC for the RemoveDebris mission
• Since January 2015, 1.7 and 3 nl CGG’s based on the Deploytech design, are being offered commercially through the Cubesatshop of ISIS (www.cubesatshop.com)
• In 2014, 8 CGG of the deploytech type have been delivered for an aircraft application. This customer has requested 100+ units of this type per year starting from 2016-2017.
• Large scale production (100+ units /yr) starts 2016/17
• Many more leads for space inflation and propulsion applications. The SMCGG is the first dedicated and proven space inflation system for cubesats
• Expected turnover resulting from Deploytech > 300 kEuro/yr for CGGT, TNO and related industries.
Scientific results
• CGG Technologies has participated in three papers, led by the Surrey Space Centre
• CGG Technologies has presented a paper in the Propulsion 2014 conference in Cologne, Germany
Societal results
• Article in the Dutch National magazine “Ruimtevaart” on Deploytech
• DeployTech is regularly mentioned on Linked groups on Cool Gas Generators and Inflatable Structures
DLR Gosssamer 2 Booms
Within the project duration of DEPLOYTECH several publications were generated such as: “Design and Sizing of the GOSSAMER Boom Deployment Concept” by Marco Straubel, presented at the 3rd International Symposium on Solar Sailing in Glasgow, Scotland, 2013, “Structural Concept Selection for the DEPLOYTECH / GOSSAMER Boom Deployment Mechanism” by Martin Richter, presented at the Space Structures, Materials and Environmental Testing Conference – SSMET in Braunschweig, Germany, 2014, and the planned publication “Environmental Testing and Analysis of a Boom Deployment Mechanism for GOSSAMER-2” by Sebastian Meyer to be presented at the IAC 2015 - 66th International Astronautical Congress in Jerusalem, Israel, 2015. Furthermore a student final thesis (Diploma thesis, Martin Richter, Structural Concept Selection for the DEPLOYTECH / GOSSAMER Boom Deployment Mechanism, Technische Universität Braunschweig, 2014) has been realized supporting the DEPLOYTECH project and leading to the afore mentioned publication. To exploit knowledge and bringing people together within the European space community, DLR supported by ESA and CNES organized the Conference Space Structures, Materials and Environmental Testing Conference – SSMET, held in Braunschweig, Germany in 2014, with a dedicated Session for Gossamer structures.
The acquired hardware for testing and the generated expertise within DEPLOYTECH will be used for future student projects dealing with Gossamer structures, and are giving a good research platform for student education in technical fields.
Highly relevant is the exchange of knowledge, expertise and findings with other European researchers and institutions that has been put into practice within DEPLYOTECH, and will be of high value for future joint projects that are currently planned with several DEPLOYTECH partners.
List of Websites:
Main Website
www.deploytech.eu
InflateSail Test Videos (Public)
https://www.youtube.com/watch?v=DlXDjxcsj3g
more videos
Project website at Surrey
https://www.surrey.ac.uk/ssc/research/space_vehicle_control/deploytech/mission/index.htm
DEPLOYTECH is a three part project whose primary focus is the increase in Technology Readiness Level (TRL) of promising deployable space technologies. The three technologies concerned are:
• Inflatable structural components for satellites in the micro-nano satellite categories;
• Bistable Reeled Composite (BRC) deployable booms (with special reference to solar array applications) for mid-large sized satellites;
• Closed-section lenticular carbon fibre deployable booms for solar sails.
Project Context and Objectives:
The overall objective of this project was to develop three innovative large space deployable technologies.
InflateSail Development
The test platform for the inflatable structure is a 3U CubeSat called InflateSail. It is earmarked for launch with QB50 (a multi-CubeSat mission) to an altitude of approximately 320 km. InflateSail is a technology demonstration mission and consists of a 10 m2 gossamer drag sail connected to the satellite body by a 1 m long inflatable-rigidisable mast. The large surface area of the deployed sail increases the aerodynamic drag on the satellite, and thereby causes it to rapidly deorbit. The complete system (deployable mast and deployable gossamer sail) is a technology demonstrator for an end-of-life satellite deorbiting system, aimed at mitigating the issue of space debris.
InflateSail will first inflate and rigidise the deployable mast, before deploying its gossamer sail. The purpose of the inflatable mast is to separate the sail from the host satellite body, reducing the likelihood of any interaction between the sail and the host satellite’s appendages, and also increasing the aerodynamic stability of the combined system. Placing the drag sail sufficiently far aft of the system centre of mass allows the system to align itself with the incoming air flow, much like the feathers of an arrow stabilise it during flight. This ensures that a maximum drag area is presented, and the satellite is therefore removed from orbit as rapidly as possible.
Cool Gas Generator Development
In support of the InflateSail development of an inflatable-deployable structure, TNO and CGGT focused on developing the inflation subsystem. A Cool Gas Generator (CGG) was developed that is able to deliver the gas required for the inflation of the structure. This document summarizes the work that has been carried out during the three years of the project. It will reference towards the design and test documents that have been produced during the project.
This report is based on the final presentation given to the EU in Brussels on February 2nd 2015. The different slides are expanded in text and where possible reference is made to the different official documents that have been made.
DLR Booms & Deployment Unit for GOSSAMER 2
The third part of the DEPLOYTECH project focuses on closed-section lenticular carbon fibre deployable booms for solar sails of DLR, their deployment mechanisms and specifically their scalability. The developed booms and mechanisms are designed for a 20 m x 20 m solar sail demonstrator featuring a full attitude and limited orbit control. This demonstrator, called Gossamer-2, is a scaled up successor of a smaller deployment demonstrator for solar sail technology, Gossamer-1. Gossamer-2 being the second step of 3 steps is part of the DLR/ESA´s “Gossamer Roadmap”, aiming to scale deployable technology in order to mature them and increase TRL, in a top-down manner regarding system size and complexity.
Cool Gas Generator (CGG)
In the first section, the start of Deploytech will be discussed, including the set-up of the requirements. In the second section, the design process of the Small Modular CGG will be discussed and in the third section, the production and testing of the SMCGG’s is described. In the final section, the design, test and verification documentation is given.
Proposal phase
In the proposal for Deploytech, the CGG was identified as an interesting option to inflate small inflatable structures. Before Deploytech two options were available:
1) A pressurized gas system with a tank, valves and a regulator. Used in most inflatable structures that have flown in space. Advantage: proven and qualified technology, gas at ambient temperature. Disadvantage: complex, may leak, high pressure, expensive, not easy to miniaturize, limited life time
2) Hot gas generator as used in the American Mars landers. Advantage: proven technology, simple and rugged, long life time. Disadvantage: only for short duration inflation, hot gas cause several thermal problems, not available in Europe (although basic gas generator technologies do exist in Europe)
Deploytech wanted to explore a new European technology, the Cool Gas Generator, developed by TNO in the Netherlands. It is similar to a hot gas generator, except that it produces a pure gas at ambient temperature instead of a mixture of hot gasses. The CGG allows for a simple and rugged system with a long life time, and gas at ambient temperature.
However the CGG had never been demonstrated with an inflatable system and in fact no suitable CGG existed. Therefore a new CGG design was conceived, the Small Modular CGG, short SMCGG. The idea was to design a small CGG that could be easily modified to provide different amounts of inflation gas for different applications.
The work would start at the start of Deploytech and was planned to be finished in two years with the delivery of QM CGG’s for testing at the Surrey Space Centre. The development followed a traditional approach with first an Engineering Model to be built and tested and then to progress to a Qualification Model. Spare Qualification Models might be used by SSC for flight units.
Introduction to CGG’s
Cool Gas Generators are solid propellant motors with a solid propellant charge in which the gas is chemically stored. When started, a chemical reaction is started in which the gas is formed. The reaction is designed in such a way that the residuals (chemicals that or not part of the gas that is formed) of the decomposition stay in the generator as a slack material. The generator is designed in such a way that the output gas has ambient temperature when it leaves the generator. The gas composition can be an almost pure gas. This combination extends the applicability of cool gas generators far beyond that of conventional solid propellant gas generators. Up to this moment, CGG’s for nitrogen and Oxygen have been extensively tested and are being commercialized. Furthermore CO2 and hydrogen generators are in development.
Project Results:
InflateSail
InflateSail is a technology demonstration mission for a drag deorbiting system. Two gossamer structures are deployed from a 3U CubeSat: a 1m long inflatable-rigidisable mast, and a 10 m2 drag sail supported by bi-stable CFRP deployable booms. The InflateSail satellite will be launched as part of the European QB50 mission in 2016.
The objectives of the InflateSail mission are to demonstrate the potential of a sail-mast system as an end-of-life deorbiting solution for larger satellites. The deployable sail would increase a host satellite's aerodynamic drag, thus reducing its orbital decay time. The inflatable mast provides an offset between the centre-of-mass of the host satellite and the centre-of-pressure of the gossamer sail, which facilitates passive attitude stabilisation and thereby maximises the presented drag area. Additionally, InflateSail will demonstrate the use of an aluminium-polymer laminate inflatable cylinder as a lightweight deployable structural member, and use a Cool Gas Generator (CGG) for storage and release of the inflation gas.
In the course of this project, the complete InflateSail satellite was designed, constructed, and tested. The primary engineering challenge was to design the large deployable structures to fit within the limited space available in a 3U CubeSat (10 x 10 x 34 cm) and reliably deploy to their full dimensions. The experimental payloads (the inflatable mast and deployable sail) were developed and their functionality verified through a qualification campaign.
Inflatable-Rigidisable Mast
In its deployed configuration the inflatable mast assumes a length of 1 m and diameter of 90 mm, and for launch it is folded down to a height of 63 mm using an origami pattern. The skin material consists of an aluminium-polymer laminate; after deployment the residual creases in the membrane are removed through plastic deformation of the aluminium-laminate material. This step ensures long-term structural performance of the inflatable boom, without the need to keep the boom pressurised.
The Cool Gas Generator (CGG) inflation system was custom-developed for this mission by TNO and CGG Safety and Systems. Two CGGs are installed immediately below the folded cylinder. A single CGG is sufficient to perform the inflatable deployment and rigidisation, with the second included for redundancy.
In the development of the inflatable mast, key results include:
• Development of the origami packaging technique, enabling the 1 m long boom to fold down to a height of less than 65 mm, while still being able to deploy rapidly. A key challenge was the limited dimensions of the inflatable mast, and a novel manufacturing technique was required.
• Demonstrating the efficacy of strain-rigidisation in ensuring long-term structural performance of the inflatable mast, by removing the residual creases in the Aluminium-laminate skin material. Characterising the stiffness and strength of the deployed boom was further complicated by difficulties in accurately measuring the material properties of the laminate material.
• Environmental testing of the deployable mast, including deployments in vacuum conditions using Cool Gas Generators. Under vacuum the gas release of the CGGs is very fast, requiring the inflatable mast to be able to deploy rapidly. Ascent vent tests demonstrated the ability of the inflatable to release any residual air inside the folded boom; this is required to avoid self-deployment of the boom during launch of the satellite.
Sail Deployment System
The sail deployment module consists of two components: the boom deployment system, which stores and deploys the four co-coiled CFRP booms, and the sail storage spindle, around which the four sail quadrants are wrapped. The system is an updated version of a design previously qualified at SSC, with as notable improvements a low-friction sail deployment spindle to reduce deployment loads on the booms, and a smaller boom coil to mitigate blossoming. The sail deployment system went through vibration testing and was successfully deployed at thermal extremes.
Gossamer Deorbiting System
The outcome of the InflateSail development was a 3U CubeSat with full avionics stack (antennas, radios, power system, attitude determination and control system) and two large deployable structures as payloads.
The decision to both move away from an inflatable sail structure, and to reduce the size of the sail to 10m2 was made in the first year of the project. A thorough discussion of the scale of InflateSail is given in deliverable D2.1 section 2.3: Geometry and Sizing. A quote from this section:
“Astrium performed a more thorough analysis using their thicker Kapton-aluminium laminate (see Section 2.2.7) and fixing the boom diameter at 20 mm. They assumed the maximum quantity of inflation gas is 4.5 g.
The results are given in Tab. 2.14 and Tab. 2.15. Astrium’s results indicate that the maximum attainable sail area using an inflatable sail structure is about 0.45 m2. This result was one of the main motivators in moving away from the completely inflation deployed and supported sail structure designs. This, together with the scaling arguments presented in Section 2.3.2 is largely what led to focus being placed on the two designs presented in Section 2.3.3.”
The change was discussed with reviewers at the M18 project review in Brussels. From the minutes of the meeting: “Deployed geometry discussion and further justification for InflateSail design change based on scaling laws governing inflatable boom strength (leading to delay in InflateSail design schedule)”
The proposal for DeployTech was writing by the end of 2010. At that time, the commercialization of the CGG was starting up and CGG Technologies was being planned, but was not yet founded. Therefore it was decided that CGG Technologies would be brought into the project if DeployTech should be awarded by the EU. This happened at the end of 2011 and at that time CGG technology was a functioning company. The activities were split among CGG Technologies and TNO in the following way. CGGT: lead, system design and interfaces, documentation, casing design and manufacturing, pressure and leak testing. TNO: grain design and testing, igniter design and testing, CGG testing, classification testing
System Definition Phase of Deploytech
After the project start early 2012, the system definition phase started in which the InflateSail system was defined. The start-up of this phase was slow as it took a long time to get the definition of InflateSail to a level that meaningful design work could be started on the CGG. In the second half of 2012 the first designs appeared and the first specifications were drawn up. By the end of 2012 the design work had begun.
SMCGG design
The system design activities for InflateSail continued in 2013 and the CGG design effort continued to feed the system design and analysis on InflateSail level with the best data on the CGG. In the summer of 2013, during a meeting at TNO, the design was frozen on its main requirements like the gas volume of 3 nl was finally selected. The requirements document [1] was adapted to include the decisions taken in these meetings. The first major issue of the design description [2] was completed soon after this meeting. I the second half of 2013, the design of the SMCGG was worked out in detail, especially the fluid and mechanical interfaces. In the production drawings for the grains were completed and they were already produced in third quarter of 2013 and put into storage.
During this phase, the planned test phases were re-organised to cope with the delay in the definition of the InflateSail structure and the SMCGG requirements. To compensate for the delay, the EM and QM test phases were merged into one larger test phase where first an instrumented re-usable CGG housing would be used for initial testing and if they went well, directly the QM types would be tested. The instrumented re-usable CGG was dubbed the “DM”, or Demonstration Model.
In the first quarter of 2014 the design was worked out in construction drawings for the machining company. Several sessions were held with TNO and the machining company were held to optimize the design in both mass as well as production costs. In May 2014 the drawings went to the machining company and production started.
During the test phase several small problems came up and the design was changed several times to solve them. Different types of O-ring were tried before a leak tight design was found. Besides the design of the SMCGG itself, the design phase also included the design of additional equipment. These include: moulds to produce the CGG grains, a transport box including mounting brackets and small transfer pieces to allow standard measurement equipment to be mounted on the small ports available in the DM. The results of the tests and the subsequent design changes were included in the final design description [3] which was produced at the end of the project.
Production and testing of the SMCGG
The first items that were produced for Deploytech were the moulds that were produced in September 2013 for the production of the grains. After production, the moulds had to be re-worked as the tolerances were not good enough. Valuable lessons were learned from this.
In April 2014 the main production phase started with the production of the DM and QM casings. At the same time the purchase of the smaller parts (O-rings, grates etc.) were started. Also additional equipment (transfer pieces, mounting brackets and the transport boxes were manufactured. The first test were conducted with the DM in April and May 2014. These tests involved testing of the rupturing foil system, designed to isolate the SMCGG grain from the environment. This foil was designed to rupture at a pre-determined pressure using a breaker to introduce a stress point in the foil.
With the results of these tests some changes were made in the design and the already manufactured CGG’s were returned to the machining shop for reworking. Early June the tests resumed with the Physical properties test of the DM and QM hardware. The results of these test can be found in the detailed test report [4]. All hardware passed these tests. The next tests involved pressure and leak testing of the CGG’s without propellant. During these tests, it was found that the O-ring design was leaking and a redesign was necessary. After the redesign, the CGG’s were again tested for leak and all but one passed. The CGG’s also passed the leak tests.
After these tests, the CGG were assembled with the already produced grains to form complete units. At TNO the firing test campaign started on the 9th of June 2014 and lasted for a week. First DM tests were conducted without grain and were used to confirm the breaker test results, later on different firing test were conducted. For the tests and conclusions, the reader is referenced to the test reports [4] and [5]. An important test was the classification test [6]. The results of this test showed that the CGG could be transported as a non-hazardous item.
After the tests the first CGG’s were shipped to the Surrey Space Centre for further testing with the other Deploytech hardware. These tests included three firings with Deploytech hardware in which the Inflatesail structure was inflated. [7] When the first tests were completed at Surrey, the remaining CGG’s were assembled and send to Surrey in September 2014.
Verification, documentation and other deliveries of the SMCGG
With the test results gathered with the tests at SSC a verification document [8] was established in which all requirements were checked against the test data. Most requirements were verified and those who could not be fully verified were discussed. Together with the SSC it was established that the CGG’s were fit for flying on the Inflatesail mission.
The following documents have been produced during Deploytech and have been provided to the SSC as input for formal Deploytech documentation
– Requirements document (CGGTTN-2012-09 v7)
– Detailed Design Description (CGGTTN-2013-01 v4)
– Test and verification plan (DPL-CGT-PL-01)
– Drawings of the CGG (both DM and QM versions)
– Assembly and test procedures (DPL-CGT-PR 1 to 4)
– Verification document (DPL-CGT-RP-02)
– Non formal: action lists, presentations etc.
Furthermore seven QM CGG’s have been delivered to SSC. One QM remain in the Netherlands as a mass dummy and the DM has been used for testing at TNO. The DM also remains in the Netherlands to be used in future tests.
Gossamer-2 concept – scaling up Gossamer-1 technology
As the second step in the DLR/ESA´s “Gossamer Roadmap” Gossamer-2 will be a 20 m x 20 m, 3-axis stabilized, squared solar sail deployment system featuring limited orbit and full attitude control. This is planned to be demonstrated in a 500 km altitude orbit. Furthermore deployment itself, monitored by several cameras and power generation using thin film photovoltaics will be demonstrated. It is obvious that such an ambitious system needs the suitable hardware components such as booms and deployment mechanisms.
Aiming for an ultra-light weight deployable technology that is scalable in size and complexity, system components are scaled up from the prior step in the “Gossamer Roadmap” Gossamer-1, a 5 m x 5 m in-orbit squared solar sail technology demonstrator. Like Gossamer-1, Gossamer-2 is utilizing the same basic design with two crossing CFRP booms mounted on the main satellite structure, which are deployed by four autonomously acting mechanisms, that hold the stowed sails as well as the flattened and coiled booms. The basic design is given in Figure 1, as the left image shows the Gossamer-1 solar sail and the right image the previous study leading to the “Gossamer Roadmap”, the ODISSEE 20 m x 20 m ground demonstrator of DLR and ESA. The typical deployment sequence of Gossamer-1 and Gossamer-2 is illustrated in Figure 2: Starting with a stowed spacecraft, four deployment units deploy the thin shell CFRP booms and sail quadrants simultaneously. Once the full size is achieved the deployment units jettison themselves off leaving a lighter sailcraft ready for function demonstration.
Within DEPLOYTECH booms as well as the deployment mechanisms are scaled up and designed to work for the 20 m x 20 m in-orbit sail demonstrator Gossamer-2. Figure 3 illustrates the scaling from Gossamer-1 sail size to the Gossamer-2 sail size. Here the booms are not only scaled up in length, furthermore they are scaled up in cross section, while the cross sectional geometry is adjusted to larger geometric dimensions.
Dealing with larger booms and larger sails, the deployment units as well are scaled and adapted to fit Gossamer-2, as part of the DEPLOYTECH project.
Boom Design and Manufacturing
The thin-shell CFRP booms used for Gossamer-2 and investigated within DEPLOYTECH are made of a 0.14 mm thin, 0/90 plain-weave prepreg (pre-impregnated CFRP material). The booms feature a double-Ω shaped cross section (sometimes referred to as lenticular). Each of the two crossing booms are joined from two 14 m long boom segments to a total length of about 28 m, thus using four 14 m boom segments. Gossamer-2 booms are scaled up from the Gossamer-1 booms as explained. In Figure 4 a size comparison of a Gossamer-2 boom and a Gossamer-1 boom manufactured at DLR is illustrating the size and material appearance.
To stow these large boom structures the boom are flattened in cross section and rolled up on a cylindrical hub that is part of the deployment unit. A partially flattened and rolled up boom in stowed configuration is depicted in Figure 5 a), while in Figure 5 b) the cross sectional dimensions in a fully deployed configuration and in stowed configuration is given. Although the booms possess intrinsic stresses when stowed, the booms alone do not deliver sufficient deployment force to deploy themselves and the sails. Thus, the deployment units are needed providing the deployment force and a controlled process of deployment.
The booms are manufactured from half-shells with a thickness of 0.14 mm, made of 0/90 plain weave CFRP prepreg cut to stripes. The CFRP raw material (prepreg) has an aerial weight of 94 g/m², resulting in the specific mass of the booms of about 60 to 70 g/m. After cutting the prepreg stripes roughly to size, they are formed into the 14 m long tools and cured under vacuum and high temperatures between 80 and 200 °C. Then each half shell is trimmed along the edges to the final size. The produced half shells (see Figure 6 a) are then bonded to another at their flanges using an adhesive, as shown in Figure 5 b). Followed by another curing cycle (tempering) to increase the adhesive´s strength, the finished boom can be unformed, as shown in Figure 6 b). For mechanical boom testing and deployment tests the produced 14 m boom was cut into shorter boom specimens (see Figure 7) in order to fit into the test stand and to be able to test different load regimes with undamaged booms.
Deployment Unit Design
Concept
As the interfaces of potential launch vehicles for GOS-2 are unknown the BDU should be used universally. In this regard upper and lower interface sections can be designed and attached later to the BDU. These interface sections shall also be used for accommodating the sail spools. For realizing a boom deployment in two planes like GOS-1 the BDU is based on a flip-over design.
BDU Design and Functionality
In Figure 9 the core components of the BDU design, which include the CFRP boom, the Belt Winding Mechanism, the Battery and Electronic Box, the Boom Guidance System as well as the Coiling Hub are shown. All structural components are machined out of aluminium. Only the boom guidance half shells are made out of CFRP.
The boom deployment is controlled by an electric gear motor, which is directly coupled to a winding mechanism for a steel belt. Beginning from the belt spool the steel belt is guided around a deflection pulley through the CFRP guidance half shells towards the boom spool. On one end it is attached to the belt spool and on the other end it is fixed to the boom spool. Furthermore the steel belt is co-coiled with the boom on the boom spool. The deployment of the boom is driven by the up reeling process of the steel belt by which the boom is pulled out of the coiled boom package.
Scaling and BDU dimensions
In the up-scaling process of the BDU from GOS-1 to GOS-2 size the principles of the mechanisms could be taken over but almost all geometrical dimensions must be adapted. So the boom spool width has to be adjusted to the bigger GOS-2 boom. Also the diameter of the boom spool must be changed from 100 mm to 200 mm to ensure an adequate boom coiling for reducing local buckling.
The outer dimensions of the BDU are driven by the boom spool width and diameter, the minimal necessary boom supporting length and the offset between the two deployment planes. Considering these parameters the outer dimensions follow to a length of 650 mm, a width of 300 mm and a height of 450 mm.
BDU Evolvement
A preliminary design study for a potential boom and sail deployment mechanism for GOS-2 size was performed by M. Richter during his diploma thesis. Within this study three different concepts are designed and evaluated. In the end the most suitable concept bases on a shell design, which shall entirely be made out of sandwich plates. As mentioned before the interfaces for possible space vehicles are unknown. That is why the concept for the deployment mechanism has changed toward a development of an universally useable BDU design. In Figure 10 the shell design of the preliminary design study (left) and the current prototype of the boom deployment mechanism (right) are shown.
Testing and Analysis of the Deployment Unit and Booms
BDU Thermal-Vacuum Tests
A thermal-vacuum test was performed with the prototype of the BDU at the test facilities of DLR Bremen. The main objective of this test was to demonstrate the functionality of the mechanisms and the deployment motor under thermal loading and after thermal cycling. Also an estimation of the increase in motor current for low temperature deployment should be done.
The test included 6 cycles from about +60°C to -40°C. After the last cycle a partial deployment test in the TV-chamber at a temperature of -40°C was successfully performed. During this test the motor current was measured. In comparison to room temperature the motor current was approximately doubled for thermal-vacuum conditions at -40°C. In Figure 11 a) a snapshot from the boom deployment unit in front of the thermal-vacuum chamber and from the partial deployment inside the thermal-vacuum chamber (Figure 11 b) are shown. After the thermal-vacuum test a full deployment test under ambient conditions at room temperature was done at the test facilities of DLR Braunschweig and TU Braunschweig. This test was also successfully performed without any anomalies. In conclusion the TVAC test was considered successful as all test goals have been demonstrated.
BDU Vibration Tests
Sine and random vibration tests of the deployment unit were performed in all 3 axes, followed by deployment tests to confirm functionality.
The main objectives were to: Confirm structural stability, suitability of motor for sine and random vibration loading and the approve functionality of mechanism after vibration testing.
The tested hardware was the before described qualification model of the deployment unit (BDU) comprised of the surrounding structure, a boom spool with a 6 m coiled boom, the belt mechanism with its motor as well as mass dummies resembling batteries and the electronic box. Additionally the model was equipped with several accelerometers for measurements. The CFRP boom was completely coiled up while the boom spool was locked with launch locks. In Figure 13 a) the tested BDU configuration fixed on the shaker system is shown for one tested axis. The test procedure started with a resonance survey, followed by sine vibrations, another resonance survey, random vibrations and a last resonance survey.
The applied load levels are based on a launch envelope of the Gossamer-1 project, taking different launch vehicles into account. These load levels were increased according to ECSS standard for Testing, but had to be adjusted for some test runs to comply with the maximum loads the shaker system is capable of. In the random vibration test very high loads were measured at the motor in the out of plane z-direction, while smaller loads at the boom spool end plate and at the side plate near the boom spool axle were detected. Overall the tests were very successful and the dynamic behavior of the BDU was consistent throughout the tests. This led to the conclusion that the structure was not damaged and no parts were loosened during these tests. Visual inspections after each test confirmed this, since no visible damages or cracks could be observed. A final deployment test under ambient conditions was successful (see Figure 13 b), and the functionality after vibrations tests was confirmed while no anomalies were observed.
BDU Test Analysis
Finite element (FE) analyses for simulating the vibration tests are performed with the FE program ANSYS R15.0. The main objective of these simulations is the validation of the FE model by comparison of measurement and simulation.
For meshing the model for all thin walled structures shell elements are used. The other parts of the model are meshed with solids. The mesh of the entire FE model consists of almost 600,000 nodes. This is shown in Figure 14. For simulating all three tested axes three different simulations are required as the boundary conditions must be adapted. The first fundamental natural frequency belongs to the longitudinal movement of the boom spool. Regarding this natural frequency a very good agreement between measurement and simulation could be observed (see Figure 15a)). Further comparisons showed that the simulated acceleration signal values differ slightly from some and strongly from other measured values. One reason for these deviations could be the non-linear dynamic behaviour of the structure caused by different effects (for example: longitudinal movement of the boom package on the spool and movement of the boom layers against each other, clearance between friction bearings and boom spool axle and more).
Mechanical Boom Testing
Mechanical testing of the considered CFRP booms for Gossamer-2 were performed within DEPLOYTECH with the objectives to determine and quantify bending, torsional and axial compression behaviour under realistic loading.
Boom bending occurs in the considered solar sail concept when loads are applied in an asymmetric fashion during deployment or in operation, when spanning the sails. This can be the case when for example one boom or sail needs higher forces to be deployed then others, due to friction or folding effects, or in the case one sail quadrant is tensioned more than an adjacent one. Here the maximum bearable bending loads in each cross sectional direction of a boom and the bending stiffness (simplified as spring rate) are important and were determined. The mechanical torsional behaviour has been investigated since combined load cases of flexural-torsional buckling and lateral-torsional buckling may occur. These are originated in asymmetric load introduction into the booms due to necessary interfaces (connections) to the sail quadrants or asymmetries in the cross sectional geometry or material of the boom. The determined torsional stiffness (torsional spring rate) gives important information about the torsional load capacity of the boom regarding the design of a sailcraft, and indicates when the boom might fail due to torsional loads. As third load type axial compression was regarded. Ideal load applications into the booms would be done in a symmetric fashion, leading to the axial compression. This is ideally for the booms since they can bear the highest loads for this type of loading. It is also the nominal load case as Gossamer-2 has a symmetric load distribution on each boom and sail. The maximum bearable load in axial direction was therefore determined. Figure 16 gives an overview of the applied loads in a cross sectional view of the boom.
The mechanical characterization and tests were performed in a vertical multi-load test stand, simulating realistic sailcraft loads on the booms, reaching over 2 floors of the building, and without the use of any gravity compensation. Booms are mounted hanging vertically with their root fixed in a massive aluminium clamping device, while its tip is freely hanging in a sensor equipped rack. The boom is positioned according to the tested specimen size with about 4.5 m in length each. The load (force) is applied under an angle of attack, utilizing a motor-pulley-system, with strings attached to an adapter at the boom tip. Furthermore to load introduction, the boom-tip-adapter holds target points for optical measurement. Forces were measured with force sensors integrated into the rack while the boom tip deflections were tracked with a photogrammetry system and additional laser sensors. The lower part of the test stand, with its rack containing the sensors and loading system as well as the photogrammetry system and the necessary computer and data acquisition system, is depicted in Figure 17 a). In Figure 17 b) the upper part of the test stand at the floor above, holding the fixed boom in its clamping device is shown.
For each load type one boom specimen with a length of 4.5 m, adding up to 3 specimens and 28 test runs in total were tested. Many test data were generated, but the bending tests show the most typical behaviour of the tested thin shell booms. When following the graph in Figure 18 a) showing the boom tip deflection versus applied loads (forces), the slope starts with a linear section in the beginning. Then, when the deflection is increased a non-linear buckling behaviour can be observed. Each drop in force in the graph indicates an occurring buckling. This continues until the largest drop in force values occurs and the boom globally buckles (column buckling) and snaps. This point of failure does not necessary have to be the same as the maximum force value as one can see in the graph.
A typical buckling pattern, when buckling failure occurs with the buckled flange and convex sides, is shown Figure 18 b). In all test runs exceeding the maximum bearable loads leading to failure, cracks and creases accompanied by breaking fibres on the CFRP boom shells were observed. This indicates local material failure.
Boom analysis – Buckling and Coiling Simulations
The packing ability of coilable booms is realized by elastic deformation of the thin boom shell material. Depending on the material properties and the geometry of the shell more or less stress states arise.
Therefore, simulation of the stowing and deploying process have been made using with ANSYS/LS-Dyna explicit FE-Software. The used boom and coiling cylinder geometries are related to the expected Gossamer-2 dimensions. Moreover a guiding shell was implemented that supports the coiling of the boom around one of the two cylinders. It is therefore a substitute for the otherwise used metallic belt. The main outcomes are the observed maximum strain values that are used to make statements on potential shell damages.
Concluding the findings one can state, that the combination of LS-Dyna and ANSYS FE-Software is able to show the qualitative means of the boom stowing and deployment processes. For generating reliable values on material strains and potential failure locations, one need to invest more calculation time for fine meshes.
Roll-Up Solar Array
The Roll-Up Solar Array development was adversely affected by procurement issues, and the poor health of one of the key members of the RolaTube organisation (see letter attached at end). Despite this, the solar array concept was taken through the design phase, and a functional Engineering Model was produced.
Potential Impact:
Potential Impact
InflateSail
A primary objective for InflateSail was the development of a technology demonstrator for a gossamer deorbiting system for larger host satellites. A 3U CubeSat was designed, built and tested, which contained two large deployable structures: a 1m long inflatable rigidisable mast and a 10m2 deployable drag sail. The system will be tested on the QB50 launch scheduled for 2016, and forms the basis of further development of European solutions for space debris mitigation.
The scientific results of InflateSail have been published in academic journals and conferences, including:
• Viquerat, A.D. Schenk, M. & Lappas, V.J (2013), "DEPLOYTECH : nano-satellite testbeds for gossamer technologies" AIAA/ASME/ASCE/AHS/ASC Structures, Structural Dynamics and Materials Conference 2013, 8–11th April 2013, Boston, Massachusetts. Paper number AIAA 2013-1805.
• Lappas, V.J. Fernandez, J.M. Stohlman, O., Viquerat, A., Prassinos, G., Theodorou, T., Schenk, M. (2013), "Demonstrator Flight Missions at the Surrey Space Centre involving Gossamer Sails. The Third International Symposium on Solar Sailing, 11–13th June 2013, Glasgow.
• Schenk, M., Kerr, S., Smyth, A.M. & Guest, S.D. (2013), "Inflatable Cylinders for Deployable Space Structures" Proceedings of the First Conference Transformables 2013, 18—20th September 2013, Seville, Spain.
• Viquerat, A, Schenk, M., Sanders, B. & Lappas, V. J. (2014), "Inflatable Rigidisable Mast For End-Of-Life Deorbiting System" European Conference on Spacecraft Structures, Materials and Environmental Testing (SSMET) 2014, April 1–4, Braunschweig, Germany.
• Schenk, M., Viquerat, A.D Seffen, K.A. & Guest, S.D. (2014), "Review of Inflatable Booms for Deployable Space Structures: Packing and Rigidisation"; Journal of Spacecraft and Rockets, Volume 51, Issue 3, pp. 762-778.
• Viquerat, A., Schenk, M., Lappas, V.J. & Sanders, B. (2015), "Functional and Qualification Testing of the InflateSail Technology Demonstrator"; 2nd AIAA Spacecraft Structures Conference, SciTech 2015, 5–9 January 2015, Kissimmee, FL.
A number of MEng/MSc theses were written on components of InflateSail:
• Andrew Smyth, "Inflatable Structures for the De-orbiting of Satellites", MEng thesis, University of Cambridge, 2013
• Stephen Kerr, "Inflatable Structures for the De-orbiting of Satellites", MEng thesis, University of Cambridge, 2013
• Charly Knight, "Characterisation of Metal-Laminate Foils for Inflatable Space Structures", MSc thesis, University of Surrey, 2014
• Thileepaan Sivamathavalingam, "Manufacturing and Testing of Inflatable Origami Booms", MSc thesis, University of Surrey, 2014
Cool Gas Generators
The SMCGG development has created a number of Economical, Scientific and Societal results that are listed here.
The CGG developed for the Deploytech project was commercialised by CGG technologies as the companies aim is to create turnover from the production and sales of Cool Gas Generators. Two channels were developed for this up till now:
Cubesat webshop:
The CGG developed for Deploytech are being marketed via the cubesatshop of ISIS BV in the Netherlands (www.Cubesatshop.com) since beginning of 2015. This marketing has given several leads but no sales yet.
Aircraft application:
The Deploytech CGG is the basis for a CGG offered to Aero Fluid Products in the US that will use it as a pneumatic emergency drive for an aircraft actuator. The product is presently in development and production and sales of several hundreds of units is expected to start in 2016. Aero Fluid products has purchased 8 CGG in 2014 for trails with their system. These trails were very successful.
Space applications:
At this moment, Airbus Defence and Space and the Surrey Space Centre have each purchased 5 shortened CGG’s of the Deploytech type for the Inflatesail mission.
Due to the Deploytech project a new innovative CGG could be developed that has good commercial potential. The Deploytech project gave the possibility to developed but also qualify the CGG and provide a first space demonstration on the Inflatesail mission. This was a great help for our company as it provided heritage and an additional product that we can market and sell.
The new IP that was generated is in the form of drawings, procedures, production and assembly plans and test results. These have been recorded. No new patentable IP has been generated by CGG technologies. The IP is protected by keeping them as company confidential records. Thy will only be shared with other organisations on a need to know basis and signing of a NDA
The test results are part of the CGG test records and are used to confirm the reliability of the CGG’s.
Economic results
• A 3 nl CGG has been developed and flight H/W has been delivered to SSC for the Inflatesail technology demonstration mission. This has been the first in-house development for CGG technologies, and DeployTech is the first “heritage” hardware project for the company
• Based on the DeployTech experience, CGGT has been asked to deliver 1.7 nl CGG units to SSC for the RemoveDebris mission
• Since January 2015, 1.7 and 3 nl CGG’s based on the Deploytech design, are being offered commercially through the Cubesatshop of ISIS (www.cubesatshop.com)
• In 2014, 8 CGG of the deploytech type have been delivered for an aircraft application. This customer has requested 100+ units of this type per year starting from 2016-2017.
• Large scale production (100+ units /yr) starts 2016/17
• Many more leads for space inflation and propulsion applications. The SMCGG is the first dedicated and proven space inflation system for cubesats
• Expected turnover resulting from Deploytech > 300 kEuro/yr for CGGT, TNO and related industries.
Scientific results
• CGG Technologies has participated in three papers, led by the Surrey Space Centre
• CGG Technologies has presented a paper in the Propulsion 2014 conference in Cologne, Germany
Societal results
• Article in the Dutch National magazine “Ruimtevaart” on Deploytech
• DeployTech is regularly mentioned on Linked groups on Cool Gas Generators and Inflatable Structures
DLR Gosssamer 2 Booms
Within the project duration of DEPLOYTECH several publications were generated such as: “Design and Sizing of the GOSSAMER Boom Deployment Concept” by Marco Straubel, presented at the 3rd International Symposium on Solar Sailing in Glasgow, Scotland, 2013, “Structural Concept Selection for the DEPLOYTECH / GOSSAMER Boom Deployment Mechanism” by Martin Richter, presented at the Space Structures, Materials and Environmental Testing Conference – SSMET in Braunschweig, Germany, 2014, and the planned publication “Environmental Testing and Analysis of a Boom Deployment Mechanism for GOSSAMER-2” by Sebastian Meyer to be presented at the IAC 2015 - 66th International Astronautical Congress in Jerusalem, Israel, 2015. Furthermore a student final thesis (Diploma thesis, Martin Richter, Structural Concept Selection for the DEPLOYTECH / GOSSAMER Boom Deployment Mechanism, Technische Universität Braunschweig, 2014) has been realized supporting the DEPLOYTECH project and leading to the afore mentioned publication. To exploit knowledge and bringing people together within the European space community, DLR supported by ESA and CNES organized the Conference Space Structures, Materials and Environmental Testing Conference – SSMET, held in Braunschweig, Germany in 2014, with a dedicated Session for Gossamer structures.
The acquired hardware for testing and the generated expertise within DEPLOYTECH will be used for future student projects dealing with Gossamer structures, and are giving a good research platform for student education in technical fields.
Highly relevant is the exchange of knowledge, expertise and findings with other European researchers and institutions that has been put into practice within DEPLYOTECH, and will be of high value for future joint projects that are currently planned with several DEPLOYTECH partners.
List of Websites:
Main Website
www.deploytech.eu
InflateSail Test Videos (Public)
https://www.youtube.com/watch?v=DlXDjxcsj3g
more videos
Project website at Surrey
https://www.surrey.ac.uk/ssc/research/space_vehicle_control/deploytech/mission/index.htm
