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Demonstrators for Conversion, Reactor, Radiator And Thrusters for Electric Propulsion Systems

Periodic Reporting for period 1 - DEMOCRITOS (Demonstrators for Conversion, Reactor, Radiator And Thrusters for Electric Propulsion Systems)

Reporting period: 2015-03-01 to 2017-02-28

DEMOCRITOS aims to conduct studies on:
1. Detailed preliminary designs of ground experiments that will allow maturing the necessary technologies in the field of MW level nuclear electric propulsion.
2. conceptualize the concept of nuclear space reactor and outline the specifications for a Core Demonstrator, based on past studies, including an analysis of the regulatory and safety framework that will be necessary for such a demonstration to take place on the ground.
3. System architecture and robotic assembly sequences that will investigate in detail the overall design of a high power nuclear spacecraft (named INPPS - International Nuclear Power and Propulsion System -) , together with a pragmatic strategy for assembly in orbit of such a large structure coupled with a nuclear reactor.
4. Programmatic aspects of an organisation that can undertake the experiments proposed in DEMOCRITOS Ground component.
5. Forming a cluster around NEP related technologies by organising an international workshop
The project has reached its conclusion. The main results of the project are:

Ground Demonstrator (WP2 and WP3):
High Level design of a ground demonstrator, based upon the test bench of the Keldysh Research Center in Moscow. The designs include details and CAD files for conversion subsystem, power management subsystem, propulsion subsystem (cluster of two high power electric thrusters), thermal management subsystem and fluidic loop. The power provided comes from a conventional gas reactor with the ability to simulate the behavior or a nuclear core. A suggestion of the ground demonstrator is that some studies on the behavior of electric thruster in clusters are needed to better understand possible issues that might arise.
1. Thrusters can interact (electrical, thermal, magnetic interactions etc.) with each other, in a way that can modify/hinder their efficient operation;
2. Thruster plume is modified, and it can modify the interaction between the thrusters and the spacecraft;
3. Performance of each thruster (thrust and other main parameters) may also be modified.
KeRC existing electric propulsion test bench will allow testing cluster of thrusters at low mass flow rate modes and with power no more than 35 kW (test bench modification of acceptable cost will be required).

Core demonstrator (WP4):
Several studies were performed under WP4. The 1992 UN Principles Relevant to the Use of Nuclear Power Sources in Outer Space specifically state that nuclear power sources for propulsive purposes are not covered in the principles. This will require a dialogue with the UN to confirm if these principles should be applied as they will influence aspects of the design. It was concluded that the small relative power and the overall scientific purpose of the Core Demonstrator places it in the category of a research reactor rather than a power reactor and justify the adoption of appropriate safety standards. Additional standards or safety measures may also be required due to the fast neutron spectrum and high temperature and pressure loops of the Core Demonstrator. This would require further investigation and would be subject to approval by the national regulatory body in the country of licensing.
The suitability of other mature space reactor concepts for the DEMOCRITOS project was examined. For this task, two existing concepts using liquid metal and gas coolants were chosen; the CEA /CNES OPUS and the USSDI /US-DOE /NASA SP-100 designs. Several standard techniques for upscaling/uprating each core design without a significant increase in volume and weight were given. An overall aim for the DEMOCRITOS project is to increase the core outlet temperature from 1300 K in order to improve thermal efficiency and reduce the size of radiator required.
The relative advantages and disadvantages of power conversion systems that are coupled, either directly or indirectly, to the primary circuit of a nuclear reactor for the generation of electricity in space were examined. The DEMOCRITOS project has decided to adopt a liquid metal cooled reactor, based on the review of reactor technologies as presented in Deliverable 4.2. This choice drives the selection of an indirect power conversion system. The indirect cycle offers advantages in terms of reduced complexity of turbomachinery, primary circuit cleanliness, terrestrial licensing, controllability and a potential system mass saving in space. This reactor uses liquid lithium as the reactor primary coolant and a secondary gas coolant as the turbomachinery working fluid in an indirect Brayton power conversion system.

Space Demonstrator (WP5)
The Concurrent Engineering (CE) workshop for DEMOCRITOS took place from the 12thto the 16th of September 2016 in the CE Facility (CEF) of DLR Bremen. The study was performed by domain experts of the consortium partners which include the European Science Foundation (ESF), the CNES Launcher Directorate (CNES-DLA), DLR institutes Bremen / Braunschweig / Lampoldshausen, the National Nuclear Laboratory (NNL), Thales Alenia Space Italia, Airbus Safran Launcher and the Keldysh Research Center. In addition, members of NASA, JAXA, SkolTech Moscow, ASL Lampoldshausen and Univer-
sity Tokyo participated as consultants and/or audited the study. The aim was to investigate a phase 0 study of the International Nuclear Power and Propulsion System, a 1MW power level spacecraft.
Two main scenarions were investigates: Scientific mission to Europa and high power transportation tag to Mars (non manned). The workshop produced preliminary designs with 2 different radiator arrangments at dry masses of ~55 tonnes and ~45 tonnes. Radiator areas are very high for both designs with a ~2.500 sq met surface. This is one of the main issues with deployment of such craft. The cost of such an endeavour is calculated at this stage at ~1Billion euros per year for 10years of development, assuming sufficient progress has been made in certain key technologies.
The project was a coordination and support action with the aim to create an international network around NEP and successful channels have been established in Europe, Russia, US , Japan and Brazil.
Due to the enormity of the undertaking of a 1MW nuclear spacecraft, it is judged that only in the decade 2030-2040 would such a spacecraft be feasible and it should be the next ISS endeavor is space on behalf of humanity. The six benefits of nuclear electric propulsion (NEP) Icompared to chemical powered rockets to MARS and deep space destinations:
1) shorter travel time,
2) an order of magnitude higher payload mass,
3) relative low mass for the spacecraft to be transported into high Earth orbit (for equivalent capabilities with traditional propulsion means),
4) especially for missions after the first one, only additional electric thruster fuel and new payload have to be added,
5) long term cost reduction, because of re-usability of INPPS and
6) disruptive space technology / transportation program realization with only initial higher technology development costs than chemical space transportation in