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S4ILS Report Summary

Project ID: 658645
Funded under: H2020-EU.1.3.2.

Periodic Reporting for period 1 - S4ILS (Solar Sailing for Space Situational Awareness In the Lunar System)

Reporting period: 2015-08-08 to 2017-02-07

Summary of the context and overall objectives of the project

The 21st of May 2010 saw the dawn of a new era in space propulsion when the Japanese Space Agency launched its IKAROS spacecraft. Twenty days into the mission, IKAROS unfurled a 14x14 m2 solar sail that would take the probe on a six-month voyage to Venus. A solar sail rides on sunlight the way that sailboats ride on the wind. Therefore, propelled solely by the solar photons reflecting off the 7.5 micrometer thin, highly reflective membrane, IKAROS was the first to demonstrate a notion that had been around for nearly a century: that spacecraft can be propelled through space by sunlight.

Solar Sailing for Space Situational Awareness In the Lunar System (S4ILS) is exploiting the potential of this new, elegant and truly exciting field of space propulsion. While it is often proposed as a propulsive means for missions around the Sun or in the Sun-Earth system, S4ILS will demonstrate its potential much closer to home, in the Earth-Moon system, which opens up radically new possibilities in spaceflight.

As an enabler of diverse products and services that are crucial to modern day society (navigation, communication, Earth observation), spaceflight is increasingly and rightfully seen as a crucial part of the global infrastructure; an infrastructure that is extremely vulnerable to threats from space objects and space weather events. Examples are abundant: disrupted GPS signals and satellite communications due to solar storms; the Iridium/Cosmos satellite collision in 2009; and the asteroid that entered Earth’s atmosphere over Russia in 2013. Space situational awareness (SSA) is therefore at the top of the world’s space agencies’ agendas and is defined as one of Europe’s key space priorities.

Combining the potential of solar sailing and the need to keep ground and space assets safe from natural and man-made threats from space, the overall objective of the S4ILS project is to deliver, for the first time, radically new solar sail periodic orbits in the Earth-Moon system and utilize these for the benefit of space situational awareness. The fundamentally new orbital dynamics that S4ILS delivers, combined with the compelling application of SSA that impacts industries far beyond the aerospace sector, will underpin the need for further European solar sail technology development.

Work performed from the beginning of the project to the end of the period covered by the report and main results achieved so far

The classical three-body system (e.g. Sun-Earth-satellite or Earth-Moon-satellite) generates five equilibrium solutions: the L1- to L5-Lagrange points. At these Lagrange points, the satellite is stationary with respect to both celestial bodies and natural periodic orbits around these equilibrium points can be found. By complementing the Earth-Moon system with a solar sail, the S4ILS project has found radically new families of orbits. Here, “families of orbits” are sets of orbits that differ from one another in one single parameter, e.g., the performance of the solar sail, to obtain a range of orbits for increasing (from near- to far-term) sail performance.

The results include a catalogue of solar sail periodic orbits in the Earth-Moon system, using (where possible) the same terminology/denomination as used in the classical system. As such, “solar sail-versions” of orbits that also exist in the classical system (e.g., Lyapunov orbits, halo orbits, vertical Lyapunov orbits, and so on) have been generated, but also some radically new orbit families have been produced, including so-called “out-of-plane flower-shaped” orbits and “clover-shaped” orbits, both centered around the Earth.

In terms of SSA applications, especially the clover-shaped orbits appear highly suitable. For example, a constellation of two mirrored clover-shaped orbits can provide near-continuous (>95% of the time) coverage of the Arctic region to observe space weather events and in particular the aurora oval, which gives insight into the direct response of the magnetosphere to changes in the solar wind.

As another example, all techniques developed for the Earth-Moon system can be translated to (binary) asteroid systems to create unique, previously unknown and geostationary-equivalent vantage points from where to monitor such asteroids over extended periods of time. Improving our knowledge on (binary) asteroid systems will increase our understanding of these primordial rocks, which will be vital for planetary defense purposes.

Besides the technical work on devising the above mentioned novel solar sail orbits and their applications for SSA, the dissemination of information to and communication activities with the host institutions, the research community and the general public have formed an integral part of the outgoing phase to maximize the project’s impact. Examples of such knowledge transfer activities include colloquia, seminars, student supervision, participation in conferences, publications in peer-reviewed journals as well as the use of public websites such as the S4ILS page on the TU Delft website and dedicated pages on platforms such as ResearchGate and Facebook.

Progress beyond the state of the art and expected potential impact (including the socio-economic impact and the wider societal implications of the project so far)

S4ILS is, for the first time, performing a thorough and systematic investigation, calculation, and cataloguing of solar sail periodic orbits in the Earth-Moon system. As a result, all orbits devised are beyond the state of the art as no such solar sail periodic orbits in the Earth-Moon system have been generated before. They therefore provide new insights into solar sail dynamics and open up entirely new opportunities in the Earth-Moon system.

Regarding the applications of solar sailing for SSA, these have been explored to a very limited extent and mainly focused on using a solar sail to hover along the Sun-Earth line for early detection of solar storms (e.g., the GeoStorm concept and NASA’s previously proposed Sunjammer mission). Investigating its further potential for SSA is already revealing capabilities unrivaled by conventional propulsion techniques. Examples include the mentioned constellation of two sailcraft in a set of “clover-shaped” orbits that can provide near-continuous observation of the Artic region. Such continuous observations will significantly enhance our observations of the auroras and will be crucial to better understand the Sun-Earth connection and the impact of solar storms on the geosphere.

Although the road to true implementation and exploitation of these newly devised orbits for SSA is still very long, once there, it will have a profound impact on the European society and economy: enabling the monitoring of space debris and furthering our understanding of space weather events as well as asteroids that are on a collision path with Earth, will improve our abilities to keep ground and space assets safe. Destruction of power grids and power outages, the need for aviation re-routing, and malfunctioning of Earth-orbiting satellites means that the users that will ultimately benefit from this work extend far beyond the aerospace sector and include telecom operators, power/energy markets, airlines, Earth observation services, and many more.

It is these discoveries by the S4ILS project, both the generation of new orbits, their novel applications and previously undiscovered capabilities, that will put solar sailing firmly on the map and will underpin the need for further European solar sail technology development.

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