Space Domain Awareness - an Earth Observation Perspective

(first published in the UK Remote Sensing and Photogrammetry Society (RSPSoc) "Sensed" journal, October 2023: https://www.rspsoc.org.uk/images/SENSED/SENSED_202310_October2023_WEB.pdf

The Importance of Space Domain Awareness

So… a small caveat. This piece is less about Earth observation [EO] specifically, and more about risks to the Earth observation industry. Plus, other ways of utilizing imaging technology developed for remote sensing. It is also a topic which spans space applications and utilizations, and a concern which is not going to go away any time soon: Space Domain Awareness [SDA].

There have always been risks in space brought about by space debris: mostly from old rocket parts in graveyard orbits. However, with a lot more hardware being launched, and continuing to be launched at rapid pace, the risk of a collision event, or conjunction, becomes more likely. Events, although infrequent, have occurred in the past, and will persist in the future. The concern is, what would happen if an event took out critical space infrastructure, or heavily pollute an orbit where a satellite constellation operates?

By 2021, the catalogued orbital population (spacecraft and debris) was over 23,000 objects, 90% of which is in Low-Earth-Orbit [LEO]. These debris are assessed by the Satellite Catalog (SATCAT) of space-based objects maintained by the US government, Combined Space Operations Center?(CSpOC). There is little data for the number of non-catalogued pieces of space debris; mostly objects <10cm. Insurance company Swiss Re estimate there is in excess of 500,000 non-catalogued pieces of space debris; ESA state there are over 130 million pieces of debris >1mm. It is widely accepted that a 10cm piece of debris would destroy a satellite and create many further pieces of debris; an object of 2cm can cause a lot of damage to a spacecraft.

The bad news for EO is that the orbit considered most at risk of a space debris event is an orbit around 800km. In LEO <500km atmospheric drag remains significant as to be able to bring down space debris for burn-up in the higher Earth atmosphere. They are considered “self-cleaning”; this is something of a misnomer, yes drag means that objects are brought into the Earth’s atmosphere, but this still takes a period of time depending on the exact altitude, mass, impact etc. The primary variable in determining the probability of collision is the spatial density of existing resident space objects. However, the collision risk increases with more satellites launched. There are also risks for satellite operators accessing higher orbits, but needing to travel through the higher risk lower orbit to position satellites. Risks would also increase with one collision due to the chain reaction effect, causing an increasing number of space debris fragments now found in the same orbital path: the Kessler syndrome.

Part of the problem for identifying risks in LEO is that the current services around SDA are geared towards assessing threats to high-value assets in GEO – such as communications satellites. Solutions are based on CSpOC data augmented by ground-based telescopes.

There is an existing SDA commercial market – albeit small, and software focused. Current solutions, such as from AGI and ExoAnalytica, provide value-adding based on CSpOC data which may be augmented by further data from optical telescopes. As part of the “New Space” paradigm there is a growing number of companies looking at SDA solutions from several approaches. These include ground-based solutions (such as LeoLabs) and space-based (such as NorthStar Earth and Space). The aim of these companies is to bring down the levels in which objects can be detected, and with higher accuracy i.e. more debris is tracked and with higher certainty that a conjunction may happen. Several orbital debris companies have also emerged with novel approaches to de-clutter the space environment: Astroscale, Turionspace, Scout etc. These companies may support mitigating strategies, remove debris, support de-orbiting strategies, or a combination of these. They may use similar camera technology to what is used in EO, but using this to monitor the environment around spacecraft assets rather than looking down at Earth. As with all New Space companies however, most are in the earlier stages of financing with greater funding required to come to fruition.

And debris isn’t the only threat. Governments have a growing concern over how space may be used as a threat to national and even global security: the key reason for the development of the U.S. Space Force. What if an adversary were about to disrupt GPS, or capture secure signals being transmitted. The unusual manoeuvres of the Russian “Luch” satellite around high-value commercial communications assets heightened commercial satellite operators’ attentions as to the potential impacts 3rd parties may have on their operations.

Despite all these concerns, however, SDA appears to be in a wait-and-see phase. To implement regulations around secure satellite operations, some kind of global consensus would be required. A significant collision in space could change everything. If this happened in the next few years – and there is a level of certainty that one will happen at some point – then it is expected that governments will need to act on the space regulatory environment. Operators will also need to be seen to be acting in the most sustainable fashion, such as investing in various SDA solutions. Insurance companies may also require that operators take on mitigating measures in insurance policies. Somewhat counterintuitively, a major event would be the most significant driver for governments and the industry as a whole to do more.?