Most governments and commercial space companies globally are now thinking about space sustainability. Global cooperation is critical to making space usable for future generations, so we have a real opportunity today to make sure this future exists. This new awareness is the result of the state and use of space today. Space is ever more used for communications, navigation and Earth observation, accelerated by the rise of mega constellations. Governments look to solve the risks that these mega constellations and spent rocket bodies have to operational satellites.
Major space and intelligence organisations worldwide are embracing non-Earth imaging (NEI) for various purposes to achieve national security objectives. Initially considered a novel sensing modality with restricted commercial licensing, NEI has evolved, and U.S. companies can now provide NEI services under the least restrictive commercial remote sensing NOAA licence (tier 1), as long as similar resolution is commercially available from a foreign entity 1.
Space is a limited and shared environment that needs careful custodianship. Space sustainability depends on commercial entities collaborating to understand and work within the constraints associated with each form of harm associated with resident space objects. If we ignore these threats, we face an imminent risk of space no longer being available to everyone for science, exploration, monitoring climate change, security, communications, and other everyday luxuries.
In this pivotal moment for the space domain, where the goal is to establish a circular space economy rapidly, NEI emerges as a valuable tool in ensuring the sustainability of the space environment, contributing to a clearer understanding of space objects and activities in orbit. This paper explores its utility beyond defence applications and highlights its significant role in enabling space sustainability. Since it’s unveiling, HEO’s satellite inspection software platform, HEO Inspect, has been actively delivering NEI to identify space junk, like “Object K” 2 and collaborating with governments to monitor rocket bodies and satellites, such as the ERS - 2 satellite 3, as they re-enter Earth’s atmosphere.
Non-Earth Imaging (NEI), also referred to as Satellite-to-Satellite imaging (sat squared) or Space-to-Space imaging (S2S), involves using space-based sensors to capture resolved imagery of Resident Space Objects (RSOs). These objects can include active or inactive spacecraft, rocket bodies and upper stages, or uncontrolled space debris.
HEO’s approach to NEI involves using ‘fly-by’ inspections, where one satellite images another satellite as it flies past, as opposed to ‘close-in’ inspection mission, which requires the imaging spacecraft to approach the RSO as a Rendezvous and Proximity Operation (RPO). Fly-by inspections do not need a dedicated platform capable of RPO, and in most cases, do it without need to manoeuvre and use propellant. These observations can be performed in a non-invasive manner, but the trade-off is that opportunities for NEI are constrained by the laws of orbital mechanics for windows when the imaging sensor is within a reasonable range (generally 30-300 kms) from the object being imaged.
To facilitate NEI at scale, HEO built HEO Inspect 2.0, a web app that allows users to task in-orbit sensors to collect resolved imagery of space objects from any internet connected device and receive results within 24 hours of successful capture. We currently employ 33 sensors in LEO with plans to grow our ecosystem to over 1000 sensors across all orbital regimes by 2027. Supporting our commitment to make space transparent and sustainable, we leverage third party sensors already in space or host our proprietary Holmes or Adler imagers on multi-use space vehicles to extend orbital coverage.
It is important to distinguish NEI from Space Situational Awareness (SSA). While SSA focuses on comprehending the risks and hazards associated with domain congestion and complexity to facilitate safe space operations, NEI contributes essential information to the broader SSA context. NEI enhances SSA by delivering in-depth details regarding the behaviour, characteristics, and capabilities of a specific object with a very high level of fidelity.
As of January 2024, 35 countries have come together to sign the Artemis Accords 4. As a multilateral arrangement between leading world governments participating in the Artemis program, the accords extend beyond the scope of lunar exploration and call out the need for a unified approach to preserving a safe and sustainable environment in space. This is critical for both public and private activities.
Similarly, it has been recognised in the G7 statement on space sustainability that Active Debris Removal services delivered by commercial entities will form an important part in maintaining space sustainability in terms of minimising the impacts of debris generated through future missions and addressing existing debris, as part of the wider action needed to address space sustainability 5.
In this paper, we explore three themes of utility for NEI in space sustainability, particularly how it can enable, de-risk and underpin many of the space sustainability activities that space leaders are calling for.
ADR missions involve the use of a spacecraft capturing and de-orbiting defunct or inactive space debris. Before launch, the ADR organisation must require detailed information about the RSO to be removed. This includes verifying the debris being removed is actually debris. In order to complete a mission safely and successfully, the organisation requires certainty on the RSO’s rotation axis and rate, possible docking ports or other fixtures to act as a capture point, any unexpected states or hazards like a broken array, and the overall condition of the object. Whilst there is usually publicly available information on a particular object, the harsh space environment could have caused unexpected damages or state changes. Ground based tracking data is invaluable for understanding the trajectory/location of an object once in space that is vital for mission planning to approach and de-orbiting the object. The key advantage of NEI is the ability to assess the orientation of the spacecraft to plan the best approach, whether the object is tumbling, and characterise the spacecraft with high confidence. Instead of relying on prior information, NEI is able to provide accurate and up-to-date information that helps paint the full picture of the object in orbit.
For example, the H-2A rocket body HEO imaged below had 34 pieces of space debris associated with its launch. In this particular case, the 18th Space Defense Squadron was able to attribute the debris to the breakup of a fairing, giving the assumption the rocket body is in its original condition 6.
This is not usually the case. Rocket bodies break up because they have a lot of complex parts and tanks of gases under pressure that can cause something to fail or burst. For instance, a breakup of a Japanese H-2A upper stage in 2019 created more than 70 pieces of tracked debris, one of which came close enough to the International Space Station to warrant a manoeuvre 7. Knowing there was a break up is an important piece of information, but which areas of the upper stage broke off are unclear through ground-based tracking sources.
How can we obtain the necessary information for a safe and successful ADR mission? One option is to perform close-in inspection of the RSO. However, this requires a dedicated mission to launch before the ADR mission which is not financially sustainable or easily scalable and is extremely high risk for further debris creation. NEI offers an alternative approach to gather critical information required for ADR mission planning without the need to launch a dedicated spacecraft or use propellant on an existing spacecraft. NEI can also be used to survey many potential RSOs in advance of any mission critical decisions during the design of the ADR spacecraft.
HEO’s imaging mission for the H-2A rocket body pictured had a 0.1 m/px resolution. With this quality, we have the ability to accurately determine an object's size, materials, assess power generation capabilities, and locate different on-board subsystems to provide a better understanding of the object's structure and appearance.
As we seek a circular space economy in space, one driver is IOSM missions. IOSM is an emerging field within the aerospace industry that involves the use of robotic technology to perform various tasks in space, such as repairing and maintaining satellites, assembling new structures like space-based solar power arrays, manufacturing materials, and refuelling satellites.
This is not an entirely new space. In recent years, significant progress has been made in this area, with several companies and research organisations working on the development of ISOM technology. Already in orbit, Hubble once found itself in trouble 8. NASA launched the STS-61 servicing mission, where astronauts added a lens to rectify the optics of the Hubble mirror, extending its lifespan from a predicted five years to almost thirty five and counting. In 2021, Northrop Grumman docked its Mission Extension Vehicle-2 to the Intelsat 10-02 communications satellite to deliver life-extension services. Demonstrating a successful manoeuvre and the need for IOSM, the spacecraft is currently providing additional years of service to the 10-02 satellite before it will undock and move on to provide services for a new mission 9.
When satellites run out of propellant, they either burn up in the atmosphere or, if they are in geosynchronous orbit, are sent to a graveyard orbit (an orbit over 36,000 kilometres above Earth)10. If they run out of propellant unexpectedly and cannot refuel or suffer a failure, they contribute to the population of space debris. Instead of sending an ADR mission, organisations are building the architecture to refuel and repair spacecraft to increase the economic viability of satellite constellations. As stated earlier, NEI has the unique ability to assess satellite attitude to determine where a docking port is pointing and verify the state of the spacecraft before a dedicated spacecraft is launched or on-orbit refuelling vehicle is deployed. NEI is a vital data source for ISOM to ensure safe, economical service or refuelling missions that will enhance operational flexibility in satellite constellations, enabling the repositioning or reconfiguration of individual satellites or constellations and reduce launches for replacement satellites.
IOSM has the potential to revolutionise the way we operate in space, making it more cost-effective and efficient. Similar to NEI’s role in ADR missions, NEI will be a vital information source in many of the IOSM activities to verify activities and characterise and monitor the state of objects, particularly as the scope and orbit regimes increase in time.
We have witnessed pieces of a satellite crash land on a sheep farm 11 and have been woken up to rumbling caused by space debris crashing nearby 12. While there are no confirmed instances of space objects colliding with aircraft, several aircraft have sustained damage from encounters with unidentified objects at high altitudes. The hazards extend beyond collisions with debris. In recent times airspace has been temporarily closed to ensure safety of aircraft and passengers during the uncontrolled reentry of a rocket body 13. The temporary closure of airspace serves as an illustration of how the economic risks associated with uncontrolled reentries are as significant as the physical risks.
Understanding and predicting the atmospheric re-entry of RSOs and their potential impact to the ground is an essential service required to mitigate physical and economic risk on Earth. When a massive RSO becomes uncontrolled at low altitude, the task of determining the re-entry window (time and location) is very difficult. This uncertainty is dominated by the effect of drag on the object’s decay, which depends on several factors, including the space vehicle’s surface area and its orientation as it re-enters.
HEO is actively studying ways to use NEI to provide precise data on both these unknowns and enable more accurate calculation of re-entry trajectory into the atmosphere and the subsequent expected debris landing zone on the Earth’s surface, potentially at several times before final re-entry 14. For example, the image below illustrates how attitude is able to be extracted from NEI.
Non-Earth imaging is a breakthrough technology that has invaluable contributions to ensure a safe and sustainable space environment. NEI is a vital information source for ADR missions, from planning, operations through to observation of the re-entry, delivering critical information to de-risk re-entry, and supporting IOSM missions. Using camera systems onboard other satellite platforms and launching HEO-owned sensors as hosted payloads on other platforms, HEO has created a steadily expanding constellation of 33 space-based sensors from which to conduct initial non-Earth imaging operations and collect detailed intelligence on RSOs in a unique ‘flyby’ operation. This inspection service can be tailored for several use cases.
As the global space sector refines our collaborative approach for space sustainability efforts and coordination, we need to garner as much information as possible, using the least resources possible, to enable safe, economical and reliable activities by all space organisations to preserve the space environment for future generations.
If you are looking to complement your mission with NEI data for space sustainability or other use cases, please reach out to the HEO team at info@heospace.com to see how we can help you win with NEI.
References
3 https://www.esa.int/Space_Safety/Space_Debris/ERS-2_spotted_by_other_satellites_during_descent
5 https://www.gov.uk/government/news/g7-nations-commit-to-the-safe-and-sustainable-use-of-space
6 https://orbitaldebris.jsc.nasa.gov/quarterly-news/pdfs/odqnv27i1.pdf
7 https://spacenews.com/space-station-maneuvers-to-avoid-debris/
8 https://science.nasa.gov/mission/hubble/observatory/missions-to-hubble/
10 https://spaceplace.nasa.gov/spacecraft-graveyard/en/
11 https://www.nytimes.com/2022/08/04/world/australia/spacex-debris-australia.html
12 https://www.abc.net.au/news/2023-08-08/space-junk-leaves-trail-across-melbourne-sky/102700674
