The Satellite TN recently had a webinar on Space Traffic Control, with a presentation by Dr Stuart Eves, SJE Space Ltd. Due to the overwhelming number of questions that were posted during the Q&A session, there wasn’t time unfortunately to get around to responding to all of them.
Stuart has kindly post event reviewed the questions and provided responses which you can see below.
If you missed the webinar the first time around, or would like to watch again OnDemand you can access it here.
Q: What will be the impact by space debris or satellites to earth in case there are situation like Carrington event or any solar flares nowadays ?
Stuart: A solar event of the size of the Carrington CME in 1859, would probably interrupt some satellite-provided services for a period of time, partly since some satellites would probably enter “safe mode” as a consequent of the transient radiation environment, and partly because the Earth’s atmosphere would scintillate and impede the effective propagation of RF signals temporarily. It is also reasonable to assume that some elderly satellites might be rendered permanently non-operational by the CME, and that these missions would then constitute part of the debris population. Since no events of this magnitude have occurred during the space era, our understanding of how severe these effects would be in practice are inevitably somewhat speculative
Q: In-orbit parking station for old satellites sounds good but what if the station gets hit by something? The entire station is essentially a giant piece of debris and a giant target?
Stuart: This is a reasonable observation. The “necropolis” would be able to manoeuvre if conjunctions were predicted, and its configuration could be designed to limit its cross-section in the ram direction. Logically, the most appropriate location for this capability would be in a relatively low-density region of Earth orbit, (e.g., somewhere around 1200 km altitude) to limit the collision risk.
Q: Which environment model gives better end of life prediction at 400 km and above?
Stuart: I am not sure which models yield the best results, but the more parameters that are included in the model, (e.g., an accurate model of the object shape), and the more forces that are taken into account, the better the lifetime prediction will be. At present, our estimates are typically accurate to about 10% of the remaining lifetime of the object, and clearly, we would wish to do better than this.
Q: Is it more realistic at this point to start focusing more on shielding satellites from impact instead of focusing on deorbit and removal?
Stuart: Unfortunately, the energies involved make shielding a mass-inefficient approach in most cases. Whipple shielding is employed on manned missions, (the ISS, for example), but for unmanned systems, the commercial case for shielding is unsustainable.
Q: How does, Space traffic look, in terms of future of human civilization.
Stuart: Looking to the future, if we don’t implement space traffic control, we are likely to compromise access to LEO, and the many services, (including climate monitoring), that are provided by satellites there. We may find other ways to acquire those services, but satellites are the most efficient.
Q: If STC is required, do you see this as a regulated by a new organisation or the extension of a mission of an existing expert body?
Stuart: An extension to the mission of the United Nations is probably the most stable construct
Q: Do you think the rapidly falling cost of satellite deployment will make satellite companies more willing to incorporate deorbit systems within their designs and fuel budgets as they become less mass constrained, or will it take laws forcing them to do so before they consider such measures?
Stuart: Particularly for constellation operators, it is clear that any derelict satellites at their orbital altitude represent a hazard to their own in-orbit assets. I’m confident that satellite operators will increasingly act in their own interests and will incorporate some form of de-orbit provision in their designs.
Q: Are you aware of any work to reach an understanding of the risk that an Earth magnetic field reversal could have on LEO systems?
Stuart: Please see the GNOSIS blog page, where you’ll see that we are planning a workshop on 5th October 2022 to discuss “Black Swan” events, one of which is a magnetic reversal!!
Q: Are there any international agreements to prevent ASAT tests?
Stuart: Not yet, although proposals have been made to UN in this regard, and I believe the US have recently made a unilateral commitment to avoid such tests, (to their great credit).
Q: How would you rate the overall responses of each constellation to debris and astronomy concerns?
Stuart: Starlink certainly get some credit for trying to reduce the reflectivity of their satellites, (although their latest batches of satellites are physically larger missions, which has pushed their visual magnitude up again). They have at least reduced the “light pollution” for naked eye observers, but their satellites are nowhere near dark enough to avoid causing problems for the professional astronomy community. They have an automated collision avoidance system, which is also good, and their relatively low orbits ensure that their satellites won’t be around for too long, (even if they fail to deliberately de-orbit at the end of their lives), because they see a fair amount of drag.
OneWeb deserve credit for working with Astroscale to include a capture mechanism in their satellite design in order to facilitate the de-orbit of any of their satellites which fail prematurely. Their satellites are at much higher altitudes than Starlink, and hence are illuminated by the Sun for significantly longer. For this reason, they represent a greater problem for the astronomy community, and to date I haven’t seen any evidence that they’re doing anything specific to address this issue, (although I’d love to be proved wrong).
Q: EADS Astrium used to be proud of how they overcame the Olympus problem and had a short film documentary on it (as far as I recall).
Stuart: Thanks for the comment – it would be great if there was a link to this video online. I’m not sure if there was enough data available to unambiguously attribute the cause of the problem to a meteor strike in this case, and this is often the issue with natural hazards emanating from the outer solar system – the incoming objects are not in any catalogue and hence arrive without warning. The first indication of a problem is normally when a satellite goes offline suddenly, and by then it’s clearly too late for diagnosis.
Q: You mentioned approximately 60 tons of naturally occurring rock, iron, water etc. hits the Earth per day and two tons of manmade space junking entering the atmosphere, is that per day or per year?
Stuart: Per day in both cases. (If the figure seems surprisingly high, recall the rate at which Starlink are launching satellites and then calculate the effective re-entry rate that is required to maintain a roughly stable satellite population size in LEO.)
Q: Given the huge reliance we now have on satellite systems and the huge threat posed by orbital debris; do you think ASAT weapon induced Kessler syndrome could become a new domain of weapon of mass destruction geopolitics in the same way that nuclear weapons are used today?
Stuart: To some extent, although the aggressor won’t have control over the baseline density of objects at all altitudes. It is an interesting “thought experiment” to consider the decision-making process that must have taken place in Russia prior to their ASAT test last year. They had many derelict satellites that they could have chosen as the target for their test. The altitude of the one they selected would appear to have caused a lot of debris that continues to directly inconvenience Starlink, (both during their deployments and at their operational constellation altitude). Is Elon Musk’s support for Ukraine intended as some form of retaliation? To be sure, you’d have to ask the individuals involved, but it wouldn’t surprise me if the actions of both parties were entirely deliberate.
Q: How does space traffic control extend to multi planetary missions? Perseverance rover’s discarded heat shield was recently imaged by perseverance on Mars.
Stuart: The principle of planetary protection focusses particularly on the desire to avoid importing biological organisms from Earth into any environment that might already harbour some form of (simple) life. One would have to hope, though, that we might be able to extend this protection principle to avoiding “littering” other celestial bodies with our discarded hardware in the way that you describe. At present, though, the mindset seems rather different. The Apollo landing sites are currently viewed as “heritage sites” that humankind should seek to preserve, rather than somewhat embarrassing evidence of our untidy nature as a species, which frequently involves leaving our junk behind….
Q: Has it gotten to the point where we should look more into shielding satellites instead of focusing on de-orbit and removal?
Stuart: Please see earlier response to this question…
Q: For satellites operated for National Security, does cooperation change on sharing orbit data?
Stuart: It does indeed. The US does not include orbital data for its own military satellites, (or those of its close allies), in the spacetrack.org catalogue, for instance. Analogies from the air and maritime domain may point the way to a solution here. Safety of navigation systems, (ADS-B and AIS respectively), are normally fitted to military aircraft and military ships, and are used in peacetime. They can, of course, be switched off in a time of crisis, at which point their operators have to ensure that they do not cause collateral damage via inadvertent collisions. It is at least feasible to consider that a similar regime might operate in space.