In an update on its website, SpaceX has reaffirmed the company’s commitment to being good stewards of space through safe and sustainable satellite operation. “SpaceX is deeply committed to maintaining a safe orbital environment, protecting human spaceflight, and ensuring the environment is kept sustainable for future missions to Earth orbit and beyond.”
SpaceX went into more detail on the exact steps the company has taken in an effort to keep space accessible for generations yet to come, but the efforts fall into four main categories.
Table of contents
Ensure satellites are highly reliable and maneuverable
SpaceX has a LOT of satellites. The company is counting in the thousands, not the single digits, so it’s important those satellites are both reliable and maneuverable. Building over 45 satellites in a single week is basically an unheard of number. With enough propellant left over to actively deobit, this means the Starlink satellites won’t be left sitting in orbit once they reach the end of their useful life.
Operate at low altitude for faster orbital decay
The lower orbit a satellite is in the faster the faster that orbit will naturally decay. SpaceX shared two graphs on its site, showing the decay time across orbital altitudes and the amount of debris across altitudes.
Starlink operates in “self-cleaning” orbits, meaning that non-maneuverable satellites and debris will lose altitude and deorbit due to atmospheric drag within 5 to 6 years, and often sooner, see Fig. 1. This greatly reduces the risk of persistent orbital debris, and vastly exceeds the FCC and international standard of 25 years
That’s why SpaceX has called on the FCC to lower the standard for the orbital life of satellites.
Working at this lower altitude, around 550km, while it has its benefits, is costly for SpaceX. It requires many more satellites to acheive consistent coverage and requires more fuel for the satellites to maintain position and overcome atmospheric drag.
Deploy satellites at lower-than-operation altitude to verify health
By deploying the satellites at an even lower altitude, less than 350 kilometers, this means any failed satellites will decay even faster after deployment. SpaceX can ensure that the deployed satellites are healthy before they increase their height to operational altitude.
This is the very move, made for the purposes of safety, that recently cost SpaceX 38 satellites. A geomagnetic storm heated the atmosphere, causing increased atmospheric drag at this low orbit. This meant many of the satellites where unable to perform the obit-raising maneuvers and prematurely reentered.
Share orbital information with other satellite operators, utilize automatic collision avoidance system.
While ensuring that satellites are reliable and in an orbital that will clear fo defunct satellites and debris quickly will help prevent collisions with uncontrolled objects, collisions with other active (and inactive) objects on orbit are still a possibility. In order to prevent these collisions, SpaceX takes two mains steps. First, SpaceX shares the orbital location of its satellites on Space-Track.org. This allows other satellite operators to be aware of the predicted locations of Starlink satellites. Secondly, each Starlink satellite is equipped with an autonomous collision avoidance system.
SpaceX has developed and equipped every SpaceX satellite with an onboard, autonomous collision avoidance system that ensures it can maneuver to avoid potential collisions with other objects. If there is a greater than 1/100,000 probability of collision (10x lower than the industry standard of 1/10,000) for a conjunction, satellites will plan avoidance maneuvers.
While the autonomous system may be suffiecient for most prediected collisions, SpaceX also states that it operators are “on-call 24/7” to respond to requests from other satellite operators. At another satellite operators request, it can disable the autonomous system on a Starlink satellite to allow the other satellite to make the necessary collision avoidance maneuvers.
The Starlink satellites can also “duck” to decrease the cross-sectional area, bringing in the solar array.
While all the methods SpaceX has implemented to ensure the safety of its assets and other assets on orbit should be lauded, the pure number of objects up there continue to increase the number of near-misses. As SpaceX notes, it is important to be responsible as satellite constellations are built out, and SpaceX certainly thinks it is doing so.
One noteable absent point from the update is the impact of satellite contstelations on ground-based (and even some space-based) atronomical observations. The satellites interrupting scientific observations was one fo the points NASA brought up in its letter to FCC expressing concerns over Starlink Gen2 satellites.
SpaceX remains (imo, rightfully) focused on the stars, but perhaps it should be consider its impact back here on Earth just a little bit more.