How Should We Quickly Replace Downed Satellites?
Keep extras in orbit? Have them ready on the ground? It depends.
For many years, there has been a debate within the space community about how best to rapidly deploy satellites in a time of need. Should they wait on the ground to be rapidly launched when called upon, or stored in orbit, waiting to be rapidly activated? The answer has become clear: both.
Russia and especially China have invested heavily in antisatellite weaponry: missiles, directed energy, co-orbiting weapons, cyber, and more. To keep U.S. and allied constellations up and running during a conflict will take several lines of effort: maneuverability, cyber hardness, networked architectures, as well as multi-layered defenses involving spacecraft deployed in multiple orbits.
Just as important is the ability to rapidly replace satellites that have been taken out of the fight. The speed of future combat means there are only two ways to do this quickly enough: have spares in orbit or ready to launch on the ground. The rapid-launch option has several advantages. The launch costs are largely deferred until required. Unlike spares on orbit, satellites can be stored indefinitely and even updated with new technology. And satellites on the ground aren’t in the wrong orbits. But no satellite on the ground can be thrown into the fight as quickly as one that is already in space.
So how do we choose? Simple. We focus on the nature of the assets we would replace.
Let’s start with the new, exciting, proliferated LEO, or PLEO, constellations. These spacecraft are placed at low altitude to facilitate high-speed, two-way data applications, like internet. Being in LEO means they are above any given location on the ground for only a few minutes at a time. Consequently, thousands are required for continuous coverage, which means that they must be small enough for a heavy launch vehicle to carry dozens per launch.
The technologies used for this mission changes frequently. All commercial providers of PLEOs today plan on a short spacecraft life and periodic upgrades (like the wireless systems we use on Earth). This means that the flexibility offered by long ground storage and accessibility offers no advantage here. The economics of launch make the storage of spares on orbit optimum. Indeed, the first commercial PLEOs are populating their constellations with around 10 percent on orbit spares. The nature of PLEOs, as well as existing commercial practices, have made it clear that the correct approach for these constellations is to store the reserves on orbit and rapidly activate them to replace casualties during the fight.
But a PLEO satellite has a tiny payload. Certain missions require large, very sophisticated spacecraft deployed in much smaller constellations. Their payloads are extremely capable, and the overall size of the spacecraft required to support them more easily accommodates enough fuel for much greater longevity. In this situation, the flexibility afforded by keeping the payload technology current through potentially long storage cycles is now very attractive. For this type of satellite, the rapid launch of an asset stored on the ground becomes the obvious answer.
Synergistically, the two strategies intersect in launch. PLEOs demand and enable high launch rates to quickly populate massive constellations. This means that there is always a launch vehicle mere days away from the pad that would be available for the rapid launch of an asset called up from ground reserve.
One might wonder if maintaining ground reserve satellites would be prohibitively expensive? The answer is no. You would not build extra satellites; you would only build early satellites. If the constellation is to have six birds, stay one ahead. When you get to the last one, have the first bird of the follow-on constellation also built ahead.
Thus, we see that the answer to this old debate is now clear. We replace casualties during the fight with the rapid activation of on orbit spares for proliferated constellations, while rapidly launching ground reserves for large, high-value assets.
Tory Bruno is the President and CEO of United Launch Alliance (ULA), the nation's most experienced space launch company with more than 150 consecutive launches and a 100 percent mission success rate.
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