A Water Economy in Space: On-Orbit but in Which Orbit?

Some posts back I analysed the scenario in which water was supplied to an LEO processing facility to make high-thrust propellant for boosting payloads to GEO. The delta-vee penalty for working out of LEO became apparent – low-thrust vehicles require a lot of propellant to produce the ~7.75 km/s delta-vee needed.

Another suggested market for in-space resources is on-orbit servicing of pre-existing satellites. Geosynchronous Orbit satellites don’t suffer from orbital decay, but their operation requires accurately pointing their antenna arrays at the Earth and doing so requires propellant expenditure over time. Eventually the propellant, either monopropellant (usually monomethyl hydrazine) or electric propulsion gas (typically xenon), runs out and the satellite becomes inoperable. Good satellite operators don’t leave a derelict satellite in a valuable orbital position. Instead the satellite is moved outwards from GEO to the ‘Graveyard Orbit’.

That’s where On-Orbit Servicing comes into play. Rather than sending an otherwise operable Comm-Sat to the Graveyard when it runs out of its consumables, On-orbit Service Vehicles (OSVs) could refuel and replenish, keeping the Comm-Sat functioning for longer. Eventually Comm-Sats do need replacing, as their electronics eventually get fried by the radiation in GEO, or those electronics become limiting as technology improves and demand increases. But extending the lifespan makes sense for newer Comm-Sats that have merely run out of propellant.

News Piece: New space industry emerges: on-orbit servicing

While the Moon isn’t a viable source of the standard propellants (hydrazine & xenon) for existing Comm-Sats, it could have a role in supplying the propellant needed for Dockable “Space Tugs” using water propellant. Plus Water Rockets are ideal for transporting resources from orbits around the Moon to GEO, opening up a role that Water Rockets might profitably play. Low-gee inter-orbit transfers powered by solar energy are something the Momentus family of Water Rockets offers.

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