The drag problems for the Powersat are still severe due to its high ballistic coefficient - it might require less propellant mass for each individual reboosting compared with Freedom, but it will need to do this more often. To counter this problem, one possibility that seems attractive is to incorporate a continuously-operating ion propulsion system on the Powersat so that it can precisely track Freedom. Ion propulsion systems have specific impulses a factor of 10 higher than the type of hypergolic propulsion systems used by Freedom. Therefore, the propellant mass consumption is lower by about the same amount. This immediately raises the question, if ion propulsion systems are suitable for a Powersat. then why aren’t they they being planned for use on Freedom? There are a number of answers, one of which is that the high mass of Freedom would require enormous clusters of ion engines, as the typical maximum thrust from a large ion engine is about 0.1 N. Further, larger solar arrays than currently planned for Freedom would be required to power these engines - thus re-creating the problem which ion thrusters are intended to solve. By contrast, the Powersat is light-weight and very “power rich.” Ion thrusters are still a relatively unproven technology, although a single thruster will fly on the first Eureca mission and two units will be configured to the Artemis data relay satellite.[9] In the Powersat era. ion thrusters are likely to be a maturing technology applicable to the Powersat mission. The Powersat cannot use ion thrusters exclusively, however. When Freedom fires its thrusters to periodically re-boost its orbit, a similar high- thrust propulsion system will be needed on-board the Powersat in order to match Freedom’s velocity increment. This high-thrust chemical propulsion system will also be needed in the event Freedom has to perform orbit change manoeuvres in order to avoid a collision with orbital debris.
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