This answer to Can ion Thrusters be used for Reaction Control System? got me thinking about the new "all-electric" class of commercial satellite buses.

Question: Are the (relatively) new "all electric" satellite buses like the Boeing 702SP really all-electric? Are RCS and momentum unloading done with ions or with traditional reaction masses like hydrazine reaction products or cold gas? Actually, using ion propulsion for orbit-raising and station-keeping, do they even need a reaction control system or RCS?

I see that the Boeing 702SP uses Xenon ion thrusters for several things, but I can't find anything about attitude and momentum unloading.

From eoPortal's All-electric propulsion and multi-satellite launch system for communication satellites:

What makes this flight especially interesting is that the satellites are based on Boeing's 702SP series program and were the first all-electric propulsion satellites when Boeing introduced it in 2012. The satellites have no chemical thrusters. They will maneuver to their intended GEO (Geostationary Orbit) entirely using a xenon-based electric thruster propulsion system known as XIPS (Xenon-Ion Propulsion System).


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According to a Spaceflight101 article on the ABS-3A communications satellite, attitude control is via reaction wheel:

The 702SP satellite platform uses a pure electrical propulsion system that performs the insertion of the satellite from its transfer orbit into Geostationary Orbit, stationkeeping in the GEO slot and desaturations of the reaction wheels at regular intervals to manage wheel momentum.

A Boeing one-sheet describing various interplanetary mission spacecraft based on the 702SP vaguely describes the attitude control as "zero-momentum, 3-axis". In a diagram of a Europa spacecraft based on the 702SP, there's a "reaction wheel ass[embl]y" callout, while an asteroid orbiter mission has both "mini momentum control system" and "reaction control system thruster" callouts. I'm guessing the platform itself doesn't provide chemical propellant thrusters but there's nothing preventing them from being added if you need faster turns; another Boeing marketing sheet repeats the same "3-axis control" point, and gives a slew rate/maximum maneuver rate of 6º/min.

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    $\begingroup$ My first clue was "The satellites have no chemical thrusters." $\endgroup$ Jul 19, 2021 at 14:29
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    $\begingroup$ @OrganicMarble I saw that and thought about it, but decided cold gas thrusters were not completely out of the question; considering the substantial mass savings of not needing a chemical rocket for GTO to GEO and station-keeping, I didn't think it was impossible that cold-gas thrusters could be there. $\endgroup$
    – uhoh
    Jul 19, 2021 at 16:02

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