Very cool. I've thought this was an important move for a long time. A permanent tug for moving things around in orbit. Starship can drop off large payloads in LEO. To have such a massive ship then add the delta V for a GEO satellite to get to GEO (or even GTO) is an enormous waste of fuel. A reusable tug seems like an important tool in the Starship future.
Yep. Starship really isn't built to put satellites into GTO, or really any orbit that's not LEO without refueling. A persistent on orbit tug would be an excellent complement for earth orbit transfers that aren't mega-mass. Such a solution could also enable operators to check out their high orbit satellites in LEO, (not a huge benefit right now, but could potentially better enable servicing/disposal should something not work)...and another upside is retrieval of dead sats from GEO on a return flight (aspirationally bringing them back to the ground with SS, since no GEO is built for re-entry demisability). One could also imagine a small fleet of tugs providing altitude services such that if one tug were to crap out another one could provide the customer their paid-for service. Getting dropped off in the wrong orbit is pretty infrequent these days, but raising as a service would significantly mitigate that risk.
Gut feel says 0deg inclination is the right place for such a tug (at least for GEO or equatorial MEO constellations like mPower), making SS do the inclination turn on the way up. We're still a long way from Starship becoming commercially viable let alone enabling a material shift in GEO philosophy of course, but this kind of solution could eventually allow manufacturers to throttle back the level of exquisite parts and redundancy schemes used on the sats, and thus lower the cost of the satellites (and ideally also shorten the planned lifespan so the frequency refresh increases). Pair with the persistent GEO platform concept and it could revitalize GEO. On the flip side, the downside (if you want to call it that) is that Starlink and follow-on internet constellations are fast obsoleting the value of GEO, so there might not actually be a huge market for rides to 36k km as time moves on.
This particular Helios solution is indeed "just" a kick/orbital stage. While it's certainly true that one has to start somewhere and this is vital tech for them to validate, the real difficulty in a tug is not making the propulsion unit or even making it survive in space for more than a few days--technology obviously exists to make things last for years if not decades in space. The difficulty is in the complexity of the LEO transfers onto the tug (the payload/satellite and the propellant), and that's going to require a LOT of development to get to the point where its a salable product.
Time will tell if they can get this there. To-date, concepts like kick stages or direct-to-GEO lifts aren't widely used because building more delta V into the satellite and potentially also waiting for an electric satellite to get where its going (which for a comm sat is effectively lost revenue) is generally more cost efficient. But...It does feel like they have something up their sleeve with the 15k lb thrust, so maybe this really is just an early stepping stone? 15,000lb is literally like two orders of magnitude bigger than the main thruster on [chemical] GEO sats that does the orbit raising from GTO.
Bit of a nit at the marketing department here, but it's also worth adding some color to the "GEO in a day" tagline: The vast majority of GEOs in the history of GEO have only taken a day to get there. Only in recent years where satellites have started to completely eliminate their chemical propulsion modules in favor of all electric has that duration increased. (It generally takes 3-6 months for an EP satellite in ~GTO to raise and turn and circularize to geosynchronous).
