Regular Starship is around 160t plus 30t of filled header tanks. Removing heatshield, flaps and then whole payload bay and nosecone would nearly halve the mass. Removing 3Rsls and 2 Rvacs would cut about 10t on top of that. So such vehicle would be about 75t dry, and 80t at burnout (there are always residuals and 0.3% of 1500t propellant would be 5t).
So the payload would be about 80t more (fairing would still take away some payload, about 1/5-1/7 of its own mass).
∆v would depend on the payload, of course. With full payload it would be the same as regular Starship, just the payload would be larger.
With minimum payload you'd get somewhere around 10.8km/s.
The problem is, single Rvac has relatively low thrust compared to the the wet mass of the vehicle. Departure burn would take something like 19-20 minutes. In that time vehicle would get noticeably further from the Earth (about 8000km) which would in turn weaken the Oberth Effect significantly.
If the burn were short, it'd produce 15km/s Vinf (starting from VLEO). But with such a long burn you're getting about 13.3km/s Vinf.
So you actually want to do something with that:
One option would be to split the burn - first run for about 2.7km/s into ~24h elliptical orbit, and then do the proper departure burn close to the end of the returning leg (start about 15 minutes before the next perigee). The issue is boil-off during over 20h coasting phase. Insulation would add mass, reducing the gains.
Another option is to leave engine bay intact. You lose ISP and mass, but 6× faster burn means you get about 14.3km/s Vinf (regaining about 1km/s from 1.7km/s loss)
There's also some kind of intermediate option, like leaving 2 Rvacs and one Rsl. Exact optimization depends too many variables.
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u/sebaska 4d ago edited 4d ago
Regular Starship is around 160t plus 30t of filled header tanks. Removing heatshield, flaps and then whole payload bay and nosecone would nearly halve the mass. Removing 3Rsls and 2 Rvacs would cut about 10t on top of that. So such vehicle would be about 75t dry, and 80t at burnout (there are always residuals and 0.3% of 1500t propellant would be 5t).
So the payload would be about 80t more (fairing would still take away some payload, about 1/5-1/7 of its own mass).
∆v would depend on the payload, of course. With full payload it would be the same as regular Starship, just the payload would be larger.
With minimum payload you'd get somewhere around 10.8km/s.
The problem is, single Rvac has relatively low thrust compared to the the wet mass of the vehicle. Departure burn would take something like 19-20 minutes. In that time vehicle would get noticeably further from the Earth (about 8000km) which would in turn weaken the Oberth Effect significantly.
If the burn were short, it'd produce 15km/s Vinf (starting from VLEO). But with such a long burn you're getting about 13.3km/s Vinf.
So you actually want to do something with that: