Quote from: Sarigolepas on 04/30/2023 06:22 pmQuote from: InterestedEngineer on 04/30/2023 03:27 pmOne can't add 500t to the Starship (Fuel + cargo + rings) and not add fuel to the booster, the rocket equation doesn't work like that.The current deltaV of the booster is about 3.5km/sec. That's a mass ratio (M_{r}) of 2.7If you add 500t of payload to the booster (aka fuel and payload and rings for Starship), to get the same deltaV, the booster needs 850t of fuel -- (M_{r}-1) times payload increaseThere's no place for that fuel to go without adding rings. Each ring adds 100t of fuel capacity. So ~8 more rings.You don't need to get the same deltaV, you can just have stage separation earlier. So the ship would do most of the work to reach orbit.earlier stage separation also means that, for a RTLS flight path, the boostback burn requires less deltaV, which reduces the booster propellant reserves needed at stage separation. This is likely only a small benefit, though.

Quote from: InterestedEngineer on 04/30/2023 03:27 pmOne can't add 500t to the Starship (Fuel + cargo + rings) and not add fuel to the booster, the rocket equation doesn't work like that.The current deltaV of the booster is about 3.5km/sec. That's a mass ratio (M_{r}) of 2.7If you add 500t of payload to the booster (aka fuel and payload and rings for Starship), to get the same deltaV, the booster needs 850t of fuel -- (M_{r}-1) times payload increaseThere's no place for that fuel to go without adding rings. Each ring adds 100t of fuel capacity. So ~8 more rings.You don't need to get the same deltaV, you can just have stage separation earlier. So the ship would do most of the work to reach orbit.

One can't add 500t to the Starship (Fuel + cargo + rings) and not add fuel to the booster, the rocket equation doesn't work like that.The current deltaV of the booster is about 3.5km/sec. That's a mass ratio (M_{r}) of 2.7If you add 500t of payload to the booster (aka fuel and payload and rings for Starship), to get the same deltaV, the booster needs 850t of fuel -- (M_{r}-1) times payload increaseThere's no place for that fuel to go without adding rings. Each ring adds 100t of fuel capacity. So ~8 more rings.

Possibly the mass ratio of Starship is less than that of Falcon upper stage?Falcon-9 MECO is ~2km/sec, so about 3km/sec deltaV.

Booster-7's MECO was supposed to be about 2.7km/sec (still looking for the source), so net 3.7km/sec deltaV. That requires ~6km/sec deltaV out of Starship, or a mass ratio of 5.3, which is pretty small really, the nominal mass ratio for Starship is 5.8 for a 100t payload and a 150t (wet) Starship at SECO.If we cut Booster down to 3km/sec deltaV (2km/sec MECO), that's a M_{r} of 2.4, but that increases Starship's mass ratio to 7, which is not doable with today's Starship configuration, it requires another 300t of fuel or 3 more rings.

Please do not mix and compare theoretical delta-vs versus real staging speeds. Even when you try to add compensation for the losses, as your compensation factors are way off.MECO for Falcon 9 is typically at about 2.25 km/s for barge landings, and there is about 3.5 km/s of theoretical delta-v, and this is for barge landing. The losses and re-entry burn, landing burn etc for falcon first stage are clearly more expensive than you think.

Quote from: hkultala on 05/01/2023 09:20 amPlease do not mix and compare theoretical delta-vs versus real staging speeds. Even when you try to add compensation for the losses, as your compensation factors are way off.MECO for Falcon 9 is typically at about 2.25 km/s for barge landings, and there is about 3.5 km/s of theoretical delta-v, and this is for barge landing. The losses and re-entry burn, landing burn etc for falcon first stage are clearly more expensive than you think.Maybe I wasn't clear, I always do calculations in terms of conic sections, so when I say deltaV for MECO I'm including only the mass ratio for that part of the flight, not landing fuel. So the mass at MECO includes the burn-back fuel, reentry burn fuel, landing fuel, the dry mass of the booster, as well as the fully fueled upper stage of course.there's about 1km/sec of gravity losses, which is not trivial to calculate. That and the angle of the vector above the earth is the only real "compensation" factor I'm guessing at.Detailed spreadsheet here:https://docs.google.com/spreadsheets/d/1bW0qWPjSl85lYLOwO9m6j9l71uWHWRSR1gMFtuR2bb0

"boost back horizontal delta-v" of only 100 m/s (6 km/min) does not seem reasonable. Clearly faster horizontal flyback velocity is needed to get back to the launch site in the time available, unless staging very very early at very vertical angle.And this is then worse if staging later

Quote from: InterestedEngineer on 05/01/2023 07:27 pmQuote from: hkultala on 05/01/2023 09:20 amPlease do not mix and compare theoretical delta-vs versus real staging speeds. Even when you try to add compensation for the losses, as your compensation factors are way off.MECO for Falcon 9 is typically at about 2.25 km/s for barge landings, and there is about 3.5 km/s of theoretical delta-v, and this is for barge landing. The losses and re-entry burn, landing burn etc for falcon first stage are clearly more expensive than you think.Maybe I wasn't clear, I always do calculations in terms of conic sections, so when I say deltaV for MECO I'm including only the mass ratio for that part of the flight, not landing fuel. So the mass at MECO includes the burn-back fuel, reentry burn fuel, landing fuel, the dry mass of the booster, as well as the fully fueled upper stage of course.there's about 1km/sec of gravity losses, which is not trivial to calculate. That and the angle of the vector above the earth is the only real "compensation" factor I'm guessing at.Detailed spreadsheet here:https://docs.google.com/spreadsheets/d/1bW0qWPjSl85lYLOwO9m6j9l71uWHWRSR1gMFtuR2bb0"boost back horizontal delta-v" of only 100 m/s (6 km/min) does not seem reasonable. Clearly faster horizontal flyback velocity is needed to get back to the launch site in the time available, unless staging very very early at very vertical angle.And this is then worse if staging later

I'm a little confused as to why they had so much more deltaV for Booster vs. Falcon-9.Possibly the mass ratio of Starship is less than that of Falcon upper stage?Falcon-9 MECO is ~2km/sec, so about 3km/sec deltaV.Booster-7's MECO was supposed to be about 2.7km/sec (still looking for the source), so net 3.7km/sec deltaV. That requires ~6km/sec deltaV out of Starship, or a mass ratio of 5.3, which is pretty small really, the nominal mass ratio for Starship is 5.8 for a 100t payload and a 150t (wet) Starship at SECO.If we cut Booster down to 3km/sec deltaV (2km/sec MECO), that's a M_{r} of 2.4, but that increases Starship's mass ratio to 7, which is not doable with today's Starship configuration, it requires another 300t of fuel or 3 more rings.I really need to make a spreadsheet to analyze the corners here.I note TWR is a completely different problem which also needs to be solved. the 250t "booster" (limited throttle) version would probably help.

I created a spreadsheet to estimate the trajectory of Booster + Starship, calculate the fuel used, etc.

The CRS10 had a horizontal velocity at apogee of about 480m/sec. So I increased the value to about 460km/sec.*snip*

Quote from: InterestedEngineer on 05/03/2023 04:33 pmThe CRS10 had a horizontal velocity at apogee of about 480m/sec. So I increased the value to about 460km/sec.*snip*460 km/s is over 15 times faster than the Earth orbits the Sun. It's nearly the escape velocity for the Galaxy.

Quote from: InterestedEngineer on 05/01/2023 01:37 amI created a spreadsheet to estimate the trajectory of Booster + Starship, calculate the fuel used, etc.The ship with 6 vacuum engines will be 10 meters taller and have more fuel, so I'm expecting it to need more delta-v to reach orbit and to have more gravity losses because of how early it will separate from the booster.My guess is slightly heavier but 50% more thrust so overall slightly more TWR just like for the booster.

Is it safe to say this stretch will get basic SSv2 to the 1500t propellant range? There's noises in the lunar starship threads that 1200t is sorta hurting the CONOPS of the whole LSS, but 1500t gets things down to VLEO refueling simplifying a lot.