Speaking of parallel stages...does anyone remember this bad boy?
Forget the booster. The ITS ship is similar in size, shape, mass, and thrust to the S-1C. Replace the fixed ring of 6 RVacs with a detachable ring of 10 or 12 SL Raptors and you have a modern S-1D. Plus it already has reentry and landing designed in.The toroidal tank is a good idea, but it only needs to be big enough to fly the ring back... Maybe 50t of methalox.
Curious to see what overall configuration results in the lowest overall launch vehicle size but can still take a crew of 7 to the ISS and bring them back. I'm thinking it could be significantly smaller than the S-1D; methalox has a more oxygen-rich mixture ratio than kerolox, and the Raptor takes densified propellants, so the higher specific impulse is really going to shine.
S-1D is monstrously over-sized for that. Raptor is too large for a upper stage sized solely for taking 7 to the ISS, or for landing anything remotely that size, it can't throttle low enough. Even Merlin only throttles down to 32 tonnes-force. So an auxiliary landing thruster setup is pretty much required. The upper stage could maybe use a production version of the 1,000 kN demo Raptor engine.
Because the upper stage always ends up heavier, the 1.5 STO does worse in my calculations than a TSTO. It always needs 20 to 40% greater GTOW mass to deliver the same payload and return. The larger tank drag area doesn't reduce the TPS requirements enough to offset the extra fuel and thrust mass needed to put that tank it in orbit.
Quote from: sevenperforce on 03/14/2017 04:47 pmQuote from: edkyle99 on 03/14/2017 04:08 pmI would start with X-34B X-37B as a hypothetical example. It is a 5-ish tonne spacecraft that reenters and flies back. What if a version also provided some appreciable ascent delta-v, allowing use of someone's already-developed recoverable first stage? The result would be a reusable Agena type stage/spacecraft bus.I like it. But where do you put it? Slung alongside to allow parallel thrust? And what kind of engine would it take?It would serve as a serial second stage. As for engine, I would start by looking at storables, since spacecraft need propellant on-board for months or years at a time.I'm suggesting an upgrade of the rocket in the first photo, which boosted an Agena that also served as the spacecraft bus in orbit. These things flew every couple weeks or so. First, replace the Thor first stage by a Falcon 9-like first stage that is recovered. Second, replace Agena by something that looks like X-37B. - Ed Kyle
Quote from: edkyle99 on 03/14/2017 04:08 pmI would start with X-34B X-37B as a hypothetical example. It is a 5-ish tonne spacecraft that reenters and flies back. What if a version also provided some appreciable ascent delta-v, allowing use of someone's already-developed recoverable first stage? The result would be a reusable Agena type stage/spacecraft bus.I like it. But where do you put it? Slung alongside to allow parallel thrust? And what kind of engine would it take?
I would start with X-34B X-37B as a hypothetical example. It is a 5-ish tonne spacecraft that reenters and flies back. What if a version also provided some appreciable ascent delta-v, allowing use of someone's already-developed recoverable first stage? The result would be a reusable Agena type stage/spacecraft bus.
I agree Ed about a X-37B like 2nd stage, when I suggested it as part of my "Flyback Falcon 9" several years back...https://forum.nasaspaceflight.com/index.php?topic=27477.0
...Three Raptors boast 9,150 kN of SL thrust, allowing us a launch mass of 666 tonnes with a brisk 1.4 T/W ratio...