3 ms·

I think the main flaw with this analysis is assuming that 320 is the upper bound ISP. There are plenty of upper stage engines that are getting over 450 (eg RL10

I think the main flaw with this analysis is assuming that 320 is the upper bound ISP. There are plenty of upper stage engines that are getting over 450 (eg RL10). Obviously making a high quality second stage that is small and durable enough isn't easy, but it's not obvious to me that it's impossible to make cost competitive. (that said they obviously are something like 95% likely to fail)

ericbarrett 4y ago
For that kind of ISP you need hydralox. Now you've got to accelerate cryogenically cooled hydrogen at 10,000g! Also if it ruptures during spin-up you've probably destroyed your launch mechanism (not that keralox would be much better). At least you wouldn't need much insulation on the tank since it only has to spend ~6-7 minutes in flight.
- JumpCrisscross 4y ago
  > that kind of ISP you need hydralox Merlin 1D and Rutherford get close to 350 in vacuum with RP-1. Hydralox would need to be insulated during spin up, which probably makes it prohibitive. In any case, if anything goes wrong in spin-up or deployment, the entire facility is toast. Whether there's a bit of extra chemical energy added to the mix is likely a rounding error.