Atlas sustainer could have been a lot better, but it was designed to run at
sea level (they didn't want to risk an air start early in the program). You
can tolerate a certain amount of overexpansion at sea level, but you don't want
the flow to separate. That beats the crap out of the nozzle. So they accepted
a lower area ratio, and took the performance hit.
Sent from my iPhone
On Apr 29, 2023, at 8:37 PM, Henry Spencer <hspencer@xxxxxxxxxxxxx> wrote:
On Sat, 29 Apr 2023, roxanna Mason wrote:
Well this was assuming low risk open cycle engines like F-1 and H-1 which 4
stages would have been necessary...
Come now, at least you should assume that upper-stage engines would be based
on the Atlas *sustainer*, which had a vacuum-Isp advantage of nearly 30s over
the H-1. But I would expect better than that -- the only reason better
upper-stage kerosene engines weren't seriously pursued was that everybody
thought LH2 made them unnecessary.
The Russian N-1 had 4 stages and used closed cycle NK-33 engines.
But, as I noted, quite heavy tanks. Especially compared to the S-IC, whose
mass ratio was impressively good and could certainly have been improved
further.
Henry