In article ,
Mike Miller wrote:
Looking only at the vacuum specific impulse of plain hydrogen-oxygen
rockets, is it possible to advance their specific impulse to 500, or
even 520?

To about 500, maybe, if you work really hard... 470-480 is the best I
recall anyone actually proposing to achieve with LOX/LH2, using
extremely-high-expansion nozzles (long enough that the limiting factor
on expansion is condensation of water in the exhaust...).

For example, I recall Mr. Spencer recently mentioning that an ideal
oxidizer:fuel ratio for hydrogen & oxygen was 4:1, but 6:1 was used
because of tankage mass penalties. Would a 4:1 ratio provide an
increase in specific impulse? If so, approximately how much?

It helps, but not hugely. Numbers depend on details, but the Saturn V's
upper-stage engines did change mixture ratios, for several reasons, and
going from 5.5 to 4.5 raised their Isp by only about 7 seconds.
--
MOST launched 30 June; first light, 29 July; 5arcsec | Henry Spencer
pointing, 10 Sept; first science, early Oct; all well. |