On Oct 3, 6:41 am, dglow wrote:

snip

Do there exist
rocket engines with the ability to switch from LOX to air-derived O2?

The proposed SABRE engines for the Skylon make the switch from air to
LOX so I suppose they could do the opposite.

Musk isn't a fan of space based solar power, but he does seem to be
trying to get the lift cost down into the range where SBSP makes sense
(100/kg to GEO).

Some years ago I came to the conclusion that even LOX/LH2 isn't good
enough and think it will take the exhaust velocity you can get from
beamed energy to get the cost down.

NASA does have a small project starting up that will investigate
hydrogen skin heaters to around 10 MW/m^2.

Keith Henson