swfo
swfo t1_j65p66f wrote
Reply to comment by Loose-Addition-5730 in Why are "metals" more effective at cooling molecular clouds than hydrogen and helium? by Thomas_Bonk
That is the definition of metals Astronomers use. I just learned it from Dr. Becky. It was shocking at first but makes sense from an astronomical point of view. Still, I will never be comfortable calling carbon or neon a metal.
swfo t1_jaczzxb wrote
Reply to Why don’t we put air intakes on the lower stages of rockets? by Squiggin1321
Well... Sometimes they do, if you think about air launch (pegasus and launcher 1) as jet powered first stages.
Also, the hybrid approach has been studied extensively, and usually it's just not practical. You can read up on the SABRE project.