Why were the Bezos and Branson space flights so short?

Yes, it is a pain in the ass. Hence why so many rockets are moving to methane. Although the performance on paper is substantially less (closer to kerosene than hydrogen), if you consider the other advantages it’s generally a win. Hydrogen:

  • Causes hydrogen embrittlement, where the atoms move into the metal of the container, making it brittle
  • Has extremely low density (about 7% the density of water), making the tanks very large
  • The low density also reduces engine thrust-to-weight ratio, since pumping those volumes becomes difficult
  • Is much more expensive than methane
  • Requires extra insulation on the tanks since it’s so cold
  • Requires insulation between the oxygen and hydrogen tanks since the oxygen will freeze solid if brought to liquid hydrogen temperatures. Heavy and also prone to flaking off.

Methane on the other hand has nice density, a good performance boost over kerosene, is cheap, and has similar temperatures to liquid oxygen (so the tanks can be in thermal contact).

Hydrogen can still make sense for upper stages since the thrust-to-weight requirements are less, and the total propellant requirements are less so the fuel/tank costs aren’t as big a deal, but it’s still pretty lame.

Somewhere I read that water in the stratosphere is not the best thing. Something about ice crystals and the ozone layer, but I can’t remember the details. Airliners put lots more water into the stratosphere, so I’m not worrying too much about the little bit that New Shepard added.

I think you mean Virgin Galactic’s SpaceshipTwo.

Yeah. Virgin also had Virgin Orbit, which uses the same air launch technology to launch small LEO satellites.

The YouTube channel Everyday Astronaut does a great job explaining a lot of this stuff.

Here is a good start. If you like that he has plenty of other videos which help take you down the rabbit hole of rocket science. These are long videos but if you like this stuff well worth a watch. While it is only Rocket Science-101 (if that) it is a good start:

Yeah, EA’s vids are quite good. Layman level but more accurate and detailed than most videos I’ve seen (there are some channels out there with pretty glaring errors).

Scott Manley has some good stuff too.

I should note the discussion on the benefits and drawbacks of various rocket fuels starts at 20:30 in the video.