Hacker News Reader

Comment by kawa | Hacker News Reader

Their starship was bullshit. On earth they needed a big Saturn 5 like rocket to bring it into space and later they fly into orbit like it's nothing.

If the planets they visited had much lower gravity then earth this may be possible, but this wasn't noticeable or talked about. And even on Mars you need much more fuel to get into orbit than could be stored in their tiny ship.

View on HN

To expand on this, if they tried to land on the water planet where time so dilated that one hour equals 7 months… what would their velocity have been when they contacted the surface? And how much energy did their spaceship need to reach escape velocity from there?

Well, if you look for this, many if not most movies will have some inaccuracy or holes in explanation like this. In the end, I watch movies for entertainment. If I'm looking for scientific precision, I see a documentary instead.

Yes. Maybe don't make scientific accuracy a big part of your marketing campaign though.

Still better than what Ad Astra! :D

Liked the killer space monkeys though. ;-)

'Ad Astra' was a real stinker.

Eh, this isn't actually that bad. It's quite easy, using a jet aircraft, to (via a ballistic trajectory) get into space. Surrounded by reaction mass as you are, the rocket equation isn't nearly so bad. You could conceivably dock with something in orbit, if you had elastic tethers or something to make the acceleration survivable. If you're much lighter than what you're docking with, you won't knock the satellite out of orbit.

Heck, you could even ignore the jet aspect, and go for full rocket. (An ICBM only weighs around 50 tonnes, after all.) Getting the heavy thing into orbit, though, requires proper, multi-stage rockets.

>It's quite easy, using a jet aircraft, to (via a ballistic trajectory) get into space

A jet engine requires atmosphere. Spaces requires no (or very little) atmosphere.

The edge of space is usually defined at 100km (the Karman line).

The highest altitude reach by an air breathing jet is around 37km. https://en.wikipedia.org/wiki/Flight_altitude_record

A scramjet might get to ~75km according to: https://aviation.stackexchange.com/questions/44837/what-is-t...

That's the point at which the jet stops working, but by that point you can be going quite fast. If there isn't enough air to run the jet engine, there also isn't enough air to slow you down (much).

Assuming no air resistance and 10m/s^2 gravity. I calculate that you would have to be doing ~1,100m/s (~mach 3.2 at sea level) straight up at 37km to reach 100km. Or ~1,600m/s (~mach 4.7 at sea level) at 45 degrees to perpendicular.

Seems about right. https://en.wikipedia.org/wiki/Project_HARP (1966) got 2100m/s from a ground-based cannon: this got the projectile to 179km.

Reply on news.ycombinator.com