Hacker News Reader

Comment by maccam94 | Hacker News Reader

If you flip around and fire the engines to decelerate, you would be flying into the exhaust.

Edit: Actually this hurts my brain. If you're going 1,000,000MPH and fire propellant at 500MPH in your direction of travel, it would travel at approximately 1,000,500MPH and you would decelerate below 1,000,000MPH, so you actually wouldn't run into it. There's no drag on your exhaust in space like there is in an atmosphere...

View on HN

According to A. Einstein you shouldn't be able to tell the difference between two inertial frames of reference. Physics would behave exactly the same. So if you don't hit your exhaust in the first instance you won't in the other either.

Yeah, I'm just so used to watching Falcon 9 landings where it's falling through the exhaust because of atmospheric drag.

You don’t fly into your exhaust until you accelerate enough to start going in the opposite direction. If you’re driving down the road and throw an apple out the window behind you, you don’t run over it if you put on the brakes, you’d have to accelerate to cross zero velocity and then start going backwards to catch up. An apple will just sit on the highway, rocket exhaust will be moving with quite a bit of speed as well.

Your analogy isn’t really valid, because in the rocket situation you’re flipping the rocket and throwing exhaust forward to slow down. That would be analogous to throwing apples forwards, not backwards.

Oh wow nice explanation. Thanks.

Reply on news.ycombinator.com