Movement of interstellar space craft

[Ponderoid]

@madmonk28

How could a rocket engine in outspace exert force to turn a vessel if space is a vacume?

Something that’s been bugging me since I was a kid.

The master speaks.

You’re not the only one who’s had trouble with this:

@The New York Times

That Professor Goddard with his ‘chair’ in Clark College and the countenancing of the Smithsonian Institution does not know the relation of action to reaction, and of the need to have something better than a vacuum against which to react–to say that would be absurd. Of course, he only seems to lack the knowledge ladled out daily in high schools.

If only the dope had been around back in 1920, the NYT could have just asked here and would never had needed to publish this retraction.

*** Ponder

[Robot_Arm]

@John_DiFool

In reality, a space battle between opposing fleets of fighters would involve them zipping past each other at e.g. 20,000 knots velocity at 5,000 km distances, having a few scant seconds to aim their energy beam weapons, take 2-3 hours to reverse course and get within weapons range of the enemy again, only to once again swoop out of sight in different directions. If you try to stay slow to maintain your “manueverability,” then you’ll find that the enemy would be in complete control of the engagement, able to harass you (or bugger off) at will.

A slow space fighter wouldn’t necessarily be outclassed by a fast one. You posit a closing speed of 20,000 knots, but who’s to say which fighter is really moving? I could be sitting perfectly still, minding my own business, while Evil Emperor Zerg goes rocketing (sorry) past me at 20k kts. If he wants to continue the fight, let him burn up his fuel to turn around and come back for me. I don’t think speed has any bearing on my maneuverability, or gives him any advantage.

[Napier]

Joe, thank you, that was frickin excellent.

[MeDrewNotYou]

@Ponderoid

The master speaks.
(snip)

Err… That was Karen. Her snark is distinctive.

[Chronos]

Just a side note, by the way: A trip to Mars isn’t “interstellar”, it’s “interplanetary”. Voyagers 1 and 2 Pioneers 10 and 11, and New Horizons (the probe to Pluto) might, if you kind of squint, sort of be considered barely interstellar, but nothing else humans have ever done is.

[Malacandra]

@Chronos

Other than the Moon, of course, and Phobos and Deimos at the other end of the trip. Once you get to the Moon, if you plan your orbit right, the rest of the trip is essentially free.

You’ll do precious little slingshotting around Deimos and Phobos though - with less than a millionth of the Moon’s mass, they’re about as gravitationally insignificant as you can think of.

[Sailboat]

@dracoi

In space, all of your maneuvering and speed comes from one source - the rocket. You rely on small attitude jets to help you spin on your axis, but any time you want to change velocity (that is, speed and/or direction), you turn the ship and fire your main rockets. So “corner speed” has no relevance to space fighters. They always have a 1:1 ratio, being able to corner as quickly as they can accelerate in any other direction. (Though the ratio might not make much sense for space fighters in the first place, since they have no top speed as it’s applied to planes).

That’s my understanding. It may be that the key element to maneuverability in space war will be the ability of the craft and crew to withstand the G-forces of sudden acceleration. A rugged craft with a well-supported, acceleration-resistant crew (suspended in fluid, maybe? Drugged?) would be able to change course more rapidly, possibly throwing off the aim of attackers.

Of course, this is probably moot – no human being will be as resistant to G-forces as solid-state electronics, and we will most likely see unmanned fighters completely replace manned fighters inside earth’s atmosphere long before we see any kind of exoatmospheric fighter craft.

[Chronos]

Before we can say anything about space fighters, we’d have to figure out what the objectives would be in a space war. Aside from shooting down other spacecraft, what are the warships trying to do? Transport troops or equipment from one planet to another? Bomb a planet from space, and if so, with what kind of bombs? Surveillance of planetary surfaces?

[Ponderoid]

@MeDrewNotYou

Err… That was Karen. Her snark is distinctive.

Oops, sorry about that, Karen. I wasn’t even looking for a column or report when I started; it was just happenstance that I linked it. The OP’s question reminded me of the classic NYT article, and I just googled for it so I could quote it accurately. The SD link was one of the first hits.

*** Ponder