Hi Pilgrim,Pilgrim wrote:Hi Selene, I fail to see what difference the temperature of "space" makes to the fact that Rockets cannot produce a thrust in a vacuum. A vacuum by its own definition has no matter to hold any temperature so is neither hot or cold and the fact the Rocket gases are hot and can only lose heat by radiation in a vacuum which takes time seems irrelevant to the immediate fact of whether they are hot gases or cold gases in terms of thrust produced by expelled mass. It should make no difference according to their logic. Of course I agree with the OP - only a reaction with another mass can produce an opposite reaction and Rocket fumes have nothing to react against in vacuum due to no pressure against anything as the vacuum offers zero resistance and will suck up all you have to offer with zero resistance so no "thrust" is possible.
it's not so much a "difference", it's more that there are more parameters affecting the behaviour of rockets in a near vacuum.
If not only the Pressure is ~0, but also the Temperature ~0 (or 2.7 K as Wiki says), then material behaviour is completely different to whatever circumstance we know of.
I agree with lux that we should have a thorough research into the topic, but it will be hard to find "lab tests" where AND Pressure AND Temperature are almost 0. And not to forget the radiation which is impossible to test as we do not even know which kinds of radiation are there. And the lack of gravity, also impossible to test. We might ask NASA to show us the test in their vomit comet, with vacuum conditions, as 24 cosmoclowns allegedly traveled to the Moon, that shouldn't be such a problem, right?
The chemical changes to the materials (either gaseous as the rocket fuel or solid as the metal can) couldn't be circumvented.
The near vacuum, so incredibly low Pressure, makes there is no friction between the rocket and space. How would you describe the temperature profile from inside to outside?
Inside - a nice comfortable 20 degrees C?
Outside - heated due to radiation? - how would this heat be transferred?
Space - near zero temperatures
The outside of the spacecraft would have such enormous temperature fluctuations even when and if it can be heated by solar radiation alone, that only that would make the rocket/craft behave very strangely.
In short, to answer your question; the pressure is indeed a crucial point, but even so crucial is the temperature which until recently was not included in the discussion.