3
$\begingroup$

Do atmospheric conditions including (but not limited to) temperature and barometric pressure and humidity play role in rocket performance?

While weather has a strong impact on decision to launch, I'm asking about the impact of these atmospheric parameters on the performance of the rocket.

Can anyone enlighten me more about this? For example, are launch vehicles ever prorated for excursions in temperature?

Extreme example illustrating the concept:

The answer to Where can the highest air density be found on Earth? shows a site and date in Siberia with a density altitude of about -7600 feet or -2.3 kilometers below sea level and a density of over 1.5 kg/m^3 compared to standard conditions of 1.2 kg/m^3!

Could something this extreme, or less extreme variations than that affect a rocket's performance in a significant way?

Improve this question
$\endgroup$
6
  • 2
    $\begingroup$ Wind, definitely. also, Related. Hint: search the site first before asking. $\endgroup$
    – user10509
    Commented Sep 28, 2018 at 9:29
  • $\begingroup$ @JanDoggen there's discussion of scrubbed launches, and one failure, but I think the OP is interested in variations in performance a little less boolean than that. $\endgroup$
    – uhoh
    Commented Sep 28, 2018 at 10:19
  • 2
    $\begingroup$ A lower atmospheric pressure should increase the performance and thrust of the first stage engine a little bit. Drag would be decreased a little. A higher atmospheric pressure would have reverse effects. $\endgroup$
    – Uwe
    Commented Sep 28, 2018 at 10:23
  • $\begingroup$ @Uwe I've just finished an edit. $\endgroup$
    – uhoh
    Commented Sep 28, 2018 at 10:27
  • 1
    $\begingroup$ Cold launches from russia resulted in some unique deicing techniques you'll not see in Florida. I vaguely remember seeing something about Russian launches from colder locations using heating for some of the tanks too. Ill see if I can find it. Not really atmospheric variable though... $\endgroup$
    – Magic Octopus Urn
    Commented Sep 28, 2018 at 14:24

1 Answer 1

Reset to default
2
$\begingroup$

As Uwe's comment indicates:

A lower atmospheric pressure should increase the performance and thrust of the first stage engine a little bit. Drag would be decreased a little. A higher atmospheric pressure would have reverse effects.

These effects will be quite small. For most launchers, the total effect of atmospheric drag is on the order of 1% of the velocity budget to orbit; weather effects will change that only a small amount. Rocket performance is always slightly variable, and the likely variation in weather is accounted for when the rocket is fueled.

As for temperature, the flight regime of a rocket normally involves a wide range of temperatures which have little effect on performance. Propellant density varies with temperature slightly, which affects thrust -- another source of variable rocket performance.

The propellant density-thrust effect should be in the opposite direction to the atmospheric drag effect, so they'll partially cancel out. That is, launching on a cold day, the propellants will be denser and thrust higher, but the air will also be colder and the drag higher.

Improve this answer
$\endgroup$
1
  • $\begingroup$ I should have written not "a little bit" but "a tiny bit". $\endgroup$
    – Uwe
    Commented Sep 28, 2018 at 14:30

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.