Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

One million pounds of thrust?

  1. Aug 3, 2006 #1


    User Avatar
    Science Advisor

    Don't laugh guys, but I'm familiar with a lot of general astronomy stuff but my question will seem very stupid.,:cry: About rockets, etc.

    I was thinking today (dangerous) and realized I don't know the answer to:
    Samples: (hypothetical)

    1. Space shuttle and all weighs 5 million pounds and total thrust of engines is 6 million pounds, net one million pounds over weight.

    2. Payload (any) weighs 500 pounds and thrust in 1,000,500 pounds, net one million pounds over weight.

    3. Payload weighs 5 pounds and thrust in 1,000,005 pounds, net one million pounds over weight.

    So, not counting air-drag, etc.
    Do all three accelerate at the same rate:confused:
    Do all three reach same velocity in the same amount of time:confused:
    Would all three reach the same orbit (if programmed the same) at the same time and velocity/altitude:confused:

    Like I said, dumb question, after midnight, drunk, and I have to pilot an America West flight in 5 hours...:zzz:
  2. jcsd
  3. Aug 3, 2006 #2


    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    No, of course they don't accelerate at the same rate.

    F = ma

    If you keep the force constant, but decrease mass, you necessarily also increase acceleration.

    - Warren

    p.s. I hope you're aware of FAA restrictions about alcohol consumption before flying. I wasn't even aware that you were a pilot? :uhh:
  4. Aug 3, 2006 #3


    User Avatar
    Science Advisor
    Gold Member

    Thrust to weight ratio is a common theme in avionics. Obviously it must be greater than 1 just to get off the ground. For the purpose of getting a payload into orbit, the bigger the better. Getting out of the earth's gravity well as soon as possible is the objective. One of the more important limiting factors is how much heat the thrusters can tolerate [and how long]. Acceleration stress, which is a form of hoop stress in structural design, is also an issue. It is a complex engineering problem.
  5. Aug 3, 2006 #4


    User Avatar
    Science Advisor

    That was easy, I said it was a midnight, drunken-stupor question! Now I'm up early too. I gotta see the doctor for more sleeping pills.

    FAA? You mean I'm supposed to follow those rules too? I guess they actually expect me to get a pilot's license too!...:biggrin:
    Last edited: Aug 3, 2006
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook