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A Question I am wondering

  1. Mar 29, 2008 #1
    I thought of something one night...

    I do not know if this has been thought of/posted/discussed anywhere/anyway.
    Please correct me if I am wrong.

    Space Shuttles or "Space Ships" if you prefer, propel themselves by forcing out energy behind them. Now... If a weapon such as a burst of energy, or a missle being launched in the front of the craft, would it slow/stop the Shuttle if it was launched with enough force?

    I am just a wondering person here.

    Thanks for reading.

    EDIT: I do not know if this is the wrong topic to post this in. Please move it if it is. Thanks :D
    Last edited: Mar 29, 2008
  2. jcsd
  3. Mar 30, 2008 #2
    The spaceship works according to the law of conservation of momentum.
    If you send momentum in the back-direction the spaceship moves forward.
    And of course if you send out something with momentum in the forward direction the spaceships momentum (and speed) in the forward-direction will decrease because of conservation of momentum.
  4. Mar 30, 2008 #3
    Okay, cause whenever I see a space-related show EG: Stargate: SG1, BattleStar Galactica, ect; I was like: Wouldn't they stop if they shot a missle that fast? So thanks for the help.
  5. Mar 30, 2008 #4


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    So, a missile launched forward from the shuttle might slow the shuttle, depending on the type of missile and how it was launched. Suppose the shuttle used a grapling hook as part of its docking or sattelite-retrieval processes. If the grapple was kept in a tube in the nose of the Shuttle, and fired like most grapples (an explosion of expanding gases inside the enclosed tube, like a bullet from a gun), then yes, the Shuttle would be slowed by the firing. But, if the missile operated more like a rocket, like the air-to-air missiles launched by fighter jets, then the missile would detatch from the Shuttle, the engines would ignite, and the thrust from the missile would be expelled out the back while the missile itself moved forward, and the shuttle would no longer be involved in, nor effected by, the whole process.
  6. Mar 30, 2008 #5


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    Even with Lurch's grappling hook example, the momentum of the ship presumably far exceeds that of the missile. It's a question of scale
  7. Mar 30, 2008 #6


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    Staff: Mentor

    I can think of one real-world example where the momentum of the projectile has a significant effect on the momentum of the launching craft: The A-10 Warthog's 30mm cannon.
  8. Mar 30, 2008 #7


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    Yeah but were talking about Stargate where they have flying pyramids and that.

    I think it's worth clarifing that Lurch's point about the grappling hook and the missile being free from the launching craft is correct, although the thrust of the missile would still affect a force on the ship for the time there are in close proximity.

    Hence why the above cannon smacks a punch.
  9. Mar 30, 2008 #8


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    That reminds me of a story that sort-of illustrates the principles being discussed here. This happened during the Korean war, when american F-86's were engaging in airial combat with Russin MIG's. The two aircraft were pretty evenly matched. The F-86 had a slight advantage in speed, but it was very slight, (like 15-20 mph or so, I believe).

    One day a veteran pilot and his fledgeling wingman were persuing a pair of MIG's that were just out of range. The F-86's were slowly closing the gap, but it was taking too long for the impatient rooky. The lead American pilot kept saying "hold your fire, you're not going to hit anythinmg from this distance," and the rooky kept chafing at the restraint. Finally, afraid the persuit was getting too close to the area where the MIG's might be joined by reinforcements, the rooky cried, "I'm gonna git me a MIG!" and fired his six 50-Cal guns. He didn't hit anything, of course, and his aircraft immediately slowed down to a speed slower than that of the MIG. Ths forced Lead to slow down in order to stay with his wingman, and both MIG's got away.

    Most of the time the kickback from a gun on a vehicle is so small compare with the mass, thrust, and velocity of that vehicle as to be negligable.

    But not allways.
  10. Mar 31, 2008 #9
    Okay, thanks for clarifying. You helped me out alot.
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