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

Could we throw stuff into space?

  1. Aug 19, 2015 #1
    hello everyone.
    just wondering with development in modular robotics, could we possibly throw a space station into space bit by bit via something as simple as a pulley system?
    doing a bit of research i found out you can get a 1000 ton crane, therefore 9,800,000N of force, i also found out that if we can throw something upwards at 11,000 m/s it will never return back to earth. aka. its in space.

    so using the v2=u2+2as
    and a simple pulley system equation, F-mg = ma
    we can come to, s=v2m/2(F-mg)

    substituting values into this, F=9,800,000N, m = 10kg (if we send stuff up in 10 kg packets) and v=11,000 m/s
    we get s=61.74m

    now if we set up 4 of these pulleys in a cross section like the bottom corner of the attached image. we can cut that down by a factor of 4.

    so what im saying/ asking why couldn't we throw stuff up into space using a contraption 15.43m or so tall?

    i feel as if i might be missing something simple here, i am only a high school student so please could you give some feed back about this, i would love to learn more about it, thanks.
     

    Attached Files:

  2. jcsd
  3. Aug 19, 2015 #2

    Nidum

    User Avatar
    Science Advisor
    Gold Member

  4. Aug 19, 2015 #3

    russ_watters

    User Avatar

    Staff: Mentor

    Cranes use hydraulics and extreme reduction gearing to support their loads. They aren't physically capable of moving anywhere close to that fast -- they are so far on the opposite end of the spectrum you may as well consider them fixed towers! So while it can apply 9.8 MN to a 9.8 MN load, that doesn't mean it can apply 9.8 MN to a 98N load.
     
  5. Aug 19, 2015 #4
    A catapult kind of mechanism that you are suggesting would impart enormous acceleration to the projectile over a very short amount of time.
    Enough to achieve Earth escape velocity in a few seconds, and a bit more as well to deal with the atmosphere problem.
    The risks involved in engineering such a catapult seem a bit high to me, and it could not be used for launching humans, the G forces on the body would make death almost certain.
    Rockets are probably a better bet.
     
  6. Aug 20, 2015 #5
    no this is just for launching dead things. i still want rockets for people.

    plus
    how about a 1000 ton press? presses tend to move much faster than cranes?
     
  7. Aug 20, 2015 #6

    phinds

    User Avatar
    Gold Member
    2016 Award

    Have you really thought about what escape velocity looks like? I mean, you listed the numbers but have your really thougth about it? Remember, this is a purely ballistic trajectory, so you have to obtain escape velocity by the time your payload leaves the launch mechanism. That means it has to travel 7 miles in the first second so if you had, for example, a 7 mile rail gun, the payload would have to traverse the entire 7 miles in one second. You really think you are going to get something moving that fast with a crane or a catapult?
     
    Last edited: Aug 20, 2015
  8. Aug 20, 2015 #7

    russ_watters

    User Avatar

    Staff: Mentor

    I'm not so sure they do. They are still hydraulically operated.

    Also recognize that if the device is accelerating a payload, the force has to be accelerating the parts of the device connected to it as well. For a standard crane, that means linear acceleration of the cable and angular acceleration of the spool of cable.

    Try another calculation: the moment before release, when still applying 9.8mn and the payload now traveling at 11 km/s, what is the POWER output of the device? Compare the answer to, say, the average nuclear power reactor.
     
  9. Aug 20, 2015 #8
    The problem with throwing something into space is both gravity and air resistance. In order to throw something into space, it's initial velocity would have to be higher than orbit velocity because it'll slow down right? What happens to something when it tears through our atmosphere at orbit velocity?

    During the Cold War, the United States wanted to test a bomb underground. They plugged a hole with a 2000 pound steel plug and were only going to blow up a small part of the weapon. There was a mistake and the nuclear bomb exploded at full force, the plug was launched at 6 times the escape velocity and was considered the fastest man made object ever. It was considered highly unlikely it ever made it to space, it most likely vaporized in the atmosphere like a meteor in reverse.
     
  10. Aug 20, 2015 #9
    okay, if the power of the crane remains the same it could achieve a higher speed if it reduces the force, right? we could simply increase the height of my catapult (as people have been calling it) and/or reduce each payload. meaning more time to accelerate and less force needed to accomplish escape velocity?
     
  11. Aug 20, 2015 #10

    russ_watters

    User Avatar

    Staff: Mentor

    Correct.
     
  12. Aug 20, 2015 #11
    At a rough guess though, the height of your of the catapult, (or whatever name is best for it) will need to be in the order of tens of kilometers.
     
  13. Aug 20, 2015 #12

    mfb

    User Avatar
    2016 Award

    Staff: Mentor

    A cable strong enough to support 10 MN of force, with a mass of just 10 kg, cannot be longer than two or three meters. And that does not even include the mechanism to accelerate the cable, which simply does not exist at the required speed (its mass would contribute as well).

    The simple pulley system shown in the first post would give a maximal acceleration of 1g = 10 m/s2, clearly impractical to reach high speeds. Most of the energy released would just go into accelerating the weights at the sides (=they just fall down).
     
  14. Sep 18, 2015 #13
    how about eliminating the cables all together? by using the same as a mag rail. set up a tower with four in facing magnetic rails. using electromagnets to accelerate the object upward. the speed would need to be kept below friction burn speed meaning a very tall structure. or deep (could always dig a mine shaft to increase the length by a couple Km's) why i suggest this method is the object leaving the rails would not have any tower based items also accelerating so no stresses of stopping something which has been accelerated with the item being tossed out.
     
  15. Sep 18, 2015 #14

    mfb

    User Avatar
    2016 Award

    Staff: Mentor

    That idea is not new. You still need some tower-like structure or a way to deal with friction in the atmosphere, and you need a long acceleration track or a ridiculously high acceleration.
     
  16. Sep 18, 2015 #15
    I'm aware its not new also aware the issues are numerous like not turning any object tossed up into a charcoal briquette. yet besides being nearly impossible to accelerate a catapult to the speeds needed to escape the atmosphere there is the problem of stopping the parts of the catapult which are moving that fast once its launched an item. the use of a cannon style launcher removes stopping parts since only the item being tossed is moving the cannon is inert (for the most part).
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook




Similar Discussions: Could we throw stuff into space?
  1. How stuff DOESN'T work! (Replies: 12)

  2. C-could it work? (Replies: 2)

  3. Really strong stuff (Replies: 12)

Loading...