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Space Science

Israeli X Prize Overview 49

Posted by michael from the up-up-and-away dept.
sckienle writes "Space.com has an article about the Israeli X Prize spacecraft. Not a lot of hard technical details, but a good overview of an attempted alternative to standard rocket launches."
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Israeli X Prize Overview More

Israeli X Prize Overview

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  • it was our idea first (Score:3, Informative)

    by hswerdfe ( 569925 ) <slashdot.org@how ... r.com minus city> on Friday July 11, 2003 @10:45AM (#6415489) Homepage Journal
    GO CANADA!!!

    http://www.davinciproject.com/beta/Technical/Tec hn icalFlight.html

    GO CANADA!!!

  • Balloon launch (Score:4, Interesting)

    by dpilot ( 134227 ) on Friday July 11, 2003 @11:40AM (#6416307) Homepage Journal
    As a kid I remember seeing a picture of one of these from back in the early days of rocketry. The rocket was shooting right up through the balloon, destroying it in the process.

    Unless they do some sort of drop first, or an initially oblique launch, I don't see how the Israeli effort can help but do the same. If they drop first, then they have to launch at negative velocity, which negates part of the benefit. If they launch through the balloon with a manned vehicle, they have to make sure they can go cleanly through it without snarling something.

    It'll be interesting. I like the idea of getting to 80,000ft without spending reaction mass.

    • Re:Balloon launch (Score:2, Informative)

      by geek42 ( 592158 )
      Looks like they intend to detach first, then fire rockets with the module at an angle of 70 to 80 degrees from horizontal.

      http://www.xprize.org/pdfs/ILAT.pdf

      Dumb question: do they retrieve the balloon later, or just let it float about up there? How long will it take to come down?

      Less dumb question: how do you control where the landing site will be when your initial, 2-3 hour ascent is at the mercy of the wind? I suspect you don't - not my favorite form of transportation, given the landing is suppose

      • Perhaps the balloon could be run teathered? If you could compress enough helium (into tanks) to give it a small negative lift, it wouldn't necessarily take an enormously strong cable to pull it back to the launch pad.
        • That'd be one long-ass tether. If you wanted to avoid taking the full force of the balloon, you'd have to activate your compression system before the manned module separated. That means you'd want a fast compression system, to minimize the impact on the module's altitude.

          If you're going to have a tether, though, why not take it a step further: make the tether strong enough to take the full lift of the balloon, and use it to winch up the next module. Sort of a space elevator, but not quite... more of a

    • Unless they do some sort of drop first, or an initially oblique launch, I don't see how the Israeli effort can help but do the same. If they drop first, then they have to launch at negative velocity, which negates part of the benefit.

      Not much. The main benefit of a balloon launch is that you're above most of the atmosphere, and so have less drag to worry about. Dropping a few hundred metres won't impact that much, and the downwards velocity you gain while falling is truly negligeable compared to the delta
      • Dropping a few hundred metres won't impact that much, and the downwards velocity you gain while falling is truly negligeable compared to the delta-v an orbit-capable rocket needs.

        X-prize rockets are *nowhere near* orbit capable, delta-v around 1400ms-1 compared to 10000ms-1 (just 2% of the kinetic energy!)

        • X-prize rockets are *nowhere near* orbit capable, delta-v around 1400ms-1 compared to 10000ms-1 (just 2% of the kinetic energy!)

          Actually, I calculate it as about 8 km/sec for orbit and about 1.8 km/sec for 100 mile altitude, and about 30 vs. 1.6 MJ/kg (about 5% of the kinetic energy).

          It's still negligeable. Gravitational potential energy is proportional to distance travelled vertically, so falling a few hundred metres gives very little kinetic energy compared to the kinetic energy required to travel up
          • if slashdot allowed mathml we could include maths equations in our comments. how cool would a simple web interface that could do math anonated graphics, could we have a firebird embedded plugin.
    • The easiest would be to have a big flamethrower on the front to incinerate the balloon and strings. Both boosters and flamethrower goes off at the same time.
    • Would it be possible to put the rocket on the top of the balloon? It's counter-intuitive, but given a large counter-balancing weight below the balloon (much heavier than the spacecraft), it could be possible. Add in some fancy balancing electronics and it's almost starting to sound practical.
  • It'd be cool to see such a balloon escape the gravitational pull of Earth. You'd have an enormous source of solid propulsion in space if you could keep pressurizing the balloon after it released some of it's helium. Not only that, the balloon could ease re-entry creating a slow descent and not risking burning up the crew.

    Could you make the external material some type of radiation barrier? Trips to Mars for instance with the balloon being a solar/radiation shield for the inhabitants?

    All together this is an

    • That is a very interesting idea. I wonder what sort of propulsion would be required once the effectiveness of the balloon 'runs out' in order to get it above the gravity well?

      Seems to me if you can float your material into space, then you can float a *lot* of material into space...
    • Have you ever seen what happens when you put rubber into liquid nitrogen? Now extrapolate that to a few degrees Kelvin and you'll see why this idea (lovely as it might be otherwise) is DOA.
  • They should use a hydrogen balloon instead of helium - that way when they ignite the rocket, they'll get extra boost as the balloon explodes.

    >:-D
    • Unfortunately, the thrust created via the explosion would be in the wrong direction.

    • They should use a hydrogen balloon instead of helium - that way when they ignite the rocket, they'll get extra boost as the balloon explodes.

      Except that hydrogen needs oxygen to burn. That's why rocket fuel usually has a lot of oxidizer in it.

      By the way- this is the reason the Hindenburg really didn't burn 'because of the hydrogen'; there wasn't enough oxygen(if there had, there would have been a massive explosion- not a huge fire). As mentioned on slashdot among other places, scientists examined the

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