StratoLaunch

Here’s an article at the WaPo about it. This isn’t correct, though:

It is always desirable to launch to the east to capi­tal­ize on the direction of the Earth’s spin. The Earth travels about 1,000 mph west to east at the equator; you need to reach a speed of 17,000 mph to get to low-Earth orbit, so there’s no point in penalizing yourself 1,000 mph by heading in the wrong direction.

No, not “always.” Only for low-inclination orbits. For very high inclination, or retrograde, it’s actually preferable to launch from a high latitude (ideally, for a retrograde orbit, you’d like to launch from a pole, to eliminate any earth rotation, because it’s rotating in the wrong direction).

6 thoughts on “StratoLaunch

  1. George Turner

    That made me think of a question. How efficient would solar-ion thrusters need to be before it’s more mass efficient to launch a retrograde satellite pro-grade from the equator, slowly boost it almost free of Earth’s orbit on ion thrusters, and then bring it back into low orbit on a retrograde path?

  2. Arizona CJ

    Hrmmm. Given that there are quite a few retrograde satellites, and two particular types of them (Synthetic-aperture radar and sun-synchronous recon) are likely payloads for Stratolaunch, I find the article’s statement doubly perplexing.

  3. dcguy

    I guess like anything you can do the math.

    7900 M/S, figure out you need to reverse that, so worst case, you need 16,000 M/S and then from there, make a guess on a mass fraction, say 98% and back out an Isp.

    or, calculate how much delta V you need to go into lunar transfer, go around the moon, backwards, and have it reverse your momentum vector. Tighter windows and some orbital mechanics, but, make some assumptions and do the math.

  4. dcguy

    I guess like anything you can do the math.

    7900 M/S, figure out you need to reverse that, so worst case, you need 16,000 M/S and then from there, make a guess on a mass fraction, say 98% and back out an Isp.

    or, calculate how much delta V you need to go into lunar transfer, go around the moon, backwards, and have it reverse your momentum vector. Tighter windows and some orbital mechanics, but, make some assumptions and do the math.

    1. George Turner

      I’m thinking lots of math. You’d want to use a low-energy transfer path over several months to work the satellite as far out as possible, similar to what the GRAIL lunar mapping mission used. Once it’s essentially escaped, it alters course slightly to fall back past the Earth and make a high-velocity aero-braking maneuver, then circularizes the new retrograde orbit.

  5. Steve A

    One other nit to pick with the article: it lists “the spacecraft would be released in rarefied atmosphere with high tail winds to kick it forward” as advantages over ground launch. The launch from rarefied atmosphere I’ll accept; the “high tail winds” is pure BS. A ground-launched vehicle would be just as apt to benefit from high tail winds as an air-launched vehicle given a specified launch trajectory. High tail winds at altitude are not a given; though seasonal in nature, they vary due to weather and the location of the jet stream.

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