Find The False Assumption

…in this article about which asteroids are good prospects for human visits. It should just jump right out to regular readers. I’ll reveal over the fold:

A heavy-lift launch vehicle capable of delta-V greater than 7.5 km/sec. is required for any of these missions to happen.

Ignoring the issue of what it meant by “delta-V greater than 7.5 km/sec” (hyperbolic excess? Usually this is described in terms of C3), you do not need a heavy-lift vehicle to do that. A propellant depot will do the job quite nicely, and isn’t constrained in size or delta-V by launch facilities.

16 thoughts on “Find The False Assumption”

  1. I think another false assumption is that we should have no interest in asteroids below a certain size. Since I come at it from a resources standpoint, I think asteroids the size of small buildings might be of great interest. But even if we can’t look at this issue from any standpoint other than science, I don’t see why the composition and makeup of small asteroids wouldn’t be as interesting as for larger ones.

  2. It’s the difference between planting a flag on an asteroid and sticking a flag in an asteroid. It’s about looking good on TV.

  3. Rand, to be fair, I expect the reported NASA work was performed under an explicit requirement to use Ares V performance as a baseline mission constraint. Reporting such a result in this way is, therefore, hardly surprising and it does reflect a degree of honesty.

    This is typical of the way these types of studies are “structured” and a good example of why the results they produce need to be taken with a degree of caution.

  4. I wasn’t sure what would be required. I understood they are talking about a delta-V from the surface of the earth. I don’t know what the dV would be from orbit (I suppose I could look it up) or the dV of any craft that would go to an asteroid from orbit. Even with depots, the vehicle would have to have enough fuel to cover that.

    But yes, it all jumped right out and reading this blog has a lot to do with it.

  5. Rand, to be fair, I expect the reported NASA work was performed under an explicit requirement to use Ares V performance as a baseline mission constraint. Reporting such a result in this way is, therefore, hardly surprising and it does reflect a degree of honesty.

    No doubt, but it’s still misleading to say that it’s required.

    I wasn’t sure what would be required. I understood they are talking about a delta-V from the surface of the earth.

    No, that would be a minimum of 11.3 km (escape velocity).

  6. Other than the previously noted flaws, what I found truly disturbing was that I actually agreed in principal with the first comment from Gaetano Morono.

  7. Here’s a mission from an actual study.

    http://quantumg.net/1999AO10.jpg

    Note the delta-v requirements:

    1. get to LEO..
    2. earth departure 3.291 km/s
    3. arrival at the asteroid, 2.193 km/s
    4. departure from the asteroid, 1.746 km/s
    5. direct reentry or aerobrake.

    Total delta-v from LEO: 7.23 km/s.

    If you want a bigger number you can add the delta-v required to get to LEO to get: 16.23 km/s.

  8. How close could one get with the faux propellant depot/DIRECT plan of “just” launching two craft and transferring as much fuel as possible?

    Ex: 2x Falcon 9, one containing no payload (or a fuel-only payload) the other containing a rendezvous craft with no extra fuel.

  9. How close could one get with the faux propellant depot/DIRECT plan of “just” launching two craft and transferring as much fuel as possible?

    I’d like to know the answer to that, too. I got the outline to the answer from Jon Goff as to why depots are clearly a better architectural choice than rendezvousing with a separately launched propellant payload. Main take away is that mating depot to tank in freefall is less wasteful and less complicated than mating tank to engine for liquid fuels. That much is plain, I’d still like to know is at what point do the lead times to work up fuel to engine rendezvous become prohibitive vis a vis depots. From what I gathered, the wait just to sound out an actual depot in space is somewhere north of five years. I have no idea how quickly they could be deployed for real afterwards.

    If rendezvous for deep space missions is operationally viable now (or nearer to now than 2015), why not pursue it until the better arch is mature enough to replace it?

  10. Which flavor of Ares 5 are they talking about? The amount of money being provided will not build the biggest versions that were bandied about over the last few years (five segments, six engines, carbon/carbon SRB casings).

    The delta v could also be cut with a judicious use of a Lunar flyby, either posigrade or retrograde.

    The direct reentry is going to be mighty fast so the heat shield is going to be very big.

    Lots of issues here to deal with.

  11. My bad, from Goff:

    You really don’t save anything over a depot–you actually have to do all the stuff you’d need to do with a depot. You still need to make and unmake propellant connections, you still have to settle the propellants before you can transfer them to the engines, etc.

    I’m not sure, but I think Goff is hinting that this is the most critical and most difficult engineering challenge to breaking out propellant payload. If we can’t already do this, and since rendezvousing with propellant payloads–swapping or running pump lines–differs from depots principally increased difficulty and inefficiency, you might as well wait for depots.

  12. Al, to almost answer your question, see my writeup of an asteroid mission using existing SpaceX hardware: http://quantumg.blogspot.com/2010/07/john-hare-has-article-about-commercial.html

    I use two Falcon 9 tanking flights, not just the one, but I also assume no Raptor (LH2/LOX) stage as it doesn’t exist yet. With the higher ISP of LH2, and simultaneous launch to eliminate some of the insulation, I imagine you could do a respectable amount of IMLEO.

  13. Depot is the way to go, we have been putting one together at the Yahoo group NEAMines. (Look for the Milestones)

    Not only are you saving weight for critical onboard instruments and grapppling or mining hardware, you get to have a tug for moving up from LEO, and most of the infrastructure for on-orbit servicing of Zombie Sats and debris clean up.

    We are also hoping to salvage some of the waste sats for shielding and solar panels.

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