Asteroids as Transportation Hubs


This is a sketch from a post I did in 2009  about moving asteroids using their own rotational energy to sling ISRU mass  to change their orbit.

With Jons’ last post, I got to speculating about other ways of getting mass from an asteroid back to Earth. What if the exploring spacecraft carried a tether to the asteroid that was long enough to serve as a beanstalk. Instead of carting the selected boulder(s) all the way home, the beanstalk is used to sling a number of samples to Cislunar space to be caught by some TBD craft.

Instead of the thousand ton boulders slung in the original post, ten or so tons per throw would send a sizable mass to explore and exploit close to home while leaving the spacecraft in the field for a continuing mission. While as in the previous it would be necessary to wait for launch windows to use the tether,  the time between arrival and window could be spent exploring the body in question and organizing multiple throws. When the window opens, the ten (or one or thirty) ton samples could be sent Earthward every time the asteroid rotates. A four hour asteroid rotational day would give six launches per Earth day. A window a week long could have forty or so samples heading home at once.

If the asteroid is considered explored by that time to the limits of the available craft, it is time to head to the next target. One way of doing that would be for the spacecraft to climb the tether to well past astrosync orbit to a point calculated to sling it to the next body to be explored. At the right time, the tether is cut loose at the asteroid end to send the vehicle and its’ tether to a new little unexplored world. Once there, the cycle is repeated. It would seem that the craft could explore and exploit indefinitely without running out of propellant.

For a second phase of exploitation, tethers are left attached to the asteroids for use by future visitors. Eventually, spacecraft could visit dozens of rocks during an operational lifetime to prospect for different substances or to test new techniques in a variety of locations.

Certain asteroids would be exceptionally useful in a third phase if they proved exceptionally well suited for transportation hubs. Instead of slinging small robotic prospectors to other rocks, long beanstalks could relay humans and cargo to Mars and other points of interest throughout the inner solar system.

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I do construction for a living and aerospace as an occasional hobby. I am an inventor and a bit of an entrepreneur. I've been self employed since the 1980s and working in concrete since the 1970s. When I grow up, I want to work with rockets and spacecraft. I did a stupid rocket trick a few decades back and decided not to try another hot fire without adult supervision. Haven't located much of that as we are all big kids when working with our passions.

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12 Responses to Asteroids as Transportation Hubs

  1. PeterH says:

    The tether sounds like an effective way to get much of the delta-V for a spacecraft to reach the next asteroid. But propulsion for course correction and stopping at the destination is still needed.

  2. Hop David says:

    John Hare, I’m happy to see you write about this. Asteroid tethers/elevators are one of my favorite daydreams. Asteroids have shallow gravity wells. Many have high angular velocity. This makes elevators more doable.

    I talked a little bit about Ceres and Vesta elevators on my look at Clarke towers.

    But playing Devil’s Advocate against one my favorite daydreams:

    The asteroid needs to rotate about a single axis. A lot of rocks tumble.

    The asteroid’s orbit needs to have low inclination, an orbit not far from the ecliptic plane. And since elevators will be in the asteroid’s equatorial plane, the asteroid should have low obliquity. Else payloads thrown by the elevator will have to do an expensive plane change enroute to earth.

    I don’t think these are show stoppers. But problems worth considering.

  3. briang says:

    single axis rotation makes the release much cleaner to calculate, but even in tumble, if you can get your (changing) orientation from star scope or gyro then there should be portions of the tumble that are in useful planes for release. definitely still need maneuvering fuel, but i love this idea. let’s go oort hopping.

  4. john hare says:

    I followed your link Hop David, kewl. Anyone that wants a more professional and detailed look at the possibilities should follow the ling to Hops’ post.

  5. Hop David says:

    Has anyone modeled a tether extending from a tumbling asteroid?

    An ordinary elevator from a body spinning about a single axis body would have some problems with oscillations. Mostly induced by coriolis force as payloads descend/ascend. Such oscillations can be damped by timing ascent/descent of payloads. Tethers in earth’s magnetic field can dampen harmonics by running current through the tether and using earth’s magnetic field and Lorentz force.

    I’d expect the oscillations induced by tumbling to be strong and chaotic. Admittedly, my opinion is uninformed. I wouldn’t even know where to begin in building a model of this.

    If elevators from tumbling rocks are viable, that would mean a lot more candidates for use. Especially among the Near Earth Asteroids.

  6. George Turner says:

    A quick thought on that is to attach a pulley to the lower end of the tether and then run another cable through it, with one anchor point in the north and one in the south. You could model it by shoving a pair of nails into a piece of fruit, tying a string (threaded through a small pulley) loosely between them, and then hanging the whole thing by another string tied to the pulley. It’s like hanging a picture frame with the usual piece of wire run through a pulley that’s suspended from a cord.

    There would be a small change in the radial distance with each wobble, but I’m not sure it would be very important

  7. Hop David says:

    In the Space Stack Exchange, 2012 Campion has taken a look at slings. Since asteroids have such shallow gravity wells, his sling model approximates an asteroid Clarke tower.

    Before reading his answer I had thought big tether tip velocities were doable. His analysis has forced me to rein in some of my more optimistic day dreams. Big tip velocities make for big taper ratios.

    I’m still enthusiastic about asteroid tethers. Taper ratios may put a ceiling on tether tip velocities but these speeds are still high enough they can take a substantial chunk out of propellent mass ratios needed to get from point A to B.

    I was looking forward to meeting some people at the Space Conference. But I need to cover a high school honors banquet on Thursday and Ajo’s Cinco de Mayo celebration on Saturday. Is anyone still going to be there Saturday evening and Sunday morning?

  8. john hare says:

    2.5 tether to payload ratio delivering 1.68 km/sec seems like a going concern to me. A little more route planning in exchange for minimal propellant use seems like a fair trade. A payload a (rock) day should keep bankruptcy away.

    I’m not making Space Access this year. The times I’ve been, people are still going into the wee hours. Once we were still at it when the sun came up Sunday morning.

  9. ken anthony says:

    The asteroid needs to rotate about a single axis. A lot of rocks tumble.

    Huh? A tumble is still a single axis, it’s just viewed from the perspective of two axis.

  10. ken anthony says:

    EM Drive seems to kill the idea. 50 tons of thrust per megawatt. Just need a nice little family reactor.

  11. Peterh says:

    Presuming EM drive isn’t an experimental artifact it will be a massively disruptive technology, both for space flight and basic physics. So far everything I’ve seen has focused on the resonant chamber and largely neglected the feed system, another potential source of error.

  12. ken anthony says:

    I wonder how they can claim it works and not publicly display it working?

    100 lbs per kWatt is a lot of thrust. Put a chair on a guide, then let morning newscasters take a 2 kWatt ride.

    Not doing this, which would be a massive fund raiser, suggests it’a all BS.

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