Flyby asteroid rotovator

Discussion in 'Science and Technology' started by publiusr, Aug 29, 2015.

  1. publiusr

    publiusr Vice Admiral Admiral

    Mar 22, 2010
    One of the problems with space elevators will be the constant attack by atomic oxygen--not to mention icing loads near the ITCZ. (Convection is deeper near the equator)

    One concept I had was an asteroid bola with a tail that could fly by Earth, deposit a large load, and yank a load upward.

    Doctor Pat from Next Big Future was kind enough to supply the math: (Scroll down)

    Minimum velocity of the center of mass of the rotovator is the minimal orbital velocity of 7.8 km/s
    Velocity of rotor tip at pickup from the ground needs to be about 0, or close enough to make no difference to this level of calculation.
    Minimum rotor length is going to be the height of LEO, so about 100 km.
    Maximum velocity of the rotor tip in the atmosphere should be lets say no more than mach 6 (~2 km/s) until it reaches at least 20 km in altitude. Based on the articles about hypersonic aircraft and what they can handle.

    Let's put that together.

    If we assume the tip of the rotor is sort of accelerating straight up with respect to the earth's surface, that means that the tip goes from 0 to 2000 m/s in 20 km.
    v[sup]2[/sup] = 2 x Acceleration x distance
    4 000 000 = 40 000 x Acceleration
    Acceleration = 100 m/s/s = 10g (actually, that turned out rather reasonable)

    Accel. = v[sup]2[/sup] / R (note, now V is relative to rotor center, not Earth)
    V = twice the rotor center speed = 15.6 km/s
    R (rotor radius) = 2.4 million meters = 2400 km.

    OK, that's a lot higher than our original Minimum rotor length, so it meets that limit too.

    But a rotor that long does not need to going to not be travelling at LEO speeds, so we can slow everything down a bit. But the minimum is still 6.7 km/s, so it isn't enough to make much difference.

    Anyway, the real problem is that to have a reasonable speed through the thick parts of the atmosphere, your rotor needs to be so long that you are looking at a 2400 km long rotor. Not quite a space elevator cable, but it would be a serious material strength problem."

    That's only 1,500 miles--not 22,500--to--60,000.

    Lunar Elevator meeting

    Supertall towers

    Misc SLS art
    Magnetic hole
    Light fibers

    ISS seen from the ground
    Last edited: Aug 29, 2015
  2. PurpleBuddha

    PurpleBuddha Rear Admiral Rear Admiral

    Apr 14, 2003
    Here's a vid about something very similar. I like the idea! It seems more feasible than a space elevator.

  3. ThunderAeroI

    ThunderAeroI Rear Admiral Rear Admiral

    Feb 28, 2002
    Perpetually being chased by airplanes
    ^, Was that video narrated by Krepky?
  4. PurpleBuddha

    PurpleBuddha Rear Admiral Rear Admiral

    Apr 14, 2003
    They do sound similar. :) He even acknowledges it in one of his other videos.