6

What force (in the form of periodic impulses) is required for thrusters (thermochemical, electrical, electromagnetic, ionic. Photonics, Hall) to keep such a disk in orbit (80 km) above a fixed point above Earth. To counteract gravitational force. And to prevent the disc from falling into orbit and its disintegration. The specific weight of such a disc could be approximately 10kg / m2

enter image description here

Ion Corbu
  • 79
  • 3
  • 4
    You can't pick an orbital period for an arbitrary orbital altitude. The two parameters are linked. To keep above a fixed point on Earth's equator, the orbital radius is 42,164 km. See https://space.stackexchange.com/a/8639/6944 A body moving around the Earth in 24 hours at 80 km altitude is not in orbit. – Organic Marble Oct 04 '19 at 12:53
  • 1
    Is there a reason for seveal such 10 km disk at 80 km altitude questions popping up recently? (Recently, there was one about the shadow such a disk casts) – Hagen von Eitzen Oct 04 '19 at 15:55
  • In terms of casting shadows, or blocking the sunlight, very similar outcomes could be achieved much more easily using a larger radius disk that was simply in proper geostationary orbit. – Jonathan Hartley Oct 04 '19 at 16:18
  • The problem is: from the 43,000 km orbit do you get more shadow? Or does the shadow turn into penumbra?

    Initially at the geostationary orbit I thought given that the centrifugal force cancels the gravitational attraction. And the force required for orbital corrections is very small. The arguments Steve Linton presented to me convinced me to abandon low orbit

    So, the quality of the shadow of the disc from an altitude of 43 km is good? Or not?

     – Ion Corbu Oct 04 '19 at 17:08
  • 1
    @IonCorbu: what is the purpose of the shadow? Do you want night over a 10km circle, to reduce insolation to fight global warming, or what? You would have all penumbra from GEO, but the reduction in solar heating over the earth would be the same. – Ross Millikan Oct 04 '19 at 20:52
  • Exact. My interest is to get a controllable shadow. On a surface of the Earth as large as possible. For various regions of the Earth. Including between Equator and Pol. Especially above the 45 degree parallel.

    Low orbit would be useful but the costs of maintaining the disk in orbit are huge.

     – Ion Corbu Oct 04 '19 at 23:42
  • The best is high orbit. This has high launch costs. But the costs of maintaining orbit are extremely low. The corrections can be made periodically, by pulses with thermochemical, ionic, photonic, Hall, etc. The disadvantage of this orbit, in my opinion, is that it reduces the shadow level. (the quality of the shadow. "the level of the shadow") Although, the surface on Earth of the shadow increases the shadow increases. – Ion Corbu Oct 04 '19 at 23:43
  • Which would be the orbital radius for an orbit to place the disc above a region in the Parallel area of 45 degrees. And the disk should behave as if placed in the Equatorial area. That is to say "geostationary"

    Another issue is whether to find an orbital slot (on high orbits) on which a large orbital disk can be placed.

     – Ion Corbu Oct 04 '19 at 23:44
  • Do you think I'm thinking well, Mr. Ross Millikan? Thanks for the intervention. Thanks for a possible point of view. – Ion Corbu Oct 04 '19 at 23:46
  • The aerodynamic drag at 80km is not negligible either. – Magic Octopus Urn Oct 05 '19 at 01:17

1 Answers1

10

The disk is in no sense in orbit if it stays above a fixed location on Earth at such a low altitude. Basically the thrust would need to do all the work to hold it up against Earth's gravity. So such a disk has an area of $5000^2\pi\ \mathrm{m^2}$ and so a mass of $2.5\pi\times 10^8\ \mathrm{kg}$ with your estimate for the area density of the disk. It would thus, to a first approximation, need a force of $2.5\pi g\times 10^8\ \mathrm N$ which is roughly $7.7\times 10^9\ \mathrm N$. This, for instance, roughly the thrust produced by 1000 of the F1 engines used to launch the Saturn V rocket burning continuously. They would consume about 2500 tons of propellants per second. This would be reduced slightly by the fact that the disk is moving around the Earth once per day and by the very slightly weaker gravity at 80 km altitude, but that would make a total difference of no more than a few percent.

Steve Linton
  • 19,594
  • 1
  • 64
  • 94
  • 5
    Carbon nanotube tether & counterweight out past geostationary orbit is more realistic than magical appearance of fuel for rockets. – Roko Mijic Oct 04 '19 at 09:42
  • Thank you Mr. Steve Linton. Your arguments are convincing. A compromise must be made between altitude, shadow quality and the effort to keep the large disk in orbit.

    Geostationary orbit is ideal. The problem is whether from the altitude of 43,000 km there is a shadow or not?

     – Ion Corbu Oct 04 '19 at 17:23