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How does an Earth based laser bring something closer to Earth with radiatipn pressure rather than pushing it further away? And how does that work in GEO? The ty

How does an Earth based laser bring something closer to Earth with radiatipn pressure rather than pushing it further away? And how does that work in GEO? The typical disposal method there is to go up to a graveyard orbit, not down to the atmosphere. The atmosphere is very far away from GEO. You are looking at 35,000 km in GEO while the ISS is skimming the atmosphere in LEO at 400 km.

zdkl 9y ago
Once you destabilise the orbit you can be pretty sure things will end either in a ball of fire somewhere in the upper atmosphere or slingshotting into space. I wouldn't want to be in the path though.
- planteen 9y ago
  Everything I see about laser broom is for LEO not GEO. https://en.m.wikipedia.org/wiki/Laser_broom https://en.m.wikipedia.org/wiki/Laser_broom
robin_reala 9y ago
Debris still rises over the horizon, so lasing the front of the object will push it both out and back. If you can balance it so that the back degrades the orbit more than the out increases it then you’re good.
- planteen 9y ago
  That makes sense for how you could do a retrograde burn. Since for GEO the debris will be fixed or nearly fixed, I guess there always a horizon point by longitude. Seems like lots of extra atmosphere for the laser to go through.
Terr_ 9y ago
> How does an Earth based laser bring something closer to Earth with radiatipn pressure rather than pushing it further away? It changes the shape of the orbit. Shooting sideways is hard (more atmosphere) but pushing it away from the center of the earth works too: The orbit becomes less circular and more elliptical. While the higher point (apogee) is further away than before, the lowest point (perigee) is closer. Lower the perigee enough, and the satellite starts grazing the atmosphere. That's what really bleeds off energy, and causes the orbit to shrink overall. > And how does that work in GEO? I'm not sure. At that distance you can't rely on the same subtle destabilization, nor really hit it from any angle but "below".
- kobeya 9y ago
  > The orbit becomes less circular and more elliptical. While the higher point (apogee) is further away than before, the lowest point (perigee) is closer. Orbital dynamics is complicated and I admit I could be wrong here, but I'm pretty sure this is incorrect. If you push radially outward from a circular orbit, it should raise the apogee but keep the perigee the same. I could see this working if you exert a radially outward force on an object in an elliptical orbit that is already coming in from apogee to perigee, because relative to the object's radial velocity that would actually be a braking maneuver. Is that what you meant?
  - freeman478 9y ago
    No if you raise the apogee without giving the object any additional speed, the perigee will be lower.
    - kobeya 9y ago
      You did give the object additional speed.
      - ScottBurson 9y ago
        No, you've deflected it in a direction perpendicular to the one it's moving in; turning it slightly away from the Earth, initially, but not speeding it up. This will increase the eccentricity of the orbit.
        kobeya 9y ago
        If x is the direction of travel at the moment of impact, Vx remains the same but it gains Vy. Total V increases.
        eyko 9y ago
        It depends on the angle at which you hit the debris with the laser, as well as the shape of the debris. The idea is, generally, to hit the debris at an angle as it approaches you (bottom front of you may)[1]. Depending on the shape of the object as well as the material of the surface, you'll be able to transfer enough momentum to actually slow it down as well as nudge it further (loss of mass?) out into a new orbit with a low enough perigee. It's obviously not easy to predict the new orbit because debris comes in very different shapes, and of many different materials. Also, because there's a transfer of energy, the part of its original Vx is lost in the process (the laser is deflected at an angle). There's no loss of total Vx (sum of laser Vx and debris Vx) however. 1: See figure 3 in page 6 of this pdf (the laser at an angle). https://arxiv.org/pdf/1004.0390 https://arxiv.org/pdf/1004.0390
emj 9y ago
Yeah, the linear scale graph from wikipedia does make GEO seem very large. I'm guessing wildly here but most things in GEO should be orbiting in the same(ish) speed and direction, which makes a cascade as those we will get in LEO less likely. Still makes you worried though.. https://commons.wikimedia.org/wiki/File:Orbitalaltitudes.jpg https://commons.wikimedia.org/wiki/File:Orbitalaltitudes.jpg
- bsmith89 9y ago
  Anything in geostationary orbit must orbit at exactly the same speed (at least on average) to stay perfectly aligned with a spot on the equator. When that _doesn't _ hold, collisions are exceedingly likely, since it's a 1-d path with more than 400 satellites [1]. It sounds like positional tolerances are about 1/10th of a degree in either direction, which leads to the back-of-the-envelope estimate of a 1800 satellite capacity at geostationary [2]. My mind is blown that a circle with a circumference of 2.65e5 km can only hold 1800 objects, safely, but that's what 1-dimensionality dictates. That number could be increased linearly with narrower positional tolerances. But there is also, presumably, the potential for a lot more room in geosynchronous orbit, since satellite paths can spread into another dimension. Does anyone know if this actually works? [1]: http://www.satsig.net/sslist.htm http://www.satsig.net/sslist.htm [2]: http://scholarship.law.berkeley.edu/cgi/viewcontent.cgi?article=1294&context=btlj http://scholarship.law.berkeley.edu/cgi/viewcontent.cgi?arti...

zdkl 9y ago

Once you destabilise the orbit you can be pretty sure things will end either in a ball of fire somewhere in the upper atmosphere or slingshotting into space. I wouldn't want to be in the path though.

planteen 9y ago
Everything I see about laser broom is for LEO not GEO. https://en.m.wikipedia.org/wiki/Laser_broom https://en.m.wikipedia.org/wiki/Laser_broom

robin_reala 9y ago

Debris still rises over the horizon, so lasing the front of the object will push it both out and back. If you can balance it so that the back degrades the orbit more than the out increases it then you’re good.

planteen 9y ago
That makes sense for how you could do a retrograde burn. Since for GEO the debris will be fixed or nearly fixed, I guess there always a horizon point by longitude. Seems like lots of extra atmosphere for the laser to go through.

Terr_ 9y ago

> How does an Earth based laser bring something closer to Earth with radiatipn pressure rather than pushing it further away? It changes the shape of the orbit. Shooting sideways is hard (more atmosphere) but pushing it away from the center of the earth works too: The orbit becomes less circular and more elliptical. While the higher point (apogee) is further away than before, the lowest point (perigee) is closer. Lower the perigee enough, and the satellite starts grazing the atmosphere. That's what really bleeds off energy, and causes the orbit to shrink overall. > And how does that work in GEO? I'm not sure. At that distance you can't rely on the same subtle destabilization, nor really hit it from any angle but "below".

kobeya 9y ago
> The orbit becomes less circular and more elliptical. While the higher point (apogee) is further away than before, the lowest point (perigee) is closer. Orbital dynamics is complicated and I admit I could be wrong here, but I'm pretty sure this is incorrect. If you push radially outward from a circular orbit, it should raise the apogee but keep the perigee the same. I could see this working if you exert a radially outward force on an object in an elliptical orbit that is already coming in from apogee to perigee, because relative to the object's radial velocity that would actually be a braking maneuver. Is that what you meant?
- freeman478 9y ago
  No if you raise the apogee without giving the object any additional speed, the perigee will be lower.
  - kobeya 9y ago
    You did give the object additional speed.
    - ScottBurson 9y ago
      No, you've deflected it in a direction perpendicular to the one it's moving in; turning it slightly away from the Earth, initially, but not speeding it up. This will increase the eccentricity of the orbit.
      - kobeya 9y ago
        If x is the direction of travel at the moment of impact, Vx remains the same but it gains Vy. Total V increases.
        eyko 9y ago
        It depends on the angle at which you hit the debris with the laser, as well as the shape of the debris. The idea is, generally, to hit the debris at an angle as it approaches you (bottom front of you may)[1]. Depending on the shape of the object as well as the material of the surface, you'll be able to transfer enough momentum to actually slow it down as well as nudge it further (loss of mass?) out into a new orbit with a low enough perigee. It's obviously not easy to predict the new orbit because debris comes in very different shapes, and of many different materials. Also, because there's a transfer of energy, the part of its original Vx is lost in the process (the laser is deflected at an angle). There's no loss of total Vx (sum of laser Vx and debris Vx) however. 1: See figure 3 in page 6 of this pdf (the laser at an angle). https://arxiv.org/pdf/1004.0390 https://arxiv.org/pdf/1004.0390

emj 9y ago

Yeah, the linear scale graph from wikipedia does make GEO seem very large. I'm guessing wildly here but most things in GEO should be orbiting in the same(ish) speed and direction, which makes a cascade as those we will get in LEO less likely. Still makes you worried though.. https://commons.wikimedia.org/wiki/File:Orbitalaltitudes.jpg https://commons.wikimedia.org/wiki/File:Orbitalaltitudes.jpg

bsmith89 9y ago
Anything in geostationary orbit must orbit at exactly the same speed (at least on average) to stay perfectly aligned with a spot on the equator. When that _doesn't _ hold, collisions are exceedingly likely, since it's a 1-d path with more than 400 satellites [1]. It sounds like positional tolerances are about 1/10th of a degree in either direction, which leads to the back-of-the-envelope estimate of a 1800 satellite capacity at geostationary [2]. My mind is blown that a circle with a circumference of 2.65e5 km can only hold 1800 objects, safely, but that's what 1-dimensionality dictates. That number could be increased linearly with narrower positional tolerances. But there is also, presumably, the potential for a lot more room in geosynchronous orbit, since satellite paths can spread into another dimension. Does anyone know if this actually works? [1]: http://www.satsig.net/sslist.htm http://www.satsig.net/sslist.htm [2]: http://scholarship.law.berkeley.edu/cgi/viewcontent.cgi?article=1294&context=btlj http://scholarship.law.berkeley.edu/cgi/viewcontent.cgi?arti...