A large satellite appears to be falling apart in geostationary orbit | Hacker News Reader

A large satellite appears to be falling apart in geostationary orbit

arstechnica.com

79 pointsrobin_reala38 comments

>"The AMC-9 could have been attacked by something"

Are we sure its a real satellite? and real news?

New Cloverfield franchise film is coming out in October: https://en.wikipedia.org/wiki/God_Particle_(film)

J. J. Abrams and his company Bad Robot is known for doing this type of guerrilla marketing ( http://cloverfield.wikia.com/wiki/Viral ), they did it for both original Cloverfield and for 10 Cloverfield Lane. It included fake YT news clips, fake websites for fake satellite/oil/power companies, fake press releases, the whole nine yards.

Fake satellite: http://cloverfield.wikia.com/wiki/ChimpanzIII

ExoAnalytic was founded in 2008, the same time Abrams ran his first viral campaign for the Cloverfield.

More about the tangled lore and extent of the viral marketing: https://www.youtube.com/watch?v=FtaCF87_d0c

Cleaning up geosync orbit is going to be tough.

There's a proposal to remove small objects from low earth orbit by shining an 10KW or so earth-based laser at them for a few hours. This exerts enough light pressure to drop their orbit deeper into the atmosphere, where they slow further, re-enter, and burn up. That's probably the most cost-effective approach proposed so far. Now that solid-state lasers in the 50KW range are available, this looks like a viable option.

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.

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.

Everything I see about laser broom is for LEO not GEO.

https://en.m.wikipedia.org/wiki/Laser_broom

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.

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.

> 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".

> 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?

No if you raise the apogee without giving the object any additional speed, the perigee will be lower.

You did give the object additional speed.

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.

If x is the direction of travel at the moment of impact, Vx remains the same but it gains Vy. Total V increases.

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

I understand, but this subthread was about what happens when you hit it when it is directly overhead, pushing it outward.

That seems unlikely, but even in that case you'll achieve a lower perigee. It's also extremely unlikely that it would happen - hitting debris when it's directly overhead, yes, but hitting it on a surface that's perpendicular to the laser, like a letter T, probably not.

But assuming we do hit it like a T, the two things happen: loss of mass (laser ablation) and transfer of momentum. Vy will increase but Vx remains constant. The debris is moving in a straight line - that speed doesn't increase, but now it's moving at a different orbit so, relative to its previous orbit, Vx will appear to have reduced (but it hasn't).

But I'm definitely not an expert in orbital mechanics so don't quote me on that.

Okay, you're right, it does speed up very very slightly, but by an amount that is not anywhere near sufficient to keep the perigee from falling, as you originally claimed. The increase in eccentricity of the orbit is the larger effect.

Before intervention, it's velocity points perpendicular to the direction of the laser fire.

Maybe you can grok it by thinking of the laser as excerting torque on its current path, twisting it so that it soars higher initially but afterwards comes closer to the center of gravity of earth?

> If you push radially outward from a circular orbit, it should raise the apogee but keep the perigee the same.

I believe that effect requires thrust to "speed up" the object along its current heading. (Prograde)

Spend some time in Kerbal Space Program to get a sense of how little energy it takes to change a low orbit to one that grazes the atmosphere.

I got better things to do than play games :)

When the laser force acts for a short enough time and is strong enough, after the impact the orbiting body will acquire non-negligible positive radial velocity while changing its distance from the Earth only negligibly.

In the limit of an instantaneous impact, the body will change its velocity in a jump while not moving from the point of impact at all. Then it will continue to orbit the Earth on a new, elliptic orbit that shares with the old circular orbit the point of impact.

Since at this point the new radial velocity is positive, the body at this point is getting further away from the Earth. This means that before it will approach the point of impact again, it will have to be nearer the Earth. Hence the perigee is nearer the Earth than the point of impact.

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

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

[2]: http://scholarship.law.berkeley.edu/cgi/viewcontent.cgi?arti...

I read another article yesterday with Vector gushing about being able to launch two per week and just thought 'more space-junk' and that's just the delivery system. Some of these are launching multiple payloads - some no bigger than a briefcase. We need some sort of international treaty on corridors and such. Anything in the flight corridor gets the laser tractor beam.

OK, I see that AMC-9 is flashing at a more-or-less regular rate, throughout the video clip. But other geostationary satellites in the field, such as the four bright ones near the beginning of the clip, don't flash. This is because AMC-9 is spinning, right? Some flat surface, perhaps the PV array, is reflecting more of the sun's light.

I'm guessing that some of the attitude-control thrusters malfunctioned. Maybe that's what rendered the satellite unresponsive.

But in any case, excessive rotation could fragment the satellite. From the observed rotation rate and the size of the satellite, one could estimate a range of relative fragment velocities. And if one knew the video's angular field of view, one could estimate observed relative fragment velocities. I don't know that, but they seem smaller than velocity differences between AMC-9 and other geostationary satellites.

https://www.ses.com/our-coverage/satellites/315

So at that rate how fast is it spinning? Says it is fairly large satellite - car sized?

It's how fast it is spinning yes but it there could be multiple surfaces that reflect more brightly.

I actually work at a telescope where we're in the business of tracking satellites. Its boring work, but it's good as a summer job, and the professor it's under has me working on much cooler projects. I'll have to find the ephemerides of the sat and point out scope there.

True. And with multiple reflective surfaces, intensities would probably differ. I can see some of that in the clip. I also get the sense that it's tumbling on at least two axes. The light curve would be instructive.

The relative speeds of pretty much all objects that are in GEO orbit is probably very small - after all they all started out orbiting the earth in the same direction at the same speed. Shouldn't this make collecting debris much, much easier? Navigating within the orbit could be done using electric propulsion. Of course such an undertaking would still be very expensive given that once you have collected a bunch of debris you need to deorbit it.

When people talk about how crowded geostationary orbit is, keep in mind, that the surface area of a sphere 86,000 km above the earth is about 30 times larger than the surface area of the earth itself.

That’s relevant for geosynchronous orbits, but for geostationary, the circumference is 7 times longer than the equator’s distance.

"space weather problem" ?

https://en.m.wikipedia.org/wiki/Space_weather

I assume electronics that are failing due to shielding that has failed?

A space weather problem would be a single event upset. Something got flipped to the wrong state and could have burned up (e.g., power electronics). You protect designs against this with circuit design but can't use shielding. Shielding is to reduce total ionizing dose, not single event upsets.

It looks like structural fault.. two possibilities here: a) debris collision and, b) hardware fault during maneuvering (e.g. Fuel tank explosion, solar panel or antena detachement). The later I think is more likely to happen towards the end of the life of the hardware.. which seems to be the case.. but in other hand we could expect a cloud of smaller debris floating around..

That video is cool

If only we knew the details ...

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