While a cascade in LEO is something to be very concerned about, this Pop Sci article gets this quite wrong:
If a chain reaction got out of control up there, it could very quickly sever our communications, our GPS system (upon which the U.S. military heavily relies)…
Most communications satellites are in GEO, thousands of miles above LEO, and GPS are in twelve-hour orbits, also very high, but not as high as GEO. Most of our communications would remain intact, as would GPS.
Things in the same/similar orbit are also traveling at the same/similar speed… unless one is a retro orbit which would tend to cause the debris to deorbit.
Somebody should collect all that valuable mass some day.
Very few objects in LEO are in the same orbit. Most are in different orbit planes. Relative velocities are many thousands of miles an hour.
This is off-topic, but has anyone seen this? It sounds interesting, to say the least.
NASA in Shock New Controversy: Two Global Warming Reasons Why by John O’Sullivan, guest post at Climate Realists
Wouldn’t objects crashing into one another lose velocity and eventually de-orbit?
Of course, the real risk of space debris is actually in GEO. LEO has enough atmosphere to clean itself out pretty quickly – but once collisions start in GEO we will very quickly have a permanent (in human terms) belt of junk. Things in GEO just don’t de-orbit fast enough.
Don’t objects in GEO need a higher speed to stay in a GEO? Thus if you slow them down a little wouldn’t they start to decelerate faster than an object in NEO? Help me along, I have never really thought about this before.
David:
True, but the threat to GEO is probably less immediate, since there are fewer satellites and junk in that orbit, and also there’s a much greater volume of space at that altitude than at LEO.
In other words, if a cascade happens, we’ll see it first in LEO, which would hopefully spur people to take action to prevent it from happening in GEO. Obviously, it would be better still if we take action before it happens in LEO.
Not really, the actual velocity in GEO is lower than in LEO. Orbital velocity goes down with altitude. Collisions in space don’t really slow down the resulting debris that much, either. You typically get two clouds of debris, one in each of the original orbits. The particles have a distribution of velocities, but a lot stays close to the original orbital speed.
Another way to look at it is that if you dropped the velocity of an object in GEO magically to 1 m/s, it would then be in a highly elliptical orbit that still intersects GEO. To prevent that, the object must intersect the Earth.
Satellites in Geosynchronous orbit are all in a “shell” at an altitude of 22,300 miles. A chain reaction caused by debris within this “shell” would essentially create a ring of debris at that altitude, making any further placement of a satellite into geosynchronous orbit impossible …. forever.
The above was for Jardinero1, of course.
Planetes
http://www.animenewsnetwork.com/encyclopedia/anime.php?id=2654
Somebody should collect all that valuable mass some day.
Indeed. The replacement cost of each kilogram of space junk is at least $5,000 just to get it into orbit. Collecting and reprocessing what’s already there would appear to offer a lucrative opportunity for someone to do some ISRU real close to home. There are thousands of tons of raw material floating around up there.
Robotic ion thruster driven tugs of various sizes could round up everything from the really big stuff down to kilogram-scale bits. If said ion thrusters are engineered to “burn” argon one could also justify a modest start on the depot infrastructure we’ll eventually need for nuclear-VASIMR-powered true human-occupied deep spacecraft.
The microgravity environment of orbit allows for advantages in breaking down space junk into piles of constituent chemical elements that are not easily duplicated here on Earth. A solar powered rig that uses lasers or RF energy to break down random junk and something like an industrial-scale mass spectrometer to segregate the elemental materials would seem to me the best general path to take. The output of this process would feed additive fabrication processes similar to certain earthbound rapid prototyping techniques. Microgravity provides both challenges and opportunities in engineering such zero-g fabs.
The ISS or a purpose-built station of Bigelow-type habs would be good places to centrally collect and process space detritus. The ISS might even be preferable as it is also a likely incremental future source of raw material that wouldn’t have to be fetched first. If the thing stays in orbit it’s going to have to be re-fit and upgraded repeatedly over the coming decades and is likely to represent the largest single orbital mass for some time to come.
To clean up the smaller stuff, one or more solar-powered continuous output lasers in the megawatt or greater range could be put between LEO and GEO and raster their east-to-west-directed beams through loci corresponding to heavily used orbital altitudes and inclinations. The laser steering would be controlled in real time by a database of known active birds and craft in transit so as to illuminate only orbital debris. A laser doesn’t have to dwell long enough to actually vaporize surface material from dust grains and shrapnel fragments, the photonic energy imparted on each contact with a piece of debris would remove a bit of orbital energy and, over time, de-orbit it. Because of the cube-square law, the sand-sized bits would fall first and the pebbles would follow in rough order of surface/mass ratio.
Just a thought: Could space junk removal be an opportunity for private companies? Would governments pay them to collect it and haul it away? Hey, you’ve got to start somewhere.
Maybe someone should hire these guys, if they’re still in business:
http://www.youtube.com/watch?v=xHUWlEB6N1s
The energy is what’s greater. You accelerate a body into a higher orbit (where it will go slower) because it needs more GPE to stay there.
This is all very interesting. NASA has an office devoted to the study of orbital debris, and its chief, Nicholas Johnson, gave a briefing at last October’s COMSTAC. The bottom line was that, no matter how they play the numbers (including collisions in orbit), orbital debris will not constitute a problem of any kind for the next 50 years, and a threat worth worrying about the next 100 (if then). That’s if we continue to operate the way we do without requiring more aggressive cleanup.
A great deal of time was spent in Q&A trying to invent scenarios that would make it a problem, and in every case he replied: “Yeah, we looked at that — and worse — and it just isn’t a big deal.”
it just isn’t a big deal
That’s what I figure. Different velocities generally means good separation with the one exception Rand gave. Even then, objects in the same orbital shell but different orbital plane while they may have huge velocity differences are still traveling at about the same speed and if they miss at the point where there orbit intersect are going to keep missing. Slight differences may allow one to catch up with the other but that should be rare.
Eccentric orbits should degrade whenever they dip below a few hundred miles leaving mostly circular orbits.
Happy to have my ignorance corrected.
Everything in GEO is traveling at the same speed in the same plane. There is no way to get a “chain reaction” there.
“Everything in GEO is traveling at the same speed in the same plane. There is no way to get a “chain reaction” there.”
Actually, that’s not so. Left to their own devices, free objects in GEO will drift east or west to one of two libration points equatorially — 105 degrees west, and 75 degrees east. And oblateness combined with solar radiation makes them walk north and south. North-south stationkeeping is the biggest consumer of GEO linear delta V.
GEO actually does indeed look like a shell, with lots of small debris orbiting in all directions. The orbital velocity is about 10,082 feet per second, so collisions are less damaging than in LEO. But still bad.
Yes, but generally, they’re not left to their own devices. Or rather, they are left to their own devices, which help them station keep. 😉
…free objects in GEO will drift east or west to one of two libration points equatorially…
But they’re all in the same dance.
So which is it, gravity forms moons or gravity forms belts?
Most communications satellites are in GEO, thousands of miles above LEO, and GPS are in twelve-hour orbits, also very high, but not as high as GEO. Most of our communications would remain intact, as would GPS.
That thought crossed my mind more fleetingly than the article passed by my eyes, but I’d assumed that PopSci wouldn’t make such an egregious error. I’m happy to be wrong. No doubt the error was flagrant to a knowledgeable reader, but thx to Rand for taking a moment to point it out.
I’d assumed that at worst it would be a race between rendering LEO uninhabitable because of junk and achieving a critical mass of human presence & technology that would underwrite a clean-up. According to Dick Eagleson and MfK, the outlook is a lot more positive than I feared.
Yes, but generally, they’re not left to their own devices. Or rather, they are left to their own devices, which help them station keep.
That only applies to operational satellites. Before they started the policy of supersynching GEO satellites as they neared end of life, satellites operated until they died and remained in the GEO belt while some recent satellites died without an opportunity to supersynch them. The end result are a number of dead satellites and some rocket bodies at GEO altitude. Without adjustment for north-south inclination, the inclination will increase approximately 1 degree per year. There are some satellites in that belt with inclinations exceeding 20 degrees. Strictly speaking, they’re not in the same plane as a geostationary satellite.
Those two libration points actually seem to act to sweep the belt clean.
Perhaps someday, they can be mined for raw material.
Long term, the best way to keep big things from running into each other and making lots of troublesome little things is to take the big things out of circulation systematically as they reach end of life. Building birds with end-of-life kick motors to place them in high “graveyard” orbits is only a kick the can down the road approach. It simply results in an ever-growing quantity of potentially reusable mass whizzing uselessly about. A modest fleet of ion-driven scrounge-bots could keep the problem from ever getting out of hand and provide reworked usable mass with a very low launch cost equivalent. There’s definitely a viable business model here.
I think the problem will be one of increasing pain rather than a sudden “you can’t operate in LEO.” I’m surprised but glad to hear Nicholas says things won’t go ‘critical,’ though we still need to be good stewards of the LEO region.
The satellites I work with are at ~705km altitude. Both the Chinese ASAT test and the Iridium/Cosmos crash were above that altitude, so there’s been a spike in the close approaches we’ve seen labeled as having one of those sources. We’ve only maneuvered once, and that was due to something entirely different.
I forget which, but isn’t Phobos or Deimos going to degrade into Mars?
If it ever becomes honestly untenable due to scattered light material, what about a ‘solar broom’? A solar collector-reflector shouldn’t need to be too large to generate a cumulative delta-v large enough to divert small particles into much more distinctly decaying orbits.
Geosync is useful enough that heroic measures would indeed be taken. Eventually.
MfK Says:
May 29th, 2010 at 9:29 am
Left to their own devices, free objects in GEO will drift east or west to one of two libration points equatorially — 105 degrees west, and 75 degrees east.
But, the speed of collision would be that drift speed. How large is it?
And oblateness combined with solar radiation makes them walk north and south… The orbital velocity is about 10,082 feet per second, so collisions are less damaging than in LEO. But still bad.
Then from Larry J @ May 29th, 2010 at 12:50 pm :
“There are some satellites in that belt with inclinations exceeding 20 degrees.”
So, the relative velocity could be 10,082*2*sin(20/2) = 3501 ft/sec or 2387 mph. That’d do some damage all right.
However, the impact parameter has to be less than the sum of the two largest spacecraft radii.The odds of that would be tiny on a single pass, but might grow measurably after many passes and with many spacecraft… I think I’ve gone as far as I feel like doing for now.
David Says:
May 28th, 2010 at 5:52 pm
“You typically get two clouds of debris, one in each of the original orbits. “
Mustn’t the system CG would remain in essentially the same orbit as before? I think so, but I’m feeling a little groggy at the moment.
Lose something in orbit? Here’s where you should lose it.
Unintended comedy… the forgotten link for prior post. Ah, nevermind.