9 Ideas For Coping With Space Junk 149
An anonymous reader writes "The space age has filled Earth's orbit with all manner of space junk, from spent rocket stages to frozen bags of astronaut urine, and the problem keeps getting worse. NASA's orbital debris experts estimate that there are currently about 19,000 pieces of space junk that are larger than 10 centimeters, and about 500,000 slightly smaller objects. Researchers and space companies are plotting ways to clean up the mess, and a new photo gallery from Discover Magazine highlights some of the proposals. They range from the cool & doable, like equipping every satellite with a high-tech kite tail for deployment once the satellite is defunct, to the cool & unlikely, like lasers in space."
Re:Hmm (Score:4, Informative)
Why shouldn't it be hard? Large changes in velocity require large amounts of fuel. Doesn't matter if you are "speeding up" or "slowing down". That's why so many of these ideas involve working out a way for satellites to increase their drag after a time.
Re:Hit or Miss (Score:2, Informative)
the tool kit dropped by astronaut Heide Stefanyshyn-Piper during a spacewalk in 2008
That tool kit re-entered the atmosphere in August of 2009. http://en.wikipedia.org/wiki/Heidemarie_Stefanyshyn-Piper#Lost_tool_bag_during_spacewalk [wikipedia.org] Come on guys. Do some fact checking.
Statistics... (Score:4, Informative)
...that is not how they work.
There are no 669,725 people that are in any more danger than anyone else. There isn't a 1/10,000 chance that it will hit each person, there is a 1/10,000 chance that it will hit any person. In other words, for every ten-thousand pieces of space junk that fall, you might get a single casualty.
If you think these are particularly bad odds, then I have some bad news about your car...
Re:Orbital Junk (Score:3, Informative)
I guess that would be "just detonate the nukes already in orbit" in that particular case.
Re:Out of dimension? (Score:5, Informative)
You need to get through all the orbits of uncontrolled junk, which takes a lot of calculation and you can only move so fast.
You have to be able to get out of the way of new junk that's moving so fast you can't accelerate quickly enough to wait and see if it might miss you.
Calculation of junk trajectory is only so precise, so you have to leave a 'safety buffer' of sorts.
There's more junk up there than we have cataloged. There will always be new junk, and collisions alter orbits of existing junk such that our known trajectories become inaccurate and we have to relocate and recalculate all the time.
So finding a safe zone which requires the least fuel usage to stay alive is becoming more challenging.
Tiny fragments that wouldn't harm anyone if you threw it at them are deadly, equipment-wrecking projectiles at high velocity. Think about a small piece of metal, like a penny. Not a problem if you drop it on your foot. Not going to destroy a vehicle if you drop if off a towering skyscraper, even. But, in space where there's no[t enough] atmosphere to slow it down or burn it up, it can theoretically approach any speed... and a 1,000 MPH penny is a fearsome entity to a fragile laboratory measurement device. We might not even be able to track that very accurately, but if you guess wrong... you transfer that momentum into multiple new shards of former expensive equipment!
So getting things into space is really getting more complicated and keeping things alive up there takes a lot more calculation and fuel as the probability of stray objects increases. Does that cut down on the exaggeration factor?
The answer is simple: Funding. (Score:3, Informative)
We don't need new strategies for getting objects down from space. We know how to get them down. When a satellite has outlived its usefulness, you reserve enough fuel so that it can deorbit itself.
The problem is that satellites are expensive and rare still, so we don't want to give them up. So we keep the missions up there for years past their expected lifetime, with the result that they don't have deorbiting fuel left over when they finally break down enough that they're no good to us anymore.
An example: I work with Landsat 5. It was launched in 1982 with a 5 year mission plan. It's still up there, 28 years later, and still a vital piece of the US remote sensing strategy. The next similar satellite won't be launched until 2012. Although it had a deorbiting plan that would have sunk it into the atmosphere a few years after it was decommissioned, that plan was waived. The current plan is to put it into an orbit that will leave it as space debris for 1000 years before it gets low enough to burn in.
If we had funded the satellite program enough, there would have been several follow-on missions and L5 would not still be essential. We would have been able to deorbit it without complaint if there were others that could have taken its role.
Fund space and you won't have space problems. Don't fund it and it'll become a graveyard. Simple as that.
Re:Lasers... (Score:4, Informative)
Re:Lasers... (Score:3, Informative)
Not to point out the obvious, but killing flies and destroying space junk are two very different things.
The insect laser only needs to wound the insect enough that it is no longer a trouble- badly damage the wings, or cause it bodily injury. The insect then tumbles harmlessly to the ground.
The debris laser needs to do one of two things- either impart enough thermal energy to the junk so that it's trajectory is changed, causing it to de-orbit, or to disintegrate it into such tiny pieces that it no longer poses a threat upon impact. Both of which are likely to need more energy than de-winging a mosquito.
Lasers are easy- we've had them for many years. Tracking the debris is easy- we're doing it now. Having something that can point accurately at something we're tracking- that's easy enough too. Having something that can do all that with enough power to actually be useful, able to do it over and over again without running out of consumables, and do that on a sane budget-that's tricky.
Re:Lasers... (Score:3, Informative)
Actually it's the same problem.
Satellite controllers use the radar-tracking derived ephemeris data from NORAD. It's a simple matter of changing a search parameter in the data request to get the debris trajectories.
Re:Out of dimension? (Score:5, Informative)
Consider that each object (in low Earth orbit) is in a separate orbit. Each pair of orbits crosses twice on opposite sides of the Earth. The eccentricity of each orbit causes the object to traverse a range of altitudes, defining the subset of all the LEO objects that are possible collision risks at any given time. The risk for two particular objects colliding is low, but each object has many other opportunities as it crosses thousands of other orbital tracks each time it circles the Earth. Then integrate over all the objects. The probability is a nested summation - integrated over time.
For example, assume there are about one hundred spacecraft (active and defunct) occupying a particular semimajor axis "zone". Each satellite orbits once every 90 minutes, ie, 16 orbits/day. Each satellite crosses the orbit of another about 200 times in that 90 minutes. Usually the other spacecraft is somewhere else entirely, but there are a lot of opportunities.
Establish a "comfort radius" - say, one kilometer. If Le Petit Prince is sitting on a satellite, he will get very nervous if another spacecraft zooms through this keyhole at 10 km/s. A typical low Earth orbit is about 42,000 of these comfort units long. So the odds (ignoring altitude for the moment) of finding a spacecraft within the same part of the orbit - during each passage - is 1/42,000. Multiply by the 200 opportunities makes this 1/210 (0.5%) per orbit or about 7.5%/day/spacecraft. There are 100 spacecraft in this zone, so that amounts to about 4 close encounters per day (divide in half since it takes two to tango) in which some spacecraft passes directly above or below another by a few kilometers.
Accounting for altitude requires a bit more physics (inverse square law and all that), but basically amounts to a similar argument of dividing the altitude range traversed by each satellite into comfort zones. The odds of passing through the keyhole drop, but not dramatically - and the orbit crossings keep piling up about a hundred thousand per day per altitude range. With each close encounter, the odds of an impact are basically very simple. What is the volume of a typical spacecraft divided by the 1 km^3 volume? (The second spacecraft either will or won't be occupying the same volume at the moment of closest approach.) Satellites can be surprisingly large - Hubble is about the size of a schoolbus - but figure a Volkswagen van or at least a Beetle.
Bear in mind that this is just one particular altitude range, the same thing is happening at different altitudes. Some spacecraft are in highly elliptical orbits and cross through several such zones. In short, what seems to be a three dimensional problem is really one dimensional. After the spacecraft collision a couple of years ago some of us were scribbling on a blackboard. A physical model would be needed to get the precise answers, but a ball park figure is that we can expect the apparently astronomically rare event of two LEO spacecraft colliding to happen about once per decade (in the absence of active station keeping). Then account for all the debris, not just complete spacecraft.
Re:Hit or Miss (Score:2, Informative)
Yes, and the first layer of ionized atoms will scatter the rest of the laser energy, and push on the object... Sigh, you Space Loons are a big, fat ZERO when it comes to reality. Again. THIS AIN'T STAR TREK.
Assuming iron, so M = 55.845, Vaporization point: 3134K, Melting point: 1811 K, Heat of fusion: 13.81 KJ/mol, Heat of vaporization: 340 KJ/mol, Specific heat capacity: 25.10 J/mol/K
.5 cm / 3740 cm/s = 134 us
v(rms) = (3RT/M)^.5
v(rms) = 37.4 m/s
Assuming you want the laser focused over 4 cm for a 3 cm object:
t = x/v =
For a 3 cm sphere:
V = 4/3*pi*r^3 = 113 cm^3
m = Vd = 113 cm^3 * 7.874 g/cm^3 = 890 g
890 g / 55.845 g/mol = 16 mol
16 mol * (25.10 J/mol/K * 3134 K + 13810 J/mol + 340000 J/mol) = 7 MJ
So, a 7 MJ burst in 134 us, or 52 GW (roughly, I didn't deal with liquid heat capacity/expansion properly). The most powerful lasers currently in existence are measured in the petawatt range, and an exawatt laser is in the works. That puts us 5 - 8 orders of magnitude higher than what we'd need to fully vaporize a 3 cm ball of iron before the gas had a chance to disperse. While there might be some scatter, you'd still be heating up the ~4 cm ball of gas (the highest energy gas molecules would be > 1 cm away, but that's the point of the whole exercise). I've taken some liberties with the math, but nothing you can't hand-wave away with up to 5 orders of magnitude above the calculated need.
In other words, the "first layer of ionized atoms" don't form a deflector shield that completely scatters laser energy. The center of mass isn't going to warp away faster than the gas can even expand, and it would still just be pushing the object away in the direct path of the laser. This isn't a spaceship battle, you don't fire the laser for 3 seconds at a time.