Orbital Debris
Published on Sep 19, 2006 at 4:54 pm.
4 Comments.
Filed under NASA, space debris, space exploration.
The Space Shuttle Atlantis is returning to Earth from a trip to the International Space Station. On this mission, they added more components to the station. However, on two occasions, bolts that were to hold components together drifted away from the astronauts. These bolts now are in orbit around the Earth. You might think that is no big deal, but it is something that NASA tries to avoid. Why the big deal with a pair of bolts?
The problem is that to maintain orbit, an object must be moving very FAST — somewhere around 17,000 mph (7.6 kilometers per second). At that speed even a small object can do a lot of damage. For example, a bolt, such as the ones that floated away from the astronauts, were it to hit a satellite or shuttle moving in a crossing orbit, it could make an impact similar to that of a 4 or 5 inch diameter solid iron cannon ball! Even a smaller object can do damage. 
On the STS-7 mission, a paint flake struck the windshield of the Space Shuttle Challenger and gouged out a crater!
Over the years, astronauts have lost several objects in orbit, including a wrench and a spare spacesuit glove. The last shuttle mission lost a sort of putty knife (generally called a “spatula” by the press) that had been used in tests of orbital heat tile repair. But, the biggest source of space debris is not manned spaceflight. Most debris comes from unmanned missions.
Obviously, once a satellite quits working, it is just so much space junk. However, there is a lot of debris associated with launching a satellite. The booster rockets that put the satellite into orbit often orbit themselves for a while. Cowlings, couplings, and the like are also shed once a rocket clears the atmosphere, or when stages separate. The satellites themselves are secured with tiedowns, and cameras have lens caps. All these things are shed. So, launching a single satellite can create a cloud of several dozen objects in orbit. A plot of the orbital properties called a Gabbard diagram (after John R. Gabbard) is used to sometimes display the properties of the orbital cloud. Clearly, you want future satellites to stay clear of the debris cloud, as impact with one of these bits of space debris (most of which is far larger than the bolts I mentioned earlier) would surely destroy the satellite — creating an even larger cloud of debris. Space debris has sometimes run into one another, creating large clouds of more things to avoid.
But, it gets worse. The spent rocket bodies often have some fuel and oxidizer left in them. Successive heating and cooling as they pass from sunlight into Earth’s shadow, with the associated expanding and contracting, eventually create leaks, and sometimes the rocket explodes, creating a large expanding cloud of debris. Even if that doesn’t happen, decals and paint can flake of in the harsh environment of space. As we have seen with the shuttle windshield, even paint flakes can be dangerous. Had that paint flake struck an astronaut on a space walk, it likely would have punctured his spacesuit.
Most of the debris is in low Earth orbit (LEO). However geostationary satellites are important commercially, so a great deal of debris is accumulating in geosynchronous orbits (GEO). 
I have placed a couple of NASA plots here of orbital debris. One shows the space near Earth (LEO), and the other backs up so that you can see all the GEO debris. NORAD keeps track of over ten thousand bits of debris, but there is far more that is too small to see. Unfortunately, most of the debris comes from putting satellites into orbit. 
Most satellites are put into commercially important orbits, so most of the debris is in the same area — just where it can do the most harm. In fact, there is already enough debris in orbit to consider the serious possibility that satellites may be struck by debris and knocked out of commision. Obviously, for manned spaceflight, space debris is a risk to the safety of astronauts. So, what can be done?
The only real solution is to have less debris. In 1995 NASA made a policy decision to limit space debris, and space debris mitigation guidelines were drawn up. Soon, the rest of the US govenment followed suit, as did several other major space powers. Now there are nearly a dozen space agencies who have space debris mitigation strategies. Even so, each launch produces numerous bits of debris, and there is still a lot of debris up there from earlier launches. Unfortunately, there isn’t much that we can do about the old space junk. All we can do is make sure that we add as little as possible to what is already there.
But, since NASA started the whole space debris mitigation program, this makes the loss of bolts and a spatula doubly embarrassing. Now, these things are small, and being in LEO, atmospheric drag will cause their orbits to decay, and eventually there will be no danger that they will run into anything.
Ironically, as I write this, another bit of space debris has NASA concerned. The picture here was taken from the payload bay of the Atlantis. The arrow points to a bit of mystery debris that the camera spotted. No one knows what it is. Is this a piece of the shuttle? It is a piece of equipment or trash that floated out of the payload bay? Is it something that is just random debris passing? No one knows. However, it appeared just after Atlantis made an orbital maneuver. At that time, impact sensors on one wing recorded some sort of event. Controllers think that this event was flexing due to the maneuver tha the shuttle had just made. But, this debris was seen soon thereafter, so they are evaluating the situation. Landing has been delayed accordingly. As to this mystery object, we can hope that it is nothing important that fell off of the shuttle.
-Astroprof
(Image Credit: NASA)
Astroprof’s Page » Atlantis struck by space debris? on October 10, 2006 at 12:51 am: 1
[…] Last month, I did a posting on space debris. Towards the end of the post, I mentioned that NASA had seen something floating away from the Space Shuttle Atlantis. Well, now I have more to report. It appears that something apparently struck Atlantis while in orbit, though this incident appears to be unrelated to the debris floating away from the orbiter. […]
Astroprof’s Page » Yet more space debris on February 25, 2007 at 3:51 pm: 2
[…] Several months ago, I posted about the increasing problem of space debris. Well, it just keeps increasing. Already this year, the number of pieces of space debris has increased by nearly 20% over what it was at the end of last year! Worse, most of that came as a result of two events. […]
Mike on April 19, 2008 at 11:55 am: 3
Hey guys I am taking a risk in even thinking about what I am about to tell you, but if you really want to know what can happen to a shuttle with things flying through space at 35,000 MPH send me an email and I will send you a picture taken by a Isralie spy satellite. It is a real picture and will explain what really happened to the shuttle that was supposedly damaged by foam. I have in my posession 5 pictures of this incident and they were given to me by a friend who has a friend in the Isralie spy community. He gave me the pictures and now he is dead. I am not sure if I want them published on the internet or not, I don’t want them to be traced back to me. Email me and tell me if you want them and how you can protect my email and identity. Thanks, NO MAN
KClark on November 26, 2008 at 11:56 pm: 4
NO MAN,
I am interested in these pics as I know there is more to the story.
I have been following the debris problem quite closely.
This is soley for my personal research in validating the need for an area of extreme orbital debris mitigation.
I can promise to destroy any record of receipt from electronically transfered data.
Please protect mine.