![LEO640[1]](http://wattsupwiththat.files.wordpress.com/2013/03/leo6401.jpg?quality=83)
Removing orbital debris with less risk
Global Aerospace Corporation (GAC) announced today that the American Institute of Aeronautics and Astronautics (AIAA) is publishing an article entitled “Removing Orbital Debris With Less Risk” in the March/April edition of the Journal of Spacecraft and Rockets (JSR) authored by Kerry Nock and Dr. Kim Aaron, of GAC, and Dr. Darren McKnight, of Integrity Applications Incorporated, Chantilly, VA. This article compares in-orbit debris removal options regarding their potential risk of creating new orbital debris or disabling working satellites during deorbit operation.
Space debris is a growing problem in many orbits despite international debris mitigation guidelines and policies. While this space environmental issue has been discussed and studied for years, many critical parameters continue to increase. For example, the number of significant satellite breakup events has averaged about four per year. Removing large amounts of material already in orbit has been a major issue for debris mitigation strategies because a large object, like a satellite or spent rocket stage, is not only more likely to be involved in an accidental collision due to its large collision cross-section but the large mass has the potential to be the source for thousands and thousands of smaller, but still dangerous, debris if involved in a collision.
Deorbit devices have been proposed for dealing with the growing problems posed by orbital debris. The authors describe these devices that can use large structures that interact with the Earth’s atmosphere, magnetic field or its solar environment to deorbit large objects more rapidly than natural decay. Some devices may be better than others relative to the likelihood of collisions during their operation. Current mitigation guidelines attempt to address this risk by calculating an object’s atmospheric drag area times its orbit decay time to compare the probability of a large object experiencing a debris-generating impact. However, the authors point out that this approach is valid only for collisions with very small debris objects. Since the peak in the distribution of the area of orbital debris occurs for objects with a size close to 2 m, some of which are operating satellites, it is important to incorporate an augmented collision cross-section area that takes into account the size of both colliding objects. This new approach leads to a more valid comparison among alternative deorbit approaches.
Two other factors that affect the potential risk of a particular deorbit device are the nature of hypervelocity impacts and the level of solar activity. The authors describe the physics of hypervelocity impacts in space that can affect the assessment of risk. In addition, they describe how solar activity level affects the decay process and alters the result of the calculation of collision cross-section area times decay time, which is a measure of the risk of the deorbit device. The authors also characterize two types of collision risk, that is, the risk of creating new debris-generating objects in hypervelocity impacts by high-energy collisions and the risk of disabling operational satellites by low-energy collisions.
The implication of this new approach to determining risk indicates that ultra-thin, inflation-maintained drag enhancement devices pose the least risk of creating new debris or disabling operating satellites, while electromagnetic tethers are shown to have a very large risk for disabling operating satellites. All deorbit devices studied appear to have less risk than leaving an object in orbit even for only 25 years, which may suggest a possible need to reconsider current orbital debris mitigation guidelines that allow objects to remain in orbit that long.
“As the orbital debris hazard increases, it will be critical that the community can use techniques that have high operational effectiveness and low risk. Inflatables have been the best balance for that approach in my mind and I hope that this paper exposes more of the aerospace industry to the benefits of using inflatables to accelerate the reentry of non-operational spacecraft,” said Dr. McKnight.
Finally, atmospheric drag deorbit devices are found to be much more efficient during periods of high solar activity and therefore pose a lower overall risk. Permitting a satellite to use a smaller drag device over 25 years, which will average about two solar cycles, means it will incur about three times the risk compared with a larger device selectively operated near solar max (including the time taken waiting for solar max). As a result, the authors recommended that drag augmentation devices be sized and timed to complete their deorbit function only during solar max in order to further reduce the risk of creating new debris.
Global warming to the rescue. /sarc
Maybe we could turn all this junk into a ring, like Saturn’s. Then we’d look like a real grown-up planet…. 😉
Perhaps we should consider increasing the size of the orbit debris cloud in order to augment the global dimming/cooling effect of India’s and China’s economic and industrial expansion.
As a result, the authors recommended that drag augmentation devices be sized and timed to complete their deorbit function only during solar max in order to further reduce the risk of creating new debris.
So if we go into a Maunder type minimum, it’s back to the drawing board.
What about all the super-secret satelite killing lasers that the military have secretly been putting into orbit since the 1980’s? Can’t they be used to vaporise the garbage?
Any one have the natural rate of debris de-orbiting is, i.e. delta debris orbit vs time? Like climate change, if we do nothing, will it/when will this problem solve itself? A lot must be in low orbits subject to atmospheric drag.
There’s more drag at solar max? More air up there? A taller atmosphere affecting pressure gradients down here and lapse rates? Higher surface temps therefrom? Well, well.
I’m not really grasping the thrust (pun?) of this article. I do note, however, that the graphic is somewhat misleading as I estimate the size of each dot to be in the neighborhood of 200 miles in diameter.
REPLY: that’s dealt with in the caption, maybe you missed it – Anthony
Space Junkers… science fiction, first- reality, later.
How big/fast would an incoming object (asteroid, comet etc) colliding with the Earth have to be to result in significant debris from the collision staying in orbit around the earth?
“Q” says – Why not just change the gravitational constant of the universe?
There’s no doubt a fleet of aerospace engineers looking at how to protect their valuable assets in space. Hypervelocity impact studies have been conducted on various materials, including carbon fiber reinforced plastics and Kevlar to face vital satellite parts. Some entrepreneur should launch several satellites with inflatable cfrp / Kevlar padding (like umpire’s chest protectors), each with small self-propulsion system. Like a big Kevlar catcher’s mitt, these could be coordinated to intercept debris objects in orbit, perhaps even utilizing impacts to re-align in new orbits, then negotiate its own decay path into the ocean. The Kevlar catcher’s mitt.
Is it baseball season yet?
Maybe the EPA could take care of that?
Are the units of collision cross-section Barns, as subatomic absorbtion cross-sections are, equal to 10^-24 cm^2 as I recall? Two related units are the outhouse (1 μb, or 10^−34 m^2) and the shed (10^−24 b (1 yb), or 10^−52 m^2)
Until it becomes economically viable for someone to go collect the garbage, we will have to keep monitoring it and avoiding it on the space flights we do take.
steveta_uk: zapping something with a laser would likely just add lots of small particles to dodge. I don’t think that would work even if the lasers were out there. Of course you probably just forgot your /sarc tag and I am taking you seriously for nothing.
I always thought the responsible thing to do with upper stages (below the payload) was to have small deorbiting rockets on them as part of the design. Then it is just the explosive bolt pieces we have to worry about, and those can be designed so the heads are retained on the part when they blow.
Rhoda Klapp asked : “There’s more drag at solar max? ”
Yes indeed, and that was discovered soon after the launch of the first artificial satellites. Higher solar activity results in higher air density, but only above about 200 kilometers.
Bloke suggests: “So if we go into a Maunder type minimum, it’s back to the drawing board.”
We seem already to be in a Grand Solar Minimum that promises to be at least the equivalent of the Dalton one of the 19th century.
It’s not a good sign for trying to clear debris from low orbits. Something else is almost certainly going to be needed.
Simple is best. A small rocket or thruster attached to the satellite, fired at the end of it’s useful life would quickly remove it from orbit. Though that isn’t sexy enough for mention in the article the chart presented seems to indicate “Immediate and controlled propulsive deorbit” as having the least hazard. The thruster wouldn’t even necessarily have to slow it down or be immediate, just make its orbit more elliptical for more frequent contact with the atmosphere.
Why not just use photon torpedo’s and laser blasters?
To get anything into space costs a lot of money.The should be looking at this junk as an asset, not a liability. Harvest it, don’t burn it up by de-orbiting it. Collect it for future use.
Where is Quark when we need him?
Chris4692 says:
March 26, 2013 at 9:19 am
Simple is best. A small rocket or thruster attached to the satellite, fired at the end of it’s useful life would quickly remove it from orbit
It is not quite that simple. It is difficult to control the point of impact. You don’t want the satellite to impact in a city or just anywhere.
30 years from now we’ll be able to deploy semi-autonomous, mass produced little robotic devices that will grab a piece of debris and decelerate it properly to burn up in the atmosphere.
Nice to see an article from AIAA which I was a member from when i worked in the field back in the Apollo era. My being a member and my work back then is why this mathematician and computer scientist is still interested in climate science today.