Oct 02 2015

The Problem of Space Junk

Published by under Astronomy
Comments: 6

We have been putting stuff into orbit around the Earth, especially low-Earth orbit, for the last 58 years. Space is a big place, so no one probably worried at first that we would start junking it up, but that is exactly what has happened in this short span of time. This is now a serious issue we have to confront.

It’s disappointing, and I hate having one more thing to worry about, but Earth orbit has become so cluttered with debris that it poses a serious risk to our assets in space. Recently former NASA scientist Donald Kessler said in an interview:

“We’re at what we call a ‘critical density’ — where there are enough large objects in space that they will collide with one another and create small debris faster than it can be removed.”

NASA scientists also fear a scenario similar to that portrayed in the movie, Gravity. There were some scientific problems with the movie, but the core idea is valid – there is so much debris in orbit that a collision of two large objects can start a chain-reaction, they will scatter debris which will collide with other objects causing more debris.

Here are NASA’s estimates for the amount of debris in orbit:

More than 21,000 orbital debris larger than 10 cm are known to exist. The estimated population of particles between 1 and 10 cm in diameter is approximately 500,000. The number of particles smaller than 1 cm exceeds 100 million.

Many of these objects may be moving extremely fast relative to other objects, like the International Space Station (ISS), for example. Even a small piece of debris can act like a bullet, causing serious damage to the station, a satellite, or any ship we may want to put into orbit.

Kessler believes the biggest problem is large decommissioned satellites. If they crash into each other that can start a chain reaction because of the amount of debris they will cause.

How to Address the Problem

So what do we do about this? First, we need to have policies in place that limit the amount of new debris we are putting into orbit. One major aspect of this is to build satellites with the capability of de-orbiting themselves once their lifespan is over. This is called “post-mission disposal” (PMD).

One solution for this uses a long (several kilometers) conducting tether. The conducting wire interacts with the Earths magnetic field and ambient plasma to create drag, essentially pulling the satellite out of orbit. Rockets can also be used to reduce the orbit to the point that atmospheric drag will do the rest.

There is also On-orbit satellite servicing (OOSS), which seeks to extend the lifespan of active satellites with missions to refuel, repair, upgrade, or otherwise service the satellites. This could reduce the need to send new satellites in orbit.

PMD and OOSS alone, however, will not solve the current problem. We also need “active debris removal” (ADR). This is very tricky, as we are dealing with a large number of small bits of debris moving in various orbits at 28,000 kph or more. However, even if we go after only the large dead satellites that will help tremendously and reduce the risk of a chain reaction.

One proposed solution is to use the upper stage of rockets that place new satellites into orbit. Once the payload is delivered, these upper stages are useless. However, they could be fitted with enough propellant and additional equipment so that, once they are in orbit, they can chase down a dead satellite, grab it, then de-orbit itself and the dead satellite. At least this way, every time we put a new satellite into orbit we will also be taking down an old one.

This is a technically non-trivial task, however, as one aerospace company describes it:

Almost no spacecraft are designed to be physically grappled once they are in orbit, and they may have antennas, solar arrays, or other fragile projections.  They may be tumbling or spinning, making them difficult to grapple and control. Many of these old satellites and rocket upper stages weight thousands of pounds, making them difficult to move. Some of the objects have been in orbit for decades and so may not be as sturdy as when launched or may contain fuel that could be triggered to explode.

To make this more efficient, there is a proposal to have a grappler that will sling a dead satellite out of orbit, and at the same time slingshot itself onto the next target.

Another solution is to attach a tether to an existing dead satellite or upper rocket stage to help drag it into the atmosphere. The tether can be as described above, or just have a balloon attached to increase atmospheric drag. Yet another alternative is to use a large sail to slow down the debris.

One interesting idea is to create puffs of air in the upper atmosphere designed to blow low orbiting debris out of orbit. This would only work for the lowest of debris, however.

Finally there is a design to used an electrified net to capture debris and drag it down into the atmosphere.

Darpa is working on a plan not to remove debris from orbit, but to recycle it. They want to grab dead satellites and then harvest pieces from them, like antenna or solar panels, and attach them to new satellites.


It is disappointing that we allowed ourselves to end up in this situation in the first place. In less than 60 years we are on the brink of making low Earth orbit unusable, and it is already highly dangerous. We treated space like we have treated our oceans or atmosphere – thinking that they were so vast nothing we could do would be a problem.

So now we have a crisis and we have to undo some of the damage we have already done, while enacting plans for sustainability that we should have thought about decades ago.

There is also a problem of political will. Hopefully this won’t be a serious problem. For example, we can’t just drag a satellite that we do not own out of orbit. We have to ask the country that owns the satellite for their permission. We need international agreements to facilitate the removal of space debris, and to enforce the extra expenditures that sustainable options will require.

Every major space agency seems to recognize the problem of space debris and is at least talking about it. The main question I have at this point is this – will we take major action to correct space debris before or after it causes a major catastrophe in orbit?

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