Scientific Method / Science & Exploration

How best to clean out satellites before they become space garbage?

Looking at options for quick and safe de-orbiting.

Space is getting crowded with old satellites and communication detritus, but scientists are still lacking an effective method of clearing out the clutter, according to a paper published in the March/April edition of the Journal of Spacecraft and Rockets. Satellites that simply go defunct are generally left to decay and fall to Earth in potentially lethal pieces—or worse, collide with functioning satellites. These are unnecessary risks when we could be using devices like the inflatable drag-inducing balloons and electromagnetic tethers at our disposal.

In the paper, researchers describe and examine a number of methods for drawing decommissioned satellites out of orbit and away from their functional brethren. The risks of not doing so are obvious; the authors cite the case of the out-of-service Russian satellite Cosmos 2251, which collided with the functional Iridium 33 satellite in Feburary 2009. Both satellites were destroyed and fell in over 2,000 potentially lethal pieces to Earth. To determine the best method for getting space detritus out of low-Earth orbit, the researchers encourage the consideration of metric called “area-time product” (the cross-sectional area of the de-orbit apparatus multiplied by the time it would take to de-orbit the satellite) to evaluate which approach is best.

One proposed method of drawing down satellites that are just taking up space is electromagnetic tethers, which use a power supply to create a flow of electrons within a conductive tether that interacts with Earth’s magnetic field to draw the satellite slowly down to Earth. But electromagnetic tethers work slowly and have a large cross-section, so in a sense they increase the risk of interrupting other satellites while trying to get the defunct one out of the way.

Another option is an inflatable attachment that increases the drag on the satellite and slows its orbit. The authors of the paper propose ultrathin envelope spheres, which don’t require a power supply of the size that an EM tether does, but it would take only a matter of months to draw the satellite down to Earth. Because it works so quickly, the envelope would greatly reduce the risk of collisions despite the temporary added girth.

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