As part of its Clean Space Initiative, the ESA is planning a satellite salvage mission called e.DeOrbit that would use a satellite to net space debris and remove it from low Earth orbit. To capture such debris using an autonomous system, it needs to be targeted effectively, which is difficult when the debris is tumbling unpredictably. To fine tune the design of the e.DeOrbit mission, the ESA will commission a study to shed light on why space debris tumbles the way it does.
In recent years, a number of de-commissioned satellites have made uncontrolled re-entries whilst under observation, as have a few operational satellites that became the victim of catastrophic system failures. It was found in every case that the satellite began to tumble uncontrollably before its orbit had decayed sufficiently to be pulled back into the Earth's atmosphere.
There are a number of theories for this tumbling behavior that the study sets out to validate. One such theory blames the behavior on the increased drag created by the Earth's atmosphere when interacting with one side of a satellite. The debris, unable to correct for the imbalance, is then slowly forced into an irreversible spin.
Other theories assert that it may be a faint but steady push of sunlight, micrometeoroid and debris impacts, internal magnetic fields, the sloshing of leftover fuel, or the release of internal pressure in the form of a gas leak or exploding battery, which is ultimately responsible for the erratic behavior.
The goal of the study is to pinpoint the drivers for the loss of equilibrium by combining detailed computer analysis with existing monitoring techniques, such as optical telescopes, ground-based radar observation. However, alongside these commonly used methods, the study will investigate the potential of rarely used techniques in an attempt to gain a more precise understanding of the movements of the space debris.
These include space-to-space optical and radar observations using satellites in nearby orbits, as well as highly accurate laser ranging. This process involves the bouncing of laser beams off the reflective surface of an object and has the ability to accurately track a piece of debris to within a few centimeters of its actual position.
It is hoped the study will provide information that will allow the design of the e.DeOrbit mission to be fine tuned to enable it to assess the condition of target debris before approaching it.