About once a week, a spacecraft reaches the end of its life, loses energy, and falls towards Earth, burning up in the atmosphere along the way. But sometimes parts of the spacecraft don't completely disintegrate and survive the journey, resulting in a violent collision with Earth's surface. With more and more satellites orbiting Earth, these incidences will become more frequent, so ESA Discovery & Preparation recently supported a study that explored partially controlling the re-entry of spacecraft through the atmosphere to keep us safe from harm.
Designing a spacecraft for fully controlled re-entry can be problematic, as it introduces many constraints and can lead to a mission being less environmentally friendly overall. The objective of this study was to find a middle ground between complete lack of control and using a lot of energy to force re-entry over a very specific area. During semi-controlled re-entry, a spacecraft is made to re-enter the atmosphere within a set number of orbits, so that operators can predict where pieces of the spacecraft will fall. The first and last parts of the entry would be uncontrolled, but the middle part would be carefully controlled. This process requires 1000 times less force – and therefore much less fuel – than controlled re-entry, but is far less risky than uncontrolled re-entry.