A small space capsule has been lost in Earth orbit after a space tether experiment went awry on Tuesday. The capsule will re-enter the Earth鈥檚 atmosphere and parachute down at an unknown location.
Despite the mishap, the team behind the mission say it shows that space tethers can provide a cheap and safe way to return a payload from an orbiting satellite back to Earth without using costly rocket boosters.
The (YES2) mission, coordinated by ESA and the Russian Space Agency, was to have unfurled the longest human-made structure in space 鈥� a 30-kilometre-long, 0.05 millimetre-thick tether, made of a super-strong polythene fibre called . This would have connected a Russian-operated satellite to the beach-ball-sized capsule called Fotino.
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In theory, the set-up should have acted as a giant pendulum, providing enough momentum to send Fotino back to Earth. . But the mission hit a snag, literally, when the tether failed to unwind at full speed. Instead of deploying to 30 km, it reached only 8.5 km before releasing Fotino.
Unknown landing point
鈥淭he most precise calculations estimate re-entry sometime between Sunday and Tuesday, but we鈥檙e not sure where it will come down,鈥� admits Michiel Kruijff, lead engineer on the YES2 mission at Delta-Utec Space Research & Consultancy.
Despite the snag, Kruijff believes the mission shows the concept can work. 鈥淭he glass is half full,鈥� he told New 杏吧原创. 鈥淢any of YES2鈥檚 mission objectives have been achieved,鈥� including more than half of the deployment goals.
鈥淭his is how our Russian counterparts have seen it,鈥� Kruijff adds. 鈥淭hey are extremely satisfied and would like to do more mission testing.鈥�
Using space tethers to return payloads to Earth was a concept first put forward by Wubbo Ockels at Delft University of Technology in the Netherlands in 1994.
The idea is for an orbiting satellite to lower its return capsule towards Earth on the end of a long tether. As the tether is extended, the causes it to swing ahead of the satellite.
Tether dangers
Once fully deployed, gravity becomes the dominant force and the capsule begins to swing back towards the vertical. Finally, when sufficient momentum is built up and when the tether is at the right point, the capsule is released, sending it back through the Earth鈥檚 atmosphere.
鈥淚t is a very simple [concept],鈥� says Ockels. Even so, there have been few space tether experiments in recent years. 鈥淎gencies calculate the financial cost [of the experiments] but not the value of the experience and data,鈥� he says.
鈥淪everal projects have been cancelled because of safety fears,鈥� says Kruijff. 鈥淚f tether deployment accidentally stops too early, the end mass will bounce back and could start to orbit the mother space craft, wrapping the tether around the craft and damaging it.鈥� To avoid this, the YES2 team introduced a system designed to automatically cut the tether if it goes out of control.
