Russian Mission Control said that an experiment that proposed to send a parcel from space to Earth on a 30-kilometer (20-mile) tether fell short of its goal Tuesday when the long fiber rope did not fully unwind.
The YES2 experiment was prepared by almost 500 students from all over Europe and other areas and put on board the Russian Foton-M3 unmanned spacecraft, which also carried other European Space Agency experiments.
It was intended to deliver a spherical capsule, called Fotino, attached to the end of the tether back to Earth - a relatively simple and cheap technology that could be used in the future to retrieve bulkier cargoes from space.
The tether was to be deployed from the spacecraft and gradually unwound, putting the capsule into a lower orbit and swinging to provide momentum, before the re-entry capsule was released. It was to glide through the atmosphere for some 20 minutes and then a parachute was to be deployed.
However, the experiment went awry when the tether only unfolded to a length of 8.5 kilometers (5.3 miles) after being released from the spacecraft orbiting around 300 kilometers (190 miles) above the Earth, Mission Control spokesman Valery Lyndin said.
The reason for the problem wasn't immediately clear.
"It could be that the tether got stuck," Lyndin said.
He said that Mission Control would try to calculate the capsule's orbit and determine when and where it would land.
Lyndin said that there had been several previous experiments involving tethers deployed in space, but they were not that long and did not carry parcels.
The tether deployed Tuesday is half a millimeter thick and is made of Dyneema, which the ESA described as the world's strongest fiber and is used by kite surfers.