The pressure of sunlight alone should drive the hub and its membrane through space.

BBC: Mini-camera pictures Japan's Ikaros solar sail

It suffered from short-circuits, faulty radio and power systems, an unreliable tape-recorder, a sticky camera platform, and the loss of much of the gas that supplied its stabilising thrusters a problem overcome by repositioning its solar panels and main antenna so that they acted as solar sails, stabilising the probe via the gentle pressure of sunlight.

ECONOMIST: The long arm of the celestial repairman

Similarly, the pressure exerted by sunlight, and the force exerted by the emissions from each probe's radio antenna, were dismissed: again, both are too weak, and they would tend to push the probes away from the sun, not towards it.

ECONOMIST: A space oddity