Lighter, smaller telecommunications satellites may be able to fly with aerodynamic surfaces and electric propulsion at 150 kilometres altitude, collecting their own gaseous fuel from the trace atmosphere
Space is generally accepted to begin at 100km (62 miles). But, even the International Space Station with its huge solar panels encounters some aerodynamic drag at its orbit four times as high, 400km. Telecommunications satellites can orbit at 650km or as high as 36,000km to stay over a single point on the Earth. The value in a Very Low Earth Orbit (VLEO) of 150 km is the big reduction in the power needed for telecoms, so satellites can be smaller and ground receivers can be mobile phone-like and cheaper.
'The [VLEO] spacecraft design needs to be radically different as it has to be aerodynamic to a degree and probably use controllable surfaces in a similar way to aircraft, like ailerons, to control, its orientation and interaction with the atmosphere,' says European Space Agency (ESA) head of future telecom programme exploration, Andrew Murrell. 'A spacecraft operating in this region would look a bit more like a spaceplane type structure.'
ESA is to carry out a study to determine if such a flying satellite is possible. Murrell adds that the spacecraft could not have typical flat panel solar arrays because of the drag they would create that would lower the satellites altitude. The solar panels would instead be placed over the spaceplane-like satellite’s fuselage. While the “ailerons” could help orientation, the study will also examine how to harvest trace gases at 150 or 200km altitude for electric propulsion. Electric propulsion accelerates particles of gas using magnetic fields to create thrust for adjusting the spacecraft’s station keeping or to raise its orbit.
The atmosphere's second highest layer is the thermosphere and it extends from 90km up to 1,000km. The air density is so thin it is considered space, and this is the layer where the auroras occur; yet trace gases can be found there. The European Union is also studying VLEO orbits for Earth observation under a project called DISCOVERER.
Because the altitude the VLEO satellites operate at would be so much lower, launch vehicles that are sub-orbital, that will not even orbit the Earth once, are considered candidates for putting these flying spacecraft into space. Blue Origin’sNew Shepard rocket, Virgin Galactic’s SpaceShipTwo and ESA’s own Space Rider, could potentially carry an upper stage to send a satellite into its orbit.