One of the big challenges in communicating with a Mars base is that Mars is in motion. Sometimes, a base might be turned away from the Earth, and every so often—approximately once every 780 Earth days—Mars and the Earth have the sun directly between them.
Satellites normally orbit planets in Keplerian orbits, named after the 17th century astronomer Johannes Kepler, who wrote the mathematically equations that describe how satellites move.
But the European and British researchers have proposed putting a pair of communications satellites around Mars in something called a non-Keplerian orbit, which basically means that instead of moving in a circular or elliptical path around Mars, they'd be off to the side a bit, so that the planet wouldn't be at the center.
In order to stay in that position, however, the satellites would have to counteract the effects of gravity, which would pull them toward Mars.
To keep them in place, the scientists have proposed equipping them with electric ion propulsion engines, powered by solar-generated electricity and using tiny amounts of xenon gas as propellant.
That would enable the satellites to relay radio signals continuously, even during periods when Mars and Earth are in conjunction.
