After the array-deployment tests on the ground, budget permitting, there could be a deployment test “near or around” the space station, possibly making use of the vehicles that deliver supplies and/or crew to it, says Gazarik. The final phase would be the $200 million free-flying space tug test-bed, notionally set for launch in 2018 but highly dependent on funding.

Ultimately NASA foresees using SEP to preposition cargo for human crews arriving later at asteroids and Mars. While the instruments and other systems on the Juno probe now en route to Jupiter are powered with three large linear arrays (AW&ST March 21, 2011, p. 50), Gazarik says studies have showed SEP will be particularly useful at those nearer targets.