The proposals are due April 1 of this year, and the Langley Research Center in partnership with the Jet Propulsion Laboratory and with Lockheed Martin, with the Draper Lab and Aurora Flight Sciences, is proposing a robotic airplane to fly over the surface of Mars, about a mile above the surface.

NPR: Revisiting the Viking Missions to Mars

That's a proposed mission that would send a robotic airplane to Mars to fly over the surface looking for the chemical signs of life.

NPR: Revisiting the Viking Missions to Mars

The orbiter was originally expected to fly in June, but technical problems with the new robotic arm on the space station forced NASA to postpone the mission.

CNN: Air lock installed on space station