Human mission to Mars Mars. Many Mars mission concepts propose precursor missions to the moons of Mars, for example a sample return mission to the Mars moon Phobos – not quite Mars, but perhaps a convenient stepping stone to an eventual Martian surface mission. Lockheed Martin, as part of their "Stepping stones to Mars" project, called the "Red Rocks Project", proposed to explore Mars robotically from Deimos. Use of fuel produced from water resources on Phobos or Deimos has also been proposed. An uncrewed Mars sample return mission (MSR) has sometimes been considered to be an essential precursor to crewed missions to Mars' surface
Phobos (moon) seen from Phobos, Mars would appear 6,400 times larger and 2,500 times brighter than the full Moon appears from Earth, taking up a quarter of the width of a celestial hemisphere. The Mars–Phobos Lagrangian L1 is above Stickney, which is unusually close to the surface. An observer situated on the Martian surface, in a position to observe Phobos, would see regular transits of Phobos across the Sun. Several of these transits have been photographed by the Mars Rover "Opportunity". During the transits, Phobos's shadow is cast on the surface of Mars; an event which has been photographed by several spacecraft.