For Mars missions, those navigational points may include asteroids, Holt says. “We would say [to the astronaut], we expect that the asteroid is going to be half-way between the two head stars in Gemini, so look over there, find that asteroid between those two stars, take your readings, then compare that against the expectations and do the maths.” If the readings are off, the astronauts correct the course to get to where they want to be.
