image: University of Arizona space systems engineer Roberto Furfaro studies a model of the Phoenix Mars Lander on display at the Osiris-Rex Science and Processing Operations Center in Tucson, Ariz., which is home to his Space Systems Engineering Laboratory. view more
Credit: Pete Brown, UA College of Engineering
TUCSON, Ariz. (September 7, 2011) -- Here's the plan: An autonomous guidance system being designed and developed by University of Arizona space systems engineer Roberto Furfaro and his colleagues will fly the privately-funded Moon Express lander to the lunar surface in 2014.
It will touch down within 10 meters of its target, and, at the same time, will capture the coveted Google Lunar X Prize.
The $30 million X Prize goes to the first privately funded group to land a spacecraft on the moon and deploy a robot, which must travel 500 meters and send back an image and data to Earth.
Furfaro, an assistant professor in the UA systems and industrial engineering department, calls this kind of rocket-assisted soft landing a "very difficult and exciting project."
"Roberto's guidance algorithm will take over with three minutes to go before landing," said Tom Gardner, chief engineer at Moon Express. "There is a big rocket burn that slows us way down to about 50 or 60 miles per hour. His guidance takes over and that's at about three miles above the surface. It takes us from there to a very precise point on the surface."
No extraterrestrial landing has ever attained this kind of accuracy. Why now?
"I think part of it is that we can take more risks as a private company," Gardner said. "We have investors who have confidence that we know how to do this."
Also, guidance technology has evolved dramatically since the Apollo era.
"Basically, landing on the moon is similar to a missile hitting a target," Gardner said. "You have to make a lot of quick decisions and you have to have a lot of agility to hit the target precisely. The only difference is we're trying to hit it at zero velocity instead of high speed."
He said three things are needed to make this happen:
1. The right guidance/approach software.
This is being developed by the Moon Express GNC (Guidance, Navigation and Control) team led by Ian Garcia. Furfaro is part of this team, as is one of his master's students, Dan Wibben. Eleanor Crane, a Ph.D candidate at Stanford University, and Gardner also are team members. Sensors that "see" the terrain and tell the spacecraft computer exactly where it is with only milliseconds delay. This is terrain-based navigation similar to the kind found on cruise missiles.
2. A high-thrust rocket engine with plenty of reserve power to execute very short, high-thrust steering pulses.
"In the Apollo era, or even in the Phoenix project, you could know you were off course, but there was nothing you could do about it because all your energy was going into slowing you down and actually landing," says Gardner. "In our case, we have excess thrust capacity to help steer to a precision target."
3. You must know the terrain.
Another important factor is that the Moon Express team knows the terrain. Arizona State's Lunar Reconnaissance Orbiter Camera, developed by Mark Robinson, is sending back images of the moon's southern polar region that have quarter-meter resolution. "These images will allow us to land in an area where we have confidence that we're not going to break the spacecraft," Gardner said.
Team registration for the Google Lunar X Prize competition closed at the end of 2010. According to the X Prize website, there are currently 28 teams located around the world who are fundraising, mission planning, and building robots in the new private sector race to the moon. Teams have until the end of 2015 to get to the moon, meet the prize objectives, and win the prize purses.
To become the lunar equivalent of UPS or Federal Express, precision landings, sometimes in areas that are less lander-friendly than the one Moon Express plans to use in 2014, will require reliable autonomous GNC systems that have built-in hazard-avoidance capabilities, Gardner noted.