London, December 21: NASA is developing sensors and smart navigation software which may enable the space agency"s Orion spacecraft to fly unpiloted and rescue astronauts stuck in orbit around the Moon.
The agency has revealed that it is planning to carry astronauts to the Moon from 2020 aboard the Crew Exploration Vehicle (CEV), also dubbed Orion. The experts say that once in lunar orbit, the crew will climb into an attached Lunar Surface Access Module (LSAM), which will take them onto the Moon's surface. The LSAM will later return to orbit, and rejoin Orion for the trip home.
However, unlike the Apollo mission, the orbiting craft will not have any person on board after the lander has started its mission. Just in case the lander malfunctions and strands astronauts in the wrong orbit, Orion will have to rescue them on its own.
In order to make this dream a reality, Ricky Howard at NASA's Marshall Space Flight Center in Huntsville, Alabama, US, is trying to provide Orion with the ability to fly unpiloted to the rescue.
He revealed that the idea was to have the craft track the lunar lander, and dock with it without human intervention.
"If they have a problem and can't get to the CEV, the CEV has to get to them. And if that can't happen automatically, it's not going to happen," New Scientist quoted him as saying.
He said that exact details as to how this would work were being worked out, though some trials had already been conducted.
Howard hinted that Orion would probably begin by listening for radio signals from the lunar lander. He said that it would detect such signals from up to several hundred kilometres away.
He further said that the spacecraft would figure out from which direction the signals were coming by using slight differences in arrival time at the different antennas, just like humans use their ears to pinpoint the origin of sounds.
Autopilot software would then fire Orion's engines to bring the craft closer to the lunar lander. Upon the spacecraft"s arrival within three kilometres, as judged by listening to the radio signals, laser-based sensors would take over.
NASA has revealed that it is trying to create a system that would facilitate the firing of a wide-angle laser out into space, and simultaneously watching for reflections from mirrors on the target vehicle with the help of a video camera.
Several of such mirrors, each a few centimetres across, would be mounted on the lunar lander, and arranged in a pattern that the sensor software could recognise.
The software may use the apparent size and shape of the pattern to judge the distance and orientation of the lander.
"It uses that to decide which thrusters to fire and for how long," Howard says.
The sensors would enable constant monitoring of the progress as Orion moved closer and docked with the craft. The astronauts could then transfer back to Orion, and pilot it home to Earth.
The system could also be used to help Orion dock with the International Space Station and to assist human pilots.
A NASA laser sensor was successfully tested on the Orbital Express satellite mission, run by the US Defense Advanced Research Projects Agency (DARPA), helping two satellites rendezvous and dock in orbit several times.
The space agency is now working on an improved version that, unlike the previous one, does not need any prior estimate of the distance to the target craft.
Howard will present test results on the laser sensor at the Space Technology and Applications International Forum in Albuquerque, New Mexico, in February 2008.