Uncrewed Orion could find astronauts lost in space

2019-02-26 10:16:01

By David Shiga NASA’s Orion spacecraft could fly unpiloted to rescue astronauts stuck in orbit around the Moon, using sensors and smart navigation software the space agency is currently developing. The agency plans to carry astronauts to the Moon from 2020 aboard the Crew Exploration Vehicle (CEV), also dubbed Orion. 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. But unlike the Apollo missions, the orbiting craft will have no humans on board after the lander has started its mission. If the lander malfunctions and strands astronauts in the wrong orbit, Orion will have to rescue them on its own. To that end, Ricky Howard at NASA’s Marshall Space Flight Center in Huntsville, Alabama, US, is working on giving Orion the ability to fly unpiloted to the rescue. The idea is 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,” Howard told New Scientist. The exact details of how this would work are still being worked out, but some trials have already taken place. Orion would probably begin by listening for radio signals from the lunar lander, which it could detect from up to several hundred kilometres away. It could figure out what direction the signals are coming from using slight differences in arrival time at the different antennas. Humans use their ears to pinpoint the origin of sounds in the same way. Distance could be judged by measuring signal strength, or the delay when messages are exchanged by the two craft. Autopilot software would then fire Orion’s engines to bring the craft closer to the lunar lander. Once within 3 kilometres or so – as judged by listening to the radio signals – laser-based sensors would take over. NASA is working on a system that could fire a wide-angle laser out into space, while a video camera watches for reflections from mirrors on the target vehicle. Several of these mirrors, each a few centimetres across, would be mounted on the lunar lander and arranged in a pattern that the sensor software can recognise. The software can 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 constantly monitor progress as Orion moved closer and docked with the craft. Then the astronauts could 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, as well as 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. NASA 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. The Russian Progress vehicle, an unpiloted cargo spacecraft, can perform automated dockings with the International Space Station, but uses a heavy, power-hungry radar system. NASA’s lighter laser system would be better for a Moon mission where weight and power are more restricted. Further in the future, Howard says similar laser guidance could help mining robots supply resources to the permanent Moon base NASA is planning. A robotic vehicle has already been equipped with a laser sensor to test out the basic concept, Howard says. “The vehicle will go up to a trailer, hitch itself up automatically, and then tow it to a designated location,” he says. But laser-based guidance has competition. NASA engineers are also working on a system that uses cameras and image recognition software to work out the distance and orientation of a spacecraft. Because that could use cameras mounted on Orion for other purposes, it would not add any extra weight. But harsh shadows created by the Sun can make image recognition difficult. Howard will present results of testing of the laser sensor at the Space Technology and Applications International Forum in Albuquerque, New Mexico, US,