The initial rover will be a scout, capturing first-hand views in high-definition video – a first from the lunar surface. Stereo cameras and flash LIDAR (laser-based imaging) enable the mission to build a high-resolution terrain map as it explores. The rover will be remotely operated from Earth, with amateur drivers selected to take control periodically. Because of the Moon’s distance, pilots will have to drive four to five seconds into the future – that’s how long it takes to see the rover react to a driving command.
Scouting rovers likely will be modified to carry drills if they’re sent to the Moon’s south pole. The drill will penetrate the top several inches of dry soil to reach the water and other ices, bringing samples up to be analyzed.
The bottom of the Scouting Rovers page has captions for three photos, but no photos.
The rover will be five feet tall, and about the same width and length. Astrobotic engineers project that the flight version will mass about 175 pounds, although 220 pounds have been set aside in the launch calculations to provide margin in case that grows. The rover structure is primarily composite, manufactured at Carnegie Mellon’s Advanced Composites Lab. (Composite materials are sandwiches of resin and fibers, producing great strength and stiffness at low weight after being baked into a solid structure.)
The two main challenges to successful roaming across the Moon are the extreme temperatures and the abrasive, sticky dust.
The cold side of the rover has a vertical logo panel to honor the expedition’s sponsors, and a sloping radiator panel angled up to radiate heat off to the black sky.
Oven-level heat
The Sun shines for two weeks straight on the Moon, followed by two weeks of frigid night. The Astrobotic robot will land about 36 hours after local dawn, when temperatures are moderate. Then soil temperatures rapidly rise to about 230 degrees F (110C) and stay there for more than a week. The rover will be baking both from the heat radiated up from the soil and the direct sunlight beating down in a cloudless, airless sky.
The robot beats the heat by keeping a cool side aimed away from the Sun to radiate heat off to the black sky. It travels toward or away from the sun (generally east or west) without turning its radiator into the light – its camera head swivels to face the new direction. This ensures that the four solar panels on the hot side remain facing the sun. It can move north and south by zig-zagging, tacking like a sailboat, to keep the solar panels mostly pointed in the right direction.
The composite materials selected by Astrobotic to hold the solar panels are highly conductive to heat, so it can be wicked away to the radiator. Other parts are enveloped in heat-conducting composites that link to the radiator. The temperature-sensitive electronics are mounted directly to the radiator’s underside to give them the coolest spot on the structure.
When the Sun sets, mission control shuts down the robot’s systems. The temperature sinks to minus 298 degrees F (-183C). Carrying sufficient reserve power to generate heat to counter this prolonged, severe cold would make the rover too heavy to move, so hibernation is the only alternative. Several key components have survived liquid nitrogen testing – batteries, solid state drives, and processors – so Astrobotic’s engineers are hopeful the rover will wake up at the next dawn to continue exploration.
Destructive dust
The Moon’s dirt is a threat to anything mechanical, so another Astrobotic innovation is a lunar-specific drive train. Unlike Mars rovers that have motors in the hub of each wheel and steering motors placed right above them, the Astrobotic design tucks two motors inside the body of the robot where they are safe from both dust and heat. One motor powers the wheels on each side of the robot, with roller chains transferring the power out to the wheels. The chains are similar to a chain saw, so they can stand up to a very rough environment. The chain drive mechanism has been tested in a vacuum chamber to ensure that is does not experience “cold welding” – a process where materials sometimes merge or weld to each other when touching in a hard vacuum.
The robot drives like a tank – it turns by making one side move faster than the other side. It can spin in place by making the opposite side run in reverse. Three prototypes have been fabricated and put through simulated lunar excursions. Some tests were done in the slag heaps of abandoned steel mills in the Pittsburgh area.
Moon dirt is fundamentally different from Earth dirt, which generally is formed by wind and water erosion of rocks. The tumbling of wind and water erosion creates rounded dirt particles. Moon dirt is created by micro-meteorite impacts that shatter rocks into smaller and smaller pieces that are jagged and sharp rather than rounded. In addition, Moon dust is electrostatically charged and clings to visiting machines. The Apollo 17 astronauts, who spent the most time of any crew working in the dust, discovered that by their third outing their suit joints were so infiltrated with abrasive dust that movement was very difficult.
