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Astrobotic Technology Inc., a spin-off from Carnegie Mellon University, is developing a series of surface robotic missions to the moon. They will deliver more than 100 kg (240 lbs) per expedition for space agencies and corporations and beam 3D imagery to billions of people on Earth.
Destinations for early missions include Apollo sites, Surveyor 6 – very near the “zero zero” coordinates at the center of the Moon’s near side – and one of the newly discovered “skylights” that are mysterious holes in the surface that may lead down to volcanic caves.
These destinations are near the Moon’s equator, where daytime temperatures exceed 100 degrees C. The robots beat this tremendous heat with an innovative asymmetric design: a substantial radiator dumps heat to black sky from the rover’s shadowed side. All solar panels are on the other side, and the rover always orients them to face the Sun. By reversing its camera head, it can travel east or west while keeping its solar panels Sunward, and it can move north and south by tacking like a sailboat while gaining partial sunpower.
In its initial 2013 mission, the Astrobotic rover will deliver more than 230 pounds of payload for space agencies, aerospace firms, academic researchers and corporate sponsors. The rover travel tens of kilometers per lunar day, delivering lunar imagery in 3D. Amateur drivers on Earth will be able to take control from time to time. The rover will answer questions in one-to-one phone conversations as it explores. Beyond capturing the prize and its scientific and engineering agenda, it will deploy art experiments, participate in music events and draw patterns in the lunar soil suggested by the global Web public.
Astrobotic’s delivery capability is well matched to NASA’s new focus on technology development, tech demonstrations and robotic precursor missions. By launching on a Space X Falcon 9 – which costs less than half of comparable Delta IV and Atlas V vehicles – and using commercial alternatives to components designed for aerospace applications, the Astrobotic team will give NASA and other payload developers low-cost access to the lunar surface. For example, creators of a 50-kg instrument package would pay only $100 million for delivery to the Moon, compared to the $200-$300 million cost of a typical space agency mission to deliver the same package to orbit around a planetary body.
The rover and its supporting spacecraft will be launched on by the Falcon 9 rocket into TLI, or trans lunar injection. The rover’s computer and navigational gear will control the spacecraft’s engines as they fire to enter lunar orbit and later as the spacecraft descends to the surface. (The trip to the Moon from Cape Canaveral will take three to five days, and then robot and spacecraft likely will loiter in lunar orbit until dawn comes to the intended landing site. ) The robot will explore for the next 10-12 days until night falls. While not specifically designed to survive the punishing cryogenic cold of the two-week lunar night, the robot will be built with as many cold-tolerant parts as the team can discover. Already, batteries without water electrolyte have successfully come back to life after freezing at liquid nitrogen temperatures.
The engineering experts at Carnegie Mellon’s Robotics Institute have built and field-tested two prototype rovers, which proved the locomotion system will be robust. Their symmetry – pyramids with solar cells and radiators on each of four equal sides – was chosen to enable flexibility to travel in any direction. But analysis showed this shape couldn’t generate sufficient electrical power nor dump enough heat to keep the robot cool at the Moon’s equator.
The third prototype now in fabrication has an asymmetrical shape that generally keeps all the solar cells facing the Sun and one large radiator on the opposite side dumping heat to black sky. Crucial innovations focus on keeping the external radiation from seeping into the rover, and wicking internally generated heat (from motors and electronic parts) away to the radiator. The structure combines several types of composite materials with excellent heat conductivity. Heat that soaks through from the solar panels, for example, reaches a structural panel that provides conductivity in addition to physical support. Inside, composite straps link heat-generating sources – such as the motors – to the structure or the radiator. The most sensitive parts, such as the computer, are mounted directly against the inside surface of the radiator.
The five-foot (1.7 meter) tall robot will generate 120 watts of electrical power and keep a 270W-hr battery pack charged for the occasional sprint through a shadow or need to turn away briefly from the Sun. The energy is sufficient to enable it to traverse the surface and transmit imagery simultaneously.
The robot’s drive train has only two motors, both mounted inside its body where they can be cooled and kept away from dust. Each motor drives bicycle-style chains to the two wheels on a side. Direction is controlled by skid-steering, making one side’s wheels turn faster than the other side. Because the wheels have no sensitive parts, they can directly experience the Moon’s heat and dust. This is unlike Mars robots where each wheel has a motor in its hub, and additional motors are required to steer wheels. Mars never gets hot – the climate is generally like North Dakota without the summer season – so Martian motors don’t need to be cooled. Martian dust also is less abrasive than Moon dust.
See www.astrobotictech.com for more information.
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