NASA’s Langley Research Center in Hampton, VA hired Honeybee Robotics Spacecraft Mechanisms Corp. to develop a totally mechanical tool changer for the end of what Langley’s Lunar Surface Manipulation System (LSMS) team describes as a robot that could unload landers. Then, after the landers were unloaded, it could, in addition to doing base assembly, mate with tools to take science experiments. This robot could be likened to a crane, but with more dexterity.
The crane was designed to work remotely so that it could be used on an unmanned mission without human interaction. It is completely autonomous — one of the driving factors. The tool changer does have other applications if they decide they want to use it on Mars or even in outer space for a robotic arm and end effectors.
Since Honeybee has been developing harsh-environment, mission-critical end effectors for over 25 years and has worked on the equipment for other space missions, they were specially suited to tackle this challenge.
Making It Work
Basically, Honeybee was given a footprint to stay within, and all the requirements for load ratings and misalignment allowances. Explained Lee Carlson, a systems engineer who was part of the Honeybee team, “The crane might be sitting on the lander deck or on the lunar surface and would be driven from quite a distance away from the tool to be mated to. This required designing for large misalignment allowances. This was our first design challenge. The end of the crane and target tool could be misaligned by as much as a couple inches in any direction with up to 20 degrees angular misalignment when attempting a mate.”
But, Carlson continued, there were other considerations. “The tool changer had to be capable of carrying around 1,000 pounds, so (the tool changer) had to be very robust. Also, since this was a lunar project, it has to be tolerant to moon dust. These two design criteria required special seals to protect large roller bearings. If this design was for space, it becomes considerably simpler. All of the loads would be reduced and dust is no longer an issue. But the Moon is a very harsh environment, and lunar dust is a major concern when designing for missions there.”
The original assignment called for ‘dummy’ tools requiring no power; the crane would do all the work. Tools would range from a forklift attachment, a shovel, or scoop for acquiring surface samples or digging, to a bucket for lifting human passengers.
Then NASA decided it wanted the capability of attaching an electronic or electromechanical tool to the end of the crane. Now, the tool changer would have to provide an electrical connection as well. Solving this problem fell to Carlson. “The contract was expanded to add an electrical connector to the existing mechanical connector. You’d have a power source on the LSMS, on the crane itself. Your tools could then be powered. So your tools capabilities could expand into the realm of cameras, or tools with cameras on them, or even a light jackhammer.” However, they had not left space to accommodate an electrical connector because it was not a part of the original contract and the budget did not allow for starting from scratch.
A Crucial Ten Square Inches
Carlson had to work within the constraints of the current design because NASA did not want a redesign of the whole tool changer. They just wanted to add an electrical connector to it without increasing the current envelope. He only had roughly 2-1/2 by 4" of free space to incorporate the male side of the new autonomous connector. The connector has to mate itself to a female connector mounted on the tool. Carlson said, “We make small stuff all the time and if there were more space, there are many different ways that I could have designed it.”