A robotic vehicle called ATHLETE-the All-Terrain Hex-Limbed, Extra-Terrestrial Explorer-is described, along with initial results of field tests of two prototype vehicles. This vehicle concept is capable of efficient rolling mobility on moderate terrain and walking mobility on extreme terrain. Each limb has a quick-disconnect tool adapter so that it can perform general-purpose handling, assembly, maintenance, and servicing tasks using any or all of the limbs.
Europa is a premier target for advancing both planetary science and astrobiology, as well as for opening a new window into the burgeoning field of comparative oceanography. The potentially habitable subsurface ocean of Europa may harbor life, and the globally young and comparatively thin ice shell of Europa may contain biosignatures that are readily accessible to a surface lander. Europa’s icy shell also offers the opportunity to study tectonics and geologic cycles across a range of mechanisms and compositions. Here we detail the goals and mission architecture of the Europa Lander mission concept, as developed from 2015 through 2020. The science was developed by the 2016 Europa Lander Science Definition Team (SDT), and the mission architecture was developed by the preproject engineering team, in close collaboration with the SDT. In 2017 and 2018, the mission concept passed its mission concept review and delta-mission concept review, respectively. Since that time, the preproject has been advancing the technologies, and developing the hardware and software, needed to retire risks associated with technology, science, cost, and schedule.
A scaled deployable device has been built and tested for the purpose of evaluating the feasibility of capturing an entire small asteroid in free space. The target asteroid was presumed to have a mass <1000 metric tons, with a longest dimension of <13 meters. It could be spinning and tumbling. It could be a "rubble pile"-a collection of loosely-bound particles whose cohesion is barely more than the minimum required by the hoop strength defined by the spin rate. It was decided that the only way to confine a rubble pile was to put it in a baga fabric or membrane enclosure which completely encapsulated the asteroid, preventing contamination of the solar arrays, radiators, and other optical surfaces of the spacecraft. Clearly this bag had to be deployed, since the largest dimension of the asteroid is significantly larger than the launch shroud of any present launch vehicle. It was decided that a hardware-in-the-loop testbed would be needed, since the physics of physical contact between the asteroid and the deployed capture bag is too complex to credibly model entirely within computer simulation. This testbed was built at 1/5 th-scale for a capture bag assumed 15 meters in diameter (the largest dimension of the asteroid plus a meter on either side). The asteroid mockup was mounted on a robotic arm and force-torque sensors were used to measure the interactions between the spacecraft and the asteroid through the soft material of the capture system. The force-torque measurements were fed into a zero-g simulation of the spacecraft and asteroid, which in turn prescribed the motion of the asteroid relative to the spacecraft. This paper describes the construction and operation of the testbed, including the selection of the bag materials, the configuration of the capture mechanism, the actuators required to deploy, control, and retract the bag, the hardware-in-the-loop simulation and the sensors used to drive it, as well as results from the system. Nomenclature ADAMS = High-Fidelity Multibody Simulation Software distributed by MSC Corporation ARM = NASA Asteroid Redirect Mission ARCM = NASA Asteroid Redirect Crewed Mission
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