Vacuum Cleaning Phobos: Acquisition of Regolith with a Pneumatic Sampler
Pneumatic Sampler (P-SMP) for JAXA’s Martian Moons eXploration (MMX) mission
An SMD-sponsored team at Honeybee Robotics is developing a Pneumatic Sampler (P-SMP) to capture material on the surface of Mars’s moon, Phobos, for sample return to Earth. Successful infusion of this capability into JAXA’s MMX mission signifies the success of long-term SMD technology development investments, which were initiated through NASA’s Small Business Innovation Research (SBIR) Program.
Led by the Japanese Aerospace Exploration Agency (JAXA), MMX has two mission goals: (1) determining the origin of the Martian moons and (2) observing processes in the circumplanetary environment of Mars, based on remote sensing, in situ observations, and laboratory analyses of returned samples of Phobos regolith. These observations and sample analyses will allow new insights about the origins of the Martian moons and how water and organics were delivered to the inner rocky planets, including Earth. An SMD-sponsored team at Honeybee Robotics is developing the Pneumatic Sampler (P-SMP) that will enable MMX to capture surface material on Phobos and prepare it for return to Earth for laboratory analysis.
To fulfill the mission goals, MMX employs a dual sampling approach using a JAXA-developed Coring Sampler (C-SMP) and the NASA-contributed P-SMP. The C-SMP, a core soil tube deployed by a robotic arm, will provide access to the building blocks of Phobos beneath the surface, and will collect a mixture of near-surface material. The P-SMP, on the other hand, will selectively sample the surface veneer and provide a reference for the surface material gathered by the C-SMP.
The double sampling approach not only enhances the scientific merits of MMX, but also reduces risks associated with sampling materials on Phobos. Since we do not have much knowledge of the physical properties, chemical properties, and the geotechnical conditions on the surface of Phobos (e.g., compositions, temperature gradient/variation, porosity, grain size distribution), operating two MMX sampling systems that utilize entirely different sampling approaches is prudent.
The P-SMP consists of three main subsystems (Figure 2). The Sampling Head, integrated into the lander footpad, contains three sets of nozzles and a funnel to collect regolith samples. The N2 Gas Tube connects the gas tank within the Control Box to the nozzles within the Sampling Head. The Sample Return Tube transports the collected regolith and gas towards the Sample Container within the Control Box. The Control Box itself houses all the components needed to actuate the pneumatic system, as well as the gas tank, valves, beam breaker to detect regolith particles within the Sample Return Tube, and finally the Sample Container itself.
Figure 3 details the PMP’s operational steps. Once actuated by the spacecraft computer, the two redundant valves between the N2 tank and the Sampling Funnel open (see 1 in the image, below). These valves can modulate gas flow duration, pressure, and frequency: that is, it is possible to send a constant or pulsed gas stream, depending on the requirements.
Once the two valves open, the gas will flow from the N2 tank, down the N2 Gas Tube, and into the three sets of gas nozzles: two of them are pointed down (excavation nozzles), two are pointed up (retrothrust nozzles), and two are pointed into the Sample Return Tube (transport nozzles). All three sets of nozzles fire gas at the same time. The excavation nozzles stir up Phobos regolith and create ejecta (2). Some of this ejecta flows back into the Sampling Head where it is hit by the gas coming from the transport nozzles. At the same time, the retrothrust nozzles fire to reduce the overall impulse to the spacecraft (the excavation nozzles are essentially ‘rocket engines’).
Once inside the Sample Return Tube (3), the gas and sample flow at high speed towards the Sample Container. Just before flowing into the Sample Container (4), the gas escapes sideways, allowing the sampled Phobos material to move into the container under its own momentum. The Control Box houses the Beam Breaker sensor (a set of two light-emitting diodes and two phototransistors), which detects material transported towards the Sample Container and allows verification of the sample delivery. The sampling operation ends with the closure of the two valves between the N2 tank and the Sampling Head.
After the MMX spacecraft ascends from the Phobos surface, the robotic arm grips the Sample Container with the Phobos material (5) and moves it into the Sample Storage Chamber (SSC) on the MMX Return Capsule (not shown).
To date, the Honeybee Robotics team has conducted over 200 tests to characterize performance of the P-SMP. All tests were done inside a vacuum chamber with a range of simulated sample materials, including the Phobos Giant Impact (PGI) simulant developed by the Exolith Laboratory at the University of Central Florida. Some of the tests included several cases with the Sampling Funnel 10 cm above the surface (Figure 4). These and many other tests confirmed the robustness of the P-SMP, even when faced with the uncertain surface properties of Phobos.
Since 2005, NASA has been providing funding to Honeybee Robotics to develop pneumatic sampling and mining systems. The technology was initially advanced in collaboration with Rob Mueller and his team at NASA Kennedy Space Center’s Swampworks and funded through phases 1 and 2 of NASA’s Small Business Innovation Research (SBIR) Program. Critical demonstrations of this technology for planetary lander applications were also enabled with Masten Space Systems via two NASA Tech Flights solicitation awards and a financial contribution from the Planetary Society.
Currently, the technology is being infused into additional programs and missions. A pneumatic-based sampler called PlanetVac will fly to the Moon’s Mare Crisium in 2023 with the goal of capturing lunar regolith and performing in situ sieving and imaging. This mission is part of the NASA Commercial Lunar Payload Services (CLPS) program and PlanetVac is being funded via the NASA Lunar Surface Instrument and Technology Payloads (LSITP) program. In addition, pneumatic-based sample delivery has been infused into a Europa lander mission concept study and several other mission concepts and proposals.
According to Honeybee project lead, Kris Zacny, “The purpose of this technology is to allow simple and inexpensive capture of planetary materials from largely unknown surfaces. Vacuum cleaners are designed to capture ‘dirt,’ hence a vacuum cleaner-like approach is ideal for working with planetary ‘dirt.’”
Kris Zacny, Honeybee Robotics
NASA SMD Planetary Science Division
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