JAXA, Japan’s aerospace research agency, is creating a niche for itself in sample return missions. Their Hayabusa mission was the first asteroid sampling mission when it brought dust from the asteroid Itokawa to Earth in 2010. Then its successor, Hayabusa 2, returned a sample of the asteroid Ryugu in 2020.
JAXA now has the Martian moon Phobos in sight and will send a spacecraft to sample it immediately after 2024. The mission is called Martian Moons eXploration (MMX) and will use a pneumatic vacuum device to collect samples.
Why go to Phobos and try it? Because this is an unusual moon, a better understanding of it could answer questions about it and our solar system. And we always want more answers.
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Phobos is the larger of the two moons on Mars, the other is Deimos. Both moons are irregularly shaped and look like potatoes, especially Phobos. Phobos has an average radius of only 11 km (7 miles). It is closer to Mars than Deimos and orbits only 6,000 km (3,700 miles) from the planet’s surface. It moves fast, taking only 7 hours and 39 minutes to complete one orbit and completes three orbits each day.
Much of the surface of Phobos is covered with strange linear grooves. New research supports the idea that these iconic canals are carved out of stones ejected from the Stickney Crater (the Great Depression on the right). Image credit: NASA / JPL-Caltech / University of Arizona
Phobos was probably an asteroid captured by rubble, although astronomers are still debating its nature. It has much in common with carbon asteroids and is one of the least reflective objects in the solar system.
The little moon is getting closer and closer to Mars. Each year it approaches about 2 cm and will eventually be destroyed. In about 30 million to 50 million years, it will either crash to the surface of Mars and be completely destroyed, or it will be torn apart by tidal forces and form a ring of debris around the planet. In fact, one hypothesis says that the moons on Mars were formed from dust created by a giant impact on Mars. Dust powder, as they say.
Illustration of Mars with a ring of debris. Image credit: SETI
Japan is leading the MMX mission, but NASA, CNES (France) and DLR (Germany) are also contributing. It has two broad objectives: (1) to determine the origin of Martian moons and (2) to observe processes in Mars’ planetary environment based on remote sensing, in situ observations and laboratory analyzes of returned Phobos regolith samples. Scientists believe that a better understanding of the Mars-Phobos-Deimos system will shed light on the process of planet formation in the solar system.
Obtaining a sample from Phobos faces several obstacles. The moon is not massive enough for a spacecraft to enter orbit around it in the usual way. Instead, MMX will orbit Mars and then perform quasi-satellite orbits. These orbits become unstable over time, but should allow several months of operation near Phobos. This maneuver also allows the MMX lander to reach the surface of Phobos.
JAXA designs the MMX mission with three components: a drive module, a survey module and a return module. The French space agency CNES has proposed a mission to bring to the surface a small rover the size of a microwave oven built by France and Germany.
But the focus of the MMX mission will be the return of the sample. We have made great strides in sending instruments to spacecraft, landers and rovers to study the bodies of the solar system. When it comes to Mars, space exploration has unleashed a stream of new evidence and insights. But the holy grail in space missions is still a testimonial. No matter how advanced the instruments we send on missions, laboratory analyzes on Earth will always be ahead of them.
MMX will collect samples in two ways. One is the Coring Sampler (C-SMP), developed by JAXA. The other is the Pneumatic Sampler (P-SMP), provided by NASA and developed by Honeybee Robotics.
The pair of samples will complement each other and partly take into account the fact that we do not know what the surface is. The sampler will be positioned on the robotic arm of the lander. He will use a special alloy with shape memory to collect a 10-gram sample of deeper than 2 cm below the regolith.
P-SMP can capture regolith even if the surface is covered with gravel-sized material. (Image Credit: Honeybee Robotics)
The pneumatic sampler will be positioned near the pad on one of the feet of the lander. It will use pressurized nitrogen gas to collect samples, and mission operators can manipulate the gas flow as required. It can be continuous or pulsed.
This is a schematic view of a P-SMP with 1. Sampling head, 2. N2 gas return tubes and sample, and 3. Control box with sample container. (Image Credit: Honeybee Robotics)
The P-SMP has three sets of nozzles to perform the procedure. Two excavation nozzles point downwards, two retro thrust nozzles point upwards and two transport nozzles point towards the sampling tube. The three pairs of nozzles ignite simultaneously.
The excavation nozzles shoot at the surface of Phobos and move regolith material. The transport nozzles direct the material to the sampling head. Retro traction nozzles are ignited to counteract traction on the spacecraft, so that its position is stable during sampling.
Honeybee Robotics is extensively testing its P-SMP and is confident that it can handle any surprises on the surface of Phobos. The company says its system can still collect samples, even if gravel covers the surface.
MMX will not be the only mission to use Honeybee’s vacuum system. NASA plans to use it on the moon to capture lunar regolith at Mare Crisium in 2023. The system is also being considered for the Europa Lander mission and several other missions that are still in the concept and design phase.
It is easy to understand why.
“The purpose of this technology is to allow simple and cheap capture of planetary materials from largely unknown surfaces,” said Honeybee project manager Chris Zackney. “Vacuum cleaners are designed to capture ‘dirt’, so a vacuum cleaner-like approach is ideal for working with planetary ‘dirt’.”
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