Japan’s next mission will use a vacuum cleaner to get its sample of Phobos

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JAXA, the Japanese aerospace exploration agency, is carving out a place for itself in sample return missions. Their Hayabusa mission was the first mission to sample an asteroid when it brought dust from asteroid Itokawa back to Earth in 2010. Then its successor, Hayabusa 2, brought back a sample from asteroid Ryugu in 2020.

JAXA now has the Martian moon Phobos in its sights and will send a spacecraft to sample it as early as 2024. The mission is called Martian Moons eXploration (MMX), and it will use a pneumatic suction device to collect its samples.

Why go to Phobos and taste it? Because it’s an unusual moon and understanding it better might 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 of Mars, the other being Deimos. Both moons are irregularly shaped and look a bit like potatoes, especially on Phobos. Phobos has an average radius of only 11 km (7 mi). It is closer to Mars than Deimos and orbits just 6,000 km (3,700 mi) from the planet’s surface. It moves fast, taking just 7 hours and 39 minutes to complete one orbit, and performs three orbits each day.

Much of Phobos' surface is covered in strange linear grooves.  New research supports the idea that boulders cleared from Stickney Crater (the Great Depression on the right) carved out these iconic grooves.  Image Credit: NASA/JPL-Caltech/University of Arizona
Much of Phobos’ surface is covered in strange linear grooves. New research reinforces the idea that these iconic rilles were carved out by boulders cleared from Stickney Crater (the Great Depression on the right). Image Credit: NASA/JPL-Caltech/University of Arizona

Phobos is probably a captured asteroid, although astronomers still debate its nature. It has much in common with carbonaceous asteroids and is one of the least reflective objects in the solar system.

The small moon is getting closer and closer to Mars. Every year it gets closer by about 2 cm and will eventually be destroyed. In about 30 to 50 million years, it will crash into the surface of Mars and either be completely destroyed or be torn apart by tidal forces and form a ring of debris around the planet. In fact, one hypothesis says that the moons of Mars were formed from dust created by a giant impact on Mars. From dust to dust, as they say.

An illustration of Mars with a debris ring.  Image credit: SETI
An illustration of Mars with a debris ring. Image credit: SETI

Japan leads the MMX mission, but NASA, CNES (France) and DLR (Germany) also contribute. It has two main objectives: (1) to determine the origin of the Martian moons and (2) to observe the processes in the circumplanetary environment of Mars, based on remote sensing, in situ observations and laboratory analyzes of returned samples of regolith from Phobos. 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.

Getting a sample from Phobos comes up against several hurdles. The moon is not massive enough for a spacecraft to 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 designed the MMX mission with three components: a propulsion module, an exploration module and the return module. France’s CNES space agency has suggested the mission should also deploy a tiny microwave-sized rover to the surface, built by France and Germany.

But the highlight of the MMX mission will be the return of samples. We have made tremendous progress sending instruments on spacecraft, landers and rovers to examine bodies in the solar system. As far as Mars is concerned, the in situ study of the planet has triggered a flood of new evidence and ideas. But the holy grail in space missions is always sample feedback. 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 samplers will complement each other and partly explain the fact that we don’t know what the surface looks like. The core sampler will be positioned on the robotic arm of the lander. He will use a special shape-memory alloy to take a 10-gram sample more than 2 cm deep under the regolith.

P-SMP can capture regolith even if the surface is covered with gravel-sized material.  (Image credit: Honeybee Robotics)
P-SMP can capture regolith even if the surface is covered with gravel-sized material. (Image credit: Honeybee Robotics)

The pneumatic sampler will be placed near the footrest on one of the legs of the lander. It will use pressurized nitrogen gas to collect the samples, and mission operators can manipulate the gas flow as needed. It can be continuous or pulsed.

This is a schematic view of the P-SMP with 1. Sampling head, 2. N2 and sample gas return tubes and 3. Control box with a sample container.  (Image credit: Honeybee Robotics)
This is a schematic view of the P-SMP with 1. Sampling head, 2. N2 Gas and sample return tubes, 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 down, two back-thrust nozzles point up, and two transport nozzles point to the pick-up tube. All three pairs of nozzles turn on simultaneously.

Excavation nozzles shoot at the surface of Phobos and stir up regolith material. Transport nozzles direct the material into the sampling head. The back-thrust nozzles fire to counter the thrust on the spacecraft, so that its position is stable during sampling.

Honeybee Robotics has tested its P-SMP extensively and is confident that it can handle any surprises on the surface of Phobos. The company says its system can still collect a sample even if gravel covers the surface.

MMX won’t be the only mission to use Honeybee’s vacuum system. NASA plans to use it on the Moon to capture lunar regolith in Mare Crisium in 2023. The system is also being considered for a Europa Lander mission and several other missions still in the concept and design phase.

It’s easy to see why.

“The goal of this technology is to enable simple and inexpensive capture of planetary material from largely unknown surfaces,” said Honeybee project manager Kris Zacny. “Vacuum cleaners are designed to capture ‘dirt’, so a vacuum-like approach is ideal for working with planetary ‘dirt’.”

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