Designing Equipment to Bite a Moon

A major component of the Martian Moon eXploration (MMX) mission is to collect a sample of the loose regolith that coats the surface of the Martian moons to return to Earth. The device that will gather from this layer of broken rocks and soil is therefore one of the most important pieces of mission equipment. When considering the design, four fundamental criteria must be fulfilled:

  1. Potential to collect a sample of more than 10g at a time (a science goal).
  2. Regolith down to a depth of at least 2cm should be collected (a science goal).
  3. It must be possible to collect multiple samples (a science goal).
  4. Effective technology for such sample gathering should be developed for use on future missions (an engineering goal).

These demands led to a vibrant discussion amongst the mission Sampling Equipment Team at ISAS. The culminating design was a robotic arm and cylindrical corer that could drive into the regolith and collect the sample. The deeper technological details are still being discussed, but tests have begun on how the sample corer will operate.

Sample return is a speciality of Japan, with the Hayabusa mission being the first in the world to return asteroid material to Earth. The spacecraft’s successor, Hayabusa2, is currently travelling to asteroid Ryugu. Techniques for gathering a sample from a small rocky body have therefore been cultivated during the design for the two asteroid missions. However, the Martian Moons eXploration mission target of a 10g sample is over a hundred times greater than the mission requirement for Hayabusa2. The Sampling Equipment Team is therefore considering adjustments to the corer mechanism that will allow material to be gathered more swiftly. This will also be a challenge for the robotic arm, which must ensure the corer firmly pierces the regolith. These improvements in the sampling technology will feed into future investigation and sample return missions.

The JAXA in-house test apparatus for the corer, experimenting on sand.

To investigate how the corer will operate, test equipment is being built in-house within JAXA. The team is currently borrowing the Lunar Planetary Exploration Laboratory to begin with a few basic tests. In a series of experiments, the diameter of the corer, the particle size of the sand being sampled and the strength of the spring that drives the corer through the material was varied. Using trial and error, the team were able to narrow down a design that worked well.

This preliminary investigation suggested that a corer with a diameter of 25mm to 30mm could comfortably dig down to the required regolith depth of 2cm. Experiments performed with ten different kinds of sand all allowed the corer mechanism to reach a depth of 7 – 8cm, and down to 5cm in larger gravel particles.

In addition to improving the control of the corer, the next steps will look at the lid mechanism that must firmly confine the sample once it enters the corer tube. Sand and gravel caught inside this cylinder must be gathered into the sample container and not fall back to the moon surface. Our Sampling Equipment Team are now developing a more detailed corer model to test.

High speed camera photographs of the test corer in action!

The equipment supporting the corer, including the robotic arm, the mechanism for keeping the sample within the spacecraft and storing the regolith safely in the sample container, and the electronic components that power the sampling procedure are all part of the detailed research and development plan being carried out in collaboration with a number of manufacturers. The result will be the complete sampling equipment for the Martian Moons eXploration spacecraft — we will report back!

(Based on the article in Japanese by Hirotaka Sawada from the ISAS Hayabusa2 Project Team and the Martian Moon eXploration (MMX) Sampling Equipment Team.)