In a few years, NASA and the ESA will conduct the long-awaited Mars Sample Return (MSR) mission. This mission will consist of a lander that will pick up the samples, an ascent vehicle that will send them to orbit, an orbiter that will return them to Earth, and an entry vehicle that will send them to the surface. This will be the first time samples obtained directly from Mars will be returned to Earth for analysis. The research this will enable is expected to yield new insights into the history of Mars and how it evolved to become what we see today.
Returning these samples safely to Earth requires that protective measures be implemented at every step, including transfer, ascent, transit, and re-entry. This is especially true when it comes to the Earth Entry System (EES), the disk-shaped vehicle that will re-enter Earth’s atmosphere at the end of the mission. In addition to a heat shield, engineers at NASA’s White Sands Test Facility (WSTF) near Las Cruces, New Mexico, are busy testing shielding that will protect the vehicle from micrometeorites and space debris during transit back to Earth and during re-entry.
According to the ESA’s Space Debris Office (SDO), there are about 32,320 debris objects in Low Earth Orbit (LEO) that are regularly tracked by Space Surveillance Networks (SSNs). These include pieces of defunct satellites, spent stages, and spacecraft that can reach velocities of up to 25,265 km/h (15,700 mph). At these speeds, even the tiniest bits of debris can pose a major collision hazard to robotic and crewed missions. But even these pale in comparison to micrometeorites, which can travel up to 85,000 meters per second (180,000 km/h; 112,000 mph).
Currently, a team of NASA engineers is testing a shield system for the EES at the Remote Hypervelocity Test Laboratory (RHTL), which has supported every human spaceflight program from the Space Shuttle and the International Space Station (ISS) to the Artemis Program. The team was led by Bruno Sarli, an aerospace engineer who has worked with NASA’s Global Trajectory Optimization Lab and the Planetary Defense Research Group since 2016.
To simulate impacts, the lab employs a series of 2-stage light gas guns to accelerate objects to the point where they have the same impact velocity as micrometeorites and orbital debris. The first stage uses gunpowder as a propellant, while the second stage pushes highly compressed hydrogen gas into a smaller tube to increase pressure inside the gun. The RHTL is equipped with four guns in total, including two 0.17-caliber (0.177-inch bore diameter), a 0.50-caliber (0.50-inch bore diameter), and a 1-inch diameter gun.
For the sake of their experiment, the team used the lab’s mid-sized 2-stage light gas gun that shoots pellets in the .50 caliber range at speeds of over 8 km/s (28,800 km/h; 17895.5 mph). The experiment took three days to set up but only one second to conduct (see the video of the team’s preparations below). The gun’s pressure gets so high during tests that it would level the entire building if one of the guns were to explode. For this reason, Sarli and his colleagues monitored the experiment from the safety of a bunker nearby.
Since micrometeorites travel six to seven times as fast in space, the team relies on computer models to simulate the actual velocities of micrometeorites. Meanwhile, the slower rate tests the computer model’s ability to simulate impacts on their shield and allows the team to study how the material reacts to the kinetic energy. As we get closer to the launch date of the Mars Sample Return mission (currently scheduled for 2028), the team will continue to run impact experiments and gather data on their shield design.
Other robotic elements in the MSR mission include the NASA/ESA-provided Sample Retrieval Lander, NASA’s Sample Recovery Helicopters (similar to Ingenuity), Mars Ascent Vehicle, Capture, Containment, and Return System (CCRS), and the ESA’s Earth Return Orbiter. The EES is being developed jointly by NASA’s Langley and Ames Research Centers, with impact testing provided through the NASA Goddard Space Flight Center (which is also developing the CCRS element).
With multiple spacecraft, launchers, and government agencies involved, the MSR campaign is one of the most ambitious endeavors in spaceflight history, involving multiple spacecraft, multiple launches, and multiple government agencies. If all goes according to plan, the MSR mission will return Martian rock and sediment samples to Earth by 2033. Bringing these samples to Earth will allow scientists to study them using instruments that are too large and heavy to transport to Mars, enabling greater scientific returns than previous robotic missions.
Further Reading: NASA
