Sample-return mission

Apollo 11 was the first mission to return extraterrestrial samples.

Moon rock from Apollo 15 interpretive sign.

Moon rock from Apollo 15 at NASA Ames Visitor Center.

The Apollo program returned over 382 kg (842 lb) of lunar rocks and regolith (including lunar 'soil') to the Lunar Receiving Laboratory in Houston.[9][10][11] Today, 75% of the samples are stored at the Lunar Sample Laboratory Facility built in 1979.[12] In July 1969, Apollo 11 achieved the first successful sample return from another Solar System body. It returned approximately 22 kilograms (49 lb) of Lunar surface material. This was followed by 34 kilograms (75 lb) of material and Surveyor 3 parts from Apollo 12, 42.8 kilograms (94 lb) of material from Apollo 14, 76.7 kilograms (169 lb) of material from Apollo 15, 94.3 kilograms (208 lb) of material from Apollo 16, and 110.4 kilograms (243 lb) of material from Apollo 17.

One of the most significant advances in sample-return missions occurred in 1970 when the robotic Soviet mission known as Luna 16 successfully returned 101 grams (3.6 oz) of lunar soil. Likewise, Luna 20 returned 55 grams (1.9 oz) in 1974, and Luna 24 returned 170 grams (6.0 oz) in 1976. Although they recovered far less than the Apollo missions, they did this fully automatically. Apart from these three successes, other attempts under the Luna programme failed. The first two missions were intended to outstrip Apollo 11 and were undertaken shortly before them in June and July 1969: Luna E-8-5 No. 402 failed at start, and Luna 15 crashed on the Moon. Later, other sample-return missions failed: Kosmos 300 and Kosmos 305 in 1969, Luna E-8-5 No. 405 in 1970, Luna E-8-5M No. 412 in 1975 had unsuccessful launches, and Luna 18 in 1971 and Luna 23 in 1974 had unsuccessful landings on the Moon.[13]

In 1970, the Soviet Union planned for a 1975 first Martian sample-return mission in the Mars 5NM project. This mission was planned to use an N1 rocket, but as this rocket never flew successfully, the mission evolved into the Mars 5M project, which would use a double launch with the smaller Proton rocket and an assembly at a Salyut space station. This Mars 5M mission was planned for 1979, but was canceled in 1977 due to technical problems and complexity; all hardware was ordered destroyed.[14]

The Earth-Orbital Debris Collection (ODC) experiment was deployed on the Mir space station for 18 months during 1996–97 and used aerogel to capture particles from low Earth orbit, consisting of interplanetary dust and man-made particles. Far from being "the last sample-return mission... in... twenty years", ODC was a portable version of an LDEF collector, decreasing collection time significantly, and effective area by orders of magnitude.

An artist's rendering of Genesis collecting solar wind.

The next mission to return extraterrestrial samples was the Genesis mission, which returned solar wind samples to Earth from beyond Earth orbit in 2004. Unfortunately, the Genesis capsule failed to open its parachute while re-entering the Earth's atmosphere and crash-landed in the Utah desert. There were fears of severe contamination or even total mission loss, but scientists managed to save many of the samples. They were the first to be collected from beyond lunar orbit. Genesis used a collector array made of wafers of ultra-pure silicon, gold, sapphire, and diamond. Each different wafer was used to collect a different part of the solar wind.

Sample-return capsule from the Stardust mission

Genesis was followed by NASA's Stardust spacecraft, which returned comet samples to Earth on January 15, 2006. It safely passed by Comet Wild 2 and collected dust samples from the comet's coma while imaging the comet's nucleus. Stardust used a collector array made of low-density aerogel (99% of which is space), which has about 1/1000 of the density of glass. This enables the collection of cometary particles without damaging them due to high impact velocities. Particle collisions with even slightly porous solid collectors would result in the destruction of those particles and damage to the collection apparatus. During the cruise, the array collected at least seven interstellar dust particles.[15]

In June 2010 the Japan Aerospace Exploration Agency (JAXA) Hayabusa probe returned asteroid samples to Earth after a rendezvous with (and a landing on) S-type asteroid 25143 Itokawa. In November 2010, scientists at the agency confirmed that, despite failure of the sampling device, the probe retrieved micrograms of dust from the asteroid, the first brought back to Earth in pristine condition.[16]

The Russian Fobos-Grunt was a failed sample-return mission designed to return samples from Phobos, one of the moons of Mars. It was launched on November 8, 2011, but failed to leave Earth orbit and crashed after several weeks into the southern Pacific Ocean.[17][18]

OSIRIS-REx collecting a sample from asteroid 101955 Bennu
— (Full-sized image)

The Japan Aerospace Exploration Agency (JAXA) launched the improved Hayabusa2 space probe on December 3, 2014. Hayabusa2 arrived at the target near-Earth C-type asteroid 162173 Ryugu (previously designated 1999 JU3) on 27 June 2018.[19] It surveyed the asteroid for a year and a half and took samples. It left the asteroid in November 2019[20][21] and returned to Earth on December 6, 2020.[22]

The OSIRIS-REx mission was launched in September 2016 on a mission to return samples from the asteroid 101955 Bennu.[23][24] The samples are expected to enable scientists to learn more about the time before the birth of the Solar System, initial stages of planet formation, and the source of organic compounds that led to the formation of life.[25] It reached the proximity of Bennu on 3 December 2018,[26] where it began analyzing its surface for a target sample area over the next several months. It collected its sample on 20 October 2020,[27][28] and is expected to return to Earth on 24 September 2023.[29]

China launched the Chang'e 5 lunar sample return mission on November 23, 2020, which returned to Earth with 2 kilograms of lunar soil on December 16, 2020.[30] It was first lunar sample return in over 40 years.[31]

Ascent vehicle in its protective shroud, 2009 ESA-NASA design.[32]

Russia has plans for Luna-Glob missions to return samples from the Moon by 2027 and Mars-Grunt to return samples from Mars in the late 2020s.

JAXA is developing the MMX mission, a sample-return mission to Phobos that will be launched in 2024.[33] MMX will study both moons of Mars, but the landing and the sample collection will be on Phobos. This selection was made because of the two moons, Phobos's orbit is closer to Mars and its surface may have particles blasted from Mars. Thus the sample may contain material originating on Mars itself.[34] A propulsion module carrying the sample is expected to return to Earth in approximately September 2029.[35]

China will launch the Chang'e 6 lunar sample return mission in 2023.

China has plans for a Mars sample return mission by 2030.[36][37] Also, the Chinese Space Agency is designing a sample-retrieval mission from Ceres that would take place during the 2020s.[38]

NASA has long planned a Martian sample-return mission,[39] but has yet to secure the budget to successfully design, build, launch, and land such a probe. The mission remained on NASA's roadmap for planetary science as of the 2013 Planetary Science Decadal Survey.[40] The Perseverance rover, launched in 2020, will collect drill core samples and stash them on Mars' surface by 2023, but it remains unclear how they will be retrieved from the stash and returned to Earth.[41]

Comet sample-return missions[42] continue to be a NASA priority. Comet Surface Sample Return was one of the six themes for proposals for NASA's fourth New Frontiers mission.[43]

Mars sample-return mission (2020; artist concepts)[44][45]

01.Mars 2020 rover obtaining samples

02.Mars 2020 rover storing samples

03.Lander landing

04.Lander unfolding

05.Fetch rover gathering samples

06.Fetching samples for lander

07.Launching from Mars

08.Releasing samples for later pickup

A collector array may be used to collect millions or billions of atoms, molecules, and fine particulates by using wafers made of different elements. The molecular structure of these wafers allows the collection of various sizes of particles. Collector arrays, such as those flown on Genesis, are ultra-pure in order to ensure maximal collection efficiency, durability, and analytical distinguishability.

Collector arrays are useful for collecting tiny, fast-moving atoms such as those expelled by the Sun through the solar wind, but can also be used for collection of larger particles such as those found in the coma of a comet. The NASA spacecraft known as Stardust implemented this technique. However, due to the high speeds and size of the particles that make up the coma and the area nearby, a dense solid-state collector array was not viable. As a result, another means for collecting samples had to be designed to preserve the safety of the spacecraft and the samples themselves.

A particle captured in aerogel

Aerogel is a silica-based porous solid with a sponge-like structure, 99.8% of whose volume is empty space. Aerogel has about 1/1000 of the density of glass. An aerogel was used in the Stardust spacecraft because the dust particles the spacecraft was to collect would have an impact speed of about 6 km/s.[46] A collision with a dense solid at that speed could alter their chemical composition or perhaps vaporize them completely.

Since the aerogel is mostly transparent, and the particles leave a carrot-shaped path once they penetrate the surface, scientists can easily find and retrieve them. Since its pores are on the nanometer scale, particles, even ones smaller than a grain of sand, do not merely pass through the aerogel completely. Instead, they slow to a stop and then are embedded within it.

Mars 5NM Design. This Probe was designed to return a sample from Mars at the end of the 70s

Illustration of Mars 5 NM Probe performing a course correction

The Stardust spacecraft has a tennis-racket-shaped collector with aerogel fitted to it. The collector is retracted into its capsule for safe storage and delivery back to Earth. Aerogel is quite strong and easily survives both launching and outer-space environments.

Some of the riskiest and most difficult types of sample-return missions are those that require landing on an extraterrestrial body such as an asteroid, moon, or planet. It takes a great deal of time, money, and technical ability to even initiate such plans. It is a difficult feat that requires that everything from launch to landing to retrieval and launch back to Earth is planned out with high precision and accuracy.

This type of sample return, although having the most risks, is the most rewarding for planetary science. Furthermore, such missions carry a great deal of public outreach potential, which is an important attribute for space exploration when it comes to public support. The only successful robotic sample-return missions of this type have been the Soviet Luna landers and Chinese Chang'e 5.