Sample return mission

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"Genesis Rock" returned by the Apollo 15 lunar mission

A sample return mission is a spacecraft mission with the goal of returning tangible samples from an extraterrestrial location to Earth for analysis. Sample return missions may bring back merely atoms and molecules or a deposit of complex compounds such as dirt and rocks. These samples may be obtained in a number of ways, including a collector array used for capturing particles of solar wind or cometary debris, soil and rock excavation, mining, and any other possible way for retrieving samples in the environment.

1 Sample Return Missions
2 Methods of Sample Return
- 2.1 Collector Array
  - 2.1.1 Aerogel
- 2.2 Excavation and Rocket Return
3 References

[edit] Sample Return Missions

[edit] Past

The first sample return mission ever was Apollo 11 in 1969. It returned approximately 22 kilograms of lunar surface material. Apollo 12 was the second sample return mission which returned about 34 kilograms of material. However, both Apollo 11 and Apollo 12 were manned missions. Perhaps 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 of lunar soil. Although it recovered far less than the Apollo missions, it did so autonomously. The Orbital Debris Collection (ODC) experiment, deployed on the Mir space station for 18 months during 1996-1997, used aerogel to capture interplanetary dust particles in orbit.

[edit] Current

An artist's rendering of Genesis while collecting solar wind

After the last sample return mission by Luna 24 in 1976, more than twenty five years passed before another mission, known as Genesis was able to return an extraterrestrial sample to Earth from beyond Earth orbit. Unfortunately, the Genesis capsule failed to open its parachute while re-entering the Earth's atmosphere, and it crash-landed in the Utah desert in 2004. There were fears of severe contamination or even total mission loss, but scientists have managed to save quite a bit of the samples--which 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.

Another sample return mission is NASA's Stardust spacecraft which returned to earth 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 empty space) which is 1,000 times less dense than glass. This permits the ability to collect the cometary particles without damaging them due to high impact velocities. Particle collisions with even slightly porous solid collectors would result in destruction of those particles and damage to the collection apparatus.

Currently, the Japan Aerospace Exploration Agency (JAXA) is operating the Hayabusa (formerly known as MUSES-C) which is in a heliocentric orbit after having rendezvoused with asteroid 25143 Itokawa. It may have collected a small sample, but mission problems mean that it will likely be in 2010 at the earliest before it returns to Earth.

[edit] Future

An artist's impression of a Mars sample return mission launching its payload back to Earth

NASA has long planned a Martian sample return mission, but has yet to successfully design, build, launch, and land a probe that would do just that. There have been mission proposals in the past, but most have not made it far beyond the drawing boards. The closest NASA has gotten to a sample return mission is the 1970s Viking landers which collected and analyzed Martian soil, but lacked the capability to launch them to Earth.

There were plans to launch a Mars Sample Return (MSR) mission in 2004, but following the twin-failures of the Mars Climate Orbiter and Mars Polar Lander, MSR was cancelled. Another attempted Mars Sample Return mission may launch around 2013 if things go smoothly for NASA. Other missions may bring back samples from asteroids and other comets.

[edit] Methods of Sample Return

Sample return methods include, but are not restricted to the following:

[edit] Collector Array

A Genesis collector array consisting of a grid of ultra-pure wafers of silicon, gold, sapphire, and diamond

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

Collector arrays are useful for collecting tiny, fast-moving atoms such as those expelled by the Sun through 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 implements 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 as to preserve the safety of the spacecraft and the samples themselves.

[edit] Aerogel

Main article : Aerogel

A particle captured in aerogel

Aerogel is a silicon-based, porous, solid with a sponge-like structure in which 99.8% of its volume is composed of empty space. It is approximately 1,000 times less dense than glass. Aerogel was implemented for use with the Stardust spacecraft due to the fact that particles smaller than the size of a grain of sand would have impact velocities at six times the speed of a rifle's bullet and collision with a dense solid could alter their chemical composition and perhaps vaporize them completely.

Since the aerogel is mostly transparent, it is extraordinarily easy for the scientists to find and retrieve the particles since they leave a carrot-shaped path once they penetrate the surface. Since its pores are on the nanometer scale, the particles don't merely pass through the aerogel completely. Instead, they slow to a stop and are embedded within it.

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. One thing that makes aerogel a good choice for missions such as Stardust is the fact that it is quite strong--easily surviving launch and space environments.

[edit] Excavation and Rocket Return

A concept of a Martian sample return mission. A rocket recently loaded with soil and rocks launches on its way to Earth

Some of the most risky and 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 in order 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 be planned out with high precision and accuracy. If even a mathematical unit conversion is wrong, the entire mission could fail (such as happened to Mars Climate Orbiter) and hundreds of millions of dollars would have been wasted.

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 publicity.

NASA is considering launching a sample return mission of this type to Mars around the year 2013, depending on its budget. Previous attempts to launch this type of sample return mission have been scrubbed due to technical difficulty, budget constraints, and other factors such as recent mission failures (e.g.: Mars Climate Orbiter and Mars Polar Lander). The only successful robotic sample return missions of this type have been the former U.S.S.R. Luna landers.