As of 2021, Space agencies such as NASA are only now sending what amounts to frequent quantities of scientific equipment, rovers and satellites to Mars to investigate ahead of sending Human Crews within the next 5 years. Much of the construction and any resources found on Mars will be used on Mars. However, there are some great examples of when we would need some material to return with the crew.
Soil and rock collection mission --> on the Moon (image edited from original). Taken near Shorty Crater. December 1972. Credit + Original: NASA/Eugene Cernan
Martian soil samples
The most clear example of material return to Earth will likely be the soil samples stored on Perseverance. These sealed tubes are filled, then stored onboard in the chassis. Our Martian crew can pick up and return them to Earth when their SpaceX starship is ready to leave. Rather than attempt to undertake analysis on Mars with the limited equipment available, taking them home enables more detailed analysis. On Mars, our human crew will be more preoccupied with establishing the systems to keep themselves alive and establish a colony with limited resources - details of genetic markers will have to wait.
The other part is to conduct detailed analysis on the structure of the soil structure and rock composition on Mars. This will help us understand more about the history of Martian geology.
Perseverance's mission, and future planned missions will all focus on soil and rock sample collections. Once sealed in tubes, these samples will be returned to Earth at the human crew change-over.
Reference materials
Most steel on Earth is contaminated by a tiny amount of background radiation. This means that within equipment for contexts which are related to detection and some medical devices, there is some error introduced. This is because the metal of the equipment itself is also a very weak radio source.
The tale of how this came to be, and how we currently work around it is intimately intertwined with the nuclear tests of the 20th Century and the steel-manufacturing process itself.
Trinity nuke test dubbed 'gadget' - July 16th 1945. Credit: United States Department of Energy
On the first part, the detonation of every nuclear warhead after the Trinity tests has generated a significant amount of background radiation, from decaying radio sources scattered around the planet from high altitude fallout, accompanied by Earth's 'recycling' processes to move material, water, and air around the planet. During these detonations, the air around the epicentre became strongly irradiated and contaminated with monatomic Cobalt-60. This air moved around the planet and now all air is contaminated as such.
Steel manufacturing, during the mid-20th century, switched over to a direct air-injection in steel manufacturing. The air is injected into the steel vat, and used to raise the temperature of the steel to the correct reaction temperature. Accordingly, because the air holds trace amounts of Cobalt-60, this is also embedded and left behind in the steel after the air has left. The result is a very very weak radio signature from the steel product itself.
So you can see how this puts a floor under the level of sensitivity which can be obtained by devices designed to detect radiation. The work-around for this is to simply use steel which was manufactured before the nuclear tests of 1945. However, due to the shortage of many materials such as steel, much of this metal was recycled into the post-war boom years. And so all of that material was also contaminated. This means that many of the easy options are simply gone. Ironically enough, tools of war also come to the rescue in this capacity - the current source for 'low-background steel' is German WW1 battleships scuttled in the Scapa flow. However, these of course have a finite supply of steel and it is costly and risky to get to.
As a result, nuclear imaging used in medicine, geiger-counting - used in a variety of nuclear industries, such as nuclear fuel processing, nuclear power generation miss these high sensitivity devices.
Similarly, as radio detectors are also used in avionics and space equipment which uses metal parts and also attempts to detect radio sources - they must have excellent sensitivity to gain the most accurate readings.
As a result, the quality of imaging from the machines we can build with materials on earth isn't quite as perfect as they could be.
It's a longer term goal, but by smelting and processing some iron ore to Iron, ingots of non-contaminated material can be sent back with the Earth crew for use as references, to supplement scavenging from old warships.
You can contact me on Twitter: @Ronnie_Writes
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