Although space probes already have sensitive instruments that can accurately map the world near them, it’s just far from the world-class laboratories on our planet. As a result, some spacecraft need to return a sample to Earth to study the materials in detail. Let’s find out how it’s done.
What is a Sample Return Mission?
A sample return mission is self-explanatory. It is a mission that collects and sends a sample of another celestial object back to our planet. It’s easy to understand, right? But it’s very tough to conduct! It requires a lot of planning, calculations, and accurate execution to get the material to the laboratory!
Selecting the Target
Firstly, we have to select a target. Obviously, this must be easily accessible because fuel has to be saved, right? The target’s orbit must be near the plane of the ecliptic, or the spacecraft will not be able to successfully conduct the orbit insertion without wasting lots of fuel to align with the target’s orbit.
Secondly, the target has to have scientific value. Mars is an excellent example because it contains organic materials and might have hosted life billions of years ago. Moreover, asteroids that preserve materials from the formation of the Solar System, such as C-type asteroids (since they’re one of the oldest objects in the Solar System) are worth exploring, too.
Thirdly, the target shouldn’t be too small. If so, its gravitational pull is too weak, and orbiting it isn’t easy. That means the spacecraft must precisely match the asteroid orbit, which may use a lot of fuel. What’s more, particles may get ejected easily from those objects, meaning that they will be obstacles to collect a sample safely.
The Launch Window
After examining possible targets, we have to figure out a launch window based on the orbits and relative positions of both objects. If you shoot your rocket at the target during launch, you will miss the object because both Earth and the target is moving. Instead, you should aim at the location where the object is when the spacecraft arrives, which involves a lot of complicated math and orbital mechanics.
If the spacecraft has to use a lot of fuel to reach the target, it may use gravity assists, which either provides or obtains angular momentum from the planet, causing it to accelerate or decelerate in a certain direction, refining its orbit. In this case, the launch window becomes more complicated as it may involve the perfect alignment of three or more objects.
The Sampling Method
After examining the trajectory, selecting a correct sampling method is vital. A spacecraft with a simple robotic arm and some rockets (like OSIRIS-REx) is enough to grab a sa1mple from an asteroid and return itself to orbit. For instance, OSIRIS-REx blew some nitrogen toward the surface, causing the particles to go all-round, and the spacecraft collects the sample that is blown primarily upward. Still, the procedure is much more complicated on larger targets since their gravitational pull is much stronger.
To return a sample from large objects like in the future Mars Sample Return mission, dedicated launch vehicles and the collaboration between robots are essential. This must carry lots of fuel to get the sample into orbit and rendezvous with the orbiter, which will be the thing that ejects the capsule and sends the sample back to Earth. Moreover, while stationary landers are used to house the launch vehicle, rovers are usually used to find ideal sampling spots, instead of doing so by the orbiter itself (though the orbiter conducts the preliminary search or relies on existing data).
If the sample coIf the sample consists of dust particles, the spacecraft must arrive at the appropriate location (like a comet’s tail) and open the capsule. The capsule should contain sample collectors like aerogel to attract the particles. Otherwise, the intended sample will slip past the container, and there will be no way to conduct studies about them in laboratories.
Although the primary purpose of the mission is to grab the sample, it needs to be backed up by data. Therefore, the spacecraft must carry instruments to measure the environment near them to choose an exact ideal location to collect the sample.
The instruments include cameras, spectrometers, hazard avoidance systems, and laser altimeters. They are used to take iThe instruments include cameras, spectrometers, hazard avoidance systems, and laser altimeters. They are used to take images, reveal compositions, dodge hazards, and measure altitude. If a spacecraft gets damaged by a sharp rock or fails to collect a sample in the scientifically valuable spot, the mission will not be successful. What’s more, when the sample is returned to Earth, the studies will be backed up by existing data about the target.
The Sample Return Capsule
No matter what, every sample return mission must contain a module: The sample return capsule. This protects and preserves the sample during atmospheric entry and landing.
When a spacecraft (or any object) enters Earth’s atmosphere (or any sufficiently thick atmosphere), it will create a lot of friction due to its immense speed and the particles. Therefore, the object decelerates quickly, and its temperature starts to increase dramatically. The capsule will experience a maximum temperature of over 1500oC, hot enough to melt metal.
What’s more, after the hottest stage of atmospheric entry, the sample will get quickly contaminated when it gets through the atmospheric particles, inhibiting studies from being conducted about the sample or even producing the wrong results when the sample is examined thoroughly.
Therefore, the sample return capsule is crucial to the mission and must be properly produced. Each capsule should consist of a heat shield, a backshell, and a parachute. The heat shield directly protects the payload from the heat, while the backshell seals the payload and houses the parachute, which reduces its speed to ensure a safe landing.
In this article, we briefly mentioned the necessary procedures of a sample-return mission, and how they are conducted. However, keep in mind that the missions are still a lot more complicated than you think, as this article doesn’t include some advanced details, such as the math that enables the spacecraft to enter the correct orbit.
References and Credits
- NASA Solar System Exploration. (n.d.). Basics of Space Flight. Retrieved July 30, 2021, from https://solarsystem.nasa.gov/basics/primer/
- NASA Jet Propulsion Laboratory. (n.d.). Mars Sample Return. Retrieved July 30, 2021, from https://www.jpl.nasa.gov/missions/mars-sample-return-msr
- NASA Goddard. (2018, December 3). Why Bennu? Retrieved July 30, 2021, from https://www.youtube.com/watch?v=4S0uk_5hm2c
- United Launch Alliance. (2016, October 14). Rocket Science in 120: Launch Windows. Retrieved July 30, 2021, from https://www.youtube.com/watch?v=MZMxqeLNwhA
- NASA Solar System Exploration. (n.d.). In Depth | Stardust. Retrieved July 30, 2021, from https://solarsystem.nasa.gov/missions/stardust/in-depth/
- NASA Mars Exploration Program. (2018, June 7). NASA Finds Ancient Organic Material, Mysterious Methane on Mars. Retrieved July 31, 2021, from https://mars.nasa.gov/news/8347/nasa-finds-ancient-organic-material-mysterious-methane-on-mars/
- (2006, September 13). NASA Developing New Heat Shield for Orion – NASA. Retrieved July 31, 2021, from https://www.nasa.gov/mission_pages/constellation/orion/orionheatshield.html
- NASA Solar System Exploration. (n.d.). In Depth | Stardust. Retrieved July 31, 2021, from https://solarsystem.nasa.gov/missions/stardust/in-depth/