Sample Return Missions
Sample return missions are, as the name suggests missions that return a sample of space. Examples include Genisis and Hayabusa, these missions are described here. Another sample return mission, maybe even the most famous sample return mission, was Apollo. Sample return missions are difficult as their mission architecture usually includes several landings and, for more complicated missions, different spacecraft. This blog post dives into the challenges of sample return missions.
Several nations have performed successful sample return missions. These nations include the Soviet Union, The US, Japan and China. Even though these capsules are often smaller than crewed capsules they enter the atmosphere with velocities significantly higher than crewed capsules.
Luna 16 - The first one
Luna 16 was part of the Soviet Luna program. A series of Soviet moon explorers. Launched on September 17th 1970, the capsule brought back 101 grams of lunar dust on the 21st of September that year. This mission was the first robotic sample return mission. The spacecraft can be described as a bit of a Matroska doll as it left its stages behind while progressing through the mission. This can be seen in the commemorative stamps made after the mission. The mission was followed up by Luna 20 and 24 who brought back 30 and 170 grams of lunar dust respectively.
Luna 16 landed on the moon after spending about a day in lunar orbit, this orbit was changed later to a 12x120 km elliptical orbit. The ascent was done by a single motor which burned for 53 seconds launching the capsule to a direct-to-Earth trajectory. No mid-course corrections were done and the capsule separated just before Earth entry. The entry was quite aggressive reaching 450 g's and 10000 deg C.
Chang'e 5 - The last one
Where Luna 16 had a fairly simple, one spacecraft and direct return mission architecture the Chinese Chang'e 5 mission had a very complicated one. Launched in 2020 in one launch on top of a Long March 5 the spacecraft consisted of three parts: The service module, the descender and the ascender. The latter two have an obvious function. When reaching the moon the service module separated from the descender/ascender elements, these two then preceded to land on the moon and launch the sample back to space. Here the ascender would dock with the service module, and hand over the sample to the Earth return capsule. The service module would start the return flight. Just before reaching the Earth, the capsule would continue by itself. Chang'e 5 then proceeded with a skipping entry before landing in inner Mongolia. The service module continued to the Earth-Sun Lagrange point L1 for an extended mission. The mission returned 1731 grams of lunar dust.
Chang'e 5 is clearly much more complicated than Luna 16. The obvious question is why? There are several reasons why a systems engineer can choose a more difficult architecture or concept. The first is a more capable mission. Chang'e 5 recovered more than a kilogram of rocks compared to 100 grams of Luna 16. The second is a demonstrator or flight test experiment for future missions. The Chang'e 5 mission demonstrated autonomous in-orbit docking and skipping entry. Vital pieces of technology for (deep space) human space flight and future sample return missions.
The Earth entry capsule of Chang'e 5 somewhat resembles the entry module of the Shenzhou. This is similar to how the Luna 16 entry capsule resembled the Vostok entry capsule.
Mars Sample Return - The next one
Samples have been recovered from all over the solar system, but never from another planet. A NASA/ESA collaboration aims to change this. With the launch of Perseverance in 2020, the first step to a Mars Sample Return was set. As perseverance drills into the ground and collects samples, a NASA/ESA team on Earth is working on a way to bring them back.
Originally a single large lander would be deployed containing a Sample Fetch Rover and the Mars Ascent Vehicle. In early 2022 this was changed to two separate landers. This choice means that the landing masses are more comparable to the Curiosity and Perseverance rovers and thus flight hardware and heritage can be used. During this change of architecture, the fetch rover was replaced with two fetch helicopters. A third launch, using Ariane 6, will send the Earth Return Orbiter (ERO) to Mars.
