MSRs

MSRs is an acronym that can refer to several terms, depending on the context. In science and engineering discussions, two uses are especially common: molten salt reactors, a class of nuclear reactors that use a molten salt mixture as the primary coolant and, in many designs, as the fuel solvent; and Mars Sample Return, a proposed space mission series to collect samples on Mars and return them to Earth for analysis.

Molten salt reactors (MSRs) are nuclear concepts in which fissile material is dissolved in a molten salt and circulated through the reactor. They can operate at high temperature and low pressure, with some designs enabling online fuel processing to remove fission products. Originating in tests at Oak Ridge National Laboratory in the 1950s and 1960s, MSRs have been revived in modern proposals, including thorium-based variants such as the thorium fluoride reactor. Claimed advantages include high thermal efficiency, passive safety features, and the potential to simplify fuel recycling and waste management. Challenges include corrosion of materials by molten salts, salt chemistry control, materials compatibility, regulatory questions, and the economics of scaling up production. As of the 2020s, no commercial MSR has been deployed, but research programs continue worldwide.

Mars Sample Return (MSR) denotes plans to collect samples from the Martian surface and bring them to Earth for analysis. The concept involves rovers or stationary collection, a Mars ascent vehicle to launch samples into orbit, and a return spacecraft to deliver them to Earth while containing the samples to prevent contamination. NASA and the European Space Agency have collaborated on MSR studies, with architectural options spanning the late 2020s and beyond. Major issues include planetary protection, mission risk, propulsion and trajectory design, and coordination of multinational space agencies and budgets.