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Dragonfly, a Pu-fueled drone heading to Titan, gets key NASA approval
Curiosity landed on Mars sporting a radioisotope thermoelectric generator (RTG) in 2012, and a second NASA rover, Perseverance, landed in 2021. Both are still rolling across the red planet in the name of science. Another exploratory craft with a similar plutonium-238–fueled RTG but a very different mission—to fly between multiple test sites on Titan, Saturn’s largest moon—recently got one step closer to deployment.
On April 25, NASA and the Johns Hopkins University Applied Physics Laboratory (APL) announced that the Dragonfly mission to Saturn’s icy moon passed its critical design review. “Passing this mission milestone means that Dragonfly’s mission design, fabrication, integration, and test plans are all approved, and the mission can now turn its attention to the construction of the spacecraft itself,” according to NASA.
Lance L. Snead, Roger A. Vesey†
Fusion Science and Technology | Volume 24 | Number 1 | August 1993 | Pages 83-96
Technical Paper | Divertor System | doi.org/10.13182/FST93-A30176
Articles are hosted by Taylor and Francis Online.
The primary concerns in the design of a divertor component are the high heat fluxes (15 to 30 MW/m2) and the surface erosion due to plasma/wall interactions, along with the associated issue of plasma contamination. A continuous belt, which would pass between two rollers inside the vacuum vessel, is proposed as the divertor surface to provide higher heat flux handling capability as well as reduced total erosion. Thermal analyses indicate that a belt passing from one roller through the divertor region to a cooling roller can achieve a cycle-to-cycle steady state while maintaining acceptable temperatures. The belt speed determines the amount of plasma energy absorbed per cycle and thus determines the maximum belt temperature and the requirements of the cooling roller. The belt material initially considered is a metal matrix/carbon fiber composite in which the carbon fibers are oriented out-of-plane in a 1-mm-thick metal belt. The carbon fibers protrude from the plasma-facing side of the belt, presenting the plasma ions a low-Z surface to impact. Because the belt surf ace passes through the entire divertor region, the erosion due to sputtering is uniform along the belt. Estimated gross erosion rates for a 7-m belt at expected International Thermonuclear Experimental Reactor (ITER) conditions are 5 to 10 cm/burn-yr. Electromagnetic forces and secondary magnetic fields induced by the belt motion appear manageable for a sufficiently resistive or toroidally segmented belt. In situ deposition of a sacrificial carbon layer will be required to replace eroded material. Such a belt also offers the possibility of continuous removal of the plasma-codeposited carbon and tritium layer prior to deposition of the sacrificial carbon.