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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.
Hiroji Katsuta, R. P. Anantatmula, Rebecca A. Bechtold, William F. Brehm
Fusion Science and Technology | Volume 6 | Number 1 | July 1984 | Pages 118-124
Technical Paper | Material Engineering | doi.org/10.13182/FST84-A23126
Articles are hosted by Taylor and Francis Online.
A 7Be transport test was performed in the Beryllium-7 Experimental Lithium Loop with hot leg at 270°C and cold leg at 230°C. The “cold leg” test stringer was in a rising temperature region at 250°C. A total of 108 test coupons were included in the material compatibility and deposition test programs, containing AISI Types 304 and 304L stainless steels, Fe-2¼ Cr-1 Mo, pure iron, molybdenum, beryllium, zirconium, titanium, yttrium, three different aluminide coatings on Type 304 stainless steel substrates, and both tubular and flat butt-welds of Type 304 stainless steel. An average lithium velocity of 1.36 m/s was established during the test, which was terminated after 3718 h. The 7Be activity data indicated that the deposition of 7Be is a function of temperature. The cold leg positions displayed maximum 7Be deposition followed by the intermediate temperature locations (cold leg test stringer) and the hot leg locations. Two chemical forms of 7Be are expected in lithium, namely, unbonded 7Be at a low concentration, and a fine precipitate of 7Be3N2 at a high concentration. The deposit in the hot leg region is presumed to be primarily 7Be, while the cold leg deposit is mostly 7Be3N2. The cold leg specimens of a given material showed more 7Be deposition than the hot leg specimens of the same material, consistent with the 7Be activity data on the piping. Based on the present investigations and previous data, it is concluded that 7Be produced in the Fusion Materials Irradiation Test (FMIT) facility will have sufficient nitrogen in the lithium system to form 7Be3N2. It is expected that the majority of 7Be will be transported to the colder parts of the loop and deposited as 7Be3N2. However, a small amount of 7Be in the unbonded form will be in the hotter parts of the loop and is expected to diffuse into the steel piping. Thus, it is recommended that a cold trap be used to effectively remove most of the 7Be from FMIT lithium.
