Exploring the ocean of Europa: Reactor or RHU?

Poston, David; Belooussov, Andrei
January 2000
AIP Conference Proceedings;2000, Vol. 504 Issue 1, p1175
Academic Journal
This paper examines the heat transfer characteristics of a probe (cryobot) penetrating through the ice layer of Europa. Initially, simple 1D calculations are used to predict the ideal (no heat losses or temperature limitations) penetration rates for various size cryobots. Next, a detailed 2D model is used to more realistically model penetration rates. It is found that for small, low power density systems, conductive losses can cause the penetration rate to be significantly lower than the ideal rate. The results of these calculations are meant to establish rough limits on the size of cryobot that can be powered by an RHU (Radioisotope Heater Unit), and at what sizes a reactor becomes enabling. It is concluded that if an RHU system (that delivers almost all power to the bit) can be developed with an overall, fully-engineered power density of ∼1 W/cm3, then an RHU system may be suitable for some mission scenarios, although slow penetration times (which increase mission risk) and/or high Pu-238 requirements (cost and availability) may still make a reactor a more optimal choice. If there is a requirement for a large payload and/or a rapid penetration time (∼months), then a reactor will probably be required. The final portion of the paper examines potential reactor designs that could be used to power a cryobot. Two potential reactor designs are discussed—a near-term, low-cost heatpipe cooled system and a conductively-cooled metal-fueled reactor. © 2000 American Institute of Physics.


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