Presentation Transcript

1. Mars Hopper Project: Baseline studies to validate RELAP5 using project results calculated for a radioisotope powered, impulse driven, long-range, long-lived mobile platform for exploration of Mars Presented by: R. Schultz Work done by: Steven D. Howe Robert C. O’Brien, William Taitano, Doug Crawford, Nathan Jerred, Spencer Cooley, John Crepeau, Steve Hansen, Andrew Klein, James Werner July 27, 2011
2. Outline Summary: Mars Hopper project Summary: approach for performing validation study.
3. Planetary exploration is getting tougher Every mission has returned knowledge different than what was expected But planetary exploration is getting increasingly expensive Orbital platforms are good but need surface exploration- more expensive MERs did great but covered only 15 km total after 5 years Surface landings necessitate flat, safe landing site but science may be in nooks and crannies We need numbers on the ground Need more science per $
4. Interest in canyon walls, mountainsides, deep canyon bottoms Olympus Mons Valles Marineris
5. Concept Initiated June, 2009 in the CSNR Summer Fellows program The Mars Hopper concept utilizes energy from radioisotopic decay in a manner different from any existing RTGs, i.e. as a thermal capacitor. Radioisotope sources have very high specific energy, j/kg, while having rather low specific power, w/kg. Pu-238 has a specific energy of 1.6x106 MJ/kg which is 160,000 times the specific energy of chemical explosives. Factoring in the 25% conversion to electricity, the system may have 4x105 MJ/kg of electrical energy compared to the 0.72 MJ/kg for Li-ion batteries. By accumulating the heat from radioisotopic decay for long periods, the power of the source can be dramatically increased for short periods.
6. Concept The basis for the concept is to utilize the decay heat from radioactive isotopes to heat a block of material to high temperatures. While the heating is taking place, some of the thermal power is diverted to run a cryocooler. The cryocooler takes in the Martian atmosphere and liquefies it at 2.8 MPa. Once the tank full, the power convertor is turned off and the core is allowed to increase in temperature. After a peak temperature of 1200 K is reached, the liquid CO2 is injected into the core, heated, expanded through a nozzle, and allowed to produce thrust. Part of the CO2 propellant is “burned” for ascent. After a ballistic coast, the remaining propellant is used for a soft landing. Once landed, the process repeats.
7. The distribution and encapsulation of radioisotope materials and nuclear fuels in an inert carrier matrix will address several issues and requirements for space power applications: Potential to address non-proliferation security requirements. The ability to survive re-entry into Earth’s atmosphere and impact under accident conditions. Assembly & handling safety Reduction in material self interaction such as -n reactions. Self-shielding properties. The SPS acquired with a INL LDRD grant enables fabrication of tungsten parts at nearly full theoretical density Universal Encapsulation - Common technology for reactor fuels and radioisotope sources
8. Core subsystem -- Thermal issues Separate heating from cooling geometries Allow radiative losses only Utilize radiative loss as source for power conversion
9. Why beryllium [
10. finished cylindrical Be elements
11. Thermal Isolation and management is crucial Three major issues exist in thermal management The thermal isolation of the low power thermal source is critical in order for the core to reach the required temperature in a practicable time period. The heat transfer requirement impacts on the length of the core and its mass. The thermal cycling qualification of the design will impose lifetime limits for the entire system. STAR-CCM model of the steady state temperature reached by a radioisotope encased
12. Evaluation of insulator thickness and temperature profiles A STAR-CCM+ model of the core was built and run in steady state and time dependent modes overall core temperature increases non-linearly as the insulator thickness is increased. T The average surface titanium radiation temperature decreases due to the increased surface area. As power conversion units, CO2 tank (with CO2 in it) and other instrumentation are included, a greater heat sink and increased surface area for heat loss to the atmosphere will be produced. An approximate usable thermal energy was calculated based on the specific heat of the beryllium and core PuO2/W matrix.
13. Co2 liquefaction The Hopper concept requires that a low mass, low power carbon dioxide (CO2) liquefaction system The liquefaction system will collect CO2 gas from the Martian atmosphere over a period of 7-8 days. Due to the high pressure ratio needed and low power available to compress the necessary CO2, a mechanical compressor was unable to complete the task. The most successful approach was to freeze the CO2 to a heat exchanger using a cryocooler to remove the heat. The frozen CO2 would then be heated and pressurized in a closed volume (an intermediate pressure vessel) to make liquid CO2. The design that meets the requirements: weighs 6.5 kg (less than the required 28 kg); uses 220 W (less than the required 250 W); liquifies 0.6 kg in 10 hours (extrapolating this amount and considering the use of two cryocooler systems results in a total of 22 kg being liquified in seven and a half Martian days) provides a low maintenance system with minimal moving parts
14. Point design Overall Total energy stored (J) 1.48e7 Isotope thermal power (W) 1000 Core max temperature (K) 1200 Core Specifications Mass Pu-O2 (kg) 2.5 Mass tungsten matrix (kg) 4.55 Length tungsten source (m) 0.30 Radius tungsten source (m) 0.0129 Beryllium mass(kg) 6.068 Outer beryllium radius (m) 0.0728 Thickness of insulation (m) 0.015 Inner pressure vessel rad. (m) 0.1868 Pressure vessel wall (m) 0.001 Core length (m) 0.30 Rad curvature of plenums (m) 0.1268 CO2 tank radius (m) 0.183 Nozzle length (m) 0.3 Total ship length (m) 1.50
15. Envisioned Architecture Small scale Hoppers with a 10 kg payload would weigh around 52 kg dry for a 5-10 km hop Each could accommodate 2-3 instruments with low power demand (e.g. NAA, n detector, XRD, etc.) Build operational platform that provides power, propulsion, data acquisition, and data transmission Provide 12-15 for Mars World-wide university competition for instrument packages and data collection Hop samples to centralized location for the Mars Sample Return ascent vehicle
16. Summary The CSNR is designing a pulse power mobile platform that can cover large areas of Mars within a few years using local in-situ resources The platform can “hop” every 5-7 days and cover 5-10 km per hop If several such platforms could be simultaneously deployed from a single launch vehicle, a surface network of science stations would be possible that provided long term assessment of meteorological conditions. The concept can be demonstrated on Earth using an electrically heated core and existing power conversion technologies for modest cost Other applications of the pulse power capability of the “thermal capacitor” concept may include satellite station keeping and burst communications The Hopper can enable samples from all over Mars to meet the Mars Sample Return descent vehicle. The Mars Hopper can revolutionize planetary exploration
17. Validation studies… Three calculational efforts underway: Hand calculations--baseline CFD: Rich Martineau Benchmarked code developed at U Idaho RELAP5 calculations Calculation performed for blowdown of CO2 tank and choking in the beryllium flow passages stemming from friction and heating. Boundary conditions: initial pressure in tank is 2.8 MPa, 270 K and Martian atmosphere is at 630 Pa Beryllium is initially heated to 1200 K