PresentationOutline I. Commercial Viability Issues To be a success, the mission must technically and commerically meet the demands of DURATION, RELIABILITY, PERFORMANCE DURATION RELIABILITY PERFORMANCE ------------- -------------- -------------- T Length of Operation Dust effects ??? Where it can go E % of time operational Development Risk What is the product C Lead times Ease of operation H Rate of progress C 2yr length for ROI <3yr leadtime Reach historic sites O DutyCycle: High qual telepres M 15hrs/alldays for ThemePark Joe Sixpack drives R 3hrs/day for Television minimal mission ctrl C 100%during events for Adver. 90m/hr over 720days II. Environmental and Launch Requirements Mass: delivered payload < 600kg, Rover allotment ~500kg, Ramps/Margin ~100kg Temperature: Surface temperatures: -180C Night, 130C Day. Space (ambient) temperature: -270C Solar Insolation: 1385W/m^2 Daytime Surface IR emmission: 1146W/m^2 Lunar Diurnal Cycle: 1lunarday = 28.5earthdays, Radiation: 3kRad/year base + 2yearSolarActivity = ~25kRad dose/2year. For extreme margin of safety use 100kRad/2 years Lunar Dust: very fine, abrasive electrostatic particles which can levitate. two major datapoints/experiences are contradictory (US, Soviet) Terrainability: Slopes = 30degrees, Bumps/Dips of 25cm on 20degrees. GroundPressure of vehicle (All Weight on 2 wheels) = 6kPa III. NightSurvival Issues Night Survival represents the greatest risk to vehicle failure, since the extreme low temperatures will kill electronics (-80C) and batteries (-20C) Extreme temperature difference means high thermal leakage even with good sealing: (sigma = stefan boltzman constant 5.67E-8) NightPowerLoss = SealedEnclosureSurfaceArea*Emmissivity*Sigma*SurvialTemp^4 Well Sealed Enclosures tend to have 0.1 emmissivity. In well engineered devices with no degredation it can approach 0.03. Joint fatigue and micrometeroite punch-throughs causes degredation over time Radiators must be blocked during night time to reduce leakage, yet relying on hermetic sealing is undesirable as dust interference is possible. Maintaining survival internal temperatures requires significant power (~50W) Vast power required to survive 15earthday nighttime: ~18kWhr Margins needed to ensure survival after degredation/leakage (factor of 2) IV. Payload Specifications Wavelet compression techniques capable of 160:1 reduction while maintaining high fidelity require ~4BOPS for a 2k x 2k x 8bit image at 8frames/sec. This can be accomplished using 2 TI MVPC80 chips. Development of custom boards build around a rad-tolerant TI MVPC80 and a rad-hard R3000 CPU (~30W total), allow the entire computing requirements to be done using ~100W. 6.0Mb/sec downlink at BER of 10-6 requires 100W input using a precisely pointed phased array. Reducing the downlink to 1.0Mb/sec while maintaining the BER would reduce the input watts required to around 40W. Imagery acquisition, vehicle safeguarding/perception and state monitoring can be accomplished using approximately 75W This generates a payload requiring ~275W and massing ~70kg (with margins) Locomotion and body structure requires power equivalent to 30% of the total vehicle mass and accounts for 35% of the vehicle mass V. Example: Purely Solar powered vehicles Night survival power must be supplied from battery discharge. Current accepted space batteries (NiCad) yield 45Wh/kg, but Lithium ion batteries (under development) would yield 100Wh/kg Regenerative Fuel Cells have better yield (150Wh/kg) but the high pressure vessels entail high risk, and expensive development and integration and are not considered viable options. The other odd alternative is to drill down into the regolith about 1m with enough surface area so that we can use the -20C temperature to keep the rover alive. We dont have any idea on more info for this and certainly we wouldnt be able to support two rovers this way with all the extra junk needed to build the drill/heat extraction mechanism. Without any night-survival safety factor, and using highly optimistic battery technology (100Wh/kg), as well as assuming ideal emmisivity (0.03) The following values are obtained: TOTAL TOTAL BATTERY INSULATION SOLAR NIGHT SURV POWER MASS MASS MASS ARRAY SIZE ENERGY Solar Vehicle without payload (just power/ 151We 462kg 176kg 100kg 1.3m^2 48.8Wther locomotion/thermal): Solar Vehicle with payload (70kg, 277We) 574We 679kg 176kg 100kg 4.9m^2 48.8Wther The base power for the payload (277We) doesnt include the 15% DCconversion inefficiencies, and the total power system has 97% inefficiency and 5% margin [FROM this we see that the pure solar vehicle really only has 40kg of room for any payload (which is about 15kg of actual payload components and 25kg of overhead to cart it around)] VI. Solar Vehicles Further Examined The above solar vehicle assumed an extremely optimistic set of conditions. If these conditions are made more realistic, the following values occur. TOTAL TOTAL BATTERY INSULATION SOLAR NIGHT SURV POWER MASS MASS MASS ARRAY SIZE ENERGY Optimistic Vehicle (100Wh/kg, 0.03E, No 574We 679kg 176kg 100kg 4.9m^2 48.8Wther NightSurvival Margin) Battery Realism (40Wh/kg, 0.03E, No 781We 1314kg 440kg 283kg 6.65m^2 48.8Wther NightSurvival Margin) Emmissivity Realism (100Wh/kg, 0.1E, No 765We 1266Kg 585kg 106kg 6.52m^2 162.7Wther NightSurvival Margin) NightSurvival Realism (100Wh/kg, 0.03E, 2x 712We 1102kg 352kg 237kg 6.06m^2 97.6Wther NightSurvival Margin) Total Realism (40Wh/kg, 0.1E, 2x 2160We 5550kg 2930kg 470kg 18.38m^2 115.5Wther NightSurvival Margin) Clearly, a totally realistic solar vehicle is amusing. Not only would it have no chance of fitting in a launch shroud (footprint would be huge due to need to have 6kPa ground pressure) but it would have to be launched in installments and assemble itself. Im not even sure it fits in the shuttle bay. [NOTE: using total realism, you cant even launch the non-payload vehicle] VII. Commercial possibilities of a pure solar vehicle Im not really sure there are any possibilities for a non-payload vehicle... or for a nice launch of 470kg worth of insulation materials. Of course, if someone is willing to pay 200mil for a pure solar launch, i would strongly suggest unnumbered swiss accounts and investigation of extradition policies on south sea islands... VIII. Alternatives to Solar. An RTG based vehicle (isotope thermal generator converted to electric power) or a RHU based vehicle (isotope thermal generator with solar power) with no batteries are also possibilities for night survival schemes. With the Solar vehicle, there is an initial issue of array deployment which increases risk. This risk is also present in the RHU design, and there is an additional complexity of having to perform conditioning over the RHU's (since the heat isnt desired during the day, but only during the night) which involves an actuated motion that again entails more risk. The RTG design eliminates both of these sources of risk, and also eliminates conflict issues between sensor positioning found on the Solar or RHU vehicle. The radiators and communication system and solar arrays and cameras all need to be positioned in such a way to avoid shadowing eachother. Without the solar arrays, everything fits nicely on the top of the rover. Solar Design 574We TotalPower, 679kg TotalMass, 4.89m^2 SolarArray 0.03E,NoFactor RHU Design 425We TotalPower, 220kg TotalMass, 3.62m^2 SolarArray 0.1E,2xFactor 14 8.5Wther RHU's, 115.5Wther NightSurvivalTemperature RTG Design 420We TotalPower, 205kg TotalMass, 2800Wther Isotope IX. RHU Design With 14 8.5Wther RHU elements providing the 115Wther of required night survival power (including a 0.1 Emmissivity and a 2x night survival factor). the RHU design doesnt depend on batteries, and so has a -70C margined night survival temperature (instead of the -10C needed for batteries). There is a possibility of using one GPHS unit instead of the RHU's for this purpose to ease the packaging and mounting constraints as well as to pick up 1.3kg and have a product available in the US instead of having to interface with the russians. This also has a possibility of interfacing with AMTEC to provide some trickle power for warming the cameras or motors or some such component which is normally outside the main thermal enclosure. This may have extra programatic risks or something since RHU's and GPHS's arent viewed as equal for launch certification purposes. Needing 425We and massing 220kg, two vehicles can be launched on the HII-A. However, with no batteries on board, the vehicles are restricted to never drive into a shadowed area. If we add 10kg of NiCad's (400Wh) so that we can drive about 30min in shadows at full tilt, the resulting rover takes 432We and masses 242kg, but we now need 39 RHUS to provide the 325Wther for night survival. The interior components consist of the electronics compartment as well as the RHU heater bank. During lunar night, the RHU unit must be placed close to the electronics, and during lunar day it must be moved away since the electronics will be producing their own heat. Earlier studies showed that keeping the RHUs inside during the entire day would require a unfeasible amount of radiator space. However, we are rerunning that concept, as it would be a huge win for the RHU environment. The vehicle requires a radiator of 1.5m^2 for the electronics enclosure. The collecting solar area needs to be 3.6m^2 in the worst case, but possible optimizations might be made to give greater than 12% efficiency after 2 years of operation in 140C. Reducing the size of the array has very little effect on the mass and power requirements of the vehicle (6.5kg/m^2 of array) but would simplify the deployment and the positioning challenge between the radiators, communication, cameras, and solar array (all of which need fairly unobstructed views in basically the same area) Our ongoing research into stuff here shows that Gallium Arsenide or amorphous silicon cells are the likely candidates and that we should be able to reduce the size of the array to about 2.7m^2 by taking into account the contribution of both arrays (the one receiving the more direct sunlight and the one with the fairly bad incident angle). The 3.6m^2 only ever depends on one array at a time, and so has more safety margin built in. The solar sail design calls for a deployed horizontal array which covers some of the vehicle (1.5m^2) and the other 1.2m^2 (or 2.1m^2) hangs off the side of the vehicle in two symmetric wings. There is also a deployed vertical array which runs on the Center_Front_to_Back axis of the rover. This array is identical in size to the horizontal array, but is covered on both sides with solar cells. The shape of the array is yet to be determined, but it is likely triangular or fin-like in nature and hangs off the back of the vehicle to some extent. X. Commercial Possibilites of the RHU/Solar vehicle Consequences: Ability to launch two rovers, and operate simultaneously. Technically believable and rational design solution Failure resulting in excessive heat leakage is fatal. Lunar Daytime operations only (but 100% duty cycle in that time) Vehicle has virtually no "stored" electrical power and so there can be no driving through shadowed areas. (alternative is 3x RHU's) Conflict between radiator/solar array/camera/comm for visibility. RHU unit may have to be actuated between moving in/out of the rover. Has some isotope programattic issues of availability and launch. Dust may have an affect on the emmissivity of the radiator and the louvre sealing on the radiators. XI. RTG Design RTG composed of 12 250Wther GPHS units (2800Wther) and has a Emmissivity of 0.1 and a night survival factor of 2x. Again, with no batteries, the night survival temperature is 203K (-70C including margin)) The thermal energy is converted to electric power using AMTEC technology. The efficiency of this conversion (including relevant system losses) is 15%. The RTG Design uses 420We and masses 205kg. The Radiator for the electronics is 1.5m^2 and the radiator which vents the excess RTG heat is 0.54m^2. There are no solar arrays, and so the vehicle is a low and sleek sort of beetle/type thing. The internal volume is the same payload/electronics enclosure as on the RHU/Solar vehicle, but the RTG unit is added as well. This changes the shape of the vehicle a little, and also increases the internal mounting and structure complexity over the pure solar design. However the relationship between the electronics and the RTG is the same in day and night, and so there is no extra actuation as in the RHU/Solar vehicle. With the extra heat we generate, we dont even need to close anything off on the vehicle. In fact, if all the insulation fell apart during the nightime we would still survive without a hitch. However, we still need insulation during the daytime to keep from frying. XII. Commercial Possibilities of the RTG vehicle Consequences: Ability to launch two rovers, and operate simultaneously. High believability in technical solution No "high probability" of fatal failure due to night survival. higher reliability without deployment or RHU conditioning cycling full lunar day/night operations (100% duty cycle) much less concern with regard to effects of dust on the radiators since we have heat to burn. increased programatic risk/development/lead time over RHU or Solar issue of integration of AMTEC thermoelectrics to GPHS source. XIII. Lander Options and Integration The HII-A launch vehicle can accept a payload which is 4.6m in diameter and 3.7m tall, and can deliver 3000kg to GEO, or estimated 5000kg to lunar orbit, The Russian Fobos lander when fully fueled (I still cant say that...) masses in at ~6700kg. Upon reaching lunar orbit, approximately 1700kg of fuel are expended. The dry mass of the lander when delivered to the surface is about 2400kg (of which 600kg are payload). These numbers are more directly from the Isela lander specs, and actually that is really the lander we are talking about using anyway. The Martin Marietta Mars lander may also be a candidate, but more info is still needed. Were putting together illustrations of this. XIV. Complete Rover/Lander/Launch Vehicle Integration The RHU/Solar rover pair fit vertically inside the Shroud on the lander, and there is a picture on this, but were not gonna show it to you yet. Seriously, were working on the body design for this vehicle, and trying to get it all to the modeller.