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Future power systems for space exploration

Future power systems for space exploration . Overall Goal of past S54 Study, 2001 -2003 Findings and Recommendations ESA Contract # 14565/00/NL/WK April 13th, 2005, M. Lang, TEC-MPC. Overall Goal and Content of past S54 Study:.

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Future power systems for space exploration

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  1. Future power systems for space exploration Overall Goal of past S54 Study,2001 -2003 Findings and Recommendations ESA Contract # 14565/00/NL/WK April 13th, 2005, M. Lang, TEC-MPC

  2. Overall Goal and Content of past S54 Study: • Study into future power systems for space exploration, aimed specifically at a human mission to the Mars surface to take place in the 2020-2030 timeframe, comprised of 5 parts + 2 extensions: • System requirements/constraints • Technology Inventory • Nuclear power systems • Architectural design of reference system • Technology Development • Ext. #1: Nuclear power for static mission element, ISRU Technologies, Regenerative Power Sources for Mobile Applications • Ext. #2: Two-Stroke Engines for Mars Exploration, Stirling Cycle Engines for Space Power Applications

  3. Study team • QinetiQ (formerly UK Defence Evaluation Research Agency, DERA) • AEA Technology (Space) • Serco Assurance (formerly AEA Technology Consulting) • Technicatome • Technical University Graz • Study management • Gas cooled nuclear power systems, nuclear technology inventory • Gas cooled reactor core design, safety assessment, nuclear technology inventory • Liquid metal cooled reactor design, nuclear technology inventory • Non-nuclear technology inventory

  4. Work flow with parallel studies Study S51 Scenarios & Architectures - Phase 1 Task 1: Requirements & Constraints Study S56 Automation & Robotics Task 2: Technology Inventory Task 3:Nuclear Power Systems ISRU design Task 4: Architectural Design of Ref. System MPL design Task 5:Technology Programme Study S51: Scenarios & Architectures - Phase 3 Aurora Task 6: Final Reporting

  5. Where are we now? • S54 study completed with 2 extensions and recommendations • S56 study completed with recommendations • S51 completed with study of 2 selected mission elements (ISRU & MPL) • Related technology studies on-going: e.g. ISRU, H2 storage, materials & structures, thermal control • Aurora programme in progress

  6. System Requirements & ConstraintsUnderstanding the problems of exploring Mars • Requirements definition - what do we want to do? • Constraints (European) • Constraints (Martian) • Definition of future power systems • Power generation • Power/energy storage • Power management and distribution • Related technologies: LSS, ISRU, materials & structures, thermal control

  7. Mission elements definition 1. Disseminated surface elements - Micro inspection rover - Autonomous research island - Long range exploration rover - Drilling platform 2. Mobile pressurised laboratory, MPL 3. Utility truck, U/T 4. Regenerative life support system testbed, ‘Greenhouse’ 5. In Situ Resource utilisation (ISRU) chemical plant - Expendable lander - Aerobot

  8. Static mission elements: power requirements

  9. Mobile mission elements: power requirements

  10. Mars environment (1): solar energy  Oversized, heavy array to account for worst case, or  Optimal sized array (NASA GRC) but higher risk if global dust storm persists.

  11. Mars (2): the atmosphere EarthMars Pressure - density 1000mBar - 1.225kg/m37mBar - 0.02kg/m3 Makeup CO2: 0.03% 95.3% N2: 78.1% 2.7% Ar: 0.9% 1.6% O2: 21% 0.13% Water: several % (var.) None   wind, structural effects   Long term corrosive effects CO2   No water, but otherwise a valuable resource

  12. Mars (3): surface effects • Gravity 0.38x terrestrial: lower traction power • Dust: 100-150ppm clay silicates, 3m . Accumulate on exposed surfaces and reduce PV array power by 0.28%/day (Pathfinder) • Wind velocity high (4x Earth typical), but low dynamic pressure • Potential highly oxidising environment • Low, highly variable temperatures: -80C to -130C night, up to 30C day. Assumed -30C mean summer day, -60 winter for PV arrays. Assumed insulation -40C min internals night.

  13. Mars (4): other effects • V Mars-Earth return: 20.5km/s, orbit aerocapture only  4kg to LEO for 1kg to Mars orbit  7kg LEO for 1kg to Mars surface • Radiation • 6mth trip time, solar flare / GCR risk (negligible to systems) • Distance • signal round trip time 6-45 mins: telerobotics difficult • orbit conjunctions every 26 mths: min surface stay 20mths (600 days) ArV++ with LH2/LOX TMI stage - 6t capability to Mars orbit - 4t max. to Mars surface

  14. Life Support Systems (LSS) Not studied in detail as part of S54, however…. • Lightweight • Active thermal control needed • Portable power: 8hr EVA, up to 300W gives 2.4kWhr • Li-ion: 6.1kg weight on Mars (now) - 2.5kg (15 yrs) possible • Fuel cells require 23wt% H2 stg. density to compete due to need to store O2. • TPV, microturbines possible but require fuel / oxidiser storage A difficult problem….

  15. In-Situ Resource utilisation (1): requirements ISRU: The use of Martian resources (& terrestrial feedstock) to generate propellant & life-support consumables on Mars, reducing required mission mass and cost. A 6 person mission to the Mars surface, staying 600 days, requires: • 7t CH4 fuel for return vehicle rocket engines • 25t O2 oxidiser to combust CH4 • 5t O2 for life-support • 24t H2O for drinking, washing, etc. • 4.5t buffer gases (usu. N2) to make up for leakage

  16. In-Situ Resource utilisation (2): the problem • No H2O, or free H2 on Mars: bring H2 from Earth • Numerous chemical reactions required for ISRU: NASA JSC estimate 3.8t • Requires significant energy to run reactors, e.g. electrolyser. NASA estimate 40-50kWe • Autonomous deployment, reliable operation to produce requirements in 12-15 mths, store for ~36mths • Bring H2 from Earth: 2-4t, e.g. LH2 • Mass intensive: 3.8t from Earth (~30t LEO) • 40-50kWe continuous, up to 15 mths • Autonomous, reliable

  17. In-Situ Resource utilisation: chemistry (i) • Centrifugal compressor: CO2 collection, ~15-20kg/hr. • Simple, deployable composite fans. • Sabatier 4H2 + CO2 CH4 + 2H2O • Goes to completion at 2-300 C (pipe reactor + catalyst), exothermic • Electrolysis 2H2O + power  2H2 + O2 • With Sabatier, produces O2 : CH4 in 2.25 : 1 ratio Problems 1) Insufficient O2 produced 2) No separation CO, N2, Ar 3) Power for storage, cooling, separation products

  18. In-Situ Resource utilisation: chemistry (ii) • Additional O2 generation • Reverse Water Gas Shift: not exothermic, separation a problem • Methane pyrolysis / catalytic reduction: temperature, scaleup • High temperature CO2 electrolysis: high power, robustness? • Photocatalytic CO2 reduction: v. recent discovery, not quantified • Ar/N2 separation • Amine absorption loop: non-ideal as large CO2 mass flow rate • Adsorption zeolites: undesirable chemical / polar effects • Physical separation: CO2 ‘snow’ - best option (NASA) • Power reduction • Cooling CH4 / O2 with H2 feedstock • Low power processes where possible

  19. Promising power storage technologies • High temperature batteries: ZEBRA, Sodium Sulphur, combined heat and power. • Not yet exploited for space despite extensive development • Li-ion batteries. Questions to resolve • performance at extreme low temperatures (-40 to -80°C) • potential for scale-up: current state-of-the-art focussed on portable consumer electronics • lifetime: currently limited to a few hundred to 1000 cycles. • H2-O2 Fuel cells: extremely high power densities. • Need to address fuel / oxidiser storage on Mars • Redox batteries (Regenerative fuel cells)

  20. Power storage technology comparison

  21. Power generation technology: PV arrays (i) Photovoltaic conversion - cell types / efficiency • Crystalline Si: 10cm B(S) FR / HiETA: up to 17% • GaAs ATJ: AM0 optimised: ~30% (40% ~possible) • CIS, CuInSe2 thin film: 12% current, >20% predicted • Cleft GaAs, thin Si, -Si, TiOx (dye sens.) not considered in detail • LILT cells to be added • GaAs cells not tested on Mars: Beagle 2 (NASA Athena rovers using crystalline Si)

  22. Power generation technology: PV arrays (ii) Photovoltaic conversion - array designs ISS: Si flexible CIS ‘rollout’ ITSAT inflatable AEC-Able ‘Ultraflex’ Pathfinder: rigid panel

  23. Power generation technology: Wind energy • Wind: viable terrestrial power generation, up to several MW per turbine • Horizontal axis 2/3 blade turbines common • Considerable European (Danish, UK, German) expertise • Studies for Mars carried out (Bremen, Houston Uni.’s) • Low dynamic pressure on Mars: 4.6x wind speed of 10x blade diameter for same power density • Geographical restriction on Mars, e.g. Tharsis Montes • Accurate forecasting data required • Erection of mast may be difficult: balloons?

  24. Temperature is constant throughout the day Power generation technology: Thermal transfer • Diurnal temperature gap utilisation - thermoelectric conversion • Large area required due to low TEC eff% • Power not available all day • Geothermal may also be a possibility (active Mars) • Accurate subsusrface mapping required Time in Martian Hours Surface cools during nighttime Surface heats up due to solar insolation Depth below surface (m)

  25. Power generation technology: Other • Power beaming from Areosynchronous orbit • Laser or microwave • >50% efficiency theoretically possible • Auburn Uni. POWOW study using =1.06m laser • 4t array in orbit, 360kWe  75kWe on surface • No hydro / wave / tidal power on Mars • No fossil fuel reserves known, CO2 non-oxidising • Combustion engines non-ideal (fuel cells higher power density)

  26. Power management & distribution (PMAD) • 28V current, ISS 120V. 600V - 5000V desirable for Mars (long distance power transmission). 160kWe over 2km @ 200V20t cable! • Paschen breakdown in Mars atmosphere / dust discharge may be an issue • PMAD efficiency (NASA estimates) • Current: 80-90%, 40-50W/kg • 5 years: 85-95%, 125W/kg • 15 years: 95%, 250W/kg, integrated bus Further research required….

  27. Nuclear power options • Radioactive heater units, e.g. Pathfinder • RTGs • Viking: SNAP 19, 2x35W • Ulysses, Galileo, Cassini: up to 875W @ 5W/kg. 2 only, 250W. • ARPS, 10W/kg; Cm-244 up to 20W/kg. Development required. • Not available in / to Europe • DIPS: dynamic isotope power (Pu-238+ Stirling): 2-10kW proposed. • Fission reactors: SNAP-10A, ROMASHKA, Topaz, SP-100. Preferred to RTGs above 1kWe.

  28. Why nuclear? • Low solar flux on Mars: at best, 22% AM0. More typically ~13% AM0, and 30% of the time, 6% of AM0 or less. • i.e. an array sized to deliver 50kWe on the Mars surface would be delivering 1MW in LEO. No capability! • Pathfinder lost 16% of its power in 83 days due to dust. 600 day surface stay = 100% power loss • PV not considered viable >50º lat., nor for req’s >20kWe. NASA considers nuclear power ENABLING for Mars surface. (ref. Cataldo, IAF 2000; SAE power systems, Nov. 2000)

  29. WP1xx: Summary • Mission elements definition • Static, mobile elements; power/energy requirements • Mars constraints • solar energy (or the lack of it…) • atmosphere, environmental effects (e.g. temperature, dust) • Mass limits to Mars • Power storage options: Li-ion batteries, flywheels, fuel cells • Power generation options: mainly solar, wind, nuclear • PMAD • Nuclear technology overview

  30. Why a technology inventory? • To establish the areas that would enhance Europe’s capabilities and the value of power systems within human Mars exploration scenarios. Innovative, enhancing. • To support study effort by searching various databases including journals, patents, proposals, web-sites, organisations and NASA archives. Up-to-date information resource. • Coordinated effort between S51, S54, S56 studies, and relevant to future work. Interdisciplinary (relevant to CDF). Roadmap to allow ESA to focus technology development resources early on for later human Mars exploration  COST REDUCTIONS

  31. ECLS Thermal control Power storage ISRU ISPP Scope of inventory Internal combustion Nuclear (fast) Solar dynamic Nuclear (thermal) Mars surface Trans- Mars Wind Regen -erative Power generation Geothermal Open Cryo- coolers PV arrays, concentrators Coatings, structures WWW based Technology inventory Regen. fuel cell Non regen. fuel cell Passive cryo/ heat storage Primary batteries Cooling loops Radiators Secondary batteries Heat Pipes Phase change materials Chemical reactions Flywheels Martian resources Systems issues EVA

  32. Primary technology selection criteria I Cost IIPhysical constraints, broken down into: • Low mass • Compact dimensions (low volume) • Long operational lifetime, without maintenance III Satisfaction of performance requirements (e.g. specific power, efficiency, etc.) IV Product assurance, broken down into: • Survivability • Reliability • Safety • Availability V Environment survivability, broken down into: • Thermal inputs, loads, ranges • Radiation • Atmospheric constituents (95% CO2) • Low gravity • Absence of water vapour • Cleanliness/contamination (planetary protection) Total technology value: 4 (lowest) - 6 (highest)

  33. Secondary technology selection criteria Total technology value: 1 (lowest) - 3 (highest) i. Introduction of new technologies. A higher rank will be given to new technologies that will be brought to maturity within the time-scale and cost constraints of the mission. ii. Breadth of expertise in Europe – is the technology unique to one supplier who could be at risk? iii. Impact of technology on international mission.

  34. Ranking: total technology score • Total technology score – this total score is a numerical output for the overall performance of a technology, incorporating the benefits of Europe’s position as a scientific leader. • Primary technology selection criteria are essential to a successful mission, and are worth between 4 (lowest) and 6 (highest) points. • Secondary evaluation parameters are important, but not essential to the success of the mission: worth between 1 (lowest) and 3 (highest) points. • Qualitative analysis of technology selection – the individual evaluation parameters for each technology are compared.

  35. Example technologies • Solar cells performance optimised for Mars surface conditions. • Regenerative fuel cells. • High T, CO tolerant fuel cells for combined heat/power • Flywheels for power storage • Efficient Thermoelectric power conversion materials • High capacity, low T Li-ion batteries for mobile applications • High density hydrogen storage, e.g. rev. complex hydrides

  36. 50kWe static power system options(1) NASA solar electric design ftp://ftp-letrs.lerc.nasa.gov/LeTRS/reports/1999/TM-1999-209288.pdf

  37. NASA assumptions • Deployment of tents by articulated mast / inflatables / rovers • No wind effect on tent stability • RFC fuel cell power storage: optimistic Wh/kg values, unclear about electrolyser power requirements • Dust removal: degradation only 5% of Pathfinder @ 0.3%/day • 18% BOL eff. from -Si PV / CIS arrays assumed: optimistic • 2 major dust storms/Martian year, severe power storage depletion: 100 day max. endurance • ISRU plant switched off during dust storms: reliabilty issue? • 600V power generation & transmission, DC switched to 120V • Precision landed at 200m from habitation

  38. 50kWe static power system options(2) Solar electric design for this study

  39. Solar-electric power - further details • Dust storms (OD 3.0) increase array area / mass by ~3x. More severe dust storms make PV power unadvisable • Array area 2000-7000m2 poses major deployment questions • AEC-Able may offer a possible solution: Ultraflex • Note ISS arrays : 2 x 400m2, required astronaut deployment, in g • Design relies on cell performance, dust mitigation, resistance to environment, etc etc. • 4450m2 requires • 15 x 10m rad modules, or • 57 x 5m rad. modules

  40. 50kWe static power system options(3) Solar-wind-electric power • Balloon tethered horizontal axis turbines • 3 turbines, each sized to generate 10kWe • Array to generate 20kWe under OD 3.0  Total mass ~8700kg, array area 2850-5600m2 inc. 1-2t vessel for storage of hydrogen lifting gas BUT • Accurate long term wind forecasting needed to reduce risk • Limited locations where adequate wind speed (10m/s year round) • Immature technology • Hydrogen lifting gas adds signifcant mass (v. tower erection)

  41. 50kWe static power system options(4) Alternative power systems • Geothermal energy • Power beaming from orbit • Temperature gap power generation • Requires thermal reservoir: as yet unproven on Mars • Power loss on tranmission thr. dust storm may be significant • Low efficiency, very large buried area required; variable power Nuclear fission reactors are the only low risk solution to providing significant quantities of power on the Mars surface

  42. Backup power system for greenhouse 1kWe for 10 hours • PEM or Solid Oxide fuel cell (combined heat / power) • 10kWh  0.5kg H2, 3.75kg O2 • HP gas storage in composite tanks  20kg, 37litres or • H2 stored as C nanofibres (25wt%, O2 as sodium chlorate  17kg, 16 litres • Li-ion battery • Secondary: 70kg, 30litres Primary: 26kg, 14litres • Ni-MH battery • 177kg, 50litres

  43. Mobile power system optionsMicro inspection rover • 7W mean, 14W peak, 45Wh; rover max. size 600x400x300mm, 15-20kg • Lowest mass option has 14W PV array for day ops, 0.25-0.4m2; fuel cell night ops, total mass 1.9-3kg. Array too large for envelope! (600 x 670mm req.) • Next best option uses 7W array and battery, peak loads supplied from both. Array area required 0.2-0.3m2, i.e. just within envelope, Mass 3kg, OK. However, dusty conditions (100W/m2) require larger array, exceeding envelope. •  PV arrays not optimal for all-weather operation if body mounted •  Fuel cell: 0.35-1.15kg, but large store required. •  Rechargeable battery: 1.5-1.8kg.

  44. Mobile power system optionsLong range exploration rover • 25-200W, est. 160-190kWh total; rover max. size not specified, 200kg total • Optimal system for good weather has • PV array, 2.2-3.3m2: deployable recommended • Fuel cell for peak power, 7.5-20kg mass • Battery for night operations, 2.8kg mass • Bad weather (100W/m2) requires • PV array, 7-10.5m2: deployable may be difficult • Fuel cell 7.5-20kg • Battery, 2.8kg Total mass 16-36kg Deployable array required Total mass 26-62kg LARGE deployable array required Operation without PV array requires 90-140kg fuel cell system due to high mass H2 / O2 storage.

  45. Mobile power system optionsDrilling station • 500-2000W, est. 920kWh total; max. size 150x150x300mm, 300kg total, 45hrs peak power • Optimal system has : • PV array for mean power (500W), min. area 25m2 in dusty conditions. • Fuel cell for peak power, 85-145kg mass • Battery for night operations, 3kg mass • Total mass 147-316kg. • Alternative system with PV array / nightime battery only: • 215kg / 250m2 using current CIS technology • 45kg / 130m2 using future technology EITHER a high total mass OR a very large array area

  46. Mobile power system optionsMobile Pressurised Laboratory + APU • 2800kWh energy, 98kWe peak power (20kWe mean), 20 day dur’n, 500km range, 1500kg mass limit (power cart) • Fuel cells are the ONLY practical option for this energy requirement • Currently: GH2 / GOX storage gives 4600kg / 7.1m3. NOT REALISTIC. • Near term developments may allow LOX / LH2 storage for 20 day mission: 2600kg, 4m3. • Longer term: H2 in CNFs, LOX may allow 2300kg, 2m3. STILL TOO HEAVY. APU, 1 day ops, 5km range, 7kWe peak, 19kWh energy  2° battery: 134kg, 61litres or RFC: 45-220kg, 18l +PV array 1500kg mass limit  ~1650kWh limit. Severe energy limitation, unless alternative power sources developed (e.g. In-Situ oxygen useage, NASA DIPS)

  47. Mobile power system optionsUtility Truck + Emergency power unit • 1500kWh energy 1 way trip, 292km; 2x this for return. 48kWe peak power, +120kWh emergency power supply. • Fuel cells are the ONLY practical option for this energy requirement • As per MPL: Near term 2600kg, 4m3. • Longer term: 2300kg, 2m3. Acceptable. • A 1500kg power supply limit  restricts operations radius max. ~150km. • Emergency power • RFC is best option. • High power electrolyser can be reduced in size if 6-10 days to ‘charge’ • 270kg / 420l / 62m2(PV array covering load floor) Limited range & reduced payload capacity with conventional power source. RFC may have potential but requires analysis of mission profile in more depth.

  48. ISRU: proposed system design Mars atmosphere 95.3% CO2 2.7% Ar 1.6% N2 @ 7mBar, 200K Buffer gas separator (e.g. CO2 solidifier) CO2 Heater Centrifugal compressor Ar N2 420K CO2, 420K CH4 Cryocooler Sabatier reactor H2, 420K Counter current heat exchanger H2O O2, ~270K Ar N2, 70K CH4, 111K Liquid O2, 90K H2O electrolyser H2, ~270K Liquid H2, 20K CO (vented) H2O Heater 670K H2 RWGS reactor CO2

  49. ISRU: summary Power: 28-43kWe Mass: 1.8-2.7t • More detailed comparison of: • RWGS • Methane pyrolysis • Catalytic decomposition of methane • Direct reduction of CO2. For additional oxygen generation. • Better understanding of : • Amine absorbers, v. • Zeolite bed extraction, v. • Solid phase separation For buffer gas separation. Suggest experimental programme. Suggest futher study

  50. Technology development suggestions2002 – 2006 (0-5 years) • PV array power generation: Testing using high efficiency (GaAs based, or crystalline Si Hi-ETA and LILT) cells, under simulated Martian conditions, investment in CIS cell manufacturing. • Power storage development: batteries and fuel cell systems . Need to be (a) tolerant to CO2 and CO, (b) integrated into combined heat and power systems, and (c) optimised for performance under Mars environmental conditions. Flywheel investigation • Space rated long duration Liquid hydrogen storage. • ISRU technology, subsystem level. Determination of preferred chemistries. • Novel means of powering mobile mision elements. • Nuclear power systems: refinement of system designs (more detailed trade-off between gas and liquid metal cooled reactors). Investigation of means of shielding, experiments to verify convective CO2 atmosphere heat rejection

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