MinMars/Surface Power

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Repository of Working Models

http://svn.developspace.net/svn/minmars/users/arthur/Mars%20surface%20power/

Preliminary Surface Power System Assessment

Preliminary_Surface_Power_System_Assessment.jpg
Preliminary Surface Power System Assessment

Mars Surface Power Generation and Energy Storage

Surface Power Architecture Tree

  • There are two basic types of analyses that can be carried out:
    • Equal power analysis: all systems provide the same (constant) power output at any point in time
    • Equal energy analysis: all systems provide the same usable energy per day (for photovoltaic systems this means increased power generation during the day)
Surface_Power_Architecture_Tree.jpg
Surface Power Architecture Tree

Modeling

  • Created model for a Mars solar array based on following major requirements:
    • Array must be sized for end-of-life power generation capabilities
    • Array must be sized to provide the required power during the year’s minimum incident solar energy period
  • Model Assumptions:
    • On Mars, optical depth of 0.4 (equivalent to hazy skies)
    • Tracking arrays at both locations are multi-axis and keep incident flux perpendicular to array over the day
    • Nighttime power of 20 kW, with daytime power enforced when sun is 12 degrees above the horizon
    • Mars analysis done for an equatorial location (actually not optimal location for solar power on Mars):
      • Optimal location at 31° N, with a minimum of 6.57(kW-h/m^2/sol) and 49% daylight/sol for a period of 100 sols
      • Northern latitudes better than corresponding southern latitude
Daily_Solar_Incidence_Energy_Levels.jpg
Daily Solar Incidence Energy Levels

Inputs

  • Minimum solar energy
  • Eclipse Time
  • Daytime/nighttime power req.
  • Power distribution eff.
  • Solar array eff.
  • Degradation per year
  • Array lifetime
  • Optical depth
  • Latitude
  • Array packing density
  • Battery type

Outputs

  • Array area
  • System mass
  • System volume

Results

Mass_Specific_Power.jpg
Mass Specific Power
Volume_Specific_Power.jpg
Volume Specific Power

Other Considerations for Large Solar Array Fields on Mars

Deployment time

  • Considered a 10,000 m^2 rollout array field which will provide 63kW average power for about 100kW daytime power
  • Assume array blankets are 2m wide for easy storage and handling by two astronauts
  • Assume each blanket weighs 100lbs again for easy handling
  • With 0.06 kg/m^2 expected array density, need only 14 blankets total
  • Assume astronauts can unroll array at a walking speed of 1m/s, requires only 3hrs for unrolling
  • Most time will be needed for unloading positioning and hookup, if assume 1hr for this for each array, total deployment time *approximately 17 work hours for 2 crew

Power delivery during deployment

  • If we are conservative and say deployment takes 1 week, we need either a 10kW RTG or fuel cell system to provide 10kW power over the week
  • RTG system would be approximately 1200kg and 0.6 m^3
  • If use RFC, need 2400kg system with volume 8.4 m^3

Future Work

  • Reassess architecture options in MinMars colony context. Previous power analysis for shorter round trip mission.
  • Operations considerations such as dust removal and maintenance.
  • Dust storm power generation.

Issues to be resolved

  • RFC performance may be significantly reduced compared to our assumptions
    • 300 Wh/kg or less
    • Could possibly be enhanced by generating oxygen for RFC in-situ (~ 25% of RFC mass)
  • Effect of wind speed on roll-out arrays
    • Would they be blown away?
  • Degradation, dust removal
  • Robotic deployment

Surface Power Architecture Analysis Follow-up

Areas of Revision

  • Regenerative fuel cell performance
    • Original Energy Density
      • ~700 Wh/kg
    • Revised Energy Density
      • ~250 Wh/kg
  • Wind considerations
    • Found that a wind speed of 7.35 m/s would in fact lift the solar array off the surface.
    • Altered conceptual array design to include Kevlar areas equal to 10% of the total array area to provide space for Martian rock placement for weighing down the array.
    • 9.2 kg/m^2 of rock is needed in the 10% Kevlar regions to secure the array against the top recorded Mars wind of 25 m/s.
    • The major effect of this consideration is increased deployment time.
  • Latitude considerations
    • Ran model for multiple latitudes to show change in performance based on location.
    • Optimal location at 31° N, with a minimum of 6.57(kW-h/m^2/sol) and 49% daylight/sol for a period of 100 sols.
    • Northern latitudes better than corresponding southern latitude.

Updated Results

Mass_Specific_Power_vs_Latitude.jpg
Mass Specific Power versus Latitude
Volume_Specific_Power_vs_Latitude.jpg
Volume Specific Power versus Latitude

Effects on Deployment Time

  • Considered the 100kW average power system located at the equator.
    • Requires a 25,000 m^2 rollout array field due to addition of the Kevlar areas.
    • Assume array blankets are 2m wide for easy storage and handling by two astronauts
    • Assume each blanket weighs 80lbs again for easy handling
    • With 0.07 kg/m^2 expected array density, need only 18 blankets total
    • Assume astronauts can unroll array at a walking speed of 1m/s, requires only 7hrs for unrolling
    • Time will be needed for unloading positioning and hookup, if assume 1hr for this for each array this adds 18hrs
    • In addition to this rocks must be placed in the Kevlar areas. Assume Kevlar areas are 1ft in length and the complete 2m width. Need 5.6kg of rock in each area. There are 225 of these Kevlar areas per array so a total of 4050 of these areas. Assuming 2 rocks are needed per area to secure the 2 sides of the array this requires 8100 rocks to be placed. If 30 seconds is needed to pick and place a rock this will take 33.75hrs for 2 crew.
  • Total deployment time is then 66hrs for 2 crew members
  • Power delivery during deployment:
    • We see that deployment gives 0.76 kW per man hour, therefore we only need 13.2 man hours to reach a capability of 10 kW which is enough for minimal stay alive power.
    • If you are conservative and neglect this and say full deployment and initial usefulness takes 1 week, we need either a 10kW RTG or fuel cell system to provide 10kW power over the week
    • RTG system would be approximately 1200kg and 0.6 m^3
    • If use RFC, need 2400kg system with volume 8.4 m^3
  • Sensitivity of total deployment time to different factors:
    • Sensitivity to array area=0.99
    • Sensitivity to walking time=0.96
    • Sensitivity to rock placement time=0.97
    • Sensitivity to off-load and hookup time=0.965
    • We see that the total deployment time is most sensitive to walking time so the design should be sure to make the unrolling of the array by astronauts in suits easy