Transcript Spring2008_Surface Power Update Follow Up

Lunar/Mars Surface Power Architecture
Analysis Follow-up
Chase Cooper
August 7, 2008
June 3, 2008
Slide 1
Areas of Revision

Regenerative fuel cell performance:
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Original Energy density:
 ~700 Wh/kg
Revised Energy Density:
 ~250 Wh/kg
Wind considerations:
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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.
Solar Cells
Kevlar Areas
June 3, 2008
Slide 2
Areas of Revision cont.
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.

Daily Solar Incidence Energy Levels
(Tracking Arrays, No Atmosphere)
12
kW-h (solar) / m^2 / sol

10
8
6
4
Equator
45-degrees North
2
45-degrees South
0
0
100
200
300
400
500
600
700
Date in Sols (Perihelion = 0)
June 3, 2008
Slide 3
Results
Mass Specific Power vs. Latitude
for a 100kW Average Power System
Mass Specific Power
(W/kg)
21
19
17
15
13
11
9
7
5
-60
-40
-20
Solar+RFC
Solar+Li-ion Batteries
Nuclear Sterling
Nuclear Brayton
0
20
40
60
Latitude (deg)
June 3, 2008
Slide 4
Results cont.
Volume Specific Power vs. Latitude
for a 100kW Average Power System
Volume Specific Power
(W/m^3)
2500
2000
Solar+RFC
1500
Solar+Li-ion Batteries
1000
Nuclear Sterling
Nuclear Brayton
500
0
-60
-40
-20
0
20
40
60
Latitude (deg)
June 3, 2008
Slide 5
Effects on Deployment Time
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Considered the 100kW average power system located
at the equator.
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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
June 3, 2008
Slide 6
Deployment Time cont.
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Power delivery during deployment:
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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:
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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
June 3, 2008
Slide 7
For Winfried
June 3, 2008
Slide 8