System studies have shown a significant advantage to reusing the hydrogen and oxygen left in these tanks after landing on the Moon in fuel cells to generate power and water for surface systems. However in the current lander concepts, the helium used to pressurize the oxygen tank can substantially degrade fuel cell power and water output by covering the reacting surface with inert gas. This presentation documents an experimental investigation of methods to remove the helium pressurant while minimizing the amount of the oxygen lost. This investigation demonstrated that significant quantities of Helium (>90% mole fraction) remain in the tank after draining. Although a single vent cycle reduced the helium quantity, large amounts of helium remained. Cyclic venting appeared to be more effective. Three vent cycles were sufficient to reduce the helium to small (<0.2%) quantities. Two vent cycles may be sufficient since once the tank has been brought up to pressure after the second vent cycle the helium concentration has been reduced to the less than 0.2% level. The re-pressurization process seemed to contribute to diluting helium. This is as expected since in order to raise the pressure liquid oxygen must be evaporated. Estimated liquid oxygen loss is on the order of 82 pounds (assuming the third vent cycle is not required).

1. National Aeronautics and Space Administration
LOX Tank Helium Removal for Propellant
Scavenging
Dr. David J. Chato
Abstract:
System studies have shown a significant advantage to reusing the hydrogen and oxygen left in
these tanks after landing on the Moon in fuel cells to generate power and water for surface
systems. However in the current lander concepts, the helium used to pressurize the oxygen tank
can substantially degrade fuel cell power and water output by covering the reacting surface with
inert gas. This presentation documents an experimental investigation of methods to remove the
helium pressurant while minimizing the amount of the oxygen lost. This investigation
demonstrated that significant quantities of Helium (>90% mole fraction) remain in the tank after
draining. Although a single vent cycle reduced the helium quantity, large amounts of helium
remained. Cyclic venting appeared to be more effective. Three vent cycles were sufficient to
reduce the helium to small (<0.2%) quantities. Two vent cycles may be sufficient since once the
tank has been brought up to pressure after the second vent cycle the helium concentration has
been reduced to the less than 0.2% level. The re-pressurization process seemed to contribute to
diluting helium. This is as expected since in order to raise the pressure liquid oxygen must be
evaporated. Estimated liquid oxygen loss is on the order of 82 pounds (assuming the third vent
cycle is not required).
www.nasa.gov 1

2. National Aeronautics and Space Administration
LOX Tank Helium Removal for Propellant
Scavenging Test
Dr. David J. Chato
Presented January 8th 2008 at AIAA
Aerospace Sciences Meeting, Orlando, FL
2
www.nasa.gov

3. National Aeronautics and Space Administration
Introduction:
• Helium used to pressurize the oxygen tank since this
produces significantly lighter gas residuals at stage
burn-out.
• Helium substantially degrade fuel cell power and
water output
• This experiment investigates methods to remove
maximum amount of helium pressurant while
retaining the maximum amount of the oxygen
residuals.
www.nasa.gov 3

4. National Aeronautics and Space Administration
Objectives
• Understand the amount of residual helium in LOX
tanks after landing
• Demonstrate the ability to remove the majority of the
helium via venting without losing significant quantities
of oxygen
• Measure the oxygen/helium content of the remaining
gases as they would be sent over time to the fuel cell
system
www.nasa.gov 4

5. National Aeronautics and Space Administration
Approach
• Thermodynamic analysis of the system processes
will be performed to predict expected helium
concentrations before and after various venting
scenarios.
• Ground testing will be conducted to validate the
analysis predictions and correct the analysis. Tests
will be conducted at SMiRF at GRC.
www.nasa.gov 5

6. National Aeronautics and Space Administration
Test Tank in Handling Fixture
www.nasa.gov 6

7. Table 2 Close Rang Diode Rake
Mean distance Height from Tank
Relative from datum Bottom
Fill (in) (in)
Volume of
total
Tank)
30% 46.5 21.5625
21.3125
21.0625
20.8125
20.5625
20.3125
National Aeronautics and Space Administration
Temperature Diode Location
Table 1 Broad Range Diode Rake
Relative Fill Volume
of Total Tank*
Height from
bottom of tank
(in)
Distance from
datum* (in)
5% 6.35 61.21
10% 9.57 57.99
20% 15.32 52.24
30% 21.03 46.53
40% 26.75 40.81
50% 32.47 35.09
60% 38.19 29.37
70% 43.91 23.65
80% 49.63 17.93
90% 55.51 12.05
95% 59.41 8.15
www.nasa.gov 7

8. to vacuum pum p 3
e from tank
bottom
5
National Aeronautics and Space Administration
Gas Sample System
5
5
www.nasa.gov 8

9. National Aeronautics and Space Administration
Tests Completed
Test ID
Number
Starting
Pressure (psia)
Ending
Pressure (psia)
Notes
8 50 20 Liquid Nitrogen
Checkout
12 50 20
18 100 20 Gas sample data not
available
21 150 20
24 50 20 Cyclic vent Three
vents total
27 50 20
29 50 20 Direct vent, No gas
sample holds
www.nasa.gov 9

10. Test 12 Start
Test 12 End
Test 27 Start
- Test 27 End
National Aeronautics and Space Administration
0
d6
50
E
Test Results for Vents from 50 psia
100
- Test 29 Start
- f - Test 29 End
G Test 24 Cycle 1 Start
- -0- - Test 24 Cycle 1 End
0
0 30 60
Height from tank bottom
www.nasa.gov 10

11. National Aeronautics and Space Administration
Test Comparison for Vents from 50 psia and 150
psia
100
A Test 27 Start
d
0 Test 27 End
E 50 Test 21 Start E
— t — Test 21 End
x
0
0 30 60
Height from tank bottom
www.nasa.gov 11

12. Test 12 Start
Test 12 End
Test 27 Start
- Test 27 End
National Aeronautics and Space Administration
0
d6
50
E
Test Results for Vents from 50 psia
100
- Test 29 Start
- f - Test 29 End
G Test 24 Cycle 1 Start
- -0- - Test 24 Cycle 1 End
0
0 30 60
Height from tank bottom
www.nasa.gov 12

13. National Aeronautics and Space Administration
Test Results for Three Cycle Vent Test
100
0
as
0
c0
50
c0
U
E0
0
0 30 60
Height from Tank Bottom (in)
www.nasa.gov 13

14. National Aeronautics and Space Administration
L
200 L
Temperature Profiles During Three Cycle Vent
400
0—Start of Cycle 1
— —*— — End of Cycle 1
Start of Cycle 2
— ^— — End of Cycle 2
e Start of Cycle 3
— ^— —End of Cycle 3
0
0 30 60
Height from Tank Bottom (in)
www.nasa.gov 14

15. National Aeronautics and Space Administration
100
as
02
50
E7
Time History of Three Cycle Vent
60
.y
C.
30 L
HHLa
n He Middle
He Bottom
o Gas Analyzer
0 _!L_
Pressure history __^ 0
6:00 AM 12:00 PM 6:00 PM 12:00 AM
Time (hours:minutes)
www.nasa.gov 15

16. National Aeronautics and Space Administration
Preliminary Results
• Significant (>90%) Helium is found in the tank after
draining
• Although a single vent cycle reduces the helium large
quantities remain
• Three vent cycles are sufficient to reduce the helium
to small (<0.2%) quantities
• Repressurization seems to contribute to diluting
helium
• Propellant loss estimated at 82 lbm assuming third
vent cycle is not required
www.nasa.gov 16