The results of studies to determine the contamination compatibility of the cross boom and dual keel Space Station configurations with attached payloads are presented. The approach was to define the 3-D configuration of the Space Station and calculate surface-to-surface view factors and solid angles between surfaces and points in an extensive point matrix around the Space Station via a modified TRASYS model. The molecular number column densities along specific experiment lines-of-sight on the cross boom generally meet JSC 30426 requirements. The deposition of contaminants on payload surfaces exceeds the JSC 30426 requirements. These model predictions require updating because of the impact on background brightness predictions. An increase of a factor of 2 to 10 in column densities would result in an unacceptable optical background

Rantanen, R. O.

English

NASA Technical Reports Server

NEUTRAL ENVIRONMENT FOR SPACE STATION 
R. 0. Rantanen 
Science and Engineering Associates, Inc. 
6535 S .  Dayton St., Suite 2100 
Englewood, GO 80111 
Abstract. The molecular number column densities along specific experiment 
lines-of-sight on the Space Station cross boom generally meet JSC 30426 
requirements. The deposition of contaminants on payload surfaces exceeds the 
JSC 30426 requirements. 
the impact on background brightness predictions. 
to 10 in column densities would result in an unacceptable optical background. 
These model predictions require updating because of 
An increase of a factor of 2 
Introduction 
The results presented in this brief position paper are a result of studies 
initiated by OSSA to determine the contamination compatibility of the cross 
boom and dual keel Space Station configurations with attached payloads. 
Details of this study are available in Space Station Contamination Assessment 
Summary, dated November 16, 1987. 
Approach 
The approach was to define the three-dimensional configuration of the Space 
Station and calculate surface-to-surface view factors and solid angles between 
surfaces and points in an extensive point matrix around the Space Station via 
a modified TRASYS model (Jensen and Goble, 1983). 
145 node model for gas collision sources and interactions and the other a 350 
node higher fidelity model for surface-to-surface deposition calculations. 
addition the RCS engines firing along z positioned at x = -750, y = +2000, and 
Z = -250 cm and the resistojet positioned at x = -3385, y = 0, and Z = -255 cm 
were included as sources for non-operational periods. 
The surfaces of  the modules and the service facility outgas at a rate of 
6.1 x 10" molecules s- '  (1 x lo-' g s- ' ) .  The solar 
panels, thermal radiators, and power radiators outgas at a higher rate, 3.1 x 
1012 molecules cm-2 s - 1  (5 x 10-10 g 0 - 2  s - 1 ) .  Outgassing mole- 
cules are considered to be emitted in a Lambertian distribution. 
The criterion for leakage from Space Station modules is a total of 2,270 g 
day-' (5 lb day-'). 
modules as follows. Seals were divided into three major categories according 
to increasing propensity for leakage: 
fixed viewing ports (called "Inactive Seals Installed in Factory"), on-orbit 
installed seals such as those between modules and nodes that are not made and 
broken repeatedly (called "Inactive Seals Installed On-Orbit"), and active 
seals that are made and broken repeatedly on-orbit (called "Active Seals"). 
Inactive seals installed in factory were considered leakfree. Inactive seals 
installed on-orbit and active seals were represented by short cylinders or 
Figure 1 shows the two levels of detail used for the geometry. One was a 
The sources used for the operational period are shown in Table 2. In 
This total leak rate was partitioned among the 
factory installed seals such as at 
K 
https://ntrs.nasa.gov/search.jsp?R=19880016007 2020-03-20T06:43:13+00:00Z
us. us *mLT 
RCYIRCL UE 
INACTIVE SEALS INSTALLED LEAKAGE 
ON ORBIT--TYPE 3 ( R I N G )  
ACTIVE SEAL (R;XG) LEAKAGE 
I 
I 
,e.- 
2270 75% N , 22% 0 , 
G W D A Y  2% E26, 1% COf 
(5 LBM/ 
TOTAL 2% H26, 1% CO; 
DAY) 75% N 9 22% 0 , 
, - CmramL KXUC Rvllar 
(145 RODE COSFIGURATIOK) I (350 NODE COXFIGURATION) 
Fig. 1. Modeled configurations. 
* Table 1. Molecular Sources-Quiescent Period 
SOURCE TYPE CONSTITUENTS RATE 
MODULE/SERVICE FACILITY OUTGASSING MEAN MOL. W. = 100 6.1 X 1 O1 MOLECULES/C?/SEC 
SURFACES 
SOLAR PANELS OUTGASSING MEAN MOL. W. = 100 3.1 xi o1 MOLECULES/C$/SEC 
THERMAL RADIATORS OUTGASSING MEAN MOL. WP. = 100 3 . 1 ~ 1 0 ~ ~  MOLECULESKK'LSEC 
POWER RADIATORS OUTGASSING MEAN MOL. W. = 100 3.1~1 o1 MOLECULES/CK'/SEC 
75% N , 22% 0 , 1 .3xi o1 MOLECULES/CI?/SEC LEAKAGE-l 2% H26, 1% COS INACTIVE SEALS INSTALLED ON ORBIT--TYPE 1 (RING) 
INACTIVE SEALS INSTALLED LEAKAGE 
ON ORBIT--TYPE 2 (RING) 
75% N , 22% 0 , 
2% H26, 1% COf 
1.7~ 1 o1 MOLECULES/CK'/SEC 
4 .ox io' MOLECULES/CK~/SEC 
AIR LOCK [ D I S K )  LEAKAGE 7 5 %  N , 22% 0 , 3.6~10~ MOLECULES/CK'/SEC 
2% HZ6, 1% CO: 
4 .ax1 o1 KOLECULES/CI.;~/SEC 7 5 %  N , 22% 0 , 
2% H26. 1% CO; 
DOCKING RING ( D I S K )  iEAKAGE] 
VENT (LOCATED AT X-0, VENT 
Y=-325 CM, Z=-831 CM, 
POINTING I N  
-Y DIRECTION) 
7 5 %  N , 22% 0 , 1 .OX 1 OZ1 MOLECULES/SEC ] E&, 2% H26, 1% CO: 
"r ings"  i n  the Space S ta t ion  model. "Type 1" ( th ree  s e a l s )  and "T e 2" r ings  
(e ight  s e a l s )  were assigned a leak  r a t e  of 1 . 3  x l O I 5  and 1 . 6  x 10 B 
2 
molecules cm-2 s-' respectively fsee Table 2), corresponding to a flow 
rate of 90.7 g day'' (0.2 lb day- ) for each seal. 
molecular flux for type 1 and type 2 rings was a result of different surface 
areas of  the rings. "Ty e 3" rings (two seals) were assigned a leak rate of 
1.7 x 
day-' (0.167 lb day-') each. 
attachment of the logistics module. 
leak rate of 4.0 x 
of  227 g day-' (0.5 lb day-'). 
air locks and docking rings, were also assigned a leak rate corresponding to a 
flow rate of 227 g day-' (0.5 lb day-'). 
rates depended on the area of the sources, which in these cases were disks 
(see table). Leakage is considered to be emitted in a Lambertian 
distribution. 
The vent passed an average flow rate of half the total average rate of 0.1 
g s - ' ,  
direction in order to give zero net thrust. The latter vent was not included 
in the model since it was entirely shadowed from the region of interest (above 
the modules). 
distribution given by 
The difference in 
molecules cm-' s-', corresponding to a flow rate of 75.7 g 
One active seal was considered at the 
molecules cme2 s-l, corresponding to a flow rate 
The remaining major leakage sources, the 
This major ring source was assigned a 
The specific molecular leak 
The other half was passed through an identical vent facing in the +y 
The vent was considered as a point source producing a density 
N(mo1ecules ~ m - ~ )  = 5.7 x cos2 (0.94 0)/r2 
where r is the distance in cm from the source and 8 is tht angle from plume 
centerline. 
Results 
Cross Boom 
the Space Station and the type of molecule and its source were tracked. A 
total of 30 different molecules or source state of the molecules was used. 
These included ambient, surface reemitted ambient, outgassing, leakage, and 
vent plus the scattered component of each of these. 
Lines-of-sight were calculated at three positions along the boom. One 
position was at the center of the boom and the others 15 meters from the 
center. 
1OI2 to 9.6 x 10" molecules cm- 
atomic oxygen ranged from 7.7 x 10" to 4.5 x 10" atoms cm-2, the 
surface reemitted N2 ranged from 1.2 x 1OI2 to 2.3 x 10" molecules 
H20 ranged from 7.3 x 10" to 2.7 x 10 
meters from the center the total density ranged from 4.7 x 10 l2 to 9.0 x 
10" molecules cm-2. 
ments at a level of 7.5 x 10" molecules cm-2 for one line-of-sight. The 
results for y - -15 meters ranged from 6.5 x 1OI2 to 1.1 x lo1* molecules 
cm-2 for total number column densities. 
10" molecules for one line-of-sight. These results are summarized 
in Figure 2. 
cross boom reached rates of 5 x 
depended on solar array position. 
forward, aft, left/right and upward along Z. For surfaces with a limited 
Densities of the molecular sources were calculated at every point around 
At the boom center the total number column density ranged from 2.4 x 
By species the surface reemitted 
O2 ranged from 3.4 x 10" to 3.9 x 10" molecules cm'2, and 
9 molecules cm-2. At y = 15 
Water was the only species that exceeded require- 
Water reached a peak of 7.3 x 
Direct flux deposition levels on surfaces at the three oints along the 
to 1.8 x lo-'' g cm-' s- '  and 
These values were for a flat surface facing 
3 
TOTAL NCO RANGC 0 
'WRING NmPERATIDNAL PERIODS THE MLLMN DENSITIES RANGED FROM 5.15X10'~ TO 5.6X1015 MOLECULESlCM2 
Fig. 2. Number columnm density ranges cross boom - quiescent period. 
DEWS1 TlON 
Glr/CM21s 
- CROSS BWM 
~ DUAL KEEL 
Fig. 3 .  Deposition ranges at payload positions on flat surfaces. 
field-of-view the direct flux did not deposit. 
contaminants via scatterin interaction with the ambient ranged from 2.3 x 
fields-of-view of 0.1 steradians only received significant deposition when 
viewing along the direction of motion 
ranged from 1.2 x to 3.9 x g cmm2 s-'. The deposition 
results are summarized in Figure 4 .  
Dual Keel 
orders of  magnitude less than the cross boom and should be acceptable for 
payload viewing. 
The direct flux deposition levels on flat surfaces at the three points 
along the keel ranged from 2.2 x to 3.0 x 
Non-Operational Periods 
contributions to number column densities along the cross boom. 
content ranged from 5.6 x to 2 x molecules cmm2. Since the 
effluent of the engines is H20 it clearly replaced the other sources as the 
predominant contaminant. The resistojet with only one jet operating roduced 
number column densities of water that ranged from 5 x 
molecules cm-2 for H20. 
increase in the column densities. 
"Space Station Contamination Assessment Summary." Figure 4 shows the is0 
density contours in the X-Z plane. 
multiples of the ambient density which was 1.3 x lo8 molecule cme3 for 
this study. Figure 5 shows lines-of-sight integrated for the contour shown in 
Figure 4 .  
The return flux of 
to 2.8 x g cm-' s-' on flat surfaces. Limited 
These levels on the +x facing surfaces 
The number column densities for the dual keel lines-of-sight were 1 to 2 
g cm-2 s-I. 
The RCS engines firing along the +Z axis (upward) were evaluated for 
The water 
1P to 1 x 10 
Multiple resistojets would cause the same 
Figures 4 ,  5 ,  and 6 show the types of graphic data that are presented in 
The numbers on the contours correspond to 
Figure 6 is the same as Figure 5 except that the densities at each 
4 
X ,  CM 
-3300 -2725 -2150 -1575 -1000 -425 150 725 1300 1875 2450 
51 50 I I 1 I 4 1 I 1 I 
4150 - 
3650 - 
3150 - 
z, CM 
2650 - 
2150 - 
Fig. 4 .  T o t a l  density in X-Z plane at Y = 0. 
point in the plane are shown so that users of the data can perform their own 
integration or use the densities directly for plasma analysis. 
are multiples of the ambient density. 
The numbers 
Conclusions 
Based on the.assumptions for the sources only a few lines-of-sight on the 
cross boom exceed the JSC 30426 number column density requirements. It is not 
clear if these meet the zodiacal background requirements also in JSC 30426. 
dual keel the major contamination problems will result from the attached 
payloads creating local contaminant conditions that may be unacceptable. 
The dual keel configuration meets all column density requirements. For the 
5 
!Y !Y !Y 
it t t 
i 3 2 
!Y t 
2 
N 
3 4 
n 
3 
N" 
7 
Deposition levels on both the cross boom and the dual keel exceed the 
requirements on a flat surface at the payload positions. 
are 1 to 2 orders of magnitude less than the cross boom. Limited 
field-of-view surfaces meet the deposition requirements except when viewing 
along the direction of motion. 
demonstrated as an engineering feasibility. A change of a factor of 2 would 
cause more lines-of-sight to have column densities that exceed the criteria. 
Japanese module have not been included. 
its effluent impact on upper hemisphere viewing but does cause a potential 
problem for Earth pointing systems. 
shown to be the best location for engineering purposes. 
was an average during volume pumpdown. 
N o  gas emissions other than cabin air were analyzed. 
Experiments with surfaces within 2 or 3 meters of each other must have 
outgassing rates less than 1 x 
deposition requirements on nearby payloads. 
densities that exceed requirements. 
The dual keel levels 
The total leakage rate of 2 2 7 0  gm day-' ( 5  lb day) has not been 
Any sources other than leakage and outgassing from the European and 
The experiment volume pumpdown vent location used in this study minimizes 
This location has not been approved or 
The flow rate used 
Higher values will occur initially. 
g cm-2 s- '  in order to meet the 
The operation of  the RCS engines and the resistojets creates number column 
Recommendations 
The following recommendations are made because of their potential impact on 
Space Station and the attached payloads. 
1. 
2 .  
3 .  
4 .  
5 .  
6 .  
Update Contamination Model/Perform Sensitivity Study 
Include Phase I extra solar arrays and remove service facility. Perform 
trades on collision cross section, scattering distribution, and surface 
emissions. 
Experiment Vent Optimization 
Determine optimum vent location taking into account, engineering 
requirements, attached payload needs, venting needs, gases used, 
densities near solar panels, microgravity needs, etc. 
Update JSC 3 0 4 2 6  Requirements 
Based on spectral brightness versus column density upgrade requirements. 
Also, revisit other updates that may be required for deposition, 
particulates, etc. 
International Module Sources 
Determine other contaminant sources that may exist from the European and 
Japanese modules. Input to the contamination model for evaluation. 
Shuttle/Hermes Visits Docked 
Determine molecular deposition and particulate source impact of the 
Shuttle docked to the Space Station and for visits by the European Space 
plane (Hermes). 
Update Outgassing Sources 
Determine levels of outgassing that may exist for sources or determine 
what is allowed based on analysis. 
8 
7.  
8. 
9 .  
10 
11 
12 
Spectral Brightness 
Continue modeling by D.G. Torr, UAH, to allow brightness predictions to 
be incorporated into number column density predictions. Support this 
study with update neutral gas density predictions. 
Flight Experiments 
Flight experiments at several altitudes to measure spectral brightness 
emissions of known sources are required to obtain necessary excitation 
data for predictions. Also gas density/direction measurements are 
required at several altitudes to verify/update contamination model 
predictions. 
Detection Sensors 
A combination of sensors to verify the contaminant environment are 
required to be placed on the Space Station at multiple locations. These 
should be decided upon, built, flight tested, and finally packaged for 
Space Station. 
Surface Effects 
Determine the surface phenomena that exist for excitation of adsorbed 
species and their subsequent remission. 
Payload to Payload Contamination 
Model the payloads on the boom to see what column densities may exist for 
near neighbors and the deposition requirements for close proximity 
payloads. 
Earth Pointing Requirements 
Develop a set of contamination number column density and spectral 
background brightness requirements for Earth pointing systems. This may 
allow vent location to be better located for upper hemisphere viewing. 
13. Model Verification Shuttle Data 
Revisit Shuttle data that has not been reduced for correlation to 
contamination predictions. Include IECM, SPAS, IR measurements, and any 
other data that are useful. 
Re fer enc e 
Jensen, C.L., and Goble, R.G., Thermal Radiation Analysis System, MCR-73-105 
(Rev. 5), June 1983. 
9 


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