Liquids partially freeze when dumped from spacecraft producing particles which are released into free space at various velocities. Recontact of these particles with the spacecraft is possible for specific particle sizes and velocities and, therefore, can become contamination for experiments within the spacecraft or released experiments as a result of waste and potable water dumped from Space Shuttle. An examination of dump characteristics was conducted on STS-29 using both on-board video records and ground based measurements. A preliminary analysis of data from this flight indicates particle velocities are in the range of 30 to 75 ft/sec and recontact is possible for limited particle sizes

Donahoo, M. E.

Fowler, M. E.

Leger, L. J.

Maley, P. D.

English

NASA Technical Reports Server

hi90- 25508
CONTAMINATION OF SPACECRAFT BY RECONTACT OF DUMPED LIQUIDS
by
M. E. Fowler*, L. J. Leger*,
M. E. Donahoo**, and P. D. Maley***
Liquids partially freeze when dumped from spacecraft producing particles which are
released into free space at various velocities. Recontact of these particles with
the spacecraft is possible for specific particle sizes and velocities and,
therefore, can become contamination for experiments within the spacecraft or
released experiments as a result of waste and potable water dumped from Space
Shuttle. An examination of dump characteristics was conducted on STS-29 using
both on-board video records and ground based measurements. A preliminary analysis
of data from this flight indicates particle velocities are in the range of 30 to
75 ft/sec and recontact is possible for limited particle sizes.
* Materials Branch, Johnson Space Center
** Orbit Analysis Branch, Johnson Space Center
*** Rockwell International
INTRODUCTION
Several times during a mission, the Space
Shuttle Orbiter has to release water which
has accumulated from the fuel cells. Due
to the vacuum environment into which they
are being released, the water flash
evaporates, leaving small ice particles.
There has been some concern that the
motion imparted to these particles could
return them to the orbiter during
subsequent orbits. This could lead to
contamination of experiments in the
payload bay and in the extreme, damage to
materials such as the thermal protection
system tiles. It has been reported that
particles contacted the orbiter on STS-8
and STS-61A during subsequent orbits after
water dumps (i) . As a consequence, water
dumps are being planned more carefully
with respect to the orientation of the
orbiter during the dump. Judicious angles
at which the water is released can lead to
the water reentering (7) the earth's
atmosphere prior to recontact with the
vehicle.
A Detailed Test Objective (DTO) was
formulated for STS-29 where the water
dumps were planned around the viewing
opportunities from both the orbiter and
ground cameras. The idea was to release
the water as the orbiter was first coming
into light over the event horizon yet
still against a black background for
better viewing. Such observations would
provide general plume shape and therefore
velocity vector information for the
released particles. The video images from
the orbiter provided the means to analyze
the particles' trajectories and velocities
in the near field. With this information,
it was possible to analyze the orbit of
the particles and determine if recontact
was possible. With this information, a
model could be developed for use
detailed mission planning.
ICE PARTICLE ANALYSIS
in
The first step to the analysis of the
recontact problem involved understanding
the ice particle flow including velocity
distribution as well as the mass of the
particles. The stream of water released
from the orbiter is very collimated up to
the burst zone (2,3). The burst zone is
mostly regulated by the vapor pressure of
the liquid, in this case water, as the
liquid begins to boil (3). Adding
dissolved gasses can decrease the length
of the collimated stream (4-6) due to the
expansion of the gases in vacuum. Other
factors involved include the orifice
diameter, temperature of the liquid, and
initial pressure of the stream before
release (2-6). In this case, the burst
zone is approximately 1-2 ft away from the
orbiter.
The size of the ice particles formed can
be estimated (4) by using a force balance
on the water droplet before evaporation
occurs
D = 30y/Pv (i)
where D is the diameter in microns, 7 is
the surface tension of the liquid in
dynes/cm, and Pv is the vapor pressure.
Table 1 gives typical diameters for water
Table i Ice particle size vs temperature
Temperature °C D (_)
0 479
i0 238
25 92.3
30 68.9
50 23.7
99
https://ntrs.nasa.gov/search.jsp?R=19900016192 2020-03-19T22:41:06+00:00Z
at various temperatures. Thesevalues are
only estimates as they use the surface
tension of pure water in air at 18°C. A
typical potable water dump is made at
temperatures between 25 and 30°C and
approximately 15-20 psia at the nozzle,
and consists of pure water. Wastewater
releases also occur under the same
conditions..
The velocity of the particles was
determined from the video tape taken on
board of the dump which occurred on orbit
49 (March 16, 1989). While time
consuming, the method was relatively
straight forward. A particle was first
found that could be differentiated from
the flow through several fields of the
video image (there are 2 fields per
frame) • If a part of the orbiter
structure was in view, the dimensions of
the structure were used as a reference in
order to find the distance traveled by the
particle. Simple geometry is used to
estimate the flight of the particle over a
given number of fields (one field = 1/60
sec.) . In other cases where the orbiter
was not in view, the downlinked data on
the movement of the camera about a pivot
allowed the same calculations to be made.
From these calculations, the relative
velocity of the particles were found to be
between 30 and 75 ft/sec. The angle at
which the particles left the orbiter were
not completely definable with the video
images available, but for this analysis
will be assumed to be perpendicular to the
orbiter out the port side, parallel to the
y-axis of the orbiter. The actual plume
is roughly conical in form. It should
also be noted that the actual size of the
particles could not be determined with any
accuracy in the video images but appear to
be larger than the theoretical. This
might be possible if the structure of the
ice particles were more porous like
snowflakes than solid ice spheres.
Trapped gasses and vapor expanding in the
particles could account for larger than
theoretical sizes.
ORBITAL ANALYSIS
All of the orbital mechanics analysis of
the ice particles was performed using
software developed at the Johnson Space
Center called High Accuracy Relative
Motion Processor (HAREM). The HAREM
program takes the atmospheric model for
the date that is specified, the shuttle
weight, altitude and orbit, along with the
particle parameters such as relative
velocity vector to the orbiter, weight,
center of mass, and moments of inertia,
and predicts the orbit of the particles
with respect to the orbiter• A parametric
study was made of such parameters as ice
mass and velocity vector in order to
Table 2 Particle size and weight
Weight (mg)Diameter (cm I
0.01 5.24x!0 -4
0.1 0.524
1.0 524
determine if recontact was possible for
the water dump of STS-29.
Table 2 describes the particles of
interest for this study. The particle
sizes were chosen to encompass the
theoretical particle sizes plus a larger
particle which might be formed due to
vapor expansion in accordance with the
video tape images. The relative speeds
used for this study were 12, 30 and 75
ft/sec. The orbiter was positioned in
such a way as to release the particles in
several directions; retrograde,
posigrade, 90 ° pure out of plane, 90 °
radially up and down, and 45 ° out of plane
relative to a local vertical, local
horizontal (LVLH) reference plane. The
orbiter was considered to be in an orbit
160 x 160 nautical miles. The date was
taken to be March i, 1989, or roughly the
date of STS-29, unless otherwise noted.
Ice Velocity Retrograde to Orbiter Velocity
300 , , . , , . ,
2OO
z
o
-100
0 10 20 30 40 50 60
Time (rain)
mE
Z
N
150
IO0
0
-100
s
• !
100 200
X (N mJ)
300
Figure 1 One mm particle in retrograde
motion release at 30 ft/sec
100
IceVelocityRetrogradetoOrbiterVelocity
6_
E
z 40
3
O 0
-2O
|
• X-coordlnale
0
0
0 o °
0
0
0
81e" ",.="
i i
50 100
Time (rain)
150
P4
2
0
-20
10
I
I
4
|
I
2i0 4 0 it 0
X (N ml)
$0
Figure 2 One cm particle in retrograde
motion released at 75 ft/sec
In Figures 1 and 2, two different graphs
are used to show the relative motion of
the ice particles with respect to the
orbiter. The first figure plots the X-
and Z- coordinates with respect to the
orbiter centered LVLH coordinate frame as
a function of time. The second plots the
Z- coordinate as a function of the X-
coordinate in the LVLH reference frame.
In the LVLH reference frame, +Z is down
toward the earth, and the origin of this
plot is therefore the orbiter. As can be
seen in these two figures, a retrograde
release of the ice particles, regardless
of the size of the particle, results in
deorbit of the particles in a timely
fashion, posing absolutely no threat to
the orbiter. This should not be
surprising since a retrograde velocity
slows the particles, causing them to fall
to a lower orbit, where drag forces cause
further decay of the orbit. It should be
noted that the larger particle stays in
orbit longer than the smaller particle,
and can be explained in terms of the
energy of the orbit. Given the same
relative velocity, the energy of the
particle is determined by its mass, thus
the larger particle has more energy and
stays in orbit longer. This poses
interesting possibilities for decreasing
Ice Released 90 ° Pure Out of Plane
4O0
300
2OO
E
z
v
100
x
-IO0
Z-ooodnm @
0
0
@
o
o •
m Om m • m •
e 01 I
i i
SO 100
Time (mln)
lS0
2O0
E lOO,
z
v
N
0
-100
Figure 3
l
w
m ! l
+oo moo 300 400
X (N mO
One mm particle released 90 °
pure out of plane at 75 ft/sec
the orbit time of the particles by
decreasing their size.
Figures 3-5 represent the orbits of
particles of 1 mm in diameter which are
90 ° pure out of plane, 90 ° radially up and
90 ° radially down to the orbiter in LVLH.
As can be seen in these figures, recontact
does not seem to be possible before
reentry. As a check, a 1 cm particle was
released at 90 ° pure out of plane at 30
ft/sec and 75 ft/sec and are depicted in
figures 6 and 7 respectively. In both
cases, the particles are well on their way
to reentry within two orbits. This is not
meant to imply that no conditions for
these particular release angles will ever
cause recontact, but this limited evidence
is promising.
Trajectories for a 1 mm particle released
in a posigrade trajectory at 30 ft/sec are
shown in figure 8. This particle, due to
its small diameter does not recontact the
orbiter. Its orbit decays below that of
the orbiter after two orbits• Figure 9
represents the case of a 1 cm particle
traveling at 75 ft/sec when it leaves the
orbiter. As can be immediately seen, this
particle stays in orbit much longer than
the previous cases, traveling in an orbit
above the orbiter initially. While
recontact is not observed, it shows that
101
2O
E
z o
.2O
m
ice Released 90 ° Radially Up
• x-,_o_lnill
• Z+coom_llte
I 0
ii
.60 ! - * " I i
0 1 0 2 0 3 0 4too 510 : 4 0
Time (rain)
Ice Released 90* Radially Down
100 ......
0 10 20 30 40 50 60
Time (min)
]0
2o
i
E
z
o
N
.lO i
"-:So *4o -]0 -20 -t0 10
X (N mi)
Figure 4 One mm particle released at 30
ft/sec away from the earth
Ice Released 90 ° Pure Out of Plane
3OO
2OO
z
0
-1 OO
I X<oon_ .ae
• Z<oo_iP, e_
.o
m_llll=, | lullllllll
L • L
100 200 300
Time (rain)
400
z
N
0 20 40 60 00 100
X (N ml)
Figure 5 One mm particle released at 75
ft/sec toward the earth
Ice Released 90 ° Pure Out of Plane
3OO
2OO
E
z
 ,oo
o
-10O
II x-_orc_ ._*
i i i
100 200 300
Time (rain)
400
2O
i
I
E
Z 10 ' i ''/"
i
_ 0
,I
i
I I I
-100 100 200 300
X (N ml)
Figure 6 One cm particle released 90 °
pure out of plane at 30 ft/sec
• l
i
E 1o. ill"
Z •
N j
i
l
0 I I Iif
-100 100 200 300
X (N ml)
Figure 7 One cm particle released 90 °
pure out of plane at 75 ft/sec
102
Ice In the Orbiter Velocity Direction
100
i 0
.100
o
-20Q
• X..0001_q_t e
• Z-ooordiflal
?o. "'" "' • mllil
O
O00
• o o
O0 D 0 0
I
100
Time (mini
mmU|g
0
0
o
O
O
I
2OO
E
o
z
N
-20
,-4O
-|00
Figure 8
I
|
• Im 1
I
i I
• 100 0 100
X (X mll
One mm particle in posigrade
motion at 30 ft/sec
there are orbits which could cause
problems. Given that recontact was
observed for STS-61A, the same particle
and trajectory was analyzed for the
November time frame" of 1985, or the
approximate time of STS-61A. The
atmosphere should have been less dense at
this altitude for this time frame since
the solar cycle is Just now reaching its
peak in the 1989-1990 time frame. The
trajectory results are found in Figure 10.
At 75 ft/sec, a 1 cm particle stays in
orbit, generally at an X-coordinate many
miles from the orbiter. The ice
particles, however, oscillate in the Z-
coordinate around the orbiter's orbit.
Somewhere around the tenth orbit after
release, recontact becomes possible as the
ice particles begin to catch up to the
orbiter. Apparently, the higher density
of the atmosphere of 1989 creates enough
drag to deorbit the particles faster.
With this in mind, it follows that other
combinations of speed and mass would
produce recontact given a posigrade
trajectory. Figure II illustrates
recontact for the case of a 1 cm particle
with an initial velocity of 12 ft/sec in a
posigrade motion with the 1985 atmospheric
model. In this case, recontact is
possible much sooner, with opportunities
twice in the first 2 orbits. Slight
angles to the pure posigrade trajectory
may also facilitate recontact.
While this study covers only limited
particle size and velocity distributions,
it points out the possibilities for
recontact given the right conditions.
Retrograde trajectories appear to preclude
particle recontact.
CONCLUSIONS
It was found that a larger particle has a
longer time in orbit. Breaking up the
particles into smaller spheres will have
some effect on the decay time and
therefore provides another means by which
recontact can be avoided.
The atmospheric density also plays a key
role in the decay of the particle orbits.
It was shown that the 1985 atmosphere had
less of an effect on the orbit of the
particles than the 1989 atmosphere. Since
density of the atmosphere is a changing
function of time, it is another parameter
to take into account for the entire
problem.
Release of water in posigrade trajectories
was found to recontact the orbiter and
could cause problems for experiments
Ice In the Orbiter Velocity Direction
300 '
O X-coo_nide O0
Z.coo_l_ O
200 /
"1_ lOO 2oo soo 4oo s. ooo
Time (mini
|
_o
li " il |•0 II
10 ell • all
Z - -."
N ,b I ",lj
0 i,-!
.f
il /
a-- i
"1._'100 0 100 200 300
X (N ml)
Figure 9 One cm particle released at 75
ft/sec in a posigrade motion
103
Ice In the Orbiter Velocity Direction
290
E Ioo
z
J
m o
5
-100
0
• Z-coee_e4b •
0
0
0
0
0
@
0 o
q_mjO_ 0_ | 8e ii ilii
| ! !
200 400 600
Time (mini
000
I
0 e •
Z • •
N 2 p m_
0
-2
*50
Figure Ii
a posigrade motion for the 1985 atmosphere
Ice inthe OrbiterVelocny Dlrect_n
104
z
B -I00
a
-20¢
so | |0 S 100 150 200
X (N ml)
One cm particle (12 ft/sec) in
_o
200 400 600 I100 1000
Time (rain)
operating in attached payload mode or even
for certain cases of release payloads.
Additional study of particle
characteristics is needed to preclude
deposition of material (residue from
impact) on experiment surfaces and field-
of-view interference.
ACKNOWLEDGEMENTS
The authors wish to thank Gene Beck of
G.E. for his efforts with the video
imaging. Many thanks also go to Joel
Montalbano of Rockwell International for
his tutelage with HAREM.
REFERENCES
i. Communication with Mission Specialist
Jim Buchli.
2. H. Fuchs and H. Legge, Acta
Astronautica, _, 1979, 1213.
3. E.P. Muntz and M. Orme, AIAA Journal,
25, 1987, 746.
4. J. Gayle, C. Egger, and J. Bransford,
J. Spacecraft, I, 1964, 323.
5. R. Mikatarian and R. Anderson, J.
Spacecraft, _, 1966, 267.
6. D. Bharathan and T. Penney, J. Heat
Transfer, 106, 1984, 407.
7. R. Naumann, "Dynamics and Column
Densities of Small Particles Ejected
From Spacecraft," NASA TN D-7590, Feb.
1974.
E
0
N
-10
-200
In | w
mm
Ilm
-100 0 100
X (N mi)
Figure i0 One cm particle released in a
posigrade motion at 75 ft/sec (1985)
I04


Contamination of spacecraft by recontact of dumped liquids

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