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Transcript of Space Habitat Deployment Opt
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American Institute of Aeronautics and Astronautics
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Deployment of Inflatable Space Habitat Models
Jeremy Hill1 and Jamey Jacob2
Mechanical and Aerospace EngineeringOklahoma State University, Stillwater OK 74078
The experiments described in this paper were performed with the goal of obtaining both
qualitative and quantitative pressure and motion data for an inflatable habitat model in both
a 1-g and microgravity environments. The experiments investigated the impact of fold
method and inflation speed on the deployment dynamics of the space habitat model. The
first part of the experiment was conducted in a microgravity environment on NASAs
modified Boeing 727 aircraft in June of 2009. The second part of the experiment was a
series of ground tests conducted in the fall of 2009 aimed at developing a more
comprehensive idea of the relationship between model size and inflation time, as well as, the
model accelerations during deployment. The runs taken under microgravity conditions
were significantly less dynamic. In addition, the roll and z-fold methods were shown to
affect the deployment behavior at certain portions of the ground deployments.
Nomenclature
P = Pressure
V = Volume
n = moles
R = Universal Gas Constant
T = Temperature
LaRC = Langley Research Center
X-Hab = Expandable Lunar Habitat
I. IntroductionAUNCH of space habitats suffer from limitations of volume constraints of current launch vehicles. The habitats
must fit in a very small space, limiting the design volume of the habitat and its usefulness. One way to overcome
this limitation is to use inflatable systems that pack in the payload and deploy in space for habitation. The primary
benefit of deployable inflatable habitats is that they enable very large volumes to be packed in small volumes for
launch. Reduced volume results in lower costs and increased options for launch vehicles. It also reduces costs since
very little, if any, on-site construction is required. A deployable inflatable space habitat is ready for use immediately
after deployment. This paper investigates the deployment of inflatable space habitat models under microgravity and
1-g conditions. Data includes deployment shape, inflation pressure and reaction forces. The resulting data will be
used to develop and verify models to design space habitats and their stowage and launch parameters.
A. BackgroundIn March of 2001, students from the University of Kentucky participated in a similar reduced gravity flight
experience on board a KC-135. The students tested the deployment characteristics of a solar concentrator model
composed of several inflatable tubes. The results showed overall consistent inflation characteristics over multiple
deployments; while showing constant pressure with increasing volume and constant volume with increasing pressure
once all of the stages were released.1 In 2002, a paper was presented by Cadogan and Grahne that described several
types of inflatable structures, as well as their potential applications in space technology. 2 Results were presented
with respect to rigidization methods and volume efficiencies: both of which result in direct reductions in launch
1 Undergraduate Research Assistant, Department of Mechanical and Aerospace Engineering, Student Member
AIAA.2 Associate Professor, Department of Mechanical and Aerospace Engineering, Associate Fellow AIAA.
L
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payload volume and weight. In 2001 AIAA paper by Clem, Smith, and Main, the structural behavior of their
inflatable model was found to a function of the inflation rate of the inflatable structure. In addition, the slower
inflation rates produced more favorable deployment behavior.3 Another observation is that the external pressure has
a substantial affect on the pressurization inside the model.4
Most recently, ILC Dover (ILC), in conjunction with NASA, has been studying inflatable, deployable structures
to expand the architectural options available for exploration in lunar and Antarctic environments. The overall
objective of this combined effort was to design, construct, and test a proof-of-concept inflatable structure, focusing
on how easy it is to deploy and how durable it is in an extremely harsh environment, i.e. Antarctica. 5 In addition,
under contract with NASA Langley Research Center (LaRC), ILC has also worked to design and fabricate an
expandable lunar habitat (X-Hab). X-Hab is a deployable cylindrical habitat designed to demonstrate packing and
deployment of an inflatable habitat under expected loading scenarios.6
B. HypothesisDuring the experiment, it was expected to see significant differences in the deployment behavior of the inflatable
space habitat model under microgravity conditions from the behavior observed in Earth gravity. The impact of fold
method and inflation speed was also expected to be significant.
C. Test ObjectivesThe objectives were to observe the deployment of an inflatable space habitat model and measure the effect of
microgravity on deployment behavior. The group investigated the impact of (i) fold method and (ii) inflation speed
on the deployment dynamics of the space habitat model. With respect to the folding methods investigated, the rolland z-fold methods shown in Figure 1 were considered. Basic models for the deployment behavior of simple
inflatable beams have already been developed and these models will be adapted based on the observations. The
results of these tests will be used to develop a high fidelity model for inflatable space habitat deployment for use in
future development of deployable space habitats.
Figure 1: Roll Fold (Left) and Z-Fold (Right)
II. Technical ApproachA. Experiment Overview
Inflatable space habitats provide an attractive solution to the problem of launching large volume habitable
structures into space using current launch systems. The ability to pack the habitats into a small volume is their
primary advantage. The deployment of an inflatable space module is complex, however, and models of the
deployment are necessary to determine deployment system and stabilization design parameters. This experiment
measures several quantities important in developing these models, including time dependent inflation pressure,
model accelerations/forces during deployment, and the model shape during unfolding. The models are packed in
different manners, notably either rolled or z-folded. The packing volumes are different for each method. Also, the
addition of an airlock on the far side will provide a large point mass that will greatly vary the deployment behavior.
These airlocks will likely be implemented in most designs to provide access to other inflatable and non-inflatable
modules. Both the effect of point masses and distributed masses only (no airlock) were examined on the deployment
dynamics of the models, as well as the packing method.
The first part of the experiment was conducted in a microgravity environment on NASAs modified Boeing 727
aircraft in June of 2009. Figure 2 shows students performing the experiment in the microgravity environment. The
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primary objective of the microgravity experiment was to provide a comparison to the ground deployments that
would take place at a later date. The second part of the experiment was a series of ground tests conducted in the fall
of 2009 aimed at developing a more comprehensive idea of the relationship between model size and inflation time,
as well as, the model accelerations during deployment.
Figure 2: In-Flight Experiment
B. Experiment DescriptionThe experiment consists of a stowed inflatable space habitat model that is deployed once the microgravity
environment is reached or when the solenoid is triggered by the computer. Deployment is initiated by a solenoid
valve through which low pressure air (
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As stated, the experiment consisted of two phases: a microgravity portion and a ground portion. Typical g-forces
from the flight parabola during a microgravity run are shown in Figure 4. Note the microgravity conditions last for
approximately 20 seconds. The microgravity phase involved the pressurization of a 6 in diameter model with and
without an accelerometer attached to the end of the inflatable model. Two cameras were used to record high speed
video from different angles. Due to the space limitations imposed by the size of the aircraft, the cameras were
mounted on the top instead of side of the frame. Both Figures 5 and 6 show the shape of the models at distinct
points of the deployment using both the roll and z-fold methods, respectively. It can be seen that the shape of the
model proceeds to its full volume state in a reasonably uniform manner for both cases. While both models reached
full volume around the same time, it was also seen in the second frame of the sequences that the roll fold method
took longer to reach full length than did the z-fold method.
The ground based portion involved the deployments of models of varying diameters. This was done not only to
offer a comparison to the microgravity runs, but to also provide a broader view of the impact of model size on
inflation time and deployment accelerations. Because the space limitations no longer applied, one of the cameras
was moved to the ground to give a side view of the deployment. Both Figures 7 and 8 show the deployments of the
6in diameter models with the roll and z-fold, respectively. It can be seen in the second frame of the deployment
sequences that the z-fold method expands to near full length sooner than the roll fold method. This was consistent
throughout all ground deployments. The corresponding accelerations will be explored later in the paper.
Figure 4: G-Forces from Typical Flight Parabola
Figure 5: Roll Fold (Microgravity)
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Figure 6: Z-Fold (Microgravity)
Figure 7: Roll Fold (Ground)
C. Model ManufacturingModels were manufactured out a polyethylene coated nylon fabric. The material thickness is approximately
0.01inches. The material was cut to dimension and seal together by a student. The models were sealed using acommon heat sealer to bond the polyethylene sides of the material. Two types of heat sealers were used to construct
the models. The first was a large straight sealer that was used to bond the length of the model. The second was a
smaller hand heat sealer that was used to for the more intricate parts of the model, i.e., the end caps. Several models
were constructed of various diameters while keeping the lengths constant. Each model took approximately 5-6
hours to make. The manufacturing process was accurate to within the measuring capabilities of the hand rulers
used, but the quality was influenced the most by the heat sealers. The models were accurate enough for the purposes
of the project without requiring more complex manufacturing processes.
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Figure 8: Z-Fold (Ground)
D. Test MatrixThe baseline test matrix is divided into three categories: Fineness Ratio, Folding Patterns, and Inflating
Pressures. An example table for how the parameters of the test matrix were varied is shown in Table 1.
Table 1: Experiment Test Matrix
The fineness or aspect ratio was developed by maintaining a constant length of 20 inches and varying the
diameters to 3 inches, 6 inches, and 10 inches. The inflation pressures were varied between 1, 3, and 5 psi for the
3inch and 6 inch diameter models, but the pressures were increased to 5, 7, and 9 psi for the 10 inch due to the large
increase in inflation time.
III. Results and DiscussionA. Pressurization Results
The pressure history was recorded for all deployments for purposes of understanding how the model inflates by
examining any changes in the internal pressure. Figure 9 shows six plots of the pressure history for the 3in diameter
model. In addition, the plots also show the cut-off pressure setting that was used to close the solenoid. These were
the runs taken on the ground. The model was tested using both the roll and z-folding methods. The plots on theright are those using the roll fold method and the plots on the left are those using the z-fold method. The model was
also run at three different inflation pressures: 1 psi, 3 psi, 5psi. The plots at the top are the 1 psi inflation pressures.
The middle and bottom plots are the 3 psi and 5 psi inflation pressures, respectively. It was decided to not go
beyond 5 psi because the inflation time became so rapid that a usable pressure history could not be obtained.
Looking at the pressure histories for the six runs, it can be seen that there are no noticeable differences in the roll
and z-fold methods. In both methods, two distinct regions can be seen. The first part of the inflation is
characterized by a constant pressure expansion until the model reaches its full volume. The model then transitions
into the second region of constant volume with increasing pressure. Both the 1 psi and 3 psi inflation runs maintain
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their respective pressures throughout the entire run; however, the 5 psi runs shows a slight disturbance in the
pressure history. The pressure initially rises to just above 5 psi and then transitions to just below 5 psi before
reaching full volume and climbing to the cutoff pressure. Comparing the data and the video showed that at this
inflation pressure, the 3 in model inflated too quickly for the pressure to stabilize back to the regulator setting.
Figure 10 shows eight plots of the pressure history for the 6in diameter model. Examining the pressure histories
for the eight runs, it can be seen that again there are no noticeable differences in the roll and z-fold methods. In both
methods, the same two distinct regions can be seen. The first part of the inflation is characterized by a constant
pressure expansion until the model reaches its full volume. The model then transitions into the second region of
constant volume with increasing pressure. Both the 1 psi and 3 psi inflation runs maintain their respective pressures
throughout the entire run; however, the 5 psi and 7 psi runs do not return to the desired pressure right away. The
pressure initially spikes above the set pressure and then drops back to the desired setting in approximately 2 seconds.
This can be explained by the large spike in pressure experienced when the solenoid opens and releases the
compressed air.
Figure 4: (3in Model) Pressure History vs. Time; z-fold (left), roll fold (right)
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Figure 5: (6in Model) Pressure History vs. Time; z-fold (left), roll fold (right)
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Figure 11 shows six plots of the pressure history for the 10in diameter model. Examining the pressure histories
for the six runs, it can be seen that again there are no noticeable differences in the roll and z-fold methods. In both
methods, the same two distinct regions can be seen. The first part of the inflation is characterized by a constant
pressure expansion until the model reaches its full volume. The model then transitions into the second region of
constant volume with increasing pressure. In all of the runs, the pressure does not return to the desired pressure
right away. The pressure initially spikes above the set pressure and then drops back to the desired setting in
approximately 1-2 seconds due to the transients generated when the solenoid valve is opened.
Figure 6: (10 in Model) Pressure History vs. Time; z-fold (left), roll fold (right)
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Figure 7: Inflation Pressure vs. Time
The data from the grounds runs was compared to the high-speed video to determine when the models reached
full volume. Figure 12 shows the time it took to inflate each model to full volume at a given inflation pressure. This
first observation is the nonlinear nature of the relationship between the inflation pressure and the time to inflate. It
can also be seen in here why higher inflation pressures were not explored for the 3 in model. Higher inflation
pressures would inflate the model in less than 2 seconds, which was reasoned to be too rapid to be useful. Similarly,
for purpose of time savings at this time, slower inflation pressures were not explored for the 10 in model. An
interesting relationship was noticed with relation to the trend of the data. When the data was normalized with
respect to volume, the data collapsed on itself. Figure 13 shows the data once it has been normalized. The x-axis is
simply the inflation time based on the volumetric flow rate Q (in 3/s).
Figure 8: Inflation Pressure vs. Normalized Time
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Using the ideal gas law, as shown in (1) the mass flow rate into the model was calculated for the several ground
runs. Figure 14 shows the linear relationship between mass flow rate and inflation pressure.
(1)
(2)
(3)
(4)
Figure 9: Mass Flow Rate vs. Inflation Pressure
Figure 10: Inflated Fabric Beam
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Figure 12: (3in Model) Acceleration vs. Time; z-fold (left), roll fold (right) [1 psi, 3 psi, 5 psi (top-bottom)]
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Figure 13: (6 in Model) Acceleration vs. Time; z-fold (left), roll fold (right) [1 psi, 3 psi, 5 psi, 7 psi (top-
bottom)]
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Figure 14: (10 in Model) Acceleration vs. Time; z-fold (left), roll fold (right) [5 psi, 7 psi, 9 psi (top-bottom)]
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C. Microgravity Pressure and Acceleration ResultsFinally, the reduced gravity runs were compared to the ground runs for purposes of finding differences, if any, in
the deployment dynamics. Figure 20 shows four plots of pressure history and model acceleration for the 6 in
diameter model with an inflation pressure of 3 psi. Looking at the pressure histories for both the microgravity and
ground run, there is no noticeable difference in the inflation profile. The microgravity run does have a large spike in pressure initially, but this is explained by the pressure source used on the aircraft and the time between runs.
Therefore, the time to fully inflate was observed to not change significantly between both runs. Looking at the
acceleration profiles, a noticeable difference can be seen in the deployment dynamics. During the microgravity
deployment, the model has motion during the initial break away from the strap and when the model is reaching full
volume. However, the model has zero acceleration during the rest of the deployment. This is unlike the ground run
which is observably more dynamic throughout the entire inflation. A point worth mentioning is the increasing in
acceleration at the end of the microgravity run. This coincides with the aircraft transitioning back into the high-g
portion of the flight profile.
Figure 15: Pressure History and Acceleration History [Microgravity (top), Ground (bottom)]
Differences in deployment behavior can be illustrated by tracking the deployment rate between the different g-
loading and packing arrangements. Here we simply track the maximum deployed dimensionless length, x/L. When
x/L=1, the model is completely deployed. Figure 16a shows the horizontal distance the 6 in model has deployed in a
microgravity environment. The inflation pressure was 3 psi and was kept consistent with the deployments shown in
Figure 16b. The distances were found by overlaying a calibrated grid of the deployment video and observing howfar the model had progressed over time. The microgravity deployments show a clear difference between the roll and
z folding patterns. The z-fold deploys more quickly requiring less inflation pressure to trigger the deployment
sequence. Figure 16b shows the horizontal distance the 6 in model has deployed in a earth environment. The model
was again inflated at 3 psi. Unlike the microgravity tests, the ground deployments do not show the same clear
difference between the roll and z folding patterns as seen in Figure 16a. Here the body force is greater than the
deployment forces in the initial deployment period. Only once filling has occurred and a critical pressure is reached
does the deployment extend beyond the initial fabric release.
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(a) Tip deployment rate in microgravity.
(b) Tip deployment rate in 1 g.
Figure 16: Measurements of deployment time of model tip for 6 in model at 3 psi.
D. DiscussionDuring the experiment, it was expected to see significant differences in the deployment behavior of the inflatable
space habitat model under microgravity conditions from the behavior observed in Earth gravity. The impact of foldmethod and inflation speed was also expected to be significant. The hypothesis was confirmed with respect to the
difference between deployment behavior in the microgravity and ground runs. The runs taken under microgravity
conditions were significantly less dynamic. In addition, the roll and z-fold methods produced different results at
certain portions of the ground deployments. Most notably, the roll fold was observed to reach full length later in the
deployment than did the z-fold method. However, the roll fold and z-fold methods were found to take the same
amount of time to inflate to full volume.
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During the inflation process, 2 distinct regions can be identified in the pressure measurements. The first is the
deployment region indicated by constant pressure. Since pressure is constant, the volume is increasing and the
model is being filled and extended during the deployment. The second region is denoted by a constant rate of
pressure increase. At this stage, the model has filled and completely expanded, but will most likely not yet be
completely deployed since the critical pressure criterion has not been met. Complete deployment occurs sometime
during this phase once the critical pressure has been reached. After this, the pressure reaches the maximum value
and the fill process is complete.
The primary difference between the models deployment behavior is seen in the early deployment stages. Once
released, the z-fold model reaches full length more quickly than the roll-fold models. This is evident from the data in
Fig. 16, where the z-fold is an unrestricted deployment and deploys more quickly requiring less inflation pressure to
trigger the deployment sequence. Unlike the microgravity tests, the ground deployments do not show the same clear
difference between the roll and z folding patterns as seen in Figure 16a. Here the body force is greater than the
deployment forces in the initial deployment period. Only once filling has occurred and a critical pressure is reached
does the deployment extend beyond the initial push provided at the start of deployment. This is due to the symmetric
tensions seen in the accordion folding pattern of the z-fold. In the z-fold configuration, average tension around the
circumference of the model is approximately equal since the packing configuration is symmetric. However, in the
roll fold configuration, non-zero tension is first seen in the outside of the rolled model. As the model inflates, this
tension increases to a constant value as the model unrolls. Only once the model is completely filled but not fully
inflated do we expect to see tension in the inside of the rolled model as shown in Figure 17.
Figure 17: Stresses in a Rolled Model
IV. SummaryThe deployment of inflatable space structures is a complex process in which both the motion and pressurization
affect each other. This experiment was focused on microgravity deployments conducted on simple inflatable habitat
models. Deployments of the models were controlled throughout the inflation. Pressurization time histories show
generally consistent inflation characteristics over multiple deployments with varying inflation pressures, including
constant pressure increasing volume and constant-volume increasing pressure once the model reached full volume.
Variations in deployment acceleration over several runs can be most likely attributed to fold inconsistencies.
V. AcknowledgmentsThe team would like to acknowledge Dr. Andy Arena and Dr. Victoria Duca-Snowden with the Oklahoma Space
Grant Consortium, Dr. Larry Hoberock and the MAE department, Dean Karl Reid, and the OSU Student
Government Association for all their assistance. Jeremy Hill, Josh Hathaway, Eric Johnson, and Alan Larson
performed the experiment on the NASA aircraft. Johnny Chandler served as the ground crew for the experiment.
The authors and team would also like to thank Sara Malloy of NASAs Reduced Gravity Education Flight Program
and Chris Nelson of Oceaneering Space Systems who served as the NASA mentor.
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VI. References1) J. E. Campbell, S. W. Smith, J. A. Main, and J. Kearns, Staged Microgravity Deployment of a
Pressurizing Scale-Model Spacecraft, Journal of Spacecraft and Rockets, Vol. 41, No. 4,
JulyAugust 2004.
2) D. Cadogan and M. Grahne, Inflatable Space Structures: A New Paradigm for Space StructureDesign, 49th International Astronautical Congress, IAF-98-I.1.02, Sept 28-Oct 2, 1998.3) Clem, A. L., Smith, S. W. and Main, J. A., A Pressurized Deployment Model for Inflatable Space
Structures, AIAA Paper No. 2000-1808, Proceedings of the AIAA SDM Gossamer Spacecraft Forum,
Atlanta, GA, April 2000.
4) Clem, A.L., S.W. Smith, and John A. Main, Experimental Results Regarding the Inflation of UnfoldingCylindrical Tubes, AIAA Paper no. 2001-1264, Proceedings of the AIAA SDM Gossamer Spacecraft
Forum, Seattle, WA, April 2000.
5) Cadogan, D.P., Scheir, C., Expandable Habitat Technology Demonstration for Lunar and AntarcticApplications, 2008-01-2024, International Conference on Environmental Systems, San Francisco CA, 29
June-2 July 2008
6) Hinkle, J., Lin, J.K., Watson, J., Deployment Testing of an Expandable Lunar Habitat, AIAA 2009-6447,SPACE 2009 Conference & Exposition, Pasadena CA, 14-17 Sept. 2009.
7) M. Salama, C.P. Kuo, M. Lou, Simulation of Deployment Dynamics of Inflatable Structures,AIAA/ASME/ASCE/AHS/ASC Structures, Structural Dynamics, and Materials Conference and Exhibit,
Apr. 12-15, 1999.
Paper v. 1.1, Dec. 28, 2009