NASA Technical Reports Server (NTRS) 20120000402: Evaluation of Drogue Parachute Damping Effects Utilizing the Apollo Legacy Parachute Model

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by  NASA Technical Reports Server (NTRS)

Evaluation of Drogue Parachute Damping Effects Utilizing
the Apollo Legacy Parachute Model
Kelly M. Currin1
NASA KennedySpace Center, FL, 32899
Joe D. Gamble2
LockheedMartinSpaceSystems/MElT, Houston, TX, 77058
Daniel A. Matz3
NASA JohnsonSpaceCenter, Houston, TX, 77058
David R. Breti
rx,
Barrios Technology/NASA JohnsonSpace Center, Houston, 77058
Abstract
Drogue parachute damping is required to dampen the Orion Multi Purpose Crew
Vehicle (MPCV) crew module (CM) oscillations prior to deployment of the main
parachutes. During the Apollo program, drogue parachute damping was modeled
on the premise that the drogue parachute force vector aligns with the resultant
velocity of the parachute attach point on the CM. Equivalent Cm and Cm
q a
equations for drogue parachute damping resulting from the Apollo legacy
parachute damping model premise have recently been developed. The MPCV
computer simulations ANTARES and Osiris have implemented high fidelity two
body parachute damping models. However, high-fidelity model-based damping
motion predictions do not match the damping observed duringwind tunnel and full
scale free-flight oscillatory motion. This paper will present the methodology for
comparing and contrasting the Apollo legacy parachute damping model with full
scale free-flight oscillatory motion. The analysis shows an agreement between the
Apollo legacy parachutedamping model and full-scale free-flight oscillatory motion.
1AerospaceTechnologist, FluidsDivision,NE-F4.
2SeniorEngineer, OrionAerosciences/GN&C,2625 BayArea Blvd/A7C, AIAA Associate Fellow.
3InsertJobTitle, DepartmentName, Address/Mail Stop, and AIAA MemberGradeforthird author.
4 SeniorScientist, Image Science&AnalysisGroup/JSC-KX, 2101 NASA Rd. l/Code: KX.
• Y.
Nomenclature
a angleofattack
Ii rateofchangeofangle ofattack
CD drag force coefficient
Cma pitchingmomentcoefficient
Cmq pitchingmomentdampingcoefficient
Dparachuteinflatedframe diameterofparachute inflated in frame
Dparachuteinflatedfullscale diameterofparachute inflated full scale
flO
angle between parachutetrim position and dynamic rotated position
Iref reference.length
L lift
Mchute momentofparachute
¢ pitch angle
q
dynamic pressure
R riser line length
S area
Sref referencearea
SF
scalingfactor
T resultantdistance vector magnitude
o
roll angle
V., freestream velocity
X vertical distancefrom centerofparachuteto centerofgrid
( yawangle
Y lateraldistance from centerofparachuteto centerofgrid
Z longitudinal distancefrom centerofparachuteto centerofgrid
I. Introduction
A. ConceptOverview
Drogue parachutes are designed to be deployed from rapid-moving objects to reduce the speed ofthe object and
provide a stable platform for the deployment ofthe main parachutes. The Orion CM employs drogue parachutes
which contribute to the system damping to reduce the CM oscillatory motion between drogue opening and drogue
release. System damping includes both the CM damping and drogue damping contributions, and the sum oftheir
contributionscreates stabledampingto reduce the amplitudeofthe CM oscillatorymotion.
The purpose ofthe analysis presented in this paper is to investigate the effect ofdrogue parachutes on Orion CM
dynamics. The Apollo legacy parachute damping model is recalled, improved, documented, and re-justified through
comparisonswith thedrogue parachutemotion from the PadAbort I (PA-I) free-flighttest.
Bass Redd, retired engineer, Johnson Space Center, is credited with developing the original legacy parachute
damping concept. Duringthe Apollo parachute testing era, drogue parachute damping was modeled on the premise
that the drogue parachute force vector aligns with the resultant velocity ofthe parachute attach point on the CM.
This methodologyappliestosimilarparachuteconfigurationssuchasthe MPCVdesign.
B. ModelOverview
The Apollo legacy parachute model (also referred to as the low-fidelity parachute model) simulates the effect ofa
parachute system on a 6-degree-of-freedom body by applying the assumption that the parachute force vector is
aligned opposite the velocity ofthe attach point. This velocity is calculated as the sum ofthe velocity ofthe center
ofmass ofthe vehicle and a component from the vehicle's rotational velocity. It is this rotational component that
causesahysteresis in the momentarmoftheparachute force, and thus createsadampingeffectonthe vehicle.
.
'
.)
The high-fidelity parachute model is a multi-body simulation, with the vehicle and each parachute in the cluster
modeled as separate 6-degree-of-freedom bodies. An elastic riser connects each parachute to the vehicle and
couples the dynamics. This multi-body approach allows the high-fidelity parachute model to capture dynamics that
the Apollo legacy model cannot, such as the pendulum motion ofthe vehicle under the parachute cluster. It also
allows the high-fidelity parachute to simulate parachute deployment to higher fidelity. Another result ofthe multi
body approach is that there is no distinct damping model. The damping behavior should instead be captured
implicitlythroughthe elasticcoupling.
The MPCV computer simulations ANTARES and Osiris have implemented high fidelity two- body parachute
damping models. However, high-fidelity model-based damping motion predictions do not match the damping
observedduring wind tunnel and full-scale free-flight oscillatory motion. Theanalysis presented in this papershows
an agreement betweenthe Apollo legacy parachutedamping model and full-scale free-flight oscillatory motion. Itis
concluded that the Apollo legacy parachute damping model provides a better simulation ofthe free-flight motion
than the two-body model for low mass drogue parachutes.
ll. Derivation ofApollo LegacyDampingModel
The Apollo legacy parachute damping model is based on the premise that the drogue parachute force vector aligns
with theresultant velocityofthe parachuteattach pointonthe CM.
Duringthe Apollo program the drogue parachute damping was attributed to a hysteresis in dynamic pressure on the
parachuteas the velocityon the parachute varieddue to the resultant velocityofthe attach pointonthe CM. Recent
analysis of the drogue damping on the Orion program has shown that the drogue damping is actually due to a
hysteresis in the moment arm ofthe parachute force as the parachute aligns with the resultant velocity ofthe attach
point. The recent analysis allowed derivation ofequations for the equivalent frequency and damping effects ofthe
drogue parachute on the CM. The following analysis provides a summary ofthe derivation ofthe frequency and
dampingequations. I
Figure I showsasingledrogue parachuteatthe alphatrimposition and ata locationcorrespondingto aCM angle of
attackdisplaced from trim.
Rotated Chute Location
Trim Chute Location
*
.QlUteOn = (CDS)Qlute R
a
(Sref I ref)CM
Figure 1.SingleDrogueParachuteDisplacementFrom AlphaTrim.
Thefollowing equations showthe equivalenceofthe drogue parachute momentdueto excursions in alphafrom trim
to the momentfrom a linearCm onthe CM.
a
MChute = -(CDS)chute *q*L =-(CDS)Chute *q*R*sin.1a (I)
Forsmall .1a, sin.1a:::::.1a(good approximation for.1aS 30°). Equatechutemomentfrom .1ato Cm momenton
a
CM.
(2)
. =- (CDS)Chute *q*R*.1a
EqUIvalentChuteCma (I )
.1a*q * Sref* ref CM (3)
(4)
If the wake behind the CM results in a reduction in the dynamic pressure acting on the drogue parachute, an
approximation forthe effectonthe parachute Cm can be obtained by multiplying bythe ratio ofthe wake dynamic
a
pressuretothe free streamdynamic pressure.
The equivalentCma from the drogue parachute is therefore dependent on the CDS ofthe parachute and the distance
from the centerofgravity(CG)totheparachuteattach point.
Asimilarapproach is usedto derivetheequivalentCrn basedon Figure2.
q
4
\ .
.;
'\
'\.
ApproximateTrimPosition
RotatedChutePosition
ChuteCm = 2(CDS)Chut, *R2
q
(S"r /2"r)CM
Figure2. RepresentationoftheDrogueAttachPointon theeM.
-R*a
(5)
tanLl8 =-V-
00
:s
Forsmall Ll8,tan M ::::;M (goodapproximation for Ll8 30°).
L=R*sinLl8 ::::; R*tanLl8 (6)
MChute = (COS)Chute *CiChute *L = (COS)Chute *CiChute *R*sinLl8 (7)
R2 *a (8)
MChute = -(COS)Chute *CiChute *-V-
00
Equatechutemomentfrom Iito Cm momenton CM.
q
(9)
_ R2 *a
(COS)Chute *qChute *-V-
=_
EquivalentChuteCm 01
q 00
a ref (- S I) (10)
2V * q* ref* ref CM
00
ChuteCmq =- 2*(COS)Chute *2CiChute *R2 (11)
(q*Sref*Iref)CM
Note CichuteisapproximatelyCiCMo Reductions in Cichute due to wake effects can be accommodated by multiplying
bythe ratio to CiCMo
(12)
5
\..
.)
The equivalent Cm from the drogue parachute is proportional to the CDS ofthe parachute and to the square ofthe
q
distance from theCG to the parachuteattach point.
These equations provide a simple method ofcalculating the equivalent frequency and damping and should be a
valuable resource for preliminary design ofdrogue parachute damping systems. The equations were validated by
modifyingthe GEMASS 6-degree-of-freedom simulation to replace the Apollo legacy chute model with equivalent
Cm and Cm values computed from the equations. The simulation results were almost identical for the two
q a
simulationruns usingthechutemodel and usingthe equations.
Itis importantto note thatthe key assumption thatthe parachute aligns with the resultant velocityofthe attach point
is only valid for small parachutes (i.e. drogue parachutes) with small mass. For larger parachutes (i.e. main
parachutes),the parachuteand enclosedair massare too largetorapidlychangewiththe attach pointmotion.
III.SummaryofAnalysis
A. Orion PA-l Free-FlightTestAnalysis
In November2010, the NESC was requested to investigate the effect ofdrogue parachutes on Orion CM dynamics
resulting from a lack ofagreement between the Orion Pad Abort I (PA-I) CM damping motion and the simulated
damping motion.2TheNESC enlistedthe supportofseveral Apollo parachute experts, Rick Barton, Bass Redd and
JoeGamble, to performthis analysis.
The PA-I full-scale free-flight test was conducted on
6 May 2010 at White Sands Test Facility (WSTF).
One of the primary objectives of the test was to
demonstrate the parachute recovery system
sequencing and performance. The test configuration
included a development launch abort system (LAS)
and a CM consisting ofa boiler plate outer mold line
(OML) structure with forward bay and cover, first
generation parachutes and flight representative mass
properties. The parachute system was comprised of
two drogue parachutes(23 ftdiametereach)deployed
at T+25 seconds and three main parachutes (116 ft
diameter each) deployed at T+31 seconds. The PA-I
trajectory isshown in Figure3.3
Figure3.PA-l Trajectory.
The PA-I test flight CM-mounted camera recorded 16mm film with an associated timestamp for each frame. The
camera was a LOCAM III 16mm film camera with a wide lens. The film was digitally converted to an HD format
(1920xI080) quicktime movie by Photochem ofBurbank, CA. Data from the PA-I test flight was recorded as a
function ofthe best estimated trajectory (BET) timestamp. The following methodology was used to sync the film
timestamp withthe BETtimestamp:
I. Make abestestimate from the PA-I film frame timestampat whichtheCMdrogues arereleased
(39:29.865)and match thattime withthe BETtimestamp forthe commandedCMdrogue release
(13:00:24.763)
2. Time-stepeach film frame timestampand BETtimestampby0.0I secondsforthe duration ofdrogue
deployment(5.365 seconds)
3. Match the BETdatato the BETtimestamp forthe periodofdrogue deployment.
It was appropriate to delay the timeframe ofanalysis until the drogue parachutes were in the view of the CM
mounted camera (film frame timestamp 39:31.355, corresponding to a BET timestamp of 13:00:26.493). The
drogues were in view for a total timeof3.740 seconds, butwere only in stable view for 3.500 seconds. Thus, 3.500
seconds was chosen as the period ofreview for the PA-I flight test drogue motion, starting at BET = 13:00:26.493
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...
seconds" and ending at BET = 13:00:29.993 seconds. The frame rate ofthe camera mounted on the CM was 200
frames persecond,resulting inatotal of700frames available for analysis.
In order to develop comparisons between the three analysis methods, it was necessary to determine the proper
variables to be analyzed. The GEMASS simulation computes the pitch, <p, and yaw, ~, angles generated by the
motion ofthe drogue parachutes in time. These angles are the basis ofthe comparison between the three analysis
methodsand will be computed in boththe manual analysis methodand the trackingprogram method for comparison
with the GEMASS simulation. Three dimensions are required to determine the pitch and yaw angles: X, Y and Z,
relative to a fixed point on the image screenshot. The manual analysis method has two ofthe three dimensions
known (Y and Z), but X must be calculated in order to compute the pitch and yaw angles. The tracking program
analysis method has all three ofthe dimensions available for computingthe pitch and yaw angles. Each ofthe three
analysis types and the methodology for determining the pitch and yaw angles for comparison will be described in
the followingsubsections.
J. ManualAnalysisMethod
In order to simplify the manual analysis method, several assumptions were made. First, the distance between the
cameraattach point and the drogue attach point on the CM was assumed to be much smallerthan the total distance
between the drogue attach point on the CM and the central point on the parachute. Second, it was assumed that the
cameraattach pointonthe CM isatthe same Xand Z locationas the drogue attach pointonthe CMand varies only
by a Y dimension. Third, the manual measurements ofthe drogue location in time were taken at the estimated
central point location ofthe deployed drogue parachute vent, and the initial measurement was taken only when the
drogueparachuteswere bothfullydeployedandstabilized.
The manual method for estimatingthe motion during drogue deploymentwas astraightforward processofcapturing
image screenshots and measuring drogue central point locations to a fixed location in the image. Due to the high
number offrames available for review, only 10% ofthe frames (every 10th frame) were manually analyzed. The
mediaavailable for review was in video format, therefore after determining the frame number correspondingto the
desired time interval, the video was paused atthe specified frame numberand an image screenshot was captured as
shown inFigure4.
A standard measurement grid was superimposed on each image screenshot and the central point ofeach parachute
was estimated and marked on the image. The lateral (Y,d) and vertical (Z,I) distance from the central point ofthe
parachutetothe centerofthe standardmeasurementgrid was measured for each parachuteasshown inFigure 5.
Thisprocesswas repeateduntilthe measurements for 70total frames wererecorded.
••Forthe manualanalysis. GEMASSanalysis beganatBET= 13:00:26.510seconds.
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Figure4.RepresentativeVideoImageScreen Snapshot.
Figure5.StandardMeasurementGridon Video Image
Snapshot.
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'\ .
.\ " •1
In order to simplify the analysis process, the two parachute Y and Z dimensions were averaged to obtain one
"effective parachute" Yand Z dimension for each image screenshot. Using Rfor the riser line length, the following
equations were usedto calculate the resultant distance vectormagnitude, T; the roll angle, 0;the Xcomponentofthe
r
Svector; scalingfactor, SF; pitch angle, ~; and yaw angle,
T =.JZ2 +y2
(13)
(~)
o=
ARCSIN
(14)
=
X RcosO
(15).
=
SF Dparachuteinflatedfullscale
(16)
Dparachuteinflatedframe
~ (~)
=ARCTAN
(17)
G)
~
=
ARCTAN
(18)
2. GEMASSSimulationAnalysisMethod
TheGeneral Electric Missilesand SatelliteSystems(GEMASS)computersimulationwas the six-degree-of-freedom
(6-DOF) simulation used for most ofthe NASA simulations during the Apollo program. The program has been
ported to a PC and is still in limited use for dynamics analyses, The PA-l vehicle properties and trajectory
parameters from the best estimated trajectory (BET) were used to initialize the simulation shortly after drogue
parachute deployment. Approximately four seconds offlight were simulated, providing almost two cycles ofCM
oscillationspriortothe drogue parachuterelease.
The GEMASS simulation computes the pitch, cp, and yaw, ~, angles generated by the motion of the drogue
parachutes in time.
3. TrackingProgram AnalysisMethod
The two drogue parachutes were tracked using version 5.2 ofthe commercially available Trackeye program using a
1920 x 1080quicktime movie digitization ofthe 16 mm film. Aconversion from the timingon the film to the Best
EstimatedTrajectory(BET) was given as BET=Film Time + II:20:54.890. Drogue Itrackingwasstarted at BET
13:00:25.660and ended4.8 seconds laterat 13:00:30.465. Drogue2trackingwas startedat 13:00:26.150and ended
4.1 seconds later at 13:00:30.245. A correlation tracking method was used and no frames were skipped during the
tracking.
With the help of Rod Bogue of Dryden Flight Research Center, information about the camera and lens were
obtained from Gil Pendley, president ofVisual Instruments in Lancaster, CA who was involved in the acquisition
and installation ofthe camera. The lens on the camera was a 5.9 mm fl1.8 R7 type by Angenieux. Using known
dimensions for the 16 mm film and sprocket holes, the focal length was converted to 841.9 pixels for the digital
moviecopyand theprincipal pointwasdeterminedto beat830pixelsfrom the leftsideand 540pixelsfrom the top.
Documentation forthe lens provided aradial distortion curve. Followingthe Brown/Bouguet lens distortion model,
a polynomial was fit to the curve to getthe appropriate parameters to compensate for the moderate amount ofbarrel
distortion ofthis lens which increases to about 38 pixels (0.27 mm) near the edges ofthe frame. These parameters
wereentered into theTrackeyesoftware, and the distortion was removed from thetrackingdata.
Motion ofthe drogues on the image in pixels relative to the principal pointwere converted to pitch and yaw angles
by using the known focal length in pixels as the distance out ofthe image plane from the principal point to the
perspective center. As was stated earlier, the distance between the cameraposition and the drogue attach pointwas
small relative to the distance between the camera and the drogues, so the angles measured at the camera can be
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AmericanInstituteofAeronauticsand Astronautics
\.
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considered equivalent to the angles that would be observed at the attach point for the drogues. The motion ofthe
drogues relativetothe principal pointand perspectivecenter isshown in FigureX.
+X
(Left, Bottom)
PP (0,0, -f)
(Right, Top)
PC Perspective Center(0,0,0)
Figure6: Motion ofDroguesUsingTrackeyeSoftware.
B. l09-CD VerticalSpin TunnelAnalysis
Results from the LaRC Vertical Spin Tunnel Test 109-CD were also compared with GEMASS simulation results
using the Apollo drogue damping model. Wind tunnel data with 1- and 2- drogue parachutes were obtained.4 The
wind tunnel data was scaledto full-scale values which were used for the comparison with the GEMASS results. C
A
and CN simulation values for the CM were based on wind tunnel data from test 82-CD and the Cm and Cm values
q
were basedontest 1l7-CD. Slightadjustments to the drogue parachute attach pointwere required to obtain the trim
angleofattackobserved in the test.
IV. Results ofAnalysis
A. Orion PA-l Free-FlightTestAnalysis
The results for the pitch and yawangles usingthe threeanalysis methods for the 700 frames when the drogues were
in view are presented in tabularform in Appendix A. The minimum and maximum values for each analysis method
are highlighted in yellow and green, respectively, for the pitch and yaw angles. Figure 7 illustrates the comparison
betweenthethreeanalysis methods.
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American InstituteofAeronauticsand Astronautics