The proposed manned Mars mission will need to be as weight efficient as possible. A way of lowering the weight of the vehicle by using aeroassist braking instead of retro-rockets to slow a craft once it reaches its destination is discussed. The two vehicles studied are a small vehicle similar in size to the Mars Rover Sample Return (MRSR) vehicle and a larger vehicle similar in size to a six-person Manned Mars Mission (MMM) vehicle. Simulated entries were made using various coefficients of lift (C sub L), coefficients of drag (C sub D), and lift-to-drag ratios (L/D). A range of acceptable flight path angles with their corresponding bank angle profiles was found for each case studied. These ranges were then compared, and the results are reported here. The sensitivity of velocity and acceleration to changes in flight path angle and bank angle is also included to indicate potential problem areas for guidance and navigation system design

Lee, Mary C.

Suit, William T.

English

NASA Technical Reports Server

NASA Technical Memorandum 101607
PRELIMINARY INVESTIGATION OF PARAMETER
SENSITIVITIES FOR ATMOSPHERIC ENTRY AND
AEROBRAKING AT MARS
(NASA-I _- IJl _.q7) PO_LiMINAPY INVr STIGATIPN
_F OA_,AMkTL:_ c t,!S!TIVTTE_S _u_ AT_,J_PLIL_IC
CSCL ?2 '_
N,_0-1 rob5 7
Mary C. Lee and
William T. Suit
September 1989
National Aeronautics and
Space Administration
Langley Research Center
Hampton, Virginia 23665-5225
https://ntrs.nasa.gov/search.jsp?R=19900008351 2020-03-19T23:56:46+00:00Z

ABSTRACq"
The proposed manned Mars mission will need to be as weight efficient as possible. This
paper will discuss one way of lowering the weight of the vehicle by using aeroassist braking
instead of retro-rockets to slow a craft once it reaches its destination. The two vehicles studied are
a small vehicle similar in size to the Mars Rover Sample Return (MRSR) vehicle and a larger
vehicle similar in size to a six person Manned Mars Mission (MMM) vehicle. Simulated entries
were made using various coefficients of lift (CL), coefficients of drag (CD), and lift-to-drag ratios
(L/D). A range of acceptable flight path angles with their corresponding bank angle profiles was
found for each case studied. These ranges were then compared, and the results are reported here.
The sensitivity of velocity and acceleration to changes in flight path angle and bank angle is also
included to indicate potential problem areas for guidance and navigation system design.
INTRODUCTION
In anticipation of a manned Mars mission as well as a Mars sample return mission, there
has been much research done and many papers written on aeroassist braking in the Earth's
atmosphere (reference 1). However, the return to Earth is only half of the trip. First, we must get
to Mars and achieve an orbit there. In order to save valuable weight, aeroassist braking will be
used to slow the craft at Mars, just as it will at Earth.
Aeroassist braking involves using the atmosphere of a planet to decelerate a craft instead of
using retro-rockets. The craft enters the atmosphere and uses the air particles to deplete its kinetic
energy, slowing the craft to a velocity that will allow orbital capture (reference 2).
The actual configuration for the aerobrake for a manned Mars mission is still being
investigated, so a range of possible vehicles was considered. Within the range of ballistic
coefficients covered in the paper a range of aerobrake sizes, weights, and L/D ratios were
considered. The purpose of this paper is to present the results of a Mars entry study using various
combinations of vehicle parameters. The study will present combinations of initial flight path
angles and bank angles required for capture at Mars. Entry windows and relative sensitivities for
various vehicle combinations will also be shown.
A
ASM
CD
EL
hpl
hp2
I_/D
M
VI
SYMBOLS
vehicle reference area, _uare meters
acceleration, meters/sec/sec
drag coefficient
lift coefficient
first pass perigee altitude, nautical miles
second pass perigee altitude, nautical miles
lift-to-drag ratio
mass, kilograms
inertial velocity, meters/sec
PRECEDING PAGE BLANK NOT FILMED
Vl
bank angle, degrees
initial flight path angle, degrees
AV change in velocity, meters/sec
ALTITO
ASMG
BNKANG
VELI
SYMBOLS FOR FIGURES
altitude, meters
acceleration, "g" units
bank angle, degrees
velocity, meters/sec
APPROACH
The studies conducted in this paper were made using a software package known as the
Program to Optimize Simulated Trajectories (POST). This program can be used to determine initial
parameters and control parameters throughout a trajectory to accomplish stated mission objectives.
For this study, all simulated entries consist of three steps, regardless of vehicle size or I_/13 ratio.
First, the vehicle enters the atmosphere at 300 km with an entry flight path angle determined by
POST. The aerodynamic forces on the vehicle are small until 125 km, however, atmospheric data
were available up to 300 km and so the problem was started there. Next, the program calculates a
set of bank angles that should result in capture. Third, the craft's final trajectory is achieved. This
trajectory can be hyperbolic, elliptical with eventual impact, elliptical with capture, or impact on the
first pass. The trajectories discussed here are either elliptical with eventual impact or elliptical with
capture. Eventual impact means that the program predicted impact on the second pass, but
achieved capture on the first pass. To correct this problem of impact, slight thrust can be added at
some point in the trajectory to give the needed boost to a higher orbit. This is another point for
additional study and will not be discussed to any great extent within this paper.
It can be observed that the individual bank angles that result in capture do not occur at
regular time intervals. The intervals were determined by looking at plots of the profiles and
decreasing the number of data points by combining adjacent times that showed little to no change
compared with one another.
A vehicle smaller than those proposed for a manned Mars mission was used in the
beginning of the study for two reasons. First, to confirm that the program would run correctly,
data from the program were checked with data available from other sources. (The second reason
was to gather data that might be used for a lander vehicle deployed from the larger manned
vehicle.) The physical and aerodynamic characteristics used for the small vehicle are given in
Table 1. Runs were made for L/D equal to 1.5, 1.0, and .5 with CD = 2.
Once the smaller vehicle runs were completed, a larger vehicle representative of a manned
Mars mission (MMM) vehicle which could carry a crew of five to seven members and the supplies
needed for the mission was investigated. Two "large" vehicles were considered. The physical and
aerodynamic characteristics of the large vehicle are presented in Table 2. The first runs of the
MMM vehicle were made with an L/D of 1.0 where CL = CD = 2. Then, the CL was changed to 1
as with the small vehicle, and runs with L/D = 0.5 were made.
SincetheViking probesreturnedtheirdataon theMartianatmosphere,severaldifferent
atmospheremodelshavebeendeveloped.Fortherunsdescribedabove,oneof theseatmospheres
(atmosphere1)waschosenandput into tablesthatweresuitableto theprogram(Table3). Near
theendof theprojecttime,whentherunswith atmosphere1werecompleted,a secondatmosphere
(atmosphere2) wastabulatedandintroducedinto theprogram.Thepurposeof thisswitchwasto
determineif therewasanysignificantchangein theacceptableflight pathanglewindowsfrom
thosedeterminedusingatmosphere1.
RESULTSAND DISCUSSION
Initially Marsentryrunsweremadetrying toachievecapturewith asinglefixedbank
angle.Theproblemwasextremelysensitiveto changesin initial flight pathangleandbankangle
andnocombinationof thetwoangleswasfoundthatwouldresultin capture.Changesof the
orderof .0001° wouldresultin eitherimpactor skip-out.At thispoint, themultiplebankangle
approachwastried. Theproblemwassplit into timeslotsandPOSTwasaskedto selectthebank
anglesthatwouldresultin acapturetrajectory.Theentryflight pathangleandbankanglesare
givenin Table4.
To determinetheflight-path-anglewindowthatwouldresultin capture,two setsof runs
were made: one set to detem'_ine the least negative entry flight path angle and a second set to
determine the most negative flight path angle possible. The difference in these entry-flight-path
angles gave the entry-flight-path-angle window.
For each of these maximum and minimum flight path angles, a bank angle profile that
would result in capture was determined for every vehicle. In addition to ensuring capture, these
runs had perigee altitudes greater than 30 km. In all of the maximum initial flight path angle (least
negative) cases and in many of the minimum flight path angle (most negative) cases the second
pass orbit also would have an acceptable perigee altitude. The results of these runs are given in
Table 4 and typical time histories are shown in figures 1 and 2. Generally, the maximum flight
path angle runs stayed higher in the atmosphere and remained in the atmosphere for longer periods
of time than the minimum flight path angle runs which plunged deeper into the atmosphere and
usually reached their minimum altitude within the first 200 seconds of the run (figure 2). From
Table 4 and figure 1, the bank angles for the maximum flight path angle runs are seen to tend
toward lift down (full lift down = 180 °) in order to keep the craft in the dense atmosphere long
enough to decelerate to capture velocity. Conversely, the minimum flight path angle runs tended
toward lift up (full lift up=0 °) to pull the craft out of the more dense atmosphere before too much
energy was lost, causing the craft to crash into the planet's surface.
In general for the vehicles investigated the entry flight path window was about 1.5 °
(figure 3). At larger L/D's the vehicles with a smaller M/CD*A tended to have a slightly smaller
window (Table 4), while at L/D=.5 no significant effect of M/CD*A was seen. Also, for a given
M/CD*A the entries had a greater energy loss as I.]D decreased. The perigee altitudes showed no
consistent trends with L/D or M/CD*A. However, the bank angle profiles were affected by
changes in both M/CD*A and L/D (figures I & 2). The changes were especially noticeable with
the minimum flight path angle runs (figure 1 & Table 4). Maximum flight path angle entries using
vehicles with higher I_,/D ratios and larger M/CD*A values tended to deviate more from full lift
down and these trends were stronger with L/D ratios of .5 where the entries were predominantly
lift down throughout the run (figure 1 & Table 4). The significant point from these runs was that,
given a 1/2 ° window in the middle of the extremes, a set of bank angles could be found so that
capturewaspossible.This impliesthattheentrycorridoris wideenoughsothatguidancesystems
thatwouldresultin capturecanbedesignedfor therangeof vehiclesconsideredin thisstudy.
Table5 showsthesensitivityof varioustrajectoryparametersto changesin flight path
anglefor agivensetof bankangles.Thesensitivitieswerenotshownfor all runssincethetrends
andvaluesseencanbeillustratedusingthetablesgiven. Thetableshowsthatif thebankangles
arefixedfor aparticularentry trajectorythenverysmallvariationsof entry flight pathanglehavea
significanteffecton thetrajectory.A secondobservationis thatthetypesof trajectoriesflown can
influencethesensitivitytoentry flightpathangle.Trajectoriesthatstayedhigherin theatmosphere
duringtheinitial partof theentrytendedto bemoresensitivetochangesin initial flight pathangle
thanthosetrajectoriesthatinitially penetratedeeperinto theatmosphere.Theimplicationis that
for afixed bankanglesequencetheentry/capturetrajectorywasmoresensitiveto changesin initial
flight pathangleerrorwhenthebrakingwasovera longerdurationthanwastruefor trajectories
thatflew higherin theatmosphere.Themessagefor designersof guidancesystemsis thatbraking
higherin theatmospherewhere"g" loadsarelessandheatingis lesscouldrequiremoreprecise
guidancesystems.Thisproblemmustbeexaminedfurther.
Table5alsoshowsthesensitivityof varioustrajectoryparametersto thedifferentbank
anglesin thebankanglesequence.As expectedthegreatestsensitivityoccurredwhenthevehicle
wasdeepestin theatmosphereandtheforceson thevehicleweregreatest(figure 1& Table5). In
mostcasesthetrajectoryparameterswerenotparticularlysensitiveto bankanglechanges.
However,sincetheminimumaltitude,"g" load,andheatratecouldbealteredbychangingthe
bankangles,furtherinvestigationof theeffectof theproblemformulationon thebankangle
sequenceshouldbeconducted.
To determinetheeffectof flying throughadifferentMartianatmosphererunsweremade
usingasecondatmosphericmodel. Atmosphere2 is givenin Table3 andwasusedduringthe
designof theViking lander.Datareceivedfrom Viking indicatedthatthisatmospherewascloseto
thatof Marsat severalaltitudes.Toexaminetheeffectof anotheratmosphere,smallvehicle2 and
largevehicle2 wereused.Bothvehicleswereassumedto haveanL/D = 1andCD = 2. The
resultsareshownin Tables6 & 7 andfigure4. Theinitial flight-path-anglewindowandthe
sensitivitiesweresimilar to thoseseenwith thepreviousatmosphere.Forthemaximumflight path
angleruns,the initial bankanglerunsweredifferentsinceatmosphere2 wasmoredenseathigher
altitudes(figure4). However,thealtitudeprofile wasnotsignificantlydifferentwhenthevehicle
flew throughatmosphere2.
CONCLUSIONS
Forthevehiclesinvestigated,entry flight-path-anglewindowsinexcessof 1° werefound.
This includedvehicleswitha M/CD*A (representativeof asix-personMarsmissionvehicle)with
a 15.24m (50ft) diameteraeroshell.While thiswindowshouldoffer areasonabletargetfor a
Martianaerocapture,thestudyalsoindicatedthatthecapturetrajectorieswereverysensitiveto
errorsin theentryflight pathangle.Trajectoriesflying higherin theatmosphereseemedtohavea
greatersensitivityto errorsthanthoseflying lowerin theatmosphere.As expected,thesensitivity
to bankangleerrorwasgreatestin theregionwheretheaerodynamicforcesweregreatest.
However,theprojectedstateerrorswerenotsolargeasto imply thata bankangle
guidance/controlsystemcouldnotbeflown.
A limitednumberof runsweremadewith asecondmodelof theMartianatmosphere.
Theserunsshowedonly minimaldifferencesfromthoserunsmadeusingtheoriginalatmospheric
model.
,,
,
SUGGESTED STUDIES
The current study looked at vehicles with four different ballistic coefficients (M/CD*A).
However, these vehicles all had the same drag coefficient and were scaled to meet various
weight or L/D combinations. Other vehicle types, blunter or more streamlined, should be
investigated.
Only two Martian atmospheres were considered, one of these for only a limited number of
runs. Additional atmospheric models need to be included in future studies.
One check on the AV required to get an acceptable second pass orbit was made. The AV
required to get an acceptable second pass was small and similar calculations need to be made
for any runs that did not have an acceptable second pass orbit.
°.
REFERENCES
Walberg, Gerald D.: A Review of Aeroassisted Orbital Transfer. AIAA Paper No. 82-1378,
AIAA 9th Atmospheric Flight Mechanics Conference, San Diego, CA, August 1982.
Walberg, Gerald D.: A Review of Aerobraking forMars Missions. IAF Paper No.
IAF-88-196, 39th Congress of theInternationalAstronauticalFederation,Bangalore,India,
October 1988.
0
TABLE I VEIiiCI,E CItARACTERISTICS
SMAI,I, VElllCI.E
Vehicle !
Vehicle 2
kg
M -- 5(X) A = 16n?,
M = 16,000 k g
--2
M ---32,(XX) kg
, A = 16n?,Cl) = 2
TABLE 2
Vehicle I
Vehicle 2
VEIIICLE CllARA('TERISTICS
I,AR(iE VEIIlCI,E
kg
M_ .= 622 A = 182n?,(:t_ _' ('D
M = 226,378 kg
kg
_M___- 1,147 ^ = 182.f, co
M -- 4 !7,560 kg
--2
=2
i.°oo_°°°o°°o°o°
rj_
R _ R _
t_ i,o
_ R _ R _ R
0 0 0 0
0
9
0 0 0 0
iO
I_ _0 0
Oi ,_,
0 0 0 0
II
0
oO
I--- I_ I% I%
O_ O_ O_ O_
O_ _1 ,
O O O O
ol
O_
0 0 0
O_
0
13
°° t_ °° _ oo _ oo
_-°, t_ oo _ _,o t_ oo
U"J
_ ® o _,
i
Jl il II IJ
I_ , I_ , I_ I_ "
i'--4 _I i--4
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, , ,Po m,m.
0 0 0 0
0 e 0 e 0
1.1
0 0
M
Q
0 0
U _ U
0 0
0 0
0 0
{D
0
o
o
I.",
p oo p oo p oo p oo
_ _ o
co
17
oo _ oo _ oo _ oo
° . .
, _
0 0 0 0
gHKflllt;
tiLT I TO
ASIIG
XIO 5
3--
A LT [ TO,
METERS
-i
309 --
\
i
t
\
I
p._ .... ._,.....
I
BNKANG,
-
DE(;
1_1_ ...............
7--
!
/
/
I
I
/
' t
#
#
/
/i
/
........ 7Z-
o
/
T IHF., SEC
(_,) Large Vehicle 2
M/CDA = 1147 LIt} = 1
Figure 1. Time llistories of Bankangle, Altitude, and Acceleration'for a
Minimum Flight Path Angle Martian Entry.
19
XIO 5
4--
3--
ASMG, _
"G" UNITS
2--
l--
g--
BNKRNG
ASMG
ALTITO
_
6--
ALTITO) _
METERS -_
4--i
2--
211tl --
15_
BNKANG,
DEG
51)
B
w
l) i'
I
' i)
)
)
)
i
mf I /
"_ I" ' V
/',, I
• s r*
/ I """
/
,/ / \
I
e
je
J ,
s
s ¢
l
L
I
J
#
#
s'
I
i
#
#
I
a
TIME, SEC
{b} l.arg(: Vuhicle I
M/CDA, 622 LID = 1.0
Figure 1. Continued
_ASMG,
"G" UNITS
_--,
I
0 ....
BHKANG
ALTIT0
ASMG
X10 S
5--
4---
3
ALTITO,
MF.TF.I_._ +-
-
2--
_+
1
-+
0 .....
\
)
/
,/
/
,/
I I I I ! I I
5BB 6BB
TIME, SEC
(c) Large Vehicle 1
M/CDA = 622 L/D = .S
Figure I. Concluded
21
ASMG,
"G" UNITS
1-
BHKANli
tiLT ! TO
ftSMI;
XI_ 5
A H" I TO,
bfl2TERS
--m
15g
BNKANG,
L)EG
(a) I.arge Vehicle 2
M/CDA = 1147 L/D = 1
Figure 2. 'time ilistories for B_mkangle, Altitude, and Acc]eration
for a Maximum Flight Path Angle Martian l'ntry.
22
2gg
ISg
_NKAN(;
I)EG
lug
5g
J
t
I
I
/
,J
t _
I
e
s
lgBg
/
/' , ,
" \ : •
1 1
g 21_tl 4tlg 6UI,I
TIME, SEC
888
(b) l,avt_e V,:hici_ I
M/CDA = 022 , t,/l) = I
Figure 2. {'ontinued
23
_B5 --n
P.8---
1.5 m
A.SMG._
"G" UNITS
ft.5
ft.0 ---_
BNKAN_
ALTITO
ASMG
4--
3--
ALTITO, _
blETERS -
fl
\
TIME, SI'C
40ff 600 888
(c) Large Vehicle 1
M/CI)A = 622 L/D = .S
Figure 2. Concluded
?-1
fl
O
,,.-i
II
,..-1
[]
ID
E
i
Or"
,J1
II
rl
II
U
E]Q
i
I_I@
i
t_
el
I
C_
0
or"
I
t/l
O
i--i
II
U
.+-I
>,
C
tn
0
I-+
0
'+I-i
?+
C
._I
°_I
r,+
25
BNKANG,
BEG
IL48
_0
I
I ............... I .................... I ................. 7
LI qU8 60_ BU_ 10UH
'I'IMI" , SEC
(a) Bankangl_
Figure 4. Time llistories of btars Entry for a V_hicle with I./1) = 1 and M/CDA = 1147
(l.argt: V_hiclo 2) using two atiaio.-;ph_:ric mode:Is.
26
Xl_ _
ALTITO,
METERS 1
1
0
\
\
\
,//4
- /'--
4tl_
I - "
.... J
......... | ......
UU_ I_UU
T 1Hl_, SI-C
(b) Altitude
Figure 4. Continued
27
VELI, -
H/SEC -
ATRDSPHERE 1
I
• ATMOSPHERE 2
TIHE, SEC
(c) Velocity
Figure 4. Concluded
28
.,_,.,0._,=_ Report Documentation Page
Spa_/_W_icraion
I. Report No. 2. Government Accession No 3. Recipients Catalog No.
NASA TM- 101607
4. Title and Subtitle
Preliminary Investigation of Parameter Sensitivities for Atmospheric
Entry and Aerobraking at Mars
5. Report Date
September 1989
6. Performing Organization Code
7. Author(s)
Mary C. Lee and William T. Suit
9. Performing Organization Name and Address
NASA Langley Research Center
Hampton, VA 23665-5225
12. Sponsoring Agency Name and Address
National Aeronautics and Space Administration
Washington, DC 20546-0001
8. Performing Organization Report No.
10. Work Unit No.
506-46-21-01
11, Contract or Grant No.
13. Type of Report and Period Covered
Technical Memorandum
14+ Sponsoring Agency Code
15. Supplementary Notes
16. Abstract
The proposed manned Mars mission will need to be as weight efficient as possible. This paper will
discuss one way of lowering the weight of the vehicle by using aeroassist braking instead of retro-rockets to
slow a craft once it reaches its destination. The two vehicles studied are a small vehicle similar in size to the
Mars Rover Sample Return (MRSR) vehicle and a larger vehicle similar in size to a six-person Manned
Mars Mission (MMM) vehicle. Simulated entries were made using various coefficients of lift (CI), coef-
ficients of drag (C_, and lift-to-drag ratios (L/D). A range of acceptable flight path angles with ttieir corre-
sponding bank angle profiles was found for each case studied. These ranges were then compared, and the
results are reported here. The sensitivity of velocity and acceleration to changes in flight path angle and bank
angle is also included to indicate potential problem areas for guidance and navigation system design.
17. Key Words (Suggested by Author(s))
Spacecraft Guidance
Aeroassist
Spacecraft Maneuvers
Manned Mars Mission
18. Distribution Statement
Unclassified - Unlimited
Subject Category 18
19. Security Classit (of this report) 20. Security Classif. (of this page) 21. No. of pages 22. Price
Unclassified Unclassified 29 A03
NASA FORM 1626 OCT 86 For sale by the National Technical Information Service, Springfield, VA 22161-2171



Preliminary investigation of parameter sensitivities for atmospheric entry and aerobraking at Mars

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