Michael Skeen Ryan Starkey University of Colorado at Boulder

CONCEPTUAL MODELING AND ANALYSIS OF DRAG-AUGMENTED SUPERSONIC

RETROPROPULSION FOR APPLICATION IN MARS ENTRY, DESCENT, AND LANDING

VEHICLESMichael SkeenRyan Starkey

University of Colorado at BoulderDepartment of Aerospace Engineering Sciences

10th International Planetary Probe WorkshopCross-Cutting Technologies IV Session

San Jose, CAJune 21, 2013

Overview

• Introduction and Background◦ Problem Statement◦ Drag-Augmented Supersonic Retropropulsion

• Aerodynamic Modeling◦ Ballistic Coefficient Comparison◦ Drag Coefficient Modeling◦ Validation and Sensitivity Analysis

• Trajectory Modeling◦ Drag-Augmented SRP Operation◦ Hybrid Decelerator Systems

• Conclusions and Future WorkM. Skeen 21 June 2013IPPW 102

Mass LimitationsPr

oble

m S

tate

men

t

Viking Mars Pathfinder

Mars Exploration

RoversPhoenix

Mars Science

LaboratoryEntry Mass (kg) 992 584 830 602 3300

Touchdown Mass (kg) 590 360 539 364 1665Payload Mass (kg) 244 92 173 167 899

Aeroshell diameter (m) 3.5 2.65 2.65 2.65 4.5Ballistic Coefficient (kg/m2) 64 63 94 65 135

M. Skeen 21 June 2013IPPW 103

𝛽=𝑚

𝐶𝐷 𝐴

Supersonic Retropropulsion (SRP)Su

pers

onic

Dec

eler

ator

s

Central Nozzle Configuration CFD images: Bakhtian and Aftosmis, 2011

Flowfield sketch: Korzun, 2012

𝐶𝑇=h𝑇 𝑟𝑢𝑠𝑡𝑞∞ 𝐴

M. Skeen 21 June 20134 IPPW 10

Supersonic Retropropulsion (SRP)Su

pers

onic

Dec

eler

ator

s

Peripheral Nozzle Configuration

CFD images: Bakhtian and Aftosmis, 2011Flowfield sketches: Korzun, 2012

M. Skeen

𝐶𝑇=h𝑇 𝑟𝑢𝑠𝑡𝑞∞ 𝐴

21 June 2013IPPW 105

Drag TrendsSu

pers

onic

Dec

eler

ator

s

(Bakhtian and Aftosmis, 2011)

M. Skeen

𝐶𝐴=𝐹 𝐴

𝑞∞ 𝐴

High-Thrust SRP

Drag-Augmented SRP

𝑀 ∞=2

𝐹 𝐴=D+T


Ballistic Coefficient Comparison

• Ballistic coefficient including SRP

• What CD is required to match IAD ballistic coefficient?

• Solve for ◦ Drag augmentation ratio

Bal

listic

Coe

ffici

ent


60

55

50

45

40

35

30

25

20

15

60

55

50

45

40

35

30

25

20

1515

20

25

30

35

40

45

50

55

60

mSRP (kg)

mIA

D (kg)

0 500 1000 1500 2000 2500 3000

150

200

250

300

350

400

450

500

15

20

25

30

35

40

45

50

55

60CD,SRP/CD0

SRP vs. SIADsB

allis

tic C

oeffi

cien

t

𝛽𝑆𝑅𝑃=𝛽𝐼𝐴𝐷 = 1.5𝛽=𝑚

(𝐶¿¿𝐷+𝐶𝑇) 𝐴¿


Bakhtian and Aftosmis, 2011

Shock CascadesSu

pers

onic

Dec

eler

ator

s

Patm

P0

Isen

trop

ic

Normal Shock

P0

Isen

trop

ic

Patm

Oblique - Normal Shock Cascade

M. Skeen

4.0x

6.9x

P0

Isen

trop

ic

Patm

Oblique-Oblique-Normal Shock Cascade

Shock angle: 40°


Drag Model MethodologyA

erod

ynam

ic M

odel

ing

Shock structure (grey) caused by SRP plumes (orange). Coefficient of pressure shown on aeroshell surface. (Bakhtian and Aftosmis, 2011)

M. Skeen

Korzun, 2012

21 June 2013IPPW 1010

Pressure Model

1. Normal shock2. Accelerated flow near capsule periphery3. Oblique-normal shock cascade4. Oblique-oblique normal shock cascade5. Separated flow6. Nozzle exit flowAer

odyn

amic

Mod

elin

g

CFD (Bakhtian and Aftosmis, 2011) Pressure Model


𝐶𝐷=∫❑

❑

(𝑃 𝑓𝑟𝑜𝑛𝑡 /𝑃 ∞)𝑑 𝐴𝑥

12𝛾 𝑀∞

2 𝐴𝑥

+𝑃𝑏𝑎𝑐𝑘 /𝑃 ∞

12𝛾𝑀∞

2

11

0 5 10 15 20 25 30 35 401

1.1

1.2

1.3

1.4

1.5

1.6

1.7

1.8

1.9

Free Stream Mach Number

Dra

g C

oeffi

cien

t

SRP DragNo Thrust Drag

Drag Coefficient Model ResultsA

erod

ynam

ic M

odel

ing

+ 14%


Model ValidationA

erod

ynam

ic M

odel

ing

M∞ Method Source Source CD Predicted CD % Difference

4-Nozzle Configurations2 CFD [17] 1.092 1.295 18.59%4 CFD [17] 1.561 1.494 -4.30%6 CFD [17] 1.630 1.628 -0.12%12 CFD / Tunnel [21] 1.450 * † 1.327 -8.47%

3-Nozzle Configurations2 Wind Tunnel [13] 1.2 ⌂ 0.993 -17.23%2 Wind Tunnel [13] 0.7 ⌂ † 0.993 41.89%2 CFD [17] 1.345 1.295 -3.71%4 CFD [17] 1.633 1.494 -8.56%6 CFD [17] 1.625 1.628 0.22%8 CFD [17] 1.543 1.700 10.17%

* Nozzles placed at a radius of 55% of the aeroshell diameter.⌂ Nozzles places at a radius of 80% of the aeroshell diameter, cone half angle of 60°.† Thrust coefficient of 1.5.M. Skeen 21 June 2013IPPW 1013

Sensitivity Analysis – ON Flow Region Size

Aer

odyn

amic

Mod

elin

g


Trajectory ModelTr

ajec

tory

Mod

elin

g

• 3 degrees of freedom◦ Planar movement only

• Mars GRAM atmosphere◦ Time and location averaged

• MSL initial / parachute deployment conditions ◦ Ballistic trajectory reference (1135 kg)

M. Skeen

• Solver Target◦ Parachute deployment (q∞, M∞

conditions)◦ Iterate mass so parachute deploys

at 10 km altitude◦ Vehicle mass at parachute deploy

→ usable mass21 June 2013IPPW 1015

-30 -20 -10 0 10 20 301745

1750

1755

1760

1765

1770

1775

1780

1785

Drag Coefficient Change (%)

Max

imum

Mas

s at

Par

achu

te D

eplo

ymen

t (kg

)

Trajectory Model Sensitivity to Drag Coefficient

Drag Coefficient SensitivityTr

ajec

tory

Mod

elin

g 2.5 %

M. Skeen

• Mass has low sensitivity to drag coefficient changes• Does not take into account operation methodology

21 June 201316 IPPW 10

Peak Dynamic Pressure RegionTr

ajec

tory

Mod

elin

g

M. Skeen

0 2 4 6 8 10 12 14 16 18 200

10

20

30

40

50

60

70

80

90

100

Drag per unit Area (kN/m2)

Alti

tude

(km

)

Pathfinder SRP PotentialPathfinder Nominal TrajectoryViking SRP PotentialViking Nominal Trajectory

21 June 2013IPPW 1017

Drag-Augmented SRP ResultsTr

ajec

tory

Mod

elin

g

Maximum Mass: Constant SRP Operation• Entry: 4433 kg (+ 232%, +3098 kg)• ‘Dry’: 1786 kg (+34%, +451 kg)

M. Skeen

Baseline Vehicle• Entry: 1335 kg• ‘Dry’: 1335 kg

21 June 2013IPPW 1018

Drag-Augmented SRP Results (2)Tr

ajec

tory

Mod

elin

g

Maximum Mass: Constant SRP Operation• Entry: 4433 kg (+ 232%, +3098 kg)• ‘Dry’: 1786 kg (+34%, +451 kg)

SRP Operation Below 50 km• 98.8 % of mass performance


Constant Thrust TrajectoryTr

ajec

tory

Mod

elin

g

Maximum Mass: Constant SRP Operation • Entry: 6690 kg (+ 401%, +5355 kg)• ‘Dry’: 1431 kg (+7%, +96 kg)

or Dynamic Pressure Targeted Operation• Entry: 3289 kg → 65% less propellant• ‘Dry’: 1449 kg (+9%, +114 kg)


SRP-IAD HybridTr

ajec

tory

Mod

elin

g

Maximum Mass: Transition to IAD• Entry: 12947 kg (+ 870%, +11612 kg)• ‘Dry’: 10770 kg (+708%, +9435 kg)• ‘Dry’ Mass Fraction: 83%

M. Skeen

Baseline Vehicle• Entry: 1335 kg• ‘Dry’: 1335 kg• ‘Dry’ Mass Fraction: 100%

21 June 2013IPPW 1021

10 15 20 25 30 35 402000

3000

4000

5000

6000

7000

8000

9000

10000

11000

12000

13000

SRP Transition Altitude (km)

Ent

ry M

ass

(kg)

D = 14 mD = 17 mD = 20 mD = 23 m

10 15 20 25 30 35 402000

3000

4000

5000

6000

7000

8000

9000

10000

11000

12000

13000


Veh

icle

Mas

s at

Par

achu

te D

eplo

y (k

g)

D = 14 mD = 17 mD = 20 mD = 23 m

SummarySu

mm

ary

Aerodynamic Modeling• IAD systems provide lower ballistic coefficient• Drag coefficient model for drag-augmented SRP

◦ Analytic model + computational results◦ Drag coefficient can increase by 14%◦ Validation and sensitivity analysis

Trajectory Modeling• Ideal drag-augmented SRP increases ‘dry’ mass by 34%• Operation in maximum dynamic pressure regime critical to efficacy

◦ 65% savings in propellant for constant-thrust case• Hybrid decelerator systems take advantage of appropriate flight

regimes◦ SRP-IAD hybrid increases ‘dry’ mass by 708%


Future Work

SRP Modeling• Expand SRP aerodynamics database

◦ Experiment or CFD• Analytic or semi-analytic modeling of SRP shock structure• Correlation with thrust coefficient• Angle-of-attack model development• Asymmetric thrust operation

Systems Analysis• Sensitivity to additional performance parameters (CT, Isp, angle of

attack, entry conditions, aeroshell size, etc.)• Maneuvering flight analysis, landing uncertainty• Conceptual vehicle design (aeroshell design, thermal

environment, hardware system selection, component sizing, etc.)Sum

mar

y


Acknowledgements

• Dr. Ryan Starkey• Busemann Advanced Concepts Lab• CU Aerospace Engineering Department

◦ Funding support through TA and CA programs

• Student Organizing Committee• Student Scholarship Sponsors


Questions?

[email protected]

Pressure Model Assumptions

• Isentropic compression between shock structure and aeroshell• No ‘mixing’ of flow regions• Neglecting ablation, chemical reaction, boundary layer effects• Symmetric pressure distribution about each quadrant (symmetric in

thirds for 3 nozzle configurations)• Flow region sizes remain constant with all parameters• Pressure distribution corresponds to CT=1.5• Pressures vary radially in same manner as nominal capsule flow

structure• Flow is accelerated around nozzle exit• Oblique shock angle of 40°• Constant backshell pressure• Neglect flow turning through shock cascades• Steady state model

Aer

odyn

amic

Mod

elin

g


Grid Size SensitivityA

erod

ynam

ic M

odel

ing


Real Gas EffectsA

erod

ynam

ic M

odel

ing

1 2 3 4 5 6 7 8 9 100

50

100

150

200

250

300

350

400

450

Mach Number

P0/P

atm

Stepped , Normal Shock (NS)Stepped , Oblique-Normal Shock (ONS)Variable , Min T, NSVariable , Min T, ONSVariable , Max T, NSVariable , Max T, ONS


Sensitivity Analysis – Specific Heat Effects

Aer

odyn

amic

Mod

elin

g

2 4 6 8 10 12 14 16 18 20

1.4

1.6

1.8

2

2.2

2.4


Dra

g C

oeffi

cien

t

= 1.25 = 1.30 = 1.35 = 1.40

2 4 6 8 10 12 14 16 18 20

1.3

1.4

1.5

1.6

1.7

1.8

1.9

2

Free Stream Mach NumberD

rag

Coe

ffici

ent

2 = 1.15

2 = 1.20

2 = 1.25

2 = 1.30


Sensitivity Analysis – Shock Wave Angle

Aer

odyn

amic

Mod

elin

g


Sensitivity Analysis – Back Face Pressure

Aer

odyn

amic

Mod

elin

g

2 4 6 8 10 12 14 16 18 201

1.1

1.2

1.3

1.4

1.5

1.6

1.7

1.8

1.9

2


Dra

g C

oeffi

cien

t

Pback/Patm = 0

Pback/Patm = 0.2

Pback/Patm = 0.4

Pback/Patm = 0.6

Pback/Patm = 0.8

Pback/Patm = 1.0


Sensitivity Analysis – NS Flow Region Size

Aer

odyn

amic

Mod

elin

g

2 4 6 8 10 12 14 16 18 201.3

1.4

1.5

1.6

1.7

1.8

1.9

2


Dra

g C

oeffi

cien

t

Drag Coefficient for Changes in Normal Shock Flow Region Area

-40%-20%0%20%50%75%


Sensitivity Analysis – Accelerated Flow Region Size

Aer

odyn

amic

Mod

elin

g

2 4 6 8 10 12 14 16 18 201.1

1.2

1.3

1.4

1.5

1.6

1.7

1.8

1.9

2

2.1


Dra

g C

oeffi

cien

t

Drag Coefficient for Changes in Accelerated Flow Region Area

60%30%0%-30%-60%


Sensitivity Analysis – OON Flow Region Size

Aer

odyn

amic

Mod

elin

g

2 4 6 8 10 12 14 16 18 20

1.3

1.4

1.5

1.6

1.7

1.8

1.9

2

2.1


Dra

g C

oeffi

cien

t

Drag Coefficient for Changes in OON Cascade Flow Region Area

-100%-50%0%50%100%


Sensitivity Analysis – Separated Flow Region Size

Aer

odyn

amic

Mod

elin

g

2 4 6 8 10 12 14 16 18 20

1.3

1.4

1.5

1.6

1.7

1.8

1.9

2


Dra

g C

oeffi

cien

tDrag Coefficient for Changes in Separated Flow Region Area

-35%-20%0%20%40%


Sensitivity Analysis – Nozzle Exit Area

Aer

odyn

amic

Mod

elin

g

2 4 6 8 10 12 14 16 18 201.3

1.4

1.5

1.6

1.7

1.8

1.9

2


Dra

g C

oeffi

cien

tDrag Coefficient for Changes in Nozzle Exit Area

-75%-45%0%55%125%


Drag-Augmented SRP Results (3)Tr

ajec

tory

Mod

elin

g


SRP Propellant Mass

M. Skeen

Traj

ecto

ry M

odel

ing

21 June 201338 IPPW 10

SRP HybridTr

ajec

tory

Mod

elin

g

Drag-Augmented → High-Thrust

Maximum mass performance occurs for fully high-thrust SRP• Low ‘dry’ mass fraction

M. Skeen

10 15 20 25 30 35 400

5000

10000

15000

20000

25000

30000

35000


Ent

ry M

ass

(kg)

T = 100 kNT = 500 kNT = 1 MNT = 1.5 MN

10 15 20 25 30 35 40800

1000

1200

1400

1600

1800

2000

2200

2400

2600

2800

SRP Transition Altitude (km)V

ehic

le M

ass

at P

arac

hute

Dep

loy

(kg)

T = 100 kNT = 500 kNT = 1 MNT = 1.5 MN

21 June 201339 IPPW 10

SRP HybridTr

ajec

tory

Mod

elin

g

Maximum mass performance occurs for fully high-thrust SRP• Low ‘dry’ mass fraction

Drag-Augmented → High-Thrust


Documents

Michael Skeen Ryan Starkey University of Colorado at Boulder