Direct-Entry, Aerobraking, and Lifting Aerocapture for Human-Rated

Lunar Return Vehicles

Stephen A. WhitmoreAssistant Professor

• Work funded by NASA Contract # NND05AC01P

Benjamin M. Andersen Patrick R. Jolley

Graduate Research Assistants

Daniel W. BanksAerospace Engineer, Aerodynamics

Branch, NASA Dryden Flight Research Center,

Edwards, CA

Summary

• Project Background– Return from the Moon

• Earth Intercept Options• Candidate Vehicles

– Aerodynamic Models– Heating Models

• Simulation– Trajectories– Results

• Individual Research Topics– Flapsule Design– Aero Assist

A New Vision for Space Exploration…

• With President Bush’s Jan 14, 2004 announcement of the Vision for U.S. Space Exploration, NASA has formed a new Exploration Systems Enterprise charged with expanding human robotic exploration of the moon, Mars, and other solar system destinations.

• Sets vision for exploration as national policy

“Return to the Moon”

• Center piece of this new exploration vision is the development of a Crew Exploration Vehicle (CEV) to act as a part of a “System of Systems” to enable space travel beyond low earth orbit.

CEV Re-Entry

• Return from the Moon presents a Very Hostile EnvironmentWith extremely high energy levels that must be dissipated

LunarReturnHohmann Orbit

• 10,000 kg Lunar-returnSpacecraft must dissipate more than 300,000 MJ of energy justto capture into low earth orbit

• Energy of Lunar returnTransfer orbit is

~190-200% of a LEO orbit

Earth Intercept Options

“Direct Entry”

“Aero Braking”How do you get rid of the excess energy?

“Propulsive Braking”

“Lifting Aero-Assist”

…. Use Drag & Lift

• A high-level mission analysis to suggest configurations that are most advantageous for accomplishing the CEV mission.

•What kind of vehicle does it take?

Purpose of Research

Candidate CEV Shapes• Maximum lateraldimension <5.5 metersfor CLV Compatibility

• Assumed totalmass < 10,000 kg

• Represent elementsof a continuumof shapes ranging from simplecapsule tolifting body

• Assumes parachuterecovery and landingsystem

Comparison Metrics• Volumetric Efficiency

• Peak Deceleration During Reentry

• Peak Dynamic Pressure During Reentry

• Available Downrange During Reentry

• Available Cross Range During Reentry

• Vehicle Handling Qualities and Controllability

• Temperatures and Heat Load

• Technology Readiness Level

• Each of the4 shapes are scoredwith respect to eachmetric, 1 beingbest, 4 being worst,low total score wins

Re-Entry G’s(Load Example)

10

8

6

4

2

1

ReE

ntry

G L

oads

Lift to Drag Ratio0.5 1 1.5 2 2.5

LEO Return

Lunar Return

De-Conditioned Crew Load Limit, Reclined (ref. NASA-STD-3000)

De-Conditioned Crew Load Limit, Upright (injured/sick, reclined)

Direct Entry Lunar Return

Aerodynamic Models• Existing 6-DOF Aero- data base used for HL-20• Biconic and Capsule 6-DOF data bases generated using

Incidence angle techniquesi) Modified Newtonian flow for stagnation regionii) Taylor-Maccol (tangent cone) for 3-D conical sectionsiii) Oblique Shock wave (tangent wedge) used for

2-D surfaces (flaps, flattened biconic section)iv) 2-D Prandtl-Meyer expansion based on local incidence

used for surface element with incidence angle > 90o

x, meters

Trim Flap

Aerodynamic�Center

Center of�Gravity

HL-20 Aerodynamics

a) Effect of Symmetric Elevon and Body Flap deflections�on Pitching Moment�Coefficient

Minimum trim α

Maximum trim α

Δ +Δ = -30°EL

Δ +Δ = -15° EL

Δ +Δ = 0°EL

Δ +Δ = 15°EL

Δ +Δ = 30°EL

Legend:

BF

BF

BF

BF

BF

b) HL-20 Trim Lift, Drag Coeffient and Lift-to-Drag Ratio��

Trim Drag CoefficientLegend:

Trim Lift CoefficientTrim L/D Ratio

HL-20:- Limited Trim α from 0° to 29°- L/Dmax ~1.24

Biconic Aerodynamics

Δ = -15°BF

Δ = 0°BF

Δ = 15°BF

Δ = 30°BF

Δ = 45°BF

Legend:

a) Effect of Symmetric Body Flap on Biconic Pitching Moment Coefficient

minimum trim α

maximum trim α Δ = -15°BF

Δ = 5°BF

Δ = 15°BF

Δ = 30°BF

Δ = 45°BF

Legend:

Δ = -10°BF

Δ = -5°BF

Δ = 0°BF

Δ = 10°BF

Δ = 0°BF

Δ = 45°BF

Δ = -15°BFDynamically

Unstable

b) Flattened Biconic Trim Lift, Drag Coeffient and Lift-to-Drag Ratio�

Trim Drag CoefficientLegend:

Trim Lift CoefficientTrim L/D Ratio

Biconic:- Trim α from -16° to 51°- L/Dmax ~0.70- Unstable at some conditions- “Hyperstable” at high α

Capsule Aerodynamics

b) Longitudinal Coefficients as Function of Vertical Cg Placement

Trim Drag CoefficientLegend:

Trim Lift CoefficientTrim L/D Ratio

a) Effect of vertical CG placement on trim angle-of-attack

V∞

V∞

Drag

−αDrag

Lift

V∞α Drag

-LiftVertical CG below Moment center

Vertical CG at Moment center

Vertical CG above Moment center

Capsule (no flaps):- Trim α up to -24°- L/Dmax ~0.39- Fixed trim angle of attack- Laterally unstable at high α

Capsule (with flaps):- Flaps allow trim a up to -28º- L/Dmax ~ 0.41- Vertical cg statically stable

Aero-Heating Models (cont’d)

• Nosecap Skin Modeled as simple Lumped-mass system• Simple Ablative Model used for Nosecap Region• Stagnation Heating calculations performed using Fay-Riddel Method with empirical incidence angle corrections and real-gas table lookups

twall

Αwall

RCC skin

FRSI TPS

Interior Wall

Ablative (Avcoat) Coating

tRCC

tAvcoat

RCC

Avcoat

FRCI Tiles

Aero-Heating Models (cont’d)

• Heating Sources Modeled:

twall

Αwall

RCC skin

FRSI TPS

Interior Wall

Ablative (Avcoat) Coating

tRCC

tAvcoat

RCC

Avcoat

FRCI Tiles

In-Flux1) Stagnation Heating from High Speed External Flow2) Radiation Heating from High Speed External Flow3) Solar Radiation Heating … negligible

Out-Flux4) Back Radiation from Nose-cap Surface5) Passive Nosecap Cooling (Ablatives)6) Circumferential Heat Conduction along Nosecap

(incidence angle correction factor)7) Thermal Conduction by the FRSI Blankets …. negligible

Non-catalytic wall

Simulation Model• Interactive 3-DOF Simulation (USU) and 6-DOF PilotedSimulations (DFRC) used to perform reentry analysis

Sample Trajectories: HL-20Legend:

Instantaneous Perigee Altitude, kmSpacecraft Altitude, km

Instantaneous Apogee Altitude, km

Initial Lunar Transfer �Orbit Apogee

Atmospheric�Interface

Initial Lunar Transfer �Orbit Perigee

Constant Altitude �Inverted Flight

Drag Reduces�Instantaneous Orbit�

Size

Vehicle Rolls Upright

Orbit Perigee "Collapses"�(Earth capture)

Apogee of Capture OrbitAtmospheric "Skip"

Final Reentry

Sample Trajectories: BiconicLegend:

Instantaneous Perigee Altitude, kmSpacecraft Altitude, km

Instantaneous Apogee Altitude, kmInitial Lunar Transfer �

Orbit Apogee

Atmospheric�Interface

Constant Altitude �Inverted Flight

Drag Reduces�Instantaneous Orbit�

Size

Vehicle Rolls Upright

Orbit Perigee "Collapses"�(Earth capture)

Apogee of Capture Orbit

Atmospheric "Skip"

Final Reentry

Sample Trajectories: FlapsuleLegend:

Spacecraft Altitude, km

Instantaneous Apogee Altitude, km

Angle-of-Attack, deg.

Instantaneous Perigee Altitude, km

Atmospheric�Interface

Orbit Perigee "Collapses"�(Earth capture)

Apogee of Capture Orbit

Atmospheric "Skip"

Final Reentry

Angle-of-Attack

Sample Trajectories: Flapsule (cont’d)

Atmospheric Interface

Final Reentry

Crossrange on Landing

Comparison Metrics (Revisited)

• 1) Volumetric Efficiency• 2) Peak Deceleration During Reentry • 3) Peak Dynamic Pressure During Reentry• 4) Available Downrange During Reentry

• 5) Available Cross Range During Reentry• 6) Vehicle Handling Qualities and Controllability• 7) Stagnation Point Heating and Temperatures • 8) Technology Readiness Level

Comparison Metrics (Revisited)

Trade Study Conclusions:

• Surprisingly, capsule with trim flaps ranks equal to far more complex HL-20 Airframe

• Biconic shows no advantage when compared to capsule with trim flaps

• Capsule with out flaps cannot meet NASA STD-3000 g-levels for sick or injured astronaut

• Capsule with flaps capable of both direct and aerocapture returns from moon

• All configurations require ablatives for initial earth capture phase

Future Study: Benjamin Andersen• Flapsule detailed analysis• CFD to improve accuracy

– Aerodynamics– Flap interactions– Flap hinge moments

• Heat management on flaps• Mass tradeoffs vs. RCS• Grid search for trajectories• Static stability analysis

Future Study: Patrick Jolley• Create Aerodynamic Database for

Waveriders• Plane Changes Using Aero Assist• Unpredictable Reconnaissance• Orbital Stabilization Using

Propulsive Energy

Step 3: Transfer Back to Original Orbital Altitude

Step 1: Retro Burn Step 1: Plane Change

Spacecraft Altitude, kmO

rbit

Dec

ay R

ate,

km

/hr

Waverider Concept

Image Courtesy of www.space-rockets.com

Questions?

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