National Aeronautics and Space Administration

www.nesc.nasa.gov

Applicability

Development of experimental techniques and CFD predictive 

capabilities to determine proper placement and orientation 

of RCS jet thrusters on hypersonic entry vehicles to minimize 

adverse RCS JI.

Historical JI Prediction Issues

Historically, the prediction of hypersonic entry RCS effectiveness 

and associated JIs with surrounding flowfields has been 

a challenging CFD problem. For example, during the bank 

maneuvers of the first space shuttle orbiter reentry, the rolling 

moment that occurred when the forward yaw thrusters were 

fired was less than expected, resulting in greater RCS fuel usage 

than anticipated. The cause of this discrepancy was attributed 

to improper scaling of wind tunnel derived RCS interaction 

correlations to the flight condition.1

 In a more recent example, 

CFD analyses of the RCS JI on the Mars Phoenix entry vehicle 

indicated the possibility of uncontrollable adverse JI, enough 

so that the project chose to not use the RCS during portions of 

the entry phase, increasing the landing footprint and the overall 

mission risk.2

The Mars Science Laboratory (MSL) mission was plagued by 

similar issues in the early design phases. The entry vehicle 

aerodynamics was based on a combination of experimental 

results, CFD calculations, and comparisons with estimates of

flight aerodynamics from previous Mars missions. Estimates of 

the RCS effectiveness and RCS JI with the aftbody flow-field 

were originally developed based primarily on CFD calculations, 

indicating the potential for large, undesirable RCS JI. Recommendations were made to change the RCS jet locations and 

orientations in an attempt to reduce plume impingement on 

the spacecraft, jet-to-jet plume interactions, and to minimize 

undesirable interaction torques. Given the uncertainties 

associated with the wake flow predictive capabilities of current 

CFD codes, a wind tunnel test was designed and executed in 

the Langley Research Center 31-Inch Mach 10 Wind Tunnel 

to provide experimental data for the new MSL RCS thruster 

configuration design.3

 This data served to provide validation 

results specific to MSL and, at the same time, the experimental 

test techniques developed would potentially be of benefit to other 

projects and programs employing blunt body entry aeroshell 

designs with aftbody RCS jet thrusters (e.g., Orion/Multi-Purpose 

Crew Vehicle or commercial crew vehicle designs). Additional 

CFD calculations were made on the new thruster configuration 

to assess effects of the aerodynamics and RCS interactions.4

Results indicated generally good agreement between the 

experimental data and CFD predictions of the RCS JI. This, along 

with recommended conservative uncertainty values for RCS JI, 

provided an appropriate degree of confidence to the MSL Project 

on the adequacy of the new thruster configuration and overall 

robustness of the entry flight control system.

Conclusions and Guidance

Appropriate consideration must be given to RCS thruster locations 

and orientations to minimize impingements and interactions. 

Modern CFD tools should be used in conjunction with welldesigned experimental testing early in development to accurately 

predict the RCS JI and overall control effectiveness. 

References

1. Scallion, W.I., Compton, H.R., Suit, W.T., Powell, R.W., 

Blackstock, T.A., and Bates, B.L.: “Space Shuttle Third Flight 

(STS-3) Entry RCS Analysis,” AIAA Paper 83-0116.

2. Dyakonov, A. A., Glass, C. E., Desai, P. N., and Van Norman, 

J. W.: “Analysis of Effectiveness of Phoenix Reaction Control 

System,” AIAA Paper 2008-7220.

3. NASA/TM-2013-218023, NESC-RP-10-00613 Mars Science 

Laboratory (MSL) Reaction Control System (RCS) Jet Interactions 

(JI) Testing and Analysis, July 2013

4. Schoenenberger, M., Van Norman, J. V., Rhode, M., and Paulson, 

J.: “Characterization of Aerodynamic Interactions with the Mars 

Science Laboratory Reaction Control System Using Computation 

and Experiment,” AIAA Paper 2013-097.

Aerodynamic Reaction Control System (RCS) Orientation

and Jet Interaction (JI) Model Validation 

Careful consideration should be given to placement and orientation of RCS jet thrusters on hypersonic entry 

vehicles in order to minimize adverse RCS JI. Modern state-of-the-art computational fluid dynamics (CFD) 

tools should be able to predict the RCS effectiveness and JI accurately when coupled with verification and 

validation studies, including the use of appropriately designed experimental wind tunnel testing. 

Comparison of MSL Aero/RCS interaction using 3 different CFD codes.

MSL model in LaRC 31-Inch 

Mach 10 Wind Tunnel.

Experimental flow image

of MSL RCS jets.

US3D Overflow FUN3D

NASA Engineering and Safety Center Technical Bulletin No. 14-02