Xiao-Yen J. Wang and James R. Yuko

Glenn Research Center, Cleveland, Ohio

Thermal Performance of Orion Active Thermal 

Control System With Seven-Panel 

Reduced-Curvature Radiator 

NASA/TM—2010-216893

October 2010
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Xiao-Yen J. Wang and James R. Yuko

Glenn Research Center, Cleveland, Ohio

Thermal Performance of Orion Active Thermal 

Control System With Seven-Panel 

Reduced-Curvature Radiator 

NASA/TM—2010-216893

October 2010

National Aeronautics and

Space Administration

Glenn Research Center

Cleveland, Ohio 44135

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NASA/TM—2010-216893 1

Thermal Performance of Orion Active Thermal Control System

With Seven-Panel Reduced-Curvature Radiator 

Xiao-Yen J. Wang and James R. Yuko

National Aeronautics and Space Administration

Glenn Research Center

Cleveland, Ohio 44135

Summary

The active thermal control system (ATCS) of the crew exploration vehicle (Orion) uses radiator 

panels with fluid loops as the primary system to reject heat from spacecraft. The Lockheed Martin (LM) 

baseline Orion ATCS uses eight-panel radiator coated with silver Teflon coating (STC) for International 

Space Station (ISS) missions, and uses seven-panel radiator coated with AZ–93 white paint for lunar 

missions. As an option to increase the radiator area with minimal impact on other component locations 

and interfaces, the reduced-curvature (RC) radiator concept was introduced and investigated here for the 

thermal perspective. Each RC radiator panel has 15 percent more area than each Lockheed Martin (LM) 

baseline radiator panel. The objective was to determine if the RC seven-panel radiator concept could be 

used in the ATCS for both ISS and lunar missions. Three radiator configurations—the LM baseline, an 

RC seven-panel radiator with STC, and an RC seven-panel radiator with AZ–93 coating—were

considered in the ATCS for ISS missions. Two radiator configurations—the LM baseline and an RC 

seven-panel radiator with AZ–93 coating were considered in the ATCS for lunar missions. A

Simulink/MATLAB model of the ATCS was used to compute the ATCS performance. Some major hot 

phases on the thermal timeline were selected because of concern about the large amount of water 

sublimated for thermal topping. It was concluded that an ATCS with an RC seven-panel radiator could be 

used for both ISS and lunar missions, but with two different coatings—STC for ISS missions and AZ–93

for lunar missions—to provide performance similar to or better than that of the LM baseline ATCS.

Introduction 

The Orion project is under the Constellation Program for the space exploration vision initiated by 

President Bush in 2004. The Constellation Program is responsible for providing the elements that will 

transport humans and cargo to both the International Space Station (ISS) and the Moon. These elements 

are the crew exploration vehicle (Orion), the crew launch vehicle (Ares I), the lunar surface access 

module (Altair), and the cargo launch vehicle (Ares V). Orion, with a crew of up to four astronauts, will 

launch on Ares I and then use its main engine to insert itself into a safe orbit to either dock with the ISS or 

with Altair. For ISS missions, Orion will be responsible for separation, entry, descent, and landing. For 

lunar missions, Orion also will have to maintain itself in low lunar orbit and perform a trans-Earth 

injection maneuver to return from the Moon. Orion consists of the Launch Abort System (LAS), Crew 

Module (CM), Service Module (SM), and Spacecraft Adapter (SA). The CM is a capsule design that 

provides the primary structure for crew support, incorporates the bulk of the avionics systems, and 

provides the capability for entry and parachute landing. The LAS will safely extract the CM from the 

launch configuration in the event of an early launch abort. The SM is the structure on which the CM rests

and interfaces with Ares I launch vehicle. It will perform in-space flight propulsion operations and power 

generation and provide the heat rejection for the Orion active thermal control system (ATCS).

This study focuses on Orion’s ATCS. The purpose of the ATCS is to control the crew environment 

inside the CM, while maintaining the temperature of all avionics under their temperature limits. As shown 

in Figure 1, two CM fluid loops will pass through the CM, take heat generated inside the CM and from all 

electronics, then pass the heat to the SM fluid loops through two interface heat exchangers. On the CM 

side, there will be a phase-change material (PCM) heat exchanger (HX) and a sublimator for thermal 
NASA/TM—2010-216893 2

Figure 1.—Active thermal control system for Orion. IFHX, interface heat exchanger.

Figure 2.—Seven-panel radiator with two fluid loops.

topping during high heat load phases of the mission. The PCM HX is used only for lunar missions and the 

sublimator is used for both ISS and lunar missions. The SM fluid loops will carry the heat to the radiator 

panels and radiate the heat to space.

The radiator panel has a thin surface with fluid channels attached at its interior surface. The interior 

surface is covered by multilayer insulation blankets. The exterior surface is coated with material that has 

high emissivity. The fluid loop will come into the header and split the flow through a number of channels 

along the panel. For the two-loop (A and B) flow configuration, the channel will flow alternately along 

fluid loops A and B, and the flow condition in the two loops can be different. 

The Lockheed Martin (LM) baseline design has an eight-panel radiator with flow going through two

loops in series for ISS missions and a seven-panel radiator for lunar missions as shown in Figure 2. The 

coating on the radiator is different for ISS missions and lunar missions. The LM baseline ISS radiator

uses silver Teflon coating (STC) that has a solar absorptivity and emissivity of 0.11 and 0.88, 

respectively. For lunar missions, the Orion radiator will use AZ–93, which has a solar absorptivity and 

emissivity of 0.2 and 0.90, respectively. 

The RC radiator concept is introduced in Reference 1 and is shown in Figure 3. The major difference 

between the LM baseline radiator and the RC radiator is that each RC radiator panel has 15 percent more 

area and a reduced curvature. Two coatings, STC and AZ–93, were considered for the RC radiator 

concept. Three radiator configurations are evaluated for ISS missions: an LM baseline eight-panel 

radiator with STC, an RC seven-panel radiator with STC, and an RC seven-panel radiator with AZ–93

coating. Two radiator configurations are evaluated for the lunar missions: an LM baseline seven-panel 

radiator with AZ–93 coating and an RC seven-panel radiator with AZ–93 coating. The performance of the 

ATCS with RC radiator was evaluated for both ISS and lunar missions and compared with that of the LM 

baseline ATCS.

A dynamic model of the ATCS built using Simulink/MATLAB was used to compute the 

performance. The model includes all major components in the ATCS: the cabin HX, cold plates on the 

CM and SM sides, the interface heat exchanger, the regenerative HX, the PCM HX, and the radiator with 

its fluid loops on the SM side. The control system also was modeled to meet the thermal requirements for 
NASA/TM—2010-216893 3

Figure 3.—Reduced-curvature (RC) radiator configuration compared with a Lockheed Martin (LM)

baseline (BL) radiator.

the ATCS. The initial conditions and the ambient radiation sink temperature for the radiators must be 

provided for the model. Reference 2 describes the model in detail.

The following sections describe the ATCS thermal performance of each configuration for both the 

ISS and lunar missions and present the results. Then the conclusions are given.

Thermal Performance of the Active Thermal Control System With a 

Reduced-Curvature Radiator for International Space Station Missions

Each RC radiator panel has 15 percent more area than the LM baseline. The LM baseline ATCS for 

ISS missions uses an eight-panel radiator. The RC seven-panel radiator has the same total area as the LM 

baseline eight-panel radiator. The RC seven-panel radiator concept was studied with two different optical 

coatings. The study’s goals were to determine if the seven-panel RC radiator could replace the LM 

baseline eight-panel radiator design, (1) providing similar performance, (2) allowing cargo to be installed 

in the bay where the eighth panel is located, and (3) reducing the amount of water sublimated and total 

mass of the vehicle. An additional goal was to determine if the STC used for the LM baseline radiator for 

ISS missions could be replaced with AZ–93 coating (the same coating used for lunar missions) to 

simplify the design and qualification test articles.

Four major on-orbit hot cases, one ISS docked case on node 3, and two on-orbit cold cases on the 

thermal timeline were selected for the study. The four hot cases were two low Earth orbit (LEO) aft to

Sun, LEO nose forward, and LEO tail nadir. The two cold cases were LEO nose forward and LEO aft to

Sun. Table 1 lists the thermal beta angle; altitude; attitude; pitch, yaw, and roll angles; ATCS heat load;

phase duration; and the orbit time for each case. The LEO aft to Sun case with a power load of 3728 W 

and the docked case were the dominant hot cases that required the most sublimator water usage. 

The ATCS performance results were computed using the NASA Glenn Research Center’s 

Simulink/MATLAB model with the sink temperature version 13 provided by LM. Table 2 lists the results 

for the three configurations.

During the four hot on-orbit cases and the one ISS docked case in the thermal timeline, the ATCS 

total water usages were

• LM eight-panel radiator with STC: 11.2 lb (baseline)

• RC seven-panel radiator with STC: 1.7 lb

• RC seven-panel radiator with AZ–93 coating: 20.0 lb

For the cold cases, the RC radiator with STC needed to have 2 to 3 percent more flow going through the 

regenerative HX than for the LM baseline radiator to keep the system as warm as required.
NASA/TM—2010-216893 4

TABLE 1.—CASE DESCRIPTIONS FOR INTERNATIONAL SPACE STATION (ISS) MISSIONS

Casesa β Altitude, 

km

Attitudea Pitch Yaw Roll ATCSb load,

W

Phase 

duration,

hr

Orbit 

time,

hr

LEO AtS hot 75 230 AtS 5 −5 0 4683 1.27 1.485 

LEO NF hot 75 230 NF 0 0 315 4429 3.62 1.485 

LEO TN hot 75 230 TN 0 0 270 4429 3.3 1.485 

LEO AtS hot 75 230 AtS 5 −5 0 3728 15.65 1.485

ISS node 3 docked 75 350 −20 −15 15 2329 5054 1.529

LEO NF cold 40 460 NF 0 0 315 2406 1.5632 

LEO AtS cold 0 460 AtS 0 0 0 1870 1.5632 a

LEO, low Earth orbit; AtS, aft to Sun; NF, nose forward; TN, tail nadir.

b

ATCS, active thermal control system.

TABLE 2.—ACTIVE THERMAL CONTROL SYSTEM (ATCS) 

PERFORMANCE FOR INTERNATIONAL SPACE STATION (ISS) MISSIONS

Casesa Lockheed Martin baseline 

eight-panel radiator with 

silver Teflon coating (STC)

Reduced-curvature seven-panel 

radiator with STC

Reduced-curvature seven-panel 

radiator with AZ–93 coating

ATCS water 

usage per orbit,

lb

Flow to

regenerative

heat exchanger

ATCS water 

usage per orbit,

lb

Flow to 

regenerative

heat exchanger

ATCS water 

usage per orbit,

lb

Flow to 

regenerative

heat exchanger

LEO AtS hot 1.68 0 0.73 0 2.4 0

LEO NF hot 1.63 0 .44 0 5.1 0

LEO TN hot 2.6 0 .0 0 2.46 0

LEO AtS hot 0 0 0 0 0.0 0

ISS node 3 docked 0 0 0 0 0 0

LEO NF cold 0 62 0 65 0 62

LEO AtS cold 0 80 0 82 0 80 a

LEO, low Earth orbit; AtS, aft to Sun; NF, nose forward; TN, tail nadir.

It can be concluded that the ATCS with RC seven-panel radiator with STC would have better 

performance than would the LM baseline ATCS and that less water would sublimate. However, the 

ATCS with RC seven-panel radiator with AZ–93 coating would sublimate more water than the LM 

baseline ATCS would.

Thermal Performance of an Active Thermal Control System

With a Reduced-Curvature Radiator for Lunar Missions

The LM baseline ATCS for lunar missions uses a seven-panel radiator. The RC seven-panel radiator 

has 15 percent more total radiator surface area than the LM baseline seven-panel radiator since each RC 

radiator panel has 15 percent more area than the LM baseline.

A larger radiator area will increase heat rejection and reduce the amount of water sublimated for the 

hot case: when the heat load on the ATCS is high and the environment is hot. For cold cases when the 

heat load is low and the environment is cold, a larger radiator area will make the system colder. Thus, a 

larger radiator area will result in increasing flow to the regenerative HX, which is used to keep the fluid 

temperature from going below a defined set point of 20 °F. We needed to find out how much the amount 

of sublimated water could be reduced and how cold the system would get when all the control 

requirements were met for the different configurations.

The study’s goals for lunar missions were to determine if the seven-panel RC radiator could replace 

the LM seven-panel radiator with the same coating (AZ–93). Seven hot cases and two cold cases on the 

timeline were used. The hot cases were LEO aft to Sun, LEO nose forward, LEO tail nadir, LEO nose

nadir, lower lunar orbit (LLO) aft to Sun, LLO nose forward, and LLO nose nadir. The cold cases were

LLO aft to Sun and lunar transit aft to Sun. The details of each case are listed in Table 3, and the results 

are listed in Table 4. 
NASA/TM—2010-216893 5

TABLE 3.—CASE DESCRIPTIONS FOR LUNAR MISSIONS

Casesa β

angle

Altitude, 

km

Attitudea Pitch Yaw Roll ATCSb

load,

W

ATCSb

load 

duration

Orbit 

time, 

hr

LEO AtS hot 56 172 AtS 20 −20 0 4500 23 min 1.466

LEO NF hot 56 172 NF 0 0 315 4134 2.3 hr 1.466

LEO TN hot 56 172 TN 0 0 270 4246 45 min 1.466

LEO NN hot 56 172 NN 20 20 0 3500 86 hr 1.466

LLO AtS cold 90 400 AtS 0 0 0 1725 2.465

Lt AtS cold AtS 20 −20 0 2512 2.0

LLO AtS hot 0 90 AtS 5 −5 0 3799 83 hr 1.949

LLO NF hot 0 90 NF 0 0 180 3650 2 hr 1.949

LLO NN hot 0 75 NN −20 20 0 2571 161.67 hr 1.925 a

LEO, low Earth orbit; AtS, aft to Sun; NF, nose forward; TN, tail nadir; NN, nose nadir; LLO, lower lunar orbit; Lt, lunar transit. b

ATCS, active thermal control system.

TABLE 4.—ACTIVE THERMAL CONTROL SYSTEM (ATCS) 

PERFORMANCE FOR LUNAR MISSIONS

Casesa Lockheed Martin baseline seven-panel 

radiator with AZ–93 coating

Reduced-curvature seven-panel

radiator with AZ–93 coating

ATCS water usage 

per orbit,

lb

Water flow to 

regenerative heat 

exchanger,

percent

ATCS water usage 

per orbit,

lb

Water flow to 

regenerative heat 

exchanger,

percent

LEO AtS hot 0 0 0 0

LEO NF hot 0 0 0 0

LEO TN hot 0 0 0 0

LEO NN hot 0 0 0 23

LLO AtS cold 0 80 0 85

Lt AtS cold 0 58 0 64

LLO AtS hot 0 0 0 32

LLO NF hot 2.33 0 1.56 20

LLO NN hot 0 50 0 60 a

LEO, low Earth orbit; AtS, aft to Sun; NF, nose forward; TN, tail nadir; NN, nose nadir; LLO, lower lunar orbit; Lt, lunar transit.

The PCM is planned to be used for lunar missions only for thermal topping. The wax in the PCM will 

melt during hot operations and will freeze during cold operations. For the LLO nose-forward hot case, the 

ATCS with the RC radiator sublimated slightly less water than did the LM baseline radiator. For other hot 

cases, the ATCS with the RC radiator melted less wax in the PCM than did the LM baseline, but no water 

was sublimated in either configuration. In all cases, the ATCS with the RC radiator had more flow going

through the regenerative HX because this radiator has more surface area, but it never reached 100-percent 

flow to the regenerative HX. Overall, the ATCS with RC seven-panel radiator had similar performance to 

the LM baseline ATCS.

In conclusion, the ATCS with RC seven-panel radiator could be used for both ISS and lunar missions, 

but with two different coatings—STC for ISS missions and AZ–93 for lunar missions—to minimize 

water usage.

Conclusions

The RC radiator concept was investigated for the Orion ATCS. The thermal performance of the 

ATCS with the RC radiator concept was computed and compared with the LM baseline design for both 

ISS and lunar missions. It was concluded that, for ISS missions, the ATCS with the RC seven-panel 

radiator with STC performs better than the LM baseline and would use less water for sublimation;

however, the ATCS with the RC seven-panel radiator with AZ–93 coating would sublimate twice as 

much water as the LM baseline ATCS. For lunar missions, the ATCS with RC seven-panel radiator 
NASA/TM—2010-216893 6

would have performance similar to that of the LM baseline. Further studies are planned to validate the 

results presented here and the ATCS performance on the entire timeline will be compared for each 

configuration.

References

1. Thomas Goodnight, Thomas Cressman, private communications, NASA Glenn Research Center, 

Cleveland, OH

2. Wang, Xiao-Yen J.; and Yuko, James: “Orion Active Thermal Control System Dynamic Modeling 

Using Simulink/MATLAB,” AIAA–2010–0810 (see also NASA/TM—2010-216252), 2010. 
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Thermal Performance of Orion Active Thermal Control System With Seven-Panel ReducedCurvature Radiator 

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13. SUPPLEMENTARY NOTES

14. ABSTRACT

The active thermal control system (ATCS) of the crew exploration vehicle (Orion) uses radiator panels with fluid loops as the primary 

system to reject heat from spacecraft. The Lockheed Martin (LM) baseline Orion ATCS uses eight-panel radiator coated with silver Teflon 

coating (STC) for International Space Station (ISS) missions, and uses seven-panel radiator coated with AZ-93 white paint for lunar 

missions. As an option to increase the radiator area with minimal impact on other component locations and interfaces, the reduced-curvature 

(RC) radiator concept was introduced and investigated here for the thermal perspective. Each RC radiator panel has 15 percent more area 

than each Lockheed Martin (LM) baseline radiator panel. The objective was to determine if the RC seven-panel radiator concept could be 

used in the ATCS for both ISS and lunar missions. Three radiator configurations-the LM baseline, an RC seven-panel radiator with STC, 

and an RC seven-panel radiator with AZ-93 coating-were considered in the ATCS for ISS missions. Two radiator configurations-the LM 

baseline and an RC seven-panel radiator with AZ-93 coating were considered in the ATCS for lunar missions. A Simulink/MATLAB model 

of the ATCS was used to compute the ATCS performance. Some major hot phases on the thermal timeline were selected because of concern 

about the large amount of water sublimated for thermal topping. It was concluded that an ATCS with an RC seven-panel radiator could be 

used for both ISS and lunar missions, but with two different coatings-STC for ISS missions and AZ-93 for lunar missions-to provide 

performance similar to or better than that of the LM baseline ATCS.

15. SUBJECT TERMS

Active thermal control system; Dynamic modeling; Spacecraft 

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