Orbital's thermal control louvers are lightweight, self-contained devices that maintain temperature control over a wide range without using any power. They have a long flight heritage in various satellite missions and sizes. Louvers work by using bi-metallic sensors to control the opening and closing of polished aluminum blades, allowing heat to dissipate as temperatures increase and reflecting heat as temperatures decrease. Custom louvers can be developed to meet unique mission requirements.

1. Features
• Lightweight
• Self-contained
• Available in many proven geometric
configurations
• Maintains temperature control over wide
spectrums
• Uses no power
Thermal
• Configurable for mission-unique
requirements
• Fully-qualified for various satellite
requirements
• Sun shielded configuration available
Control
• Laser impingement protection available
• Cover for Micrometeorite or EVA protection
Sizes
flight proven and available.
Louvers
Orbital has provided thermal control louvers for many spacecraft in numerous sizes. The following table
represents fabricated louver sizes readily available for delivery; however, tailored geometric configuration
can be supplied to specification. Two of Orbital's larger louver units (42 blades each) mounted
on the Multimission Modular Spacecraft (MMS) for use on the
Upper Atmosphere Research Satellite
Program Number Length Width Weight➂ Area Weight/Area Description
Description
M/N Name of Blades cm (in) cm (in) kg (lbs) m2 (ft2) kg/m2 (lbs/ft2)
Thermal louvers have gained a wide acceptance in the causing the blades to rotate to a closed position so that heat
41901 AMPTE➀ 3 20.00 (07.88) 36.20 (14.25) 0.37 (0.81) .072 (0.78) 5.14 (1.04) Aerospace industry as highly-efficient devices for controlling from the baseplate/radiator can be reflected by the highly
61201 GOES➀ 20 63.35 (24.94) 60.96 (24.00) 1.62 (3.57) .386 (4.16) 4.20 (0.86) the temperature of a satellite. Orbital's first louvers were polished blade surfaces. The opening and closing of the
Space Telescope➀ 24 75.72 (29.81) 60.96 (24.00) 1.95 (4.30) .462 (4.97) 4.22 (0.86) flown in 1965. Since then, more than 500 Orbital louver louver blades continues throughout the orbital flight to
JRI/XTE➀ 22 69.55 (27.38) 50.80 (19.99) 1.63 (3.60) .353 (3.80) 4.61 (0.95)
units have flown on numerous satellites, including maintain thermal control within a narrow temperature band.
NIMBUS-4, 5, 6 & 7; Landsat-2, 3, 4 & 5; OAO A2 & A4; Furthermore, since a pair of louver blades is driven by
GPS 16 42.01 (16.54) 59.70 (23.50) 0.82 (1.81) .250 (2.70) 3.28 (0.67)
ATS-6, Viking-1 & 2; Voyager-1 & 2; NAVSTAR/GPS independent sensors, local thermal control across the
31801 VRM Magellan➁ 16 42.01 (16.54) 39.37 (15.50) 0.63 (1.40) .165 (1.78) 3.82 (0.78) series; Solar Maximum Mission; AMPTE, SPARTAN, Space emitting base is afforded. Louver assemblies have been
45001 GPS/Spartan 18 47.10 (18.54) 54.86 (21.60) 0.91 (2.00) .250 (2.77) 3.64 (0.72) Telescope, Magellan, GRO, UARS, EUVE, TOPEX, GOES, designed to operate between fully-closed and opened
45002 SPARTAN 26 67.41 (26.54) 54.86 (21.60) 1.16 (2.56) .368 (3.96) 3.15 (0.65) MGS, MSP, MTSAT and TRMM. positions in either a 10°C or 18°C temperature differential.
GRO/Topex➁ 26 72.44 (28.52) 55.63 (21.90) 1.77 (3.90) .403 (4.34) 4.39 (0.90) Louvers are thermally activated shutters that regulate the They are capable of operation within an environmental
MMS/UARS, Topex➁ 42 110.33 (43.44) 55.63 (21.90) 2.63 (5.78) .614 (6.61) 4.28 (0.87) structural and electronic equipment thermal- environment range of -85°C (-120°F) to +120°C (+250°F), with a minimum
5K202 MGS➁ 10 26.77 (10.54) 40.50 (15.95) 0.58 (1.27) .108 (1.17) 5.37 (1.08) during spaceflight. The louver assemblies sense the operation capability (open-to-close/close-to-open) of well
temperature of a baseplate, or space radiator, and react to over 30,000 cycles with no degradation in performance.
5K201 MGS➁ 16 42.01 (16.54) 40.50 (15.95) 0.84 (1.83) .170 (1.83) 4.91 (1.00)
control that temperature. These assemblies consist of
5L1021 MSP 14 36.93 (14.54) 40.50 (15.95) 0.68 (1.49) .148 (1.61) 4.59 (0.93) Orbital's thermal control louvers are lightweight, self-
highly-polished aluminum blades set in a frame and driven
➀ contained, consume absolutely no power, and can be
Louver blade operation open to closed = 10°C (18°F); all other open to close = 18°C (30°F) by bi-metallic sensors. (See Figure 1.)
➁ Design includes sunshield adjusted to maintain temperature control over wide thermal
➂ Weight w/o sun shield or mounting hardware As the temperature increases, the bi-metallic sensor, or spectrums. They have an extensive space flight heritage
actuator, contracts and applies torque to rotate the blades in many tailored geometric configurations. Louvers having
toward an open position, thereby allowing heat to dissipate. specific configurations and operational parameters can be
Orbital Technical Services Division
5010 Herzel Place As the temperature decreases, the actuator expands, developed to meet mission unique requirements.
Beltsville, MD 20705
Phone: (301) 902-1152 Fax: (301) 931-0396
www.orbital.com
S27.97

2. PERFORMANCE DATA Qualification Testing Summary
Thermal control louvers have been flight qualified to various environment conditions, depending on spacecraft requirements.
The radiative capacity as a function of temperature (for The following table presents the results of emittance tests and environmental conditions.
blade opening angle) is related to an "effective emittance,"
defined as the ratio of net heat transfer from a louvered
surface to the energy that would be radiated from an
equivalent black area at the same temperature, but in the
absence of louvers.
HEATER POWER (WATTS)
Mathematical models have compared favorably with re-
sults of tests to find effective-emittance and absorptance as
functions of blade-and solar-incidence angle. The numeri-
cal data obtained from these tests form the basic solution
to discovering the temperature of a louvered panel, corre-
sponding to a particular dissipation-and solar-environment.
EFFECTIVE EMITTANCE
A typical variation of emittance with temperature and corre-
sponding power profile is shown in Figure 2.
Orbital has also designed and tested prototype louver
assemblies that can reflect up to 98% of directed laser
energy away from themselves, as well as the satellite. As
part of this survivability-enhancement, Orbital designed
and developed a quick-closing louver mechanism that
allows the retention of an efficient, low absorptance, high-
emittance, second surface-mirror on a space radiator. AVERAGE PANEL TEMPERATURE
Without protection, these materials would be unacceptable
for a design which could be subjected to laser impingement. Figure 2. Typical Louvers Performance Data
Actuator Housing
Actuator Adjustment Screw Adjustment Cylinder
Structural Frame
Louver Blade
(Typical)
Spool
Actuator Spring
Figure 1. Typical Thermal Louver Assembly Schematic