Two of Orbital's larger louver units (42 blades each) mountedon the Multimission Modular Spacecraft (MMS) for use on theUpper Atmosphere Research Satellite

S27.97

causing the blades to rotate to a closed position so that heatfrom the baseplate/radiator can be reflected by the highlypolished blade surfaces. The opening and closing of thelouver blades continues throughout the orbital flight tomaintain thermal control within a narrow temperature band.Furthermore, since a pair of louver blades is driven byindependent sensors, local thermal control across theemitting base is afforded. Louver assemblies have beendesigned to operate between fully-closed and openedpositions in either a 10°C or 18°C temperature differential.

They are capable of operation within an environmentalrange of -85°C (-120°F) to +120°C (+250°F), with a minimumoperation capability (open-to-close/close-to-open) of wellover 30,000 cycles with no degradation in performance.

Orbital's thermal control louvers are lightweight, self-contained, consume absolutely no power, and can beadjusted to maintain temperature control over wide thermalspectrums. They have an extensive space flight heritagein many tailored geometric configurations. Louvers havingspecific configurations and operational parameters can bedeveloped to meet mission unique requirements.

Description

Thermal louvers have gained a wide acceptance in theAerospace industry as highly-efficient devices for controllingthe temperature of a satellite. Orbital's first louvers wereflown in 1965. Since then, more than 500 Orbital louverunits have flown on numerous satellites, includingNIMBUS-4, 5, 6 & 7; Landsat-2, 3, 4 & 5; OAO A2 & A4;ATS-6, Viking-1 & 2; Voyager-1 & 2; NAVSTAR/GPSseries; Solar Maximum Mission; AMPTE, SPARTAN, SpaceTelescope, Magellan, GRO, UARS, EUVE, TOPEX, GOES,MGS, MSP, MTSAT and TRMM.

Louvers are thermally activated shutters that regulate thestructural and electronic equipment thermal- environmentduring spaceflight. The louver assemblies sense thetemperature of a baseplate, or space radiator, and react tocontrol that temperature. These assemblies consist ofhighly-polished aluminum blades set in a frame and drivenby bi-metallic sensors. (See Figure 1.)

As the temperature increases, the bi-metallic sensor, oractuator, contracts and applies torque to rotate the bladestoward an open position, thereby allowing heat to dissipate.As the temperature decreases, the actuator expands,

Features

• Lightweight

• Self-contained

• Available in many proven geometricconfigurations

• Maintains temperature control over widespectrums

• Uses no power

• Configurable for mission-uniquerequirements

• Fully-qualified for various satelliterequirements

• Sun shielded configuration available

• Laser impingement protection available

• Cover for Micrometeorite or EVA protectionflight proven and available.

Thermal

Control

LouversSizes

Orbital has provided thermal control louvers for many spacecraft in numerous sizes. The following tablerepresents fabricated louver sizes readily available for delivery; however, tailored geometric configurationcan be supplied to specification.

Description

Orbital Technical Services Division5010 Herzel PlaceBeltsville, MD 20705Phone: (301) 902-1152 Fax: (301) 931-0396www.orbital.com

Program Number Length Width Weight➂ Area Weight/Area M/N Name of Blades cm (in) cm (in) kg (lbs) m2 (ft2) kg/m2 (lbs/ft2)

41901 AMPTE➀ 3 20.00 (07.88) 36.20 (14.25) 0.37 (0.81) .072 (0.78) 5.14 (1.04)

61201 GOES➀ 20 63.35 (24.94) 60.96 (24.00) 1.62 (3.57) .386 (4.16) 4.20 (0.86)

Space Telescope➀ 24 75.72 (29.81) 60.96 (24.00) 1.95 (4.30) .462 (4.97) 4.22 (0.86)

JRI/XTE➀ 22 69.55 (27.38) 50.80 (19.99) 1.63 (3.60) .353 (3.80) 4.61 (0.95)

GPS 16 42.01 (16.54) 59.70 (23.50) 0.82 (1.81) .250 (2.70) 3.28 (0.67)

31801 VRM Magellan➁ 16 42.01 (16.54) 39.37 (15.50) 0.63 (1.40) .165 (1.78) 3.82 (0.78)

45001 GPS/Spartan 18 47.10 (18.54) 54.86 (21.60) 0.91 (2.00) .250 (2.77) 3.64 (0.72)

45002 SPARTAN 26 67.41 (26.54) 54.86 (21.60) 1.16 (2.56) .368 (3.96) 3.15 (0.65)

GRO/Topex➁ 26 72.44 (28.52) 55.63 (21.90) 1.77 (3.90) .403 (4.34) 4.39 (0.90)

MMS/UARS, Topex➁ 42 110.33 (43.44) 55.63 (21.90) 2.63 (5.78) .614 (6.61) 4.28 (0.87)

5K202 MGS➁ 10 26.77 (10.54) 40.50 (15.95) 0.58 (1.27) .108 (1.17) 5.37 (1.08)

5K201 MGS➁ 16 42.01 (16.54) 40.50 (15.95) 0.84 (1.83) .170 (1.83) 4.91 (1.00)

5L1021 MSP 14 36.93 (14.54) 40.50 (15.95) 0.68 (1.49) .148 (1.61) 4.59 (0.93)

➀ Louver blade operation open to closed = 10°C (18°F); all other open to close = 18°C (30°F)➁ Design includes sunshield➂ Weight w/o sun shield or mounting hardware

PERFORMANCE DATA Qualification Testing SummaryThe radiative capacity as a function of temperature (forblade opening angle) is related to an "effective emittance,"defined as the ratio of net heat transfer from a louveredsurface to the energy that would be radiated from anequivalent black area at the same temperature, but in theabsence of louvers.

Mathematical models have compared favorably with re-sults of tests to find effective-emittance and absorptance asfunctions of blade-and solar-incidence angle. The numeri-cal data obtained from these tests form the basic solutionto discovering the temperature of a louvered panel, corre-sponding to a particular dissipation-and solar-environment.A typical variation of emittance with temperature and corre-sponding power profile is shown in Figure 2.

Orbital has also designed and tested prototype louverassemblies that can reflect up to 98% of directed laserenergy away from themselves, as well as the satellite. Aspart of this survivability-enhancement, Orbital designedand developed a quick-closing louver mechanism thatallows the retention of an efficient, low absorptance, high-emittance, second surface-mirror on a space radiator.Without protection, these materials would be unacceptablefor a design which could be subjected to laser impingement.

Thermal control louvers have been flight qualified to various environment conditions, depending on spacecraft requirements.The following table presents the results of emittance tests and environmental conditions.

Figure 1. Typical Thermal Louver Assembly Schematic

Figure 2. Typical Louvers Performance Data

AVERAGE PANEL TEMPERATURE

EF

FE

CT

IVE

EM

ITT

AN

CE

HE

AT

ER

PO

WE

R (

WA

TT

S)

Actuator Adjustment ScrewStructural Frame

Louver Blade(Typical)

Spool

Actuator Spring

Actuator Housing

Adjustment Cylinder