Micro Electro-Mechanical Louvers for Thermal Radiators

Objectives

The Thermal Louvers developed by MAGNA Steyr are a low mass micro-engineered device based on Micro Electro-Mechanical Systems (MEMS) technology. The MEMS Louvers are designed to be controlled by solar radiation temperature and to protect a radiator against external thermal fluxes (> inverse Thermal Louvers).

The MEMS Louvers were developed and verified at breadboard level. Verification testing was done on a Breadboard model dimensioned to cover a radiator area of 500 x 500mm.

The objective of the project was the development, manufacture and verification of thermal louvers able to protect a radiator against external environmental hazards such as solar radiation, planetary infrared radiation and albedo effect. The Louvers have to be developed for a transition temperature range of +30°C (fully open) to +40°C (fully closed) at a selected satellite interface mounting surface temperature of +40°C.

In open configuration the Louvers should have a heat rejection capability of ≥ 85% while the heat leak to the S/C in closed configuration should be less than 15W/m2. The MEMS technology was used to limit the mass of the device to 450g/m2. The development was also driven by the requirement for a passive - non power consuming - actuation system. The louvers were subjected to 60000 open/close cycles to simulate an operational life of 15 years.

Challenges

The key issue in this project was the application of memory material for the actuator. The SMA is designed as a two-way memory actuator – which means that it memorises two shapes, one in cold- and one in hot condition. Extensive training of the memory material makes it possible to manufacture two-way actuators which work without a retaining spring - one means for maintaining a low total mass.

The SMA is trained for inverse actuation as an adaption of the given requirements (to protect the radiator against sun radiation). That means it bends when hot and is straight when cold.

Based on this SMA applied Louvers design, non-inverse Thermal Louvers can be realised by implementation of the design change of thermally coupling a normal actuating SMA to the radiator surface.

Benefits

The main benefit of the project is the gain in knowledge concerning the utilisation of shape memory alloy for the actuation of Thermal Louvers in Space application.

The results of this development show that the MEMS Louvers are able to shadow radiators or other sensitive satellite areas and protect them in an effective way against external heat fluxes.

As far as a comparison with normal thermal louvers is feasible, such a comparison shows that the MEMS louvers give a better thermal and mass-efficient performance than all other louvers on European and U.S. market where data are available.

Features

The MEMS Louvers are a self-supporting foil system which comprises an array of CuBe-wings. These wing rows, covered with a surface mirror foil (3mil ITO coated VDA Kapton) are operated by a shape memory alloy (SMA) actuator. The actuator and the wings are attached to a support bar. The bar is fixed with thermally insulated brackets on the radiator side of the satellite structure. When the actuator is heated by solar radiation the SMA changes shape and bends the wings by 90° from the nominal open position so that the wing rows shadow the radiator area.


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The total mass of the MEMS Louvers Model (530x490mm), consisting of 12 wing rows is 129,7g which corresponds with 498g/m2. The results of the thermal analyses and thermal performance tests (e.g. sun simulation tests) show a heat leak in the closed configuration of 24 W/m2. A heat leak prediction for a Space environment of 12 W/m2 is considered feasible. The measured efficiency of the MEMS louvers expressed by the heat rejection capability is 85.2%.

The MEMS Louvers are designed to have a transition temperature range between +30°C (fully open) and +50°C (fully closed). The reliability of the MEMS louvers is verified with a 60000 actuation cycling test. The single SMAs, trained to operate at the required transition temperature range, were successfully lifetime-tested with 270000 operation cycles.

Plan

The plan of the project was the breadboard qualification of the MEMS louvers developed according the given requirements. A future step could be flight qualification on a demonstrator S/C if a realistic application of the inverse louvers is considered feasible. An additional option could be the development of non-inverse Thermal Louvers by utilisation of the same MEMS Louvers technology.

Current status

The current status of the project is that the developed MEMS Louvers Breadboard model is completely tested and qualified by fulfilling the given technical requirement.

This achievement and gain in know-how gives MAGNA Steyr the capability to proceed with the development of SMA actuated non-reverse Thermal Louvers and/or to improve the design of the current MEMS Louvers to be capable of flight qualification.

Contacts

Status date

Monday, December 22, 2008 - 10:31