MLI Materials Overview
Today's Spacecraft's see a multitude of temperature fluctuations that can range from lows of -100°C to highs of +150°C (-150°F to +300°F), depending the Spacecraft’s orbit. This can be low earth orbit (LEO), Geosynchronous Earth Orbit (GEO), Synchronous or Interplanetary Orbit and whether the spacecraft is of a design that spins, or is stationary in orbit.
Orbiting in the shade of earth or the spacecraft's own shadow can pose a challenge in keeping the vessel stable in the rigors of space. The craft can swing quickly to the cold side (typical -125°C / -195°F) when in the shadows. Adversely, the Spacecraft can see extremely high temperatures, typically +150°C (+300°F), when exposed to the sun. Furthermore, there is a substantial amount of heat generated from the spacecraft's onboard equipment. Therefore, the Spacecraft material must be highly adaptive to protect from both extreme heat and cold. These conditions can be controlled by using Multi-Layer Insulation blankets (MLI) to protect the delicate instrumentation for both internal and external applications.
Polyimide and/or polyester layers (according to design, could be from 5 to 30 layers) that are vapor deposited with 99.99% aluminum, on one or both sides, assist in the MLI material's heat management. As it is very difficult to design an MLI blanket that reflects 100% of incident radiation, an MLI design can range from a few simple layers, to a complex array of blankets that completely surround the Spacecraft and many of its external components. The designs of these layers typically reflect 95% of radiation back away from the Spacecraft. The total effect by the time the radiation energy makes its way to the innermost layers, is effectively a 100% reflective barrier. Many of these DUNMORE materials are used in our Thermal Protection Systems (TPS) and are found in our catalog. Ideally, temperatures which are most desired for Spacecraft to operate at maximum capacity, is between -23°C to +40°C (-70°F to +107°F).
This is accomplished by using thermal control materials that will work for both active, as well as passive systems. Active systems can be best described as energy sources such as battery powered heaters (electric), which work to keep the Spacecraft at nominal temperatures (+70°F) during cold cycles. Passive systems are best described as using engineered materials, as are found in MLI blankets and offer radiation heat barriers to retard and control the flow of energy.
The terms absorption and emittance are two critical factors in the design and effectiveness of an MLI Blanket. Absorptance is a materials ability to reflect solar energy. Typically, a material that has low solar absorptance will have high reflective properties, such as a mirror would deflect heat (solar energy) away from the Spacecraft. Depending on the requirements, various levels of solar absorptance can be achieved. DUNMORE's MLI's or TPS are specifically designed for these applications. Vacuum Deposited Aluminum (VDA) is the most commonly used coating as it offers low absorptance and emittance properties at an affordable cost. Emittance is a materials ability to radiate energy in the form of heat. Similar to a hot coal, once the energy source (in this instance - fire) is removed, the coal continues to emit heat. MLI materials with high emittance will radiate heat long after the Spacecraft is out of the sun's exposure. By design, both Absorptance and Emittance properties can be configured to control the temperature of the Spacecraft surfaces.
DUNMORE TPS materials, with engineered absorptance and emittance properties, are used for passive thermal control systems. These materials are used for many applications on the Spacecraft, such as structural members, instrumentation, antennas, radiators, wiring harnesses and sunshield covers. DUNMORE TPS materials have been part of nearly all space programs worldwide since the mid 80's and is widely used in the Space Shuttle refurbishment programs and the International Space Station, as well as all US and European launch vehicles.
***NASA does not endorse commercial products or service.
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