Spacecraft that fly to planets with atmospheres require heat shields to reduce atmospheric drag and absorb any sudden increases in temperature during reentry. These shields also serve to abate any high heat peaks encountered upon reentry.
Most spacecraft use refractory insulation as a protective measure. Perhaps most recognizable are the black tiles lining the bottom and nose of Space Shuttles.
Passive Cooled Protectors
Passive thermal control is often the only viable means of maintaining temperatures on spacecraft systems, particularly smaller satellites as large thermal radiators would be impractical due to mass and volume restrictions.
Technology is being created for these small spacecraft to improve their ability to dissipate heat efficiently from their surfaces, such as multifunctional thermal structures and refractory insulation materials.
Multifunctional thermal structures integrate thermal control capabilities directly into spacecraft structures. These multifunctional thermal structures utilize technology developed by Thermal Management Technologies and tailored specifically for use on small satellite configurations such as 6U, 12U and launch U size CubeSats.
These include MLI blankets, coatings/surface finishes, interface conductance materials and sunshades/thermal straps such as Redwire Space’s FlexCool heat pipe recently used on TechEdSat-10 CubeSat deployed from the ISS in 2020. This flat heat pipe offers up to 10x the thermal conductivity of copper and up to 6 W/cm2 when 1mm thick.
An important part of a spacecraft’s thermal protection system (TPS) on all rocket-powered spacecraft, and one reason many famous spacecraft such as the Apollo Command Module feature thousands of black heat-absorbing tiles to safeguard it during entry is frictional heat produced during its high-speed entry into Earth’s atmosphere. This material acts like an ablative coating to shield its surfaces. This effect burns away layers of an evaporating substance protecting its surfaces – something the friction generated during entry also does for its protection.
Orion Multi-Purpose Crew Vehicle’s Ablative Heat Shield relies on carbon-phenolic-based ablator materials like AVCOAT and PICA-X for its ablation products; however, more experimental data must be accumulated on ablation products in order to validate turbulent transport models used to model this process and verify codes for modeling it.
The present invention provides a novel ablative heat shield for spacecraft that features an enhanced ablative heat shield with a controlled gap between its impregnated portion and substrate, achieved via openly structured spacer means sewn onto the back face of base member which are used to stand off front-face piles of ablation material to form this controlled gap.
Refractory Insulation Materials
Reentry requires extremely high temperatures, and to reduce this threat effectively a thermal blanket or ablative shield is best. An effective shield must possess three essential properties: thermal insulation, radiation cooling and good thermal stability.
Since NASA began using them on Apollo missions, ablative shields have become an indispensable part of spaceflight operations. This huge and heavy device depends on a material called Avcoat to gradually burn off during entry burns to deflect heat away from spacecraft and deflect energy back out into space.
The Space Shuttle employed various kinds of refractory tiles and blankets. Low-density ceramic insulating tiles with about 90% void space served both insulating and cooling-by-radiation functions while being significantly lighter due to their reduced density. Toughened Unipiece Fibrous Insulation tiles (TUFI), an upgrade on HRSI tiles used on various surfaces of the Space Shuttle, provided greater strength, resistance against coating cracking, weight reduction, and were sometimes even installed as replacement surfaces on certain parts.
These blankets, commonly referred to as Mylar blankets, are constructed with metallized polyethylene terephthalate (MPET) material which reflects radiation and redirects infrared energy in order to keep astronauts warm. You might recognize MPET from sun shields at beaches; its metallic surface reflects light off its metallic surface like mirrors.
Thermal blankets are an important element in spacecraft heat shields, yet they can become damaged during reentry as the shuttle approaches Mach 3-4 atmospheric entry speeds and comes into contact with Earth. Engineers worry that should any loose pieces break free during reentry they could hit critical components such as the tail or Reaction Control System/Orbital Maneuvering System pods on the rear of the craft causing structural damage.
NASA deploys a team of MLI blanket professionals on each mission, to check that its blanket remains undamaged prior to takeoff.