The mechanical strength of thermal protection system (TPS) insulation foam has been substantially enhanced by adding nano-sized Kevlar fibres, tests have found, with the potential for it to reduce or eliminate TPS debris on NASA's future Constellation programme Ares launchers.
NASA needs to use insulation foam for its Ares I crew launch vehicle's upper stage and its Ares V's core and Earth departure stages for the same reason it uses it for the Space Shuttle external propellant tank (ET). All of them use liquid oxygen and liquid hydrogen, which need to be stored at cryogenic temperatures.
The tests began in April at NASA Marshall Space Flight Center and are part of a collaboration between DuPont and the US space agency, with which the chemicals company has an unfunded space act agreement. The insulation foam is created by mixing a polyol with an isocynate. DuPont produces the polyol with the kevlar fibres and NASA provides the isocynate and mixed the two.
"These are new results from the last two to three weeks. This research is central to the reduction of debris," says NASA's principal investigator on the Kevlar work, Edmund Semmes.
However, the technology is deemed to require too much development to introduce it into Shuttle production and reduce foam loss from its ETs.
The Columbia Accident Investigation Board (CAIB) report stated that a number of factors brought about the loss of foam that struck the Space Shuttle Columbia's port wing, later bringing about the vehicle's destruction on re-entry.
The CAIB report did not conclude that cryogenic pumping, the explosive expansion of trapped liquids when they become gases, was the sole cause of STS-107's substantial foam loss.
Instead the CAIB's range of factors included "severe load, thermal, pressure, vibration, acoustic, and structural launch and ascent conditions".
According to Semmes the increased mechanical strength could improve the foam's ability to resist these forces.
Source: Flight International
