NASA, Space Portal and Daniel Rasky
PICA heat shield
Rasky had been a key part of the PICA-X carbon tile, without which there would have been no Mars Curiosity on Mars in 2013.
I was curious about the applications of such a material in electronics or semiconductor processes such as a heat shielding material that might be used in conjunction with a heat sink in high temperature areas. I asked Rasky if such an application has been found. Rasky replied that, yes, the one for electronics is a cousin to PICA called SIRCA, that is, Silicone Impregnated Resuable Ceramic Ablator. It’s a silica-based tile with silicone impregnation. It’s RF transparent and non-conductive, so unlike the carbon-fiber PICA material, it would not conduct electricity or block RF signals. The SIRCA material would be good around antennas in that it would not interfere with the RF transmission/reception.
Rasky continued, “So SIRCA is a sort of ‘sibling’ to PICA. They were developed as a family of what’s called a lightweight ceramic ablator that started with ceramic substrates. So you could use a silica substrate or a carbon substrate and then add in a polymer impregnant that you can add in. In effect, you add silicone into the silica substrate and get SIRCA; you add phenolic to the carbon substrate and get PICA.
The family was developed so that you could alter both the ceramic substrate material and the polymer impregnant. You could optimize the material for whatever application you had in mind.”
“It turns out that PICA had a higher heat ablative performance which was of interest to SpaceX, but they also use a variant of SIRCA on the back shell which they call XIRCA, a flexible silica blanket that has silicone impregnation”, Rasky told us. SpaceX developed PICA-X, a version of NASA’s PICA, to protect the Dragon spacecraft on its return to Earth.
A sample of PICA-X heat shield material subjected to temperatures of up to 1850 degrees Celsius (3360 degrees Fahrenheit), at the Arc Jet Complex at NASA Ames Research Center, Moffett Field, California. The NASA-originated PICA material holds the
record for high-speed reentry into the Earth's atmosphere. The SpaceX-developed and manufactured PICA-X variants meet or exceed the performance of the original material, to protect the Dragon spacecraft on its return to Earth. (Image courtesy of SpaceX)
“The real innovation”, Rasky said, “was how to put in a polymer at low density into a largely air void material.” Both the substrates for SIRCA and PICA are 80% to 90% void with only 10% to 20% fiber volume making pretty much an open void. This is how the density is kept low and thus the weight is also low. The innovation came in when they found out how to impregnate uniformly into this type of void structure and not fill it up with the impregnating material which would make if quite heavy---not good for exiting the Earth’s atmosphere or for efficient space travel.