Cold Launch Sled

Neodymium (NdFeB) magnet remanence (magnetization, in Teslas) decreases with temperature above 20C. Remanence is maximum, 3% higher than 20C "room temperature", at -110C. Remanence falls off below that temperature, reduced to 100% again at -155C, and reduced to 87% at -196C (liquid nitrogen boiloff temperature at one atmosphere pressure). Chilling the sled magnets below 150C before launch will maximize their remanence later, during the middle of the launch run, and also reduce the resistivity of the aluminum eddy current shield.

attachment:coldMdMag.png

attachment:cryoaluminum1.png

LN2 seems a little too cold to be an optimum "contact" coolant. It has a heat capacity of 1040 Joules per kilogram-Kelvin, slightly better than liquid water around room temperature. So how about dry ice, frozen CO2?

attachment:CO2ice.png