Challenges associated with replicating heat shield re-entry
temperatures using Joule heating has been discussed using a prototype
of the Orion-MPCV.
Thermal diffusivities of tungsten and graphite materials play a
significant role in the temperature distribution field along the
entire heat shield. The temperature irregularity zone is due to the
heat sinking effect of tungsten material, however the temperature
irregularities tries to regulate as temperature contours move further
away from the stagnation region.
Coupling prototype heat shield with cylindrical tungsten rod of
diameter 8-10mm at a current rating of 600-800A gives the best
temperature distribution field to a maximum of 1700K which is lesser
than re-entry temperatures of the Orion-MPCV.
The heat shield used had a 50mm diameter and 2mm thickness. However,
the 2mm thickness was too small to produce any temperature deviation
in the stagnation line within temperature irregularity zone.
Future work should aim at optimising the model (heat shield plus
electrical connections) that will enable heat shield to attain
temperatures up to 3000K for re-entry applications. This can be done
by optimising material thickness through series of simulation. Also
the cooling effect at the tungsten/graphite junction has to be
carefully investigated.