Intersil has added a radiation tolerant ultra-low dropout voltage regulator (LDO) that can operate over the full military temperature range of -55C to +125C and is offered in a 18-lead hermetic package.

The ISL75051SRH is an SMD-approved single output, ultra-low dropout linear regulator that is immune to high dose radiation up to 100krads (Si), and to single event effects without the need for additional diodes or filters.
 
Dropout voltage is an ultra-low 65mV at 1A, and 225mV at 3A, permitting increased efficiency and battery life. They operate over an input voltage range of 2.2V to 6.0V and can provide output voltages of 0.8V to 5.0V.

The ISL75051SRH can be used for DSP, FPGA and microprocessor core power supplies, post-regulation of switch mode power supplies and down-hole oilfield drilling equipment.

It is currently available in an 18-pin ceramic flat pack package. 

http://www.intersil.com/products/deviceinfo.asp?pn=ISL75051SRH