When NASA needed to cool a space-based spectrometer that will measure X-rays coming from distant astronomical objects to 0.065°K, it turned to adiabatic demagnetization.
It is efficient enough to let its helium last for extended periods in orbit and does not require gravity.
In the device, calorimeters measure heat input, while a heat switch periodically dumps heat into a helium bath (not shown in the illustration). Copper rods serving as a thermal bus connect the calorimeters with a salt pill, where cooling takes place. The salt pill, made of ferric ammonium alum, has wires running through it for good thermal contact between pill, heat switch, and bus. The pill slides into a superconducting magnet. Changing the field of the magnet cools or heats the pill.
The shell of the device, a series of metal rings and tubes, supports the pill with Kevlar cords. The cords hold the pill in place during launch, but have low thermal conductivity, so little heat leaks through them and into the pill.