The total heat flux to the stored helium is only 0.8 milliwatts. In designing this dewar Goddard has pushed the design of helium dewars far beyond the previous limits. We have performed a series of studies on every conceivable heat input. As a result of these studies we are now convinced that it should be possible to build a small, light weight dewar that could fly on a small rocket such as the Pegasus. These systems combine stored cryogen systems with either radiative coolers or mechanical coolers.
Hybrid systems can obtain very long lifetimes.
References , with some absracts.