In addition to application for ZBO of stored cryogenic propellants, sub-cooling to densify LOX and LH2 has the potential to reduce the gross launch weight of a vehicle by up to 20%. Additional applications exist to cool instruments to temperatures as low as 4K. Currently this is accomplished primarily by launching a dewar of liquid helium with the instrument payload. The modified Colling cycle cryocooler technology is particularly well suited to cooling applications in a temperature range from 4K to about 60K. At temperatures above 60K the efficiency advantages of the modified Collins cycle become less significant with respect to that of Stirling and pulse-tube cryocoolers. However, significant technology applications exist in the sub-60K temperature range. These include cooling HTS-transmission cables (60K and lower), the NASA ZBO application (20K), cooling space optical systems (10K), and terrestrial applications such as cooling MRI & NMR magnets (4K) and cooling LTS superconductors and devices (4K).