This work was supported by the ASAS Program Office Techbase Program, and by DARPA under contract #DABT63-91-C-0028. The content of the information does not necessarily reflect the position or the policy of the Government and no official endorsement should be inferred. This work was supported in part with equipment provided by the Center for Research on Parallel Computation with National Science Foundation Cooperation Agreement No. CCR-8809165--the Government has certain rights in this material.