Communications in the 21st century is expected to include a large demand for broadband multimedia services. This demand will be driven by the continued and increasing proliferation of broadband services to fixed users, the growing need for information exchange, and market forces and competition on a global scale. A future need is projected to extend these broadband multimedia services to users aboard mobile platforms. The objective of this report is to utilize the systems engineering process to define requirements for this future system and propose a conceptual design. Communications deficiencies are projected based upon an analysis of communications service needs, projection of the fixed communications architecture of the future, and an assessment of currently planned communications systems. Future mobile communications needs are defined and developed into system operational requirements. Preliminary systems analysis and tradeoffs are performed to propose potential system solutions. Several system planning and management considerations are also addressed towards the realization of this future system. This report proposes that the future need identified would best be satisfied by a Low Earth Orbiting (LEQ) satellite communications system utilizing digital B-ISDN technology, high data rate satellite crosslinks, and distributed management through intelligent network concepts. A Life Cycle Cost (LCC) model is also developed to evaluate complete life cycle costs of the LEO SATCOM system at various orbital heights and satellite and launch parameters.