Hughes Space and Communications Company (HSC), now known as Boeing Satellite Systems, Inc. (BSS), has been a major part of the Milstar system team since 1982, supplying sophisticated, state-of-the-art radio frequency (RF), microwave, and antenna subsystems hardware.

The Milstar system is a tactical and strategic multiservice program involving the Air Force, Army, Navy, and other agencies. Milstar provides protected communications for command and control of the United States war-fighting forces. These include the National Command Authority (NCA), military tactical and strategic forces, Air Force Space Command (AFSPC), and other users. The Program is managed by the U.S. Air Force Space and Missile Systems Center.

The Milstar system provides uplink communications at extremely high frequency (EHF), 44 GHz, and ultrahigh frequency (UHF), 300 MHz, and downlink communications at super high frequency (SHF), 20 GHz, and UHF, 250 MHz. It will provide survivable medium data rate (MDR) and low data rate (LDR) communications services between terminals worldwide using crosslinks operating in the 60 GHz region. Survivability and endurability requirements are satisfied by anti-jam, hardening, and system autonomy features.

The Milstar system is composed of three segments: the satellite or space segment, the mission control segment, and the terminal segment. The Milstar space segment is procured in two versions. The first two satellites (Milstar 1) provide secure LDR communications. Subsequent satellites (Milstar 2) carry secure MDR communications in addition to the existing secure LDR communications. Milstar 1 and 2 satellites are fully interoperable for LDR communications.

Lockheed Martin Space Systems is the prime contractor responsible for the space and mission control segments, as well as system interfaces.

Boeing has the prime responsibility for supplying the MDR and crosslink payloads as tactical extensions to the existing robust LDR payload. TRW is the major subcontractor, supplying the MDR antennas and the digital subsystem.

Mission
The Milstar satellite communications system will provide sufficient capacity to execute essential strategic and tactical missions under stressed conditions and will support multiple users simultaneously without reliance upon physically vulnerable nodes.

Strategic missions require survivable communications among the NCA, the commanders in chief (CINCs), and other nuclear capable forces. Tactical missions require survivable communications among forces in the same tactical theater and among forces in different tactical theaters.

Milstar LDR supports strategic and tactical users' requirements for high anti-jam and nuclear scintillation protection. Milstar MDR will meet the needs of multiple users by supporting the connectivity of tactical and conventional forces.

MDR payload
The Milstar MDR payload, located on the Milstar satellite X wing (above), provides tactical connectivity via thirty-two uplink channels shared among eight uplink coverage areas. Although the capacity of each channel is greater than 2 Mbps, the maximum allocatable to a single user is compatible with commercial T1 standards (1.544 Mbps). MDR communications data are linked between adjacent satellites in the Milstar constellation by the crosslinks at a 10 Mbps encoded data rate. On-board switching ultimately provides user connectivity to a single downlink switched among the eight coverage areas.

Tactical coverage is provided by the MDR antenna coverage subsystem (ACS), consisting of eight narrow spot beam antennas: two narrow spot beams with nulling capabilities (nuller antennas) and six distributed user coverage antennas (DUCAs), each supporting simultaneous uplink and downlink communications. Narrow spot beams provide good isolation of users from out-of-beam jammers. The nuller antennas resist in-beam jamming by sampling the beamforming elements in the uplink signal, processing correlations, and providing feedback to the beamforming network to null the antenna pattern in the direction of the jammer.

The received EHF signal is amplified, de-hopped, and downconverted by the MDR RF subsystem (RFSS). The baseband signal is passed on to the digital subsystem (DSS), for demodulation and routing. The routed signal is passed back to the RFSS for differential phase shift key (DPSK) modulation, hopping upconversion, amplification and filtering. Finally it is switched on a hop-by-hop basis among the eight downlink coverage areas provided by the ACS. The RFSS also supplies the high fidelity frequency references by the MDR payload derived from the references provided by the LDR payload.

Uplink/downlink/crosslink connectivity is provided by the DSS. The DSS demodulates uplink baseband data, and deinterleaves and decodes uplink and crosslink messages. It also routes uplink and crosslink data to the appropriate downlink and crosslink, encodes and interleaves downlink and crosslink messages, and provides time tracking responses to terminal uplink timing probes.

Crosslink payload
The crosslink payload provides V-band (60 GHz) data communication between Milstar satellites for both the MDR and LDR payloads, including modulation and demodulation of the data, upconversion, amplification for transmission, and downconversion. Performing the above functions are two millimeter wave assemblies (MWAs), which are located on the -X wind and the +X wing, along with the antennas. The MWAs contain all the millimeter wave equipment, and a panel located on the -X wing contains all the equipment necessary for data modulation and demodulation at the IF frequencies.