Lockheed Martin Space Systems is the prime contractor for Milstar, a military satellite communications system that provides the Department of Defense and troops in the field with reliable, secure, jam-proof communications between fixed-site, mobile, and portable terminals.

An artist's concept of a Milstar satellite in space. Photo: Air Force

The Milstar system is composed of three segments: The space segment, comprised of six satellites; the terminal segment, composed of communications terminals installed on ships, submarines, aircraft and vehicles; and the mission control segment, based at Falcon Air Force Base, Colorado Springs, CO.

Milstar is the first satellite communications system of any kind that uses signal processing algorithms on the satellites, allowing commanders from every service to establish customized networks within minutes. Current networks must be configured on the ground, require multiple remote locations, and can take weeks to establish using existing commercial and military systems.

Of the five Milstar satellites that constitute the constellation, two first-generation Milstar Block I were deployed in 1994 and 1995. Block I satellites feature a low data rate payload built by TRW Space and Electronics Group, El Segundo, CA, and two satellite crosslink antennas, built by Boeing Satellite Systems , El Segundo, CA. Both of the Milstar I spacecraft, DFS-1 and DFS-2, were launched on Lockheed Martin Titan boosters from Cape Canaveral Air Station, FL.

Three subsequent launches will each deploy a second-generation Milstar Block II spacecraft (DFS-4 through DFS-6), which carry the low data rate payload and a medium-data-rate payload. DFS-4 through DFS-6 will operate in conjunction with both Block I satellites. The DFS-4 spacecraft was launched in 2001.

The Milstar 2-F2 (or DFS-4) seen atop the Titan 4B rocket at the launch pad. Photo: Russ Underwood, Lockheed Martin Space Systems

Milstar communicates via terminals that are compatible among all the military services, including shipborne, man-portable, vehicle-mounted and carried in command and control aircraft. Each terminal transmits and receives voice and data in the Extremely High Frequency and Super High Frequency spectrum. The low data rate payload is designed to transmit voice, data and fax information at 75 bits per second (bps) to 2400 bps. The medium data payload, making its debut on the first Milstar II spacecraft will be able to transmit 1.5 Mega bps.

This combination of data rates and operational frequencies provides U.S. military forces with capabilities not available on current Defense Satellite Communications System satellites or by commercial systems. These capabilities include immunity to jamming and interception and increased mobility for sea, air and ground forces. The Milstar satellite provides enhanced communication security by frequency hopping -- a first for communication satellites.

Illustration of orbiting Milstar satellites in communication with military aircraft, ships and troops. Photo: Lockheed Martin

The Milstar program is led by the MILSATCOM Joint Program Office at the Air Force Space and Missile Systems Center in El Segundo, CA. The on-orbit system is managed by the U.S. Space Command at Falcon Air Force Base, CO.

Lockheed Martin Space Systems ã Sunnyvale Operations, Sunnyvale, CA, is the prime contractor. TRW Space and Electronics Group provides the low data rate payload. Boeing Satellite Systems is providing the medium data rate payload for Milstar Block II. Space Systems ã Denver provides the Titan IV launch vehicle and the wide-body Centaur upper stage. Milstar launches are managed by the 45th Space Wing, Patrick Air Force Base, FL.

General Characteristics

Milstar Satellite:

• Weight: 10,000 pounds
• Length: 51 feet (across payload axis)
• Solar array power: 5,000 watts
• Orbit altitude: 22,500 miles geosynchronous
• Launch vehicle: Titan 4/Centaur upper-stage

Milstar Low Data Rate Payload:

• Data rates: 75 bps for data to 2,400 bps for voice or data
• Channels: 192 channels (100 at 2,400 bps)
• UHF service: Four AFSATCOM IIR channels; One fleet broadcast channel

Antenna arrays:

• Earth coverage horns - one uplink; one downlink
• Agile beams - five uplink; one downlink
• Spot beams - two up/downlink narrow spots (dual use) and one up/downlink wide spot (dual use)
• UHF antennas - one up/downlink (Earth coverage)
• Crosslinks - Crosslink antennas ã one on the +X wing; one on the ãX wing

Milstar Medium Data Rate Payload:

• Data rates: 4.8 kbps for low speed data to 1.544 Mbps for high speed data
• Channels: 32 MDR channels
• Antenna arrays: Six distributed user coverage antennas; two narrow spot beam antennas (nulling antennas)
• Crosslinks - Crosslink antennas - one on the +X wing; one on the -X wing

Milstar Frequencies:

• EHF uplink: 44-GHz
• SHF downlink: 20-GHz
• SHF crosslink: 60-GHz