Military Strategic, Tactical and Relay (Milstar) Satellites
Military Strategic, Tactical and Relay (Milstar) satellites are a U.S. military satellite communications system developed to provide highly secure, survivable communications for strategic and tactical users, particularly in nuclear or otherwise highly contested environments. The Milstar program originated in the early 1980s following earlier US Air Force studies, including the STRATSAT concept of the 1970s, which proposed extremely high-altitude EHF satellites for post-nuclear communications but was judged impractical.
Milstar was initially designed as a constellation of eight heavily radiation-hardened satellites operating primarily in the EHF bands, with extensive use of inter-satellite crosslinks. The original concept prioritised survivability and anti-jam performance over capacity, supporting only a small number of users simultaneously. After the end of the Cold War, system requirements were revised to increase data rates, with some reduction in radiation hardening.
Milstar satellites use a unique bus, consisting of three boxes, which are folded during launch and deploy in orbit. The first generation, known as Milstar I, provided low-data-rate (LDR) communications for essential command and control. The first Milstar I satellite was launched on 7 February 1994, followed by a second on 7 November 1995. LDR services support approximately 200 channels carrying voice and teletype traffic at data rates from about 75 bps to 2.4 kbps. These satellites operate in geostationary orbit at 120°W and 4°E.
Milstar II introduced a medium-data-rate (MDR) capability. The first Milstar II satellite, launched on 30 April 1999, failed shortly after launch. Three subsequent Milstar II satellites were successfully launched on 27 February 2001, 16 January 2002, and 8 April 2003. MDR services support data rates ranging from approximately 4.8 kbps up to 1.544 Mbps. User uplinks operate in Q band (around 44 GHz), with downlinks in K band (around 20 GHz).
A defining feature of the Milstar system is its use of inter-satellite crosslinks, enabling global communications without reliance on terrestrial ground infrastructure. These crosslinks operate in V band (around 60 GHz) and support both LDR and MDR services. The satellites incorporate onboard processing, adaptive nulling antennas, and other anti-jam measures, allowing secure and jam-resistant communications with steerable coverage tailored to specific geographic regions.
On 15 December 1995, Milstar was the world’s first satellite system—governmental or commercial—to demonstrate operational inter-satellite crosslinking. A message was uplinked from the national Military Command Center at Fort Belvoir, Virginia, through the Milstar F-1 satellite, crosslinked to the Milstar F-2 spacecraft, then downlinked to commanders at Pacific Command at Camp H.M. Smith, Hawaii, and US Atlantic Command at Norfolk, Virginia.
An enhanced EHF capability, sometimes referred to as Milstar III, was launched in 2006. Milstar user terminals include systems such as the Single Channel Tactical Terminal (SCOTT) and the Single-Channel Advanced Milstar Portable (SCAMP). The Milstar constellation is being replaced by the Advanced Extremely High Frequency (AEHF) satellite system, which builds on Milstar concepts while providing substantially increased capacity and flexibility.