Because of the greatly reduced threat of nuclear war in the post-Cold War era, Congress directed DoD in the fall of 1990 to restructure the Milstar program (now designated Milstar 2) to emphasize its utility for tactical military forces and to reduce system costs. The system's survivability and endurability features and constellation size also were reduced. The first Milstar-2 satellite, scheduled for launch in FY 1999, would carry a medium-data-rate (MDR) payload. A complete constellation of LDR and MDR satellites would be achieved with the launch of the fourth Milstar 2 satellite. Replenishment of the four-satellite Milstar-2 constellation would occur between FY 2006 and FY 2009, with the exact launch dates to be determined by actual satellite longevity. Under the plan developed by the Bush Administration, nine Milstar 2 satellites would have been purchased through FY 2011, including a spare satellite planned for delivery in FY 2003. Total expenditures for the Milstar program during FY 1994-99 would be almost $12 billion, including satellites and terminals. Milstar 2 satellites would weigh approximately 10,000 pounds and, consequently, would have to be launched on Titan 4 rockets-an expensive launching mode.(1)
Requirements for a classified payload were deleted. "Heroic" survivability features envisioned for the Cold War environment were eliminated. A higher-capacity Medium Data Rate payload was planned for the second generation Milstar 2 satellite, which expanded its tactical utility. This MDR payload would greatly increase communications capacity compared to the Low Data Rate capabilities on the initial Milstar I satellites. Use of both LDR and MDR would greatly enhance the utility of Milstar II satellites in a wide range of future potential scenarios. The restructured Milstar program also reduced the numbers of strategic terminals and defined new mobile terminals for tactical uses. It reduced program life cycle costs by 25 percent, FYDP [future years defense program] costs by 30 percent and terminal costs by 35 percent.(2)
The Medium Data Rate (MDR) payload (located on the underside of the right spacecraft wing) would be included on the fourth and subsequent Milstar communications satellites. The MDR payload would support 1.544 megabit channels that would be in addition to the 2.4 kilobit low data rate channels originally planned for Milstar satellites. The higher data rate of the MDR payload would enhance support to tactical users in the field. Other segments of the Milstar antenna suite include two crosslink antennas at the ends of the satellite wings. On the left wing are the helical Ultra High Frequency antennas, two of the three directional spot beam antennas (the third is hidden by the wing structure), and the box-shaped agile beam antennas. The large solar arrays generate power to operate the satellite.(3)
Failures within the Centaur upper stage software development, testing and quality assurance process led to a 30 April 1999 Titan IVB mission mishap that resulted in the loss of MILSTAR 3. Loaded with the incorrect software value, the Centaur lost all attitude control. The reaction control system of the upper stage attempted to correct for these errors and fired excessively until it depleted its hydrazine fuel. As a result, the Centaur went into a very low orbit and the MILSTAR 3 satellite separated from the Centaur in a useless orbit, with high and low points of 3,100 and 460 miles. Although Air Force and satellite contractor personnel at Schriever Air Force Base CO tried to save the mission, the Milstar satellite was declared a complete loss 04 May 1999.
Each Milstar satellite weighs about 10,000 pounds and can be described as a “switchboard” in space, directing the traffic it receives from terminal to terminal anywhere on Earth. Since each satellite has the capability to process the received signals on board and then “crosslink” with the other Milstar satellites, there is no need for ground controlled switching stations. Milstar satellites respond directly to service requests from users - establishing, maintaining, reconfiguring, and disassembling the required communications circuits as directed by the users on the ground.
The first two satellites (Milstar I) carried a low data rate (LDR) payload. The LDR payload can transmit 75 to 2,400 bps of data over 192 channels in the extremely high frequency (EHF) range. Encryption technology and satellite-to-satellite crosslinks provide secure communications, data exchange and global coverage. The other three satellites (Milstar II) carry both LDR and medium data rate (MDR) payloads. The MDR payload can transmit 4,800 bps to 1.544 Mbps of data over 32 channels. The higher data rates provide the user the ability to transmit large amounts of data in a short period of time. These 5 satellites, continuous 24-hour LDR and MDR coverage to the warfighter between 65 degrees north and 65 degrees south latitude. The follow-on to Milstar, Advanced EHF consisting of 5 satellites, is fully backward compatible with Milstar and would form an integrated constellation of satellites.
Harris Corporation announced 09 August 2006 that it is the first company to successfully acquire and track low and medium data-rate waveforms on the Milstar 6 satellite using an Advanced Extremely High Frequency (AEHF) Navy Multiband Terminal (NMT) prototype system. An SCA 2.2.1-compliant software programmable modem developed by Harris was instrumental in the successful demonstration. Once fielded, NMT will serve as the common element of naval information networks, providing interconnection of individual naval assets with other services and, eventually, with the global information grid.
Acquisition and tracking of the Milstar 6 satellite was performed at the Harris Naval SATCOM Integration and Test Facility in Palm Bay, Florida, utilizing a KGV-136 — the newest generation cryptographic unit. The successful demonstration was the culmination of two years of Harris-sponsored waveform design and hardware and software development as part of the NMT prototype competition sponsored by the Navy Program Executive Office for C4I and Space.
The Milstar 6 is the last in a series. On April 8, 2003, a Titan 4B rocket blasted the last Milstar satellite into space. There were cheers and applause from the many military customers, engineers, and aerospace professionals who designed, planned, constructed and worked for years to see the first worldwide, secure, anti-jam communications service for tactical users. Milstar 6 was successfully placed into a geostationary orbit about 22,300 miles above the earth. It joins four other Milstar satellites already in orbit to complete the constellation (one satellite suffered a malfunction at launch and was placed in a safe but unusable orbit).
With the MDR payload, Milstar 6 is capable of processing data at speeds up to 1.5 megabits per second. With the LDR payload, the satellite can transmit voice and data at 75 to 2400 bits per second. After testing and systems evaluation, the $800 million Milstar 6 was expected to be fully operational within two months and will aid military forces worldwide by ensuring critical information reaches its destination quickly and securely. The Milstar 6 satellite was expected to last at least ten years.
USA 169 aka MILSTAR 6 / Milstar-II-4 [27711, 2003-12A] was retired in June 2020. MILSTAR 4 and 5, USA 157 and 164 respectively remain in operation in this predecessor to the AEHF constellation in overlapping coverage over Asia, Africa and Europe. MILSTAR 6 used 2257.5 and 2262.5MHz for TT&C.
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