TacSat-4

Spacecraft nº:

USAF spacecraft nº:

Launch data: Designation  37818 / 11052A Launch date  27 Sep 2011 - 15:49 UT  (11:49 a.m. EDT; 7:49 a.m. Alaska time) Launch site  Kodiak Island, LP-1 Launch vehicle  Minotaur-4+ Mission  Military: Technology, Communication Elliptical Earth orbit on Oct 5, 2011: Perigee / Apogee  748 x 12001 km Eccentricity  4,43E-01 Inclination  63.64 deg Period  239.0 min

Spacecraft data:

The TacSat-4 spacecraft, both the COMMx payload and bus, is now in storage awaiting the launch date and new launch vehicle. Credit: Naval Research Laboratory

Description:

• TACSAT 4 is a U.S. Navy satellite flying in a unique, gravitationally-stable orbit ranging from 400 miles (644 km) high to more than 7,300 miles (11,748 km) in altitude. From that orbit, the craft's UHF communications package will connect military units via radio. The satellite was developed under the auspices of the military's Operationally Responsive Space office, which was chartered to investigate and fly less costly niche missions designed to serve tactical needs. TacSat 4 flies three times closer to Earth than traditional military communications satellites, meaning users on the ground have nine times the signal strength compared to legacy systems in higher orbits.
• 10 Ultra High Frequency (UHF) channels; allows forward deployed troops to communicate using existing hand-held radios without the need to stop and point an antenna towards the satellite

Mission details:

• The Naval Research Lab's Tacsat-4 UHF communications satellite was launched into elliptical orbit by a Minotaur IV rocket from Kodiak Island.
  This was the first use of a souped-up Minotaur IV where an ATK Star 48V motor replaces the usual Orion 38 motor. The Star 48 family of motors first flew in the 1980s as part of the PAM-D upper stage for Delta and Shuttle; the 48V variant was the upper stage for the Conestoga 1620 vehicle used in one failed 1995 launch; the Tacsat-4 launch was the Star 48V's first chance to actually fire in space.
• The Minotaur IV was launched at 1549 UTC and inserted Tacsat-4/Star 48V on a ballistic trajectory at 1552 UTC, still attached to the SR-120 third stage. At 1612 UTC the SR-120 separated, and the Star 48V burned to insert the satellite into a 189 x 11833 km x 63.4 deg orbit. After stage 4 separation, Tacsat-4 coasted to apogee and fired its own orbit control motor at 1837 UTC to change the orbit to 340 x 11843 km. The satellite has a 3.7-meter-diameter UHF communications antenna to support military handheld satphones; the vehicle was built by NRL and APL.
• On Sep 28 the orbit was further raised to 646 x 11836 km and the inclination adjusted to 63.6 deg. On Oct 5 another orbit raise put Tacsat-4 in a 748 x 12001 km x 63.6 deg orbit.
• The Minotaur IV stage 4 is built around the GCA (Guidance Control Assembly) package, containing the Star 48 solid motor. The post-burnout mass of stage 4 must be in the 500 to 1000 kg range (?), of which only 139 kg is the empty Star 48V motor.