Screenshot from ULA Webcast of the launch of SBIRS GEO-6. Morning is breaking in purple colors
Mission Rundown: ULA - Atlas V 421 - SBIRS GEO-6
Written: December 7, 2022
Sixth ‘redeye’ taking to the sky
ULA launched the SBIRS GEO-6 satellite on an Atlas V rocket in the 421 configuration for the United States Space Force’s Space Systems Command (SSC).
Liftoff of the SBIRS GEO 6 mission from Space Launch Complex-41 at Cape Canaveral Space Force Station occurred at the opening of a 40-minute window at 6:29 AM EDT (10:29 UTC) on August 4, 2022.
The Space-Based Infrared System, or SBIRS, plays a key role in defending the United States and its allies from missile attacks. Combining dedicated satellites in geosynchronous orbit and sensors hosted on other spacecraft in inclined elliptical orbits, it keeps a constant watch for the signs of rocket and missile launches around the world.
SBIRS satellites are equipped with infrared sensors to detect launched missiles by the heat signatures of their exhaust plumes.
Thursday’s launch deployed the constellation’s sixth geosynchronous satellite. SBIRS GEO 6 is also expected to be the last SBIRS satellite to launch before a next-generation missile detection system begins deployment in the coming years.
The SBIRS GEO-6 Payload
The SBIRS GEO 5 and 6 spacecraft are of an upgraded design, based around Lockheed Martin’s modernized LM 2100M satellite bus. GEO 5 launched in May 2021, with Thursday’s launch of GEO 6 completing the constellation.
Two additional satellites had been planned but were canceled in the Air Force’s 2019 budget to free up resources for the successor program, Next-Generation Persistent Overhead Infrared (NG-OPIR). DSP, SBIRS, and NG-OPIR were all transferred from the Air Force to Space Force upon Space Force’s formation in 2019, with Space Delta 4 responsible for the projects.
NG-OPIR will use satellites in both geosynchronous and Molniya orbits. The first NG-OPIR GEO satellite is currently slated for launch in 2025, while the first launch of the NG-OPIR Polar series – the Molniya orbit spacecraft – is expected no earlier than 2027.
A pathfinder satellite, Wide Field of View (WFOV) Testbed, was launched as part of the US Space Force 12 (USSF-12) mission on the previous Atlas V launch.
The Rocket Launch
Atlas rolled out to the launch pad on Tuesday atop the MLP. Departing the VIF at 10:00 a.m. local time (14:00 UTC), the launch platform was “hard down” at the pad one hour and 22 minutes later. Fuelling of the first stage propellant tanks with RP-1 – rocket-grade kerosene – was completed on Tuesday evening.
Loading of the second stage’s liquid hydrogen (LH2) fuel and the liquid oxygen (LOX) oxidizer for both stages takes place on launch day as these propellants boil off at ambient temperatures. One way of keeping cryogenic propellants chilled is using liquid Helium as gas bubbles or liquid Nitrogen in pipes as heat exchangers.
The first stage is powered by a single RD-180 engine with two combustion chambers. At the T-2.7 second mark in Thursday’s countdown, the RD-180 ignited, with the twin GEM-63 motors also lighting shortly afterward.
At T+1.1 seconds the thrust produced by the rocket exceeded its weight, so it lifted off and began its climb toward space. Six seconds into the flight, Atlas initiated its first pitch and yaw maneuver to put it on the right track - azimuth - for its destination orbit.
Atlas flew east from Cape Canaveral, out over the Atlantic Ocean. It took 48.9 seconds for the rocket to reach Mach 1, the speed of sound. Three and a half seconds later Atlas V passed through Max-Q, the area of maximum dynamic pressure.
The GEM-63 solids burned for about 98 seconds before depleting their propellant. After burnout, the spent casings remain attached to Atlas until conditions are right to ensure a clean separation with no risk of recontact between the spent motor casings and the Atlas vehicle. The SRMs were jettisoned at two minutes, 13.3 seconds mission elapsed time.
With the GEM-63s gone, the RD-180 engine continued to fire alone. It burned for the first four minutes and 12.4 seconds of the mission, with its shutdown being a mission milestone designated Booster Engine Cutoff (BECO).
Six seconds after BECO the Centaur upper stage separated from the booster and began its prestart sequence. Ignition of Centaur’s RL10C-1-1 engine took place 10 seconds after stage separation. Eight seconds after Centaur ignites, the rocket’s payload fairing separated, exposing SBIRS GEO 6 to space.
The SBIRS GEO 6 mission marks the second flight of the RL10C-1-1 engine, in place of the RL10C-1 that has been used on most of Atlas V’s recent missions. This new version of the veteran RL10 engine was first flown on the SBIRS GEO 5 launch last year and incorporates an extended nozzle for increased thrust, and improved manufacturing techniques.
Despite performing nominally during its first flight and successfully delivering the payload into orbit, the engine nozzle - bell - was observed to be vibrating far more than had been expected, so engineers have taken their time to review data from that mission before allowing the new engine to fly again.
For Thursday’s launch, the engine flew without deploying its full nozzle extension, leaving it about the same length as the RL10C-1.
Although the RL10C-1-1 is being introduced on Atlas V, it is expected to go on to power a new version of Centaur under development for ULA’s next-generation rocket, Vulcan.
Thursday’s mission called for Centaur to make three burns of its RL10C engine. The first burn was the longest, lasting eight minutes and 27 seconds to place Centaur and SBIRS GEO 6 into an initial parking orbit.
After a ten-minute coast phase, Centaur made another four-minute, 44-second burn to raise itself into an elliptical transfer orbit. This burn is followed by an extended coast as the upper stage and its payload gain altitude.
During this coast phase two small satellites, named EZIO-5 and 6, are expected to be deployed from Centaur’s Aft Bulkhead Carrier. These are likely similar to the EZ-3 and EZ-4 satellites deployed during the first coast of the SBIRS GEO 5 mission, which were 12U CubeSats flown as part of Space Systems Command’s Technology Demonstration Orbiter (TDO) program.
Two and a half hours after the second burn concludes Centaur fired again for 58 seconds to further raise the orbit.
SBIRS GEO 6 separated two minutes and 49 seconds after the end of the third burn.
Centaur then performs a blowdown and passivation before the official end of the launch mission at T+3 hours, 59 minutes, and 27 seconds mission elapsed time.
The Atlas V rocket
The Atlas V that carried out Thursday’s mission has the unique tail number AV-097. The vehicle is in the 421 configuration, which incorporates a four-meter-diameter payload fairing, a pair of solid rocket boosters to augment the thrust of the first stage, and a single-engine Centaur upper stage. AV-097 lifted off from Space Launch Complex 41 (SLC-41) at the Cape Canaveral Space Force Station in Florida.
Atlas V is a two-stage rocket. Its Common Core Booster (CCB) first stage powers the early stages of flight as the rocket climbs through Earth’s atmosphere. Centaur, a highly-efficient cryogenic fuel upper stage, then takes over to deliver the payload into its prescribed orbit.
Thursday’s launch targeted a geosynchronous transfer orbit with a raised perigee – the point of the orbit closest to the Earth’s surface – of 5,218 kilometers (3,243 miles, 2,818 nautical miles), an apogee of 35,335 km (21,956 mi, 19,079 nautical miles), a inclination of 17.63 degrees.
Facts on the Atlas V launch vehicle
Height of Atlas V 421: 194 feet (59.1 meters)
Fuel onboard: 91,000 gallons of liquid propellant
First stage Atlas: 25,000 gallon RP-1 - 48,800 gallon LOX
Second Stage Centaur: 13,050 gallon LH2 - 4,150 gallon LOX
LOX+LH2 = 66,000 gallon of cryogenic liquid propellant
150 kg (340 lb) of Hydrazine is stored in a pair of bladder tanks
Helium storage tanks: Unknown so far
2 GEM-63 SRB: 200,000 pounds of solid fuel
Mass at liftoff: 969,500 pounds (439,758 kg)
Thrust at liftoff: 1.6 million pounds (7.1 mega-Newtons)
Orbit: Geosynchronous Transfer Orbit - 3,243 x 22,000 miles (5,218 x 35,500 km)
Graphic of Atlas V 421 split in its major pieces. The 12 U ‘toolbox’ sized EZIO 5 and 6 leaves first
