Screenshot from ULA Webcast of SBIRS GEO-4. A beautiful night. What should I do tonight?
Mission Rundown: ULA - Atlas V 411 - SBIRS GEO-4
Written: December 10, 2022
FYI - SV-4 got launched before SV-3
United Launch Alliance’s Atlas V has launched its 78th flight, lofting the SBIRS GEO-4, a missile early warning satellite. Friday’s attempt was issue free, launching at the opening of the window at 19:48 Eastern time (00:48 UTC on Saturday).
The launch took place from Space Launch Complex 41 (SLC-41) at the Cape Canaveral Air Force Station on Florida’s Space Coast.
SBIRS GEO-4 is the fourth geostationary satellite, but was built as Satellite Vehicle SV-3 when SV-4 was launched fresh off the production line as SBIRS GEO-3 in its place. SBIRS GEO-4 is part of the Space Based Infrared System (SBIRS), a constellation of satellites that use infrared sensors to detect and track missile launches.
Notam: Dangerous areas where Atlas V 411 will drop off one SRB, two fairings and a core booster about 2500 km downrange. The fairing landing site around W 70 degree is missing though.
Replacing the Defense Support Program (DSP), a fleet of satellites that began watching for missile launches in the 1960s, SBIRS is designed to provide the United States with advance warning of an enemy nuclear strike, while also allowing the country to monitor other missile and rocket launches around the world.
United Launch Alliance performed the launch, using an Atlas V rocket. The two-stage Atlas V consists of a Common Core Booster (CCB) first stage, which is powered by an RD-180 engine, and a Centaur upper stage. Up to five Aerojet AJ-60A solid rocket motors can be clustered around the first stage to increase the rocket’s payload capacity, while single and dual-engine versions of the Centaur are available.
Payload fairings with diameters of four or five meters (13-16 feet) are available, with three different lengths available for each diameter.
The SBIRS GEO-4 Payload
The SBIRS GEO-4 satellite was constructed by Lockheed Martin. Based on the A2100M platform, it carries two infrared sensors: a scanning sensor which watches the full disc of the Earth for infrared events and a “staring” sensor to detect smaller short-range missiles which do not produce as much infrared radiation. The satellite has a mass of about 4,500 kilograms (9,920 lb) and is intended for a twelve-year mission.
SBIRS GEO-4 will join the three existing geostationary satellites and four SBIRS HEO sensors in orbit. The previous geostationary satellites were deployed in May 2011, March 2013 and January 2017. Two further GEO satellites, GEO-5 and GEO-6, were ordered in 2012 for launch in the early 2020s.
SBIRS GEO-4 tucked in the fairing getting ready for launch. Do you ever feel the walls closing in?
The Rocket Launch
Atlas V 411 is piece by piece assembled vertically on a mobile launch platform in the Vertical Integration Facility (VIF), about 550 meters (1,800 ft) south of the pad. The mobile launch platform then rolls to launch pad SLC-41.
In preparation for the launch, Atlas was transported to the launch pad on Wednesday.
The SBIRS launch began with ignition of Atlas’ RD-180 engine, 2.7 seconds before the countdown got to zero. Burning RP-1 propellant oxidized by liquid oxygen, the RD-180 is a twin-chamber engine derived from the four-chamber RD-170 series developed for the Soviet Union’s Zenit and Energia rockets.
The RD-180 engine is built by Russian firm NPO Energomash. That fact is a thorn in the side of most Americans. They don’t like to pay royalties to a Russian company.
At about T+1.1 seconds, the AJ-60A solid rocket motor ignited and AV-067 lifted off. The rocket began a series of pitch and yaw maneuvers 6.8 seconds into its flight, putting it on an easterly course over the Atlantic Ocean towards geostationary transfer orbit.
Atlas reached Mach 1, the speed of sound, 57.9 seconds after liftoff, passing through the area of maximum dynamic pressure – Max-Q – 13.3 seconds later.
The AJ-60A burned for about 98 seconds before tailing off and burning out. The spent casing remained attached to Atlas’ Common Core Booster until two minutes and 20.5 seconds into flight, at which point it was jettisoned.
The CCB itself continued to burn until booster engine cutoff (BECO) occurred at four minutes and 3.3 seconds mission elapsed time.
Six seconds after cutoff, the Common Core Booster separated from the Centaur upper stage. Centaur’s single RL10C-1 engine began its chilldown and prestart sequences, with the engine igniting 9.9 seconds after stage separation.
The rocket’s payload fairing separated from Centaur 8.1 seconds into the first of the stage’s three planned burns. The first burn, to insert the upper stage and its payload into an initial low Earth parking orbit, lasted nine minutes and 30.7 seconds.
Following the end of Centaur’s first burn, an event designated Main Engine Cutoff 1 (MECO-1), the mission entered a ten-minute, 26.9-second coast phase.
When Centaur reaches the African Equator line, it is restarted to inject SBIRS GEO-4 into geostationary transfer orbit. After a five-minute, 1.8-second burn the Centaur entered a second much longer elliptical coast phase.
Thirteen minutes and thirteen seconds after MECO-2 – the end of the second burn – SBIRS GEO-4 separated from Centaur to begin its mission.
The expected orbit of SBIRS GEO-4 at separation will be 185.2 by 35,851 kilometers (115.1 by 22,277 miles,) at an inclination of 16.88 degrees from Equator.
SBIRS GEO-4 will use its own propulsion, including a LEROS-1C apogee motor, to reach its operational geostationary orbit.
Using an Atlas V 411 for the launch allows Centaur to make a third burn after spacecraft separation, in order to remove itself from its 185.2 by 35,851 kilometer orbit.
This disposal burn will begin 31 minutes and 45.6 seconds after SBIRS GEO-4 separates, and will last ten seconds. This burn will change the orbit to -30 km by 35,851 kilometers.
That will deorbit Centaur second stage, with reentry expected over the Pacific Ocean, about nine hours and 25 minutes after liftoff. On the way back down it will vent its tanks in order to empty them for propellant and orbit maneuver hydrazine propellant.
The Centaur second stage has 14 minutes 35 ‘42’ seconds of burn time available on this mission with the amount of propellant liquid hydrogen and oxygen. The throttle setting on the engine is unknown, but there is a limit to the g-load on the payload. At full throttle it would burn out sooner, and the payloads solar panels could be damaged.
The reported or planned timeline of events in this launch differs from the recorded video timeline on some points. The computer animation is delayed 4 seconds so that the call outs happen before the computer reacts. The lengths of Centaurs two main burns are slightly shorter compared to the articles mentioned start times and shutdowns.
7 second less burntime means a different throttle setting or more change in inclination given to the payload. So in conclusion: ‘Don’t sweat it’. It’s rocket science after all.
Centaur could give it all to change SBIRS GEO-4 inclination a little more at apogee. Top of an elliptical orbit. Bottom of an elliptical orbit is perigee. But then Centaur would become derelict space debris for several years.
The Atlas V 411 rocket
Atlas V was originally developed by Lockheed Martin as part of the US Air Force’s Evolved Expendable Launch Vehicle (EELV) program. The maiden flight of Atlas V was made in August 2002, carrying Eutelsat’s Hot Bird 6 communications satellite into orbit as part of a commercial mission contracted by International Launch Services (ILS). The SBIRS GEO-4 mission is Atlas V seventy-fifth flight.
The Atlas, with the tail number AV-076, flew in its 411 configuration with a four-meter payload fairing, single-engine Centaur (SEC) upper stage and a single solid rocket booster. The launch used a Long Payload Fairing (LPF), which despite its name is the shortest of the three four-meter fairings with a length of 12.2 meters (40 feet).
This Atlas configuration differs from the 401 version used for the previous three SBIRS GEO launches – which did not use any solid rocket boosters. The change of configuration has ostensibly been made to ensure Centaur can be deorbited after spacecraft separation, helping to mitigate space debris. On previous SBIRS launches, Centaur has remained in a disposal orbit, close to geostationary transfer orbit, at the end of its mission.
Atlas V 411 split in its major parts. The orange booster burns RP-1 kerosene and liquid Oxygen
