Screenshot from ULA Webcast of the launch of AFSPC-6. Looking like a real rocket for a change
Mission Rundown: ULA - Delta IV M+4,2 - AFSPC-6
Written: December 30, 2022
Second to last Delta IV M+4,2
United Launch Alliance (ULA) successfully launched a Delta IV rocket in the early hours of Friday morning, carrying out the AFSPC-6 mission for the US Air Force. The launch, which took place from Cape Canaveral, occurred slightly after the opening of a 65-minute window, with T-0 at 00:52 local time (04:52 UTC).
Delta IV launches at Cape Canaveral took place at Space Launch Complex 37, consisting of a single active launch pad – SLC-37B – and surrounding processing facilities.
Friday’s mission, Air Force Space Command 6, or AFSPC-6, saw a second pair of satellites for the Geosynchronous Space Situational Awareness Program (GSSAP) being deployed directly into near-geosynchronous orbits.
GSSAP is a four-satellite constellation deployed by the Air Force to monitor satellites in the geosynchronous belt. Therefore USA-270 and USA-271 joins the constellation.
The AFSPC-6 Payload
The GSSAP spacecraft were constructed by Orbital ATK and are based around the GeoStar-1 satellite bus – also known as Aquila.
The GeoStar-1 platform was previously used for the MiTEx-A satellite, USA-187, which formed Orbital’s contribution to DARPA’s Microsatellite Technology Experiment (MiTEx) along with the Lockheed Martin-built MiTEx-B, or USA-188.
The two MiTEx satellites were launched together atop a Delta II rocket in 2006, conducting an experimental geosynchronous satellite inspection mission; a precursor to GSSAP.
The GSSAP spacecraft operate in near-geosynchronous orbits, allowing observations of other spacecraft from above and below.
There is speculation that a GSSAP spacecraft is equipped with Lidar and Radar to enable the US Air Force Space Command to scan foreign or enemy satellites for - shall we say - ‘nasty surprises’ that can be used to disable allied satellites.
The ESPA ring observed on the Delta Cryogenic Second Stage - DCSS indicates a secret delivery system from where seven CubeSats will be deployed. When and where these seven ‘Dwarfs’ will be deployed is unknown since the ULA broadcast ends with fairing jettison per usual.
NRO is the most likely source of funding for these seven test CubeSats.
Computer graphic of the 4 meter DCSS inserting 2 GSSAP Aquilla Surveillance Satellites into orbit
The Delta IV M+4,2 Launch
The Delta IV RS-68A engine ignites five seconds before liftoff, with the solid rocket motors lighting up once the countdown reaches zero; a point the rocket is committed to launch.
Delta 375 began to climb away from its launch pad, initiating a series of pitch and yaw maneuvers eight seconds into its flight to attain the proper trajectory for its ascent to orbit.
Flying on an easterly azimuth over the Atlantic Ocean, the rocket reached Mach 1, the speed of sound, 43.8 seconds after liftoff, passing through the area of maximum dynamic pressure, or Max-Q, 12.8 seconds later.
The GEM-60 motors burned for 93.8 seconds, providing additional thrust as the Delta climbed through the thick lower layers of Earth’s atmosphere.
Once their propellant was depleted, the boosters remained attached for 6.3 seconds to ensure optimal conditions before their jettison 100.1 seconds into the mission.
The Common Booster Core provided thrust for the first three minutes and 57.7 seconds of the launch, after which time it shut down, a point in the flight designated Booster Engine Cutoff, or BECO.
The spent stage was jettisoned 7.4 seconds after cutoff, falling back to Earth to burn up in the atmosphere or fall into the ocean.
After separation, the second stage’s RL10 engine deployed its extendable nozzle and began a pre-start sequence, igniting fourteen and a half seconds after stage separation. Ten and a half seconds later the payload fairing separated from the nose of the rocket.
Timings for mission events after fairing separation have not been announced, and all official coverage of the mission – other than an announcement of successful spacecraft separation – ended at this point.
In order to achieve a geosynchronous orbit, the Delta Cryogenic Second Stage (DCSS) will be called upon to make three burns over a period of at least six hours. Its first burn will last around eight minutes, to establish the vehicle in an initial low Earth parking orbit.
Once the burn concludes the mission will enter a coast phase. Assuming the second burn occurs on the orbit’s first ascending node – the first time the rocket crosses the equator from the southern hemisphere into the northern hemisphere, this coast will last around an hour.
The DCSS’ second burn will be shorter in duration than the first; raising the orbit’s apogee close to geostationary altitude.
After its completion the mission will enter a second coast phase, this time lasting about five hours.
At its conclusion, the stage will restart for a third and final burn – shorter still – to raise the perigee, circularizing the orbit.
About six and a half hours after launch the GSSAP spacecraft will separate from their carrier rocket. ULA confirmed this milestone on Friday.
About six minutes after spacecraft separation the DCSS will perform a collision avoidance maneuver; shortly afterwards it will vent its remaining propellant to mitigate the risks of exploding in orbit. During the AFSPC-4 launch, the plume from the second stage venting was visible to the naked eye over the continental United States.
The Delta IV M+4,2 rocket
United Launch Alliance used a Delta IV rocket to conduct the AFSPC-6 mission, with the rocket flying in the Medium+(4,2) configuration.
This consists of a Common Booster Core first stage with an RS-68A engine, augmented by two GEM-60 solid rocket motors, and a four-meter Delta Cryogenic Second Stage powered by an RL10B-2. The rocket uses cryogenic propellant – liquid hydrogen oxidized by liquid oxygen – in both liquid-fuelled stages.
The Medium+(4,2), or M+(4,2) is the second-smallest of the five Delta IV configurations to have flown; however the smallest, the Delta IV Medium, has not been used since 2006 and is not expected to fly again. The M+(4,2) is the most-flown version of the Delta IV; Friday’s mission will be its fourteenth launch and the thirty-third Delta IV overall.
Last Delta IV M+4,2 to fly split in its major parts. Tank sizes were converted from gallons
The AFSPC-6 launch was the first to use an upgraded version of the Delta IV M+(4,2), with the RS-68A engine replacing the original, less powerful, RS-68 which had been used since the first launch in 2002. This upgrade has already been introduced with all of the other configurations that are still flying; the Medium+(5,2) and (5,4) and the Delta IV Heavy.
With the Delta IV intermediate configurations being phased out, Friday’s launch is expected to be the penultimate flight of the Delta IV Medium+(4,2), and with it the four-meter second stage. The configuration’s final launch is expected to carry the first Block III GPS satellite, and is currently scheduled for 2017.
The Delta IV was integrated in the pad’s Horizontal Integration Building before being transported to the launch pad and raised to vertical. The GSSAP satellites, already encapsulated within their payload fairing, were mounted atop the rocket at the pad.
The rocket that conducted Friday’s launch was numbered Delta 375, indicating that it was making the 375th launch of a Delta-family rocket; derived from the Thor-Delta vehicles first launched in the 1960s consisting of a first stage derived from the Thor missile and a second stage derived from the AJ-10-powered Delta.
