ULA Delta IV successfully launches AFSPC-6 mission

by William Graham

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 Launch:

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.

AFSPC-6 follows July 2014’s AFSPC-4 mission, which successfully deployed the first two GSSAP satellites. Following over a year of testing, the first pair of spacecraft were declared operational in September 2015. Friday’s launch will complete the constellation.

OA-NASA-Space-Flight-304x234-FinalThe 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.

2016-08-19-003632As with the 2014 launch, 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 oxidised 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.

The AFSPC-6 launch was the first to use an upgraded version of the Delta IVM+(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.

2016-08-19-003716With the Delta IV’s 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.

Delta IV launches at Cape Canaveral take place at Space Launch Complex (SLC) 37, consisting of a single launch pad – SLC-37B – and processing facilities.

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.

Z6Complex 37 was originally built for the Apollo program, serving as a secondary launch facility for the Saturn I and IB rockets during the 1960s.

The original complex consisted of two pads – 37A and 37B – with a shared mobile service tower running on rails between them.

All eight Apollo-era launches from Launch Complex 37 were made from Pad B; including all six orbital launches of the Saturn I and the first orbital launch of the Saturn IB – which flew without a payload. The final Saturn launch from the pad was the Apollo 5 mission, the first test flight of the Lunar Module, which operated unmanned in Earth orbit.

Along with the nearby Launch Complex 34, Complex 37 was mothballed once Apollo’s lunar missions began; although the pads were expected to be reactivated as part of an “Apollo Applications” program to include further Earth orbit missions that would make use of the smaller Saturn configurations.

When the Apollo program was scaled back in favour of what would become the Space Shuttle, most of these missions were abandoned; with only the Skylab space station and the Apollo-Soyuz mission surviving.

NASA determined that for the four Saturn IB launches that were required it would be more cost-effective to adapt the Saturn V launch infrastructure at the Kennedy Space Center than to reactivate either of the old pads – with the launches taking place from a modified Saturn V Mobile Launcher at Launch Complex 39B.

In the 1970s the Apollo-era Complex 37 was demolished, and the site remained abandoned until its selection for the Delta IV program in the 1990s.

The Delta IV’s only East-coast launch pad, SLC-37B was the site of the rocket’s maiden flight in November 2002. That launch carried Eutelsat W5 – since renamed Eutelsat 33B – the only spacecraft the Delta IV has ever launched for a commercial operator.

2016-08-19-003851Friday’s launch was the twenty-seventh flight of a Delta IV from SLC-37 and the thirty-fifth launch overall from the complex.

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 – an upgraded version of the Able, developed as the second stage of the Vanguard rocket.

Through continual upgrades, the Delta grew into more-and-more powerful configurations, culminating in the Delta II which remains in service.

The short-lived Delta III introduced a four-meter cryogenic upper stage similar to the one now used by the Delta IV, while retaining a heavily modified version of the Delta II’s first stage; the Delta IV replaced the first stage will the cryogenic Common Booster Core (CBC).

The numbering of Delta rockets is sequential, and includes the Delta III and Delta IV, but excludes a small number of Thor vehicles with Delta upper stages used by the US Air Force for suborbital missile reentry vehicle tests in the 1960s, and versions of the rocket built under license in Japan as the N-I, N-II and H-I.

Because the Delta IV does not use a stage descended from either the Thor or the Delta, independent analysts do not always include its launches – and in some cases the three Delta III launches – with launches of more traditional Delta vehicles.

2016-08-19-004125The Delta IV’s RS-68A engine ignites five seconds before liftoff, with the solid rocket motors lighting up once the countdown reaches zero; at which point the rocket is committed to launch.

Delta 375 began to climb away from its launch pad, initiating a series of pitch and yaw manoeuvres 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.

2016-08-19-004203The 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 for their jettison, before separating 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.

2016-08-19-004258After separation, the second stage’s RL10 engine deployed its extendable nozzle and began a prestart 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.

2016-08-19-004349Once 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, circularising 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.

2016-08-19-004415About six minutes after spacecraft separation the DCSS will perform a collision avoidance manoeuvre; 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.

Friday’s launch was the third of four Delta IV launches which United Launch Alliance (ULA) will conduct in 2016; following February’s NROL-45 mission from Vandenberg – which carried a Topaz radar imaging satellite – and June’s NROL-37 Delta IV Heavy mission from Cape Canaveral which launched an Orion signals intelligence spacecraft.

The next scheduled launch, planned for mid-October, will deploy the eighth Wideband Global Satcom communications satellite. AFSPC-6 is the eighth launch of the year for ULA, who have also conducted four missions with the Atlas V rocket.

Friday’s launch was the 110th to be conducted by ULA – which operates the Delta IV and Atlas V along with the smaller Delta II – since its formation in December 2006.

The company’s next launch is scheduled for 8 September, when an Atlas V will deploy NASA’s OSIRIS-REX comet sample return mission. It is one of six Atlas launches currently scheduled for the remaining months of the year.

(Images via ULA and L2 Historical).

Related Articles