Spaceflight Insider

Delta IV thunders off the pad with AFSPC-6 payload

United Launch Alliance Delta IV Medium+ 5,2 rocket lifts off from Cape Canaveral Air Force Station's Space Launch Complex 37 in Florida. Photo Credit: Jared Haworth / We Report Space

Photo Credit: Jared Haworth / We Report Space

CAPE CANAVERAL, Fla. — Lighting up the early-morning sky over central Florida, the United Launch Alliance (ULA) Delta IV Medium+ (4,2) rocket thundered off the pad on the sixth U.S. Air Force Space Command (AFSPC-6) mission. As part of the Geosynchronous Space Situational Awareness Program (GSSAP), two Orbital ATK-built satellites were sent to a near-geostationary orbit (GEO).

Liftoff from Space Launch Complex 37 took place at 12:52 a.m. EDT (04:52 GMT) Aug. 19, about five minutes into the 65-minute launch window. The two GSSAP satellites will allow for more accurate tracking and characterizing of human-made objects in orbit. While the spacecraft will be sent to near-GEO, due to the military nature of the mission, the exact parameters of the orbit were not revealed.

United Launch Alliance Delta IV+ Medium 4,2 rocket lifts off with AFSPC-6 from Cape Canaveral Air Force Station Space Launch Complex 37 in Florida. Photo Credit Mike Deep SpaceFlight Insider

Photo Credit: Mike Deep / SpaceFlight Insider

According to Wayne Monteith, 45th Space Wing commander and mission Launch Decision Authority, the Delta IV launch was the culmination of many long hours of work by the entire mission team.

“Congratulations to the AFSPC-6 integrated team and all our mission partners on a successful launch that will enhance our capabilities in space situational awareness and our space-based space situational awareness architecture,” Monteith said in a press release. “Today’s mission is just another example of our unwavering focus on mission success and guaranteeing assured access to space for our nation while showcasing why the 45th Space Wing is the ‘World’s Premier Gateway to Space’.”

This rocket, the Delta IV Medium+ (4,2), is a two-stage, 207-foot (63-meter) tall rocket. This particular version sports a 4-meter fairing and two strap-on solid rocket motors.

The rocket’s common booster core (CBC), the first stage, is 133.9 feet (40.8 meters) tall and 16.7 feet (5.1 meters) in diameter. The CBC has a single Aerojet Rocketdyne RS-68A engine on the bottom that consumes liquid hydrogen and oxygen to produce 702,000 pounds (3,123 kilonewtons) of thrust at sea level.

Each of the Orbital ATK-built strap-on GEM 60 solid rocket motors are 60 inches (152 centimeters) in diameter and 53 feet (12.2 meters) tall. They burn for about 90 seconds and are detached from the stack some 100 seconds into the flight. They will each produce 280,000 pounds (925 kilonewtons) of thrust.

The second stage of the vehicle is the Delta Cryogenic Second Stage (DCSS). It utilizes a single RL10B-2 engine. According to ULA’s product sheet, the engine is the world’s largest carbon-carbon extendable nozzle. Aerojet Rocketdyne also provided 12 MR-106H hydrazine monopropellant thrusters, each with 9 pounds of force (40 newtons) to provide pitch, yaw, and roll control.

The DCSS produces 24,750 pounds (110 kilonewtons) of thrust. It burns liquid hydrogen and oxygen for up to 465 seconds. The second stage is 13.1 feet (4 meters) wide and 39.5 feet (12 meters) long.

A Delta IV Medium+ (4,2) is capable of sending 28,440 pounds (12,900 kilograms) into low-Earth orbit and 13,580 pounds (6,160 kilograms) into geostationary orbit.

Weather for tonight’s launch was predicted by the 45th Space Wing to have an 80 percent chance of acceptable conditions at the scheduled time of liftoff with cumulus clouds being the primary worry. However, those never materialized. At the launch viewing site, skies were clear and the weather remained in the green throughout the countdown.

Fueling of the vehicle began about 3.5 hours prior to liftoff when about 100,000 U.S. gallons (378,541 liters) of liquid hydrogen started filling into the rockets CBC. Liquid oxygen started not long after. Altogether, the four cryogenic fuel tanks (a set for both stages) took about two hours to fill.

At eight minutes prior to flight, the launch director polled the team to verify all was still GO for liftoff.

The Delta IVs RS-68A engine ignited five seconds before liftoff, allowing time for the engine to throttle up to full power and for the flight computer to ensure all was well with the vehicle. At T–0, the rocket’s two Orbital ATK-built strap-on GEM 60 solid rocket motors ignited to provide an extra push off of terra firma.

Delta-IV Medium+ (4,2) AFSPC-6 liftoff

Delta-IV Medium+ (4,2) AFSPC-6 liftoff. Photo Credit: ULA

The rocket began its pitch and yaw maneuver eight seconds after liftoff, angling over the Atlantic before reaching maximum dynamic pressure, also known as Max Q, some 48 seconds later.

The two strap-on solid rocket motors, blasting bright orange flames, burned for just over 90 seconds before being jettisoned seven seconds later.

Delta IV launch streak

Photo Credit: Michael Deep / SpaceFlight Insider

Near the four-minute point into the launch, the white light of the first-stage booster engine ceased and the stage separated. Fourteen seconds after that, the Aerojet Rocketdyne RL10B-2 second stage engine ignited to send the payload on its way to its final geostationary transfer orbit.

Four-and-a-half minutes into its flight, the Delta IV’s four-meter payload fairing jettisoned, revealing the payload to space. Not long after that, due to the military nature of the satellite, ULA ended its live broadcast so as not to reveal the final orbit of the payload.

The two AFSPC-6 satellites will join the other two GSSAP satellites launched in 2014. All four spacecraft will operate in near-GEO, where they will monitor other spacecraft as well as orbital debris. They are designed to perform Rendezvous and Proximity Operations (RPO), which will allow them to maneuver near space objects for a closer look while still maintaining a safe distance.

GSSAP’s goal is to provide up-to-date and accurate tracking of space traffic and debris, enhancing the USAF’s knowledge of the GEO environment while reducing potential collisions in orbit through early detection of potentially hazardous objects. Currently, the USAF tracks over 23,000 pieces of orbiting debris.

GSSAP satellites will communicate through Air Force Satellite Control Network (AFSCN) ground stations. The 50th Space Wing’s satellite operators of the 1st Space Operations Squadron (1 SOPS) out of Schriever Air Force Base, Colorado, are responsible for controlling day-to-day operations.

AFSPC-6 was ULA’s 110th mission overall and the final launch of the GSSAP constellation. Additionally, it was the seventh ULA launch and the second Delta IV Medium variant rocket in 2016. Historically, it was the 375th flight of any rocket in the Delta family, the first having launched in 1960.

The next Delta IV launch is scheduled for Oct. 20. It will launch the eighth Wideband Global SATCOM spacecraft into geostationary orbit.

Video courtesy of United Launch Alliance


Bart Leahy is a freelance technical writer living in Orlando, Florida. Leahy's diverse career has included work for The Walt Disney Company, NASA, the Department of Defense, Nissan, a number of commercial space companies, small businesses, nonprofits, as well as the Science Cheerleaders.

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