Sunday, June 12, 2016

Heavyweight Delta IV Launches Classified Satellite for NRO

A United Launch Alliance Delta IV Heavy lifts off from Cape Canaveral Air Force Station’s Space Launch Complex 37 in Florida with the classified NROL-37 mission for the National Reconnaissance Office. Photo Credit: Mike Deep / SpaceFlight Insider

A classified satellite for the National Reconnaissance Office roared skyward atop a United Launch Alliance (ULA) Delta IV Heavy rocket on the first of five national security launches planned to take place in the next four months. The mission got underway at 1:51 p.m. EDT (17:51 GMT) on Saturday, June 11.

The mission was designated NROL-37 and was conducted to launch an NRO satellite, likely bound for a geostationary perch of some 22,300 miles (36,900 kilometers). It lifted off from Cape Canaveral Air Force Station’s Launch Complex 37 at the very opening of today’s launch window.

The weather was not expected to be very good for today’s launch attempt. The 45th Weather Squadron had predicted only a 40 percent chance of favorable conditions during the attempt, citing the possibility of cumulus clouds, lightning, anvil clouds as well as surface electric fields. However, none of those materialized, and ULA‘s rocket lifted off on time.

Delta IV Heavy rockets are used primarily to send large payloads to geostationary Earth orbit (GEO) directly, instead of the more highly-elliptical geostationary transfer orbit (GTO). Smaller rockets usually insert GEO-bound spacecraft into GTO with the high point of the orbit at approximately the altitude of the spacecraft’s ultimate circular orbit.

Once in GTO, the spacecraft used onboard thrusters to slowly circularize its orbit. This version of the Delta IV is powerful enough to both have a large satellite and place it directly into GEO.

The triple-core Delta IV Heavy is the world’s highest-capacity rocket currently in operation. It can send upward of 63,470 pounds (28,790 kilograms) to low-Earth orbit, 31,350 pounds (14,220 kilograms) to GTO, or 14,880 pounds (6,750 kilograms) to GEO.

“We produce all of the composite components on the Delta IV; pretty much all of the white parts that you see on the rocket were made by Orbital ATK,” Bryan Warren, who works for the Dulles, Virginia-based firm told SpaceFlight Insider. “We also provide some booster separation motors which aid in the separation of the core booster from the others.”

Each of the three Common Booster Cores (CBC) measures an estimated 134 feet (40.8 meters) tall and 17 feet (5.1 meters) in diameter. At the bottom of each CBC is a single liquid hydrogen (LH2) and liquid oxygen (LOX) consuming RS-68A engine, produced by Aerojet Rocketdyne. Together, the three engines generate a total liftoff thrust of 2.1 million pounds-force (9,420 kilonewtons).



The upper stage is powered by a single RL10-B-2—also consuming LH2 and LOX. That stage is 45 feet (13.7 meters) long and 17 feet (5.1 meters) in diameter. The thrust of the single engine is 25,000 pounds-force (110 kilonewtons). It has a total burn time of 1,125 seconds available to use.

Fueling for today’s launch began just around five hours prior to liftoff. The first to be fueled were the three Common Booster Cores (CBC). About three hours before T–0, the upper stage’s fueling was started.

At about T–5 minutes, a planned 15-minute hold began. This delay allowed for one more weather update. Additionally, the launch conductor performed the final readiness poll before liftoff.

After the hold had ended and the countdown resumed, the first thing to occur was the transfer of the launch vehicle to internal power. Three minutes before launch, the propellant tanks in the CBCs were secured at flight pressure; the second stage was pressurized a minute later.

At one minute prior to liftoff, the range gave the final “go” for launch. Then came the call of “green-board!”

About 4.5 seconds before launch, the three RS-68A engines ignited and began throttling to full thrust, at which point the rocket lingered off the pad.

The liftoff was slow due to the enormous size of the vehicle. However, after about 10 seconds, the 1.6 million lbs (733,000 kilograms) rocket cleared the tower and accelerated toward space. Throughout much of the flight, the rocket was visible as weather conditions were only partially cloudy.

About 20 seconds after liftoff, the vehicle started pitching over and began rolling, aligning itself for its designated orbit.

Some 44 seconds into the flight, the center CBC throttled down to 55 percent of its rated thrust to conserve fuel prior to booster separation. Less than a minute after that, the vehicle passed Mach 1.

Within two-and-a-half minutes into the flight, the Delta IV Heavy weighed about half of what it did at liftoff.

Booster separation occurred around four minutes into the flight at an altitude of about 50 miles (80 kilometers), traveling about 10,000 mph (16,000 kph) with a downrange distance of nearly 200 miles (320 kilometers).

The center core engine then throttled back up to full thrust before burning out about 86 seconds later. The center CBC then separated with the upper stage.

About 10 seconds later, the upper stage engine ignited and continued to power its secretive payload to orbit. About 40 seconds after RL10-B-2 ignition, the payload fairing was jettisoned revealing the spacecraft to the harsh environment of space.

While the live broadcast from ULA ended at the request of the customer, the remaining elements of the rocket continued to power toward orbit, arriving in a parking orbit some nine minutes after launch. Over the next hours, the spacecraft will presumably be placed into a classified position in GEO.

This launch was only the ninth flight of the massive Delta IV Heavy—the first since December 2014 (when the rocket was used to send NASA’s Orion spacecraft on its maiden voyage into the silent ocean of space). Overall, 32 launches have been performed by the Delta IV family (including medium versions of the launch vehicle).

The Florida skies won’t hear another Delta IV Heavy for more than two years, when on July 31, 2018, NASA’s Solar Probe Plus is scheduled to launch from the Cape.

That year could see two of the massive boosters fly. Sometime in 2018, another NRO mission, NROL-71, is planned to launch from California’s Vandenberg Air Force Base.

In the meantime, this launch was the first of five national security launches in four months. Next up is the fifth Mobile User Objective System satellite. It will launch on June 24 atop an Atlas V 551 (5-meter fairing, five solid rocket motors, and a single-engine upper stage).

After that, an Atlas V and a Delta IV will fly with NROL-61 and AFSPC 6 back to back July 28 and August 4, respectively.

Finally, another Delta IV will launch the eighth Wideband Gapfiller Satellite for the U.S. military.

Written by: Derek Richardson
Original source: spaceflightinsider.com

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