Delta Heavy Comes To California

The first Delta IV Heavy liftoff from Vandenberg AFB, Calif., illustrated the dramatic purge of hydrogen that results in flames swirling around the three Pratt & Whiney Rocketdyne RS-68 Common Core Booster engines that comprise the first stage.

The Jan. 20 launch from Space Launch Complex-6 (SLC-6) boosted the classified NROL-49 mission into a highly inclined orbit for the National Reconnaissance Office (NRO). Because it was classified, details on the payload, its orbit and the results of the liftoff were not announced. But United Launch Alliance (UAV) reports, “The pad is in great shape and the rocket performed as the customer desired.”

The Delta IV Heavy is capable of lifting 50,000 lb. into 225 low Earth orbits.

The 132-acre SLC-6 site has a storied history as an “almost” important pad whose previous, unrealized, assignments include the U.S. Air Force’s Manned Orbiting Laboratory in the 1960s and being designated the West Coast site for polar-orbiting space shuttle missions. The pad reportedly cost $4 billion to develop and was refurbished for nearly $300 million to accommodate the Delta family of evolved expendable launch vehicles.

It has previously accommodated two Delta IV Medium launchers, but this was the first in the Heavy configuration. The Delta IV Heavy is the largest expendable launcher in the U.S. inventory since the retirement of Titan IV. The combined thrust of its three liquid-fueled Common Core Boosters (CCBs) is nearly 2 million lb.

ULA has a Delta IV Medium launch set for the NRO scheduled for spring 2012 and a Delta Heavy for 2013.

Aside from the size of the vehicle—253 ft. tall and 1.5 million lb.—a spectacular feature of the initial climb-out of a Delta IV Heavy is the intentional fire that swirls around the CCBs. Seconds before liftoff, thousands of pounds of hydrogen are dumped through the three RS-68 engines to optimize their hydrogen/oxygen mix for ignition.

The excess of this hydrogen forms a cloud around the vehicle that is deliberately burned off with spark generators—called radial outwardly firing igniters—just prior to ignition.

Mostly, the excess hydrogen dissipates in a swirl of yellow flame that does little more than blacken the exterior of the first stage. But some of the hydrogen clings so tenaciously to the CCBs that pockets of it are the source of flame shooting out from the sides of the vehicle. ULA says these are harmless and disappear as the vehicle slowly rises.

Photographic evidence gives no indication that any of the hydrogen spectacle reaches the second-stage P&W Rocketdyne RL-10 or the payload fairing, much less the satellite inside.