The Delta IV Heavy rises from the launch pad Dec. 21, 2004, at Cape Canaveral Air Force Station in Florida. A flight anomaly that occurred following the demonstration launch is under investigation. Photo: Carleton Bailie, The Boeing Co.

Aerospace Aids in Delta IV Heavy Launch Anomaly Investigation

EL SEGUNDO, Calif. (2/23/05) -- The Aerospace Corporation is working with the Air Force and contractor team in investigating a flight anomaly that occurred during the demonstration launch of the Delta IV Heavy from Cape Canaveral Air Force Station on Dec. 21, 2004. The Delta IV is the largest of the new generation of rockets known as evolved expendable launch vehicles, or EELVs, which will provide military, civil and commercial users a significantly more flexible, less costly launch capability.

The launch demonstrated the capability of the ground and flight systems for the heavy-lift vehicle configuration and successfully met a number of primary flight objectives. However, the mission did not achieve the desired final orbit. This anomaly was due to a premature commanded shutdown of the three RS-68 engines, resulting in a performance shortfall of approximately 1,500 feet per second at the end of the first-stage flight.

Premature engine shutdown also resulted in a missed target altitude for the demosat, a nonfunctioning payload simulator, and for two secondary payloads.

To date, the team has cleared 47 of 50 potential causes through a rigorous “fault-tree” process. These potential causes included the engine cut-off (ECO) sensors; the main engines; avionics system; basic structure; and external flight environments. Additional data review and analysis will be required to determine whether or not the remaining “branches” could be causes of the anomaly.

“While complex computer simulations are being run to understand what interrupted the Delta’s main engines from finishing their firings, the initial post-flight data reviews conducted by the contractor and Aerospace experts indicate that nearly all other aspects of the systems appeared to have performed quite well,” said Ken Holden, general manager of The Aerospace Corporation’s Evolved Expendable Launch Vehicle Division.

Dr. Mark Brosmer, Delta IV program manager, indicated that Aerospace had performed numerous independent reviews and analyses as part of its launch-verification process and had highlighted to the Air Force a number of technical risks and mitigation plans for this first-of-a-kind vehicle. The preliminary data reviews seem to indicate that all risk areas identified pre-launch were successfully mitigated.

“It’s important to remember that the primary payload for this mission was really the instrumentation we carried onboard,” said Col. John Insprucker, EELV Program director at the U.S. Air Force’s Space and Missile Systems Center. “Our investment in telemetry and additional special instrumentation is helping us quickly zero-in on the cause of the anomaly, and I’m confident the data will also enable us to fine tune all aspects of our future Delta IV heavy-lift missions.”

The leading theory, according to the investigating team, continues to be a condition called cavitation, where liquid oxygen flowing through the feedline from the tank to the engine turns to gaseous oxygen, resulting in a false fuel depletion indication at the ECO sensor. Holden said a test program is also being developed to validate the conclusions, and Aerospace is conducting complementary analyses and test programs to gain additional confidence in the contractor results and to better characterize the response of the ECO sensor in a two-phase liquid oxygen and gaseous oxygen mixture.

“The flight data review process is extremely thorough, scrutinizing not only the extensive, standard flight telemetry data, but also the additional data from more than 500 channels of special instrumentation specifically installed for this first heavy mission,” said Insprucker.

Based on progress to date, the investigation team aims to complete the fault tree closeout and identify the root cause by the end of February. The Delta IV Heavy is scheduled to launch on its maiden voyage carrying a Defense Satellite Program satellite in August 2005.

The root cause investigation should eliminate unlikely and noncredible branches of the fault tree and fishbone analysis, and provide enough confidence for the contractor to clear the GOES-N (Geostationary Operational Environmental Satellite) mission scheduled to launch on May 4. That satellite will fly on the Delta IV Medium, which shares the same propulsion system as the Delta IV Heavy. However, the root cause investigation will likely continue through March when the contractor expects to complete its computational fluid dynamics analyses. Holden said Aerospace will complete most of its tasks by the end of March as well, with some residual verification analyses continuing through the spring.

“I’m extremely proud of the effort that the Aerospace team put forth in support of this historic launch of the first Delta IV Heavy,” Holden said. “The team has continued to provide exemplary support to the investigation now underway to continue to improve the odds of mission success,” he said.

The Aerospace Corporation, based in El Segundo, Calif., is an independent, nonprofit company that provides objective technical analyses and assessments for national security space programs and selected civil and commercial space programs in the national interest.