Heart of Boeing's Delta 4 rocket put to the test
BY JUSTIN RAY
Posted: May 7, 2001
Over the past two months the 141-foot tall Common Booster Core and its Rocketdyne RS-68 engine have undergone four firings on the B-2 test stand at Stennis Space Center in Southern Mississippi.
The most recent test on Sunday is expected to conclude this phase of Boeing's Delta 4 development leading to the inaugural launch next March from Complex 37 at Cape Canaveral Air Force Station in Florida, a site that, ironically, also has its historical roots tied to NASA's Apollo program.
Called static hotfirings, the tests have acted as simulated launches for Common Booster Core by putting its propulsion, hydraulics and avionics through their paces.
"The entire program substantially reduces the risks involved in launching a new vehicle," Dan Collins, the program manager of Boeing's fleet of Delta rockets, said of the hotfirings.
The CBC serves as the first stage for all five versions the Delta 4 rocket family, which have the ability to lift cargos from 9,300 to 29,000 pounds to geosynchronous transfer orbit.
Although an additional hotfire is possible, officials are likely to end the tests now. The 553 seconds worth of firings have been successful, proving the Common Booster Core, the heart of Delta 4, and its powerplant work together properly.
The first firing occurred on March 17 and lasted 15 seconds.
"We were real pleased with the results and got an enormous amount of data from that relatively short firing that let us confirm all of our predictions and let us see the whole system perform together," Collins said.
"We were also able to verify all of our (liquid oxygen) and hydrogen fuel filling exercising. We were able verify the timelines and came away very, very happy with how the system is performing."
"Another very successful test," explained Collins. "We gimbaled the engine at both full power and throttled power and were able to see a sustained test. Everything looked very good from the propulsion side. The control system acted just as predicted. And again, got an enormous amount of data that helped us verify that our predictions are right and that the systems acted properly."
The third test on April 23 ran 90 seconds. The engine cutoff occurred when the hydraulics system driving the bell-shaped engine nozzle hit the test limit and an automatic shutdown was triggered. Officials said the system worked as designed; though the test limit would be changed.
Collins described the other objective of the third firing: "We have been adjusting some of orifices in our tank re-press system where we bleed off hydrogen and use it to keep the tanks pressurized. We have been able to do more fine-tuning and we believe we have really got that to exactly where we wanted."
Collins said the extended firing was aimed "to get the time on the entire system and show that we are good to go and there isn't some transient that happens later in the flight regime."
Once the test program is declared complete, the CBC will be lifted from the massive test stand for its transport to Cape Canaveral in early June to serve as a pathfinder for ground handling equipment and the launch pad itself.
Riding in the cargo hold of the Delta Mariner ship, the stage will be delivered to nearby Port Canaveral. After a short trek to Complex 37 on a specially-designed truck, it will enter Boeing's new Horizontal Integration Facility -- the Delta 4 hangar -- where engineers will have the chance to ensure their tools, support equipment and handling structures fit with the rocket. Rollout to the launch pad will follow and the vehicle erected to ensure everything fits in the brand new tower.
The pathfinder exercises are expected to last through August. The first flight-worthy Delta 4 rocket destined to fly the maiden launch next March is due to arrive at the Cape in September.
"In post-testing inspections we found that one of the turbine blades had actually failed and fractured and came off," Collins explained in a recent interview. "We found out that at running 101 percent, which is the baseline where we are going to run the engine, that we had a resonance with a higher frequency mode."
The problem occurred late in the powerplant's lifetime. The particular engine in question had far exceeded its endurance limit. Nonetheless officials ordered a design change.
"We went in and modified the geometry of the blade itself. We redesigned the geometry of the leading and trailing edge to be not quite as sharp and therefore have a thicker leading and trailing edge that would retard the initiation of a crack. Just having a bigger area gives you a lower stress.
"Then we also did some machining on the tip of the blade which took some mass out of it and changed its frequency out of the resonance area.
"We made the blade more resistant to cracking and moved it away from the forcing function that was causing it."
Collins says he is pleased with the recovery effort made.
"We sat down in December and put together a plan that would show us moving towards implementing the modifications to the turbopump and then moving towards getting through development and certification this summer. We are very, very pleased with the progress we've made."
"The engine is proving to be extremely robust. We are basically seeing very few problems in our testing and the system is performing just as predicted to our analytical models."
In addition to the engine on the CBC hotfiring unit, there is another RS-68 being tested at Stennis along with one on a stand at the Air Force Research Laboratory in California.
For a time it appeared the turbopump problem might cause the government to abandon the Delta 4 in favor of rival Lockheed Martin's Atlas 5 rocket for the first military launch as part of the Evolved Expendable Launch Vehicle program. The two rocket families were born out of the Air Force-led EELV effort aimed at reducing the cost of space launches by 25 percent.
Boeing won 21 government satellite launches; Lockheed won 7. But the EELV program calls for one rocket to back up the other, providing the government with two paths to space. The first launch is scheduled for mid-May when a Delta 4 is to carry a Defense Satellite Communications System (DSCS) spacecraft into orbit.
"Now we have choices. We have never been in this position before," said Col. Robert Saxer, the System Program Director for EELV at the Air Force's Space and Missile Systems Center.
"If someone gets in trouble we can stay with that guy or jump over to the other."
Earlier this year the Air Force awarded Lockheed Martin a $420,000 contract to begin the preliminary work required to launch DSCS on an Atlas 5 should the Delta 4 not be ready.
The chores include designing the launch profile and running countless analyses to sketch out the mission.
Since the time of the contract award, the RS-68 testing has gotten back on track and been successful, easing Boeing's concerns of losing the prestigious first government EELV mission.
"We are really pleased by what we see," Col. Saxer said in a recent interview. "The real wild card is getting through the next 90 days and engine tests."
Barring any surprises and the engine is qualified for flight by September or October, Saxer says the Air Force would keep the DSCS satellite on the Delta 4.
The DSCS launch would come 60 to 90 days after the Delta 4's maiden flight, which will be a commercial mission.
Boeing is seeking a paying customer to fly a satellite on the inaugural launch, and the search might be wrapped up soon.
"We are very, very hopeful that within the next couple of weeks we will be making that announcement," Collins said of the first Delta 4 payload.
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