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Investigators probing what went wrong with AEHF 1

Posted: September 2, 2010

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As tiny thrusters continue to nudge the U.S. military's AEHF 1 satellite toward a higher orbit, investigators hope to know within the next few weeks what knocked out the craft's main engine and whether the program's next launch will be delayed.

An artist's concept of AEHF 1. Credit: Lockheed Martin
The original plan of maneuvering the communications spacecraft toward geosynchronous orbit was aborted after the Liquid Apogee Engine failed to accelerate the satellite during two attempted burns on August 15 and 17.

The system detected that the proper boost wasn't being generated and immediately terminated the operations, leaving the satellite in its initial orbit where the Atlas 5 rocket deployed the craft during launch August 14.

So what could be the culprit behind the troubles?

"We actually don't know...We just know it's not performing the way it's supposed to," Dave Madden, Military Satellite Communications Systems Wing program director at the Air Force's Space and Missile Systems Center, told reporters in a briefing this week.

"What makes it confusing is it wasn't that it failed. Because the overall propulsion performance wasn't what was expected, the system shut it down. That's why we are going through the root cause analysis. The problem could range all the way from the propulsion system up inside the spacecraft, to a flaw in the LAE engine. We could have a bad valve in the system, all the way to the propellant wasn't heated or cooled properly, or we had a bad engine."

Four different teams were assembled with "hand-picked" representatives from the Air Force, satellite-maker Lockheed Martin and the Aerospace Corp. to direct activities, oversee mission replanning, monitor the satellite's health and investigate the anomaly.

The Liquid Apogee Engine consumes hydrazine fuel and nitrogen tetroxide to produce about 100 pounds of thrust. It was supposed to perform three burns over a few days to push the satellite into an intermediate orbit where its electric propulsion system would take over and finish circularizing the orbit to the intended 22,300-mile altitude over the equator.

The new strategy developed to save the satellite will use the craft's 5-pound-thrust steering jets to partially raise the orbit, then rely heavily on the so-called Hall Current Thrusters in xenon-fed electric propulsion system to get AEHF 1 into the proper orbit by next summer.

The first burn in the "crawl, walk, run" scheme occurred on Sunday and lasted 40 minutes. Another has since been performed, increasing the orbit's low point by an additional 100 miles.

"We have a number of more burns that are going to gradually get longer, then we'll go into a second phase where they will get even longer as we basically qualify out these engines to make sure these 5-pound thrusters can support the demand," Madden said.

Despite the main engine no longer being usable, Madden says he's confident the new plan can get the satellite into geosynchronous orbit with enough remaining fuel to keep the craft operational for its entire 14-year mission life as required.

But it will take considerably longer because controllers must perform the maneuvers only when its most optimal to conserve every drop of fuel possible. AEHF 1 will need sufficient hydrazine and xenon supplies left over to perform orbital maintenance and repositioning tasks throughout its life.

"I gave them an allocation of fuel that they can use (for orbit raising) and can't exceed because we need a certain amount of fuel when we get to orbit. So we're going to fire and get part ways to where the LAE was going to get us, then the Hall thrusters will take us the rest of the way.

"Believe it or not, the efficiency we are getting on how we are burning them and spreading it out over time is making up the difference," Madden said.

As for the investigation, officials say the inquiry has telemetry relayed from the satellite, plus records saved from the propulsion system's ground testing and the pre-launch processing activities.

"When you put those three things together, that's how we'll end up figuring out root cause," Madden said.

After the initial aborted burn on August 15, controllers altered the telemetry stream to get additional data when the second attempt was made two days later.

"When we did the second burn, we significantly increased the data points, which gave us a better subset of data to help us evaluate the whole propulsion system."

Madden said one of the first questions he asked was whether the system had experienced problems on the ground before launch. The answer was no.

"The propulsion system has been clean since Day 1. We've had no major issues, and that's why the root cause analysis is focusing so heavily on the entire propulsion system to see if we've had some process failure or a component failure that caused this issue."

The original plan called for three months of orbit raising to deliver the satellite to its geosynchronous test location at 90 degrees West longitude. The communications payload would undergo rigorous testing over the subsequent months, clearing the way for the Air Force to launch the AEHF 2 satellite in early 2011.

However, the slow maneuvering that AEHF 1 must endure means the craft won't reach geosynchronous orbit until next June or July, Madden estimates, and the communications testing won't be finished until late 2011.

"It was three months to get to orbit and then it was three-to-four months of checkout. Now we're probably talking about 10-11 months to get to orbit and still three-to-four months to check it out," Madden explained.

"We've been scheduled on the Range and we're on track for a February launch (of AEHF 2). That's been the plan all along. The foundation of that plan was that you'd launch SV-1, (spend) 90 days to get to orbit, check out the vehicle and ensure the payload is operating, then you'd launch the second Advanced EHF," Madden said.

"With the root cause analysis in question and the aspects of not being able to check out the payload till a later date, we need to sit down with senior leadership and see where they want to go from here. Right now, we have uncertainty as to when we'd launch the second vehicle."

Officials are eager to hear what investigators find in their inquiry and whether the problem could strike the upcoming AEHF 2, too. That craft currently resides at Lockheed Martin's factory in Sunnyvale, California.

"The biggest driver is we have SV-2 is working its way through its environmental checks and final checkout tests. (The investigation) will drive, potentially, a modification or check associated with that vehicle," Madden said.

A decision to delay AEHF 2 from early 2011 could result in the launch slipping an entire year. The Atlas 5 rocket schedule at Cape Canaveral is jammed with other Air Force launches for the Global Positioning System, the new SBIRS missile-detection spacecraft and possibly the second X-37B spaceplane in the first half of 2011. The second half is consumed with time-critical NASA launches of the Juno probe to orbit Jupiter in August and the Mars Science Laboratory rover Curiosity in November, which must lift off when the planets are aligned.

"If you look at the launch schedule, it is pretty busy right now, and there's also a NASA planetary blocked out period next year where they have a couple interplanetary missions going on. So if we miss our February slot, it'll be pretty sporty getting back into the manifest anytime quickly," Madden said.

"But that's an operational decision. They could re-prioritize missions or they could delay us to a later date. The bottom line is right now the manifest is pretty busy and senior leadership would have to make the call as to whether they want to change the firing order of the satellites going up."

The AEHF series of spacecraft will replace the aging Milstar constellation to provide secure communications for the military. Madden said the five Milstars continue to operate, giving the Air Force some breathing room to wait on AEHF 1.

"Right now, all of the vehicles are healthy and the gap analysis we've done shows we're fine in the window we're operating in. So we have no concern about losing a Milstar before this Advanced EHF gets entered into the ring."

As for Lockheed Martin facing contract penalties over the AEHF 1 problem, Madden told reporters he didn't want to discuss that yet. The company's responsibilities include getting the satellite into the proper orbit and successfully checked out.

"I won't get into the financial aspects. There's nothing worse than beating somebody up while they're trying to help you fix a problem," Madden said.

"When you're in a middle of crisis, the last thing I want to be doing is speculating on punishment phases when I want to keep focused on recovery."