Spaceflight Now: Mission Report

U.S. weather satellite grounded till at least April

Posted: January 23, 2001

The Titan 2 rocket's Space Launch Complex 4-West pad at Vandenberg Air Force Base in California. Photo: Justin Ray/Spaceflight Now
Efforts to understand and correct a mysterious problem that could have doomed the $430 million mission of a U.S. military weather satellite while work to service the craft's ride to orbit -- a Titan 2 rocket -- will delay launch until at least mid-April, the Air Force said Tuesday.

The Defense Meteorological Satellite Program F16 spacecraft was supposed to be in orbit around Earth's poles by now, but nagging glitches scrubbed weekend launch attempts at Vandenberg Air Force Base in California.

And in the end, fate may have smiled on the Air Force late Sunday when the satellite's Inertial Measurement Unit guidance brain suffered two problems while still on the launch pad.

First, the gyroscopes within the IMU suddenly dropped out of flight mode. That incident was followed 20 minutes later by the AC and DC power supplies autonomously switching from primary to backup systems.

"We felt those types of events were consistent with a loss of the clock signal from the spacecraft to the IMU," Col. Randy Odle, the DMSP program office director explained in an interview Tuesday. "Essentially that is a devastating situation for the spacecraft."

In fact, the satellite would have been in serious trouble if the problem occurred during launch because it would have rendered the craft unable to navigate itself. The IMU computer is vital in controlling the satellite during the apogee kick motor firing needed to reach orbit and subsequent operations in space.

"It would be very hard to convince ourselves that we didn't have a problem after seeing these kinds of things. If we would have launched and these events would have occurred on ascent, we would have essentially had no navigation capability for our satellite and would have lost the mission."

The near-three month postponement is a "best case scenario" if the yet unexplained trouble inside the satellite can be fixed quickly and the Titan 2 rocket's engines reconditioned.

But the delay could very well stretch into September or beyond if more extensive troubleshooting is required to diagnose and fix the problem.

  DMSP in pad clean room
A file image shows the last DMSP weather satellite atop its Titan 2 rocket in launch pad clean room in 1999. Photo: Lockheed Martin
The first task at hand is putting the Titan 2 rocket back into a safe condition so technicians can gain access to the Lockheed Martin-built satellite next week.

Launch pad crews have already installed safing pins in the Titan 2's ordnance, and are now setting up the process of draining the Aerozine 50 hydrazine fuel and nitrogen tetroxide oxidizer from the rocket's stages. The ordnance then will be disconnected and the rocket's three-section nose cone removed, Air Force Launch Director Lt. Col. James Hyatt said in an interview Tuesday.

The nose cone, or payload fairing, must come off the rocket for the investigation to begin in earnest.

"The sooner we can get to the spacecraft, the sooner we will be able to check it out to see if we can convince ourselves the problem is something that we can identify and correct while the spacecraft is still mated to the booster," Odle said.

In the best case scenario, the Air Force is hoping that it can determine exactly what went wrong, implement a quick fix and be ready for launch possibly around April 13.

"Whether that is likely or not, we won't know until we open up the fairing," said Odle.

And that assumes rarely required engine work on the Titan 2 can be accomplished in time and the launch of a Titan 4 rocket from the neighboring pad at Vandenberg's Space Launch Complex-4 with a secret national security payload does not take priority over the DMSP.

During the most recent countdown for the Titan 2, which ended in a last-minute halt on Sunday, the prevalves on the rocket's stages were opened in the final 30 seconds and allowed fuel and oxidizer to be released into the engines. The valves can't be closed and a deadline of 48 hours was imposed on the launching the rocket in such a condition or else face an extensive servicing.

When the IMU problem cropped up late Sunday and the scheduled Tuesday blastoff called off, technicians were instantly presented with the chore of refurbishing some parts of the engines while examining others to ensure they are suitable for use when the launch finally does occur.

But it is a job never done before on a Titan 2 rocket at Vandenberg, Hyatt said. And exactly how long it might take is very unclear.

"We are still getting our hands around where we are going," said Hyatt, noting it could be two weeks before a more definitive game plan is devised.

Odle said it could be 60 to 70 days for the Titan 2 is ready for launch again, but that is only a rough estimate.

  G-9 mission patch
The mission patch for this Titan 2 launch. Photo: 2SLS Vandenberg SEE FULL PAGE IMAGE
Whether the satellite's ailment can be determined with craft atop the Titan 2 on the launch pad is somewhat of a long shot, Odle admitted. The inspections at the seaside pad will be limited to the external surfaces of the satellite; specifically the cabling used to carry the clock's signal to the IMU.

"The odds of finding the answer with the limited troubleshooting that we can really do with the spacecraft stacked, I don't have a high confidence we are going to find the answer...but we may," Odle said.

If engineers need to look deeper, the 3,300-pound satellite will have to be removed from the rocket and shipped back to a processing facility for more invasive prodding.

In fact, Odle said the "expected case scenario" would be destacking the satellite from the Titan 2, fixing the problem and heading to a launch sometime in June.

The worst prospect is uncovering a design flaw with the satellite, which would require significant work and delay the launch into the second half of the year.

"In that worst case scenario, we're probably talking in the September time frame that we could be ready to launch from a spacecraft standpoint, and it may be later depending on what really is the extent of the problem that we find.

"The expected case scenario is we believe we may have to destack, probably have some reasonable troubleshooting and fix time, that we would not find a major system design issue that would cause major rework and that we believe a June'ish time frame that we could be ready for launch."

An interrupt in that signal is the prime suspect in what caused the mysterious IMU anomalies and that is where technicians plan to focus attention in the near-term.

The clock and associated wiring are also being called into question because a broken cable was replaced on that system of the satellite a couple of months ago. Officials are worried that earlier trouble could be masking a separate, deeper problem.

"We have seen some other similar things in our earlier testing and we thought we'd resolved the issues. There may have been something that was masked by other things we found in testing. That is one of our concerns."

"We are going to do a real good test of the spacecraft, try to fix this and get it ready for launch later this year if we can," Odle pledged.

"We understand that our business is to have 100 percent mission success and we still have an opportunity for that," Hyatt said.

An artist's concept of a DMSP weather satellite in space. Photo: Lockheed Martin
The DMSP F16 satellite is destined to circle 458-nautical miles around Earth's poles. With its complement of seven instruments, the craft will track clouds, hurricanes and storm systems around the world for weather forecasting, plus monitor ice and snow coverage, pollution and fires.

The Department of Defense currently has two main DMSP satellites and a pair of backups working in space giving meteorologists the information needed to generate forecasts that commanders and troops rely upon in strategic and tactical planning.

The Air Force wants to get this new DMSP craft safely into orbit as soon as possible because it will replace an aging sister-spacecraft launched in March 1995 that is working long past expectations.

Flight data file
Vehicle: Titan 2 (G-9)
Payload: DMSP 5D-3-F16
Launch date: NET April 2001
Launch window: 1358-1408 GMT (8:58-9:08 a.m. EST)
Launch site: SLC-4W, Vandenberg AFB, Calif.