This story was updated July 22
WASHINGTON — The U.S. Air Force has seven aging Defense Meteorological Satellite Program (DMSP) spacecraft in orbit that are susceptible to the kind of explosive battery rupture that destroyed the 20-year-old DMSP-F13 in February, producing more than 100 trackable pieces of orbital debris.
Of those seven satellites, only one — DMSP-F14 — is still in service. But all seven have the same kind of battery charger that an Air Force review released July 20 identified as the likely cause of the DMSP-F13 incident.
“More than two decades ago, the design of the battery charger made it very difficult to assemble, and the entire block of Lockheed Martin 5D-2 Battery Chargers are potentially susceptible to this short circuit failure over time, despite a functional history within the design life,” the Air Force’s 50th Space Wing said in a statement. “The assembly is common to nine DMSP satellites, Flight 6 through Flight 14,” launched between 1982 and 1997.
“While only one of these satellites, DMSP Flight 14, remains operational, six remain in orbit and analysis has shown that the risk of potential short circuit remains even after a satellite is permanently shut down,” the Air Force said.
DMSP-14 — the last of the afflicted satellites — launched in April 1997. The satellite’s recorder failed in 2008, preventing it from providing global data. Its microwave temperature and humidity sensors are also no longer operational, according to a World Meteorological Organization registry.
“While there are no indications of an issue with the battery charge assembly housing on DMSP Flight 14, the results of the DMSP Flight 13 review coupled with ongoing technical analysis will be included in our routine constellation sustainment planning process moving forward,” Col. Dennis Bythewood, commander of the 50th Operations Group, said in a statement.
In an interview with SpaceNews, Bythewood said the battery charge assembly has “an inherent design flaw.”
The review, which included input from DMSP prime contractor Lockheed Martin, concluded there were no actions DMSP-F13’s operators could have taken to prevent the incident. Swift action to “safe” the vehicle after operators noticed spiking battery temperatures, the Air Force said, prevented “what could have been a much greater debris event.”
Still, when one of the batteries onboard the DMSP-F13 weather satellite ruptured, it burst with enough force to produce a field of spacecraft debris analysts say is likely to remain in orbit for decades.
Blown Out of Proportion?
The Air Force objects to the term “explosion” to describe what happened to DMSP-F13.
“The inaccurate term ‘explosion’ was used by many media outlets to describe the nature of the event,” the Air Force said in its report. “AFSPC and 50SW/PA built a sound communications plan to address accurately the events of 3 Feb 2015, however the media distorted the story … Once one media outlet, reported the vehicle exploded, then the explosion became the story.”
Air Force Space Command did not disclose the loss of DMSP-F13 until Feb. 27, when it responded to questions from SpaceNews about debris spotted near the satellite.
The Air Force detailed the Feb. 3 incident, and its subsequent investigation, in a lightly redacted 12-page report dated March 31 but released July 20.
According to the report, DMSP operators in Suitland, Maryland, first noticed something was amiss with DMSP-F13 when the satellite sent down troubling telemetry during a late-afternoon pass over a tracking station. At 4:34 p.m. Eastern time, none of DMSP-F13’s two nickel-cadmium batteries “reported dangerously anomalous overtemperature (maxed out thermal reading),” the report says.
All the current generated by the satellite’s solar arrays apparently was being diverted to one battery, causing its temperature to hit at least 45.2 degrees Celsius — the maximum temperature reading that could be sent down in telemetry. The flight crew notified the engineers, who declared a spacecraft emergency after realizing they were dealing with a “life threatening power subsystem anomaly.”
Additional data would eventually show that “a major kinetic event” — likely due to the overheated battery rupturing — occurred at 5:20 p.m., causing the satellite to lose attitude control.
But DMSP engineers did not realize DMSP-F13 had begun to spin until 6 p.m., when a remote tracking station in Fairbanks, Alaska, again made contact with the satellite. By then, the Air Force wrote, the situation had “deteriorated significantly” — the overheated battery now appeared dead and the remaining battery was only intermittently charging and quickly running out of juice. The satellite was tumbling and its nitrogen propellant tank was empty.
A few minutes later, the U.S. Space Surveillance Network picked up its first indications of a debris event near the satellite. But the DMSP team scrambling to troubleshoot the rapidly dying satellite did not receive word that the satellite had already broken apart until hours later, after radars in North Dakota; Cape Cod, Massachusetts; and Greenland made confirming orbital debris reports. The Air Force’s Joint Space Operations Center (JSpOC) at Vandenberg Air Force Base, California, officially confirmed DMSP-F13’s breakup at 10:36 p.m.
In the meantime, knowing only that they were dealing with a rapidly dying satellite, the DMSP team convened an emergency meeting at 7 p.m. to discuss how to safely shut down DMSP-F13 if its power problem could not be halted. During the next two passes, the team disabled additional subsystems to further reduce the load on the remaining battery.
By 8:30 p.m., the satellite was in an “uncontrollable tumble.” The team decided there likely would be only one chance to decommission the satellite before it ran out of power and shut itself down. Bythewood’s group declared DMSP-13 Operations Capability Red and notified JSpOC.
“The window was very tight,” Bythewood said.
With less than 10 minutes until the next pass, officials asked Lt. Gen. Jay Raymond, the commander of the 14th Air Force and the Joint Functional Component Command for Space, for approval for an emergency disposal of DMSP-F13. Raymond was not immediately available, so officials went to the vice commander, who OK’d the plan.
“Since the spacecraft had mostly powered itself down and expended all of its pressurized propellant, the decommissioning sequence was abbreviated, sending only those commands which had not been rendered moot by previous events,” the report said.
Operators turned off the final transmitter at 9:43 p.m., a little over five hours after Suitland first spotted trouble.
The Air Force praised the DMSP team’s actions for averting what could have been an even worse debris event.
“The engineers did not receive word of the debris event until after end-of-life commanding,” the report says. “Nonetheless, they were able to safe the vehicle in the face of total loss of attitude control preventing what could have been a much greater debris event.”
The JSpOC is tracking 147 pieces of debris from DMSP-F13 ranging from baseball- to basketball-sized objects, according to the service’s July 20 statement.
The Air Force said approximately 110 payloads are in the same general vicinity as DMSP-F13, whose elliptical orbit took it as high as 1,200 kilometers and as low as 300 kilometers.
So far, the Air Force said, there have been “no reportable conjunctions” between the DMSP-F13 debris and any of its orbital neighbors.
The Air Force has ruled out space weather as a factor in DMSP-F13’s demise and said it does not believe an orbital debris strike is to blame, either.
“While it is impossible to definitively ascertain the exact cause of the debris event, lab tests have shown that large battery packs such as those flown on DMSP Flight 13 can burst from increased pressure caused by high temperature operations,” the report says.
The semiretired DMSP-F13 satellite had been providing U.S. Navy ship and shore receivers and various tactical military users with real-time cloud-cover imagery prior to the Feb. 3 incident, but the National Weather Service and Air Force and Navy meteorologists had already long since ceased incorporating DMSP-F13 data into weather forecasting models.
As for what exactly caused one of DMSP-F13’s batteries to overheat and rupture, the Air Force concluded that one of the wiring harnesses “lost functionality due to compression over a long period of time in the battery charge assembly.”
“Once the harness was compromised, the exposed wires potentially caused a short in the battery power, leading to an overcharge situation with eventual rupture of the batteries,” the Air Force said.
Bythewood, meanwhile, said since the Feb. 3 failure, the Air Force has worked on a software modification that would help provide pinpointed data about potential problems faster.
The Air Force has a total of six DMSP satellites in service following the launch in April 2014 of DMSP-F19. The Air Force and congressional appropriators disagree over the need for the launch of the final satellite in the series, known as Flight 20.