SpaceX completes failure probe, gears up for new launch
 |
| © U.S. Launch Report/Handout via REUTERS An explosion on the launch site of a SpaceX Falcon 9 rocket is shown in this still image from video in Cape Canaveral, Florida, U.S. September 1, 2016. |
SpaceX engineers believe the Cape Canaveral Air Force Station mishap was triggered by the failure of a high-pressure helium tank, one of three used to pressurize the second stage liquid oxygen tank.
Putting corrective actions in place, the company said Monday it plans to resume flights with a launch from Vandenberg Air Force Base northwest of Los Angeles on Jan. 8 to boost 10 Iridium NEXT satellite telephone relay stations into orbit.
It is not yet known when SpaceX plans to resume flights from Cape Canaveral. Launch complex 41 at the Florida Air Force station was heavily damaged in the Sept. 1 mishap, and the company plans to use a repurposed space shuttle launch pad at the nearby Kennedy Space Center for its next Falcon 9 flight from Florida.
Watch: Elon Musk's vision of life on Mars
Sources indicate the first flight from Kennedy will be another commercial mission. The next SpaceX flight to deliver cargo to the International Space Station, the company’s 10th under contract to NASA, is expected to take place some time after the commercial mission.
SpaceX’s Falcon 9 rocket uses super-cooled, or “densified,” liquid oxygen and RP-1 kerosene fuel to provide additional performance during ascent. To achieve and maintain the desired low temperatures, propellant loading begins just 35 minutes before launch.
To push propellants to the rocket’s engines, the Falcon 9 uses highly pressurized helium stored in aluminum bottles, wrapped in a tough, insulating carbon composite material. The bottles, known as composite overwrap pressure vessels, or COPVs, are mounted inside the propellant tanks, submerged in frigid liquid oxygen and chilled kerosene.
On Sept. 1, about five minutes before a planned test firing of the Falcon’s nine Merlin 1D first stage engines -- a routine pre-launch test for SpaceX -- the second stage suddenly exploded in a spectacular conflagration that was caught on video and widely seen around the world.
The rocket and its $195 million payload, a commercial communications satellite, were destroyed, causing heavy damage to launch complex 41 at the Cape Canaveral Air Force Station. Just 93 milliseconds elapsed from the first signs of trouble to the explosion.
“Investigators scoured more than 3,000 channels of video and telemetry data covering a very brief timeline of events,” SpaceX said in a statement posted to its website. “Because the failure occurred on the ground, investigators were also able to review umbilical data, ground-based video, and physical debris.
Watch: SpaceX rocket explodes on launch pad
“To validate investigation analysis and findings, SpaceX conducted a wide range of tests at its facilities in Hawthorne, California and McGregor, Texas.”
SpaceX is generally tight-lipped when it comes to technical details, and the statement posted Monday provided only a general overview of the team’s findings. It said accident investigators “concluded that one of the three composite overwrapped pressure vessels (COPVs) inside the second stage liquid oxygen (LOX) tank failed.”
“Specifically, the investigation team concluded the failure was likely due to the accumulation of oxygen between the COPV liner and overwrap in a void or a buckle in the liner,” the company said.
Investigators believe those extremely low temperatures may have caused some of that trapped oxygen to solidify. In any case, when the tank was pressurized, trapped oxygen pushing against the carbon overwrap fibers likely generated friction “leading to ignition and the subsequent failure of the COPV.”
Liquid oxygen has a temperature of around minus 298 degrees Fahrenheit, but SpaceX chills the propellant to around minus 340 degrees for use aboard the Falcon 9. The RP-1 kerosene fuel, which normally is stored at a room temperature 70 degrees, also is chilled. The lower temperatures increase the propellants’ density.
A rocket engine’s thrust is directly proportional to the rate propellants are consumed and expelled. By “densifying” the Falcon 9 propellants, more fuel can be stored and pumped through the engines, increasing performance.
While earlier rockets, including the Titan 2 booster used to launch NASA’s Gemini spacecraft in the 1960s, used propellant cooling to increase density, and thus engine performance, the upgraded Falcon 9 is believed to be the first utilizing super-cooled cryogenic oxygen.
SpaceX founder Elon Musk said in 2015, when propellant cooling was first implemented in the Falcon 9, that “we’re sub-cooling the propellant, particularly the liquid oxygen, close to its freezing point, which increases the density quite significantly.”
Failure investigators “identified several credible causes for the COPV failure, all of which involve accumulation of super chilled LOX or SOX (solidified oxygen) in buckles under the overwrap,” the company said in its statement.
“The corrective actions address all credible causes and focus on changes which avoid the conditions that led to these credible causes. In the short term, this entails changing the COPV configuration to allow warmer temperature helium to be loaded, as well as returning helium loading operations to a prior flight proven configuration based on operations used in over 700 successful COPV loads.”
The company did not provide any details about those earlier helium loading procedures but said it plans to redesign the helium bottles in the long term “to prevent buckles altogether, which will allow for faster loading operations.”
The Sept. 1 failure was the second involving the Falcon 9’s second-stage helium pressurization system.
During a June 2015 launch to deliver supplies to the space station, a strut holding a second-stage helium tank in place inside the liquid oxygen tank failed, allowing the helium bottle to shoot up and crash into the top of the oxygen tank, triggering a catastrophic rupture.
It was SpaceX’s first outright Falcon 9 failure in 19 launchings dating back to the rocket’s maiden flight in June 2010. After taking steps to ensure all internal struts met design specifications, SpaceX launched nine successful missions in a row before the Sept. 1 launch pad disaster, all of them using densified propellants.
SpaceX Says It’s Ready to Launch Rockets Again
After the explosion in September of one of its rockets, SpaceX is now ready to get back into the business of sending payloads to space, the company announced on Monday, with its next rocket headed to orbit as soon as Sunday.
In a statement, SpaceX — or more formally, Space Exploration Technologies Corporation — said that an investigation had determined the likely cause: an unexpected interplay of supercold helium and oxygen with carbon fibers and aluminum.
The statement Monday added technical details about what went wrong, and the company said it had devised workarounds to prevent a recurrence.
The cascade of explosions on Sept. 1 that destroyed a Falcon 9 rocket on the launchpad at Cape Canaveral Air Force Station in Florida was perplexing and concerning, because it occurred during what is usually regarded as a safer portion of operations — the fueling of propellants — about eight minutes before the ignition of the engines for a planned test. (The launch had been scheduled for two days later.)
The trouble appeared to start near the liquid oxygen tank on the second stage of the two-stage rocket, and in less than a tenth of a second, that section was in flames, followed by the destruction of the entire rocket and a $200 million communications satellite whose customers included Facebook, which had planned to use it to expand internet services in Africa.
Under current federal laws, investigations into such explosions are led by the company that built the rocket, not by a government agency. The investigation panel included representatives of the Federal Aviation Administration, the United States Air Force, NASA and the National Transportation Safety Board. Falcon 9 rockets are used to carry NASA cargo to the International Space Station and are to provide transportation for astronauts beginning in 2018. SpaceX is also competing to win contracts to launch Department of Defense spy satellites.
With few obvious clues to the explosion, the company initially considered hypotheses like sabotage, that a sniper had fired a shot rupturing the oxygen tank from the roof of a competitor’s building nearby.
“The accident investigation team worked systematically through an extensive fault tree analysis,” SpaceX said in its statement.
The investigation narrowed in on three helium containers within the second-stage liquid oxygen tank. The containers consist of an aluminum liner with an outer layer of strong carbon fibers. During launch, as the liquid oxygen is consumed, the helium is heated and released to maintain pressure within the tank.
In December 2015, SpaceX began using an upgraded Falcon 9 design that uses supercooled liquid oxygen at minus 340 degrees, 40 degrees colder than what is typically used. The lower temperature makes the oxygen denser, which improves engine thrust.
But the helium was even colder. As the carbon and aluminum cool, they shrink at different rates, opening gaps into which liquid oxygen could flow. In addition, the helium may have been below the temperature at which oxygen freezes, and some of the trapped oxygen may have become solid.
“Really surprising problem that’s never been encountered before in the history of rocketry,” Elon Musk, the chief executive of SpaceX, said in an interview on CNBC in November.
Both carbon and aluminum can burn, and with oxygen sandwiched in between, all of the ingredients for a conflagration were present. Friction or the breaking of fibers could have provided the energy for ignition, the company said.
Tests at SpaceX’s facilities in Hawthorne, Calif., and McGregor, Tex., supported that conclusion, the company said.
The configuration of the helium containers has been shifted, and the fueling procedures will change so that the helium will be warmer, SpaceX said.
The next SpaceX launch is to carry a 10-pack of satellites for Iridium Communications, which provides communications services including satellite telephones through a constellation of satellites. Iridium is looking to replace the surviving 65 original satellites with 70 new satellites, each about the size of a Mini Cooper car.
A month ago, Iridium issued a statement saying it hoped that SpaceX would be able to launch its satellites in mid-December, but less than a week later, SpaceX said it was pushing back the launch date to early January.
The Iridium satellite is to be launched by SpaceX from a leased launchpad at Vandenberg Air Force Base in California.
For launches from Florida, SpaceX hopes to complete renovations at Launchpad 39A at the Kennedy Space Center, once used for space shuttle launches. SpaceX is tentatively aiming to resume cargo flights to the space station this month.
SpaceX completes failure probe, plans new launch
After an exhaustive investigation, SpaceX engineers have identified the most likely cause of the spectacular explosion of a Falcon 9 rocket during a pre-launch test Sept. 1 that destroyed the booster and its $195 million satellite payload, the company announced Monday.
SpaceX engineers believe the Cape Canaveral Air Force Station mishap was triggered by the failure of a high-pressure helium tank, one of three used to pressurize the second stage liquid oxygen tank.
Putting corrective actions in place, the company said Monday it plans to resume flights with a launch from Vandenberg Air Force Base northwest of Los Angeles on Jan. 8 to boost 10 Iridium NEXT satellite telephone relay stations into orbit.
It is not yet known when SpaceX plans to resume flights from Cape Canaveral. Launch complex 41 at the Florida Air Force station was heavily damaged in the Sept. 1 mishap, and the company plans to use a repurposed space shuttle launch pad at the nearby Kennedy Space Center for its next Falcon 9 flight from Florida.
Sources indicate the first flight from Kennedy will be another commercial mission. The next SpaceX flight to deliver cargo to the International Space Station, the company’s 10th under contract to NASA, is expected to take place some time after the commercial mission.
SpaceX’s Falcon 9 rocket uses super-cooled, or “densified,” liquid oxygen and RP-1 kerosene fuel to provide additional performance during ascent. To achieve and maintain the desired low temperatures, propellant loading begins just 35 minutes before launch.
To push propellants to the rocket’s engines, the Falcon 9 uses highly pressurized helium stored in aluminum bottles, wrapped in a tough, insulating carbon composite material. The bottles, known as composite overwrap pressure vessels, or COPVs, are mounted inside the propellant tanks, submerged in frigid liquid oxygen and chilled kerosene.
On Sept. 1, about five minutes before a planned test firing of the Falcon’s nine Merlin 1D first stage engines -- a routine pre-launch test for SpaceX -- the second stage suddenly exploded in a spectacular conflagration that was caught on video and widely seen around the world.
The rocket and its $195 million payload, a commercial communications satellite, were destroyed, causing heavy damage to launch complex 41 at the Cape Canaveral Air Force Station. Just 93 milliseconds elapsed from the first signs of trouble to the explosion.
“Investigators scoured more than 3,000 channels of video and telemetry data covering a very brief timeline of events,” SpaceX said in a statement posted to its website. “Because the failure occurred on the ground, investigators were also able to review umbilical data, ground-based video, and physical debris.
“To validate investigation analysis and findings, SpaceX conducted a wide range of tests at its facilities in Hawthorne, California and McGregor, Texas.”
SpaceX is generally tight-lipped when it comes to technical details, and the statement posted Monday provided only a general overview of the team’s findings. It said accident investigators “concluded that one of the three composite overwrapped pressure vessels (COPVs) inside the second stage liquid oxygen (LOX) tank failed.”
“Specifically, the investigation team concluded the failure was likely due to the accumulation of oxygen between the COPV liner and overwrap in a void or a buckle in the liner,” the company said.
Investigators believe those extremely low temperatures may have caused some of that trapped oxygen to solidify. In any case, when the tank was pressurized, trapped oxygen pushing against the carbon overwrap fibers likely generated friction “leading to ignition and the subsequent failure of the COPV.”
Liquid oxygen has a temperature of around minus 298 degrees Fahrenheit, but SpaceX chills the propellant to around minus 340 degrees for use aboard the Falcon 9. The RP-1 kerosene fuel, which normally is stored at a room temperature 70 degrees, also is chilled. The lower temperatures increase the propellants’ density.
A rocket engine’s thrust is directly proportional to the rate propellants are consumed and expelled. By “densifying” the Falcon 9 propellants, more fuel can be stored and pumped through the engines, increasing performance.
While earlier rockets, including the Titan 2 booster used to launch NASA’s Gemini spacecraft in the 1960s, used propellant cooling to increase density, and thus engine performance, the upgraded Falcon 9 is believed to be the first utilizing super-cooled cryogenic oxygen.
SpaceX founder Elon Musk said in 2015, when propellant cooling was first implemented in the Falcon 9, that “we’re sub-cooling the propellant, particularly the liquid oxygen, close to its freezing point, which increases the density quite significantly.”
Failure investigators “identified several credible causes for the COPV failure, all of which involve accumulation of super chilled LOX or SOX (solidified oxygen) in buckles under the overwrap,” the company said in its statement.
“The corrective actions address all credible causes and focus on changes which avoid the conditions that led to these credible causes. In the short term, this entails changing the COPV configuration to allow warmer temperature helium to be loaded, as well as returning helium loading operations to a prior flight proven configuration based on operations used in over 700 successful COPV loads.”
The company did not provide any details about those earlier helium loading procedures but said it plans to redesign the helium bottles in the long term “to prevent buckles altogether, which will allow for faster loading operations.”
The Sept. 1 failure was the second involving the Falcon 9’s second-stage helium pressurization system.
During a June 2015 launch to deliver supplies to the space station, a strut holding a second-stage helium tank in place inside the liquid oxygen tank failed, allowing the helium bottle to shoot up and crash into the top of the oxygen tank, triggering a catastrophic rupture.
It was SpaceX’s first outright Falcon 9 failure in 19 launchings dating back to the rocket’s maiden flight in June 2010. After taking steps to ensure all internal struts met design specifications, SpaceX launched nine successful missions in a row before the Sept. 1 launch pad disaster, all of them using densified propellants.
0 Response to "SpaceX completes failure probe, gears up for new launch"
Post a Comment