SpaceX is set to Return To Flight (RTF) no sooner than January 14, with the Falcon 9 launch of the first Iridium NEXT mission from Vandenberg Air Force Base in California. SpaceX’s return follows a stand down related to the September loss of the Falcon 9 that was scheduled to launch the Amos-6 satellite during a Static Fire anomaly.
Path To RTF:
SpaceX – along with the Federal Aviation Administration (FAA), NASA, the US Air Force and industry experts – have been working through the fault tree to pin down the root cause of the explosion – or fast fire – that resulted in the demise of the Falcon 9 and Amos-6 payload during what was a standard Static Fire test.
This test is carried out ahead of all Falcon 9 launches, allowing for a dress rehearsal for its launch team, along with a full countdown, prop loading and engine test of the rocket, with the results feeding into the Launch Readiness Review (LRR).
For controllers at the Cape, there was no pre-warning of the failure that occurred in the second stage of the Falcon 9.
In fact, the failure was almost instantaneous, with the first signs of an anomaly on the 3000 channels of information fed from the Falcon 9 to the launch control center occurring at about 93 milliseconds ahead of loss of data.
Despite a large amount of data – along with video and audio from the pad – the cause of the failure was not immediately obvious.
The wide-ranging investigation then became more focused on a breach of the cryogenic helium system on the second stage liquid oxygen (LOX) tank, aided by real-life testing at the McGregor Test Center in Texas.
Destructive testing of hardware – as seen in this photo (left) – associated with Composite Overwrapped Pressure Vessels (COPVs) at the McGregor test site aided the investigation process – which focused on the unique conditions associated with the interaction between the helium pressurization bottles, carbon composites and solidification of the LOX propellant.
Updating status on Monday, SpaceX published its findings.
“Over the past four months, officials at the Federal Aviation Administration (FAA), the U.S. Air Force (USAF), the National Aeronautics and Space Administration (NASA), the National Transportation Safety Board (NTSB), along with several industry experts, have collaborated with SpaceX on a rigorous investigation to determine the cause of the anomaly that occurred September 1 at Space Launch Complex 40 (SLC-40) at Cape Canaveral Air Force Station in Florida.
“This investigation team was established according to SpaceX’s accident investigation plan as approved by the FAA. As the primary federal licensing body, the FAA provided oversight and coordination for the investigation.
“Investigators scoured more than 3,000 channels of video and telemetry data covering a very brief timeline of events – there were just 93 milliseconds from the first sign of anomalous data to the loss of the second stage, followed by loss of the vehicle. 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.”
The update provided more specifics on the failure mode of the COPV in the LOX tank, which caused the destruction of the entire rocket and payload – along with causing major damage to the SLC-40 pad at Cape Canaveral. The recovery of several COPV “bottles” from the debris has proved to be a major help in the investigation.
“The accident investigation team worked systematically through an extensive fault tree analysis and 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, leading to ignition and the subsequent failure of the COPV,” added SpaceX.
“Each stage of Falcon 9 uses COPVs to store cold helium which is used to maintain tank pressure, and each COPV consists of an aluminum inner liner with a carbon overwrap. The recovered COPVs showed buckles in their liners. Although buckles were not shown to burst a COPV on their own, investigators concluded that super chilled LOX can pool in these buckles under the overwrap.
“When pressurized, oxygen pooled in this buckle can become trapped; in turn, breaking fibers or friction can ignite the oxygen in the overwrap, causing the COPV to fail. In addition, investigators determined that the loading temperature of the helium was cold enough to create solid oxygen (SOX), which exacerbates the possibility of oxygen becoming trapped as well as the likelihood of friction ignition.”
As part of the corrective process, SpaceX has opted to avoid certain elements related to helium temperatures for the interim until they are confident they can redesign the COPVs to cope with the colder chill process.
“The investigation team identified several credible causes for the COPV failure, all of which involve accumulation of super chilled LOX or SOX in buckles under the overwrap. 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. In the long term, SpaceX will implement design changes to the COPVs to prevent buckles altogether, which will allow for faster loading operations. ”
Next Launch – Iridium NEXT:
While the investigation was progressing, SpaceX positioned itself to be ready to return to launch action.
Several Falcon 9 rockets put through the regular pre-launch processing flow that involves shipping from their birthplace in Hawthorne, California.
Stages associated with at least three Falcon 9 rockets have been shipped to McGregor for test firings.
Two Falcon 9 rockets that have been through the Texas site are now at their respective launch locations, one at Vandenberg Air Force Base and another at the Cape/Kennedy Space Center (KSC).
Although the long-term manifest won’t become clearer until SpaceX is back into a regular launch cadence, it is known the first mission to launch since the Amos-6 related anomaly will be the Iridium NEXT mission from California.
The Falcon 9 tasked with this mission arrived at the Space Launch Complex -4E (SLC-4E) Horizontal Integration Facility (HIF) in November. It was initially hoped this mission would launch in December.
With SpaceX silent – likely due to the company remaining in “investigation mode”, which holds a strong level of restrictions on what the company can make public – milestone information for this mission came from Iridium CEO Matt Desch via his Twitter posts.
Those updates showed the processing flow had progressed to the encapsulation of the 10 satellites that will ride uphill with the Falcon 9.
“Our first 10 IridiumNEXT satellites are all fueled now, tucked in and dreaming of flying in space. Very. Soon. Happy Holidays!” Tweeted Mr. Desch on December 25.
The next milestone will be the rollout of the Falcon 9 – minus the payload – for a Static Fire test, which was set to occur on Tuesday. However, a non-rocket related issue requires resolution, moving the test to Wednesday and then Thursday. The Flight Readiness Review (FRR) ahead of the test was conducted on Monday.
The Falcon 9 finally fired up on Thursday at 21:30 UTC.
The Static Fire test involved a full fuel loading process and countdown, highlighted by a short firing of the nine Merlin 1D engines. The firing is much shorter than the stage has already successfully conducted at McGregor. However, the Static Fire test is the first time both the integrated First and Second stages have been loaded with propellant together.
A successful test will result in rollback to the HIF ahead of mating with the payload. The next rollout will be for launch, which is currently scheduled to occur No Earlier Than (NET) January 14.
“SpaceX is targeting return to flight from Vandenberg’s Space Launch Complex 4E (SLC-4E) with the Iridium NEXT launch on January 8,” added the company on Monday, prior to the delays to the Static Fire moving the launch to NET January 9 and then January 14. “SpaceX greatly appreciates the support of our customers and partners throughout this process, and we look forward to fulfilling our manifest in 2017 and beyond.”
The date was moved twice – once relating to the delay in the Static Fire test, and then via very poor weather forecast in the area early in the week – along with range availability.
Providing the mission is conducted without incident, SpaceX will switch its attention to the East Coast, with the launch of the EchoStar 23 satellite.
The Falcon 9 for this mission has also completed testing at McGregor and was shipped to the Cape before the end of 2016. It is scheduled to launch from Pad 39A at KSC in what will be a milestone debut launch from the famous launch pad.
While planning documentation shows a preliminary date of January 15 for this mission, it is highly unlikely that schedule will hold, given the focus on the success of the Iridium mission and final work to prepare 39A for its first launch since Atlantis concluded the Shuttle Program with the launch of STS-135.
A launch schedule towards the end of the month is more likely. UPDATE: On Tuesday, L2 schedule information from KSC showed a request date of January 26 as a new preliminary placeholder. This date is currently lacking Eastern Range approval.
(Images: SpaceX and L2 – including NSF L2 member Gary Blair (McGregor Testing) Amos-6 Failure Evaluation video by Jay Deshetler, Marek Cyzio and L2 artist Nathan Koga – The full gallery of Nathan’s (SpaceX Dragon to MCT, SLS, Commercial Crew and more) L2 images can be *found here*)