Monday, July 20, 2015

Struts and Frets


Click here to watch the SpaceX CRS-7 launch and loss. Video source: NASAKennedy YouTube channel.

“Life's but a walking shadow, a poor player, that struts and frets his hour upon the stage and then is heard no more; it is a tale told by an idiot, full of sound and fury, signifying nothing.”

— “Macbeth”
Written by William Shakespeare

Click here to listen to an audio recording of the media event. Audio source: NASAWatch.com.

SpaceX founder Elon Musk held a teleconference today to announce the preliminary findings of the company's investigation into the June 28 loss of the Dragon CRS-7 cargo delivery to the International Space Station.

According to an accompanying SpaceX press release:

Preliminary analysis suggests the overpressure event in the upper stage liquid oxygen tank was initiated by a flawed piece of support hardware (a “strut”) inside the second stage. Several hundred struts fly on every Falcon 9 vehicle, with a cumulative flight history of several thousand. The strut that we believe failed was designed and material certified to handle 10,000 lbs of force, but failed at 2,000 lbs, a five-fold difference. Detailed close-out photos of stage construction show no visible flaws or damage of any kind.

In the case of the CRS-7 mission, it appears that one of these supporting pieces inside the second stage failed approximately 138 seconds into flight. The pressurization system itself was performing nominally, but with the failure of this strut, the helium system integrity was breached. This caused a high pressure event inside the second stage within less than one second and the stage was no longer able to maintain its structural integrity.

Despite the fact that these struts have been used on all previous Falcon 9 flights and are certified to withstand well beyond the expected loads during flight, SpaceX will no longer use these particular struts for flight applications. In addition, SpaceX will implement additional hardware quality audits throughout the vehicle to further ensure all parts received perform as expected per their certification documentation.

Musk said he thought the next Falcon 9 launch wouldn't be until at least September, and could not predict which customer it might be. A F9 was scheduled to launch this month from Vandenberg AFB in California Jason 3 ocean topography satellite for NOAA and other agencies. The next Cape Canaveral launches were to be commercial satellites for SES of Luxembourg and New Jersey-based Orbcomm.

The next Dragon cargo delivery, CRS-8, had been scheduled to launch in September. Among the payloads is the Bigelow Expandable Activity Module (BEAM), a technology demonstrator for the larger expandable habitats now being built at the Bigelow Aerospace factory in North Las Vegas.


A 2014 Bigelow Aerospace promotional film. Video source: Bigelow Aerospace YouTube channel.

Bigelow's expandable habitat technology is cited by many as a critical component for government and commercial space operations in upcoming decades. The habitats may be the eventual replacement for the ISS, as well as colony structures on the Moon and perhaps the habitat module for a multi-year human space flight to Mars.

The ISS has suffered the loss of three cargo deliveries in less than a year — an Orbital ATK Cygnus last October, a Roscosmos Progress last April, and the SpaceX CRS-7 flight last month. Another Progress delivery on July 5 helped with station supplies, but the Dragon is key as the only vehicle capable of returning significant amounts of payload to Earth, including experiments and samples.

The investigation also redirected SpaceX resources working on operational status for the next-generation Falcon Heavy rocket to launch at Kennedy Space Center's Pad 39A. Musk now believes the earliest a test vehicle could launch is Spring 2016.

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