12
$\begingroup$

Today's CRS-7 launch from Cape Canaveral (unfortunately) ended rather spectacularly, with an explosion about a minute after reaching Max-Q (maximum dynamic pressure), and with the rocket apparently disintegrating afterwards. The mission blurb said that an 'anomaly' had been observed, and engineers were looking into it.

enter image description here

From the live SpaceX feed, a few seconds after the explosion.

What exactly went wrong with the launch? Whose fault (if at all) is it? What corrective measures will they take to secure future launches?

Note: I understand that more details will come soon, I'm looking for an answer compiling the best information to answer my three questions.

$\endgroup$
  • 4
    $\begingroup$ Elon Musk ‏@elonmusk on Twitter: "There was an overpressure event in the upper stage liquid oxygen tank. Data suggests counterintuitive cause." $\endgroup$ – Jerard Puckett Jun 28 '15 at 16:17
  • 2
    $\begingroup$ youtube.com/watch?v=fTom8xVzFdo NasaTV press conference to begin soon. $\endgroup$ – Jerard Puckett Jun 28 '15 at 16:22
  • 8
    $\begingroup$ The rocket doesn't love the landing pad and committed suicide rather than flying there! (You're asking this question way too early.) $\endgroup$ – Loren Pechtel Jun 28 '15 at 21:05
  • 5
    $\begingroup$ @LorenPechtel Or someone forgot to read the instructions for the rocket, because nothing reminded them to do so. $\endgroup$ – Philipp Jun 28 '15 at 22:18
  • 3
    $\begingroup$ @AnthonyX apparently not. twitter.com/TildalWave/status/615226763174506497 $\endgroup$ – Vedant Chandra Jun 29 '15 at 4:36
24
$\begingroup$

Update 7/20/2015 via Elon Musk's Conference Call, compiled by /r/spacex and twitter sources

Preliminary conclusion is that a COPV (helium container) strut in the CRS-7 second stage failed at 3.2Gs. We analysed a lot of data, took 0.893 seconds before first sign of trouble and end of data. Preliminary failure arose from a strut in the second stage liquid oxygen tanks that was holding down one composite helium bottle used to pressurize the stage. High pressure helium bottles are pressurized at 5500 psi, stored inside in LOX tank. Several helium bottles in upper stage. At ~3.2 g, one of those struts snapped and broke free inside the tank. Released lots of He into LOX tank. buoyancy increases in accordance w/ G-load. Data shows a drop in the helium pressure, then a rise in the helium pressure system. Quite confusing. As helium bottle broke free and pinched off manifold, restored the pressure but released enough helium to cause the tank to fail. it was a really odd failure mode. Data indicates helium tank did not burst.

What Happened?
At T+139 seconds after launch, the second stage Liquid Oxygen Tank(LOX) experienced an overpressure event. The Falcon 9 flight computer determined a failure had occurred and activated its Flight Termination System. Dragon decoupled from the rocket and made a hard impact in the Atlantic.

Why did this happen?

We will not know for sure until SpaceX releases more information which will not occur until after their investigation is closed. However we can do some basic detective work based on the information that's been released so far.

There was an overpressure event in the upper stage liquid oxygen tank. Data suggests counterintuitive cause.

— Elon Musk (@elonmusk) June 28, 2015

Just before Main Engine CutOff(MECO), the second stage disintegrated. Elon Musk said that the LOX tank experienced an overpressure event. Basically, the tank ruptured from the inside out. The tanks of a rocket form its main structure. Once the tank failed, the aerodynamic pressure from the leading edge destroyed the second stage and Dragon detached and fell off.

Did the landing attempt cause this?

Both the Dragon capsule and Falcon 9 first stage were performing nominally and were sending telemetry back to ground after this event occurred. In the video, you can see that the first stage engines keep firing for a few seconds after the initial explosion. None of the landing modifications(fins, legs, etc) were the cause of this incident.

If the the problem was with the second stage, why did the whole rocket explode?

Every Falcon 9(and almost all rockets in general) have a Flight Termination System(FTS). This is usually a line of plastic explosive(C4) that runs down the body of the rocket. There are many reasons why this system is in place. It is better to blow up a rocket once it starts going out of control than to let it fly in an uncontrolled direction and crash. Also rockets contain an immense amount of chemical energy in their fuel. Crashing those tanks can cause the fuel to compress and ignite all at once creating a massive explosion. The FTS 'unzips' the tanks, allowing it to burn in the air instead of exploding. The Antares Failure resulted in a large fireball, but the FTS was actually activated before it hit the ground, preventing a lot of serious damage to the pad.

Since SLC-40 is an Air Force base, the Air Force has the responsibility to maintain Range Safety. They have a metaphorical big red button that will instantly destroy the rocket if it deviates from the flightpath. However the Air Force didn't blow up the rocket, the Falcon 9 did it itself. Once the rocket clears the range, it is now SpaceX's responsibility. Usually they would have someone also holding a big red button. However SpaceX implemented an automatic FTS based on GPS as well as the rocket's own sensors. Once the vehicle detected the failure it automatically "safed" itself.

Why didn't SpaceX try to land the first stage?

Landing a 150 foot tall rocket stage is already an improbably hard task. The second stage disintegrated close to Max-Q, where the rocket is under the most air pressure during its flight. It's highly unlikely the stage could have maneuvered sufficiently to attempt to land. Also the incident occurred close to shore(~13km) while the landing barge was 318km from shore.

Whose fault (if at all) is it?

This is a tricky area. SpaceX's rocket exploded. Something went wrong in either the manufacturing or engineering of the vehicle causing it to fail. However, the contract awarded to SpaceX by NASA, like most launch contracts, is based on launch attempts not successes. Since SpaceX successfully got the payload off of the pad, they will still get paid.

What corrective measures will they take to secure future launches?

The first measure, unfortunately, is that Falcon 9 is grounded until the problem is resolved.

Cause still unknown after several thousand engineering-hours of review. Now parsing data with a hex editor to recover final milliseconds.

— Elon Musk (@elonmusk) June 29, 2015

The next step is to gather as much data as possible on the incident. That includes all pictures, any debris they can recover, as well as the telemetry the rocket broadcast during flight. There were over 3000 telemetry sensors on CRS-7 according to the post-incident briefing. Then what is called a Fault Tree Analysis will begin. SpaceX engineers will work back from the smallest changes in the rocket to find what went wrong in the second stage LOX tank.

Once the problem is identified, they will need to fix it. If it is a manufacturing error, a change of processes or stricter quality control may be enough to fix it. If it is an engineering error, the design must be fixed to prevent it from happening again.

Upgrades in the works to allow landing for geo missions: thrust +15%, deep cryo oxygen, upper stage tank vol +10%

— Elon Musk (@elonmusk) March 2, 2015

There is some hope in that the SES-9 launch is/was supposed to be the introduction of the Falcon 9v1.2 "FullThrust" which uses its engines at full throttle, uses densified LOX, and has an improved/lengthened second stage. If the problem has already been fixed on v1.2 then we could see Falcon flying relatively quickly.

$\endgroup$
  • $\begingroup$ This is much quicker than I expected! I'll wait a day for updates and then accept, thank you for the answer :) $\endgroup$ – Vedant Chandra Jun 29 '15 at 21:11
  • 2
    $\begingroup$ TJ: Are you sure that they get paid for the attempt, not the delivery? I was pretty sure the CRS contract was pay after delivery, not after attempt. Of course, all attempts for SpaceX to date had succeeded. (Cygnus being the example for later in the process and more info). $\endgroup$ – geoffc Jun 30 '15 at 19:00
  • 2
    $\begingroup$ @geoffc according to the CRS contract, the provider receives no more than 30% of the value of the contract before launch for milestones, and at least 20% for the final milestone. There are a variety of milestones per mission, such as vehicle delivery, integration, launch, rendezvous, etc. SpaceX got paid for part of the mission although it was a failure. nasa.gov/centers/johnson/pdf/418857main_sec_nnj09ga04b.pdf $\endgroup$ – T.J. Tarazevits Jun 30 '15 at 23:35
  • $\begingroup$ Strut failure as the cause sounds like really good news for SpaceX - no need to redesign the He tanks or pressurization system. $\endgroup$ – Russell Borogove Jul 20 '15 at 21:09
  • $\begingroup$ You may want to add this quote: 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. From: spacex.com/news/2015/07/20/crs-7-investigation-update $\endgroup$ – Hobbes Jul 21 '15 at 6:50

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.