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#1 to #160 (Updates)



Each flight log entry usually represents a launch or test day, and describes the events that took place.
Click on an image to view a larger image, and click the browser's BACK button to return back to the page.

Day 39 - Catastrophic Failure During Test
Getting ready for a static full pressure test of staging and parachute deployment mechanisms. The sun is shining on the sustainer.
For the actual test we replaced the sustainer with a small bottle tied to string so it wouldn't fly off.
As we approached 120psi - Acceleron III's operational pressure - BOOM!
Bits of the booster were scattered everywhere.
We believe this is the point of failure. The damage is outward from this point. This coupling is still missing.
The strapping tape helped contain a lot of the plastic shrapnel.
This bottle was turned inside out from the force of the explosion. The neck of the bottle is resting against the base from the inside.
These bottles were also compressed. Notice how the top of the bottle ripped off.
The pod sustained only minor damage, despite this view.
The sustainer air supply non-return valve. Lid is cracked, but you can see what's left of the throat of a bottle still screwed into the lid.
A collection of recovered debris.
Date: 5th July 2007   12:30 pm
Cool and sunny.
(click the name for rocket details)
Name Capacity Notes
Acceleron III 24.75 L A new rocket expanding on Acceleron II's capacity. It is also our first two stage rocket booster.

Team Members at Event: GK and PK

This was going to be a run of the mill pressurisation test to mainly test the staging and parachute deployment mechanisms. It was to be the last full test before launch. We set the booster on its launcher and put a dummy sustainer on top. As we began to fill and the pressure switch started to activate, I turned on the flight computer and armed it. Then we stood back and continued filling it. We were filling it quite slowly, so I put the video camera down. Then as we were approaching maximum operating pressure of 120psi, BOOM!

The failure was totally unexpected as the booster had been tested previously to the operating pressure. It was a very loud boom, and my ears rang for a couple of minutes afterward. You could hear it echo through the neighbourhood. One of the neighbours came out to see what had happened. Luckily the other neighbour was away, otherwise we would not have heard the end of it from them.

Since we didn't have footage of the actual failure, and neither of us was looking directly at the rocket at the time we didn't know exactly what had happened. We picked up as many of the pieces as we could to try to reconstruct the rocket and see where the failure occurred.

What Happened?

Although 6 bottles were pretty well shredded and there was a whole lot of pieces, we believe we know where the failure happened. It looks like a bottle failed at one of the holes of the base-to-base coupling. The reason is because of the damage done to both bottles at that point. The two bases are completely shredded but it looks like they flew apart at that point. The lower bottle was turned inside out as the coupling failed and the big hole acted as a nozzle and forced the bottle down over the other one. Also it is the only coupling still missing. All others are still attached to bottles or pieces of bottles.

The root cause is likely to be a hairline fracture that developed at the hole of the bottle and after numerous flights and pressurisations it has propagated until finally completely failing. We are now going to modify our technique how we make the holes for the couplings and heat treat the edges with a soldering iron to reduce any areas for stress fractures to develop. We may also try another reinforcing technique for the bottle bases other than the strapping tape we have been using.

As the bottle ruptured, it caused a cascading effect and the other highly stressed bottles around it also exploded. One of the bottles also shot upwards and hit the pod. It looked like there was a lot of damage to it, but when we later pulled it apart, it turns out there was only minor damage to a couple of lids, some of the bulkheads, and the bottom cover. The staging mechanism, flight computer, and servos all survived well.

We also noticed that the nozzle from the sustainer was missing. This we found surprising, but later we found it and half of the lid that was holding it. The nozzle flange snapped and so the nozzle can go in the bin. Something probably hit the sustainer during the explosion and broke the nozzle, which then shot out of the staging mechanism.

The Tachyon sustainer was not fitted to the booster during the test and hence suffered no damage.

What's Next?

We rebuild of course! We have set a time frame of two weeks to fully rebuild it. Since last night most of the damage to the pod has been repaired, and tonight it should be fully operational again. We will have quite a bit of lemonade to drink over the next few days to replace the damaged bottles.

We are going to pull apart the Polaron rocket as it already has 3 of the bottles with couplings and use it on the Acceleron IIIb rocket. We have a couple of empty spare bottles as well so it should go quite quickly.

We will keep more frequent updates on the Blog of how the rebuild is going.

Lessons Learnt

  • This was an example of what can happen when working with water rockets. They can be dangerous, and hence all possible safety precautions should be taken. We had the kids inside the house, and will continue do that in future tests. I might inform the neighbours too that if they hear loud booms its probably only us.
  • Bottles should be inspected after every flight or test, and if excessive stress is visible, they should be replaced.
  • Always keep the video going during any test. It can always be edited later.

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