[X] My Assistant

[ljk4-1]

Saturn's fury: effects of a Saturn 5 launch pad explosion
---

It was the worst-case scenario for the Apollo program: a Saturn 5
rocket blowing up on the pad. Dwayne Day explains how NASA studied
the risks of such an explosion and what could be done to save the
Apollo crew.

http://www.thespacereview.com/article/591/1

[Guest_Myran_*]

Me four on sodium chlorate and sugar!
And yes also I noted the instability and moved over to powder explosives, experiments in which I did loose my eyebrows.

I smiled when reading

edstrick: No rocket. Just the engine.

Yes same here, just the engine, about 6 inch long if I remember correctly and I test fired it only twice.
I must have been around 10 years old or so, quite amazing what ideas I had as a child.

[stevo]

I tried sodium chlorate and sugar too, once. The stuff is too unstable to be safe.

It was fairly widely used as a weedkiller back in the 60's and I once heard a story about a boy who walked over a meadow treated with the stuff on his way to a soccer match. It had been raining and his shoes and stockings got wet. Halfway through the match they had dried out and one of his shoes exploded! I don't know if it's true, but it might well be, practically any organic compound mixed with sodium chlorate becomes explosive.

tty

Just as well he didn't sit down ...
http://www.nzherald.co.nz/section/story.cf...jectID=10362358

[DEChengst]

I tried sodium chlorate and sugar too, once. The stuff is too unstable to be safe.

You think that's unstable ? Try sodium chlorate with red phosphorus. A tiny spark will make it go off. Been there, done that, garden full of instant smoke The joys of being young and ignorant

[edstrick]

I believe <may be quite wrong, but I'm too lazy at 5:21 am to google it> that cap-gun explosive caps use teeny chlorate and red phosphorus paste under the paper.

Of course, my favorite home brew explosive is soaking tiny pieces of iodine in household ammonia for an hour to form nitrogen tri-iodide.... contact explosive when dry.. and not very safe when still damp. I recommend making samples no larger than rice grains.

[Bill Harris]

As a youngster I made a multi-stage, multi-engine rocket (using Estes motors) that cocked at 20' and flew on the ground along a golf course. We followed, and found a burned spot and debris field at each staging. Recovered the fourth stage with the "If Found Return To..." tag and got the heck out of there.

It's amazing that we survived childhood...

--Bill

[djellison]

Two stage Mongoose Estes effort for me was a highlight - some proper altitude on that.

Also - did a summer space school as a teenager and made a sort of hang-glider type affair that sat on the side of a fairly simply rocket, and deployed with the nose cone. Sadly - the rocket took off - turned 90 degrees and deployed at about 10ft, but it deployed perfectly and flew gently to the ground

Doug

[Ames]

NACA Langley engineer Francis Rogallo developed his patented kite design into the Rogallo wing glider - the forerunner of hang gliders - into the Paresev (Paraglider Research Vehicle) wich would allow a spacecraft to glide back to the earth and land at normal air fields.

http://en.wikipedia.org/wiki/Paresev
http://en.wikipedia.org/wiki/Francis_Rogallo


Nick

[tty]

Of course, my favorite home brew explosive is soaking tiny pieces of iodine in household ammonia for an hour to form nitrogen tri-iodide.... contact explosive when dry.. and not very safe when still damp. I recommend making samples no larger than rice grains.

My favorite was salpeter, sulphur and potash (found the recipe in a nineteenth century chemistry book). Perfectly safe and stable at room temperature, but sprinkle some of it on the bottom of an overturned tin can, put a candle underneath and once the stuff has melted it goes very satisfactorily bang! In addition to being safe to handle this technique gives you time to make your getaway before waking up the neighborhood.

I never did figure out what the potash is good for, but it does not work without it.

Otherwise I tend to agree with Bill.

tty

[Guest_BruceMoomaw_*]

Saturn's fury: effects of a Saturn 5 launch pad explosion
---

It was the worst-case scenario for the Apollo program: a Saturn 5
rocket blowing up on the pad. Dwayne Day explains how NASA studied
the risks of such an explosion and what could be done to save the
Apollo crew.

http://www.thespacereview.com/article/591/1

A very interesting piece for me -- because, a couple of years ago, I stumbled across one of NASA's dirty little secrets: the fact that Apollo 13 suffered TWO near-fatal accidents during its flight! I'll have to look up the references (I have an awful headache right now); but that engine-out incident on the second stage -- which I had always assumed was innocuous -- turns out to have been due to the fact that the center engine started massively pogo-ing up and down in its mounts at least 20 times per second with tons of force, and NASA had never thought to provide any sensors to shut down the engine or trigger the escape system if this happened! It was apparently within a few seconds of tearing loose from its mounts -- which of course would have caused the second stage to explode -- when another sensor responded to the resulting wild fluctuations in propellant pressure by shutting down the engine. And the above article makes it clear that such an explosion would have killed the crew.

NASA didn't actually censor this incident, but they have made a point of never talking about it conspicuously -- not even Aviation Week ever mentioned the details, as far as I know. You have to dig for it in technical papers on Pogo, which is where a Canadian space blogger found it. And with that clue, there are at least two papers on the Web that mention it, without emphasizing the deadly nature of the malfunction. What enabled NASA to hush it up was, ironically, the foofaraw over the SECOND near-fatal accident on that flight -- along with the fact that they had already decided, after the lesser second-stage pogo-ing on Apollos 10 and 12, to institute a technical fix starting on Apollo 14, which freed them from the need to officially do so in response to the Apollo 13 malfunction. The fix completely eliminated the problem on all future flights.

[Guest_BruceMoomaw_*]

After digging around on the Web, what little I've found seems to confirm the story of Canadian blogger Henry Spencer ( http://yarchive.net/space/apollo/apollo_13.html ): "Apollo 13 is a lot harder to find information on [than Apollo 6], because the Saturn V problem was overshadowed by later events. The second-stage center engine did not shut down early on a random whim. It shut down early because it had gone berserk, with the most violent Pogo oscillation ever seen, and quite by accident the violent pressure oscillations in its chamber tripped a 'low chamber pressure' sensor and the computer shut it down. In the second or so before the shutdown, two tons of engine, solidly bolted to a massive thrust frame, was bouncing up and down at 68G, flexing the frame three inches at 16Hz. Had this continued, it surely would have either torn itself off its mounts or broken the thrust frame, and either event would have wrecked the second stage.

"Center-engine Pogo had been seen before, in a much milder form, on Apollos 11 and 12, and a fix was already in the pipeline. Retrofitting it to Apollo 13's already-stacked booster had been deemed too difficult and not very important. Later Saturn Vs had the fix and the problem did not recur. (This was another reason why the problem didn't attract more attention -- it was considered solved by the time it occurred!)

"Documentation on this is scarce. The only good account I've found is in a survey article on Pogo in the Spring 1992 issue of Threshold, which is/was a Rocketdyne internal publication."

The "Threshold" article is at http://www.engineeringatboeing.com/articles/pogo.htm : After a modest amount of pogo in the center second-stage engine on all of Apollos 8 through 12, amounting to a maximum of about 12Gs at the engine (and very little of which was felt in the Command Module), "Rockwell's Space Division Rocketdyne (now Expendable Launch Systems, a part of The Pratt & Whitney Company) had designed, built, and tested a helium-bleed toroidal pogo suppresser for the oxidizer that we all felt would eliminate the problem. On the other hand, flight AS-508 was ready to go. To install it would require that technicians crawl over cable harnesses to get into the center engine, plus inspection and verification would be difficult. The unanimous vote was to fly AS-508 as is, just like AS-507, and let the built-in nonlinearities do the limiting. We should have known better - this was Apollo 13.

"Two early occurrences of second-stage II pogo at 16 Hz were consistent with earlier experience, while a third seemed to be teetering on the edge of acceptability and then just took off. Thrust chamber pressure oscillations in the center engine diverged from a level of 10-500 psi (peak-to-peak) in only 3 seconds. Acceleration reached 68 Gs at the center engine attachment, which translated into 3 inches of stroke. The center engine was shut down by a thrust chamber pressure 'OK' switch that sensed low average chamber pressure and initiated shutdown before any detectable failure. The vibration was confined to the center engine of the S-II stage, however, and the outer four engines burned extra long to make up for the center engine's early cutoff. The astronauts continued on, only to have a LOX tank explosion abort their lunar mission.

"The suppresser left waiting in the wings was installed for succeeding flights. Other than a little 10.5-Hz buzz in the last few seconds of S-II burn and a small concern about the S-IVB on each flight, pogo was eliminated as a Saturn problem."

An August 1970 NASA technical paper notes: "During POGO on SA-508 (Apollo 13) the S-II center engine experienced +34 g's longitudinal acceleration [at 15 Hz]. There has been considerable interest in the response of the thrust cone and center engine beam to this load as it was nearly equal to the ultimate capability of the structure." (No doubt.) Jim Lovell's oral account of the flight on the Web virtually ignores the incident, but Fred Haise says: "...There was a brief episode that from where I was...certainly you felt the vibrations for a few seconds, like the feel of maybe holding a jackhammer...Then it went away. Then...Jim and Jack could see the center engine light come on that it had shut down...[The pogo] gave us this chatter, and, as I understand it pegged out the accelerometers on that center engine... Later, talking to Marshall people, they were happy it shutdown when it did, when it hit a low pressure point. Because much greater excursions in that g-level may have caued structural damage to that crossbeam and, of course, even more catastrophic effects."

Edgar Mitchell added during an interview that the pogo, "if left unchecked, probably would have destroyed the launch vehicle", although the forces at the Command Module were only about 0.1 G. Certainly it's a very good thing the engine shut down when it did, although it's uncertain how much longer the crossbeam would have held together and it's also not clear from these accounts how inevitable it was that the thrust pressure sensor would have quickly caused a shutdown. Dwayne Day's account above makes it clear that if the engine HAD torn loose, the crew would almost certainly not have survived the resulting explosion.

[ljk4-1]

There are a number of relevant NASA documents linked to from
this page, if you scroll down about 2/3 of the way:

http://www.geocities.com/bobandrepont/saturnpdf.htm

[Bob Shaw]

Dwayne Day's account above makes it clear that if the engine HAD torn loose, the crew would almost certainly not have survived the resulting explosion.

Bruce:

I didn't read it that way. I think he was saying that a CM exposed to the maximum overpressure from an exploding Saturn stage had to be beyond a certain point to survive, and the main thrust of his article was about near-pad accidents. The 155,00lb thrust LES was still active for the first 30 seconds of S-II flight, and if triggered would have pulled the CM rapidly away; what the SM RCS/SPS engines could have done after tower sep is obviously somewhat less, though! The question is, I suppose, whether at high altitude there would have been such an overpressure on the CM (remember the sad fate of the Challenger cockpit, which appears to have fallen almost unharmed out of the explosion which sealed it's fate, and that was *much* lower).

Great detective work, though!

Bob Shaw

[tty]

It seems to me it would be a good idea to add ejection seats to future manned spacecraft. Gemini had them, and so had the Space Shuttle on the first flights, and Buran was intended to have them.

Even a standard seat like the russian K-36 is good for Mach 2.5 and 80,000 feet which is well past Max Q. By adding a protective clamshell around the seat like those used on B-58 and B-70 it should not be too hard to extend the envelope to at least Mach 3 and 100,000 feet.

The main drawback would be the weight (perhaps 100-300 lb per seat plus the weight penalty for a jettisonable hatch) and the risk of having a large amount of pyrotechnics aboard during the flight. However I can only remember ever hearing about a single case of accidental ejection in flight (but several on the ground).


tty

[Guest_BruceMoomaw_*]

[quote name='Bob Shaw' date='Apr 5 2006, 05:22 PM' post='49395']
Bruce:

I didn't read it that way. I think he was saying that a CM exposed to the maximum overpressure from an exploding Saturn stage had to be beyond a certain point to survive, and the main thrust of his article was about near-pad accidents. The 155,00lb thrust LES was still active for the first 30 seconds of S-II flight, and if triggered would have pulled the CM rapidly away; what the SM RCS/SPS engines could have done after tower sep is obviously somewhat less, though! The question is, I suppose, whether at high altitude there would have been such an overpressure on the CM (remember the sad fate of the Challenger cockpit, which appears to have fallen almost unharmed out of the explosion which sealed it's fate, and that was *much* lower).

Great detective work, though!
__________________

I live to serve others (usually medium rare). Actually, while digging all that stuff up, I DID run across one Web discussion of how likely it was that the crew could have aborted in time. Not good, if the second stage engines hadn't been shut down by the emergency escape system -- the acceleration from the Service Module main engine was only 1/3 G, as against 12 Gs for the escape tower. But then, any emergency escape system that had been properly designed to sense pogo per se would have instantly shut down the engines at the same time that it triggered the escape system, so there probably wouldn't have been an explosion at all.

But Day's article made it clear to me for the first time that if the second stage had exploded with the Apollo still attached, there was virtually no chance that the Command Module and the crew could have survived the explosion and reentered. As I say, a very near thing, which only the SECOND near-disaster -- plus the fact that NASA had already instituted a fix for the problem on the next mission -- enabled it to keep quiet. (I'll try to dig up the URL for that discussion.)