Author Topic: On-Pad Explosions  (Read 23309 times)

Offline Chrup4

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Re: On-Pad Explosions
« Reply #40 on: 09/05/2016 10:54 AM »
A factor in the rapid repair of the old IRBM and ICBM pads in the 60s was that these were top-priority national programs with unlimited funding, so spare pad hardware was stockpiled. Pad explosions were expected and planned for. Note how launch support equipment was well separated from the pads and protected by concrete blast walls (or the long-vanished 'Blockhouses"). Also, the RP-1 usually burned off quickly, so there usually was not thermal damage to the underlying concrete structure.

I had heard that the damage from Atlas AC-5 was mostly repaired in three months even though the next launch from LC-36A was not for over a year (probably more fire than structural damage). The Atlas-Centaur launch rate was small (only two during the time LC-36A was offline) and probably 36B alone was enough to handle it. Also while LC-13 was offline six months following Atlas 51D, some of that delay could have been due to converting the pad for Atlas E launches.

As for the RP-1 burning off quickly, you have to remember also that most of it doesn't actually go off in an explosion. Even on N1-5L, about 80% of the propellant load in the booster did not ignite and what did was mostly in the first stage. After the blockhouse crew were allowed outside, there were unburned droplets of RP-1 raining down from the sky. Despite the blast being intense enough to level the service towers and cave in the concrete launch stand, they still recovered most of the vital telemetry tapes intact from the rubble.

Online kevin-rf

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Re: On-Pad Explosions
« Reply #41 on: 09/05/2016 11:00 AM »
Will Space X have to pay the bill for the repairs or is that the responsibility of the CCAFB?

Considering they are the ones who built and operate it, I would assume they (or insurance) has to not only pay for any pad repairs, but also any damage they inflicted on other people's equipment.
« Last Edit: 09/05/2016 11:02 AM by kevin-rf »
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Offline Chrup4

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Re: On-Pad Explosions
« Reply #42 on: 09/05/2016 02:25 PM »
Operation Fishbowl in 1962 involved a series of high altitude nuclear tests launched from Johnson Island in the Pacific on Thor IRBMs. After the "Bluegill" launch failed on June 2, the next attempt, code named Bluegill Prime, was made on July 25 but ended disastrously when the Thor caught fire on the pad. A stuck engine value cut the flow of LOX to the combustion chamber and RP-1 ignited on contact with the hot engine. The Range Safety Officer sent the destruct command and blew up the Thor on the pad, also destroying the nuclear warhead.

The pad area was extensively contaminated with plutonium and had to be cleaned up before the destroyed launch stand could be rebuilt.

Offline Jim

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Re: On-Pad Explosions
« Reply #43 on: 09/05/2016 03:25 PM »

SpaceX clearly thought pad explosions were a thing of the past, since the fueling and other support equipment was located close to the pad

Not really, they were protected by berms just like days of old.  They reused the existing Titan berms

You can see here

http://forum.nasaspaceflight.com/index.php?topic=40868.msg1578330#msg1578330
« Last Edit: 09/05/2016 03:32 PM by Jim »

Online catdlr

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Re: On-Pad Explosions
« Reply #44 on: 09/05/2016 10:22 PM »
video of pad explosion of Atlas-Centuar AC-5 (video of explosion starts at 2:13)

Largest Explosion

https://www.youtube.com/watch?v=NgqnlUifggw?t=000

« Last Edit: 09/05/2016 10:24 PM by catdlr »
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Offline MattMason

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Re: On-Pad Explosions
« Reply #45 on: 09/06/2016 04:02 AM »
Very fascinating series, Ed.

But what I'm taking away from this is why there were over 43 separate launch pads in the old days.

Blow one up? Go fly on another while you examine the charred, painted rocket pieces and rebuild the pad.

Took a while to rebuild pads, and it is only slightly faster today with light-gantry launches using strongbacks.
"Why is the logo on the side of a rocket so important?"
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Offline Chrup4

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Re: On-Pad Explosions
« Reply #46 on: 09/06/2016 10:36 AM »
video of pad explosion of Atlas-Centuar AC-5 (video of explosion starts at 2:13)

Oddly enough, in all this time nobody's turned up the postflight launch reports for AC-1 or AC-5 although the reports for several early Centaur launches are online.

Offline Chrup4

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Re: On-Pad Explosions
« Reply #47 on: 09/06/2016 11:17 PM »
The final Titan I R&D launch was that of Missile V-4 from VABF's 395-A1 on the evening of May 1, 1963. In an ominous prediction of Atlas 45F five months later, the missile experienced a stuck engine valve that prevented the LR-87 engines from achieving sufficient thrust to lift the 110 ton missile, which then tipped over and exploded on impact with the ground. 395-A1 was repaired in two months and hosted Titan SM-7 on August 15.

I should add, I saw a video of Titan I V-4 on the net a long time ago. It was just like Atlas 45F--nighttime launch where the thing tipped over as soon as it was released. There's a closeup shot on the engines which are essentially not firing at all. I also once saw a brief clip of Redstone RS-3 on a Youtube rocket failure compilation. Otherwise most of those videos just have failures everyone's already seen hundreds of times like Juno AM-16, Atlas 27E, and Delta II 241.

Offline koroljow

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Re: On-Pad Explosions
« Reply #48 on: 03/12/2017 06:02 PM »
Samos 3 exploded on LC 1-1 at PALC on September 9, 1961. A pad umbilical did not detach at liftoff, which caused the Atlas-Agena B to switch from internal to external power. The engines shut down and the Atlas dropped back onto the pad and exploded in a huge fireball, resulting in the total loss of the photoreconnaissance satellite.

Pad damage was evidently not that bad as Samos 4 flew from LC 1-1 only nine weeks later.
Thanks for adding this one!   This was Atlas 106 D and Agena B A2201.  I have to date found no photos of the failure or its aftermath.  This could have been a more powerful explosion than Atlas-Able, the previous U.S. largest.  At the time, Atlas Agena B was the largest, most-powerful U.S. launch vehicle.  The next launch from Point Arguello LC 1-1 (later renamed VAFB SLC 3 West) took place on November 22, 1961.  It also failed, but not on the pad.

 - Ed Kyle

Sorry (again) for digging up an old thread.  But if someone (Ed?) ist still interested: this is the link to a video showing Atlas 106D's fate:


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Geschichte und Geschichten aus mehr als 5 Jahrzehnten Raumfahrt:
http://www.raumfahrtkalender.de

Offline WallE

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Re: On-Pad Explosions
« Reply #49 on: 04/05/2017 05:49 PM »
To answer one of the earlier queries, the reason the Agena appears to break up before the fireball reaches it is because of the Inadvertent Separation Destruct System. This system was present on most Atlas-Agena vehicles, and it was designed to destroy the Agena if it would prematurely separate from the stack. So essentially what happened on Samos 3 is that the Atlas started to break up and this tripped the ISDS charges.

An ISDS malfunction caused the loss of the very first Atlas-Agena flown, and you may recall that they had to destroy Mariner 1's booster just before staging occurred since the Range Safety charges on the Agena would then be disabled.


Offline WallE

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Re: On-Pad Explosions
« Reply #50 on: 04/05/2017 08:26 PM »
Note the thrust ring and forward portion/adapter section of the Atlas LOX tank survived more-or-less intact. The second photo shows what I believe are the remains of the Agena.

There were a high number of VAFB failures caused by problems with the launcher/pad equipment for some reason. Samos 1, Samos 3, Discoverer 9, Midas 6, Atlas 71F, Atlas 64E (sort of), a couple of Atlas D failures off 576-B, Titan II N-7. The only Cape failures caused by the pad equipment (that I know of) were Titan I B-5 and Atlas 7D, neither of which were orbital launches.

Edit: I just remembered another Cape failure--Titan I AJ-10, again though not an orbital launch.
« Last Edit: 04/08/2017 12:46 AM by WallE »

Offline WallE

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Re: On-Pad Explosions
« Reply #51 on: 04/06/2017 07:17 PM »
Atlas 48D suffered a failure very similar to Atlas 51D.  It flew just a few feet from LC 11 on April 8, 1960 before falling back on its pad after a booster engine suffered combustion instability.  This failure did less damage to the launch pad this time.  LC 11 hosted its next launch only three months later.

I read the postflight report for 48D. The B-2 engine malfunctioned, causing a thrust section explosion, and an automatic shutoff command was sent to the entire propulsion system. This happened before it developed sufficient thrust, so the missile never lifted from the pad. It sat there and burned for 60 seconds until the propellant tanks exploded.

As for 51D, the failure occurred in the B-1 engine and it did lift from the pad. There was a post in here claiming it was an RSO destruct, but while I don't have a postflight report for 51D, the 48D report and several other Convair docs have no allusions in them to it being destroyed intentionally. In the photo here, you can see the engines are still running which would not happen in an RSO destruct (propulsion system shutoff followed by detonation of the destruct charges). It seems that what actually happened is that an explosion in the thrust section damaged the pneumatic system and caused structural failure of the missile. I could still be wrong but unless the postflight report for 51D turns up, sketchy details are all I have.

They had also taken the turbine exhaust duct off LC-11 and LC-13 in early 1960 and after the back-to-back pad explosions, it was decided to put it back on just as a precaution although there wasn't any evidence that the absence of the duct had caused the failures.

Edit: LC-12 and LC-14 still had their ducts because they were used for space launches which did still have PFRFs. My mistake
« Last Edit: 04/07/2017 12:49 AM by WallE »

Offline Proponent

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Re: On-Pad Explosions
« Reply #52 on: 04/06/2017 10:50 PM »
Thanks much, WallE -- that's a very interesting account.  Was there any particular reason for removing the turbine duct in the first place?
« Last Edit: 04/06/2017 11:00 PM by Proponent »

Offline WallE

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Re: On-Pad Explosions
« Reply #53 on: 04/07/2017 12:45 AM »
Thanks much, WallE -- that's a very interesting account.  Was there any particular reason for removing the turbine duct in the first place?

They took the duct off because it impeded the removal of covers installed on the turbine exhaust during pressure testing and since they had stopped doing Pre Flight Readiness Firing tests (aside from space launcher Atlases) by early 1960, there was no concern about the Atlas's thrust section being exposed to the turbine exhaust for long periods of time.  After the 51D and 48D failures, in addition to reinstalling the duct, camera coverage of the flame deflector pit was increased. Also they wanted the pads to comply with the configuration of Atlas D missile silos.

Offline WallE

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Re: On-Pad Explosions
« Reply #54 on: 04/08/2017 01:03 AM »
As one more pad explosion not yet mentioned, Atlas 19D exploded on 576-A1 at VAFB March 5, 1960 when a fire started during a fuel loading exercise. This brings the Atlas pad explosion tally to five for both the East Coast (9C, 51D, 48D, 11F, and AC-5) and West Coast (19D, 27E, 106D, 45F, and 3F).

Offline Blackstar

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Re: On-Pad Explosions
« Reply #55 on: 04/08/2017 02:06 AM »
I think that a few years ago Joel Powell did an article on Atlas pad crumples. Not all of them went boom. In fact, I think he was more interested in the ones that crumpled but did not explode, because they were not recorded regularly.

Offline WallE

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Re: On-Pad Explosions
« Reply #56 on: 04/08/2017 02:48 AM »
I think that a few years ago Joel Powell did an article on Atlas pad crumples. Not all of them went boom. In fact, I think he was more interested in the ones that crumpled but did not explode, because they were not recorded regularly.

Atlas 190D famously crumpled on SLC-4W May 11, 1963 and was recorded on camera, we've all seen than one. The booster intended to launch Mariner 6 also crumpled, but its collapse was averted by two quick-thinking technicians. Atlas collapses also happened a couple of times at operational silo facilities.

The Mercury astronauts were in a high risk profession; John Glenn flew when the Atlas was batting .500. Atlas 52D blew up during an operational test from the West Coast only about 24 hours after Glenn's launch. When Gordon Cooper flew at the end of the Mercury program, things didn't get much better; there were four Atlas failures in the first three months of 1963, three of which were D-series (ie. a potential direct problem for Mercury).

Offline Jim

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Re: On-Pad Explosions
« Reply #57 on: 04/10/2017 01:49 PM »

An ISDS malfunction caused the loss of the very first Atlas-Agena flown, and you may recall that they had to destroy Mariner 1's booster just before staging occurred since the Range Safety charges on the Agena would then be disabled.

Staging does not disable the upper stage FTS

Offline WallE

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Re: On-Pad Explosions
« Reply #58 on: 04/10/2017 03:17 PM »
Staging does not disable the upper stage FTS

https://archive.org/stream/nasa_techdoc_19750065548/19750065548_djvu.txt

"5. 3 AGENA B FLIGHT TERMINATION SYSTEM

This system consists of two independent circuits which utilize the dual command destruct signal inputs from the Atlas first booster. These circuits and destruct charge are located in the adapter section between the Agena B and the Atlas. This provision will permit the destruct system to remain with the Atlas on separation which will eliminate weight and destruct capability during the Agena boost phase. Dual independent premature separation destruct circuits are also provided. Each circuit consists of independent battery, wiring, and squibs for the initiation primer. These circuits are actuated when a lanyard releases either of the two (2) separation switches mounted on the adapter at the base of the vehicle. Some components of each circuit are shared with the command destruct circuits. These circuits are disarmed and "safed" before programmed separation of the Agena B. Detailed information on this system is provided in LMSD-447590-A, Ranger Flight Termination System, 28 February 1961, Confidential. "

"2. 3 WAIVER REQUIREMENTS

The Flight Range Safety Waiver requested in accordance with AFMTC instructions* is required because:

a. The instantaneous impact point will have to cross South Africa.

b. Due to weight considerations which would compromise the mission, a separate and independent destruct system with R-F receivers and attendant electronic equipment is not desired."

To make a long story short, the Agena didn't have its own FTS due to weight restrictions, only the ISDS which was disabled at staging. The details on Centaur are less clear. The mission reports for AC-6 indicate that it had an ISDS, but it doesn't seem that it was carried on all launches (certainly not on AC-43 anyway). All Centaurs did have a separate FTS, which was used several times over the years. So it's technically correct that staging didn't disable the FTS since the Agena lacked its own FTS and was left without any Range Safety destruct capability post-staging.

The Mod 3 GE guidance system on the Atlas was a reliability disaster and it malfunctioned numerous times (Samos 1, Samos 4, Mariner 1, a couple of Ranger launches, several missile tests, etc) before the Lewis Spaceflight Center stepped in and initiated a quality improvement program on Atlas.
« Last Edit: 04/10/2017 05:14 PM by WallE »

Offline Jim

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Re: On-Pad Explosions
« Reply #59 on: 04/10/2017 05:04 PM »

1.  The details on Centaur are less clear. The mission reports for AC-6 indicate that it had an ISDS, but it doesn't seem that it was carried on all launches (certainly not on AC-43 anyway). All Centaurs did have a separate FTS, which was used several times over the years.

2.  I probably should have phrased that earlier post better since it makes it sound as if the Agena had a separate FTS, which it didn't.

1.  ISDS is not really a "system".  It is just a series of lanyards or break wires across stage planes or SRM attach points that are enabled and then disable at appropriate times.  The basic stage/SRM FTS charges are used and there are no additional charges. 

2.  That was important for GATV. 

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