Author Topic: On-Pad Explosions  (Read 25427 times)

Offline Chrup4

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Re: On-Pad Explosions
« Reply #20 on: 09/03/2016 07:31 AM »
The fifth Thor test on October 3, 1957, was launched from LC-17A. In a near repeat of Thor 101, the missile lost thrust almost immediately at liftoff, fell back through the launch stand, and exploded. This incident was traced to a failure of the gas generator valve to open.

Pad damage was evidently quite minor, as LC-17A hosted the launch of Thor 108 on October 24, only 21 days later.
« Last Edit: 09/03/2016 07:36 AM by Chrup4 »

Offline Chrup4

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Re: On-Pad Explosions
« Reply #21 on: 09/03/2016 07:40 AM »
(no picture)

Thor 121 launched from LC-17B on April 19, 1958 and resulted in yet another loss of thrust at liftoff followed by an explosion. This time, the culprit was apparently a collapsed fuel duct.

LC-17B was out of service for two months and hosted its next launch in June.

Offline Chrup4

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Re: On-Pad Explosions
« Reply #22 on: 09/03/2016 08:04 AM »
A couple of points about the Atlas/Titan failures mentioned earlier.

It is probably correct that the explosion of Titan C-3 was less damaging than B-5 due to the nature of the failure. Since the RSO charges went off, they would have split the first stage tanks open and largely prevented propellant mixing from occurring (which is exactly what they're designed to do), resulting in a much less energetic blast. I would imagine that Titan B-5's RP-1 tank probably rammed into the LOX tank when the vehicle broke apart (somewhat like what happened with Challenger's external fuel tank), causing a lot of propellant mixing and thus a rather violent explosion.

Atlas 51D was intentionally destroyed by the Range Safety Officer once it became apparent that there was a malfunction in one engine. There is a closeup shot showing the tanks splitting open and an explosion in the area of the common bulkhead where the RSO charges were located.

Atlas 48D did not get off the pad to my knowledge. I've never seen film of this launch, but as I understood it, the sustainer engine exploded prior to liftoff which would explain why the thrust section is resting inside the launcher mechanism in the aftermath photo.

Also I can't account for the quick damage recovery from Samos 3 given the similarity of the failure to Titan B-5 and Atlas AC-5, except maybe the Agena's hypergolic propellant did not explode with as much force as the cryo propellants in the other vehicles and thus less pad damage.

Offline Hobbes-22

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Re: On-Pad Explosions
« Reply #23 on: 09/03/2016 11:21 AM »
N-1 5L: The LOX turbopump for engine no. 8 exploded just before liftoff. The rocket managed to clear the tower, at 10 seconds into the flight the KORD system started shutting down 29 of the 30 engines. The rocket crashed on the pad, wiping it out and damaging the second N-1 pad nearby.

The photo shows the escape system firing to yank the capsule away from the N-1 as it begins to fall back down onto the pad.


Offline kevin-rf

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Re: On-Pad Explosions
« Reply #24 on: 09/03/2016 12:24 PM »
So how is the Sea Launch NSS-8 launch failure in jan. 30, 2007 counted. Would this be considered an American launch failure due to partial Boeing ownership? Also wouldn't, okay just checked F9 contains ~20% more propellants than the Zenit. So would it be the second largest US pad explosion? Third going to AC-5?
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Offline edkyle99

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Re: On-Pad Explosions
« Reply #25 on: 09/03/2016 03:23 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
« Last Edit: 09/03/2016 03:31 PM by edkyle99 »

Offline edkyle99

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Re: On-Pad Explosions
« Reply #26 on: 09/03/2016 03:37 PM »
So how is the Sea Launch NSS-8 launch failure in jan. 30, 2007 counted. Would this be considered an American launch failure due to partial Boeing ownership? Also wouldn't, okay just checked F9 contains ~20% more propellants than the Zenit. So would it be the second largest US pad explosion? Third going to AC-5?
To me, Zenit 3SL was a Ukrainio-Russian rocket with a U.S. payload fairing.  It definitely was not an "American launch vehicle".  It might fall into an "International" category.  (Atlas 5 has a European payload fairing, but I've never heard anyone suggest that it is a European launch vehicle.)

In terms of U.S. pad (or near-pad) explosions, Falcon 9 is likely most powerful, followed by Antares and Atlas Centaur 5.  The three had GLOWs of about 587 tonnes, 286 tonnes, and 138 tonnes, respectively.  (We can debate whether Antares fits the "on-pad" category.  I think it fits due to the severe pad damage.  We can also debate whether Antares is a "U.S. launch vehicle", but maybe not here!) 

Amazing that we've seen the two worst such U.S. failures during just the past two years.

 - Ed Kyle
« Last Edit: 09/03/2016 03:45 PM by edkyle99 »

Offline HMXHMX

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Re: On-Pad Explosions
« Reply #27 on: 09/03/2016 04:11 PM »
The fifth Thor test on October 3, 1957, was launched from LC-17A. In a near repeat of Thor 101, the missile lost thrust almost immediately at liftoff, fell back through the launch stand, and exploded. This incident was traced to a failure of the gas generator valve to open.

Pad damage was evidently quite minor, as LC-17A hosted the launch of Thor 108 on October 24, only 21 days later.

A second-hand personal note about Thor failures...

My good friend and mentor the late Max Hunter (Thrust into Space, 1966, and the fictional movie character "Dr. Hunter" in "2001: A Space Odyssey" hibernaculum, as a homage from his friend Arthur C. Clarke), once told me why Thor pads could be brought back on line so quickly.  Max was Chief Engineer on Thor (and also the S-IV and S-IVB stages).

The Thor was built with separate propellant tanks.  If it fell back onto the pad in a more or less vertical orientation, the vehicle descended below the pad deck through the center hole, hit the flame deflector and skidded along it, breaking neatly into two parts, one fuel and one oxidizer. One tank would break open below the deck, the other above. The propellants didn't inertially mix as thoroughly as was the case on other pads, such as Atlas.  While there was a still large conflagration, the blast effects were less than were seen on other stands.

Offline Archibald

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Re: On-Pad Explosions
« Reply #28 on: 09/03/2016 06:26 PM »
Ah. So SpaceX explosion was bigger than Atlas Centaur AC-5 ? That record stood for 51 years.
(my favorite rocket explosion of all times)
 Didn't realised it, but of course Falcon 9 is a lot bigger than the old Atlas.
« Last Edit: 09/03/2016 06:34 PM by Archibald »

Offline Nomic

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Re: On-Pad Explosions
« Reply #29 on: 09/03/2016 07:04 PM »
Stretching to test stand explosions, what about the Titan IV booster (after a redesgin became the srmu)  explosion at Edwards AFB? Only 280 tonnes of prop though...

Offline HMXHMX

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Re: On-Pad Explosions
« Reply #30 on: 09/03/2016 11:40 PM »
Stretching to test stand explosions, what about the Titan IV booster (after a redesgin became the srmu)  explosion at Edwards AFB? Only 280 tonnes of prop though...

OK, another anecdote...I was on that stand with my business partner something like a month before the firing (and kaboom). Being a liquid guy, and not liking solids at all, I remember being very nervous walking under the plugged nozzle, and he said something soothing like "if it blows up you'll never even feel it."  Neither of us had any idea that it was going to do that, of course. 

If you can visit the Evergreen Air Museum in Oregon, you can see an unloaded version of the composite case they used.

Offline WBailey

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Re: On-Pad Explosions
« Reply #31 on: 09/03/2016 11:59 PM »
If the Titan II ICBM silo explosion of 1980 counts, and we're including other nationalities:

Nedelin Disaster: On the 24th of October, 1960 at Baikonur the second stage engines of an R-16 ICBM prototype activated on the pad. The missile was instantly destroyed and over 90 people were incinerated, including Nedelin himself. The pad was closed until 1961, and serves as a memorial to the disaster today.





Offline Chrup4

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Re: On-Pad Explosions
« Reply #32 on: 09/04/2016 01:17 PM »
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.

The video of the launch is on CriticalPast, but I've also never found any still photos of Samos 3 other than the prelaunch one I posted earlier. One of the more peculiar things I noted in the video is that the Agena appears to break apart before the fireball reaches it. The best I figure out is that the RSO charges on the Agena went off from vibration as the Atlas started to break up. This was not the first time the umbilicals on LC 1-1 caused trouble since they were also responsible for the loss of Samos 1 eleven months earlier.

For the record, Atlas 9C was a larger blast than Samos 3 because the common bulkhead between the propellant tanks collapsed, which caused the entire load of LOX to fall into the RP-1 tank and turn into explosive gel. The explosive force was tremendous, enough to completely level the pad umbilicals and hurl a one-ton piece of the service tower about 50 feet. As noted earlier, LC-12 took seven months to restore while the damage from Samos 3 was completely repaired in a month and a half.

I'm also fairly certain that Vanguard TV-3, Samos 3, and Cygnus CRS-3 were the only pad explosions of a US launch vehicle during an actual orbital launch attempt (assuming you discount Atlas-Centaur AC-5 because it had only a dummy Surveyor probe for a payload). Every other pad explosion I can think of was suborbital or occurred during a PFRT.
« Last Edit: 09/04/2016 06:12 PM by Chrup4 »

Offline Chrup4

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Re: On-Pad Explosions
« Reply #33 on: 09/04/2016 01:37 PM »
The Thor was built with separate propellant tanks.  If it fell back onto the pad in a more or less vertical orientation, the vehicle descended below the pad deck through the center hole, hit the flame deflector and skidded along it, breaking neatly into two parts, one fuel and one oxidizer. One tank would break open below the deck, the other above. The propellants didn't inertially mix as thoroughly as was the case on other pads, such as Atlas.  While there was a still large conflagration, the blast effects were less than were seen on other stands.

It could be a combination of the pad design and the nature of the failure. Like noted earlier, Titan I B-5 caused enough damage to put LC-19 out of service for six months while C-3 only put LC-16 out for two months. As I understand, most of the damage to LC-19 was the umbilical tower, which suffered extensive fire damage.

B-5 also got further off the pad than C-3, a couple feet before the engines cut off. Most likely, the engines struck the flame deflector pit and got rammed upward into the RP-1 tank, which then rammed up into the LOX tank. Since it fell down from a couple of feet up, there must have been considerable force being imparted into the missile as it hit the flame deflector. The propellants thus mixed, blew, and caused extensive damage.

C-3 really didn't even lift, maybe an inch or so when the RSO charges activated and split the first stage tanks open, which would have mostly just spilled out the propellants and caused a low intensity deflagration.

Offline Chrup4

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Re: On-Pad Explosions
« Reply #34 on: 09/04/2016 01:49 PM »
The third Redstone missile test, RS-3, took place from LC-4 at CCAS on May 3, 1954 and ended ignominiously when the engine cut off one second after liftoff, causing the missile to fall back onto the launch stand in a ball of white flame.

Afterwards, Major General Holger Toftoy asked Werner Von Braun "Werner, why did the rocket explode?" Von Braun replied that he had no idea, but they would review telemetry data to find out. When Toftoy continued to press Von Braun for the cause of the failure, he replied "It exploded because the damn sonofabitch blew up!"

Von Braun subsequently pushed for better quality workmanship on the Redstones, noting acidly "Maximum reliability will be achieved when the target area of the missile becomes more dangerous than the launching area."

Offline Chrup4

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Re: On-Pad Explosions
« Reply #35 on: 09/04/2016 02:05 PM »
N-1 5L: The LOX turbopump for engine no. 8 exploded just before liftoff. The rocket managed to clear the tower, at 10 seconds into the flight the KORD system started shutting down 29 of the 30 engines. The rocket crashed on the pad, wiping it out and damaging the second N-1 pad nearby.

The photo shows the escape system firing to yank the capsule away from the N-1 as it begins to fall back down onto the pad.

There were many Soviet pad explosions that were spectacular beyond belief, but the last one to date was the 1990 Zenit disaster. I'm not aware of any happening in the post-Soviet era unless there was a missile test or two at some point.

Aside from the Nedelin Catastrophe and N-1 5L, there were numerous R-7s that blew on or near the pad over the years. The very first R-36 launch in 1963 lost thrust at liftoff and fell back onto the pad. Two Kosmos (R-14) boosters blew on the pad in the early 70s, one lost thrust at liftoff, the other caught fire during servicing and killed 9 people.

Offline Chrup4

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Re: On-Pad Explosions
« Reply #36 on: 09/04/2016 04:13 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.

Online Phillip Clark

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Re: On-Pad Explosions
« Reply #37 on: 09/05/2016 03:04 AM »
I am surprised that no-one has mentioned the on-the-pad explosion of the Brazil's third VLS.

The launch was scheduled for August 25, 2003 and it was planned to orbit the SATEC and UNOSAT 1 payloads.   On August 22 one of the four strap-on boosters exploded, with the launch pad being destroyed and 21 people being killed.

Work on the VLS continued until earlier this year, when it was decided to develop the VLM-1 instead.

Offline Arch Admiral

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Re: On-Pad Explosions
« Reply #38 on: 09/05/2016 06:13 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.

SpaceX clearly thought pad explosions were a thing of the past, since the fueling and other support equipment was located close to the pad and was completely fried by the prolonged RP-1 fire. Also, witnesses report spalling and cracking of the concrete pad and exhaust duct. It will take a long time to get LC-40 operational again.

Online Phillip Clark

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Re: On-Pad Explosions
« Reply #39 on: 09/05/2016 06:50 AM »
Will Space X have to pay the bill for the repairs or is that the responsibility of the CCAFB?

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