Tuesday's Proton-M rocket explosion on the steppes of Kazakhstan is definitely not the first time an unmanned rocket has exploded at launch, and it won't be the last. As good as the various space agencies have become at launching rockets, it should never be forgotten that the vehicles we lob into space are fragile things, perched carefully atop what is essentially an enormous, carefully-managed continuous explosion. Launch vehicles are extremely complex machines, requiring the careful balance of a multitude of different forces, including constantly shifting mechanical and aerodynamic loads.
Space launch isn't (and perhaps never will be) a routine happening, but over the past sixty years or so we've become good enough at it that things go right far more often than they go wrong. Still, rockets remain fuel-filled tubes, and when they blow up, they tend to blow up real good.
As Americans today set off fireworks and watch Independence Day to celebrate our Independence day, Ars invites you to sit back and take a gander at these five rocket launches gone colossally bad. But take heart: for all their fire and thunder and billions of dollars gone up in smoke, none of the mishaps below resulted in any injuries. Though, man, I'd hate to have had to don a hot suit and mop up after any of them.

Vanguard TV3, 6 December 1957

The Soviet Union's launch of Sputnik in October 1957 was seen by the United States as a sign that the USSR controlled the high ground and could place objects in orbit over the United States; nothing in the USA's technological arsenal could prevent Soviet overflights of US territory. NASA did not yet exist; the USA's aerospace policy was still being determined by its predecessor, the National Advisory Committee for Aeronautics (NACA). Under intense political pressure, the US Navy pushed forward with the Vanguard program, which if successful would have resulted in the first US satellite to reach Earth orbit, just two months after Sputnik. Unfortunately, it was not to be. Vanguard TV3 exploded at lift-off on December 6, 1957, due to a pressurization problem with the fuel system that allowed burning fuel to creep back up into the engine. The US wouldn't successfully place a satellite into orbit until the following February, with Explorer 1.

Titan 34D-9 (KH9-20), 18 April 1986

The loss of Titan 34D-9 near the beginning of 1986 wasn't just bad because its failure echoed that of the recently-destroyed Space Shuttle Challenger, but also because the rocket was carrying the final billion-dollar KH-9 HEXAGON reconnaissance satellite. The KH-9 was a mainstay of the US photo reconnaissance efforts throughout the 1970s and 1980s; the giant satellites stayed in orbit for between one and nine months and photographed targets in specific areas of interest using its big main cameras, which could scan areas up to 120 degrees wide and could resolve details as small as two feet. Almost all of the imagery produced by the main cameras of KH-9 satellites remain classified.
The loss of the Titan 34D itself was also quite bad; the central liquid-fueled engine of the launch vehicle ran on storable but extremely poisonous hypergolic propellants, which complicated the recovery and clean-up efforts. All together, the Titan 34D-9 mishap is regarded as one of the most expensive launch failures in US history.

Delta 178 (GOES-G), 3 May 1986

1986 was just a bad year for space launches, period. Following the Air Force's Titan 34D-9 disaster, NASA's attempt to place a new weather satellite into orbit met with failure when, 71 seconds after launch, an electrical fault triggered a premature shutdown of one of the Delta 3914 rocket's center liquid engines. In the video, the flame-out can be seen at 1:55; the rocket yaws to one side and the payload is quickly sheared off by aerodynamic stresses. Shortly after, the Range Safety Officer detonates the rocket's range safety package, which is designed to "unzip" the propellant tanks and separate the fuel as quickly as possible from the burning rocket body.

Delta II D241 (GPS IIR-1), 17 January 1997

In what was certainly one of the most spectacular-looking launch vehicle failures ever, a Delta II 7925 rocket violently exploded just 17 seconds after lift-off in January of 1997. The rocket had just started its journey and was absolutely stuffed full of fuel; for its payload, it carried the first of a new, upgraded series of GPS satellites. The explosion was later determined to be caused by a crack in one of the twin solid rocket motors (one source says the crack was "17 feet long"). The crack quickly spread across the solid rocket motor's casing, and a few seconds later the booster suffered a massive structural failure. This in turn automatically triggered the rocket's built-in range safety package.
Unfortunately, the rocket was only about 1,600 ft (~500 meters) in the air when this happened, and the burning debris rained down on the Cape Canaveral Air Force Station like mortar fire. Miraculously, no one was injured, though several parking lots and dozens of vehicles were destroyed.

Titan IV 4A-20 (NROL-7 Mercury), 12 August 1998

The Titan IV-A series of launch vehicles didn't quite achieve the illustrious send-off that its designers at Lockheed-Martin might have hoped for; the final Titan IV-A launch ended in a sudden and explosive climax that would have done any fireworks display proud. The heavy lift vehicle was carrying an expensive (and very classified) National Reconnaissance Office SIGINT satellite when things went very suddenly from nominal to bad.
The problem started with a short that reset the launch vehicle's guidance system. Without positive control, the rocket began to pitch forward. One of the SRBs tore loose and self-destructed; which finished the destruction of the main vehicle that the pitchover had started, and a moment later the other solid booster destroyed itself as well. Within seconds, the flight was over, and the NRO was down one satellite.

Source: arstechnica