In Depth: Long-Range Missiles Are Tough to Master

Why long range missiles are touch to master? A complete story is available on Discovery channel's website. I'm putting the Excerpts from discovery, quite interesting(If you like scinence and technology :P). Here it goes ..

PICTURE: U.S. Missile Made to Defend
A ground-based Interceptor missile launches from the Ronald Reagan Test Site in the Marshall Islands during a test in December, 2005. In response to North Korea's movements toward testing a long-range missile, the United States moved its ground-based interceptor missile defense system from test mode to operational in June 2006.

North Korea's test fire this week of a long-range missile, the Taepodong 2, raises questions about the country's intention for launching a nuclear weapon into U.S. territory, roughly 7,200 kilometers (about 4,500 miles) away.

Defying international pressure is one thing, but developing a missile that can travel a quarter of the distance around the globe while carrying a nuclear payload is quite another.

So-called intercontinental ballistic missiles are riddled with countless and costly technological challenges that include everything from the fuel to the missile's structure; from the rockets to the payload.

To work well, the system must work flawlessly, and the failure of Taepodong 2 just 40 seconds after launch suggests that North Korea is not quite there — yet.

To date, the United States, Russia and China have some of the largest long-range missiles that, on record, can reach distances between 11,500 and 13,000 kilometers (between 7,145 and 8,077 miles).

North Korea, on the other hand, has yet to test a missile that can reach anything beyond 1,000 kilometers (621 miles), said David Wright, co-director and senior scientist in the Global Security program at the Union of Concerned Scientists in Cambridge, Mass.

"It's the reason that I was not at all surprised that this launch failed," said Wright, who in the 1990s focused a great deal of technical analysis on North Korea's missile technology.

A Matter of Thrust

The challenge in launching an intercontinental missile is that in order for it to go far, it needs to go fast. That's because ballistic missiles are powered early in flight and then rely on gravity to fall toward their destination. It's just like throwing a baseball: if you want to throw it long, you have to throw it hard.

To maximize the thrust and minimize the weight of fuel and fuel tanks, engineers typically design long-range missiles with two or three separate rockets. The first rocket launches the missile just beyond the upper atmosphere before breaking off and falling away.

A smaller second (and later, third) rocket automatically ignites, using less fuel in the thinner air to boost the missile to the top speed of its trajectory.

"Not only does the missile have to be robust enough to withstand the extreme temperatures experienced during blast-off and high altitude flight, it must be reliable enough to separate each stage of the booster rocket so it falls away without altering the trajectory of the missile," said Minh Luong, assistant director of International Security Studies at Yale University.

If a fuel line breaks or an O-ring cracks, the entire system can fail.

"The [Taepodong 2] didn't even get to the end of the first stage before it blew," said Owen Cote, associate director of the Security Studies program at the Massachusetts Institute of Technology.

Even the fuel itself could cause flaws. According to Luong and Wright, the North Koreans use liquid fuel instead of the more reliable but more chemically complex and technologically sophisticated solid fuel.

The liquid fuel, a mixture of kerosene and nitric acid, which helps it burn, makes fueling the rockets a very dangerous process.

"A spark caused by metal-to-metal contact could ignite the fuel and there would be a tremendous explosion," said Luong.

What's more, the fuel decomposes over time and the nitric acid can quickly corrode seals, seams, sensors, pumps, pipes, and other important components.

"Once you fill the missile, the clock starts ticking," said Wright.

Packing a Lightweight Punch

If the rocket manages to launch error-free and propel the missile into its trajectory, it still needs to achieve a high orbit and withstand the tremendous speed and intense heat that will rattle it upon reentry into the atmosphere.

And even if it can do all of that, a long-range ballistic missile is only as dangerous as the weapon it carries. It has taken the United States 30 years and billions of dollars of weapon development to build a nuclear bomb that weighs just a few hundred pounds, said Cote.

The Taepodong 2 would have been capable of lifting just 100 or 200 pounds.

"It's unlikely that the North Koreans are capable of producing nuclear weapons that weigh that little," said Cote.

In the near term, the country's long-range missile program doesn't appear to pose an immediate threat, at least to the United States.

But for those within short range, such as Japan, it's another story.

(Excerpts drwan from: dsc.discovery.com/news)