The space shuttle is often said to be the most advanced traveling machine ever built, but most of its rocket thrust comes from a design essentially unchanged in 800 years.

The ancient Mongols used this model. Medieval Europeans used it, too. And in a few days on the Fourth of July, you may be using it too: The solid-fuel rocket.

The Chinese invented gunpowder and soon saw its potential for warfare. They filled bamboo tubes with gunpowder and lobbed them as bombs, later attaching them to arrows to launch them farther.

Those early Chinese rockets were very simple devices; nothing more than a tube filled with propellant, with a cap on one end and fuse at the other. They had no moving parts and precious little control. Once lit, they burned furiously until their fuel was spent and they fell flaming to Earth, a simple but very effective weapon.

The Chinese used rockets against the Mongols at the Great Wall, the Mongols launched them at the Arabs in Baghdad, the Arabs used them against French crusaders, the French fired them at the English in the Hundred Years War.

The English lobbed exploding rockets at Napoleon at Waterloo, and they also used them against the Americans in the War of 1812. (When the British warship Erebus bombarded Fort McHenry during that war, the nightlong barrage of rocket-propelled bombs provided "the rockets red glare" mentioned by Francis Scott Key in The Star Spangled Banner.)

In modern times the bazooka, the antiaircraft missile, and the recoilless rifle have all been based on the simple solid-fuel rocket.

Since its invention the simple rocket has also had a peacetime use: fireworks. The same gunpowder-in-a-tube design of rockets can also be used to make fireworks, usually with a slower-burning powder mix. Often other materials, such as metal dust, are mixed in to provide sparks and bright colors.

The basic fireworks used today firecrackers, the fireworks rocket, and what we call a Roman candle -- are not unlike from the fireworks of the 13th-century Chinese. The tiny bottle rockets sold by the millions around Fourth of July are near-perfect miniature replicas of the war rockets used by the Chinese and Mongols in the Middle Ages.

Even the spectacular new commercial fireworks designs owe much to those ancient Chinese fireworks, using the same rocket design and the same basic chemicals.

Certainly the most spectacular application of the ancient Chinese rocket design is on the space shuttle. The largest solid-fuel rockets ever built are the two huge external motors (known as Solid Rocket Boosters, or SRBs). The two cylindrical SRBs, mounted on each side of the shuttle's large liquid-fuel tank, provide the bulk of the vehicles lifting power during launch. They provide over a million pounds of thrust each.

Its not much of a stretch to compare the shuttle boosters to common fireworks because, except in size and use, theyre really very similar to a fireworks rocket.

One might expect them to be very complex variants of this old technology, but in fact theyre not. Just like ancient Chinese rockets, they are in essence simple tubes filled with a propellant mixture, capped at one end with a fuse at the other (though the fuse is now electric).

They also function in the same way: Once ignited, they burn with full fury until all the fuel is expended, with no throttle or other control possible. At times they have been described as giant Roman candles, and that is a fairly accurate description.

So as you watch the dazzling displays this Fourth of July, take a moment to marvel at this simple Chinese invention, a clever little device that has served us well in war and peace for more than 800 years.