Since we’ve had our Canada Day fireworks and our American readers are getting geared up for their big blast, a quick primer on fireworks is in order.
Gun powder, or black powder is something that when you set fire to it, produces huge amounts of hot gas and smoke, very quickly. This called going High Order. Contain that pressure in a tube and you can make the hot gas move things. A musket ball, or a flare, or an artillery round are the common examples.
The whole thing is Newton’s First Law. For every action there is an equal and opposite reaction. Expanding gas with only one way for it to go, with more force that the weight of what it is lifting, will move the thing, usually at a very high speed, in slices of time measured in millionths of a second.
In aerial fireworks, the shell is cardboard or light plastic. On the bottom of the shell is a lift charge, made of black powder. The shell snugly sits in a tube, called a pot or a mortar. There is only one direction for the gas to escape, as the bottom of the tube is buried in sand and closed off. This means the gas will push the shell itself.
The pressure of the gas moving the firework charge stops at the open end of the mortar, depending on the size of the shell, 6 to 24 inches. From that point on, the firework shell is coasting, based on where the mortar tube is pointing: A big lob shot. Up is the preferred direction.
This works for aerial fireworks shells, as you’re lifting, at the most, 10 pounds; the shell proper. For aerial shells, they top out around 1,000 feet in the air; most around 600 feet up.
If you tried that kind of lob with humans you have a problem: Accelerating live people that fast in a very short period of time would turn the people into puddles of elemental goo all over the back wall of the space craft. Humans can go fast, but we need to get to fast, slowly.
To get around that little hiring and human resources problem, you bring the things that produce big quantities of gas and smoke with your space ship, rather than lobbing the space ship out of a tube. In the case of the Space Shuttle, the speed you want to get to is 17,800 miles per hour and the altitude is 200 miles, or so. Both numbers are give-or-take a bit.
The Space Shuttle is the whole thing you see on the launch pad. The Orbiter is the actual airplane looking device. It is about the size of a DC-9 and is about as old as a DC-9, meaning 30 year old technology. There’s nothing wrong with thirty-year old technology as long as the maintenance is done. Be assured, the Shuttle maintenance is done, to orders of magnitude higher standard than any airline on Earth.
The issue is more of an essential nature. By design, the Space Shuttle uses two solid-rocket boosters; those two long rockets down the outside of the creature. The problem, as was demonstrated by the Challenger disaster, is that when solid rocket motors go wrong, there is nothing you can do to shut them down. They are fireworks. Light a fuse and get out of the way.
The solid rockets are electronically fired; there is no geek sitting in the basement with a Bic lighter, counting backwards from 10. What happens in the solid rocket motors is a long jet of flame is shot down the length of the motors, igniting the solid propellant. The fuel is a very complex piece of chemistry: It’s solid, but a little bouncy, like a scuba diving suit, as one of the components is a polymerized synthetic rubber.
All the stuff in the fuel burns relatively slowly, compared to the lift charge of an aerial firework, producing huge gobs of smoke and expanding superheated gas. The metal casings of the solid rockets keep all the ferocious pressures in, until it squirts out the nozzle in the bottom at a hellacious speed. When the force downwards of the gas is greater than the weight of the Shuttle, then the whole Shuttle moves in whatever direction the rocket is pointed. Up being the preferred direction.
The other three motors, the ones that are on the tail of the Orbiter proper, are fed by that big zeppelin-shaped tank until the Orbiter gets to earth orbit. Those are liquid fueled motors that are individually controlled, even turned a bit as need be. You can shut them down and restart them. Computers do all the heavy thinking; there is no gas pedal on the Orbiter.
The tank holds about 500,000 gallons of liquid hydrogen and liquid oxygen that are combined and lit off in the Orbiter rocket motors to produce huge quantities of expanding gas and smoke. The Orbiter itself can’t carry enough gas for launch, which is why the external tank is tossed after it is emptied. That takes about three minutes. Gas mileage is not the long suit of the Orbiter.
There is sprayed-in-place foam insulation all over the outside of the external fuel tank to keep the liquid oxygen and hydrogen super cold until it is ignited. Since metal contracts with cold and the foam is sprayed on at room temperature, some of the foam will crack and fall off. It always has, since the first launch. It is a known design problem and NASA is very good at managing known design risks.
The problem has been big lumps of foam falling off the external tank at high speeds and whacking into the Orbiter. If it is going fast enough, hospital-grade banana pudding would damage the Orbiter: The Shuttle goes real fast. A big piece of foam fell off from the shaking of launch and walloped the Columbia, damaging enough tiles on a critical place of the Orbiter to destroy the machine and incinerate the astronauts on re-entry.
What we have is a thirty-year old piece of somewhat fragile technology, bolted to a big gas tank that sheds parts of its skin, with two massive, vaguely controlled fireworks strapped to the outside. To get it off the planet, we set fire to parts of it.
Humans train for years to ride in it. I’d go. A reminder that a slim majority of the panel said I am not crazy, so there you are.
The Space Shuttle, the whole space thing, is about managed risk. Today, you get to watch how good NASA is at managing risk. Tonight, in the US, you get to watch Newton’s First Law in action. Enjoy.
RoadDave 