This year, several aspirants to the edge of space will each consummate years of preparation and sacrifice to compete against the past (and each other), to shatter several high-altitude records and set one for longest free-fall. In the process, one of those high-minded individuals may also become the fastest human alive — fast, as in supersonic. Here are some facts behind the hype…
CHASING HISTORY: When Joe Kittinger jumped into the history books in 1960, he did it from almost 103,000 feet and reached a speed of 714 mph in free-fall. As he explained to me in a recent correspondence, he did *not* do it to set a record, but to gather badly needed data for the forthcoming Space Age and to research ‘high altitude escapes.’ Call it the convergence of available technology; call it a sign of decadent prosperity; call it contagious — there are now at least five different teams in various places around the world with a need for speed and altitude … lots of it.
GETTING THERE IS HALF THE FUN
BALLOONS: Short of riding in a resurrected X-15, the only way someone can claw their way up through the upper fringes of the atmosphere is in a balloon. How high can balloons go? Well, it depends on how you get there. We’ve launched balloons into outer space, actually. Echo 1A (commonly known as Echo 1) was a 100-foot diameter balloon that first orbited the earth in 1960 at an altitude of about 1000 miles, but a rocket put it there. For the same reason that a tennis ball held underwater will pop to the surface and go no higher, no balloon will ever leave the atmosphere without help.
MathSpeak: Buoyant force basically equals gravitational acceleration times the volume of the lifting gas, multiplied by the difference between the densities of ambient air and that gas. Density is mass per unit volume so, in the buoyancy equation, the volume “cancels” and you’re left with something much like Newton’s F=ma. Then, you have to subtract your payload and the resultant figure tells how high you’ll go. There are a few popular methods and they all have limitations…
- A LOT OF HOT AIR — It can be approximately 275 degrees Fahrenheit inside a nylon hot air balloon and that temperature reduces the density of the air contained there-in by about a third. Unfortunately, that ain’t near enough to get you to 102,800 feet. The altitude record using a hot-air balloon is just under 65,000 feet.
- HELIUM — When you get above 160,000 feet, the apparent molecular weight of air approaches that of helium! You get to the point where you need HUGE multi-million cubic foot helium balloons just to lift a small payload.
- HYDROGEN — If you’re thinking of hydrogen, don’t. It leaks out through polyethylene (the lightest) balloons, it only buys you a very few thousand more feet … and then there’s that whole Hindenberg thing.
THE RECORD AND THE RISKS: So far, the “highest ever” balloon reached its “float altitude” at about 171,000 feet. (It was NASA’s, and unmanned.) That’s one third of the way to low-earth orbit! The highest manned balloon flight was piloted by Nicholas Piantanida and reached a bit over 123,500 feet in 1966, but that attempt was never ‘officially’ recognized as a ‘record.’ On a subsequent flight, Piantanida suffered a pressure leak at 57,000ft. He died after spending several months in a coma. Two people who hope to beat the 1966 ‘record’ are shooting for about 130,000 feet (about 25 miles up.)
AND AFTER THAT, IT’S ALL ‘DOWN-HILL’
ALONE WITH MACH 1: At 25 miles up the sky above is midnight blue, the distance to the horizon is 440 miles and one would easily see the curvature of the earth. Stepping out of a gondola at that height should put you at Mach 1 in 30 seconds after traveling about three miles, straight down.
JOE AND MACH 1: Kittinger — himself — hit 714 mph and some have questioned whether that speed was sufficient to break the sound barrier at altitude. The speed of sound depends on air temperature only, not density. As we ascend, the speed of sound drops steadily because the temperature drops. Mach 1 starts out at about 761 mph at sea level and drops to near 660 mph in the coldest layers of the atmosphere — those altitudes between where passenger jets fly and where the Concorde used to (ahem). Ascending from there, the temperature rises and so does the speed of sound, which peaks near 740 mph somewhere around 160,000 feet (about the edge of today’s balloon-only technology.) Kittinger fell from 102,800 feet through air as cold as negative 110 degrees Fahrenheit.
Translation: Someone may go faster, but Joe Kittinger broke the sound barrier (with his body) in 1960.
THE UNKNOWNS: Whether those who follow will hear a sonic boom through their flight suits remains to be … heard. (Joe didn’t.) Also unknown is whether or not they will accelerate much past Mach 1 because of “high-mach drag rise”. Why: Effective drag area of an object moving through air near and beyond Mach 1 rises appreciably due to shock wave attachment to outer surfaces, effectively increasing cross-sectional area.
All that’s fine and nice, but I’m still stuck on one thing: once nobody’s minding the store, how do they get those balloons back!
The folks who are attempting jumps are all backing the effort with their own time and money. If you’d like to follow up on their progress, visit:
http://www.legrandsaut.com/
http://208.56.77.49/story/story.htm
