SpaceShipOne 100 km Attempt Slated for June 21

apsmith writes "Scaled Composites has just announced their first attempt at breaking 100 km, scheduled for June 21. This would make it the first commercial manned vehicle to officially enter space. This is not quite an Ansari X prize attempt since it will carry only one person without the extra mass corresponding to the 3-person prize requirement; they have to give at least 30 days' notice for that. Past flight history is available from their site; the Discovery Channel is producing a documentary on the whole project, 'Rutan's Race For Space.'" Roger_Explosion adds "If successful, the craft - named Space Ship One - will become the world's first commercial manned space vehicle. Space Ship One will temporarily leave the earth's atmosphere, and the pilot (yet to be announced) will experience about three minutes of weightlessness."

Comments

Re:Space vs. Weightlessness

[aardwolf204]

Sounds like the vomit comet. Your post interested me so I've been reading WikiPedia's article on weightlessness, Microgravity, the Vomit Comet and more. Check it out here

Weightlessness is not due to an increased distance to the earth: the acceleration due to gravity at a height of, for example, 100 km is only 3% less than at the surface of the earth.

Weightlessness means a zero g-force: acceleration is equal to gravity.

Re:Space vs. Weightlessness (clarification)

[Goldenhawk]

Since this flight won't go into orbit (or anywhere close to far enough from Earth to ignore it's gravity), the weightlessness effect is simply a result of the flight trajectory including free-fall on re-entry.

Yep, this is more or less correct, but let's clarify one point. The only significant difference between this attempt (or any similar 100km up-then-down mission) and an orbit mission is how far you fall.

You can go a thousand kilometers straight up, and fall straight back down, and never go into orbit. You never can "ignore" gravity - even out at the lunar orbit distance, at hundreds of thousands of kilometers, gravity is still a factor. Fact is, that's what keeps the moon nearby.

An orbit is, essentially, simply falling in an arc that never intersects the ground (or atmosphere). You have to get a whole lot more energy into the vehicle so that the trajectory falls past the planet's "edge" - at which point you end up "falling" forever around the earth. (And yes, for you rocket science purists, you also have to expend some additional energy to reshape the path through which you fall, usually at the highest point of your trajectory, to make the orbit more circular - that's called an "orbit injection maneuver".) So it's not a matter of HEIGHT, it's a matter of which DIRECTION you expend the energy.

As a matter of fact, if the atmosphere and terrain were not an issue, you COULD do an orbit a hundred feet off the ground. And you could enter this orbit by going straight sideways. It just requires moving a lot faster than a higher orbit. Our current launch profiles are designed to minimize the fuel (and therefore change in energy, a.k.a. "delta-V") required.

So to wrap up the thought here, weightless is BECAUSE the vehicle trajectory is a free fall (one that's not being modified by expending energy or using winged lift or drag). Doesn't matter whether it's a complete orbit or one that will hit the ground before going around one complete time.

And here's the most relevant point to SpaceShip One - to achieve true orbit (a true free fall all the way around the earth), quite a bit more delta-V is required - which requires more fuel, which requires more vehicle structure, which increases vehicle weight, which requires more fuel to lift, which requires more structure... etc. (And let's not even THINK about reentry heating yet...) So as neat as this trick is, SpaceShip One and any other X-Prize vehicles are a LONG way from a viable orbital launch vehicle.