SpaceX And/Or Rocketry In General

Since much has been made of elevation to 100 km ( official edge of space ) vs. orbital velocity at that height, here's a quick precis :

- gravitational potential energy change ~ m * g * h ( ignoring slight reduction of g at surface ~ 9.8 m/s²  to altitude )

- kinetic energy on orbit = 1/2 * m * v²  ( ditto with v = 7.8 km/s ) 

Mass is a common factor. For each one kilogram mass of payload :

Grav_pot = 9.8 * 100,000 = 980,000 J

K.E. = 0.5 * (7800)² = 30,420,000 J

K.E./Grav_pot ~ 31

Meaning that whatever potential energy is gifted to a payload to climb up to 100km, you need ~ another 30 times that amount to orbit the Earth at that height. This is why bouncing on a trampoline won't cut it ! :-))

Cheers, Mike.

( edit ) One can link height and orbital velocity using an independent equation. That could give a relation involving Earth's surface radius and orbital height and Newton's gravitational constant G. Then throw in either Earth's mass or average density and one can deduce how close to impossible it can be to launch to orbit via a particular chemical means. That's because one can view unused fuel retained to a certain height as part of payload mass elevated and sped up thus far. In turn that decides the required available energy density that the fuel(s) must have. That may exceed known yields from some given reaction stoichiometry. The upshot is that for some planets ( fortunately not ours ) that have certain combinations of mass and surface radius to launch from you can't actually get to orbit at all for known/best choices of reactants to operate a rocket on.

Clearly smaller and denser planets are the hardest to escape from via chemical rocket methodology. What about Jupiter, say, known to have ~ 12g at the visible radius ? Yup, that depends on where you think the solid surface would be. Mega-trebuchet anyone ?? :-))

Falcon tanks had been loaded with explosive stuff to produce some 1 million pounds of thrust. Impressive. Live coverage on NASA channel. Afterwards in the press conference they announced that a first crew will be sent to ISS with a Falcon next year. Two crew names to be announced probably next month (Adam and Eve, I guess?).

Professor Hawking knows mankind has to leave earth in a hundred years, 'cause earth will be done by then. Will require a lot more thrust. Most impressive, but definitely not enough to induce a gravitational wave, which would have been helpful to announce the event to the universe. So mankind will have to rely upon Twitter: "Hey universe, we're prepared for launch. Peaceful mission! We're all sitting here on top of explosive stuff, in pairs of two on 1 million pounds each. Live coverage on all channels!"

LOL. That's the trick indeed ! :-)

Cheers, Mike.