"pacplyer" wrote in message
om...
snippage
Pac sez:
I like this idea. A 747-200F can carry 250,000 lbs of fuel and 250,000
of cargo at the same time. But at that weight 820,000 lbs it could
only make ~FL280. It would have to leave most of the gas behind: no
sweat there. Since it burns a rough average of 25,000 lbs an hour a
t/o fuel load could be as low as around ~50,000lbs of fuel for
twenty-nine minutes of ascent plus return and skinny reserves so, you
would have good rate of climb to the service ceiling of FL450 (45,000
ft.) The combined tow weight of OrbitOne plus fuel and Colonauts
could be easily be greater than 200,000 lbs if all your tow apparatus
could handle it. So figure a total Mojave t/o weight of ~650,000lbs.
These numbers are off the top of my head, I could look up the exact
ones if you want me to. Don't know if this would be cheaper than a
Vandenberg launch, but Rutan would control it all, and stay away from
gov turd interference. **** I like it. You should email this idea to
Scaled Composites Tim. Bet you a nickle Burt is already considering
it. Evergreen in Oregon is already using 74's for fire fighting.
This might be the next great role for that old queen of the sky.

pacplyer


I think the mission might turn out to be longer than a thirty minute climb.
It's going to take some time to pay out all that tow line -- payout winch
launches are slower than auto tows, and much slower than regular winch
launches.
OTOH, the tow plane doesn't have to _lift_ the spacecraft -- it just has to
overcome the drag.
In fact, once the spacecraft is in high tow, it should be pulling up and
back (or up and out, in the slingshot portion of the flight). If things are
going right, in high tow, the spacecraft is always lifting the weight of the
tow cable that's extended, so as the tow line gets longer, the payload that
the 747's wing is lifting gets smaller. At peak altitude, the 747's wing
should only "see" the remaining fuel as a load. If the tow cable is pulling
down, then you haven't got enough tension in the tow cable. If you can't
increase the tension, then you've got too much line out.
But I expect the drag is going to be considerably higher than a stock 747.
20 km of cable an inch or so in diameter is going to be quite a bit of drag,
even at altitude. Thus my suggestion that some more engines (and higher
fuel burn) might be in order. Or do you need to throttle back a 747 at
altitude to keep the speed in limits?

I'm sure that after the publicity of the SpaceShip1 flight, Rutan is getting
all the hare-brained ideas that he can use via email, snail mail and
telephone. As I mentioned in the first post, Kelly Aerospace is working on
a tow-to-altitude and launch scheme, so some of the idea isn't new, anyway.

I wonder about the flight dynamics of a 20 km tether. I don't think anyone
has modeled anything like that. Why would they?

But a reusable 747 "first stage" that could get the "second stage" to
100,000 feet, albeit only at a little below Mach 1 (I think the drag would
go WAY up if the tether went supersonic!) is certainly cool to think about.

Tim Ward