Space Elevator

"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

"Tim Ward" wrote in message ...
"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



Whoops, I forgot the weight of the cable and winches! 100,000 lbs.
So figure t/o weight at ~750,000lbs (including glider/orbiter weight.)
No sweat for t/o but now getting to FL450 is going to be tough. We
may need some JATO bottles to get to FL450 with the -200 tow plane.
The gross on the -400 is 875,000lbs, may have to take that old KLM
bird sitting out in the desert instead.

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.

Yeah, figure an hour climb with all the drag. I think we're back in
business with the 747-200F though. The NASA 747-100 is an old
American Airlines bird with P&W JT9D-7F engines IIRC (about 50,000 lbs
thrust ea. engine and it pulls the drag of the space shuttle orbiter
O.K.) vs. 67,000 ea. engine for our 747-200 freighter with dash 7Q
engines.) So we're good to go again adding another 20,000lbs for the
new normal 1 hr clmb total and return plus reserves. If you don't
count the weight of the lifting body/orbiter we're back to a t/o
weight of 570,000lbs. That's a rocket ship in 747 land. We just need
to figure out the drag of your Kevlar/Carbon Fiber tow lanyard. Maybe
you can weave it like a kite with horizontal stablizers flaps so that
it too produces lift as you pay it out? Naw dumb idea, too draggy,
forget that part.

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?

As Han Solo freighter Captain said to Ben Obiwan Kenobi: "She's fast
enough for you old man."

Empty, we flew the -249 model to FL430 one day, kept it at MCT power
and had to pull it back to keep it from busting through the MMO limit
of .92 Mach. I saw .94 on the Capt's Mach at one point. The mach
tuck was tremendous over .88. The a/p mach cruise trim motor took off
like a horse. Think about that for a minute. An airplane that big
that will cruise at .92 mach. It's now the fastest transport in the
world. That's why I laughed when the (now sacked) Boeing CEO Condit
introduced the Sonic Cruiser. What a dull machine. It wasn't really
any faster than a stock 747 (abeit empty at MCT.) No you want a 747
for this. C5's can't go as fast or as high and can't approach the
load. The AN-124 has more power but again is slow and draggy.


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.

Don't discount this idea. Rutan picked up a lot of his crew from guys
who mailed in hair-brained ideas. John Ronz (sp?) corrected Burt on
his selection of laminar airfoils via mail and became a fixture at
Scaled. If you pointed something like this out at Nasa as a junior
engineer they'd probably laugh in your face and stick you on designing
space toilets for daring to upstage the gov turds who are entrenched
there. In the wake of SS1 the NASA Administrator O'Keef or something,
is completely reorganizing the agency to foster the kind of ingenuity
that SS1 has. Watched it on the NASA channel a couple of days ago.
They are reeling from the SS1 success. But moving desks around is not
going to make Nasa like Scaled IMHO.


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

It's more than cool Tim. It's the way to open a commercial spaceport
with private ships bound for the New World. I think you're on to
something here. We should ask Dave Hyde or somebody (does he do aero
equations?) to get his buddies to model the drag on a 20km tether. If
the data is good, I know an engineer at scaled that will look at it.

Cheers,

pacplyer

pacplyer wrote:

Whoops, I forgot the weight of the cable and winches! 100,000 lbs.
So figure t/o weight at ~750,000lbs (including glider/orbiter weight.)
No sweat for t/o but now getting to FL450 is going to be tough. We
may need some JATO bottles to get to FL450 with the -200 tow plane.
The gross on the -400 is 875,000lbs, may have to take that old KLM
bird sitting out in the desert instead.

Cheers,

pacplyer

I think somebody may have overlooked the effect of that 'snap the
whip' manouver on the tow plane too.

I'd almost expect the sudden increase in drag to stall the 747...

Richard

Richard Lamb wrote

I think somebody may have overlooked the effect of that 'snap the
whip' manouver on the tow plane too.

I'd almost expect the sudden increase in drag to stall the 747...

Richard

The airplane is op specs limited to +2.5 g's and -1.0g. Not worried
about stalling a 747. There's so much mass the tow rope would break
before any instant degradation would show up on the airspeed
indicator. Airspeed trends take A LONG LONG time to develop on this
bird. It's not like anything you've every flown before. I use the
analogy of surfing on a mountain of metal to describe a visual
approach on the 74 because the previous vector it was on before you
made the change is what it will be on for a number of seconds. By the
time you've pulled off the thrusters because you're too fast, the huge
inertia will keep it accelerating. You must use speed brakes or drop
the gear to arrest the buildup and start a deceleration trend.
(anticipate desired changes big time!) But if you're deep into flaps
already and the wheels are already down; it's a go around if you can't
get below speed for final flaps! Speed brakes can't be used down
here. You need to have this airplane stable at the Outer Marker or
you can get hopelessly out of phase with the airspeed trends in a
hurry. If you think you're headed for a stall, going to full power,
Scottie, will, after a number of seconds delay, start pushing the
mountain faster again. The power to weight of this thing at mid
weights below gross is just incredible. But the shear mass of the
mountain will always delay a desired acceleration direction reversal.

You cruise at Mach .86, typically ~550kts IIRC, stall might be at
about 180kts clean at heavy weights. But you would want a cruise
climb of say mach .82 to mach .84 to conserve fuel and keep a good
buffet boundary margin at higher altitude. What we always did was
stay at max climb power for a while at the target altitude to crawl up
to .86. But in this case, I'd think you'd want to try to get as close
to .92 before release in a turn. You can pull G/A power in this thing
rated anyway, for five minutes. Then you'd have to notch down to MCT.
Very do-able. If there's too much drag on the line, then maybe put
the thing on top like the Space Shuttle?

Anyway I always marvelled at the fact an old 747-100 could carry the
Space Shuttle around on it's back. Maybe that's the real way to go.

pac

In article ,
(pacplyer) wrote:

Richard Lamb wrote

I think somebody may have overlooked the effect of that 'snap the
whip' manouver on the tow plane too.

I'd almost expect the sudden increase in drag to stall the 747...

Richard

The airplane is op specs limited to +2.5 g's and -1.0g. Not worried
about stalling a 747. There's so much mass the tow rope would break
before any instant degradation would show up on the airspeed
indicator. Airspeed trends take A LONG LONG time to develop on this
bird. It's not like anything you've every flown before. I use the
analogy of surfing on a mountain of metal to describe a visual
approach on the 74 because the previous vector it was on before you
made the change is what it will be on for a number of seconds. By the
time you've pulled off the thrusters because you're too fast, the huge
inertia will keep it accelerating.

Read a physics text and then say that again...

You must use speed brakes or drop
the gear to arrest the buildup and start a deceleration trend.
(anticipate desired changes big time!) But if you're deep into flaps
already and the wheels are already down; it's a go around if you can't
get below speed for final flaps! Speed brakes can't be used down
here. You need to have this airplane stable at the Outer Marker or
you can get hopelessly out of phase with the airspeed trends in a
hurry. If you think you're headed for a stall, going to full power,
Scottie, will, after a number of seconds delay, start pushing the
mountain faster again. The power to weight of this thing at mid
weights below gross is just incredible. But the shear mass of the
mountain will always delay a desired acceleration direction reversal.

You cruise at Mach .86, typically ~550kts IIRC, stall might be at
about 180kts clean at heavy weights. But you would want a cruise
climb of say mach .82 to mach .84 to conserve fuel and keep a good
buffet boundary margin at higher altitude. What we always did was
stay at max climb power for a while at the target altitude to crawl up
to .86. But in this case, I'd think you'd want to try to get as close
to .92 before release in a turn. You can pull G/A power in this thing
rated anyway, for five minutes. Then you'd have to notch down to MCT.
Very do-able. If there's too much drag on the line, then maybe put
the thing on top like the Space Shuttle?

Anyway I always marvelled at the fact an old 747-100 could carry the
Space Shuttle around on it's back. Maybe that's the real way to go.

pac

--
Alan Baker
Vancouver, British Columbia
"If you raise the ceiling 4 feet, move the fireplace from that wall
to that wall, you'll still only get the full stereophonic effect
if you sit in the bottom of that cupboard."

The airplane is op specs limited to +2.5 g's and -1.0g. Not worried
about stalling a 747. There's so much mass the tow rope would break
before any instant degradation would show up on the airspeed
indicator. Airspeed trends take A LONG LONG time to develop on this
bird. It's not like anything you've every flown before. I use the
analogy of surfing on a mountain of metal to describe a visual
approach on the 74 because the previous vector it was on before you
made the change [control input] is what it will be on for a number of seconds. By the
time you've pulled off the thrusters because you're too fast, the huge
inertia will keep it accelerating.


Alan Baker wrote

Read a physics text and then say that again...



Inertia: a property of matter whereby it remains at rest or continues
in uniform motion unless acted upon by some outside force.

The uniform motion in my example was acceleration. In this bird it
takes longer for the opposing force: drag to arrest the motion. Due
to it's large Kinetic Energy. Can you be more specific? What part do
you disagree with?

pacplyer

In article ,
(pacplyer) wrote:

The airplane is op specs limited to +2.5 g's and -1.0g. Not worried
about stalling a 747. There's so much mass the tow rope would break
before any instant degradation would show up on the airspeed
indicator. Airspeed trends take A LONG LONG time to develop on this
bird. It's not like anything you've every flown before. I use the
analogy of surfing on a mountain of metal to describe a visual
approach on the 74 because the previous vector it was on before you
made the change [control input] is what it will be on for a number of
seconds. By the
time you've pulled off the thrusters because you're too fast, the huge
inertia will keep it accelerating.


Alan Baker wrote

Read a physics text and then say that again...



Inertia: a property of matter whereby it remains at rest or continues
in uniform motion unless acted upon by some outside force.

The uniform motion in my example was acceleration. In this bird it

Acceleration is not uniform motion.

takes longer for the opposing force: drag to arrest the motion. Due
to it's large Kinetic Energy. Can you be more specific? What part do
you disagree with?

That an object will keep accelerating in the absence of an external
force on the object. Inertia will keep it moving at a constant velocity,
but it won't keep it accelerating.

--
Alan Baker
Vancouver, British Columbia
"If you raise the ceiling 4 feet, move the fireplace from that wall
to that wall, you'll still only get the full stereophonic effect
if you sit in the bottom of that cupboard."

"pacplyer" wrote in message
om...

Inertia: a property of matter whereby it remains at rest or
continues
in uniform motion unless acted upon by some outside force.

The uniform motion in my example was acceleration.

Disclaimer: It's 5:30AM. I'm an engineer, not a physicist. BUT...

Acceleration **by definition** is **not** uniform motion! ;-)

I think I understand what you were saying, but...?

I was addressing the 'crack the whip' idea that someone thought
might could be used to toss the tow-ee into orbit.

First, the tow line 'can't' break for this maneuver, or the whole
idea 'breaks down' with it. But we'll come back to that after the
commercial.

Next, remember that we want to be as high as practically possible.
VERY high density altitude?

Stall speed at extreme altitude would not the benign 180 knots,
but something appreciably higher (can you help me out with the
high altitude 747 data - actual stall speed at FL 450?).

I believe the OP was suggesting something on the order of 20 kilometers
(!) of cable? (That part I don't even want to think about!)

We are cruising fat and happy at FL 450, pulling a bunch of miles of
cable with a real slick 'kite' on the end.

The kite supplies enough drag to keep the cable tensioned. (?)
(and carries it's half of the cable weigh too!)

That drag reduces the 747's speed by some amount, causing the 747 to
have to fly at a higher angle of attack (AoA) already.

Then the kite starts the pull up maneuver, (which by the way is going
to increase the amount of cable load that _it_ is carrying).

The pitch up increases drag on the kite due to the zoom climb.

THAT will be (eventually - cable stretch?) will be applied to the 747.

And the 747, although massive, WILL decelerate due to the increased
cable load (and probably cable drag too, since the cable is no longer
in trail).

As the angular difference between the two aircraft increases so the
cable load on the 747 increase.

The kite's speed has increased during this maneuver. Sure enough,

But it is PULLING AGAINST the 747, and sure as God made little green
apples, that load will also decelerate the big momma.

So we get to the disconnect point.

ALL the energy transferred to the kite comes from the 747.
All of it.
All of that energy is removed (just as quickly?) from the 747.

And at some critical point, big momma finds herself below critical
flight speed and above critical AoA, and things could get a little
- critical?

Now in reality, all of that could probably be dealt with. Some of
those perimeters would define the limits of this kind of operation.

From a PAWKI standpoint, it's probably cable tensile strength.

But if that held, I'd suspect this event is going to feel a lot like
catching a Three Wire - at FL 450.

Richard

Standard disclaimer:

Take all this with a grain of salt.
If I really knew what I was talking about,
I'd be working for Burt...

Ta, Yaw'll

"Richard Lamb" wrote in message
...

I think I understand what you were saying, but...?

I was addressing the 'crack the whip' idea that someone thought
might could be used to toss the tow-ee into orbit.

No, just get the spacecraft part of the way out of the atmosphere


First, the tow line 'can't' break for this maneuver, or the whole
idea 'breaks down' with it. But we'll come back to that after the
commercial.

Next, remember that we want to be as high as practically possible.
VERY high density altitude?

Yep.

Stall speed at extreme altitude would not the benign 180 knots,
but something appreciably higher (can you help me out with the
high altitude 747 data - actual stall speed at FL 450?).

I actually want to fly the 747 pretty fast. If its speed at 45000 feet is
fast enough so that the spacecraft's airspeed at 100000 feet is at the
spacecraft's best rate of climb speed, then the turning maneuver isn't
required.
This is a booster. It just happens to get its oxidizer at 45000 feet. The
assumption is that there is enough excess thrust on the 747 to overcome the
drag on the towline and whatever is attached to it. If that means extra
engines, that's okay with me.


I believe the OP was suggesting something on the order of 20 kilometers
(!) of cable? (That part I don't even want to think about!)

Ain't imagination great? ;-)

We are cruising fat and happy at FL 450, pulling a bunch of miles of
cable with a real slick 'kite' on the end.

The kite supplies enough drag to keep the cable tensioned. (?)
(and carries it's half of the cable weigh too!)

The kite carries the _entire_ weight of the cable. If it doesn't, the cable
is sagging below the towplane, and you have too much line out. Might as
well shorten it and reduce drag, because it isn't helping the kite get
higher.


That drag reduces the 747's speed by some amount, causing the 747 to
have to fly at a higher angle of attack (AoA) already.

I would expect it to require quite a lot of additional power. That's why I
originally suggested extra engines on the 747. I wasn't envisioning it as a
dynamic maneuver. More like impedance matching. The 747 is buzzing around
at a relatively low altitude. The spacecraft is up really high (we hope),
and so it's minimum sink speed is probably very high, because there's durn
few air molecules bumping into it. There's a constant force between the two
aircraft, but the spacecraft probably needs to be flying faster. By
turning, the 747 can fly at some reasonable speed, and the spacecraft can
fly at a higher speed.


Then the kite starts the pull up maneuver, (which by the way is going
to increase the amount of cable load that _it_ is carrying).

No. As originally posted, the kite is constantly trying to climb, pulling
out more and more cable as it does so. And of course you're coupling power
from the towplane into the kite/towline combo. That's the whole point of
the exercise.

The pitch up increases drag on the kite due to the zoom climb.

THAT will be (eventually - cable stretch?) will be applied to the 747.

Yep -- although it's not a zoom climb. There's a constant tension on the
cable.


And the 747, although massive, WILL decelerate due to the increased
cable load (and probably cable drag too, since the cable is no longer
in trail).

All the forces are coupled to the 747 through the tow line. But they're
relatively constant, because of the payout winch.

I never expected the towline to be in trail. Because of sag in the
towline, the towline would probably be nearly horizontal at the towplane,
and nearly vertical at the kite at release.

As the angular difference between the two aircraft increases so the
cable load on the 747 increase.

No, there's a constant tension. This is not difficult with a payout winch,
since the mechanism pays out cable above a certain tension, which lowers the
tension, so it slows down the payout, raising the tension... it stays
pretty constant. The line length changes.


The kite's speed has increased during this maneuver. Sure enough,

But it is PULLING AGAINST the 747, and sure as God made little green
apples, that load will also decelerate the big momma.

It's pulling against the constant tension of the payout winch

This constant tension is additional drag, and will need additional
hrust -- but that's just a higher power setting.


So we get to the disconnect point.

ALL the energy transferred to the kite comes from the 747.
All of it.
All of that energy is removed (just as quickly?) from the 747.

No. You have a 747 being slowed by cable tension. (Dammit! the cable has
to carry the aerodynamic drag as tension-- so that _is_ something I
overlooked. I figured on cable weight and the tow force, but the drag on the
cable adds another load.)
The kite's energy is energy of position, which it's already got. When the
cable is released, or breaks, the 747 is going to accelerate, not slow. An
instant additional 100,000 lbs of thrust. (or reduction in drag) It'll
still be a kick in the butt, but it will be speeding the 747 up, not slowing
it down.

And at some critical point, big momma finds herself below critical
flight speed and above critical AoA, and things could get a little
- critical?
Now in reality, all of that could probably be dealt with. Some of
those perimeters would define the limits of this kind of operation.

From a PAWKI standpoint, it's probably cable tensile strength.

Probably. This basically puts a limit on how long the towline can be.


But if that held, I'd suspect this event is going to feel a lot like
catching a Three Wire - at FL 450.

I think it would be more like a cat shot -- though I haven't experienced
either one.
On a commanded release, you could gradually decrease the tension on the
payout winch over a number of seconds prior to cutting loose, and you might
be able to throttle down at a similar rate, but if the line breaks, you're
gonna speed up.

Tim Ward



Richard

Standard disclaimer:

Take all this with a grain of salt.
If I really knew what I was talking about,
I'd be working for Burt...

Ta, Yaw'll