Space Elevator

On Tue, 29 Jun 2004 08:02:51 -0700, Tim Ward wrote:


"Richard Lamb" wrote in message
...
Sorry dude, I wasn't refering to the release itself.
Just the problems associated with _getting_ there.

I'll refer you to Pacman's post (and conclusions) with the
gentle reminder that he _does_ know what he's talking about
as opposed to my questionable speculation).

Sure. I never really thought a stock 747 would work for an idea as extreme
as this one. I was actually thinking of a 747-sized canard design -- gets
all the control surfaces out of the way, makes hooking to the CG easier --
and so on. From Pac's information, it will probably have to have a lower
wing loading and higher aspect ratio if we want it to tow at FL450.


Also, Keith gave us some first hand info on what is actually
involved in tow ops - something I've never even tried to do.

Oddly enough, I have. I aerotow my sailplane on weekends. I used to
aerotow and ground launch hang gliders with both straight auto tow (long
line with a tensionmeter), and the payout winch. Out at El Mirage dry lake,
in the 80's, we got six thousand feet of line out one evening.
That was just to see if we could do it. The sag in the line made the
release altitude not as high as you might think. There were diminishing
returns.


PAWKI is a mean and evil term that stands for "Physics as we know it".

Please don't be too upset with the 'ain't gonna work' mentality
you find here. The guys on this group are a different kind of
dreamer. Fantasy, with a hard dose of reality blended in.

I'm not upset. But I do find it interesting that some posters have argued
against concepts I never proposed: e.g. 8:1 speed ratios between the towed
and towing aircraft.

Sorry if I was putting words into your mouth - I thought this was what you
meant by the 'whiplash' effect, and I was just trying to work it out in my
own mind.

The use of a stock 747.
Of course PAWKI limits the possible. Right now, we _know_ that it's
possible to tow a smaller aircraft with a 747-sized aircraft. It's been
done six times with a thousand foot tow line.
That gives us one data point. What _are_ the limits imposed by PAWKI? I
doubt that it's a tow line of 1001 feet. How high could you reasonably
expect to get the towed vehicle on a CG to CG aerotow? How much advantage
is that for a rocket launch? I don't know, but it's kind of interesting to
speculate.

This is a question I've been asking myself too. My understanding is that
the primary problem in getting to space isn't flying high - it's flying
fast. Hence my assumption that you were looking to get a large dV from the
'whiplash' effect.

A few of the threads on Spacship One have said that the advantages of an
air-launch were to do with keeping the weight of the landing gear down,
and optimising the rocket engine to work at high-altitude rather than sea
level. There may be other things too - for example is skin-heating
more of a problem at low-altitude, or does reduced drag mean that you get
disproportionate gains in efficiency if you start at 100kf rather than sea
level?

I don't know the answers to these questions, but it seems to me that it
would be useful to answer them. For example, perhaps getting to 60,000
feet gives 90% of the advantage of getting to 100,000 feet. What would
the cost:benefit ratio be for different altitudes?

AC


Tim Ward

You have to expect that attitude from people who actually BUILD
and FLY their own dreams.

I once heard it said that we don't really build airplanes.
We build bridges - between dreams and reality.

Well, I gotta go clean up my messy shop now.

Later.

Richard

Richard Lamb wrote

It won't help, Pac.
The cable is not the problem.

The only thing that counts is _excess_ thrust.
That's what ever is left over after the airframe is straight and level.

Then, there is the _second_ airframe! Strangely enough, at the same
speed and altitude, the second ship will have perty near the same
drag as the tow plane.

A simple way to tell (real rough estimate) how high this rig can go
might be to pull all four go levers back to half power.
Whatever altitude you finally stabalize at is gonna be right near the
service ceiling of the combined lash up.

Just for grinn and giggles, check with NASA and see how high the
747/Shuttle piggyback arrangement cruises. 22K maybe?

Damn good ideas Richard.



And that would be balls to the wall, barely hanging in the air!

When the glider _starts_ to manouver, we goin' _down_. Fast.

Other than that, Mr. Lincoln, how was the play?

Richard



Sorry Richard my friend, but the show must go on!

Bones! Quick! Get over here and treat Mr Lincoln! You space actors
aren't getting out of this Ford Theater production this easily!

Actors! They drop the ball every time someone gets shot in the VIP
box…

John Wilks Booth is a drag, no doubt about it. But a huge drag may
not kill us yet…

Anyway I called a friend of mine at NASA. He's out on a motorcycle
trip to Alaska, but his wife works there as well and is going to try
to come up with some data, including talking to one of the 747-100
pilots there.

So before you guys bury this 747 towship thing under the sounds of
"TAPPS," somebody ought to check for a 21st century pulse.

Hey Tim and Richard, here's what my friend at Scaled said:



************************************************** ***************************

Most interesting. Hmmm....I wonder just how much drag a 10 mile tow
cable will create at Mach 1. Let's see Cd=1.0, Diameter = 0.5",
dynamic pressure at Mach 1 is somewhere between 69 psf at 50,000 ft
and 16 at 100,000 ft....call it average at 75,000 ft where it's 51 psf
and we get:

D = 50,000 * 0.5/12 * 51 * 1.0 = 106,250 lbs!

Not scientific but certainly within an order of magnitude or so. Need
to apply a little higher order calculus to narrow the uncertainty down
a bit.

Anyway, ya might just need (4) GE-90s on that 747--eh?

Do-able ? Yeah, Maybe!

************************************************** ******************************

in message ...
pacplyer wrote:


However, before we abandon ship like the rest of the world, I think
maybe we're being too conservative on the drag figures. Tim
calculated a 24mm line which is 0.944882 Inches wide. So Richard
you need to recalculate your formula using numbers for a *one inch*
line instead.

pacplyer

up periscope!, damn the torpedoes, full speed ahead! (you guys are
going to need big hangars to put all you're new toys in!) ;-)

"pacplyer" wrote in message
m...
snippage
Hey Tim and Richard, here's what my friend at Scaled said:




************************************************** **************************
*

Most interesting. Hmmm....I wonder just how much drag a 10 mile tow
cable will create at Mach 1. Let's see Cd=1.0, Diameter = 0.5",
dynamic pressure at Mach 1 is somewhere between 69 psf at 50,000 ft
and 16 at 100,000 ft....call it average at 75,000 ft where it's 51 psf
and we get:

D = 50,000 * 0.5/12 * 51 * 1.0 = 106,250 lbs!

Not scientific but certainly within an order of magnitude or so. Need
to apply a little higher order calculus to narrow the uncertainty down
a bit.

Anyway, ya might just need (4) GE-90s on that 747--eh?

Do-able ? Yeah, Maybe!


************************************************** **************************
****

Well, he certainly sounds optimistic on the size of the tow line! I was
figuring more than twice that thick, but of course that was for a commercial
12-strand braid.
A jacketed line instead of braid would probably be a little smaller, but I
can't see half the diameter.

Now you're talking about lowering the 747 altitude, which will increase the
drag even more.

The tow line has to carry _all_ the drag force as well as its own weight, so
between the weight and the drag, it's not clear that at breaking tension (or
braking tension, with the winch) we're going to have much residual force at
the high end of the line to apply to the spacecraft to overcome its drag.

Tim Ward

"Tim Ward" wrote in message
...

"pacplyer" wrote in message
m...
snippage
Hey Tim and Richard, here's what my friend at Scaled said:





************************************************** **************************
*

Most interesting. Hmmm....I wonder just how much drag a 10 mile tow
cable will create at Mach 1. Let's see Cd=1.0, Diameter = 0.5",
dynamic pressure at Mach 1 is somewhere between 69 psf at 50,000 ft
and 16 at 100,000 ft....call it average at 75,000 ft where it's 51 psf
and we get:

D = 50,000 * 0.5/12 * 51 * 1.0 = 106,250 lbs!

Not scientific but certainly within an order of magnitude or so. Need
to apply a little higher order calculus to narrow the uncertainty down
a bit.

Anyway, ya might just need (4) GE-90s on that 747--eh?

Do-able ? Yeah, Maybe!



************************************************** **************************
****

Well, he certainly sounds optimistic on the size of the tow line! I was
figuring more than twice that thick, but of course that was for a
commercial
12-strand braid.
A jacketed line instead of braid would probably be a little smaller, but I
can't see half the diameter.

Now you're talking about lowering the 747 altitude, which will increase
the
drag even more.

The tow line has to carry _all_ the drag force as well as its own weight,
so
between the weight and the drag, it's not clear that at breaking tension
(or
braking tension, with the winch) we're going to have much residual force
at
the high end of the line to apply to the spacecraft to overcome its drag.

Tim Ward


Take a look at the pull vector of the cable at the glider/spacecraft. The
weight of the cable and its drag will create a huge sag. The pull vector is
likely to be nearly straight down.

Winch launching gliders works very well but the height achieved is due to
the lift of the glider's highly efficient wings. If the spacecraft doesn't
have the L/D of a sailplane, this may not work as well as you think.

Bill Daniels

On Mon, 12 Jul 2004 02:16:50 GMT, "Bill Daniels"
wrote:


"Tim Ward" wrote in message
...

"pacplyer" wrote in message
m...
snippage
Hey Tim and Richard, here's what my friend at Scaled said:





************************************************* ***************************
*

Most interesting. Hmmm....I wonder just how much drag a 10 mile tow
cable will create at Mach 1. Let's see Cd=1.0, Diameter = 0.5",
dynamic pressure at Mach 1 is somewhere between 69 psf at 50,000 ft
and 16 at 100,000 ft....call it average at 75,000 ft where it's 51 psf
and we get:

D = 50,000 * 0.5/12 * 51 * 1.0 = 106,250 lbs!

Not scientific but certainly within an order of magnitude or so. Need
to apply a little higher order calculus to narrow the uncertainty down
a bit.

Anyway, ya might just need (4) GE-90s on that 747--eh?

Do-able ? Yeah, Maybe!



************************************************* ***************************
****

Well, he certainly sounds optimistic on the size of the tow line! I was
figuring more than twice that thick, but of course that was for a
commercial
12-strand braid.
A jacketed line instead of braid would probably be a little smaller, but I
can't see half the diameter.

Now you're talking about lowering the 747 altitude, which will increase
the
drag even more.

The tow line has to carry _all_ the drag force as well as its own weight,
so
between the weight and the drag, it's not clear that at breaking tension
(or
braking tension, with the winch) we're going to have much residual force
at
the high end of the line to apply to the spacecraft to overcome its drag.

Tim Ward


Take a look at the pull vector of the cable at the glider/spacecraft. The
weight of the cable and its drag will create a huge sag. The pull vector is
likely to be nearly straight down.

Winch launching gliders works very well but the height achieved is due to
the lift of the glider's highly efficient wings. If the spacecraft doesn't
have the L/D of a sailplane, this may not work as well as you think.

Bill Daniels


Well, one solution might be, as someone else has already suggested, to
have a two part vehicle. Part of it would be the actual space
vehicle, the other part a sailplane type configuration to get the
needed altitude. Let the sailplane glide home on it's own.

Plenty of holes in the theory, anybody care to put plugs in the Swiss
cheese or at least tell me what they are?

--
dillon

When I was a kid, I thought the angel's name was Hark
and the horse's name was Bob.

"Dillon Pyron" wrote in message
...
On Mon, 12 Jul 2004 02:16:50 GMT, "Bill Daniels"
wrote:


"Tim Ward" wrote in message
...

"pacplyer" wrote in message
m...
snippage
Hey Tim and Richard, here's what my friend at Scaled said:






************************************************* **************************
*
*

Most interesting. Hmmm....I wonder just how much drag a 10 mile tow
cable will create at Mach 1. Let's see Cd=1.0, Diameter = 0.5",
dynamic pressure at Mach 1 is somewhere between 69 psf at 50,000 ft
and 16 at 100,000 ft....call it average at 75,000 ft where it's 51
psf
and we get:

D = 50,000 * 0.5/12 * 51 * 1.0 = 106,250 lbs!

Not scientific but certainly within an order of magnitude or so. Need
to apply a little higher order calculus to narrow the uncertainty
down
a bit.

Anyway, ya might just need (4) GE-90s on that 747--eh?

Do-able ? Yeah, Maybe!




************************************************* **************************
*
****

Well, he certainly sounds optimistic on the size of the tow line! I
was
figuring more than twice that thick, but of course that was for a
commercial
12-strand braid.
A jacketed line instead of braid would probably be a little smaller,
but I
can't see half the diameter.

Now you're talking about lowering the 747 altitude, which will increase
the
drag even more.

The tow line has to carry _all_ the drag force as well as its own
weight,
so
between the weight and the drag, it's not clear that at breaking
tension
(or
braking tension, with the winch) we're going to have much residual
force
at
the high end of the line to apply to the spacecraft to overcome its
drag.

Tim Ward


Take a look at the pull vector of the cable at the glider/spacecraft.
The
weight of the cable and its drag will create a huge sag. The pull vector
is
likely to be nearly straight down.

Winch launching gliders works very well but the height achieved is due to
the lift of the glider's highly efficient wings. If the spacecraft
doesn't
have the L/D of a sailplane, this may not work as well as you think.

Bill Daniels


Well, one solution might be, as someone else has already suggested, to
have a two part vehicle. Part of it would be the actual space
vehicle, the other part a sailplane type configuration to get the
needed altitude. Let the sailplane glide home on it's own.

One problem with the glider carrier aircraft concept is that a sailplane
configuration has a low MMO - probably no more than .5 Mach. (Research the
Perlan high altitude pressurized sailplane project.) On the other hand, a
supersonic or transonic airframe will have a much lower L/D.

Another problem is that aeroelastic flutter is proportional to true airspeed
so the Vne, expressed as IAS, will be lower at extreme altitudes unless
strong measures are taken to contain flutter. High aspect ratio
sailplane-like wings are prone to flutter.

The idea still has merit if the payoff sought is merely altitude and you can
accept low speeds. The airtow/winch launch approach could get a booster to
70 - 80 thousand feet fairly cheaply by keeping the tow aircraft lower in
the atmosphere where the engines produce more thrust - and the towing TAS
can be kept low to match the needs of the sailplane carrier aircraft at high
altitude.

One need take care that the pull on the tow line doesn't upset the towing
aircraft. If the tow line is long enough, the sag will have the pull vector
at the tug nearly horizontal.

Notwithstanding the above, you probably wouldn't encounter any problems
finding glider pilots willing to take the ride.

All-in-all, I'm inclined to think that a flyback, air-breathing first stage
ala Scaled Composites "White Knight" is the best solution. There is no
reason to think that it couldn't deliver a second stage booster to the same
altitude and airspeed as the winch launch method could. It would be
operationally simpler too.

Bill Daniels

"Bill Daniels" wrote in message
news9oIc.58807$MB3.890@attbi_s04...

One problem with the glider carrier aircraft concept is that a sailplane
configuration has a low MMO - probably no more than .5 Mach. (Research
the
Perlan high altitude pressurized sailplane project.) On the other hand, a
supersonic or transonic airframe will have a much lower L/D.

Another problem is that aeroelastic flutter is proportional to true
airspeed
so the Vne, expressed as IAS, will be lower at extreme altitudes unless
strong measures are taken to contain flutter. High aspect ratio
sailplane-like wings are prone to flutter.

Yep. The conceptual idea currently being kicked around is a "joined wing",
where an aft-swept forward wing is joined at the tip by a forward-swept aft
wing. Structurally, this allows them to torsionally stabilize each other a
bit.

The idea still has merit if the payoff sought is merely altitude and you
can
accept low speeds. The airtow/winch launch approach could get a booster
to
70 - 80 thousand feet fairly cheaply by keeping the tow aircraft lower in
the atmosphere where the engines produce more thrust - and the towing TAS
can be kept low to match the needs of the sailplane carrier aircraft at
high
altitude.

Yep, altitude before rocket ignition was the original idea.

One need take care that the pull on the tow line doesn't upset the towing
aircraft. If the tow line is long enough, the sag will have the pull
vector
at the tug nearly horizontal.

Yep, that's why the tow line is attached near the CG of the towplane.


Notwithstanding the above, you probably wouldn't encounter any problems
finding glider pilots willing to take the ride.

All-in-all, I'm inclined to think that a flyback, air-breathing first
stage
ala Scaled Composites "White Knight" is the best solution. There is no
reason to think that it couldn't deliver a second stage booster to the
same
altitude and airspeed as the winch launch method could. It would be
operationally simpler too.

Bill Daniels

Tim Ward

"Tim Ward" wrote
Well, he certainly sounds optimistic on the size of the tow line! I was
figuring more than twice that thick, but of course that was for a commercial
12-strand braid.
A jacketed line instead of braid would probably be a little smaller, but I
can't see half the diameter.

Now you're talking about lowering the 747 altitude, which will increase the
drag even more.

Yeah, I think maybe you're right. Good point Tim. My friend at
Scaled doesn't want to be down there either. Well, I used FL350 about
half for stock engine thrust considerations and half for my little
pink ass to have a nice wing margins at heavier weights. You gotta
remember that I see things from a conservative line pilot perspective,
and these guys are pushing new envelopes. Also I was trying to give
you max speed. Now that we are using not quite double the power with
GE-90's we may be able, in our hypothetical carrier towship model to
get up in a mated configuration to about 50,000 ft. according to my
pal at Scaled. Now that's outside the certified ceiling of the 747
airframe but these guys are not worried about that at all. Gulp. 8-/
Guess we'll have to raise the **** out of the cabin altitude (at
least keep a pressure differential of below 9.2 psi) At 9.4 psi diff,
there's a couple of man-hole sized overpressure relief circles on the
port side that will blow, so we gotta run in semi-auto or manual valve
mode, so we have to have a good engineer. Trust me; you don't want
this max diff to happen. Don't ask how I know. First blood runs out
of your ears; then it get real cold down there on the main deck aft of
the L-1 door. I mean reeeeeallllll cold.

So let's see where that demon lives.
Let's plan to operate at FL500 in a 30 degree bank so we can avoid
some line drag, and sling this puppy up to some partial speed before
disc and lightoff. Extrapolating up out of the top of my Buffet
Boundry table says I have to put this bird on an low-carb weight
reduction program and get it down to 400,000 lbs max in-flight weight
to sling the line. Now I think I know now why NASA uses a 747-100
airframe: Although it has smaller engines and it can't carry as much
on t/o, the structure is lighter weight; hence the BOW (basic op wt;
kinda like empty wt) is much lighter also at 323K. I figured a BOW on
the -200 airframe at 340k plus 40k in structural mods (horizontal
tailplane stabilizers and carry-through floor structure for a total
BOW "empty wt" of 380K) But it's clear that's just too much heavy
crap. So now I'll use the data for our old 747-132SF (ex Pam Am
bird.) We're going to have to pull the end of the tether from the
winch pallet sitting on the main deck through the ceiling , and just
tie the other end of the spool off around the titanium spar through a
hole in the floor near CG. We can loose some more weight by tearing
out the upper deck lav, galley, and supernumerary (hump) seats and
flooring. (Oh, the humanity!) We can ditch the APU in back (real
heavy,) the center tank, weather radar, about half the avionics, the
aux "tip" tanks, All the hot wing garbage, the jumpseats, and the
biggest weight savings of all: jettison all the paperwork! (Hey I
think I'm going to like this job after all!)

In flight weight at ‘slingshot' event is now:
BOW 323K
Winch pallet 20k
Fuel remaining 57k

Total in flight wt (sans OrbitOne) at FL500: 400K


Back to buffet speeds in a 30degree 1.15g bank: we're going to have
to hold 230kts IND/CAS plus or minus 4kts is as good a guess as any.
Forget about a 45 degree bank up here. Forget about top end speeds.
So a little flight test is in order unless Boeing has 1969 graphs on
this (which I bet they do.)


The tow line has to carry _all_ the drag force as well as its own weight, so
between the weight and the drag, it's not clear that at breaking tension (or
braking tension, with the winch) we're going to have much residual force at
the high end of the line to apply to the spacecraft to overcome its drag.

Tim Ward

So we wouldn't shed the 200 ft swing wing glider "diamond" till the
last second before we start slingshot-ing; since it's kiting almost
*ALL*? the weight of the near vertical portion of the line? Right?
And is the line drag number split between the two ships?

Line drag's a lot less at FL500. Thrust is 110K, lbs x 4 = 440K (at
sea level :-) I wonder if Kevin Horton can give me max thrust in lbs
in the high 40's for a GE C-90 engine?

This whole thing reminds me of water skiing when I was a kid, and
finding myself at incredible speeds near-even with the driver in a
turn.

pacplyer

On Mon, 12 Jul 2004 04:08:52 GMT, "Bill Daniels"
wrote:


"Dillon Pyron" wrote in message
.. .
On Mon, 12 Jul 2004 02:16:50 GMT, "Bill Daniels"
wrote:


"Tim Ward" wrote in message
...

"pacplyer" wrote in message
m...
snippage
Hey Tim and Richard, here's what my friend at Scaled said:
snippage.

One problem with the glider carrier aircraft concept is that a sailplane
configuration has a low MMO - probably no more than .5 Mach. (Research the
Perlan high altitude pressurized sailplane project.) On the other hand, a
supersonic or transonic airframe will have a much lower L/D.

Another problem is that aeroelastic flutter is proportional to true airspeed
so the Vne, expressed as IAS, will be lower at extreme altitudes unless
strong measures are taken to contain flutter. High aspect ratio
sailplane-like wings are prone to flutter.

The idea still has merit if the payoff sought is merely altitude and you can
accept low speeds. The airtow/winch launch approach could get a booster to
70 - 80 thousand feet fairly cheaply by keeping the tow aircraft lower in
the atmosphere where the engines produce more thrust - and the towing TAS
can be kept low to match the needs of the sailplane carrier aircraft at high
altitude.

One need take care that the pull on the tow line doesn't upset the towing
aircraft. If the tow line is long enough, the sag will have the pull vector
at the tug nearly horizontal.

Notwithstanding the above, you probably wouldn't encounter any problems
finding glider pilots willing to take the ride.

All-in-all, I'm inclined to think that a flyback, air-breathing first stage
ala Scaled Composites "White Knight" is the best solution. There is no
reason to think that it couldn't deliver a second stage booster to the same
altitude and airspeed as the winch launch method could. It would be
operationally simpler too.

Simple? Who said we were looking for simple? We want something
complex to stimulate our brains. It doesn't have to work, although
we'll likely all pay to see someone else try it. :-)


Bill Daniels

--
dillon

When I was a kid, I thought the angel's name was Hark
and the horse's name was Bob.

"Dillon Pyron" wrote in message
news
All-in-all, I'm inclined to think that a flyback, air-breathing first
stage
ala Scaled Composites "White Knight" is the best solution. There is no
reason to think that it couldn't deliver a second stage booster to the
same
altitude and airspeed as the winch launch method could. It would be
operationally simpler too.

Simple? Who said we were looking for simple? We want something
complex to stimulate our brains. It doesn't have to work, although
we'll likely all pay to see someone else try it. :-)

dillon

Why not visit the nearest glider operation launching gliders with a winch
and get a ride. It's not a space launch but it will feel like one.

Bill Daniels