Space Elevator

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).

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

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.

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

I missed this post of yours Tim, since I was in the middle of a "High
Anxiety" spiral/flat spin flashback. O.K. I'll come back to work for
you guys if you promise me: no banks over 30 degrees up there in the
tow/tug plane and no ‘walking the dog' type stunts with the cable.
(now I see why Rutan built his own high-G' White Knight "toss"
airplane. He was able to release at up to 90 degrees bank if he
wanted to.) But we're going for Low Earth Orbit here, so getting to
the ‘barber pole' (VMO/MMO; airspeed limit pointer) is probably
important. I figured on a tow plane release weight of 550,000 lbs in
a 30 degree bank, which is 50,000 too heavy to prevent upset (damn.)
Also we only get five minutes of GA thrust to get up to MMO (Mach Max
Operating) after leveling off at FL450 or we may start cooking some
engines. "If I give you any more Captain, she going to blow!"


"Tim Ward" wrote the following are excerpts
from his longer post earlier in the thread

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.

You may be right about the need for bigger engines (or more of them;
hanging engines will mean re-certifing the airplane; and that's going
to run the cost up by tens of millions.) I don't think a -400's going
to work because; the tailplane is probably smaller; this was a trick
used by later designs to increase range. They pump gas back to the
smaller horz stab to get a more aft CG (equals better range.) It's
closer to upset than a -200 airframe AFAIK.

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.


This methodology sounds very promising. I'm a little worried about
the centrifugal recoil of the cable after release, but maybe the
payout winch will absorb some of it? That lanyard's gotta sling
across down somewhe "Break left! Cable at Two O'clock!" Don't
need a string tangled up in the Slats or gear on approach either. ;-)

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.


Pretty clever. I like it.

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.

Not sure it's the same, but a 74 jock in training changes thrust by
nearly 100,000 lbs on empty go-arounds from idle and I'm here to tell
you: it's a frickin earthquake in the air. You commonly bust your
level off altitude as a student, even after you've slammed the thrust
levers to idle. There's just too much power to weight. Those Big
Fans wagg on the pylons like a dog's tail. It scared the **** out of
me riding in the supernumerary area (the hump) while letting the other
student do his bounces in SMF on "MLO" one of our two PAX birds.
Without the weight of 531 other bodies, belly freight and large fuel
load, a go-around is a violent maneuver. Looking down out the window
from the upper deck at the inboard engine: one second you're looking
into the intake, the next you can only see the outer engine cowling,
the next your looking into the engine inlet….. I was just waiting for
a loud SNAP! of the pylon, since I thought: "NO Way would they design
it to do THAT!

So I think the airplane can handle a 100,000lb change in
acceleration/deceleration if you can time release to coincide with
idle pwr, speed brakes and pull up. Actually the aircraft pitch up
from the down moment at the tail attatch point would help in
preventing overspeed stall. Remember at 30 degree bank, I've only got
nine knots to play with.

Think I'll call in sick on that day. Better call Bob Hoover to take
that flight for me! If he's too old than call one of those U2 guys.

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


Any way you slice it, it's going to be an interesting ride for both
vehicles. But as Chuck Yeager once said after drinking whiskey the
night before and falling off a horse while drinking and driving and
busting his ribbs and showing up for the mission the next morning and
lighting the candle: "I don't advise it mind you, but it *can* be
done."

pac "no wonder these guys are all on the bottle" plyer

On Mon, 28 Jun 2004 20:23:11 -0700, Tim Ward wrote:


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.

pacflyer gave a 1g speed range for the 747 at 45,000 ft and 580,000 lb of
208 kt to 251 kt. I'm assuming those numbers are in KCAS. If so, that
works out to 444 KTAS to 524 KTAS under standard day conditions.

At 100,000 ft, those same true airspeed values work out to 56 KCAS to 68
KCAS. The equivalent airspeed, which is what the wing sees, is a bit
lower at 52 KEAS to 61 KEAS. That means the orbiter needs to have a very,
very low wing loading, which doesn't seem compatible with a re-entry. And
it has to support the weight of the tether too. I'm not sure this idea
will work, unless we can get a much faster tow aircraft.

--
Kevin Horton RV-8 (finishing kit)
Ottawa, Canada
http://go.phpwebhosting.com/~khorton/rv8/
e-mail: khorton02(_at_)rogers(_dot_)com

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.

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.

Sure, you hope for a smooth intentional release. "Can't break?"
Anything can happen in flight test. :-) I believe designing for the
line to break before high momentary loads are transferred through the
aft pressure bulkhead area is an important engineering goal: You don't
want the keel-beam of the aircraft to be pulled apart or
stringers/longerons to stretch and allow the pressure bell to blow
like it did at JAL. They lost all four hydro systems and crashed.
There is no manual reversion system (cables) in the whale. All four
hydro systems run to the elevators in that area.


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

Same kind of idea: High *Pressure Altitude*. Out of 17,000 (in the
cont.U.S.) everyone switches over to Standard 29.92 so the term
Density altitude is not used (since the pressure part of the equation
is constant.) ISA+/- (non-standard) temperature becomes important for
climb/cruise performance and mach number. Our actual, true altitude
above MSL varies from day to day at the same flight level.


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?).

Just cause you asked, I spent an hour digging through boxes and
finally found my "buffet boundry" charts. Initial Low and High Speed
Buffet (standard temp) is dependant on aircraft weight and G
load/bank. But you're right, at FL450 you are up in "coffin corner"
and on the straight and level chart (1G) at 400,000lbs the LSB (low
speed buffet) is like I remembered at 178kts. HSB (high speed buffet)
is VMO/MMO (.92 mach)

Now let's take our theoretical weights (subject to tweaking.)
Empty Weight: ~380,000lbs
Skinny Fuel: ~70,000lbs (30k up, 10 dwn, 10 aprch, 20k res)
Winches and 20km tether: ~100,000lbs
Drag ‘weight' ~30,000lbs (a complete WAG till somebody gives me a
#)
Total 747 T/O WT ~580,000lbs

Orbit One plus fuel and three plastic pax: 200,000 lbs


[note: the space vehicle with swept glider wings really weighs nothing
since Tim Ward promised us that it will lift itself after t/o. ;-)
So we're at the modest t/o weight of 580,000 (lot's of margin here
since the 747 gross is 820,000.)

So we take off with Orbit one in tow and arrive an hour later, fat
dumb and happy at FL450 again. (which must be done in smooth air at
GA thrust since we have no upset margin) The 1G chart yields a Low
Speed Buffet onset of 208kts and a high speed mach buffet of 251. In
other words: we stall outside that range. No sweat.

But you hotdog rocket jocks aren't going to be happy in straight and
level at 1G! You're going to want old "Hand Solo" Cargo Dog here to
do some hair brained "deathwhip" maneuver at a 45 degree bank and risk
my pink little ass in a flat spin if the ****ing cable breaks or if it
pulls the Jesus rivets out of the goddam tail (in which case the cabin
blows taking out all elevator control on the way out! What a ****
poor deal! You rocket jocks get all the glory and I crash and burn.
*******s!

So just for you *******s here's the 45 degree bank chart at FL450 and
1.41G's: XXX to XXX…… **** what does that mean? I'm going to have
little X's in my eyes? I'm going to fall out of the sky and do a
supersonic recovery like China Airlines did at SFO? So we can't do a
45 degree bank over 400,000lbs (that's empty) or else we do the
****ing Hoot Gibson High Dive…Gulp!

Damn we can only do a 30 degree bank at this weight and live; let's go
back to that chart and not embarrass ourselves in front of CNN:
FL450, 500,000lbs max (damn,) 1.15G, 30 degrees bank equals 229kts
low speed stall, and 238kts high speed mach stall. That's only a
nine knot range! I can't do that! I can only hold a tolerance of
about plus or minus one inch on the gauge! You crazy "Jet-eyes" are
trying to get me killed! I quit!

pacplyer – over and out!

pacplyer wrote:


Damn we can only do a 30 degree bank at this weight and live; let's go
back to that chart and not embarrass ourselves in front of CNN:
FL450, 500,000lbs max (damn,) 1.15G, 30 degrees bank equals 229kts
low speed stall, and 238kts high speed mach stall. That's only a
nine knot range! I can't do that! I can only hold a tolerance of
about plus or minus one inch on the gauge! You crazy "Jet-eyes" are
trying to get me killed! I quit!

pacplyer – over and out!

Thanks for the info, Pacman.

And for the correction - Pressure altitude - not density.

Aw heck, the U-2 guys did it tighter than that for hours on end.
Stall at 90 knots (indicated?) and mach buffet sets in at 95 knots???

(Reality really sucks, don't it.)

Richard

Richard Lamb wrote in message ...

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

Naw, using unobtainium cable takes care of that. The real PAWKI issue
is conservation of energy.

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

At least you have some room to recover from the spin....

On 29 Jun 2004 12:44:56 -0700, (Corrie) wrote:

Richard Lamb wrote in message ...

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

Naw, using unobtainium cable takes care of that. The real PAWKI issue
is conservation of energy.

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

At least you have some room to recover from the spin....

The debris field, however, will be quite immense.
--
dillon

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

"pacplyer" wrote in message
om...
"Tim Ward" wrote in message
...
"pacplyer" wrote in message
om...
snippage
yet more snippage

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.

I'd settle for a stable low-drag shape. But I think we're stuck with round.

According to http://www.neropes.com/techdata/v12.htm
16mm Vectran rope has a tensile strength of 49000 lbs and weighs 13.6
lbs/100 ft
Assuming tensile strength and weight per unit length scales with cross
section, a 200,000 lb tensile strength would be about 24mm and weigh 54
lbs/100 feet

So, for 100,000 lbs of 200,000 lb tensile strength tether, we can get
(100,000/54.4) x 100 ft length :
183000 ft = 55 km? Yow! That's probably more than we can reasonably use.
Still, at least it means it's not unobtainium, and a 10 to 20 km tapered
length might even have some safety factor.

even more snippage

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.

Well, it wouldn't be a stock 747, anyway. The vertical fin is going to be
in the way. A conventional tow is just off the tail of the airplane, but
this scheme needs to be able to pull from the CG of both aircraft so they
stay controllable.


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.

Well, I'm gratified by your enthusiasm, but it's just an idea to noodle
around. I've seen way too many posts with the Final Ultimate Solution to
Some Problem, that have pretty obvious faults. I won't be terribly
surprised if someone points out some reason why this won't work.
Embarrassed, maybe, but not surprised.

One poster pointed out that the G's get really high as the speed
differential goes up, but I think he thought I intended this scheme to get a
substantial fraction of orbital velocity. I don't, but it is something I
hadn't considered. Still, with a 20 km towline and low speed ratios, I
think it's manageable, though not negligible.

Temperature of the towrope is another potential problem. Vectran keeps it's
strength with temperature better than Spectra -- but it's still not what
you'd call a high-temperature material.

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.

Apparently Al Bowers and Jim Murray of Dryden Flight Research have done some
modelling of shorter tethers. The tether they flew was 1000 feet of Vectran
with some nylon webbing in the middle to damp oscillations.
You could read about it (and see some really cool pictures) he
http://www.nasatech.com/Briefs/July98/DRC9833.html

Their analysis assumed the tow line was a straight line, which would be
nowhere near true for
a long line. They found some significant limits in position to stability.
The simulation was a little conservative, but apparently the limits were
there in flight test as well.

OTOH, neither of the aircraft had the towline attached near the CG.
In my proposed scheme, the payout winch is supposed to damp oscillations,
but eventually you come to the end of the line. There, I would expect the
oscillations to have a very long period.

So, as is usually the case, I dunno.

Tim Ward

On Sun, 27 Jun 2004 12:16:08 -0700, "Tim Ward"
wrote:

I'd settle for a stable low-drag shape. But I think we're stuck with round.

According to http://www.neropes.com/techdata/v12.htm
16mm Vectran rope has a tensile strength of 49000 lbs and weighs 13.6
lbs/100 ft
Assuming tensile strength and weight per unit length scales with cross
section, a 200,000 lb tensile strength would be about 24mm and weigh 54
lbs/100 feet

This looks very promising. You meant the diameter to be 32 mm,
I expect. Their table gives an AVERAGE tensile strength at break.
They warn to derate 2 SDs for a minimum break strength.
Then the boring engineering realities creep in.
Derate a little for wet and contaminated line.
Derate a bit for the UV breakdown which the coating is intended to
reduce.
Then add the factors of safety. They recommend X15 for man rated uses.
For an experimental use, maybe you could use a more generous factor -
as low as X4? That would give say 14 kilometers.
One end would need to support its own weight and any load you might
apply, of course.

So, for 100,000 lbs of 200,000 lb tensile strength tether, we can get
(100,000/54.4) x 100 ft length :
183000 ft = 55 km? Yow! That's probably more than we can reasonably use.
Still, at least it means it's not unobtainium, and a 10 to 20 km tapered
length might even have some safety factor.

"Tim Ward" wrote snip

So, for 100,000 lbs of 200,000 lb tensile strength tether, we can get
(100,000/54.4) x 100 ft length :
183000 ft = 55 km? Yow! That's probably more than we can reasonably use.
Still, at least it means it's not unobtainium, and a 10 to 20 km tapered
length might even have some safety factor.

even more snippage

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.

Well, it wouldn't be a stock 747, anyway. The vertical fin is going to be
in the way. A conventional tow is just off the tail of the airplane, but
this scheme needs to be able to pull from the CG of both aircraft so they
stay controllable.



Maybe not a bad problem. The APU sits between the elevators and could
be either be removed or carry-though stucture could envelop it (better
for CG.) So we'd have a nice long tow hitch/pulley past the sweep of
the vertical stab. The tailplane (THS) is huge and has a massive rage
of trimable positions, so I would think that you could use a
conventional tow, loading the winch and line at the far aft CG limit.
Orbiter+glider wings pulling up on the tail would eliminate tailplane
downloading (which on -100's and -200's is many thousands of pounds)
requiring less power to maintain alt (equals more pwr avail to get up
to .92 mach.) A sudden break however, could result in a severe pitch
up, causing a jet upset, and tumble of tens of thousands of feet. But
this is test pilot stuff and I believe could be managed within
acceptable risk levels.

All things considered: Still a tantalizing idea. :-)

pac