Space Elevator

Mike Beede wrote:

From a standpoint of aviation, the biggest concern would be finding enough
red lights so you could put three of them at each hundred foot level, and hiring
enough guys to keep changing them. I make that 9.9 million bulbs.

Of course, they could change the lighting regulations, but if it only takes twenty
years to build the elevator, they might have to put them on anyway....

Our guvunmit radar balloons, don't have lights on their tethers...
They geaux up something like 15 to 25k'...

According to the newspaper article I read, the proposed fiber is a "tape"
roughly three feet wide and a few thou thick. A flat ribbon is
aerodynamically unstable and will vibrate axially in any wind. This thing
would seem to be the ultimate Tacoma Narrows Bridge. Just my first
impression.

--
Bob (Chief Pilot, White Knuckle Airways)

I don't have to like Bush and Cheney (Or Kerry, for that matter) to love
America

"Howard Eisenhauer" wrote in message
news
On Fri, 25 Jun 2004 22:42:15 -0700, Richard Riley
wrote:

On Fri, 25 Jun 2004 20:47:03 -0500, Big John
wrote:

:Scientist Sees Space Elevator in 15 Years
:
:By CARL HARTMAN, Associated Press Writer
:
:WASHINGTON - President Bush (news - web sites) wants to return to the
:moon and put a man on Mars. But scientist Bradley C. Edwards has an
:idea that's really out of this world: an elevator that climbs 62,000
:miles into space.

OK, so you use a whole lotta solar power beamed at your cart to climb
62,000 miles straight up (without becoming a crispy critter, but
that's another topic).

Where are you going to get the mass and energy to accelerate yourself
laterally to reach orbital velocity? Aren't you just going to
decelerate the beanstalk and send it whipping to the west as the earth
rotates beneath you, winding the beanstalk along the equator like an
earth sized yo-yo?


At 24,000 mile you're at geosynchronis orbit, ready to float free. If
you want an orbit lower down you just burn a little rocket fuel (that
you brought up with you) to slow down & drop lower.

The other 38000 miles of line wants to pull away from the Earth so
acts as a counter weight keeping the whole thing pulling straight up.
If you keep going past the 24,000 mark before cutting loose you start
picking up the velocity you need to get to the Moon, as well as many
other fun spots around the system .

Any deflection caused by sending payloads up gets cancelled out by
stuff coming back down, i.e "My Parents Went to Jupiter & All They Got
Me Was This Cheap T-Shirt" x 10-6.

H.

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

Brian Whatcott wrote in message . ..
On 27 Jun 2004 09:39:26 -0700, (pacplyer) wrote:

///
No you want a 747 for this.
C5's can't go as fast or as high and can't approach the load.
///

pacplyer

Maybe: but did you ever see a 747 do a soft field takeoff?

Brian W

Mojave is a hard surfaced runway. A soft field takeoff is not part of
the equation here. 74's have landed on lakebeds before at lower
weights, however. There is an increased risk of FOD of the inboard
engines compared to the highwing C-5. Since they are five million
dollar engines, you are right, it's role is not soft field.

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."

"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

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

Todd Pattist wrote:

The last time I looked at this, the load on a space elevator
due to its own weight exceeded the load that any other known
material could carry. I suspect it will pretty damn stiff
under the required tension. I also suspect they will do an
aerodynamic analysis that's better than the one done for the
Tacoma Narrows bridge . In view of aerodynamic
considerations, I agree it does "seem" like it's a poor
selection to use a thin tape, but perhaps our "gut feelings"
are not calibrated for the properties of carbon nanotube
materials.

And I almost hate to bring it up, but the thing would be the ultimate
terrorist target. Hit it anywhere with just about anything that
flies, and billions of dollars (and whatever's on the other end...)
down the tubes.

Mark Hickey

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