Author Topic: Space Elevator Project Shoots for the Moon  (Read 30076 times)

Offline StephenB

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Space Elevator Project Shoots for the Moon
« on: 08/27/2012 07:08 pm »
Haven't seen this posted yet: Space Elevator Project Shoots for the Moon.

Offline A_M_Swallow

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Re: Space Elevator Project Shoots for the Moon
« Reply #1 on: 08/28/2012 05:20 am »
The ground attachment system may work on asteroids with big rocks.



A firm with no money will find trying to build a lunar space elevator within 8 years difficult.

Offline mto

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Re: Space Elevator Project Shoots for the Moon
« Reply #2 on: 08/28/2012 06:04 pm »
So how high would the lunar version be? How high is a geostationary (if that's the right term) orbit for the moon?

Offline grakenverb

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Re: Space Elevator Project Shoots for the Moon
« Reply #3 on: 08/28/2012 06:31 pm »
So how high would the lunar version be? How high is a geostationary (if that's the right term) orbit for the moon?

http://www.universetoday.com/10049/space-elevator-build-it-on-the-moon-first/

Offline Robotbeat

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Re: Space Elevator Project Shoots for the Moon
« Reply #4 on: 08/28/2012 06:42 pm »
So how high would the lunar version be? How high is a geostationary (if that's the right term) orbit for the moon?
Well, if the Moon were all by herself (rotating at the usual once per month), then it'd be ~90000km or so. But the Moon is orbiting the Earth, and close enough to the Earth such that the Hill Sphere radius of the Moon is less than 90000km. So, instead, the lunar elevator would go to Earth-Moon Lagrange 2, which is roughly a Hill Sphere radius from the Moon, or about ~60000km. So the answer is about 60000km (plus whatever is needed for the counterweight).
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Offline Celebrimbor

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Re: Space Elevator Project Shoots for the Moon
« Reply #5 on: 08/28/2012 06:52 pm »
Did anything come of Pearson's $75,000 NIAC study?
« Last Edit: 08/28/2012 07:07 pm by Celebrimbor »

Offline Celebrimbor

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Re: Space Elevator Project Shoots for the Moon
« Reply #6 on: 08/28/2012 07:43 pm »
Ah: http://www.lpi.usra.edu/meetings/leag2011/pdf/2043.pdf

The only clue to the expected cost is that it would be Discovery class.

That's about twice the UKSA budget ;D

Offline A_M_Swallow

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Re: Space Elevator Project Shoots for the Moon
« Reply #7 on: 08/28/2012 10:00 pm »
The aim is to put the counter weight 263,980 km above the lunar surface.
L1 is 56,000 km above the lunar surface.

Offline mto

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Re: Space Elevator Project Shoots for the Moon
« Reply #8 on: 08/28/2012 10:21 pm »
Thanks to all for your answers and links.

Offline Comga

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Re: Space Elevator Project Shoots for the Moon
« Reply #9 on: 08/28/2012 10:42 pm »
The aim is to put the counter weight 263,980 km above the lunar surface.
L1 is 56,000 km above the lunar surface.

263,980 km?
I was going to ask if this counterweight was going to ride in a boat, but it couldn't be, because your sense of humor is dry.  ;)
What kind of wastrels would dump a perfectly good booster in the ocean after just one use?

Offline A_M_Swallow

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Re: Space Elevator Project Shoots for the Moon
« Reply #10 on: 08/29/2012 05:49 pm »
The aim is to put the counter weight 263,980 km above the lunar surface.
L1 is 56,000 km above the lunar surface.

263,980 km?
I was going to ask if this counterweight was going to ride in a boat, but it couldn't be, because your sense of humor is dry.  ;)

Distance between the Earth and Moon is 384,405 km - 6,378 km - 1,738 km = 376,289 km
http://en.wikipedia.org/wiki/Moon

So on average there is a gap of 376,289 - 263,980 = 113,000 km between the Earth and counter weight.

p.s. So the counter weight will be a dry rock.  If you want a siren I sure that we can transmit a recording of a woman singing.  ;)  :o
« Last Edit: 08/29/2012 06:01 pm by A_M_Swallow »

Offline Hop_David

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Re: Space Elevator Project Shoots for the Moon
« Reply #11 on: 08/29/2012 07:04 pm »
So how high would the lunar version be? How high is a geostationary (if that's the right term) orbit for the moon?
Well, if the Moon were all by herself (rotating at the usual once per month), then it'd be ~90000km or so. But the Moon is orbiting the Earth, and close enough to the Earth such that the Hill Sphere radius of the Moon is less than 90000km. So, instead, the lunar elevator would go to Earth-Moon Lagrange 2, which is roughly a Hill Sphere radius from the Moon, or about ~60000km. So the answer is about 60000km (plus whatever is needed for the counterweight).

A counterweight in the neighborhood of EML1 would provide very few newtons per kilogram. So a weight at 60,000 km above the moon would need to be huge. Pearson's chart on the upper right of page 7 shows a counterweight massing between 100 and 1000 times that of the ribbon.

I believe that's why Liftport is suggesting such a long tether. A tether extending far enough earthward has more newtons per kilogram at the tetherfoot. If it extends far enough earthward, a counterweight may not even be needed.

Deploying it would be tricky, in my opinion. The EML1 part of the tether needs to be held in place while the ends are heading earthward and moonward. A small nudge from EML1 can send a mass far from EML1. Once the tether's anchored on the moon and the tether foot is well earthward, the tether is gravity gradient stabilized. But until the tether ends reach their destination, it's a tricky balancing act:



And what speeds are the tether ends traveling as they move from EML1? Falling from EML1, the moon harpoon would impact the lunar surface at near escape, around 2.4 km/s. I'm not sure how fast the earthward end of this whip would be traveling when it's fully uncoiled.

There have been a number of tether attempts, some more successful than others. Giving these a quick scan, looks like the longest have been in the neighborhood of 20 kilometers. The Liftport proposal is orders of magnitude longer.

A lunar beanstalk is much more plausible than an earth anchored Clarke tower. Regardless, the Liftport proposal is a long shot.

Offline A_M_Swallow

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Re: Space Elevator Project Shoots for the Moon
« Reply #12 on: 08/29/2012 09:52 pm »
{snip}

Deploying it would be tricky, in my opinion. The EML1 part of the tether needs to be held in place while the ends are heading earthward and moonward. A small nudge from EML1 can send a mass far from EML1. Once the tether's anchored on the moon and the tether foot is well earthward, the tether is gravity gradient stabilized. But until the tether ends reach their destination, it's a tricky balancing act:
{snip}

Surprisingly that is the easy bit.  They use gravity and inertia to make the tether self stabilizing.  (They are using different methods during operation and construction of the space elevator.)

During construction the tether is a satellite whose centre of gravity (or mass or what ever it is called) is at EML-1.  At the start of the deployment the counter weight is placed at EML-1.   Liftport then feed out cable from the counter weight, this causes the counter weight to get further from the Moon and the foot to get nearer to the Moon.  Conservation of momentum then takes care of the ratios.

Offline Hop_David

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Re: Space Elevator Project Shoots for the Moon
« Reply #13 on: 08/29/2012 11:04 pm »
{snip}

Deploying it would be tricky, in my opinion. The EML1 part of the tether needs to be held in place while the ends are heading earthward and moonward. A small nudge from EML1 can send a mass far from EML1. Once the tether's anchored on the moon and the tether foot is well earthward, the tether is gravity gradient stabilized. But until the tether ends reach their destination, it's a tricky balancing act:
{snip}

Surprisingly that is the easy bit.  They use gravity and inertia to make the tether self stabilizing.

Gravity and inertia in a rotating frame are accelerations parallel to the line between earth and moon. and it is along this line a mass is most unstable.

If earthward acceleration exceeds moonward acceleration at any time during the deployment, the whole thing is thrown out of EML1 into a chaotic orbit that will carry it far from where it's supposed to be. The same is true if moonward acceleration exceeds earthward acceleration.

During construction the tether is a satellite whose centre of gravity (or mass or what ever it is called) is at EML-1.  At the start of the deployment the counter weight is placed at EML-1.   Liftport then feed out cable from the counter weight, this causes the counter weight to get further from the Moon and the foot to get nearer to the Moon.  Conservation of momentum then takes care of the ratios.

Tether length earthside of EML1 is about 4 times that of the tether length moonside of EML1, presumably 4 times as massive. So if you sent the moonward roll off at 1 km/s, conservation of momentum would see the earthward roll sent off at .25 km/s.

If velocity remained constant, which end would reach it's destination first? At 1/4 the length and 4 times the velocity, the moon harpoon would impact the moon when the earthside length is only 1/16 uncoiled.

But velocity wouldn't remain constant. In that neighborhood, acceleration gradient falls more steeply as you go moonward.

So this method sounds like a way to drop a big pile of tether near Mösting Crater.
« Last Edit: 08/29/2012 11:05 pm by Hop_David »

Offline QuantumG

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Re: Space Elevator Project Shoots for the Moon
« Reply #14 on: 08/29/2012 11:19 pm »
What's the smallest lunar "elevator" that could be built?

Could it bootstrap?

This LADDER concept looks interesting, is it fleshed out anywhere or is that it?

Human spaceflight is basically just LARPing now.

Offline Robotbeat

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Re: Space Elevator Project Shoots for the Moon
« Reply #15 on: 08/29/2012 11:48 pm »
What's the smallest lunar "elevator" that could be built?

Could it bootstrap?

This LADDER concept looks interesting, is it fleshed out anywhere or is that it?


Minimum length is 600000km, other dimensions are up to you! ;)

(Needs to have enough surface for the climber to grab on to.)
Chris  Whoever loves correction loves knowledge, but he who hates reproof is stupid.

To the maximum extent practicable, the Federal Government shall plan missions to accommodate the space transportation services capabilities of United States commercial providers. US law http://goo.gl/YZYNt0

Offline QuantumG

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Re: Space Elevator Project Shoots for the Moon
« Reply #16 on: 08/30/2012 12:04 am »
Minimum length is 600000km, other dimensions are up to you! ;)

(Needs to have enough surface for the climber to grab on to.)

hmmm..

Quote
The LADDER mission would erect a 264,000 km space elevator from the
Lunar surface, past the L1 Lagrange point, to a counterweight deep in cislunar space.

I guess it's the mythical counterweight that allows them to claim a shorter distance.
Human spaceflight is basically just LARPing now.

Offline Robotbeat

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Re: Space Elevator Project Shoots for the Moon
« Reply #17 on: 08/30/2012 12:06 am »
Minimum length is 600000km, other dimensions are up to you! ;)

(Needs to have enough surface for the climber to grab on to.)

hmmm..

Quote
The LADDER mission would erect a 264,000 km space elevator from the
Lunar surface, past the L1 Lagrange point, to a counterweight deep in cislunar space.

I guess it's the mythical counterweight that allows them to claim a shorter distance.

Actually, no, I added one too many zeros. The minimum distance is 60000km, not 600,000km.
Chris  Whoever loves correction loves knowledge, but he who hates reproof is stupid.

To the maximum extent practicable, the Federal Government shall plan missions to accommodate the space transportation services capabilities of United States commercial providers. US law http://goo.gl/YZYNt0

Offline Comga

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Re: Space Elevator Project Shoots for the Moon
« Reply #18 on: 08/30/2012 03:58 am »
The aim is to put the counter weight 263,980 km above the lunar surface.
L1 is 56,000 km above the lunar surface.

263,980 km?
I was going to ask if this counterweight was going to ride in a boat, but it couldn't be, because your sense of humor is dry.  ;)

Distance between the Earth and Moon is 384,405 km - 6,378 km - 1,738 km = 376,289 km
http://en.wikipedia.org/wiki/Moon

So on average there is a gap of 376,289 - 263,980 = 113,000 km between the Earth and counter weight.

p.s. So the counter weight will be a dry rock.  If you want a siren I sure that we can transmit a recording of a woman singing.  ;) :o

Oops.  Got that metric vs Imperial issue again.  250,000 miles 376,000 km.

Once upon a time I did a numerical evaluation of the minimum mass of an Earth space tower.  It was an astonishingly large number.  For some useful amount of force at the bottom, what is the mass of this 326,000 km long lunar space tower, even with some magic material like mass-produced graphene cable?

P.S  Re-transmit someone singing from a system far out in space?  Who would do such a silly thing?  (On, yeah.  JPL just did that with MSL, and were so very proud of it.)
What kind of wastrels would dump a perfectly good booster in the ocean after just one use?

Offline Hop_David

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Re: Space Elevator Project Shoots for the Moon
« Reply #19 on: 08/30/2012 06:44 am »
Actually, no, I added one too many zeros. The minimum distance is 60000km, not 600,000km.

From the moon to just past EML1 may be the minimum length.

But not the minimum mass. According to Pearson, a counterweight at 60,000 km would need to be somewhere between 100 to a 1000 times the mass of the tether.
« Last Edit: 08/30/2012 06:45 am by Hop_David »

Online Lampyridae

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Re: Space Elevator Project Shoots for the Moon
« Reply #20 on: 08/30/2012 08:14 am »
The aim is to put the counter weight 263,980 km above the lunar surface.
L1 is 56,000 km above the lunar surface.

263,980 km?
I was going to ask if this counterweight was going to ride in a boat, but it couldn't be, because your sense of humor is dry.  ;)

Distance between the Earth and Moon is 384,405 km - 6,378 km - 1,738 km = 376,289 km
http://en.wikipedia.org/wiki/Moon

So on average there is a gap of 376,289 - 263,980 = 113,000 km between the Earth and counter weight.

p.s. So the counter weight will be a dry rock.  If you want a siren I sure that we can transmit a recording of a woman singing.  ;) :o

Oops.  Got that metric vs Imperial issue again.  250,000 miles 376,000 km.

Once upon a time I did a numerical evaluation of the minimum mass of an Earth space tower.  It was an astonishingly large number.  For some useful amount of force at the bottom, what is the mass of this 326,000 km long lunar space tower, even with some magic material like mass-produced graphene cable?

P.S  Re-transmit someone singing from a system far out in space?  Who would do such a silly thing?  (On, yeah.  JPL just did that with MSL, and were so very proud of it.)

Too bad the MSL doesn't actually even have an audio codec. All it did was send back a string of (to it) ones and zeroes.  :)

As for the cable mass, it states right there in the paper: approximately 11 tonnes, of which most is presumably cable.

A simple BOTE calculation tells me that, for an *average* area of 1mm^2 and a density of 1gm/cc (for simplicity's sake), I get a cable that weighs 264 tonnes. So, given Zylon's density of 1.5gm/cc we probaly get a thin cable of about 0.0025 mm^2 or about a twentieth of a mm across.
« Last Edit: 08/30/2012 08:18 am by Lampyridae »

Offline oldAtlas_Eguy

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Re: Space Elevator Project Shoots for the Moon
« Reply #21 on: 08/31/2012 01:19 am »
The aim is to put the counter weight 263,980 km above the lunar surface.
L1 is 56,000 km above the lunar surface.

263,980 km?
I was going to ask if this counterweight was going to ride in a boat, but it couldn't be, because your sense of humor is dry.  ;)

Distance between the Earth and Moon is 384,405 km - 6,378 km - 1,738 km = 376,289 km
http://en.wikipedia.org/wiki/Moon

So on average there is a gap of 376,289 - 263,980 = 113,000 km between the Earth and counter weight.

p.s. So the counter weight will be a dry rock.  If you want a siren I sure that we can transmit a recording of a woman singing.  ;) :o

Oops.  Got that metric vs Imperial issue again.  250,000 miles 376,000 km.

Once upon a time I did a numerical evaluation of the minimum mass of an Earth space tower.  It was an astonishingly large number.  For some useful amount of force at the bottom, what is the mass of this 326,000 km long lunar space tower, even with some magic material like mass-produced graphene cable?

P.S  Re-transmit someone singing from a system far out in space?  Who would do such a silly thing?  (On, yeah.  JPL just did that with MSL, and were so very proud of it.)

Too bad the MSL doesn't actually even have an audio codec. All it did was send back a string of (to it) ones and zeroes.  :)

As for the cable mass, it states right there in the paper: approximately 11 tonnes, of which most is presumably cable.

A simple BOTE calculation tells me that, for an *average* area of 1mm^2 and a density of 1gm/cc (for simplicity's sake), I get a cable that weighs 264 tonnes. So, given Zylon's density of 1.5gm/cc we probaly get a thin cable of about 0.0025 mm^2 or about a twentieth of a mm across.

You are off by a factor of 100. A 1mm^2 cross sectional area cable that has a weight of 1.5gm/cc would weigh 1.5gm for a length of 1 meter. And for 60,000km would weigh 90mt. So a cross section of .2 mm^2 would give you less than 20mt weight for the cable.

Offline Hop_David

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Re: Space Elevator Project Shoots for the Moon
« Reply #22 on: 09/01/2012 05:18 pm »
As for the cable mass, it states right there in the paper: approximately 11 tonnes, of which most is presumably cable.

A simple BOTE calculation tells me that, for an *average* area of 1mm^2 and a density of 1gm/cc (for simplicity's sake), I get a cable that weighs 264 tonnes. So, given Zylon's density of 1.5gm/cc we probaly get a thin cable of about 0.0025 mm^2 or about a twentieth of a mm across.

You are off by a factor of 100. A 1mm^2 cross sectional area cable that has a weight of 1.5gm/cc would weigh 1.5gm for a length of 1 meter. And for 60,000km

The Liftport paper is suggesting a 264,000 km length, not 60,000 km.

would weigh 90mt.

396 tonnes given a 264,000 km length.

So a cross section of .2 mm^2 would give you less than 20mt weight for the cable.

The Liftport paper says 11 tonnes of tether. So we'd need to shrink Lampyridae's cross section by a factor of 11/396. That's .027. So the cross section should be .027 mm2. Lampyridae got an extra zero in there somehow.

sqrt(.027) = ~.167. So the tether cross section would average a sixth of a millimeter by a sixth of a millimeter.


Offline Robotbeat

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Re: Space Elevator Project Shoots for the Moon
« Reply #23 on: 09/04/2012 06:39 pm »
...
sqrt(.027) = ~.167. So the tether cross section would average a sixth of a millimeter by a sixth of a millimeter.


In other words, almost impossible to climb...
Chris  Whoever loves correction loves knowledge, but he who hates reproof is stupid.

To the maximum extent practicable, the Federal Government shall plan missions to accommodate the space transportation services capabilities of United States commercial providers. US law http://goo.gl/YZYNt0

Offline Hop_David

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Re: Space Elevator Project Shoots for the Moon
« Reply #24 on: 09/07/2012 05:14 pm »
...
sqrt(.027) = ~.167. So the tether cross section would average a sixth of a millimeter by a sixth of a millimeter.


In other words, almost impossible to climb...

The Liftport paper linked to earlier said it could bring up 10 kg sample return or set down 20 kg instrument packages.

I don't know how fast the elevator cars are, but with that sort of tether lengths, it could easily take months to ascend or descend the tether.

I don't regard elevators as a panacea, they're like sucking a thick milkshake through a very long thin straw. Throughput should be considered when looking at elevator feasability

That said, I regard a moon elevator as more plausible than an earth elevator. It's interesting enough that I've invested time and effort to follow the cites posted in this thread.

Offline Comga

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Re: Space Elevator Project Shoots for the Moon
« Reply #25 on: 09/07/2012 07:16 pm »
The Liftport paper says 11 tonnes of tether. So we'd need to shrink Lampyridae's cross section by a factor of 11/396. That's .027. So the cross section should be .027 mm2. Lampyridae got an extra zero in there somehow.

sqrt(.027) = ~.167. So the tether cross section would average a sixth of a millimeter by a sixth of a millimeter.

So for Zylon with a strength of 5.8 GPa, an .027 mm2 cable has a limit of 157 N.

So if the factor of safety is set down at 2, a single crawler, payload, power supply, motor, etc. of under 50 kg can be hung on the elevator at any time.  And that's assuming that there is zero force on the cable base when the elevator is just above the surface.

This speaks to the throughput issue.
Did I get those calculations correct?
What kind of wastrels would dump a perfectly good booster in the ocean after just one use?

Offline Hop_David

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Re: Space Elevator Project Shoots for the Moon
« Reply #26 on: 09/07/2012 10:18 pm »
The Liftport paper says 11 tonnes of tether. So we'd need to shrink Lampyridae's cross section by a factor of 11/396. That's .027. So the cross section should be .027 mm2. Lampyridae got an extra zero in there somehow.

sqrt(.027) = ~.167. So the tether cross section would average a sixth of a millimeter by a sixth of a millimeter.

So for Zylon with a strength of 5.8 GPa, an .027 mm2 cable has a limit of 157 N.

So if the factor of safety is set down at 2, a single crawler, payload, power supply, motor, etc. of under 50 kg can be hung on the elevator at any time.  And that's assuming that there is zero force on the cable base when the elevator is just above the surface.

This speaks to the throughput issue.
Did I get those calculations correct?

Let's see, a 50 kg elevator car just above the lunar surface would give a tug of about 80 newtons. This 80 newtons would be felt throughout, including at EML1. At EML1, the tether is feeling the 80 newtons of the elevator car as well as the weight of all the tether between EML1 and the moon's surface. As well as the weight of all the tether between EML1 and earth's surface.

Offline A_M_Swallow

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Re: Space Elevator Project Shoots for the Moon
« Reply #27 on: 09/08/2012 06:25 pm »

Let's see, a 50 kg elevator car just above the lunar surface would give a tug of about 80 newtons. This 80 newtons would be felt throughout, including at EML1. At EML1, the tether is feeling the 80 newtons of the elevator car as well as the weight of all the tether between EML1 and the moon's surface. As well as the weight of all the tether between EML1 and earth's surface.

If the elevator car is moving then its engine and brakes will also be supplying a force on the cable.

Offline Comga

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Re: Space Elevator Project Shoots for the Moon
« Reply #28 on: 09/08/2012 08:45 pm »

Let's see, a 50 kg elevator car just above the lunar surface would give a tug of about 80 newtons. This 80 newtons would be felt throughout, including at EML1. At EML1, the tether is feeling the 80 newtons of the elevator car as well as the weight of all the tether between EML1 and the moon's surface. As well as the weight of all the tether between EML1 and earth's surface.

If the elevator car is moving then its engine and brakes will also be supplying a force on the cable.

Yes, Hop David.  80 N is about half of 157 N, which is the safety factor of two.  But this is just the maximum tension that could be supported by that size Zylon cable, which would be felt at the ground anchor.

No, A_M_Swallow.  An elevator moving at constant speed imparts no additional along-cable force beyond its weight.  (There would be lateral Coriolis force, but these would be tiny with a once-per-month rotation rate.) Once the elevator climbs up a ways where its weight is decreased, it can accelerate, adding force, but staying within the limit.  It might help to push off the ground with a spring, coming or going, to not add the force of the initial acceleration or final deceleration to the cable tension.

The point remains:  The notional plan is for more than 11 tons of hardware starting at EML-1 and then capable of infrequently lofting or lowering 50 kg elevators.  This does not make practical sense.
« Last Edit: 09/08/2012 08:48 pm by Comga »
What kind of wastrels would dump a perfectly good booster in the ocean after just one use?

Offline Nathan

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Re: Space Elevator Project Shoots for the Moon
« Reply #29 on: 09/08/2012 10:11 pm »
It makes sense if it is simply a test system. If it can be utilized to occasional send payloads to the surface then that may help pay for the thing.
System needs testing before something capable of sending people is built.

My concern is how to dispose of the system once it's use has passed.

I'm also not convinced by the surface anchor in the liftport video. I think those drills will need to be much longer.
Given finite cash, if we want to go to Mars then we should go to Mars.

Offline Hop_David

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Re: Space Elevator Project Shoots for the Moon
« Reply #30 on: 09/08/2012 11:58 pm »
Yes, Hop David.  80 N is about half of 157 N, which is the safety factor of two.  But this is just the maximum tension that could be supported by that size Zylon cable, which would be felt at the ground anchor.

The calculations assumed a uniform thickness throughout the tether's length.

So the tether cross section at EML1 would also be .027 mm^2.

The EML1 portion would also feel the 80 newtons of the ground car. It would also feel the weight of the all the tether moonward of EML1. As well as the weight of all the tether earthward of EML1. It is at EML1 where it would suffer the maximum stress which would be somewhat above 80 newtons.

Offline A_M_Swallow

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Re: Space Elevator Project Shoots for the Moon
« Reply #31 on: 09/10/2012 01:03 am »
Yes, Hop David.  80 N is about half of 157 N, which is the safety factor of two.  But this is just the maximum tension that could be supported by that size Zylon cable, which would be felt at the ground anchor.

No, A_M_Swallow.  An elevator moving at constant speed imparts no additional along-cable force beyond its weight.  (There would be lateral Coriolis force, but these would be tiny with a once-per-month rotation rate.) Once the elevator climbs up a ways where its weight is decreased, it can accelerate, adding force, but staying within the limit.  It might help to push off the ground with a spring, coming or going, to not add the force of the initial acceleration or final deceleration to the cable tension.

The point remains:  The notional plan is for more than 11 tons of hardware starting at EML-1 and then capable of infrequently lofting or lowering 50 kg elevators.  This does not make practical sense.

For the slow speed at which the elevator car climbs it has to worry about stopping and restarting when in the Moon's shadow.  We can live with slow acceleration say 0.1 m/s/s.

Offline neilh

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Re: Space Elevator Project Shoots for the Moon
« Reply #32 on: 09/13/2012 12:15 am »
9 hours left, looks like LiftPort has raised almost $97,000 so far on Kickstarter, a fair bit more than their $8K goal.
« Last Edit: 09/13/2012 12:15 am by neilh »
Someone is wrong on the Internet.
http://xkcd.com/386/

Offline Hop_David

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Re: Space Elevator Project Shoots for the Moon
« Reply #33 on: 09/20/2012 01:16 am »
I did a look at elevators here. Earth elevators as well as Mars, Ceres and Vesta. Also tide-locked moons like Luna, Phobos or Deimos.

P. K. Aravind gives some nice equations on conventional elevators from stationary orbits. Using his equations I was able to give some stats on elevators, for example taper ratio with Kevlar or bucky tubes.

Tethers from L1 or L2 are messier and I still don't know how to do their taper ratios.

Offline baldusi

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Re: Space Elevator Project Shoots for the Moon
« Reply #34 on: 09/20/2012 06:17 pm »
Couldn't a 50kg elevator keep elevating new threads?

Offline A_M_Swallow

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Re: Space Elevator Project Shoots for the Moon
« Reply #35 on: 09/20/2012 07:58 pm »
Couldn't a 50kg elevator keep elevating new threads?

On Earth definitely.  It is a little harder on the Moon.

Offline Hop_David

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Re: Space Elevator Project Shoots for the Moon
« Reply #36 on: 09/21/2012 05:29 pm »
Couldn't a 50kg elevator keep elevating new threads?

On Earth definitely.  It is a little harder on the Moon.

Right.

Speed of a lunar tether would be moon's ω * r. ω is about 2 pi radians/27 days, r is distance from earth's center.

My drawing of the Liftport Lunar elevator:



Apogee velocities of the red ellipses match ω * r, so tether rendezvous at these apogees would take virtually no delta V.

The tether's about 3 km/s from LEO and 1 km/s from GEO.

Delta V to LEO is about 9 km/s, so it's take about 12 km/s to get Zylon to the tether. Then the elevator would need to haul the material 160,000 km to EML1, the region of maximum stress.
« Last Edit: 09/21/2012 05:31 pm by Hop_David »

Offline A_M_Swallow

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Re: Space Elevator Project Shoots for the Moon
« Reply #37 on: 09/21/2012 11:15 pm »
{snip}
The tether's about 3 km/s from LEO and 1 km/s from GEO.

Delta V to LEO is about 9 km/s, so it's take about 12 km/s to get Zylon to the tether. Then the elevator would need to haul the material 160,000 km to EML1, the region of maximum stress.

Also the delta-v at EML-1 is about 0 km/s, it is a docking.  A robotic arm with a special grip should be able to berth to the cable.  Delta-v LEO to EML-1 is 3.77 km/s.

Alternate thickening the cable above EML-1 and below EML-1.  The ratio is about 3:1 with modifications for tapering.
« Last Edit: 09/21/2012 11:29 pm by A_M_Swallow »

Offline Hop_David

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Re: Space Elevator Project Shoots for the Moon
« Reply #38 on: 09/22/2012 12:10 am »
{snip}
The tether's about 3 km/s from LEO and 1 km/s from GEO.

Delta V to LEO is about 9 km/s, so it's take about 12 km/s to get Zylon to the tether. Then the elevator would need to haul the material 160,000 km to EML1, the region of maximum stress.

Also the delta-v at EML-1 is about 0 km/s, it is a docking.

This is like saying it's 42 kilometers to Tampa. From Where?? Unless you say where you're coming from, your statement is meaningless.

A robotic arm with a special grip should be able to berth to the cable.  Delta-v LEO to EML-1 is 3.77 km/s.

True. But Baldusi was asking "Couldn't the elevator keep elevating new threads?" I was showing the elevator could, but you'd need at least 3 km/s from LEO and that would deliver the new threads to a point well below EML1.

Alternate thickening the cable above EML-1 and below EML-1.  The ratio is about 3:1 with modifications for tapering.

It was easy for me to find papers for tapers to synchronous orbit. But I still haven't been able to put together a spreadsheet for tapers to L1 or L2. Where'd you get that 3:1 taper? A cite would be helpful.

Pearson, Levin, Oldson and Wykes write "For the Moon, we can build a non-tapered lunar ribbon if the characteristic height is 275 km or more." bottom page 11 of this pdf


Offline A_M_Swallow

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Re: Space Elevator Project Shoots for the Moon
« Reply #39 on: 09/22/2012 12:37 am »
{snip}
The tether's about 3 km/s from LEO and 1 km/s from GEO.

Delta V to LEO is about 9 km/s, so it's take about 12 km/s to get Zylon to the tether. Then the elevator would need to haul the material 160,000 km to EML1, the region of maximum stress.

Also the delta-v at EML-1 is about 0 km/s, it is a docking.

This is like saying it's 42 kilometers to Tampa. From Where?? Unless you say where you're coming from, your statement is meaningless.

EML-1 to cable at EML-1.

Quote
A robotic arm with a special grip should be able to berth to the cable.  Delta-v LEO to EML-1 is 3.77 km/s.

True. But Baldusi was asking "Couldn't the elevator keep elevating new threads?" I was showing the elevator could, but you'd need at least 3 km/s from LEO and that would deliver the new threads to a point well below EML1.

You can thicken a cable by adding at the 'middle' instead of the ends.  Due to weird gravity and orbital effects the centre of mass is at EML-1.

Quote
Alternate thickening the cable above EML-1 and below EML-1.  The ratio is about 3:1 with modifications for tapering.

It was easy for me to find papers for tapers to synchronous orbit. But I still haven't been able to put together a spreadsheet for tapers to L1 or L2. Where'd you get that 3:1 taper? A cite would be helpful.

Pearson, Levin, Oldson and Wykes write "For the Moon, we can build a non-tapered lunar ribbon if the characteristic height is 275 km or more." bottom page 11 of this pdf

3:1 was not the taper it it the approx ratio of the length below EML-1 to above, see the diagram.

Offline Hop_David

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Re: Space Elevator Project Shoots for the Moon
« Reply #40 on: 09/22/2012 02:37 am »
{snip}
The tether's about 3 km/s from LEO and 1 km/s from GEO.

Delta V to LEO is about 9 km/s, so it's take about 12 km/s to get Zylon to the tether. Then the elevator would need to haul the material 160,000 km to EML1, the region of maximum stress.

Also the delta-v at EML-1 is about 0 km/s, it is a docking.

This is like saying it's 42 kilometers to Tampa. From Where?? Unless you say where you're coming from, your statement is meaningless.

EML-1 to cable at EML-1.

EML1 would be part of the elevator. This is a little like saying it's 0 kilometers from Hawaii to the earth.

Quote
A robotic arm with a special grip should be able to berth to the cable.  Delta-v LEO to EML-1 is 3.77 km/s.

True. But Baldusi was asking "Couldn't the elevator keep elevating new threads?" I was showing the elevator could, but you'd need at least 3 km/s from LEO and that would deliver the new threads to a point well below EML1.

You can thicken a cable by adding at the 'middle' instead of the ends.  Due to weird gravity and orbital effects the centre of mass is at EML-1.

The region of maximum stress is at EML1. If it needs to be thickened, EML1 is where it'd need it the most. If you added to the elevator you would start at EML1 and build earthward and moonward simultaneously.

Baldusi was asking if the elevator could deliver more threads to the elevator. The answer is yes. 3 km/s from LEO could deliver material to a point 160,000 km below EML1. Then the elevator could lift the materials 160,000 km to EML1.

Of course the same materials could be delivered directly to EML1 from LEO and it would take 3.77 km/s as you say. But the question was whether materials to add to the elevator could be lifted by the elevator.

Because of asymmetry of acceleration gradient, EML1 isn't in the middle. The strands dangling earthward from EML1 are longer. If the strand were of uniform thickness throughout, it would need to be a total of 290,000 kilometers instead of the 264,000 kilometers Liftport suggests. But I believe liftport plans include a counterweight at the end of that 264,000 kilometers.

« Last Edit: 09/22/2012 02:53 am by Hop_David »

Offline A_M_Swallow

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Re: Space Elevator Project Shoots for the Moon
« Reply #41 on: 09/22/2012 12:23 pm »
{snip}
The tether's about 3 km/s from LEO and 1 km/s from GEO.

Delta V to LEO is about 9 km/s, so it's take about 12 km/s to get Zylon to the tether. Then the elevator would need to haul the material 160,000 km to EML1, the region of maximum stress.

Also the delta-v at EML-1 is about 0 km/s, it is a docking.

This is like saying it's 42 kilometers to Tampa. From Where?? Unless you say where you're coming from, your statement is meaningless.

EML-1 to cable at EML-1.

EML1 would be part of the elevator. This is a little like saying it's 0 kilometers from Hawaii to the earth.

Repeated mistake on your part Hop_David delta-v is in km/s not km.

To dock the two items have to be at the same speed and same velocity, anything else causes a crash (or a miss).

The lunar elevator has zero relative velocity to an item next to it at only 2 places - the lunar surface and EML-1.

Quote
Quote
A robotic arm with a special grip should be able to berth to the cable.  Delta-v LEO to EML-1 is 3.77 km/s.

True. But Baldusi was asking "Couldn't the elevator keep elevating new threads?" I was showing the elevator could, but you'd need at least 3 km/s from LEO and that would deliver the new threads to a point well below EML1.

That point had better be the lunar surface, any where else and you are doing an aircraft carrier landing.  The cable would be acting as both deck and catch cable.  The cable is weak so if the speed difference between the point on the cable and a fast moving spacecraft is more than a couple of miles per hour the cable will snap.  This is an instantaneous docking between two moving items.

You can thicken a cable by adding at the 'middle' instead of the ends.  Due to weird gravity and orbital effects the centre of mass is at EML-1.

The region of maximum stress is at EML1. If it needs to be thickened, EML1 is where it'd need it the most. If you added to the elevator you would start at EML1 and build earthward and moonward simultaneously.

Baldusi was asking if the elevator could deliver more threads to the elevator. The answer is yes. 3 km/s from LEO could deliver material to a point 160,000 km below EML1. Then the elevator could lift the materials 160,000 km to EML1.

Of course the same materials could be delivered directly to EML1 from LEO and it would take 3.77 km/s as you say. But the question was whether materials to add to the elevator could be lifted by the elevator.

Because of asymmetry of acceleration gradient, EML1 isn't in the middle. The strands dangling earthward from EML1 are longer. If the strand were of uniform thickness throughout, it would need to be a total of 290,000 kilometers instead of the 264,000 kilometers Liftport suggests. But I believe liftport plans include a counterweight at the end of that 264,000 kilometers.



The spacecraft and cable laying machines will make a good addition to the counterweight.

Offline Hop_David

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Re: Space Elevator Project Shoots for the Moon
« Reply #42 on: 09/22/2012 07:19 pm »
To dock the two items have to be at the same speed and same velocity, anything else causes a crash (or a miss).

The lunar elevator has zero relative velocity to an item next to it at only 2 places - the lunar surface and EML-1.

Given an ellipse with a 300 km altitude  perigee and 160774 km altitude apogee, speed at apogee is .4280 km/s.

At an 160774 km altitude the lunar elevator is also moving .4280 km/s

At apogee, relative velocity of payload to tether is 0 km/s.

As the payload approaches the tether it can detect distance and velocity and make adjustments as it approaches. Docking has been done many times. I know you believe typical docking speeds are 7 km/hr. Do you imagine the Dragon slammed into the I.S.S. at 7 km/hr? Not so. "At the 10-Meter mark,  Mission Control verified that the relative motion between ISS and Dragon was zero."

At an altitude of 160774 km, there is an .013 meter/sec^2 earthward acceleration. If we wait 10 seconds after matching velocities, mass falls .65 meters and has a downward velocity of 4.6 km/hour.

Is it possible to hover in a .00132 g gravity field? I don't think that'd be a huge problem.

At that altitude a 50 kg elevator car would weigh about 1/7 of a pound.

The spacecraft and cable laying machines will make a good addition to the counterweight.

If the cable could receive a 7 tonne payload, it be possible to start laying at the rendezous point and work 160,000 towards EML1. But recall we're talking about 50 kg elevator cars. It would be shorter lengths.

11000 kg for 264,000 km comes to about 24 km/kg. A 50 kg strand would be 1200 kilometers.

So we'd be laying strands a one thousand two hundred kilometers per payload starting from the 160774 km altitude. After 20 payloads, we'd have an additional tonne well below EML1. Stress at EML1 would quickly exceed the breaking point.

No, the 1st 1200 kilometer strand hauled by elevator car would need to be taken to EML1 and then attached. From there additional lengths would simultaneously work their way moonward and earthward.

Hauling lengths 160,000 km to EML1 could be horribly time consuming. It will be interesting to see what sort of speeds Liftport can accomplish with their elevator cars.

As I've mentioned several times, throughput is a major problem with the proposed elevator.

Rendezvous with the tether, not so much. I think you're exaggerating this obstacle.

« Last Edit: 09/22/2012 07:36 pm by Hop_David »

Offline genius

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Re: Space Elevator Project Shoots for the Moon
« Reply #43 on: 04/03/2013 06:26 pm »
I've been working on a project that will hopefully be used to form a space elevator between earth and the moon.  Projection of this elevator is the most difficult aspect of my project.  Any suggestions?

Offline MP99

Re: Space Elevator Project Shoots for the Moon
« Reply #44 on: 04/03/2013 06:31 pm »
Surely, an elevator from Earth to Moon is quite impossible - Moon orbits Earth at quote the wrong rate.

cheers, Martin

Offline genius

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Re: Space Elevator Project Shoots for the Moon
« Reply #45 on: 04/03/2013 06:32 pm »
I think you misunderstand the orbit.  The elevator will adjust to the changes and fluctuations.  This was the easiest problem to solve.

Offline MP99

Re: Space Elevator Project Shoots for the Moon
« Reply #46 on: 04/03/2013 06:41 pm »
Sounds impossible to me.

Would be fascinated to hear how that works.

cheers, Martin

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