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#76 2019-07-21 13:38:10

tahanson43206
Member
Registered: 2018-04-27
Posts: 1,615

Re: Space Towers and Skyhooks

This is a follow up to #75 for Odd numbered Cylinders of a model Pneumatic Tower

Shapeways has given the green light (printable) to the model for Even numbered Cylinders.

https://www.shapeways.com/product/ZHWPJ … =113434417

The price quoted for the black printed version is $278.00.

It will take me about a year to save up to print the pair, and see if they interface as designed.

On the other hand, if someone has (or acquires) (or has a friend who has) a 3D printer, I'd be happy to make the models as Downloadable, so they could be printed for just the cost of filament (and electricity). 

As noted previously, I omitted the platform at the top and (now) the air seal base at the bottom, because these are simple to make and add to the telescoping elements.

The descriptions of the models both mention the NewMars.com forum as the location of the project discussion.

(th)

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#77 2019-07-29 11:14:26

tahanson43206
Member
Registered: 2018-04-27
Posts: 1,615

Re: Space Towers and Skyhooks

For SpaceNut ....

A few weeks ago, (as I recall) you posted a link to a company using a specialized metal 3D printer to make components of a small rocket.

By any chance, can you find it again?  I've tried several search patterns using your ID as the author, and while I found a number of interesting citations about 3D printing related to rockets, I did not find the article I'm remembering.

Possibly the post was by another member?

(th)

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#78 2019-07-29 17:50:14

SpaceNut
Administrator
From: New Hampshire
Registered: 2004-07-22
Posts: 17,333

Re: Space Towers and Skyhooks

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#79 2019-07-29 20:16:59

tahanson43206
Member
Registered: 2018-04-27
Posts: 1,615

Re: Space Towers and Skyhooks

Thanks SpaceNut! 

SpaceNut wrote:

The video at the link above is (apparently) about the British (UK) development of a SSTO engine which can cool incoming air using extremely close cooling fins.

https://www.youtube.com/watch?v=R5mhUm6NzqE

The video at the link above is about a company which uses a very large, multi-armed 3D printer to fabricate rocket components using metal.

These Engineers Want to 3D Print an Entire Rocket in 60 Days

The company name appears to be "Relativity" (Deduction from label on door of lab)

Web site: https://www.relativityspace.com/

SearchTerm:3dprintrocket
SearchTerm:3dPrintMetal
SearchTerm:3dRocket

(th)

Last edited by tahanson43206 (2019-07-29 20:41:30)

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#80 2019-09-13 08:54:28

tahanson43206
Member
Registered: 2018-04-27
Posts: 1,615

Re: Space Towers and Skyhooks

Space Elevators are a popular and perennial topic here in NewMars forum.

Here is another installation in the long running series:
https://techcrunch.com/2019/09/12/scien … -the-moon/

The tone of the article is a bit on the skeptical side, which makes sense (to me at least) considering the intended audience (Yahoo News Feed readers).

However, the content appears to have substance, and I hope others here will explore a bit further.

(th)

Last edited by tahanson43206 (2019-09-13 08:55:55)

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#81 2019-09-17 12:02:07

elderflower
Member
Registered: 2016-06-19
Posts: 1,149

Re: Space Towers and Skyhooks

Did they allow for the moon's libration, I wonder? It would shift their anchorage point around by many miles. I would expect the other end to act like a whip,

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#82 2019-09-17 12:44:10

tahanson43206
Member
Registered: 2018-04-27
Posts: 1,615

Re: Space Towers and Skyhooks

For elderflower re #81 ...

Thank you for your follow up to this reporter's summary of an iteration of an old idea!

It had not occurred to me to wonder where the Earth pointing end of the cable would ride, beyond the assurances that the terminal would be above Earth orbit traffic.

The Spaceline would be more like a skyhook than a tower. A thin, strong piece of material (think the width of a pencil lead) that extends about 225,000 miles from the surface of the Moon to a safe distance above the planet, where it won’t interfere with satellites or encounter our pesky atmosphere.

To start with I asked Mr. Google for the length of the cable in kilometers: 362102 (and change)

Then I asked for information about the variation in distance between the Earth and the Moon:

Eclipses and the Moon's Orbit - NASA

https://eclipse.gsfc.nasa.gov › SEhelp › moonorbit
Jan 12, 2012 - Thus, the Moon's center-to-center distance from Earth varies with mean values of 363,396 km at perigee to 405,504 km at apogee. The lunar ...

So right off the bat, I can see the estimated length of the tether is too great by a significant amount.

I believe (by inspection) that the answer to the question you posed is ... NO!

The distances given above are for Center of Earth to Center of Moon, so the actual cable length would need to be shortened to ride well above GEO at Perigee.

The good news appears to be that if the math works for 225,000 miles, then it should certainly work for whatever a practical length would be.

However, that said, I have long chafed at the limited vision of space elevator folks who can (apparently) only imagine a machine crawling up the cable at some ridiculously slow pace, as demonstrated by space elevator climber competitions, which have been going on for some years now.

To me a much faster plan is to design a belt system which rotates at some pace sufficient to move pods from Earth to Moon (and back) in a day or less.

The cable needs to be twice as long (of course) but the motion of the cable allows for constant inspection, and for (relatively) simple repair when needed.

(th)

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#83 2019-09-17 16:58:00

SpaceNut
Administrator
From: New Hampshire
Registered: 2004-07-22
Posts: 17,333

Re: Space Towers and Skyhooks

The moon orbits the Earth once every 27.322 days. It also takes approximately 27 days for the moon to rotate once on its axis. Which means the tether line does not face earth for more that 14 days out of its orbit around earth.
th?id=OIP.YK3Kzc1oU6RPotTF9VMRcQAAAA&w=160&h=159&rs=1&qlt=80&pid=3.1
The tip pointing towards earth will trail the moons rotation as well making it shorter and longer as it spins around the earth. One thing to do would to do a rail with the end of the tether rolling around the moon as it spins to keep it always the same legnth and facing towards the earth. The rocket would hoover near the end before attaching to it and would auto climb the length as the elevator climbers do.

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