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#1 2017-02-19 20:01:09

SpaceNut
Administrator
From: New Hampshire
Registered: 2004-07-22
Posts: 23,099

Artificail Gravity Cable Tether experiments

We have talked about the cable versus hard rigid structure with little to no actual hard testing being done.
That is changing slowly....as the Japanese tether experiment hits snag

An electrodynamic tether experiment being conducted by the Japan Aerospace Exploration Agency has apparently run into some problems, according to The Japan Times.

The tether, called Kounotori Integrated Tether Experiment or KITE, was attached to the outside of the Japanese Kounotori 6 cargo spacecraft, which departed from the International Space Station on Jan. 27, 2017, after six weeks attached to the orbiting lab.

KITE is composed of a 2,300-foot (700-meter) long tether made from thin wires of stainless steel and aluminium and a 44-pound (20-kilogram) end-mass.

It was supposed to be deployed soon after leaving the station, but, according to France 24, the Japanese space agency is unsure if the device actually deployed.

After leaving the outpost, Kounotori 6 was commanded to go to a safe distance of about 12 miles below and 23 miles ahead of the outpost. KITE was then supposed to deploy to its full length and spend a week extended. A current of no more than 10 milliamps was expected to run through the tether to demonstrate how it could affect the orbit of an object. The hope is this technology could be used to help remove space debris in the future.

tether_wide-7df993d119ce90551d025d339eae7818a9df96e7-s1500-c85-1280x719.jpg

Seems like it needs to be repeated....

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#2 2017-02-20 23:16:06

GW Johnson
Member
From: McGregor, Texas USA
Registered: 2011-12-04
Posts: 4,576
Website

Re: Artificail Gravity Cable Tether experiments

Well,  a deploy glitch is not a doesn't-work glitch.  They need to try again,  for sure.

I have no idea how the thing is supposed to work,  but then,  that could be said of my understanding of electromagnetics in general,  including EM approaches to particulate radiation shielding. 

GW


GW Johnson
McGregor,  Texas

"There is nothing as expensive as a dead crew,  especially one dead from a bad management decision"

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#3 2017-02-21 17:32:13

SpaceNut
Administrator
From: New Hampshire
Registered: 2004-07-22
Posts: 23,099

Re: Artificail Gravity Cable Tether experiments

They were testing power flow to the end of the tether from this

A current of no more than 10 milliamps was expected to run through the tether to demonstrate how it could affect the orbit of an object.

Or they are looking at the field effect from the conductor moving in space fields as it rotates....
But yes I agree a redux is in order.

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#4 2017-02-21 18:08:16

GW Johnson
Member
From: McGregor, Texas USA
Registered: 2011-12-04
Posts: 4,576
Website

Re: Artificail Gravity Cable Tether experiments

Why are we focused on the unproven technology of tethers,  when semi-rigid spinning bodies are well proven?

GW


GW Johnson
McGregor,  Texas

"There is nothing as expensive as a dead crew,  especially one dead from a bad management decision"

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#5 2017-02-21 18:29:41

Oldfart1939
Member
Registered: 2016-11-26
Posts: 2,221

Re: Artificail Gravity Cable Tether experiments

GW-

The tether was part of the original Mars Direct proposal by Robert Zubrin. It's light, inexpensive, and gets tangled easily. ;-)

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#6 2017-04-01 10:49:08

SpaceNut
Administrator
From: New Hampshire
Registered: 2004-07-22
Posts: 23,099

Re: Artificail Gravity Cable Tether experiments

I did a report mark on the last few of these new members which due to changes that the directors have made to the flood gates we are now going to either delete them right away or if its just a mild case of advertising just leave it for a bit....

We have just 2 admins and 2 mods to help keep the site clean...
Will need to checks this ones IP and email to see if its the same as another spammer....

I wish they had left the web block in place which kept them out and only let the real people gain access.
The web site was averaging about 100 new sign ins but most never posted even under the old system..

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#7 2017-04-01 10:51:46

SpaceNut
Administrator
From: New Hampshire
Registered: 2004-07-22
Posts: 23,099

Re: Artificail Gravity Cable Tether experiments

I am going to delet the quoted post and the original to clean up the topic once more but thanks for noticing....

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#8 2021-07-18 07:13:53

SpaceNut
Administrator
From: New Hampshire
Registered: 2004-07-22
Posts: 23,099

Re: Artificail Gravity Cable Tether experiments

bump AG

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#9 2021-07-18 08:42:56

GW Johnson
Member
From: McGregor, Texas USA
Registered: 2011-12-04
Posts: 4,576
Website

Re: Artificail Gravity Cable Tether experiments

I will hazard the guess that when these experiments with cable tether spinning are actually done,  you will find that the spin up/spin down forces have to be applied to both masses at equal acceleration levels,  lest you excite large oscillations in the tether that risk breaking something. 

I will also hazard the guess that you will find the same fatal oscillation risk ensues if you apply pulsed thrusters to change the spin plane attitude,  or if you attempt a course correction delta-vee maneuver,  even if the thrust is aligned along the spin axis.  Such a force tries to convert a spin plane into a conical shape,  leading to all sorts of instabilities and oscillations in 3-D.

In comparison,  the dynamics of spinning rigid bodies are well-understood and well-known.  Spin is stable about two of possibly 3 axes:  the axes with the min and max moments of inertia.  The intermediate one is unstable.  It works far,  far better if you have the symmetry to zero-out the cross products of inertia.  Simple as that. 

And with a rigid spinning object,  the precessions and changes for small applied forces in any direction are predictable from the theories we have already.   And if you apply a thrust aligned with the spin axis,  there is no risk of the shape going conical,  there are just the stresses from the extra applied forces.  The spin is still planar and stable.

If you can afford the extra weight of the rigid structure,  you have a far easier time making spin work.  If not,  you have to solve some horrendous design analysis problems.  THAT is your trade. 

Spin AG is "easiest" and most practical if your spacecraft design is already shaped and of a size to provide the AG you want,  without adding any other structure.  The easiest,  lightest solution is baton spin (max moment of inertia) on an object exceeding about 112 m in length,  so that you need not exceed 4 rpm (the long-term inner-ear limit).  That gets you 1 gee at the tips,  smoothly and linearly decreasing to 0-gee at the spin center. 

The classic notion of spin AG in the various literature is rifle-bullet spin about the long axis (if much longer than diameter,  this is the min moment of inertia,  otherwise it is the max).  That takes a truly enormous structure exceeding 112 m diameter in order to be stable,  and still stay at or under 4 rpm for 1 full gee.  This was the genesis of the 1930's designs for wheel-shaped space stations. 

I like baton spin better,  because you need not build anything so enormously-large as the wheel space stations,  and a lot of large spacecraft designs are already almost big enough to serve,  especially if you couple several together by docking,  then spin it up. 

GW

Last edited by GW Johnson (2021-07-18 08:46:00)


GW Johnson
McGregor,  Texas

"There is nothing as expensive as a dead crew,  especially one dead from a bad management decision"

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