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#1 2019-12-05 14:16:59

louis
Member
From: UK
Registered: 2008-03-24
Posts: 5,792

Artificial Gravity using 3 Starships

Interesting video setting out a proposal for producing AG on two Starships with a 3 Starship system.

https://www.youtube.com/watch?v=3CRiJTJikjk

I think the rigid truss system is a much better bet than a steel cable.

I like this proposal - not as a serious proposal for Mission One, but maybe soon thereafter. Could be tested on a trip to the Moon.


Let's Go to Mars...Google on: Fast Track to Mars blogspot.com

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#2 2019-12-05 16:06:56

tahanson43206
Member
Registered: 2018-04-27
Posts: 2,569

Re: Artificial Gravity using 3 Starships

For Louis re #1

First, thank you for posting the link to this (to me) interesting presentation.

The animation seems first rate, and the first order physics seems reasonable.

However, a comment from four days ago caught my eye, regarding instability in a rotating system such as this.

I followed the suggestion of the comment maker, and watched a video of an experiment aboard the ISS to demonstrate instability of a rotating asymmetric object.

asymmetric object’s intermediate principal axis

The publisher of the video you showed us was appropriately cautious in his reply.

My recollection (at this point vague) is that the famous "Ringworld" of Larry Niven was found to be unstable and therefore unlikely to succeed if actually built.

However, the fact remains that a ** perfectly ** symmetrical set of objects should be able to rotate in space without tumbling.

Modern electronic control systems might be able to tame the forces that would lead to instability, but I would ** really ** like to see some experiments on a small scale to discover potential pitfalls as well as potential solutions.

Because artificial gravity via rotation of habitat modules is so frequently cited as a possible solution to the problems caused by microgravity, I am hoping there will be sufficient interest in the topic world wide to generate funding for actual experiments.

(th)

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#3 2019-12-07 14:49:00

GW Johnson
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From: McGregor, Texas USA
Registered: 2011-12-04
Posts: 3,905
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Re: Artificial Gravity using 3 Starships

Y'all do realize that a variation on Spacex's refuelling concept for "Starship" is a way to get artificial gravity on "Starship"?  Docked tail-to-tail,  two such ships are a 96 m long baton.  Spun end-over-end at 4 rpm,  you get about 0.7 gee in the pressurized spaces in the noses. 

Baton spin mode is a stable spin mode,  being the highest moment of inertia.  Spinning like a rifle bullet is the lowest-inertia mode,  also stable,  but cannot produce much gee at inner-ear-limited 4 rpm.

The only problem with baton-spin mode is that "down" will be toward the nose,  not the tail as when standing on Earth (or Mars).  It means your appurtenances in the pressurized spaces,  and the unpressurized cargo bay,  need to be "double-ended".  Nasty design problem,  but not fundamentally impossible.

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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#4 2019-12-07 21:02:19

Oldfart1939
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Registered: 2016-11-26
Posts: 1,835

Re: Artificial Gravity using 3 Starships

In order to simplify the problem--consider a docking nose to nose through a girder supported tunnel arrangement. That would allow one vessel to be the "storehouse" of supplies and additional room for exercise apparatus, and the other for habitation and living activities. Weight the two spaceships so the barycenter of rotation is between the 2 and, voila! Artificial gravity is not a problem.

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#5 2019-12-07 21:43:39

SpaceNut
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From: New Hampshire
Registered: 2004-07-22
Posts: 18,565

Re: Artificial Gravity using 3 Starships

The oldfart1939 ship design would make for an issue when re-entering earths atmospher as a glide path nose up first would not be possible. Of which if these are just transit ships to mars thats going to create the issue for mars for aerobraking to slow down for the same reason of the nose temperature could ingress into the ship.

GW Johnson baton means that no course correction can be had and they would need to stop both ships spin and de-link to allow for the rear ship to turn around before it can course correct before relinking and beginning spin up once more.

Starship design makes AG problematic at best...

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#6 2019-12-08 06:30:24

RobertDyck
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From: Winnipeg, Canada
Registered: 2002-08-20
Posts: 5,929
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Re: Artificial Gravity using 3 Starships

Or this from Mars Direct...
images?q=tbn:ANd9GcSfBJvyzcR4Ov3326MXpGqIFiqc2AJPwHBSsP8h-ILS2FKYhvbj&s

The Mars Direct concept is a direct development from Gemini 11, flown September 1966. They generated 0.00015g by slowly rotating.
260px-Gemini_11_Agena.jpg

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#7 2019-12-16 13:17:37

Lake Matthew Team - Cole
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Registered: 2016-12-21
Posts: 119
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Re: Artificial Gravity using 3 Starships

GW Johnson wrote:

Y'all do realize that a variation on Spacex's refuelling concept for "Starship" is a way to get artificial gravity on "Starship"?

Conceivably, yes, and it's a concept explored wrt motivations, variations and applications at NasaSpaceFlight forum.

Some old posts: 

SingleWindowMarsWith38g.png

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#8 2019-12-16 18:12:52

SpaceNut
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From: New Hampshire
Registered: 2004-07-22
Posts: 18,565

Re: Artificial Gravity using 3 Starships

The center of spin axis is not the center of length as its the equalized mass location over the distance. The fuel tanks are not likely to have the same mass remaining in them after leaving earth orbit refueling and departure allowing for fuel slosh. The design also leave no means for course correction without decoupling, wasting more fuel to do the dance all over again to recouple only to be still off balance. A cargo ship will be much heavier in the payload than a crewed ship will be as its payload is consumed and not repurposed to conteract the shifting mass.

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#9 2019-12-16 18:44:35

tahanson43206
Member
Registered: 2018-04-27
Posts: 2,569

Re: Artificial Gravity using 3 Starships

For SpaceNut re #8

The purpose of this comment is NOT to take issue with the concerns you have raised.  Hopefully other forum members will be able to offer suggestions to improve the outlook for the proposal.

I would like to point out a tiny detail that might make a difference as the analysis proceeds.  A rotating system CAN be accelerated along the axis of rotation. This can be demonstrated with a hand held gyroscope, which can be raised and lowered without disturbing the rotation.  How this fact would lend itself to the problem of celestial navigation for a Mars-bound vehicle is not clear to me, so again, I'm hoping someone in the forum can comment further.

(th)

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#10 2019-12-16 19:13:29

SpaceNut
Administrator
From: New Hampshire
Registered: 2004-07-22
Posts: 18,565

Re: Artificial Gravity using 3 Starships

The Magnetic Gyro Wheel is sort of what I think you are describing.

WireRollerTM.jpg

242-1054-thickbox.jpg

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