Hi guys,

I was playing last night with endcaps of various shapes (now that we
have all the moments of inertia calculations built in). It led to what
I think is a really interesting result. Details and pictures here:

http://highfrontierblog.com/2014/08/12/invented-endcaps-are-better/

Cheers,
- Joe

"So lets adjust: how long can the cylinder be, with flat endcaps, to get a stability ratio of at least 1.2? Its easy to tweak the dimensions, and let High Frontier calculate the result. It turns out that, for a flat-capped cylinder of 250 m radius to be stable, it must be no longer than 285 m long. That gives us a livable area of 0.45 square km.

Why did you get different results from the Kalpana One paper? Ive gone over (your) math from that paper a number of times and it always looked solid. Are there some different parameters?

On Aug 12, 2014, at 10:48 AM, Joe Strout joe@strout.net [spacesettlers] wrote:

> Hi guys,
>
> I was playing last night with endcaps of various shapes (now that we
> have all the moments of inertia calculations built in). It led to what
> I think is a really interesting result. Details and pictures here:
>
> http://highfrontierblog.com/2014/08/12/invented-endcaps-are-better/
>
> Cheers,
> - Joe
>

So lets adjust: how long can the cylinder be, with flat endcaps, to get a stability ratio of at least 1.2? Its easy to tweak the dimensions, and let High Frontier calculate the result. It turns out that, for a flat-capped cylinder of 250 m radius to be stable, it must be no longer than 285 m long. That gives us a livable area of 0.45 square km.

Why did you get different results from the Kalpana One paper? Ive gone over (your) math from that paper a number of times and it always looked solid. Are there some different parameters?
On Aug 12, 2014, at 10:48 AM, Joe Strout
joe@...
[spacesettlers] <
spacesettlers@yahoogroups.com
> wrote:
Hi guys,
I was playing last night with endcaps of various shapes (now that we

have all the moments of inertia calculations built in). It led to what

I think is a really interesting result. Details and pictures here:
http://highfrontierblog.com/2014/08/12/invented-endcaps-are-better/
Cheers,
- Joe

On 8/15/14 11:09 AM, Al Globus alglobus@... [spacesettlers] wrote:

> "So lets adjust: how long can the cylinder be, with flat endcaps, to
> get a stability ratio of at least 1.2? Its easy to tweak the
> dimensions, and let High Frontier calculate the result. It turns out
> that, for a flat-capped cylinder of 250 m radius to be stable, it must
> be no longer than 285 m long. That gives us a livable area of 0.45
> square km.
>
> Why did you get different results from the Kalpana One paper? Ive gone
> over (your) math from that paper a number of times and it always looked
> solid. Are there some different parameters?

I believe there are two differences that both nudge the result in the
same direction. First, Kalpana One has that radiator skirt, which
improves stability; my little High Frontier experiment had no such
thing. Second, in the paper, we used the approximation of an
infinitesimally thin cylindrical shell. High Frontier uses a thick
shell, taking into account the shielding and pressure shell; and also
adds in the air mass inside. The ideal thin shell moves mass more away
from the spin axis, and thus is more stable (though of course
unattainable in real life).

So, on the one hand the High Frontier simulation is more detailed than
what we did for the paper, but on the other hand, it leaves out the
skirt. Both hands push (slightly) toward a squatter cylinder.

Eventually we will add parts like radiator skirts to High Frontier, and
then we'll be able to model Kalpana One in more detail there.

Best,
- Joe

The thin skin issue makes sense. Note, though, that the radiator belt is not included in the Kalpana One paper calculations.

Probably the safe thing to say is that given flat end caps the length must be somewhere around 300 m for rotational stability a bit more or less depending on the details of the interior mass distribution.

On Aug 15, 2014, at 10:55 AM, Joe Strout joe@... [spacesettlers] wrote: