Former astronaut says it is extremely important to study artificial gravity...

[Phil Hobbs]

Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net

as Fred Kaempffer and Dirk Walecka. Asymptotic methods, series summation,
and so on, I mostly learned from an EE-turned-Matho , Stefanos Venakides
(may his tribe increase ).

@&%#+%# predictive text


--
Dr Philip C D Hobbs Principal Consultant
ElectroOptical Innovations LLC / Hobbs ElectroOptics Optics,
Electro-optics, Photonics, Analog Electronics

 

[Phil Hobbs]

John Larkin <jlarkin@highlandSNIPMEtechnology.com> wrote:

On Sun, 23 Jul 2023 13:51:18 -0000 (UTC), Phil Hobbs
pcdhSpamMeSenseless@electrooptical.net> wrote:

Martin Brown <\'\'\'newspam\'\'\'@nonad.co.uk> wrote:
On 21/07/2023 15:12, Phil Hobbs wrote:

If you have the fuel tanks rotating, you need to be very very careful
about rotational stability.  A rotating system with internal dissipation
(due e.g. to fuel sloshing around) very rapidly changes its angular
velocity vector to be along the largest principal axis of the inertia
tensor.  For instance, a long skinny tank rotating about its
longitudinal axis will wind up tumbling end over end.
The math for this is really pretty--small deviations from perfect axial
rotation initially grow exponentially.  You fix that by rotating about
the stable axis, because trying to do active control is too risky.

I have the distinct feeling that at some stage in our academic careers
we encountered the same (visiting?) lecturer on slender body dynamics
and turbulence. His other big interest on the turbulent flow side was
Pade (aka Shanks) transform for turning hard won analytic but divergent
polynomial \"solutions\" into something that engineers could actually use!

I got good value out of his course but his name escapes me now.


I’ve never taken a course like that, alas. I learned most of what I know
about it from regular classical mechanics classes. Profs were folks such
as Fred Kaempffer and Dirk Walecka. Asymptotic methods, series summation,
and so on, I mostly learned from an EE-turned-Marho, Stefanos Venakides
(may his tribe increase).

I did do a fun class on orbital mechanics with Michael Ovenden, but it was
mostly planetary systems and globular star clusters. He also taught
galactic dynamics (also a fun class).

One guy you might know is Gordon Walker, who taught an instruments class.

I owe those guys a lot.

Does clestial mechanics include the time-lag caused by the finite
speed of gravity? As if the many-body problem wasn\'t bad enough
already.

Sort of. Relativistic mechanics is a classical theory, as opposed to a
quantum one. Most of the time you don’t need its full power, so you do a
zero-order nonrelativistic solution and then apply perturbation theory.

Cheers

Phil Hobbs


--
Dr Philip C D Hobbs Principal Consultant
ElectroOptical Innovations LLC / Hobbs ElectroOptics Optics,
Electro-optics, Photonics, Analog Electronics

 

[Martin Brown]

On 23/07/2023 16:54, John Larkin wrote:

On Sun, 23 Jul 2023 13:51:18 -0000 (UTC), Phil Hobbs
pcdhSpamMeSenseless@electrooptical.net> wrote:

Martin Brown <\'\'\'newspam\'\'\'@nonad.co.uk> wrote:

I have the distinct feeling that at some stage in our academic careers
we encountered the same (visiting?) lecturer on slender body dynamics
and turbulence. His other big interest on the turbulent flow side was
Pade (aka Shanks) transform for turning hard won analytic but divergent
polynomial \"solutions\" into something that engineers could actually use!

I got good value out of his course but his name escapes me now.


I’ve never taken a course like that, alas. I learned most of what I know
about it from regular classical mechanics classes. Profs were folks such
as Fred Kaempffer and Dirk Walecka. Asymptotic methods, series summation,
and so on, I mostly learned from an EE-turned-Margo, Stefanos Venakides
(may his tribe i).

I did do a fun class on orbital mechanics with Michael Ovenden, but it was
mostly planetary systems and globular star clusters. He also taught
galactic dynamics (also a fun class).

I always thought his conjecture on solar system dynamics and stability
was inspired and seemed to match how test systems evolved but AFIAK
still unproven.

Does clestial mechanics include the time-lag caused by the finite
speed of gravity? As if the many-body problem wasn\'t bad enough
already.

Celestial mechanics has to include light travel time from objects though
since where you see them is where they were at time -distance/c ago.

There is no time delay for gravity in the classical Newtonian
approximations normally used for planetary orbital dynamics (apart from
Mercury where soe relativistic corrections are needed).

If there were such a delay in Newtonian physics then it would act as a
net drag force on the planets and they would spiral in to their doom. It
was this instantaneous action at a distance that is a necessary feature
of Newtonian gravitational dynamics and one that Newton disliked.

https://www.astronomy.com/science/why-do-physicists-think-gravity-travels-at-the-speed-of-light/

It is changes in the gravitational field that propagate away at the
speed of light - the field is just there in spacetime distortions
(unless the mass distribution suddenly changes). This isn\'t a bad
introduction at a popular science level (best I can find anyway)

https://www.britannica.com/science/relativity/General-relativity

Binary pulsars and BH mergers being the most extreme test of fully
relativistic dynamics and losses by gravitational radiation. They really
do see a powerful drag force especially in the last few moments of their
existence before they merge.

The new gravitational wave detectors have pretty much nailed the speed
of gravitational waves to be the speed of light now. This helps to
pinpoint where to point optical telescopes to try and see the flash.

--
Martin Brown