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Re: Propellant fluid dynamics at zero-g



Hi All:

One clarification about liquid at zero-g, according to the article.

The researchers claim that the surface tension and "wetting" properties of a
liquid change in microgravity. Thus, the fluid behaves in counterintuitive ways.
If you spun up a propellant chamber, intuition would say that the fluid would
behave as one mass uniformly pressed against the sidewall, in radial symmetry.
However, this is governed not only by centrifugal force (the substitute for
gravity here), but by surface tension of the liquid. If the surface tension became
different or even dynamic (as the article claims is possible), then the liquid
might not be held by surface tension as one continuous mass, all pressing against
the sidewall. Without normal 'adhesion' (by whatever force) to the sidewall, the
centrifugal force could cease to be present for some of the fluid. Thus, zero-g.

steve rector - nu7b - AMSAT #31750
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mailto:stefano@amug.org
home page:
http://www.fastq.com/~stefano/

stephen rector wrote:

> I ran across an article today in New Scientist from 27-May-2000 which may be of
> interest to the folks doing the post-mortem on the 400-N motor burn events.
> Titled "Slosh, rattle and roll," it described how the "slosh" of liquids at
> zero-g is poorly understood, leading to large spacecraft maneuver errors as
> recently as two years ago when the JPL Near Earth Asteroid Rendevous satellite
> badly missed a target in a course correction burn. The motor apparently was
> starved of oxidizer at some point during the maneuver, due to "slosh;" the burn
> thus terminating prematurely and with an unpredicted tumbling motion which
> caused LOS for 27 hours. They minimized the effect of slosh in later burns by
> making the burn durations small. "Slosh" can cause oxidizer/fuel starvation, or
> excess (boom), at the site of combustion. If the propellant is a large fraction
> of the spacecraft weight, it can cause unpredicted dynamics after the burn due
> to the momentum of the liquid bouncing around.
>
> This doesn't at first glance explain the 24 hour delay between the burn and the
> AO-40 LOS. However, the subject of the article may merit some attention - I
> havent heard it mentioned previously. And I definitely don't want to
> second-guess or start a long thread of speculation.
>
> This particular New Scientist article isn't available online, but the article
> gives a URL for one of the more recent attempts at modeling what happens at
> zero-g:
>
> http://www.math.rug.nl/~veldman/cfd-gallery.html
>
> steve rector - nu7b - AMSAT #31750

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