Internal Rocket Effect

OK, I gotta ask, if only to try to figure out exactly
how some here think, and hopefully I get this device
right. (I am convinced it will *not* work. You know
who you are. ;-) )

A sealed tube, containing some air, is somewhere in free
space (if one likes, somewhere between Earth and Moon,
Earth and Mars, or Earth and ... wherever). The tube is
surrounded by the usual solar panels, in order to extract
energy from Sol, converting it to electricity.

For the purpose of argument assume it is and of size
maybe 5 m in length with maybe a 50 cm inside diameter,
and initially motionless. [+] The air pressure might be 2
megaPascal, or 20 atmospheres, in the high-pressure side,
and maybe 10 milliPascal on the low-pressure side. [%]

A partition in the tube acts as a barrier, with two valves
in the middle dividing the tube into two largely sealed
halves, with the valves providing the only permeation
between. The valves are actuated by a reasonably simple
control system.

The low-pressure side contains an electrically powered
pump with a connecting tube to one of the valves; the pump
is designed to pump air from the low pressure side to the
high pressure side. The air is then quickly released back
into the low pressure side, at a rate far faster than the
pump can pump it back.

There are no harnessable electric or magnetic fields in
the device's immediate vicinity. [*]

How fast does this device accelerate?

[1] Not at all. The total momentum is always zero,
as is the angular momentum. At most, it will
jiggle and wiggle a little.

[2] The device will move extremely slowly in the
direction of the low-pressure end of the tube, as the
high pressure side gets hot, and the infrared radiation
will therefore push it just a smidge, if the solar
panels being pushed by sunlight and the solar wind
don't swamp the effect.

[3] The device will accelerate at a high rate of speed
towards the high-pressure end of the tube, as the gas
is released very quickly but the pump works slowly.
Over time, it will move faster than light if enough
energy is available.

[4] The device will accelerate at a high rate of speed
towards the low-pressure end of the tube, as the
gas creates a slight gravity gradient. This gravity
gradient is converted into momentum.

[5] The device will spin like a top and ultimately fly
apart because of the off-center valving required
by one of the valves.

[6] None of the above.

Standard physics answers [1]. A more refined physics might
answer [2], since light quanta do have momentum, although
the effect, expressable as p = E/c, is extremely small;
a 1 kW floodlight might exert a force of 33 microNewtons.

But there's at least one poster who thinks standard physics
is all wrong. (No, it's not me. I remain a skeptic,
especially given Deep Space 1, which, despite its emphasis
on novelle rocket technology, is still at its heart a
rocket -- with xenon instead of LOX and liquid hydrogen.
Once the xenon's gone, it's gone. Why didn't we use
a sealed tube instead? Because it wouldn't have worked.)

Now explain away, if you can! :-)

====

[+] A more accurate answer would have it be in an orbit
around Sol or Earth. Not that it matters.

[%] it is possible several pumps might be needed, and
maybe one valve per pump. The pumps would be activated
in sequence, with the first pump getting a slight
vacuum, the second improving on it, and the third
getting the highest. One might also contemplate
chillers, cooling the air to liquid temperature and
reducing the pressure that way.

[*] Sol's magnetic field does rotate, and I could see
a different device attempting to leverage that,
though it might have to be rather bigger than this
sealed tube. There might be an electric gradient as
well; one rather famous shuttle experiment, however,
had to be curtailed as the cable broke.

--
#191, ewill3@xxxxxxxxxxxxx
If your CPU can't stand the heat, get another fan.
** Posted from http://www.teranews.com **
.

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