ISP of compressed air - Larry Niven idea

Arthur Hansen opined

(Gordon D. Pusch) wrote in message
...

DEFINITELY Unobtainium, and one of the many, many Niven physics bloopers
where he ROYALLY screwed the pooch. (It's pretty obvious why he dropped out
of astrophysics; his former Ph.D. advisor must _wince_ every time he hears
about some of Niven's screw-ups...)

If you had materials with a large enough tensile strength to hold
almost-degnerate gas, or even gas compressed to the point that its
effective I_sp significantly exceeded H2/O2, then you wouldn't
_NEED_ rockets --- you could quite easily build untapered Beanstalks.

You forgot the most important reasons he didn't just do beanstalks.

A. Slow.

B. Non-glamorous.

C. Not invented when he wrote the stories.

-ash
for assistance dial MYCROFTXXX

In article ,
someone whose name I can't untangle from the deeply-nested quoting
wrote
| Our fasted horizontal rolling vehicles (sometimes called "cars") can
| *almost* break the speed of sound, 700 mph (roughly)with jet engines.

As of 1998, the "rail vehicle" speed record was 9,851km/h (around Mach 8),
achieved by a rocket sled at the White Sands missile range in the USA.
From pictures I've seen on the White Sands web site, I believe their
rocket sleds use steel wheels on (very carefully levelled!) steel rails,
and so would count as "horizontal rolling vehicles".

(White Sands uses the rocket sleds to test ICBM/SLBM inertial guidance
packages. The sleds do _not_ carry people.)

ciao,

--
-- "Jonathan Thornburg (remove -animal to reply)"
Max-Planck-Institut fuer Gravitationsphysik (Albert-Einstein-Institut),
Golm, Germany, "Old Europe" http://www.aei.mpg.de/~jthorn/home.html
"It's every man for himself, said the elephant as he danced on the
anthill!" -- T. C. "Tommy" Douglas's description of ((you guess))

"Ash Wyllie" writes:

Arthur Hansen opined

(Gordon D. Pusch) wrote in message
...

DEFINITELY Unobtainium, and one of the many, many Niven physics bloopers
where he ROYALLY screwed the pooch. (It's pretty obvious why he dropped out
of astrophysics; his former Ph.D. advisor must _wince_ every time he hears
about some of Niven's screw-ups...)

If you had materials with a large enough tensile strength to hold
almost-degnerate gas, or even gas compressed to the point that its
effective I_sp significantly exceeded H2/O2, then you wouldn't
_NEED_ rockets --- you could quite easily build untapered Beanstalks.

You forgot the most important reasons he didn't just do beanstalks.

A. Slow.

B. Non-glamorous.

C. Not invented when he wrote the stories.

Since the Soviet writer Yuri Artsutanov first proposed it in 1960 (based on
much earlier ideas going back to Tsiolkovsky), and a number of Western authors
picked up on in, http://www.islandone.org/LEOBiblio/SPBI120.HTM, that cannot
be the correct explanation.

What _is_ correct is that the idea was not widely _PUBLICIZED_ in the West
at the time Niven was most active, and did not really impinge on pop culture
until Arthur C. Clarke wrote _The Fountains of Paradise_ and Charles Sheffield
wrote _The Web Between the Worlds_. (While Clarke did write about Artsutanov's
concept much earlier in one of his 1960's factual books on space, it sesm to
have had very little impact.)


-- Gordon D. Pusch

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In article ,
Bill Bogen wrote:
"Ash Wyllie" wrote in message ...
Arthur Hansen opined

(Gordon D. Pusch) wrote in message
...

DEFINITELY Unobtainium, and one of the many, many Niven physics bloopers
where he ROYALLY screwed the pooch. (It's pretty obvious why he dropped out
of astrophysics; his former Ph.D. advisor must _wince_ every time he hears
about some of Niven's screw-ups...)

If you had materials with a large enough tensile strength to hold
almost-degnerate gas, or even gas compressed to the point that its
effective I_sp significantly exceeded H2/O2, then you wouldn't
_NEED_ rockets --- you could quite easily build untapered Beanstalks.

You forgot the most important reasons he didn't just do beanstalks.

A. Slow.

B. Non-glamorous.

C. Not invented when he wrote the stories.

Well, they haven't actually been invented yet, in a prototype sense.
But the concept has been around since 1895 when Tsiolkovsky first
wrote about it. Niven wrote 'Tales of Known Space' in '75 and Clarke
wrote 'Fountains of Paradise' in '78 but Niven used a

Clarke refered to them in the 1960s in non-fiction articles
in a manner that makes me think he read Artsunov's paper (?) soon
after publication.

gravity-gradient, really-big-structure idea in 'The Integral Trees'.
I'd bet money he has been aware of the concept of beanstalks for a
good long while.

Except if he did, you'd think the attraction of such a
Big Dumb Object would have been irresistable long before the two
Smoke Ring books.
--
It's amazing how the waterdrops form: a ball of water with an air bubble
inside it and inside of that one more bubble of water. It looks so beautiful
[...]. I realized something: the world is interesting for the man who can
be surprised. -Valentin Lebedev-

Gordon D. Pusch opined

"Ash Wyllie" writes:

You forgot the most important reasons he didn't just do beanstalks.

A. Slow.

B. Non-glamorous.

C. Not invented when he wrote the stories.

Since the Soviet writer Yuri Artsutanov first proposed it in 1960 (based on
much earlier ideas going back to Tsiolkovsky), and a number of Western
authors picked up on in, http://www.islandone.org/LEOBiblio/SPBI120.HTM,
that cannot be the correct explanation.

What _is_ correct is that the idea was not widely _PUBLICIZED_ in the West
at the time Niven was most active, and did not really impinge on pop culture
until Arthur C. Clarke wrote _The Fountains of Paradise_ and Charles
Sheffield wrote _The Web Between the Worlds_. (While Clarke did write about
Artsutanov's concept much earlier in one of his 1960's factual books on
space, it sesm to have had very little impact.)

You're correct. I had meant to ", or at least no one had heard of it back
then."

What Niven wanted was an exotic non-polluting launch system. If nothing else
compressed air is not polluting.


-ash
for assistance dial MYCROFTXXX

"Jonathan Thornburg" wrote in message
...
In article ,
someone whose name I can't untangle from the deeply-nested quoting
wrote
| Our fasted horizontal rolling vehicles (sometimes called "cars") can
| *almost* break the speed of sound, 700 mph (roughly)with jet engines.

I would consider generating a sonic boom to be more than *almost* breaking
the sound barrier.
There is clear evidence that Thrust2 achieved this both ways on its final
runs.

Clearly no competition to rail guns :-)


--
John Travell
john - at - travell - dot - uk - dot - net
http://www.travell.uk.net/





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"Ash Wyllie" wrote in message
...
Gordon D. Pusch opined
"Ash Wyllie" writes:

What Niven wanted was an exotic non-polluting launch system. If nothing
else
compressed air is not polluting.

If you compress air to near-degeneracy, will it react to form nitrogen
oxides?

"Roger Stokes" writes:

"Ash Wyllie" wrote in message
...

What Niven wanted was an exotic non-polluting launch system. If nothing
else
compressed air is not polluting.

If you compress air to near-degeneracy, will it react to form nitrogen
oxides?

If you compress air to near-degeneracy, all molecules will be destroyed,
and a significant fraction of the atoms will be pressure-ionized: The atoms
will not be able to hold onto their outermost "valence" electrons, which
will merge into a "soup" in which the pressure-ionized atoms will form a
"couloumb liquid" or "coulomb crystal" --- neither of which are "normal"
molecular matter as we know it.

As for what it would become as it expands once the pressure were released:
Who knows ??? But I woild not be surprised if nitrogen oxides would be among
the various products.

Bottom line: It was a stupid throwaway idea that Niven didn't think through
adaquately --- which is a common failing of his. While his (early) work is "fun,"
his technical accuracy and plausibility leave more than a little to be desired ---
even when he _isn't_ deliberately writing "shaggy dog" stories...

-- Gordon D. Pusch

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Roger Stokes wrote:

If you compress air to near-degeneracy, will it react to form nitrogen
oxides?

And it STILL has an ISP of 1.
It's not going anywhere.

Aloha mai Nai`a.
--
"Please have your Internet License http://kapu.net/~mjwise/
and Usenet Registration handy..."

Michael J Wise wrote in message ...
If you compress air to near-degeneracy, will it react to form nitrogen
oxides?

And it STILL has an ISP of 1.
It's not going anywhere.

I can't claim to be able to calculate the Isp of this hypothetical
rocket, but given that basically-equivalent cold-gas thrusters have
specific impulses in the 70 second range, I'm fairly confident that
it's not 1.

-jake