Directions in space?

Gene wrote:
Robert Carnegie wrote in news:0f81f0ac-47d1-48d0-
:

Larry Niven's "One Face" isn't quite this; in a spaceship accident,
the computer turns out to be broken, but also the ship is dumped into
the far-distant future, but handily near Earth tidally locked to the
Sun.

What happened to the Moon?

Space 1999 and moonbase alpha ;-)

Regards,
Martin Brown
** Posted from http://www.teranews.com **

On Sat, 21 Jun 2008 21:49:46 -0600, "David M. Palmer"
wrote:

In article , dlzc\
wrote:

Wonder why we don't use vacuum tubes for high power circuits in
space? We have vacuum, so we don't need the glass envelope...

They actually do use 'traveling wave tubes' (Wiki or Google for
details) for some transmitters on spacecraft. But they don't send them
up without envelopes.

One of the reasons for this is that spacecraft systems require a lot of
testing. And it would be helpful to test them without having to put
the whole system into a huge expensive vacuum chamber.

Actually, spacecraft are in fact tested by putting them in huge
expensive vacuum chambers.

However, we still don't use vacuum tubes for anything but the main
RF or microwave output amplifiers, because there's a whole list of
reasons why vacuum tubes are a really crappy way to build electronics,
not just "they need vacuum!"


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In rec.arts.sf.science "N:dlzc D:aol T:com \(dlzc\)" wrote:
Dear Michael Ash:

"Michael Ash" wrote in message
...
In rec.arts.sf.science "N:dlzc D:aol T:com \(dlzc\)"
wrote:
Wonder why we don't use vacuum tubes for high
power circuits in space? We have vacuum, so
we don't need the glass envelope...

Even without the glass, I imagine that a vacuum
tube will be significantly bulkier, more massive,
and more expensive than the semiconductor
equivalent.

A FET is not very far from a vacuum tube. It uses applied an
E-field to "choke" the flow of electrons.

In a semiconductor, not a vacuum. Still seems to me to be firmly in the
realm of "semiconductor", with all the low power usage, cheapness of
manufacture, and reliability that implies.

Vacuum tubes don't have to be large, but they do still need
"heaters" (what the dopants do in a semiconductor). And I accept
that near-Earth vacuum isn't good enough for sensitive
applications.

Vacuum tubes do have to be large and heavy compared to semiconductors,
although certainly they aren't required to be the giant stereotypical
"light bulbs". The requirement for the heater is just another reason not
to use them on spacecraft, or indeed anywhere else.

--
Mike Ash
Radio Free Earth
Broadcasting from our climate-controlled studios deep inside the Moon

Dear Michael Ash:

"Michael Ash" wrote in message
...
In rec.arts.sf.science "N:dlzc D:aol T:com \(dlzc\)"
wrote:
....
Vacuum tubes don't have to be large, but they
do still need "heaters" (what the dopants do
in a semiconductor). And I accept that
near-Earth vacuum isn't good enough for
sensitive applications.

Vacuum tubes do have to be large and heavy
compared to semiconductors, although
certainly they aren't required to be the giant
stereotypical "light bulbs". The requirement for
the heater is just another reason not to use
them on spacecraft, or indeed anywhere else.

Actually, the best guitar amps still use them. And CRTs (won't
be long now, though). So "anywhere else" is a bit broad... ;)

David A. Smith

In message , Michael Ash
writes


Vacuum tubes do have to be large and heavy compared to semiconductors,
although certainly they aren't required to be the giant stereotypical
"light bulbs". The requirement for the heater is just another reason not
to use them on spacecraft, or indeed anywhere else.

The heater isn't strictly necessary if you can find another method of
generating an electron stream. There are new techniques for doing that.
They don't produce the sort of currents that were used in the technology
of the 50s but we don't need that these days, we can pretty much work
with a single electron. Imagine firing a single electron into a pachinko
table of differently charged pins and detecting where it exits. Could
you get something of comparable processing power to that of a silicon
chip?



--
Bernard Peek
London, UK. DBA, Manager, Trainer & Author.

In rec.arts.sf.science "N:dlzc D:aol T:com \(dlzc\)" wrote:
Dear Michael Ash:

"Michael Ash" wrote in message
...
In rec.arts.sf.science "N:dlzc D:aol T:com \(dlzc\)"
wrote:
...
Vacuum tubes don't have to be large, but they
do still need "heaters" (what the dopants do
in a semiconductor). And I accept that
near-Earth vacuum isn't good enough for
sensitive applications.

Vacuum tubes do have to be large and heavy
compared to semiconductors, although
certainly they aren't required to be the giant
stereotypical "light bulbs". The requirement for
the heater is just another reason not to use
them on spacecraft, or indeed anywhere else.

Actually, the best guitar amps still use them. And CRTs (won't
be long now, though). So "anywhere else" is a bit broad... ;)

While technically tubes filled with vacuum, CRTs aren't vacuum tubes in
the sense used above, as an electronic valve.

I'm sure I'll get flamed for this, but my impresion of tubes used in
guitar amplifiers is that they are essentially psychological at this
point. There's nothing preventing you from building a semiconductor
circuit with identical response, and it would be cheaper and use less
power. But they would fail in the psychological department, because people
*think* that tubes sound better. This, in my mind, doesn't constitute a
decent reason to use tubes.

--
Mike Ash
Radio Free Earth
Broadcasting from our climate-controlled studios deep inside the Moon

In rec.arts.sf.science message , Sun, 22 Jun 2008
02:15:48, Wayne Throop posted:
:: Larry Niven's "One Face" isn't quite this; in a spaceship accident,
:: the computer turns out to be broken, but also the ship is dumped into
:: the far-distant future, but handily near Earth tidally locked to the
:: Sun.

: Gene
: What happened to the Moon?

IIRC, they didn't know. It's just gone. Possibly the earth had been moved,
as in "World out of Time", since this is long after any expanded-red-sun
state, but I don't recall for sure about that. I do remember they were
puzzled about a lot of things, and Just Didn't Know what had happened
in detail.

YDNRC. Lourdi Coursefinder locates it in Trailing Trojan position,
about 40% through the story.

--
(c) John Stockton, nr London, UK. Turnpike v6.05 MIME.
Web URL:http://www.merlyn.demon.co.uk/ - FAQqish topics, acronyms & links;
Astro stuff via astron-1.htm, gravity0.htm ; quotings.htm, pascal.htm, etc.
No Encoding. Quotes before replies. Snip well. Write clearly. Don't Mail News.

On Sun, 22 Jun 2008 09:10:27 -0500, Michael Ash
wrote:


Vacuum tubes do have to be large and heavy compared to semiconductors,
although certainly they aren't required to be the giant stereotypical
"light bulbs". The requirement for the heater is just another reason not
to use them on spacecraft, or indeed anywhere else.

When you learn how to build the solid-state equivalent of a
klystron, or even a 500 kW RF amplifier, let me know.

--
Bill Snyder [This space unintentionally left blank]

Bill Snyder wrote:
On Sun, 22 Jun 2008 09:10:27 -0500, Michael Ash
wrote:


Vacuum tubes do have to be large and heavy compared to semiconductors,
although certainly they aren't required to be the giant stereotypical
"light bulbs". The requirement for the heater is just another reason not
to use them on spacecraft, or indeed anywhere else.

When you learn how to build the solid-state equivalent of a
klystron, or even a 500 kW RF amplifier, let me know.

I don't know the current figure, but
http://www.nasa.gov/centers/johnson/.../iss99-16.html
on early setup of the International Space Station shows available
power to /them/ way less than x 100 kW. And you'd suppose that was
one of the hotter birds up there. But maybe that wasn't your point.

On Sun, 22 Jun 2008 17:47:31 -0700 (PDT), Robert Carnegie
wrote:

Bill Snyder wrote:
On Sun, 22 Jun 2008 09:10:27 -0500, Michael Ash
wrote:


Vacuum tubes do have to be large and heavy compared to semiconductors,
although certainly they aren't required to be the giant stereotypical
"light bulbs". The requirement for the heater is just another reason not
to use them on spacecraft, or indeed anywhere else.

When you learn how to build the solid-state equivalent of a
klystron, or even a 500 kW RF amplifier, let me know.

I don't know the current figure, but
http://www.nasa.gov/centers/johnson/.../iss99-16.html
on early setup of the International Space Station shows available
power to /them/ way less than x 100 kW. And you'd suppose that was
one of the hotter birds up there. But maybe that wasn't your point.

I was aiming at the "anywhere else."

--
Bill Snyder [This space unintentionally left blank]