Space & Astronomy/Space and Astronomy (October 1993).iso/mac/TEXT/SPACEDIG/V08/V8_336.TXT

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Date: Wed, 24 Aug 88 19:06:14 PDT
From: Ted Anderson <[e-mail]>
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Subject: SPACE Digest V8 #336

SPACE Digest                                      Volume 8 : Issue 336

Today's Topics:
                   Re: SETI
             Re: fixing Oscar-10
    Re: Space Station power supply (was Re: Lithium cells)
       Re: SETI (was Re: Time dilation affecting SETI)
             Re: skintight suits
                  Aerospike
            Re: 95% vs. 99.9% reliability
                Re: Aerospike
                 Ozone layers
           Re: Destinies lives again - was Skinsuit
       Re: Orbital Data and Observation Relay Satellite
----------------------------------------------------------------------

Date: 12 Aug 88 18:43:08 GMT
From: attcan!utgpu!utzoo![e-mail]  (Henry Spencer)
Subject: Re: SETI

In article <[e-mail]> [e-mail] (Jonathan Zweig) writes:
>Isn't it pretty ridiculous to envision a species that is (a) nasty enough
>to want to exploit other civilizations, (b) has the capability for
>interstellar travel and the weaponry to actually get away with it and (c)
>can't sniff out intelligent life forms unless they are broadcasting?

No, not really.  As far as the capabilities go, we might be able to do it
in another century or so, even assuming no breakthroughs.

>Sheesh. I thought a pretty sensible assumption with SETI is that it simply
>isn't feasible for *any* of the parties involved to travel (else they would
>be here now, etc. etc.) and that's why we use gigawatt radio beacons...

The trouble is that the assumption is untenable, unless there is some deep
problem that we can't see.  Interstellar travel simply isn't that hard, if
you're willing to accept high costs and long transit times.  There are a
dozen different propulsion systems that we could probably build within a
century which would work.  "Interstellar travel is not feasible" used to be
the standard answer to "why aren't they here now?", but not even the most
fervent SETI advocates can keep a straight face when saying that now.
The fact is, we *don't know* why they aren't here now, and it's a major
puzzle.
--
Intel CPUs are not defective,  |     Henry Spencer at U of Toronto Zoology
they just act that way.        | uunet!attcan!utzoo!henry [e-mail]

------------------------------

Date: 12 Aug 88 21:11:04 GMT
From: attcan!utgpu!utzoo![e-mail]  (Henry Spencer)
Subject: Re: fixing Oscar-10

In article <[e-mail]> [e-mail] (Phil R. Karn) writes:
>... 1) With both present and forseeable
>technology, manned missions are inherently orders of magnitude more
>expensive than unmanned missions...

Present, maybe, although I think you should check Soviet prices before
assuming that the Shuttle represents the current state of the art for
cheap manned missions!  Foreseeable, nonsense, unless by "foreseeable"
you mean "what NASA can foresee".

There is no *inherent* reason why launching a repairman to a satellite
should cost significantly more than launching a 3000-lb satellite into
the relevant orbit.  (The Mercury capsule, built with late-50s technology,
weighed 3000 lbs loaded; I think one can safely assume that more modern
hardware would cut the weight enough to add the maneuvering and EVA
capability that Mercury lacked.)

Of course, if one is really smart and doesn't need a particular orbit,
one can avoid having to launch the repairman by making the satellite
co-orbit with Mir...

> 2) There are VERY few situations
>(either practical applications or scientific research) where specific
>mission goals can be met more cost-effectively with humans on board...

If you define "mission goals" to be those selected for funding today,
when human presence is very expensive (except for the Soviets), this is
vacuously true.
--
Intel CPUs are not defective,  |     Henry Spencer at U of Toronto Zoology
they just act that way.        | uunet!attcan!utzoo!henry [e-mail]

------------------------------

Date: 14 Aug 88 09:06:41 GMT
From: [e-mail]  (Alan Larson)
Subject: Re: Space Station power supply (was Re: Lithium cells)

In article <[e-mail]> [e-mail] writes:

>In article <[e-mail]> [e-mail] writes:

>>    Also, this is going to make it impossible to operate induction motors
>>(unless you want them to go VERY fast) without using electronic conversion of
>>the power to get the frequency down.
>
>Or DC motors, from a power supply. My source hasn't seen a single motor
>specified on the station, though.

Hmmm.  Something sounds strange here.  What about the fans that move
air around the cabin.  (I hear that these are rather necessary due to
the lack of convection.  Breathing fresh air is considered nice.)

Speaking of fans, there may be fans (and pumps) in the restroom facilities.


my opinion:
The best reason for 220 VAC at 20 KHz is that it provides the contractors
with the opportunity to engineer custom parts at great profit.  It seems
unlikely that the savings in size by 20 KHz power are worth the trouble.

DC could be used without great difficulty in many places.  DC to DC
converters are common in small modules.  Using DC would help eliminate
the need to filter continuing background hum of the power system from
the electronics and experiments.

Common AC frequencies (60 Hz, 400 Hz) could be used with more easily
available equipment.  Filtering and processing these frequencies is not
much of a problem, since the technology of building power supplies
operating with normal forms of power is well developed.

If a large assembly or rack needs a special type of power, it makes more
sense to provide that power in local busses.  This could provide the
savings that 20 KHz power would be expected to provide.

20 KHz power would, it seems, be at higher risk to coupling from the
power lines by both magnetic and capacitative couplikng means.  This
would mean that the supply lines would need extra protection to keep
them away from the data lines.  Failure to do that would contaminate
the non-power lines with the same AC 'hum' that was filtered out by
the power supplies.

    Alan

------------------------------

Date: 14 Aug 88 03:13:17 GMT
From: tektronix!percival!bucket![e-mail]  (Leonard Erickson)
Subject: Re: SETI (was Re: Time dilation affecting SETI)

In article <[e-mail]> [e-mail] (Edwin Hoogerbeets) writes:
<Let's imagine for a moment that we want to send out a strong message in
<the Hydrogen band to other intelligent life in the galaxy. Which way
<would we send it?
<
<I think it would be obvious to send it in the direction of the center of
<the galaxy to reach the most prospective planets(?) where life would
<exist.
<
<Now think of *our* galactic location. We're on the edge of the galaxy.
<Maybe we're just missing out on all the fun because we're on the
<sidelines? Everyone is sending their message the other way! By the time
<the messages from the other side of the galaxy get to us, they are too
<weak to detect.

This is the worst possible direction to send a signal! The galactic core is
primarily first generation stars. This means that there isn't anything except
hydrogen and helium to make the planets out of. It is rather difficult to
evolve life under these conditions.

Second generation stars aren't much better, they won't have any elements
with higher atomic numbers than iron, and they'll have damn little of
anything that heavy! Life as we know it is impossible on these planets
as too much of life relies on metals that would be unavailable.

Even if life *did* evolve on the planets of a second generation star,
they couldn't develop technology. No metals. No gold or copper nuggets,
no ores that can be smelted with charcoal. No magnetic minerals. So the
would never have an inkling of electricity or magnetism. So no radio.

Assume by some miracle, a second generation star had life-bearing planets,
and due to several nearby supernovae had an sun-like elemental abundance.
Fine, that means that the civilization on this planet would be 1-2 Billion
(1x10 to th 9th = billion here) older than ours. Somehow I doubt that
we'd have anything to say to each other. The gulf would be too great.

Finally, we have third generation stars such as the sun. The solar system
is thought to have a typical elemental abundance for a third generation
star system.  But the sun is one of the older third generation stars in
this part of the galaxy... it may be a long way to the neaerest civilization
of a similar or greater age.

Yes, *we* may be the most advanced civilization for a thousand or so
light years.... sobering thought...

--
Leonard Erickson        ...!tektronix!reed!percival!bucket!leonard
CIS: [70465,203]
"I used to be a hacker. Now I'm a 'microcomputer specialist'.
You know... I'd rather be a hacker."

------------------------------

Date: 13 Aug 88 21:27:07 GMT
From: att!chinet!mcdchg!clyde!watmath!utgpu!utzoo![e-mail]  (Henry Spencer)
Subject: Re: skintight suits

To add some comments to John Hogg's discussion...

In article <[e-mail]> [e-mail] (John Roberts) writes:
>  ... The fabric can support the skin overall, but
>  not on a microscopic basis. At the microscopic level, the skin, rather than
>  being a continuous sheet of dead tissue, is full of pores, and the pores
>  contain important living, wet cells exposed to the outside pressure. At
>  body temperature, the partial pressure of water is ~50mm, meaning that if
>  the ambient pressure falls below this point, rapid boiling of water at and
>  for a short distance below the surface will begin. It seems highly unlikely
>  that these living cells could be directly exposed to vacuum without a
>  considerable number being killed.

If boiling starts, the cell will swell, pressurizing itself against the
surrounding cells (which, overall, are confined by the suit pressure).
Rupture is unlikely; cells are tougher than you'd think.

>  I would like to know about the results of long-term exposure, which I
>  suspect would at least cause the skin to become dry and brittle, and
>  might kill the hair follicles, oil and sweat glands...

Humans survive for decades in deserts, where the partial pressure of water
approaches zero for months at a time.  For that matter, the partial pressure
of water in the atmosphere is usually lower than in the body even in non-
deserts.  The outer layers of the skin *are* dead, dry, and brittle in
normal human beings; dead skin cells flake off your body constantly, and
are a major component of the dust you vacuum up when you clean house.
The human skin is not in equilibrium with its environment even at one
atmosphere of pressure; rather, it is a steady-state system maintained
by constant effort by the body.  It appears that with mechanical support,
it should work about equally well in vacuum.
--
Intel CPUs are not defective,  |     Henry Spencer at U of Toronto Zoology
they just act that way.        | uunet!attcan!utzoo!henry [e-mail]

------------------------------

Date: 15 Aug 88 01:09:00 GMT
From: aramis.rutgers.edu!klaatu.rutgers.edu![e-mail]  (J Storrs Hall)
Subject: Aerospike


What is an aerospike?  What is meant by its being (or not being)
"plugged"?

What is the specific impulse of hydrazine?

--JoSH

------------------------------

Date: 14 Aug 88 02:53:41 GMT
From: clyde!watmath!utgpu!utzoo![e-mail]  (Henry Spencer)
Subject: Re: 95% vs. 99.9% reliability

In article <[e-mail]> [e-mail] writes:
>One comment, Henry, about flying the shuttle with the old boosters: The real
>risks isn't the loss of the crew, it's the loss of the vehicle...

Agreed.  However, we aren't *quite* at the point where replacement is
impossible; almost but not quite.  Challenger was lost just in time.

>As I understand it, replacing the vehicle will exhaust the complete stock of
>structural spare parts. In other words, the total number of flights including
>the rebuild vehicle will not be much greater than operating with three
>vehicles and using the spares as intended...

As I recall, there is a new set of structural spares in the works, so the
situation isn't quite that bad.  However, I detect no signs that anyone has
really paid attention to NRC's comment that ongoing orbiter production is
an absolute requirement for a viable fleet.  (Their reasoning, briefly, was
that the fleet is so small in comparison to the significant chances of
losing another orbiter that it is impossible to make long-range plans based
on using the shuttle unless replacement orbiters continue to be available.)
--
Intel CPUs are not defective,  |     Henry Spencer at U of Toronto Zoology
they just act that way.        | uunet!attcan!utzoo!henry [e-mail]

------------------------------

Date: 15 Aug 88 03:56:30 GMT
From: rochester!kodak![e-mail]  (barry ornitz)
Subject: Re: Aerospike

In article <[e-mail]>
[e-mail] (J Storrs Hall) writes:
>What is an aerospike?  What is meant by its being (or not being)
>"plugged"?
Heck if I know!
>What is the specific impulse of hydrazine?
This maybe I know!  It depends on the oxidizer - see table below:

Oxidizer   Oxy/Fuel Ratio    Chamber Temp, deg. F   Specific Impulse, sec.
O2               0.75              5370                   279
H2O2             1.70              4690                   265
N2O4             1.1               4950                   262
F2               2.0               7740                   318
RFNA (NO2-15%)   1.3               4980                   260
Red Fuming Nitric Acid

All of the above is for a 500 PSI chamber pressure.
Kit, Boris and Douglas Evered, "Rocket Propellant Handbook," Macmillan Co.,
New York, 1960.
                                                   Barry

------------------------------

Date: Mon, 15 Aug 88 10:16:30 PST
From: Peter Scott <[e-mail]>
Subject: Ozone layers
X-Vms-Mail-To: EXOS%"[e-mail]"

Can someone please explain why ozone produced as a component of smog is
apparently not a factor in regenerating the ozone layer that everyone's
so worried about?  I know ozone is poisonous; is it just the case that
smog-ozone is trapped under the inversion layer?  How?

Peter Scott ([e-mail])

------------------------------

Date: 15 Aug 88 16:08:58 EDT
From: [e-mail]
Subject: Re: Destinies lives again - was Skinsuit
To: [e-mail]

Re:

> Date: Sun,  7 Aug 88 20:04:53 -0400 (EDT)
> From: Kevin William Ryan <[e-mail]>
> Subject: Re: Skintight suit reference
   ...
>    The preceeding reference comes courtesy of J. E. Pournelle, from the
> Summer 1980 (Vol. 2, No. 3) _Destinies_, now a defunct publication.  Pity...

"Destinies" died in 1983 or so, but "New Destinies" started publishing
quarterly in 1987.  Same editor, Jim Baen, now under his own imprimatur:
Baen Books. Available as before in the paperback SF section of your
bookstore, rather than the magazine rack.
                        -Hans Moravec

------------------------------

Resent-Message-Id: <[e-mail]>
Resent-Date: Mon, 15 Aug 88 16:35:46 -0400 (EDT)
Resent-From: Ted Anderson <[e-mail]>
Resent-To: [e-mail]
Return-Path: <[e-mail]>
Date:     Mon, 15 Aug 88 12:34 EST
From: <[e-mail]>
Subject:  Re: Orbital Data and Observation Relay Satellite


Todd (uop![e-mail]) writes

>In watching the re-run of NOVA's "Death of a Star".. it occured to me that
>a network of satellites capable of swapping telemetry and digitized phone
>and visual communications would be a good thing to have towards better
>connectivity with remote sites.
>
>They could be accessed from earth stations using small dishes (comparitively).
>
>I am sure someone is working on something like this.. someplace..

     It is, in northern Canada.  I'm not exactly sure who is involved,
but it is sure to include Telecom Canada, Bell Canada, and Bell Northern
Research.  The idea is to use one of the Anik satellites and small
dishes (that can be mounted onto vans if needed) to provide telephone
communications, etc. for remote communities in the Northwest and Yukon
Territories.  From there it is just a small step to doing what Todd has
suggested.

     Of course, since this is being done in Canada, no one in the US or
the rest of the world has any inclination of what is going on! :-)

     Actually, I wouldn't be surprised if the Soviets are working on a
similar system, since they have the same communication/terrain/remote
population difficulties as Canada.

                                         -=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-
Arnold Gill                             | If you don't complain to those who  |
Queen's University at Kingston          | implemented the problem, you have   |
gill @ qucdnast.bitnet                  | no right to complain at all !       |
                                         -=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-

------------------------------

End of SPACE Digest V8 #336
*******************