Date: Wed, 17 Aug 88 19:05:08 PDT
From: Ted Anderson <ota@angband.s1.gov>
Message-Id: <8808180205.AA04259@angband.s1.gov>
To: Space@angband.s1.gov
Reply-To: Space@angband.s1.gov
Subject: SPACE Digest V8 #328

SPACE Digest                                      Volume 8 : Issue 328

Today's Topics:
		    Re: 95% vs. 99.9% reliability
				 SETI
			   Re:  Solar Sails
	Re: Space Station power supply (was Re: Lithium cells)
			      lightning
			   Re: SETI (& STI)
			   fixing Oscar-10
		    Re: 95% vs. 99.9% reliability
			    Re: Satellites
	Re: Space Station power supply (was Re: Lithium cells)
		    Re: 95% vs. 99.9% reliability
		    Re: 95% vs. 99.9% reliability
----------------------------------------------------------------------

Date: 8 Aug 88 20:42:31 GMT
From: adelie!infinet!rhorn@xn.ll.mit.edu  (Rob Horn)
Subject: Re: 95% vs. 99.9% reliability

In article <1231@eos.UUCP> eugene@eos.UUCP (Eugene Miya) writes:
>The problem, as Feynman pointed out, is how do you quanitify this?
>I can easily say 99.9 or 95 percent based on some metric, but which.

Well, the current launch-to-correct-orbit reliability for Delta-class
expendibles is 95%.  A fairly generous metric, and one that I sure
wouldn't want to ride in.

-- 
				Rob  Horn
	UUCP:	...harvard!adelie!infinet!rhorn
		...ulowell!infinet!rhorn, ..decvax!infinet!rhorn
	Snail:	Infinet,  40 High St., North Andover, MA

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

Resent-Message-Id: <4Wzl6Vy00VseI-eFI7@andrew.cmu.edu>
Resent-Date: Tue,  9 Aug 88 10:52:17 -0400 (EDT)
Resent-From: Ted Anderson <ota+@andrew.cmu.edu>
Resent-To: space@angband.s1.gov
Return-Path: <Ingemar.Hulthage@isl1.ri.cmu.edu>
Date: Tue, 9 Aug 1988 09:59-EDT 
From: Ingemar.Hulthage@cs.cmu.edu
To: Ted Anderson <ota@angband.s1.gov>
Subject: SETI

I don't think one can assume that advanced civilizations do broadcast
signals with the purpose to make themselves known, for the following
reason. 

Suppose there exist some incredibly vicious species somewhere out
there, a race that routinely seeks out intelligent civilizations and
exploit them rutlessly. Now, if that is so, any civilization that
broadcasts its existence would soon be found and silenced, but even if
it is wrong it is still irresponsible to take the risk of broadcasting
unless the horror scenario can be ruled out with 100% certainty and
that may be hard or impossible.

I therefore think that its more likely that some advanced civilizations
deem regular wide angle transmission safe and useful for some purposes,
as we do on earth. Hence, I don't think there is much hope of SETI
being successful until a capacity to detect regular transmissions is
developed.

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

Date: Tue, 9 Aug 88 10:23:41 CDT
From: sedspace@doc.cc.utexas.edu (Steve Abrams)
Posted-Date: Tue, 9 Aug 88 10:23:41 CDT
Subject: Re:  Solar Sails
Cc: spd7924%tamvenus.bitnet@cunyvm.cuny.edu


In SPACE Digest V8 #319, Nathan Ulrich (ulrich@grasp.cis.upenn.edu) 
and John DuBois (spcecdt@ucscb.ucsc.EDU) respond to my reply to 
someone (*with a poor physics background*) on the mechanism by 
which radiation pressure can transfer momentum to a light sail.

Nathan Ulrich:

>I don't know if I am a purist, but it won't satisfy me.  
>
>One indisputable law of the universe, "You can't get something for nothing."
>Your explanation above will result in an increase in the total mass-energy
>of your system.  

	You're a purist.  Although I didn't make it clear, I was 
describing a "perfectly" reflecting sail (R=1.0) in an attempt to get the 
idea across without burdening the original questioner with a lot of 
homologous information.  You are absolutely correct.

John DuBois:

>Surely the frequency of the photon as reflected from the sail will be 
>lower than the original photon (thus it will have lower energy)?

	In a *real* (R<1.0) sail, this is true.  Again, I was responding 
pedagogically, trying to present the explanation without rigor, but 
with clarity.  In a subsequent posting, I am much more clear in my 
presentation.

>It sounds to me like there would be a double Doppler effect (once 
>upon absorbtion, and once upon emmision).

	Doppler effect?  The Doppler effect arises from motion (in the 
frame of the observer) of a "source" with respect to an observer.  
While I agree that a solar sail moving away from the Sun will "see" 
red-shifted photons (and, hence, gets slightly less - for 
interplanetary sails - push, as the "peak" of the solar irradiance 
curve is red-shifted from around 490 nm), it doesn't depend upon 
their absorption and re-emission.  It wouldn't be a double effect as, 
when the photon is re-emitted, the sail would be both "source" and 
"observer."  Since the sail has no velocity relative to itself and the 
sail will never interact with that photon again, there is no Doppler 
effect with respect to emission.

	This belongs in sci.physics...

							Steve Abrams

"The reality we describe with physics is derived from the reality we 
observe with our senses which doesn't necessarily relate to the 
reality that is..."

2721 Hemphill Park, Apt. C	ARPANET:  sedspace@doc.cc.utexas.edu
Austin, TX  78705		CompuServe:  [70376,1025]
(512)480-0895			
				OR
     c/o Students for the Exploration and Development of Space
   P.O. Box 7338, 358 Texas Union, University of Texas at Austin
              Austin, TX  78713-7883  (512)471-7097

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

Date: 9 Aug 88 11:32:11 GMT
From: bungia!meccts!viper!dave@umn-cs.arpa  (David Messer)
Subject: Re: Space Station power supply (was Re: Lithium cells)

In article <1110001@hpfclm.HP.COM> myers@hpfclm.HP.COM (Bob Myers) writes:
 >
 >>Main power on the space station is specified as 220 VAC at 20 kHz.
 >
 >AC?  Why AC?
 >
 >Bob M.

AC is easy to convert to whatever voltage you want by means of
a transformer.  DC is obtained with a simple rectifier.  A
high frequency is used because the transformer needed is
smaller and higher frequencies are easier to filter out when
DC is needed.
-- 
If you can't convince |   David Messer - (dave@Lynx.MN.Org)
them, confuse them.   |   Lynx Data Systems
   -- Harry S Truman  | 
                      |   amdahl   --!bungia!viper!dave
                      |   hpda    /

Copyright 1988 David Messer -- All Rights Reserved
This work may be freely copied.  Any restrictions on
redistribution of this work are prohibited.

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

Date: 9 Aug 88 16:55:47 GMT
From: ubc-cs!fornax!zeke@beaver.cs.washington.edu  (Zeke Hoskin)
Subject: lightning

The NASA lightning research is interesting and
potentially (pun accidental) useful, but incomplete
as it is framed. It isn't enough to predict lightning
or lighning-harden spaceships on the pad. What we
need is a way to USE the stuff.  Getting the power
onto the grid would be nice...but consider that one
of the problems with electromagnetic launch is:
where can we get that much energy in a short burst?
The hell with huge capacitors and slowly growing
currents in superconducting coils!
  The Ultimate El Cheapo Spaceship: a shielded
compartment, a big strong nozzle full of ice, and
a ground wire. Lightning strikes, ice vaporizes, up
she goes...somewhere over the rainbow....:-{)>  
-- 
What makes one step a giant leap|Zeke Hoskin/SFU VLSI group,Burnaby,BC,Canada
Is all the steps before         | ...!ubc-cs!sfu_fornax!zeke

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

Date: 9 Aug 88 22:31:20 GMT
From: spdcc!eli@husc6.harvard.edu  (Steve Elias)
Subject: Re: SETI (& STI)

In article <587138396.iaeh@ISL1.RI.CMU.EDU> Ingemar.Hulthage@CS.CMU.EDU writes:
>Suppose there exist some incredibly vicious species somewhere out
>there, a race that routinely seeks out intelligent civilizations and
>exploit them ruthlessly.

	suppose that species is man.  

	perhaps such a vicious species would destroy itself
	long before it evolved far enough to destroy species 
	away from its home system.

	a species which survived its
	own nuclear self destruct phase would have evolved past
	any vicious tendencies long before the reach into deep space.

	(or so they say).

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

Date: 9 Aug 88 22:14:33 GMT
From: thumper!karn@faline.bellcore.com  (Phil R. Karn)
Subject: fixing Oscar-10

Henry's comments about AMSAT Oscar-10 and its problems (caused by a
post-separation collision with the Ariane third stage) came just before
I left for Europe for two weeks, and I didn't get a chance to respond.
At the risk of re-opening the manned-vs-unmanned argument, here goes:

Yes, of *course* it would have been very nice had somebody been up there
to fix our satellite, even if all he could do was to bend the 2 meter
antenna element back into place. But you evade a fundamental and crucial
question:
			AT WHAT COST?

All told, our mission cost us only a few hundred thousand US dollars.
That kind of money might be enough to buy a toilet seat on the Shuttle.
But I doubt even AMSAT (with a proven track record for low-cost space
engineering) could send up a fixit person for the same amount and get
him back safely.

The simple and sad facts of life that the "I wanna go!" crowd has got to
learn sooner or later are these: 1) With both present and forseeable
technology, manned missions are inherently orders of magnitude more
expensive than unmanned missions, and 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
it's *entertainment* you're after, then you should at least be honest
about your motivations.

The cheapest way BY FAR to "fix" a malfunctioning satellite, especially
a small one, is almost always to launch a replacement. That's exactly
what we did this year. Not only did we get a perfectly healthy satellite
in orbit, but one with twice as many communications transponders and
twice as much onboard computer memory because we were able to take
advantage of newer technology.

Phil

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

Date: 9 Aug 88 23:54:43 GMT
From: mike@ames.arc.nasa.gov  (Mike Smithwick)
Subject: Re: 95% vs. 99.9% reliability

[]
In article <1181@infinet.UUCP> rhorn@infinet.UUCP (Rob Horn) writes:
>Well, the current launch-to-correct-orbit reliability for Delta-class
>expendibles is 95%.  A fairly generous metric, and one that I sure
>wouldn't want to ride in.
>
>-- 
>				Rob  Horn

Remember, that the majority of the failures in a given rocket program are 
concentrated in the first few flights until the engineers can get all
of the bugs worked out. So the success-rates of a vehicle should not 
include the first dozen missions or so.

I'm sure that Henry has the figures right at his fingertips, but I believe
that we've launced over 180 of them Delta thingies, and only lost a couple 
in the last 160 or so.

*** mike ***
-- 
			   *** mike (starship janitor) smithwick ***
"Due to the Writer's Guild of Amierica strike, this signature is
 temporarily cancelled".
[disclaimer : nope, I don't work for NASA, I take full blame for my ideas]

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

Date: 9 Aug 88 17:25:35 GMT
From: tektronix!teklds!mrloog!dant@ucbvax.berkeley.edu  (Dan Tilque;1893;92-101;)
Subject: Re: Satellites

Steve Hix writes:
>
>> You also missed Pioneers 10 and 11, heading out of the solar system.
>
>Also two Mariners, as pointed out in another message.

Actually, you missed 4 Mariners.  Besides Mariners 9 and 10, You also
missed Mariners 6 and 7.  These were two Mars flybys in 67 (I think).
In case anyone is interested, Mariner 8 was also launched as a
companion to Mariner 9, but some problem caused it to end up on the
bottom of the Atlantic.  They had to do some quick fixing to Mariner 9
to avoid the same problem with it.

>
>This is what comes of trying to scan through 2,979 launches during 
>lunch. :}

Perhaps you should first look at the list in the Information Please
almanac which has only those launches which have gone beyond Earth
orbit.  It doesn't give the current status so you would have to refer
to your other list for that.


---
Dan Tilque	--	dant@twaddl.LA.TEK.COM

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

Date: 9 Aug 88 18:09:25 GMT
From: attcan!utzoo!henry@uunet.uu.net  (Henry Spencer)
Subject: Re: Space Station power supply (was Re: Lithium cells)

In article <1110001@hpfclm.HP.COM> myers@hpfclm.HP.COM (Bob Myers) writes:
>AC?  Why AC?

Same reason we use AC here:  transformers.  The big problem with DC power
is that there is no simple equivalent of the transformer, meaning that
any equipment that needs a different voltage has to work hard to get it.
If you want to provide service to a wide variety of gear with a wide
variety of needs, AC is the clear choice.
-- 
Intel CPUs are not defective,  |     Henry Spencer at U of Toronto Zoology
they just act that way.        | uunet!attcan!utzoo!henry henry@zoo.toronto.edu

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

Date: 9 Aug 88 20:55:20 GMT
From: attcan!utzoo!henry@uunet.uu.net  (Henry Spencer)
Subject: Re: 95% vs. 99.9% reliability

In article <646@a.lanl.gov> jkw@a.lanl.gov (Jay Wooten) writes:
>You can bet the Soviets would have hardly missed a beat in sending up
>another one (something they've proved several times in the past).

As somebody wrote in Aviation Week a few months afterward (roughly, from
memory):  "If the same thing had happened to the Soviets, they would have
swept the debris off the launch pad, hoisted the next launcher onto the
pad, and started the countdown.  Anyone who objected would have been told
where to go, or sent there."
-- 
Intel CPUs are not defective,  |     Henry Spencer at U of Toronto Zoology
they just act that way.        | uunet!attcan!utzoo!henry henry@zoo.toronto.edu

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

Date: 9 Aug 88 20:53:36 GMT
From: attcan!utzoo!henry@uunet.uu.net  (Henry Spencer)
Subject: Re: 95% vs. 99.9% reliability

In article <20043@cornell.UUCP> dietz@gvax.cs.cornell.edu (Paul F. Dietz) writes:
>... The Rogers
>commission did NOT say that the shuttle would be safe to launch in warm
>weather.  They said that so many things were wrong with the joint design
>that it was impossible to determine what actually caused the leak...

True, as far as it goes.  From the data they supplied, though, it is
reasonable to infer that the combination of warmer temperatures and going
back to the old low-pressure leak-test procedure would greatly reduce the
risks.  Neither cold nor high-pressure leak tests had a perfect correlation
with joint problems, but both correlations were quite strong and the
combined correlation was even stronger.

Since there is no such thing as perfect safety, reduction of risk is all
one can realistically discuss.  Many people thought that a handful of
simple precautions, including those mentioned above, should reduce risk
enough to permit urgent missions to be flown by volunteer crews.  Sigh,
NASA didn't agree...
-- 
Intel CPUs are not defective,  |     Henry Spencer at U of Toronto Zoology
they just act that way.        | uunet!attcan!utzoo!henry henry@zoo.toronto.edu

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

End of SPACE Digest V8 #328
*******************