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Subject: SPACE Digest V10 #272

SPACE Digest                                     Volume 10 : Issue 272

Today's Topics:
            Re: Shuttle Launch Orientation
             Re: shuttle question
             Why NASA wants to go to Mars

          Re: So how elastic is the market?
                HST resolution
            Re: Shuttle Launch Orientation
           Re: Why NASA wants to go to Mars
----------------------------------------------------------------------

Date: 22 Nov 89 18:17:33 GMT
From: cs.utexas.edu!hellgate.utah.edu!mailrus!jarvis.csri.toronto.edu!ists!yunexus!utzoo![e-mail]  (Henry Spencer)
Subject: Re: Shuttle Launch Orientation

In article <[e-mail]> [e-mail] (Mark C. Widzinski) writes:
>Why does the space shuttle have to execute such a drastic roll
>maneuver?  I know that the correct flight configuration is to have
>the orbiter hanging upside down under the ET/SRB stack, but why
>don't they start out that way?  i.e., why doesn't the shuttle face
>east with the ET to the west?  ...

Sigh...  We really need a *real* frequently-asked-questions list, not
the travesty Eugene is posting these days.

The shuttle's orientation at launch is constrained by the need to use
pad facilities originally built for Saturn Vs.  A shuttle pad built from
scratch probably would put the orbiter on the east side.  Doing this
with the existing pads would have been difficult and expensive, and there
is nothing particularly hard about the roll maneuver.
--
A bit of tolerance is worth a  |     Henry Spencer at U of Toronto Zoology
megabyte of flaming.           | uunet!attcan!utzoo!henry [e-mail]

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

Date: 23 Nov 89 18:41:57 GMT
From: attctc![e-mail]  (Robert Johnson)
Subject: Re: shuttle question

In article <[e-mail]> [e-mail] writes:
>
>What's all that sparks that fly around under the shuttle before it launches?
>They seem to get all excited just before the real launch and fizzle around
>the next. isn't it dangerous to have open flames near the gas nozzles? what
>if rocket fuel leaks out? anyway I'm sure there must be a good reason
>for them.
>I wonder if some ineexpensive addative could be made that wouldn't
>reduce fuel effectiveness but make the sparks or better yet the
>flame blue.

Well, actually, they are there to ignite the engines.  If you listen
carefully to the controller durring the launch, you will hear
"pyrotechnics on...", at which point the sparcks will start
dancing under the engines.  At about T-3s the engines are ignited
by the pyrotechnics and away she goes.  The shuttle engines are not
able to ignite themselves (there is a word for this, can't remember
it though), so they need these pyrotechnics.

             Hope this helped,
                           Robert

--
|  Robert C. Johnson                |  "Minds are like parachutes.       |
|   [e-mail]         |   They only function when they are |
|   [phone]                  |   Open."  -Sir James Dewar         |

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

Date: 22 Nov 89 02:45:48 GMT
From: uhccux![e-mail]  (Jeff Goldader)
Subject: Why NASA wants to go to Mars

I saw this in the most recent issue of "Aviation Week" to hit our
library's shelves.  I found it very enlightening, and thought some
of you might like to see it.

From "Aviation Week and Space Technology," Oct. 30, 1989 (p.15):

`SAY WHAT?
Franklin D. Martin, NASA's associate administrator for exploration, has a
host of reasons for sending humans to Mars.  He went to the trouble of
compiling the reasons on a viewgraph, which he hauled out recently for the
NASA Advisory Coucil's space station committee.  As Martin expatiated on
the mission's benefits to the national spirit, one committee member thought
he noticed an omission.  "Hey, Frank, you left off science," A. Thomas
Young, the president of Martin Marietta Electronics and Missiles Group,
said.  "Yeah, maybe so.  Yeah," Martin acknowledged.  But he quickly
brushed Young's comment aside, remarking offhandedly that "science is
one of the reasons you do these things, but it's not the driver." '

Personal Editorial Begins:

Am I the only one who nearly became physically ill after reading this?
Is this truly what our space program has become, a bunch of administrators
who are no longer aware that space exploration is meant for science?  These
are the same people who ask us for billions of dollars to construct a
space station.  These are the same people who lied to Congress about the
shuttle's capabilities, who are lying to Congress about the space station's
capabilities, and who will shortly be lying to Congress to get money
to put people on Mars.

I would rant and rave about cancelling the whole damned mess, but you've all
heard that before.  If any of you hopeful ones needed proof of the final
collapse of the United States' space program, here it is.

Jeff Goldader
[e-mail]

No disclaimer; this is just me talking, and I won't even name my employers
this time.  They bear no responsibility for this posting.

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

Date: 11/21/89 15:49:43
From: [e-mail]
Comment: CROSSNET mail via SMTP@INTERBIT
Return-Receipt-To: [e-mail]
Subject:

>>From: mcsun!ukc!edcastle![e-mail]  (Bob Gray) (17 nov 89)
>>A small asteriod "hung" from the Moon by cables would be
>>more stable yet, and make a good base to build a shipping
>>station on.
>   Yes, this would shorten the required length of cable. The ballast
>would have to lie somewhere between L1 and earth. (18 nov 89)
> Christopher Neufeld....Just a graduate student  | "Out of my way,
> [e-mail]                    | I'm a scientist!"

I'm afraid this is not the point. To see why, let's discuss the
general aspect of a space lift. Seen horizontaly, the cable looks
like this:
  *----=====*0*====----( . )
  ^          ^         ^ ^
  !          !         ! +- Cross-section of Earth/Moon (center)
  !          !         +--- Equator - anchor point of the cable
  !          +---- stationary orbit - largest section/Midway station
  +----- End of cable: counterweight.

The good place to place a station is of course at the stationary
orbit:  since any mass is weightless at this place, it can be as
bulky as needed. Now once the cable construction is over, its end
will reach the ground without any pull: the station is still at an
equilibrium.  The bottom end is then anchored, and then a
counterweight is added at the opposite side. Since centrifuge force
exceeds gravitation in that area, the effect is to pull on the
cable, resulting in a tension that is balanced by the anchor point.

Once the cable operational, the counterweight pull is balanced
either by the anchor point or by a payload rising from the planet's
surface. To remain balanced, the ground weight of the maximum
payload should not exceed the cable's tension. The weight falls
toward zero as the payload reaches the stationary station (mmm - how
would you call it?) and the traction is gradually transferred from
the ascending payload to the ground anchor. Coriolis forces tend to
slow the cable's rotation while the payload is climbing, so that the
cable bends backwards: cinetic momentum is thus transferred from the
planet to the ascending object.

The first remark here is that no mass can be permanently added
between the ground and the stationary orbit: this would result in a
useless increase of the cable's tension. The second one is that a
payload should not go beyond the stationary point unless the
counterweight is accordingly lowered: otherwise the cable's tension
would exceed its working point.

Now, a small asteroid hung on the cable can make a good
conterweight, but it has to be realy small so as not to split the
cable under its weight. And it can not be used as a building station
on the stationary point, since that would mean bringing it in an
unstable Lagrange orbit. Also, it can not be used both as a
counterweight and as a shipping station, since the cable's tension
cannot remain constant if payloads routinely go beyond the
stationary point. Furthermore, if too massive it cannot be placed
on Moon's stationary orbit at all, since the lagrange point is
unstable: if the intermediary L2 station is too massive, the
stabilisation effect of the ballast will not be enough and the whole
construction will go adrift. This is not the case for Earth, where
the stationary station (re-sic) can be of nearly any mass.

Now for the cable's length: of course, the ballast has to lie
somewhere beyond the stationary point, but this does not shorten the
cable. Indeed, the more massive the counterweight is, the shorter
the distance needed between stationary point and ballast, for a
given cable tension. But all the lengths given are those between
ground (or planet center) and stationary orbit, which is the only
useful part: the extra length needed to hold the ballast is never
included in these figures.

Finally, -flame time: beware!- I would like to comment some figures
Christopher Neufeld quoted without his teacher's permission: (I
re-quote without permission):

>...through L1 would be...300_000km...An L2 skyhook is 550_000km long...

Don't forget the Moon-Earth distance is about 380_000 km: the first
point cited here is one of the two placed on an equilateral triangle
with respect to Earth and Moon, probably given with a mile-km
conversion error (nautical mile vs. statute mile, perhaps, followed
by truncation?). The second one being twice as far is probably the
one behind Earth, roughly on the point symetric of the Moon's
position. Both of these points are of course completely useless.
This is the second time you quote _The Endless Frontier_.  Seeing
something printed dosen't make it true (keep smiling- we all make
mistakes).

                             Bertrand MICHELET
                             UDOC140 at FRORS31 (BitNET)

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

Date: 22 Nov 89 17:35:15 GMT
From: cs.utexas.edu!usc!samsung!shadooby!sharkey!itivax!vax3![e-mail]  (Allen W. Sherzer)
Subject: Re: So how elastic is the market?

In article <[e-mail]> [e-mail] (Henry Spencer) writes:
>>...some estimate of how elastic the market is. In other words,
>>if the cost to launch a pound were cut in half, how much bigger
>>would the market get in terms of pounds to orbit?

>This is one of the Catch-22s of the launch industry.  Nobody knows how
>elastic the market is, really, because cutting the price in half has
>never been tried.

But there still should be some estimate. I'm sure there are lots of
missions which would become feasible or profitable at some launch
cost. Besides, buisnesses estimate the size of markets for products
frequently.

  Allen
----------------------------------------------------------------------------
| Allen W. Sherzer                    |  Is the local cluster the result   |
|  [e-mail]                        |  of gerrymandering?                |
----------------------------------------------------------------------------

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

Date: 23 Nov 89 00:48:38 GMT
From: mailrus!shadooby!terminator!ronin![e-mail]  (Allan M. Bjorklund)
Subject: HST resolution

>>From: John Roberts <[e-mail]>
>>>From: cs.utexas.edu!samsung!aplcen!haven!uvaarpa!hudson!astsun9.astro.Virginia.EDU![e-mail]  (Greg S. Hennessy)
>>>The resolution of HST is [roughly] 20 milliarcseconds. Let us consider
>>>Alpha centuri. It is about 1.3 parsecs away, this 1 arcsecond will be
>>>1.3 AU or about 130 million miles. 20 mas will be about 26 million miles.
>>.......................

>>>>, [e-mail] (Allan M. Bjorklund) writes:
>>>> I redid the calculations, and came up with the HST being able
>>>> to resolve a 3000 mile wide object at 39 AU

>>There have been several calculations similar to this posted recently, and
>>most of them seem to be off (with respect to my calculations) by roughly
>>a factor of 1.5-2. My reasoning is as follows:

>>With 60 seconds of arc in an arcminute, 60 minutes in a degree, and 360
>degrees in a full circle, an angle of 20 milliarcseconds makes up
>1/10800000 of a full circle.
>...Thus, by both of these methods,
>the width of the projection ~= d * 5.818E-7.
[States a corretion to his method]
>bacomes width = d * 9.696E-8. For 1.3 parsecs and 39 AU, this gives about
>2.4 million miles and 350 miles. The original calculations by Hennessy
>and Bjorklund are therefore off by a factor of about 8-10.
>
>Does it look right now? (This shows why engineers like to have someone else

No, it doesn't.  You using just basic trigonometry, and ignoring
the diameter of the mirror and some basic optics.



|                         |
|                         |
[[[[[[[[[[[[[[[[[[[[[[[[[[[

The | are wavelengths of light coming in (ie lambda)
and the [[[[[...[[[ is the mirror with diameter d.

The angular distance resolvable by the mirror is determined by its
ability to resolve the incoming wavelengths from one side of the
mirror to the other, being as they are going to be brought to a
focus.  So the angle resolvable from the top of a | that has
just hit the mirror to the other side of the mirror is

theta = lambda/d

But this is in radians and we want arc seconds. So we multiply by
206265, which is the number of arc seconds per radian.
This then gives us

theta = (lambda/d)*206265

Now we also multiply this by 1.22, which is the correction for the
Airy disk, which is cuased by natural diffraction, so our final
equation is:

theta = 1.22 * (lambda/d) * 206265

This equation can be found in any basic astronomy book dealing with telescopes
and will give us the theoretical limit of resolution for a telescope.
Once we have theta we can take the sine of it, and multiply by the
distance to the object which will give us the resolvable object
size at the distance in question.  Another way is to take W (the width of the
object) and divide it by R (the distance to it) and note that it is also a
radian value.  Thus we can obtain 1.22*(lambda/d) = (W/R).  A little rearranging
gives 1.22*R*(lambda/d) = W.  Putting in .88m for d, 6*10^-7m for lambda, and
5.83*10^12m (39AU) for R, we get W = 4.8*10^6m which equals 3007 miles.

Doing it the trigonometric way, we obtain theta = 1.7*10^-1 arc seconds.
(How was the 20 milliarcseconds previously quoted determined?  That would
apply only if the HST were looking in the extreme ultraviolet/Xray region.)
Take the sine of that, multiply by 39AU, convert to miles and the answer
comes out to be 3009 miles.

So I stand at my previous estimate of 3000 miles at 39AU.


Allan Bjorklund                   Co Administrator of the
[e-mail]      University of Michigan's
[e-mail]     MsDos Archives.
[e-mail]          terminator.cc.umich.edu 35.1.33.8

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

Date: 23 Nov 89 05:07:00 GMT
From: ux1.cso.uiuc.edu!ux1.cso.uiuc.edu!uxa.cso.uiuc.edu![e-mail]
Subject: Re: Shuttle Launch Orientation


I don't normally read sci.space, but now that I have a paper to do....
how come? Can some one send me the response they sent that guy?

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

Date: 23 Nov 89 20:33:39 GMT
From: mailrus!jarvis.csri.toronto.edu!ists!yunexus!utzoo![e-mail]  (Kieran A. Carroll)
Subject: Re: Why NASA wants to go to Mars

> [e-mail] (Jeff Goldader) writes:
>
> Am I the only one who nearly became physically ill after reading this?
> Is this truly what our space program has become, a bunch of administrators
> who are no longer aware that space exploration is meant for science?

This question strikes a strong chord in my mind, but not for the reason
that you would expect, Jeff.  I, for one, am concerned with the perception
(obviously shared by many people) that science is the only reason for exploring
space. I disagree strongly!

In my judgement, the >main< reason for exploring space is because we intend
that people live and work there, someday soon. We explore space in order to
prospect for resources, look for sites for bases and colonies, and get an idea
of what we'll be doing once we move out there. Science is merely one of the
many human activities that we'll be carrying out, once we get there.

The urge to make scientific discoveries is not, and >should not be mistaken to
be< the main driver for space exploration. At the moment in the U.S., however,
many people feel that it is or that it should be. It's difficult to justify an
enormously expensive space program just on the basis of its scientific merits,
though. As Richard Feynman commented when he was working on the commission
investigating the Challenger explosion, he had been led to believe that the space
shuttle was all about science; however, he hadn't noticed the sort of flood of
papers that one would expect in the scientific journals after spending billions
of dollars on a scientific endeavor. That is to say, when spending money on
space, you get very little scientific bang for your buck. If the only reason to
explore space is to get scientific results, then Van Allen would be right -- you
should limit yourself to sending out a few automated observatory spacecraft like
Voyager, rather than manned spacecraft, and use the money you saved funding
cancer research.

Science is just one of the things that people do. They do many other things, too.
Why should this one activity be considered especially applicable to space? Is
space an especially scientific place, by its nature? I don't think so. I think
that many people in the U.S. have simply lost sight of the vast potential of
space as an arena for human activity; the scientists have taken it over by
default. If this attitude had prevailed 500 years ago, the "exploration" of the
Americas by the Europeans would have amounted to sending a few botanical
sample-collecting mission across the Atlantic; then, once the main features of
American plant life had been classified, funding could have been diverted back
into more productive activities.



--

     Kieran A. Carroll @ U of Toronto Aerospace Institute
     uunet!attcan!utzoo!kcarroll [e-mail]

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

End of SPACE Digest V10 #272
*******************