Space & Astronomy/Space and Astronomy (October 1993).iso/pc/text/spacedig/v11_0/v11_029.txt

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Subject: SPACE Digest V11 #29

SPACE Digest                                      Volume 11 : Issue 29

Today's Topics:
              Re: Imperial measurements
          Re: Galileo Update - 02/06/90 (Forwarded)
               RE: SPACE Digest V11 #25
            Re: metric vs. imperial units
        Re: More Info On SSX (What Is HR2674?)
                Voyager Update
          Re: Spacecraft drives and fuel efficiency
----------------------------------------------------------------------

Date: 8 Feb 90 18:11:02 GMT
From: mnetor!utzoo![e-mail]  (Henry Spencer)
Subject: Re: Imperial measurements

In article <[e-mail]> [e-mail] (John Roberts) writes:
>... As I
>understand it, there are (or recently have been) two acceptable formats
>for SI expressions, chosen because they produce "convenient" values for
>many everyday measures: centimeter-gram-second (arg! hate that one - and its
>in all my old books!) and meter-kilogram-second (the most common one now, and
>probably the "true" standard). ...

You're slightly confused here.  The problem is that the original metric
system did not tie down a lot of the details, particularly as scientific
and technical use spread into new areas like electromagnetism.  So there
was a wild profusion of different metric systems with different units in
the more esoteric areas.  For example, c-g-s and m-k-s defined different
units of energy, the erg and the joule respectively.  SI is the definitive
attempt to clean up the mess and settle on a single unified system.  There
is *one* acceptable format for SI expressions, and only one, basically a
cleaned-up version of m-k-s.  C-g-s is pre-SI and has nothing to do with it.

> Both of these formats suffer from an
>idiosyncrasy left over from the beginnings of the system - measures are in
>terms of either a hundredth of one basic unit (length) or a thousand of
>another basic unit (mass). Also, common usage includes units that are not
>part of SI, such as the liter (the vulgar term for the cubic decimeter).

Again, this is confused.  SI stresses 10^3 as the basic multiplier very
heavily, with tenths and hundredths strongly discouraged.  One or two
exceptions are made for everyday use, notably the centimeter and the liter,
but these are officially considered concessions to convenience and their
use for technical purposes is theoretically discouraged.

>It is very seldom that an astronaut desperately needs to know the diameter of
>a bolt in terms of an eighteenth-century survey of the distance from the
>North Pole to the Equator through Paris - it's more important to quickly
>pick the right size wrench. Thus, bolt sizes should be "number 1", "number 2",
>and so on...

In fact, this is what is normally done.  Sometimes there is a unit attached
to the arbitrary numbering, but it is often meaningless -- a "one-inch"
pipe has no dimension that measures one inch, and a "two-by-four" is never
two inches by four inches (not even when rough-sawed, nowadays).  As you
point out, in applications like this the actual measurement is not very
important, so long as X matches Y and the user has a feel for what the
numbers mean.  That's actually true of many of the non-metric uses in
aviation as well:  if the unit of altitude, the foot, magically changed
in size by 5% overnight, and all the instruments and charts changed to
match, almost nobody would notice.  The issue is seldom how many meters
up you are, but whether you are where others expect you to be, whether
you have adequate clearance above that mountain ahead, or whether your
rate of descent is too high for your landing gear to absorb.
--
SVR4:  every feature you ever |     Henry Spencer at U of Toronto Zoology
wanted, and plenty you didn't.| uunet!attcan!utzoo!henry [e-mail]

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

Date: 9 Feb 90 17:17:42 GMT
From: zaphod.mps.ohio-state.edu!usc!elroy.jpl.nasa.gov!jato!mars![e-mail]  (Ron Baalke)
Subject: Re: Galileo Update - 02/06/90 (Forwarded)

>In article <[e-mail]> [e-mail] (Jon Binkley) writes:
>>
>>When the craft makes its second Earth flyby, will it come close
>>enough to the sun that they have to cover up the antenna again,
>>or will it remain unfurlled for the rest of its journey?
>
The High Gain Antenna will be unfurled on 05/01/91 and remain unfurled
for the rest of its journey. Galileo at this time will have made its
1st Earth flyby and will be on its way for its first passage through
the asteroid belt.

 Ron Baalke                       |    [e-mail]
 Jet Propulsion Lab  M/S 301-355  |    [e-mail]
 4800 Oak Grove Dr.               |
 Pasadena, CA 91109               |

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

Date: 9 Feb 90 14:18:00 EST
From: "MRGATE::"A1::SULLIVANP"" <sullivanp"%mrgate."[e-mail]>
Subject: RE: SPACE Digest V11 #25
To: "space+" <[e-mail]>

From:    NAME: Patrick Sullivan
    FUNC: R640
    TEL: [phone],AV560  <SULLIVANP AT A1 AT UVAX1>


 PLS UNSUBSCRIBE ME

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

Date: 9 Feb 90 06:06:01 GMT
From: cs.utexas.edu!samsung!munnari.oz.au!cluster!metro!otc![e-mail]  (Greg Wilkins)
Subject: Re: metric vs. imperial units

In article <[e-mail]> [e-mail] (Dan Tilque) writes:
>
>And in the air, you auger into the side of the mountain you didn't expect
>to be there.
>
>More points you didn't make:
>
>1. The Shuttle pilots have thousands of hours flying, every one of
>which was done using nm and feet.  These units are ingrained into their
>bones.  Switching to km and meters would be disastrous.
>
>2. All the support equipment for lauch and landing are calibrated in nm
>and feet.  A lot of it is standard aviation equipment like radar.
>Converting this would be an unholy mess as well as pointlessly
>expensive.
>
>---

You guys just keep making excuses!!!!   Yes an entire country can convert
from imperial to metric -> Eg Australia and we have the safest airline in
the world.  If any airline or spaceflight relies on the pilots ability to
do mental arithmetic in his native units, then it aint safe!!

The whole point is that metric has many big points in its favour:

 - The rest of the world is using it

 - To some extent, when designing physical systems, recurring decimal
   places can be avoided, hence round off errors can be reduced.

 - To do any sort of calculation by computer, metric is by far better than
   imperial, thus reducing the possibility of program error.


I am told that America is the most inwardly looking nation on the planet,
and boy does it show!!!   If you guys are serious about international
cooperation you have to pick a set of common units (for more cost and
saftey reasons), and when it comes to the choice metric wins hands down.


By the way, Now that I have been hollier than thou! I will have to say that
changing over is a long process, but that living with two systems is not
that hard.  Australia changed over to metric when I was < 10 years old,
but it still means nothing to me when somebody says " I am 185 cm tall" or
that they got 9 litres per hundred kms.

scuba diver, and I learn diving through PADI which is American based and
teaches the course in PSI and feet.  As a result, I think of all my
recreational diving in imperial (ie I KNOW how deep 45ft is, but I only
know how deep 15m is).  However, when I go DEEP diving (not unlike being an
astronaut - pressure problems and you cant go home without time and
equipement with killing yourself), i use metric.  When I am stress loaded
at 58m depth, narced out of my scull, and trying to perform a difficult
task, I know that I am under 1 + 5.8 atmospheres pressure, so I use my air
6.8 times faster than on the surface!!  I can work it out in metric, but
would not stand a chance in imperial.   BUT even though I can do the mental
arithmetic, you don't rely on it -> before you do a deep dive you have
a well learn dive plan, you have alternative dive plans for longer/deeper
dives, you have it all written on your fins or slate, you have a dive
computer, you have a dive buddy, on difficult dives you have comms with the
surface and you never rely on mental calculations.  But metric would allow
me to if I ever needed to  much easier than imperial -> Not due to my
education or upbringing, but due to its intrinsic relationships between
units and the physical world!


Anyway, to sum up, stop making excuses, start making changes, put a bit
of effort in , and maybe, just maybe you will be able to talk technical
with the rest of the world in twenty years or so!

PS. Who does calculations in degrees rather than radians anyway???





[e-mail]

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

Date: 9 Feb 90 20:49:12 GMT
From: swrinde!zaphod.mps.ohio-state.edu!samsung!umich!ox.com!itivax!vax3![e-mail]  (Allen W. Sherzer)
Subject: Re: More Info On SSX (What Is HR2674?)

In article <[e-mail]> [e-mail] (John A. Weeks III) writes:
>I have seen HR2674 mentioned, but I don't know what it is.  Could
>someone please give me a 1 or 2 sentence summary?  Thanks.

HR 2674 is the Space Transportation Services Purchase Act. It was written
by the Tucson NSS chapter and introduced by Ron Packard of CA.

It mandates that the government send up all its payloads using commercial
launch services. The only exceptions will be payloads certified to require
government launch.

The upshot of the bill is that it will allow commercial launch vendors to
mass produce vehicles and bring prices down.

If you want, I can get you a copy of the bill. It is a VERY important piece
of legislation.

   Allen

----------------------------------------------------------------------------
| Allen W. Sherzer     | Cthulhu for President -                           |
|  [e-mail]         | If you're tired of choosing the LESSER of 2 evils |
----------------------------------------------------------------------------

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

Date: Fri,  9 Feb 90 15:56:18 PST
From: Peter Scott <[e-mail]>
Subject: Voyager Update
X-Vms-Mail-To: EXOS%"[e-mail]"
Lines:  120

Extracted from NASA' _Voyager Bulletin_, Mission Status Report #98, January
29:

On February 14, Voyager 1 will take advantage of an historic and unique
opportunity to image most of the solar system's planets, taking a final
look back at where the Voyagers have been and showing Earth among its fellow
planets.

Earth, Venus, Jupiter, Saturn, Uranus and Neptune will be targeted in a
sequence of wide- and narrow-angle images.  Mars may be visible, but it
will be a slim crescent close to the Sun, while Mercury will be masked in
the Sun's glare.  Pluto is too far away and too small to be imaged.  From
Voyager 1's viewpoint, the planets will appear to be clustered along the
constellation Eridanus (The River).

Voyager 1 will be approximately 40 [AU] from Earth and 32 degrees above
the ecliptic plane at an ecliptic longitude of 242 degrees.  A series of
about 64 images will be taken, beginning with Neptune.  The wide-angle frames
will be taken through clear filters, while the narrow-angle frames, each
centered on a planet, will be shuttered through blue, violet, and green
filters.  The spacecraft will roll to take images of regions that would
otherwise be obscured by the spacecraft's high-gain antenna.  Images of
the inner planets will be mosaicked around the Sun to avoid direct sunlight.
The final wide-angle frame will be centered on the Sun.

Due to tracking schedules, the images will be recorded on board the spacecraft
and returned to Earth in late March.  Several weeks will then be needed
to process the images to reveal as much detail as possible.  Most of the
planets will be smaller than a pixel in size; however, Jupiter may be as
large as four pixels.  (Voyager's imaging frame is 800-by-800 pixels.)

Due to the scale, it is unlikely that the entire set of images can be mosaicked
to produce for publication a single photograph showing all the planets
stretched from Jupiter to Neptune.  A display of this mosaic would requirea
wall 100 to 150 feet long, depending on the chosen size of the individual
prints.  Imaging team members hope to release at least the central frames
showing Earth, Venus, and perhaps Mars together.

Voyager 1 was chosen over Voyager 2 for this task due to operational
considerations.  Another factor is the fact that Jupiter would be too close
to the Sun to be visible from Voyager 2's point of view this spring.

Although the ultraviolet spectrometer is still on, the sunlight will be
too bright to allow observations during this imaging sequence.  The infrared
spectrometer and photopolarimeter instruments will not be on.  The only
potential damage from pointing these optical instruments too close to the
Sun is that the shutter blades of the wide-angle camera might warp due to
the increased heat of the sunlight focussed on the blades.


UPDATE

Contact with Voyager 1 has been normal since a partial loss of contact last
fall.  On October 23, Voyager 1 stopped sending its telemetry signal, by
which science and engineering data are transmitted.  The carrier signal,
a single frequency used to track the spacecraft's location, continued.
Commands were sent to reset the spacecraft's telemetry modulation unit.
Controllers waited 11 hours for the signal to reach the spacecraft and a
return signal to reach Earth before they knew that full contact had been
restored.  Flight controllers had no explanation for the one-time event,
but there was smoe conjecture that it was related to high solar activity.
Several other spacecraft also experienced computer problems during last
fall's spate of huge solar flares.  The high-speed particles ejected by
solar flares can cause computer bits to "flip" from the desired position.


NEPTUNE RESULTS

The Voyager science teams have submitted their "30-day reports" on the Neptune
encounter, as required in their contracts with NASA, and these reports have
been published in the December 15, 1989 issue of _Science_ magazine.  As
the papers were being written, data analysis continued, bringing new
information to light.  Changes from what has been previously reported in
the _Bulletin_ are summarized below.

Neptune's rotation rate is now cited as 16 hours 7 minutes +/- 1 minute,
based on data from the planetary radio astronomy instrument.

Winds near the Great Dark Spot are now believed to be a rip-roaring 560
[m/s] (1230 [mph]), the strongest winds yet measured in the solar system.
(Voyager measured winds on Saturn up to 500 [m/s] or 1100 [mph].)

The cloud streaks seen near latitudes of 27N and 71S are estimated to be
about 100 km (60 mi) and 50 km (30 mi) respectively, above the cloud banks
on which their shadows were seen.

Temperatures at high altitudes in Neptune's stratosphere have been measured
to be about 750K.

The tilt of Neptune's magnetic field is now given as 47 degrees from the
rotational axis, while the offset of the magnetic pole from the center of
the planet is 0.55 radius.  The strength of the surface magnetic field varies
from more than 1 to less than 0.1 gauss.

As Voyager 2 passed through the ring plane, the maximum impact rate from
ring particles was measured at 250 hits per second.

Triton's surface temperature has been revised to 38K (about -391F), while
the surface pressure is now believed to be about 14 microbars.  Methane
and nitrogen form a thin veneer on the moon's surface, while the underlying
topographic features are suspected to be formed of water ice.  Methane and
nitrogen ices are too weak to support their own mass for very long in such
formations.

At least six small, previously unknown satellites, ranging in diameter from
54 to 400 km, have been identified in Voyager images.  [...]  Names will
be assigned by the nomenclature committee of the [IAU].

Researchers will continue to publish science results of the Voyager mission
in professional journals such as _Geophysical Research Letters_ [gotta be
an oxymoron there - PJS] and the _Journal of Geophysical Research_ for many
years to come.  The Voyager mission has provided a unique data set for
comparative planetology; four planetary systems studied by the same instruments.


Peter Scott ([e-mail])

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

Date: 9 Feb 90 17:34:18 GMT
From: zaphod.mps.ohio-state.edu!samsung!cs.utexas.edu!jarvis.csri.toronto.edu!utgpu!watserv1!ria!uwovax![e-mail]  (Ket M'thau)
Subject: Re: Spacecraft drives and fuel efficiency

In article <[e-mail]>, [e-mail] (H Keith Henson) writes:
> A civilization actually able to travel between the stars it seem likely to
> me is going to be tapping stars for energy.  We already know of one way to
> do that, build a bunch of monster solar power plants, and convert the
> energy to laser light.  Lasers will levitate against 1g, and as someone
> (Henry?) recently said, a year at one gee is the speed of light.
> (How to stop is left as an exercise)  Keith Henson


...Actually, the accelleration for a given force isn't constant as velocity
increases...  To accellerate at one gee when you're at half the speed of light
takes over half again as much force as the same accelleration from rest does


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End of SPACE Digest V11 #29
*******************