Space & Astronomy/Space and Astronomy (October 1993).iso/mac/TEXT_ZIP/spacedig/V11_0/V11_006.ZIP/V11_006

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Date: Sat,  3 Feb 90 01:34:16 -0500 (EST)
Subject: SPACE Digest V11 #6

SPACE Digest                                       Volume 11 : Issue 6

Today's Topics:
              RE: SPACE Digest V10 #452
            vol10 #16 is missing.
Re: Magellan Update - 01/17/90: really about metric vs. imperial units
          Re: Spacecraft drives and fuel efficiency
Re: Magellan Update - 01/17/90: really about metric vs. imperial units
              Re: Temperature of Space?
              Re: NASA 905 name
    More results on third and fourth Soviet Space walks this year
----------------------------------------------------------------------

Date:     Fri, 02 Feb 90 11:32:38 -0900
Sender: <[e-mail]>
Reply-To: <[e-mail]>
From: "Ken Burnside"  <[e-mail]>
Subject:  RE: SPACE Digest V10 #452

PLEASE unsubscribe me from this list.  I have asked before, and am still
getting deluged.  If and when your server dumps them on me in reasonable
batches, I may be able to subscribe again.

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

Date:     Fri, 2 Feb 90 14:20 EST
From: <[e-mail]>
Subject:  vol10 #16 is missing.

Help!
In reviewing the archives of all previous postings, I noticed that
Volume 10:#16 is not there.  This is the issue containing the raw
data for the so-called Mars face.

I'm trying to get this particular issue again, as I accidentally
erased the previous posting from my account.

What happened to it?


Thanks in advance,
[e-mail]

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

Date: 31 Jan 90 14:56:16 GMT
From: att!drutx!druhi![e-mail]  (Neal D. McBurnett)
Subject: Re: Magellan Update - 01/17/90: really about metric vs. imperial units

In discussing why he thinks nautical miles are an advantageous unit
for navigation, John writes this:

From article <[e-mail]>, by [e-mail] (John H. Kim):
> ...  So instead of measuring
> the arc distance on a mercador(sp?) projection to figure out your
> great circle route length, you can just use the Lat/Long of your start
> and end points with some trig to get the distance.  I suspect there are
> other advantages as well.

Wait a minute.  As I understand your reasoning, first you use latitude
and longitude for the start and end points in a classy spherical
trigonometry equation to find the arc distance between the points.
Then you multiply the arc distance (whether in radians or degrees) by
60 to get the number of arc minutes, which equals the number of
nautical miles.

After using several trig functions to get the arc distance, why is it a
hassle to multiply the number of degrees by 111.1 to get kilometers
rather than multiplying by 60 to get nautical miles?

Remember that you must go to even more trouble if you want an answer
accurate to more than a few tenths of a percent, because the earth is
not spherical.

Also, while you reflect on the fact that nautical miles were defined
with respect to the earth and navigation, remember that the meter
was defined as one ten millionth of the distance from the north pole to
the equator, so it is easy to remember that the earth is about 40,000
km around.

I think it is long past time for NASA and other government agencies to
start using metric units, and I see practically no benefit from a
computational standpoint to the use nautical miles.

-Neal McBurnett // AT&T Bell Labs, Denver // [e-mail], att!druhi!neal

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

Date: 2 Feb 90 18:27:55 GMT
From: zaphod.mps.ohio-state.edu!wuarchive!mailrus!jarvis.csri.toronto.edu!utgpu!utzoo![e-mail]  (Henry Spencer)
Subject: Re: Spacecraft drives and fuel efficiency

In article <[e-mail]> [e-mail] (Mark Gellis) writes:
>A friend of mine pointed out that the Daedelus design is a highly
>inefficient fusion engine.  It is, he claims, based on the bomb-version
>of fusion propulsion.  He suggested that you could get a much higher
>Isp by using fusion power to superheat reaction mass--hydrogen, probably--
>and then spew it out at very high velocity...

Um, what does he think Daedalus was doing?  It was using fusion reactions
to superheat reaction mass, mostly hydrogen, and then spew it out at very
high velocity.  It happened to be doing this in a rather bursty way rather
than with a continuous reaction.

The Daedalus engine was not a terribly efficient one, but that's because
it was designed with the constraint of being as close to current technology
as possible.

>... Actually, if you can get
>controlled fusion at all (meaning you can control magnetic fields and
>deal with multi-million degree temperatures) it sounds like it would be
>more efficient this way...

Much depends on details.  Remember that a big continuous-fusion reactor
is likely to be heavy, and that matters.  Practical interstellar missions
need not only very high exhaust velocities, but also respectable acceleration,
otherwise the acceleration phase simply takes too long.  Accelerating to
0.1c at 0.001G takes most of a century; a substantial fraction of one
gee is pretty much a requirement.  (The rule of thumb for such calculations,
incidentally, is that the speed of light is roughly one gee-year.)

>I know that, in theory, you cannot get an Isp
>better than 30,000,000 (because it means you have an exhaust velocity of
>the speed of light), and I am curious as to how much you could get...

My recollection is that fusion peters out at a few million.  There is an
inherent limit because the fusion reaction requires a specific mass of
fusion fuel to produce a given amount of energy.  The net mass consumption
has to include that fuel mass.  Phrased another way, the exhaust includes
the "burned" fusion fuel -- keeping it on board just adds dead weight --
and this limits the exhaust velocity.  Unless I've goofed up on the math,
it turns out that dumping the spent fuel at low velocity while using the
fusion energy to accelerate other mass to high velocity always gives a
net loss in exhaust velocity.  The theoretical limit for fusion is when
all of the fusion energy goes into accelerating the fusion products.

If you want really high exhaust velocities, antimatter is better.  The
idea of antimatter rockets is now being taken very seriously.  We
(probably) know how to make antihydrogen cheaply enough to make them
viable.
--
1972: Saturn V #15 flight-ready|     Henry Spencer at U of Toronto Zoology
1990: birds nesting in engines | uunet!attcan!utzoo!henry [e-mail]

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

Date: 2 Feb 90 22:16:31 GMT
From: skipper![e-mail]  (Mary Shafer (OFV))
Subject: Re: Magellan Update - 01/17/90: really about metric vs. imperial units

In article <[e-mail]> [e-mail] (Neal D. McBurnett) writes:

[In reference to my comment that civil aviation uses feet for altitude
and knots for airspeed and John's (lost the last name) exegisis on why
knots]

   Also, while you reflect on the fact that nautical miles were defined
   with respect to the earth and navigation, remember that the meter
   was defined as one ten millionth of the distance from the north pole to
   the equator, so it is easy to remember that the earth is about 40,000
   km around.

   I think it is long past time for NASA and other government agencies to
   start using metric units, and I see practically no benefit from a
   computational standpoint to the use nautical miles.

We're not talking about NASA and other government agencies here, we're
talking about every airliner and every private airplane in the world.

Feet and knots are the standard, good, bad, or indifferent, in civil
aviation worldwide.

Actually I wasn't defending this, I was just pointing out that even the
most metric nations still use feet and knots in the air.  France, even.

They also use English.  So?  It's just the standard.

--

Mary Shafer  [e-mail] or ames!skipper.dfrf.nasa.gov!shafer
         NASA Ames Dryden Flight Research Facility, Edwards, CA
                   Of course I don't speak for NASA

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

Date: 3 Feb 90 04:26:49 GMT
From: calvin.spp.cornell.edu![e-mail]  (John Sahr)
Subject: Re: Temperature of Space?

A couple recent postings have suggested that there is something
unusual about the notion of "temperature" when applied to the
interplanetary medium.  This is not so.  The temperature of the very
tenuous fluid that occupies the space between planets is defined
exactly the same way as it is for the air we breathe, namely, the
average kinetic energy of the thermal motions of the particles.  By
"thermal motions" I mean the motions of the particles in the frame of
reference where the average velocity is zero.

There is nothing mysterious about it.  Because the interplanetary
fluid is so tenuous, it has very little heat capacity, and also very
little inertia: satellites coast through it for years before losing
enough energy to fall back to Earth.  The upper atmosphere is not
negligible, though.  There is enough of it to cause significant
scattering for radar analysis.  Arecibo, for example, can measure
fairly accurately the temperature and density, and even composition of
the plasma that the Shuttle flies through, and use that information to
make inferences about the state of the neutral atmosphere at the same
altitude.  Such "incoherent scatter" radar analysis has been
accomplished for just over 30 years in the scientific community, and
somewhat longer in the military world; in the latter case, the
ionosphere provides confusion which obscures the desired target.
--
John Sahr,                   | Electrical Engineering - Space Plasma Physics
[e-mail] | Cornell University,         Ithaca, NY  14853

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

Date: 2 Feb 90 17:11:33 GMT
From: nyevax.CAS.ORST.EDU![e-mail]  (Bart Eleveld)
Subject: Re: NASA 905 name

In article <[e-mail]> [e-mail] (Leif Kirschenbaum) writes:
>How about Little John?  He carried Robin Hood across the river early in the tale
>of Robin Hood.  In addition, both of them were pretty poor, as NASA seems to
>be compared to the total U.S. budget.
>Also, the hyperbole of calling a big aircraft "Little John" is sort of neat.
>
I'm afraid you have your Robin Hood characters mixed up a bit.  It was Friar
Tuck who carried Robin Hood across the river (and then forced RH to carry him
back).  I would have suggested Friar Tuck as a name for NASA 905 but the
potential for spoonerisms by TV news announcers was just too horrible a prospect
to contemplate.  Little John and Robin had the duel with staffs on the bridge
which resulted in Robin being dumped in the river.  Now there's a hyperbole we
can avoid with the shuttle.  Luckily 905 usually doesn't fly over water (or does
it cut across the Gulf of Mexico on its way to KSC?).

Bart Eleveld
[e-mail]

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

Date: Sat, 3 Feb 90 01:24:04 EST
From: Glenn Chapman <@ll-vlsi.arpa:glenn@vdd>
To: [e-mail], [e-mail],
        [e-mail], [e-mail],
        [e-mail], [e-mail]
Subject: More results on third and fourth Soviet Space walks this year

     More information has been released about the fourth Extra Vehicle
Activity that Alexander Serebrov and Alexander Viktorenko made from the Mir
space complex on Feb. 1. As noted previously the main activity there was
the first test flight of the Soviet Manned Maneuvering Unit, called a
Space Bicycle or Icarus.  Serebrov took the 220 Kg (484 lbs.) Icarus further
than originally expected, some 30 meters (99 ft.) from Mir (preflight
statements had called for a 5-10 meter test).  The main core of Mir itself
is some 13 meters long, though with the Kvant 1 module and the Soyuz TM
at one end plus Progress M-2 at the other the total axial length is about
30 meters, the distance travelled.  He tested the 32 compressed air rockets
of the system, stability at both low and high velocity, and the retro
rockets (the "breaking system").  During this time Viktorenko was
controlling the teether to ensure no problems, and apparently did tests of
checking the flight with it.  In addition Viktorenko filmed the Icarus
on a video camera.  Currently the crew is checking out the space suits in
preparation for Monday, Feb. 5th fifth and final space walk of this
mission.  Vikorenko will then fly the Icarus a distance of some 60 meters
from the station.  (Radio Moscow Jan 30 - Feb. 2, TASS announcements of Jan
31-Feb. 1)
     [Here is a report on the third space walk which I was not able to post
due to my travels].  The third space walk of Serebrov and Viktorenko began
on Jan. 26th at 15:09 Moscow Time (7:09 EST) when they exited the new large
(more than 1 meter diameter) airlock at the end of the Kvant 2 module for
the first time (all the previous walks had used the smaller airlock on Mir
itself).  This EVA was also the first to test out the new Orlan DMA space
suits which will be used in future missions.  To begin with the crew
removed an antenna section from the Kurs docking radar system on the Kvant
2 module (which is docked perpendicular to the main body of the Mir
station).  The cosmonauts then mounted television cameras on the Kvant 1
module at the rear end of Mir which can be maneuvered to observe the
outside of the station.  They also checked the exterior of the Kvant 2
module, especially the solar panel section that had initially failed to
deploy properly during after the launch in Nov. '89.  Total space walk time
was 3 hours, 2 minutes.  On Jan. 29th Serebrov and Viktorenko held a series
of 5 lectures for school children from orbit in memory of US
teacher/astronaut Christie McAuliffe who died in the Challenger failure
some four years ago.  Serebrov, who is president of the Soyuz Soviet Youth
Space Society, told them about the life support system, while Viktorenko
(mission commander) described the space suites.  TV shoots of the outside
of Mir were given using the camera system just mounted two days before in
the fourth EVA.  Crystal growth experiments were also shown.  Tapes of
these lessons are going to be made available to other countries.  (Radio
Moscow, Jan 25-29th, TASS Jan 25, 26, 29th - Thanks to John Biro for the
TASS reports).
     One interesting point to note is that currently the Russians have over
400 hours of manned EVA time, while the US has about 300 hours.  However,
over 50%, some 170 hours, of the US total was not in zero G but rather on
the Lunar surface.  That is what you get when you run a space station
program for some 19 years.  Their space walk time is rising rapidly on Mir
also, indicating that as time goes on they feel more confident of just what
people can do for them in space.

                                                       Glenn Chapman
                                                       MIT Lincoln Lab

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

End of SPACE Digest V11 #6
*******************