Space & Astronomy/Space and Astronomy (October 1993).iso/mac/TEXT/SPACEDIG/V11_4/V11_417.TXT

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Subject: SPACE Digest V11 #417

SPACE Digest                                     Volume 11 : Issue 417

Today's Topics:
            Re: orbit definitions
    Re: Terraforming Venus (was: Manned mission to Venus)
            Re: Deep Space Relay Satellite
             Re: Mirrors in space
               Re: Oxygen prebreathing
              Re:  SPACE Digest V11 #412
               Re: Sagan vs. asteroids
                 Re: Magellan
              Re: The Vatican Connection
----------------------------------------------------------------------

Article: 18613 of sci.space:
Newsgroups: sci.space
Path: utzoo!henry
From: [e-mail] (Henry Spencer)
Subject: Re: orbit definitions
Date: Fri, 6 Apr 90 16:41:20 GMT

In article <[e-mail]> [e-mail] (Bart_Eleveld) writes:
>Would some kind soul(s) out there post definitions for the various types of
>orbits that are often talked about on the net; e.g., Clarke, geosynchronous,
>geostationary...

Well, let's see...

LEO        Low Earth Orbit, generally somewhere between 250-300 km
        (where air drag starts to get serious) and 1000 km (where
        the inner Van Allen belt starts to get serious).  Usually
        implicitly at a modest inclination to the equator, i.e. the
        lowest achievable from the launch site.

Polar orbit    Technically, an orbit with an inclination of 90 degrees.
        More usually, LEO with an inclination near 90 degrees.

Retrograde    Technically, an orbit with an inclination over 90 degrees.
orbit        More usually, an orbit with an inclination a lot over 90
        degrees.  Rare; pretty useless.

Geosynchronous    Any orbit synchronized with the rotation of the Earth, i.e.
orbit        with a period which is some multiple or divisor of 24 hours.
        Often used sloppily to mean geostationary.

Geostationary    The 24-hour equatorial orbit, where a satellite appears to
orbit        hang motionless in the sky.  Most comsats are found here,
        as are an assortment of others that want a constant view
        of the Earth (early-warning satellites, some weather sats)
        or just easy communications in high orbit (some astronomy
        satellites).

Clarke orbit    Some people prefer this to "geostationary", given that
        Arthur C. Clarke was the first person to realize how useful
        this orbit would be for comsats.

HEO        High Earth Orbit.  Rather vaguely defined.  Usually means
        anything from Clarke orbit up; the region between LEO and
        Clarke orbit is very unhealthy due to the Van Allen belts.

GTO        Geostationary Transfer Orbit, an orbit at modest inclination
        with perigee at LEO and apogee at Clarke orbit.  The usual
        intermediate step en route to Clarke orbit; Ariane launches
        directly into GTO, some other launchers launch into LEO and
        then boost into GTO.

Molniya orbit    Elliptical orbit at a specific inclination, 60-odd degrees,
        usually with apogee above the Northern Hemisphere.  The
        Earth's equatorial bulge normally causes the position of
        apogee&perigee to rotate in the plane of an elliptical
        orbit, but at the particular inclination of the Molniya
        orbits, this effect is zero and the apogee stays where
        it's put.  The Soviets use it for their Molniya comsats
        (whence the name) because it makes them more visible from
        very high latitudes than Clarke orbit.  The inclination is
        high enough to miss the worst part of the inner Van Allen
        belt, which is near the equator.

Sun-synchronous    Another effect of the Earth's bulge is rotation of the plane
orbit        of the orbit.  With the right combination of altitude and
        inclination, the rotation can be set to 360 degrees/year,
        keeping the orbital plane in a roughly constant relation to
        the Earth-Sun line.  For low orbits, the inclination turns
        out to be slightly over 90 degrees.  Very popular for remote
        sensing, weather, and spy satellites that want to view the
        ground at constant Sun angle.

>... Also, how much more
>energy (in relative terms) does it take to launch a payload to the west, or
>to the poles (N or S) rather than to the east?

The difference is the Earth's rotation, which is 460m/s times the cosine
of the latitude.  Launching due east from the equator gets you a free
460m/s contribution toward orbital velocity.  Launching due north or south
eliminates that freebie.  Launching due west adds 460m/s to the necessary
velocity.  Orbital velocity is about 8km/s, so the difference is not huge
but is quite noticeable.  This is why spaceports are at the lowest possible
latitudes and maximum payload is had by launching due east.
--
Life is too short to spend    |     Henry Spencer at U of Toronto Zoology
debugging Intel parts. -Van J.| uunet!attcan!utzoo!henry [e-mail]

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

Date: 17 May 90 17:12:54 GMT
From: crabcake![e-mail]  (Kenneth Arromdee)
Subject: Re: Terraforming Venus (was: Manned mission to Venus)

>Personally I'd use Venus as a toxic waste dump or an environmental
>testbed (just what is the effect of a gigaton bomb on a planet? would
>a nuclear winter really occur? etc). Too much effort to terraform.

Hmm.  Why not _deliberately_ start a nuclear winter on Venus?  Would that
cool it off enough to be of any help?
--
"And they shall be cast out where there is no outlet for their evil doings..."
    -- the Book of Ubizmo, on sinful uses of electricity

Kenneth Arromdee (UUCP: ....!jhunix!arromdee; BITNET: arromdee@jhuvm;
     INTERNET: [e-mail])

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

Date: 17 May 90 03:37:05 GMT
From: clyde.concordia.ca!news-server.csri.toronto.edu!utgpu!utzoo![e-mail]  (Henry Spencer)
Subject: Re: Deep Space Relay Satellite

In article <[e-mail]> [e-mail] (Doug Mohney) writes:
>What's the feasability of getting a mid-point "relay" station put into
>place to support transmissions of deep space probes such as Voyager and
>future missions?

Doubtful.  For one thing, they're not all going in the same direction!
Even now, we have two Pioneers and two Voyagers heading out of the
solar system in four different directions.

It is generally more cost-effective to build bigger and better receiving
systems here on Earth.

>Seems a waste for them to collect all that data and
>not be able to get access to it because either A) the 70 meter Deep Space
>Tracking network here on Mother Earth wasn't available

Building a few more antennas and receivers for DSN would fix this cheaply.

>or B) The wattage
>coming out of 'em in future years will be too low to be heard by anything
>sitting on the ground.

Not an issue.  The Pioneers and Voyagers will run out of electrical power
before they are beyond communication range.
--
Life is too short to spend    |     Henry Spencer at U of Toronto Zoology
debugging Intel parts. -Van J.| uunet!attcan!utzoo!henry [e-mail]

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

Date: 15 May 90 23:53:39 GMT
From: mcgill-vision!clyde.concordia.ca!news-server.csri.toronto.edu!torsqnt!lethe!yunexus!ists!helios.physics.utoronto.ca!physics.utoronto.ca![e-mail]  (Christopher Neufeld)
Subject: Re: Mirrors in space

In article <[e-mail]> [e-mail] (William Lewis) writes:
>In article <[e-mail]> [e-mail] (Daniel Ake CAROSONE) writes:
>
>|Just how big would this mirror appear to an earth-bound observer? Could
>|it put out enough light to be used for search and rescue, or something
>|requiring diffuse but noticeable light?
>
>  Scale it up a few times (or use a several separate sails,
>which would present no new engineering problems), make them parabolic,
>read lots of Larry Niven and the world is your oyster, ready to cook =8)
>(Well, that's a bit of an exaggeration, but I'm sure you could greatly
>disrupt climates in small areas by focusing on them all night and all
>day, especially the sidereal rhythms of the plants and such.
>
   Well, of course for this reason the doomsayers will keep such a
mirror from ever being built. Just think, it's perfectly possible for a
terribly (un)likely course of events to take place. After all, if the
mirror ballooned outward by exactly the right amount at the centre, and
something (cause unknown) made the extremely massive mirror rotate about
its vertical axis, and it wasn't cloudy on the ground below, and it was
pointed at part of the 30% of the Earth not covered by water, and if
nobody noticed any of this going on, or the scuttling charges built into
the mirror to cover this contingency (multiply redundant charges) all
happened to fail when the destruct was sent, well, then, somebody might
just get hurt. Much, much too dangerous in a world where nothing can be
done unless it can be proved that the chance of hurting something is
mathematically zero. The amount of light which hits the mirror and
which could get through to the ground for a 300km diameter reflector
amounts to about 71 terawatts.

   BTW, the mirror could not shine onto the ground in daytime, not and
still be balanced between solar flux and the Earth's gravity. The
geometry doesn't work.

>JESUS SAVES   |  [e-mail]       Seattle, Washington
>but Clones 'R' Us makes backups!  |  47 41' 15" N   122 42' 58" W


--
 Christopher Neufeld....Just a graduate student  |  "Spock, comment?"
 [e-mail]              |  "Very bad poetry
 [e-mail]          Ad astra! | captain."
 "Don't edit reality for the sake of simplicity" |

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

Date: 17 May 90 03:49:03 GMT
From: clyde.concordia.ca!news-server.csri.toronto.edu!utgpu!utzoo![e-mail]  (Henry Spencer)
Subject: Re: Oxygen prebreathing

In article <[e-mail]> [e-mail] (John Roberts) writes:
>... there has been mention of the risks from
>bubbles formed out of dissolved nitrogen and other gases. Oxygen bubbling
>never seems to be mentioned. Is that because the oxygen is chemically bound
>to the hemoglobin in the blood? ...

Virtually all of the oxygen in blood is indeed chemically bound; the blood's
ability to carry oxygen by just dissolving it is tiny by comparison.  I am
not sure why oxygen bubbles aren't an issue, on thinking about it, but the
obvious contributing factors are that microscopic oxygen bubbles would very
quickly react with surrounding materials (not good, but better than having
them stay bubbles!) and that nitrogen is very soluble in body fats.

The Bioastronautics Data Book does sound one unsettling note:  occasional
cases of the bends are seen even after many hours of prebreathing.
--
Life is too short to spend    |     Henry Spencer at U of Toronto Zoology
debugging Intel parts. -Van J.| uunet!attcan!utzoo!henry [e-mail]

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

From: [e-mail]
Date:     Thu, 17 May 90  12:50:43 EDT
Subject:  Re:  SPACE Digest V11 #412

>
> Date: 15 May 90 22:23:23 GMT
> From: attcan!utgpu!watserv1!maytag!watdragon!watyew![e-mail]
>  (Brian or James)
> Subject: Re: Why no ETs
>
>
>  The ETs avoid us because of our habit of tying
> string into knots involving only a single string,
> which is pornographic.
>                     JDN
>
> ------------------------------

I beg your pardon! Where I come from, the idea of tying a knot with
any MORE than a single strand of string is entirely repugnant. Why,
how would anyone know just what those intimately intertwined strands
might be up to, what with their very fibers rubbing against each
other in the most obscene way, and their spiral flutes pressed deep-]
ly into each other, undulating together under the influence of the
most minute motion, and what if it were a blue string with a red
string, or (heaven forbid) a green string with a yellow. No sir, no
decent folk will tolerate anything except strictly parallel strings.

                                            Marc Arlen
                                            AZM@NIHCU

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

Date: 17 May 90 06:16:25 GMT
From: bfmny0![e-mail]  (Tom Neff)
Subject: Re: Sagan vs. asteroids

>>>One should remember that Chairman Carl seems to have heavy-duty ulterior
>>>motives of the political kind these days, and that colors his views...
>>As did LBJ's, JFK's, Kruschev's, ...
>
>The point is, when LBJ talked about space, everyone *knew* this was a
>politician speaking.  But people still think of Sagan as a scientist,
>and incorrectly attribute primarily scientific motives to his statements.

Bull.  The man in the street only knows about him because of the TV
shows.  He's a telegenic public figure who speaks his mind, and does so
fairly well.

I have listened to him defend the international Mars mission on TV, and
he does so in a very straightforward way: he says Mars is the next great
challenge for human exploration, and that doing it in cooperation with
the Soviets is a great challenge for world peace.  No hidden motives
there!  And no pseudoscientific trappings.

The professional Sagan haters are not a whit less "political" than their
target -- they just have an opposing agenda, or think they do anyway.
And nobody has a monopoly on "colored" views.  The best you can hope for
is that space debaters at least know what their own views *are* and how
to express them ably.

Personally, I wouldn't take all (even most) of Sagan's recommendations
as gospel, but I'm glad he's here -- he says things that need to be said.

And I would never make remarks about "Chairman Henry" just because some
guy at the Toronto zoology lab presumes to speak his mind about space
related public issues.

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

Date: 17 May 90 15:33:01 GMT
From: usc!cs.utexas.edu!news-server.csri.toronto.edu!utgpu!utzoo![e-mail]  (Henry Spencer)
Subject: Re: Magellan

In article <[e-mail]> [e-mail] (Raymond Lister) writes:
>  >  Letter from James Duval in Pasadena...  "If Columbus or Magellan had
>  >  been victims of the same 'analysis paralysis' that seems to grip NASA
>  >  management, they'd still be pacing the decks pondering the weather,
>  >  food preservation, scurvy and the possible long-term effects of
>  >  constant seasickness and salt air exposure.  Fortunately, they were
>  >  explorers, not bureaucrats...
>
>
>Somebody should tell Mr Duval that Magellan died during his fleet's
>circumnavigaton of the globe.

It doesn't affect the argument.  Remember what Gus Grissom said, about
a month before he died in the Apollo fire:  "If we die, we want the
program to continue... The conquest of space is worth the risk of life."
--
Life is too short to spend    |     Henry Spencer at U of Toronto Zoology
debugging Intel parts. -Van J.| uunet!attcan!utzoo!henry [e-mail]

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

Date: 17 May 90 20:40:27 GMT
From: frooz![e-mail]  (Steve Willner, OIR)
Subject: Re: The Vatican Connection

From article <[e-mail]>, by
[e-mail]:
>      Last night (5-10-90) on _Prime Time Live_ there was a story on the
> observatory complex that the University of Arizona is planning to build.

The use of Mt. Graham for an observatory has become an extremely
controversial and emotional issue.  Prime Time Live presented only one
side.  (The phrase "hatchet job" comes to mind.)  I can't correct all
of the errors and omissions, but this statement:

>       The university was able to pressure Congress because of the backers of
> the project were quite powerful: the Max Planck Institute, the Smithsonian,
> and even the Vatican!  Pope John Paul II even met with university officials
> in 1987 to discuss the project.  (And by backing I mean funding.)

is incorrect as regards the Smithsonian.  (Mr. Brierly's quotation is
accurate; it is the claim made on PTL that is wrong.)  The Smithsonian
was involved in the testing to investigate Mt. Graham's quality as an
astronomical site, but Smithsonian takes no position on whether the
site should or should not be used for an observatory.  The Smithsonian
is not funding current efforts to develop the site.

For those interested in the latest news, earlier this week (90-05-15?),
the Federal Appeals Court overturned the District Court's injunction.
The University of Arizona plans to seek construction bids immediately
but will not start actual construction until after Congressional
hearings (scheduled for some time in June, I think).
-------------------------------------------------------------------------
Steve Willner            Phone [phone]         Bitnet:   willner@cfa
Cambridge, MA 02138 USA                 Internet: [e-mail]

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

End of SPACE Digest V11 #417
*******************