Space & Astronomy/Space and Astronomy (October 1993).iso/pc/text/spacedig/v16_3/v16no375.txt

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Date: Sat, 27 Mar 93 05:30:35
From: Space Digest maintainer <[e-mail]>
Reply-To: [e-mail]
Subject: Space Digest V16 #375
To: Space Digest Readers
Precedence: bulk


Space Digest                Sat, 27 Mar 93       Volume 16 : Issue 375

Today's Topics:
                       Space Ship - Outer Space
Speculation: the extension of TCP/IP and DNS into large light lag enviroments
                 SS-25 conversion launches satellite
                STS-55 (Columbia) abort (was Aurora?)
                          Tethered satellite
           The Ninth Planet (Was: Space Ship - Outer Space)
                            Time Machine!?
            Timid Terraformers (was Re: How to cool Venus)
                         Why is Venus so hot?

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

Date: Fri, 26 Mar 1993 19:31:03 GMT
From: "Phil G. Fraering" <[e-mail]>
Subject: Space Ship - Outer Space
Newsgroups: sci.space

[e-mail] (David Lai) writes:

>Hi netters,

>    I remember that a spacecraft was around the nineth planet some
>years ago.  Is there any spacecraft travelling beyond the nineth planet
>now?  If so, what discovery has it make?  Can it still communicate with
>the Earth?

>                            David.

A spacecraft called Voyager II flew past the current ninth planet
a couple years back; it was flying very fast, as is typical for
flybys. It's made lots and lots of discoveries: Neptune was the
fourth planet it flew past.

Keep in mind that currently Neptune is the ninth planet, and
Pluto the eighth. NASA and JPL are currently looking at trying
to send a probe to Pluto while it's still inside of Neptune's
orbit and/or relatively close to the sun, because after it moves
away, and becomes the ninth planet again, the atmosphere freezes
out and it becomes boring.

--
Phil Fraering         |"...drag them, kicking and screaming,
[e-mail]|into the Century of the Fruitbat." - Terry Pratchett,
                       _Reaper Man_

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

Date: Fri, 26 Mar 1993 19:35:45 GMT
From: "Phil G. Fraering" <[e-mail]>
Subject: Speculation: the extension of TCP/IP and DNS into large light lag enviroments
Newsgroups: alt.internet.services,sci.space

[e-mail] (M. Sean Bennett) writes:

>As man moves outward into space it will become essential to provide an information
>structure for communication of data.

>    The current set of protocols make no alowance for light 'lag' between
>targets of wide divergence. (Mars-Earth). The current DSN is expensive to
>use for continous data flow. If however we could use a series of store and
>forward systems for data - we have no mechanism to ensure that the data is
>delivered securely (Appart from ad-hoc protocols constructed by NASA).

>    We need some form of ISO standard (I know they are hard to set,
>but if NASA/GlavCosmos publish a protocol it will be the defacto standard)

>    How are we to devide the domains to deal with other worlds?

>        (yes I know this sounds mad - but if we have not made some
>    form of descision we will have moonbase.nasa.gov - implictly
>    making that instalation part of the USA..a dangerous precedent)

Why is it a dangerous precedent? Should NASA or the CIS be building bases
that aren't under any jurisdiction?

You seem to be under the impression that not only was the COPOUS treaty
signed, but that it was a "good thing." If so, perhaps you should look
for someone who isn't a Marxist to teach an economics course for you.

>These are just my random thoughts. I make no claims that they hold great
>thought or meaning.

Neither do I. I won't even claim that I'm not flaming.

>    [e-mail]

>Sean

--
Phil Fraering         |"...drag them, kicking and screaming,
[e-mail]|into the Century of the Fruitbat." - Terry Pratchett,
                       _Reaper Man_

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

Date: 26 Mar 93  09:26:00
From: [e-mail]
Subject: SS-25 conversion launches satellite
Newsgroups: sci.space

The new Russian launcher is probably not a "START" launcher, but rather
a "STAR" launcher. I would imagine that the AP added an extra letter, with the
confusion of the Russian word "start" meaning launch.

BTW, any USAF types out there know if this new rocket will be designated the
SL-18?

--- Maximus 2.01wb

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

Date: Fri, 26 Mar 1993 20:04:57 GMT
From: Henry Spencer <[e-mail]>
Subject: STS-55 (Columbia) abort (was Aurora?)
Newsgroups: sci.space

In article <[e-mail]> [e-mail] (Gary Coffman) writes:
>>>holddowns can't keep the Shuttle on the pad against both main engines and
>>>boosters.
>>There's no good reason why they couldn't.  The Saturn V holddowns could,
>>and did.  And they didn't even use pyrotechnic release...
>
>Yeah, but how much re-engineering would be involved, not just to the
>pad, but to the Shuttle structure as well? Beefing the pad is relatively
>easy, and I guess the new holddowns could be on the boosters rather than
>the Shuttle structure, but it would be a nasty problem.

Gary, the holddowns *are* on the boosters, not the orbiter.  Neither the
orbiter nor the ET has any structural connection to the pad; the whole
stack sits on the SRBs, which are bolted to the pad.  (Explosive nuts
blow to release them.)  I doubt that you'd need to change the pad very
much, since it was built for Saturn Vs.  The boosters probably would
need some attention, but the question was asked in the context of
liquid-fuel boosters, which would have to be a full redesign anyway.

>On the other hand, if liquid boosters were used (in your dreams), the
>extra holddowns would be *necessary*...

Not strictly necessary.  The "hold it down until everything looks good"
approach is not universal in launchers, even liquid-fueled ones; Delta
has never worked that way.  Probably a good idea, though.
--
All work is one man's work.             | Henry Spencer @ U of Toronto Zoology
                    - Kipling           |  [e-mail]  utzoo!henry

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

Date: 26 Mar 93  09:28:52
From: [e-mail]
Subject: Tethered satellite
Newsgroups: sci.space

So what did happen with the tethered satellite that was to have been launched
on March 18  by a Delta II from the Cape?

--- Maximus 2.01wb

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

Date: 26 Mar 1993 20:16 UT
From: Ron Baalke <[e-mail]>
Subject: The Ninth Planet (Was: Space Ship - Outer Space)
Newsgroups: sci.space

In article <[e-mail]>, [e-mail] (David Lai) writes...
>Hi netters,
>
>    I remember that a spacecraft was around the nineth planet some
>years ago.  Is there any spacecraft travelling beyond the nineth planet
>now?  If so, what discovery has it make?  Can it still communicate with
>the Earth?

When Pluto crossed inside of Neptune's orbit in 1979, Neptune became the
farthest planet from the Sun, so technically it is the ninth planet.  Pluto will
cross back over in 1999 to reclaim this title.  Voyager 2 flew by Neptune
in 1989, and among its discoveries was that Neptune had a Great Dark Spot
similar to Jupiter's Great Red Spot, and active geysers were found on Triton.
There are four spacecraft that have left the solar system (Pioneer 10 & 11,
Voyager 1 & 2), and their main purpose now is to find the heliopause
boundary.
     ___    _____     ___
    /_ /|  /____/ \  /_ /|     Ron Baalke         | [e-mail]
    | | | |  __ \ /| | | |     Jet Propulsion Lab |
 ___| | | | |__) |/  | | |__   M/S 525-3684 Telos | Don't ever take a fence
/___| | | |  ___/    | |/__ /| Pasadena, CA 91109 | down until you know the
|_____|/  |_|/       |_____|/                     | reason it was put up.

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

Date: 26 Mar 1993 11:19 PST
From: SCOTT I CHASE <[e-mail]>
Subject: Time Machine!?
Newsgroups: sci.space

In article <[e-mail]>, [e-mail] (Dave Jones) writes...
>
>Its all been theory.  There were claims that certain situations, which
>weren't necessarily practical to engineer, would result in 'timelike world
>lines' which is jargon for going into your own past.  The latest one to

You mean "Closed Timelike Curves".

>appear suggests that one method, involving wormholes connected together and
>move around each other at high speed, would fail because (if memory serves)
>the quantum effects resulting from bringing them back together would destroy
>the setup, in the same way that black holes are supposed to evaporate over
>time.

Here is what the sci.physics FAQ says on the subject:

TIME TRAVEL - FACT OR FICTION?                  updated 23-MAR-1993
------------------------------                  original by Jon J. Thaler

    We define time travel to mean departure from a certain place and
time followed (from the traveller's point of view) by arrival at the same
place at an earlier (from the sedentary observer's point of view) time.
Time travel paradoxes arise from the fact that departure occurs after
arrival according to one observer and before arrival according to another.
In the terminology of special relativity time travel implies that the
timelike ordering of events is not invariant.  This violates our intuitive
notions of causality.  However, intuition is not an infallible guide, so we
must be careful.  Is time travel really impossible, or is it merely another
phenomenon where "impossible" means "nature is weirder than we think?"  The
answer is more interesting than you might think.

THE SCIENCE FICTION PARADIGM:

    The B-movie image of the intrepid chrononaut climbing into his time
machine and watching the clock outside spin backwards while those outside
the time machine watch the him revert to callow youth is, according to
current theory, impossible.  In current theory, the arrow of time flows in
only one direction at any particular place.  If this were not true, then
one could not impose a 4-dimensional coordinate system on space-time, and
many nasty consequences would result. Nevertheless, there is a scenario
which is not ruled out by present knowledge.  This usually requires an
unusual spacetime topology (due to wormholes or strings in general
relativity) which has not not yet seen, but which may be possible.  In
this scenario the universe is well behaved in every local region; only by
exploring the global properties does one discover time travel.

CONSERVATION LAWS:

    It is sometimes argued that time travel violates conservation laws.

For example, sending mass back in time increases the amount of energy that
exists at that time.  Doesn't this violate conservation of energy?  This
argument uses the concept of a global conservation law, whereas
relativistically invariant formulations of the equations of physics only
imply local conservation.  A local conservation law tells us that the
amount of stuff inside a small volume changes only when stuff flows in or
out through the surface.  A global conservation law is derived from this by
integrating over all space and assuming that there is no flow in or out at
infinity.  If this integral cannot be performed, then global conservation
does not follow.  So, sending mass back in time might be alright, but it
implies that something strange is happening.  (Why shouldn't we be able to
do the integral?)

GENERAL RELATIVITY:

    One case where global conservation breaks down is in general
relativity. It is well known that global conservation of energy does not
make sense in an expanding universe.  For example, the universe cools as it
expands; where does the energy go?  See FAQ article #1 - Energy
Conservation in Cosmology, for details.

    It is interesting to note that the possibility of time travel in GR
has been known at least since 1949 (by Kurt Godel, discussed in [1], page
168). The GR spacetime found by Godel has what are now called "closed
timelike curves" (CTCs).  A CTC is a worldline that a particle or a person
can follow which ends at the same spacetime point (the same position and
time) as it started.   A solution to GR which contains CTCs cannot have a
spacelike embedding - space must have "holes" (as in donut holes, not holes
punched in a sheet of paper).  A would-be time traveller must go around or
through the holes in a clever way.

    The Godel solution is a curiosity, not useful for constructing a
time machine.  Two recent proposals, one by Morris, et al. [2] and one by
Gott [3], have the possibility of actually leading to practical devices (if
you believe this, I have a bridge to sell you).   As with Godel, in these
schemes nothing is locally strange; time travel results from the unusual
topology of spacetime.  The first uses a wormhole (the inner part of a
black hole, see fig. 1 of [2]) which is held open and manipulated by
electromagnetic forces.  The second uses the conical geometry generated by
an infinitely long string of mass.  If two strings pass by each other, a
clever person can go into the past by traveling a figure-eight path around
the strings.  In this scenario, if the string has non-zero diameter and
finite mass density, there is a CTC without any unusual topology.

GRANDFATHER PARADOXES:

    With the demonstration that general relativity contains CTCs,
people began studying the problem of self-consistency.  Basically, the
problem is that of the "grandfather paradox:"  What happens if our time
traveller kills her grandmother before her mother was born?  In more
readily analyzable terms, one can ask what are the implications of the
quantum mechanical interference of the particle with its future self.
Boulware [5] shows that there is a problem - unitarity is violated. This is
related to the question of when one can do the global conservation integral
discussed above.  It is an example of the "Cauchy problem" [1, chapter 7].

OTHER PROBLEMS (and an escape hatch?):

    How does one avoid the paradox that a simple solution to GR has
CTCs which QM does not like?  This is not a matter of applying a theory in
a domain where it is expected to fail.  One relevant issue is the
construction of the time machine.  After all, infinite strings aren't
easily obtained.  In fact, it has been shown [4] that Gott's scenario
implies that the total 4-momentum of spacetime must be spacelike.  This
seems to imply that one cannot build a time machine from any collection of
non-tachyonic objects, whose 4-momentum must be timelike.  There are
implementation problems with the wormhole method as well.

TACHYONS:

Finally, a diversion on a possibly related topic.

    If tachyons exist as physical objects, causality is no longer
invariant. Different observers will see different causal sequences.  This
effect requires only special relativity (not GR), and follows from the fact
that for any spacelike trajectory, reference frames can be found in which
the particle moves backward or forward in time.  This is illustrated by the
pair of spacetime diagrams below.  One must be careful about what is
actually observed; a particle moving backward in time is observed to be a
forward moving anti-particle, so no observer interprets this as time
travel.

                t
One reference   |                    Events A and C are at the same
frame:          |                    place.  C occurs first.
                |
                |                    Event B lies outside the causal
                |          B         domain of events A and C.
     -----------A----------- x       (The intervals are spacelike).
                |
                C                    In this frame, tachyon signals
                |                    travel from A-->B and from C-->B.
                |                    That is, A and C are possible causes
                                     of event B.

Another         t
reference       |                    Events A and C are not at the same
frame:          |                    place.  C occurs first.
                |
                |                    Event B lies outside the causal
     -----------A----------- x       domain of events A and C. (The
                |                    intervals are spacelike)
                |
                |   C                In this frame, signals travel from
                |                    B-->A and from B-->C.  B is the cause
                |             B      of both of the other two events.

    The unusual situation here arises because conventional causality
assumes no superluminal motion.  This tachyon example is presented to
demonstrate that our intuitive notion of causality may be flawed, so one
must be careful when appealing to common sense.  See FAQ article # 6 -
Tachyons, for more about these weird hypothetical particles.

CONCLUSION:

    The possible existence of time machines remains an open question.
None of the papers criticizing the two proposals are willing to
categorically rule out the possibility.  Nevertheless, the notion of time
machines seems to carry with it a serious set of problems.

REFERENCES:

1: S.W. Hawking, and G.F.R. Ellis, "The Large Scale Structure of Space-Time,"
   Cambridge University Press, 1973.
2: M.S. Morris, K.S. Thorne, and U. Yurtsever, PRL, v.61, p.1446 (1989).
   --> How wormholes can act as time machines.
3: J.R. Gott, III, PRL, v.66, p.1126 (1991).
   --> How pairs of cosmic strings can act as time machines.
4: S. Deser, R. Jackiw, and G. 't Hooft, PRL, v.66, p.267 (1992).
   --> A critique of Gott.  You can't construct his machine.
5: D.G. Boulware, University of Washington preprint UW/PT-92-04.
   Available on the [e-mail] bulletin board: item number 9207054.
   --> Unitarity problems in QM with closed timelike curves.

-Scott
--------------------
Scott I. Chase            "It is not a simple life to be a single cell,
[e-mail]         although I have no right to say so, having
                 been a single cell so long ago myself that I
                 have no memory at all of that stage of my
                 life." - Lewis Thomas

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

Date: Fri, 26 Mar 1993 20:15:03 GMT
From: Ken Arromdee <[e-mail]>
Subject: Timid Terraformers (was Re: How to cool Venus)
Newsgroups: sci.space

In article <[e-mail]> Callec Dradja <[e-mail]> writes:
>Bill, I am afraid that you did not quote all of what I said. The reason
>that I do not like the idea of using nuclear weapons to blast the
>atmosphere into space is because I feel that this would be a waste of
>Oxygen. At one time, the trees of Earth seemed limitless but today
>we realize that we should use these resources carefully. Oxygen, as I
>am sure you know, I an important resource that mankind will need as we
>move out to the other planets and stars. We should use it carefully.

Oxygen is an element.  You can't destroy it.  There is no way for mankind to
"use up" the oxygen it already has; it just gets recycled and recycled.

It is also one of the most common elements in the universe.
--
"On the first day after Christmas my truelove served to me...  Leftover Turkey!
On the second day after Christmas my truelove served to me...  Turkey Casserole
    that she made from Leftover Turkey.
[days 3-4 deleted] ...  Flaming Turkey Wings! ...
   -- Pizza Hut commercial (and M*tlu/A*gic bait)

Ken Arromdee ([e-mail])

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

Date: Fri, 26 Mar 1993 21:09:26 GMT
From: Josh Hopkins <[e-mail]>
Subject: Why is Venus so hot?
Newsgroups: sci.space

[e-mail] writes:

>Seems the way to cool venus down is basically to find some way to burn off the
>Sulfar and all the nasty gases and turn down the green house effect..

Hmm.  Burning CO2 would be a cute trick.   Pretty counterproductive too.

>Im not a technical person but.. I think I have some
>interesting ideas..

I've always said that reality impairs creativity.

>Now what is the parameters for a "normal
>planet" basically so we have something to know how to work towards??

I think you could argue that "normal planet" is an oxymoron. What you want is
a habitable planet -- something very different from a "normal" one.  In order
to accomplish this you need to some how eliminate a large amount of atmosphere,
turn what's left into something breathable, and add lots of water.  In order to
understand how to do that, you need to become a technical person (or at least
learn their language).



--
Josh Hopkins                                          [e-mail]
          "Tout ce qu'un homme est capable d'imaginer, d'autres hommes
                     seront capable de la realiser"
             -Jules Verne

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

End of Space Digest Volume 16 : Issue 375
------------------------------