Space & Astronomy/Space and Astronomy (October 1993).iso/pc/text/spacedig/v16_6/v16no639.txt

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Date: Fri, 28 May 93 14:17:27
From: Space Digest maintainer <[e-mail]>
Reply-To: [e-mail]
Subject: Space Digest V16 #639
To: Space Digest Readers
Precedence: bulk


Space Digest                Fri, 28 May 93       Volume 16 : Issue 639

Today's Topics:
Comet Shoemaker-Levy, Possible Collision With Jupiter in 1994 (4 msgs)
                  Detecting planets in other system
                  Hey Sherz! (For real!) Cost of LEO
                            Hubble vs Keck
                              Moon Base
                   Moon vs. asteroids, Mars, comets
                  Moon vs. Mars vs. planetoids, etc.
                    Philosophy Quest.  How Boldly?
                      Space Marketing -- Boycott
                      The crew is toast (3 msgs)
Voyager Discovers the First Direct Evidence of the Heliopause (2 msgs)
                   Why a far side Science station.

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

Date: Thu, 27 May 1993 15:11:33 GMT
From: Leigh Palmer <[e-mail]>
Subject: Comet Shoemaker-Levy, Possible Collision With Jupiter in 1994
Newsgroups: sci.space

In article <[e-mail]> Stupendous Man,
[e-mail] writes:
>I strongly suspect that Hubble
>isn't the right instrument for observing such collisions - my guess
>are that the exact time of impact(s) wouldn't be known very well, and
>HST is too important to leave lolly-gagging at Jupiter for hours and
>hours.  Furthermore, I think any _collision_ would produce much too
>bright a burst to be observed with HST.

The exact times of the impacts will be refined by observation over the
next year. I suspect the three-day interval refers to the fact that
the pieces of the comet are dispersed over the present orbit, which is
highly eccentric. The nature of such motion is that the dispersion in
space is proportional to the velocity. The velocity will increase
greatly over the next year because of the high eccentricity of the
orbit, and I will guess that the impact times can be determined much
more precisely nearer impact time.

I think that WFPC on Hubble is the natural instrument to use to
observe these impacts. It is the highest resolution telescope
available to do so, and there should be several events, perhaps with
some action to be observed. These should be low-angle impacts. They
would make very bright meteors for local observers, but will they
really be too bright for Hubble? I would have expected that if any
problem were present, it would have been one of threshhold of
observability. For one thing, I do not even know that the collisions
will occur on the side of the planet which is presented to us. That
should be known before the times of collisions are. Does anyone out
there know?

I hope that Hubble will go for this rather rare event and use it to
restore some of the flagging enthusiasm of the public which supports
our efforts.

Where will Galileo be at the time of the collisions? It has a
different aspect of Jupiter visible to it. Shouldn't it try for pix?

Leigh

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

Date: 27 May 1993 15:21 UT
From: Ron Baalke <[e-mail]>
Subject: Comet Shoemaker-Levy, Possible Collision With Jupiter in 1994
Newsgroups: sci.space

In article <[e-mail]>, [e-mail] (Stupendous Man) writes...
>      Phil Fraering asks:
>
>> Finally: where *do* I get those forms for Hubble Telescope
>> Time?
>
>      Sorry, Phil, but Cycle 4 proposals (which ask for observing time
>during 1994) were due Friday, May 14.

Note that a collision between Comet Shoemaker-Levy and Jupiter is not definite,
but was determined to be possible based on what we currently know of the
comet's orbit.

Even though the deadline for Cycle 4 has passed, there were contigencies
for Hubble to study what is called "targets of opportunity" for unscheduled
celestrial events (such as a supernova).  Assuming the comet does collide
with Jupiter, and we call this event a target of opportunity (with plenty of
advance notice to boot), then what is the procedure to have Hubble observe
this event?
     ___    _____     ___
    /_ /|  /____/ \  /_ /|     Ron Baalke         | [e-mail]
    | | | |  __ \ /| | | |     Jet Propulsion Lab |
 ___| | | | |__) |/  | | |__   M/S 525-3684 Telos | Never laugh at anyone's
/___| | | |  ___/    | |/__ /| Pasadena, CA 91109 | dreams.
|_____|/  |_|/       |_____|/                     |

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

Date: Thu, 27 May 1993 15:31:41 GMT
From: Leigh Palmer <[e-mail]>
Subject: Comet Shoemaker-Levy, Possible Collision With Jupiter in 1994
Newsgroups: sci.space,sci.astro,alt.sci.planetary

In article <[e-mail]> Paul Dietz,
[e-mail] writes:
>I expect a significant fraction of the energy would be
>converted to light, and radiated over a period of seconds or minutes.
>Jupiter could become significantly brighter, even to the naked eye.

Please elaborate on your expectation that a significant fraction of
the gravitational energy will be converted to (visible) light. This is
a surprise to me, but I don't know nearly enough about it. What I do
know is that, for an equivalent collision of an asteroid with earth
(a lot denser object) there was one hell of a lot of energy left to be
dissipated when the object reached the surface. In my (unsophisticated)
mind there exists the possibility that the same may be true in these
collisions at the point where the objects reach one optical depth into
Jupiter's atmosphere.

Leigh

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

Date: 27 May 1993 16:23 UT
From: Ron Baalke <[e-mail]>
Subject: Comet Shoemaker-Levy, Possible Collision With Jupiter in 1994
Newsgroups: sci.space

In article <[e-mail]>, Leigh Palmer <[e-mail]> writes...
>
>Where will Galileo be at the time of the collisions? It has a
>different aspect of Jupiter visible to it. Shouldn't it try for pix?
>

Galileo will be 17 months away from arrival to Jupiter - too far away
to get any reasonable images.
     ___    _____     ___
    /_ /|  /____/ \  /_ /|     Ron Baalke         | [e-mail]
    | | | |  __ \ /| | | |     Jet Propulsion Lab |
 ___| | | | |__) |/  | | |__   M/S 525-3684 Telos | Never laugh at anyone's
/___| | | |  ___/    | |/__ /| Pasadena, CA 91109 | dreams.
|_____|/  |_|/       |_____|/                     |

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

Date: Thu, 27 May 93 16:37:09 BST
From: Greg Stewart-Nicholls <[e-mail]>
Subject: Detecting planets in other system
Newsgroups: sci.space,sci.astro

In <[e-mail]> Brenda Kalt writes:
>In article <[e-mail]>, [e-mail] (Thomas Clarke) writes:
>|> In a recent issue of Science there is a discussion of a project
>|> to look for MACHOs (Massive Compact Halo Objects - things like
>               ^^^^^
>Sexism in research strikes again. Obviously, a modern, non-sexist name
>for this phenomenon would be McHalos...
>
 Uh no, that would be a distinct reference to a US based food company.
Linguistic Police are Go !!
 -----------------------------------------------------------------
Greg Nicholls ...         : Vidi
[e-mail] or     : Vici
[e-mail] : Veni

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

Date: 27 May 1993 14:56:03 GMT
From: Doug Mohney <[e-mail]>
Subject: Hey Sherz! (For real!) Cost of LEO
Newsgroups: sci.space

In article <1u0p1g$[e-mail]>, [e-mail] (Pat) writes:

>    Actually, here is a real condemnation of SHuttle.  If shuttle
>is so great,  why did the soviets Abandon BURAN?

They have no money.  That's easy enough.  None, zippo.

> Buran  is 99% like
>shuttle in capacity,  except BIG PLUS, it has Liquid Boosters,

You left out that they don't keep the engines on the actual machine, which
increases payload somewhat.  No SSMEs to drag around.

>Yet the Soviets abandoned BURAN totally, once they saw how operationally
>inefficient it would be,  and with the observation of how STS is strangling
>our space program.

Pat, as usual, you are spreading mis-information.

They haven't abandoned it totally.  They'd like to do a couple of launches,
but they don't have the cash.  If you could come up with the proper money (oh,
say $250 mil U.S.), you could probably get a flight out of them.

They are also adapting a more conservative test flight regime than we did with
the shuttle.  Henry can fill in the blanks, but the next test they'd like to
run would be unmanned to Mir... then fly back with passengers picked up there.



    Software engineering? That's like military intelligence, isn't it?
  -- >                  [e-mail]                        < --

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

Date: Thu, 27 May 1993 14:44:57 GMT
From: Anita Cochran <[e-mail]>
Subject: Hubble vs Keck
Newsgroups: sci.space

In article <[e-mail]>, [e-mail] writes:
> In article <[e-mail]>, [e-mail] (Henry Spencer) writes:
> > In article <[e-mail]> [e-mail] (Phil G. Fraering) writes:
> >>it would probably be cheaper to build another Hubble. Or to simply
> >>write off the Hubble program entirely and build 2.5 more Keck
> >>Interferometers. (Which could be done for the cost of fixing
> >>Hubble).

> > It wouldn't give you Hubble's UV or faint-object capabilities, even
> > assuming that the Keck Interferometer works as well as projected.  The
> > extent to which the new ground-based telescopes can (probably) equal
> > or surpass Hubble is exaggerated; they do so in only one of several
> > dimensions.


> Henry, I'm not sure what you mean here by HSTs 'faint object capabilities'. A
> 10m telescope gathers an awful lot more light than a 2.5m, so can get fainter
> in that sense, whilst in the optical the background from the earth isn't too
> much of a problem, so the higher spatial resolution df HST doesn't win back
> this factor. The short integration times on one target (45 mins I think)
> necessetated by HSTs low oprbit also are a problem on faint sources as you have
> to cope with rather more read out noise than one 10 hour exposure, say, with
> Keck would. The FOC, I think, has low readout noise, but this has a very
> limited FoV.

Actually, having just gone through all of this for my HST proposal, Henry is
correct.  The reason why HST wins, despite the 45 minutes per cycle and
smaller telescope, is that the sky background is so much lower.
A dark site on the ground has a sky background of 21.5 or 22 (very dark
such as McDonald Obs) per sq arcsec.  With typical CCD plate scales,
the background per pixel is around 22.5 mag.  Contrast that with
the HST WFPC2 numbers of a sky background of ~27.2 mag/pixel.  Thus,
to reach a given signal/noise, one can use shorter integration times
on Hubble that on a comparable sized telescope on the ground.  As you
point out, Keck is much larger but the sky background is a surface brightness
and Keck just gathers more sky.  Additionally, with Keck, you have seeing
effects which hurt you.  So, all in all, HST can reach pretty impressive
limiting magnitudes.  Tyson and his co-workers have probably gone the
deepest on the ground and have reached S/N=3 (I think) for m in the R band
of 27.8 in 22000 sec with the 4-m CTIO prime focus.  We figure we can reach
m=28.5 with S/N=4 in R in 18000sec on HST.  Yes, one has to reacquire
each 45 minutes with HST but in practice, 22000 sec on the ground takes
a long time too since one has to worry about airmass so it takes several
nights.

Incidentally, if one believes the specs in the call for proposal and instrument
manual books, the FOC is not really the instrument that can go the faintest.
WFPC2 can easily go fainter.  FOC could beat out WFPC1 but not the new
instrument.  FOC has superior plate scale for some things and has a
long slit mode but the detector is an outdated vidicon.
--
 Anita Cochran  uucp:  !utastro!anita
                arpa:  [e-mail]
                snail: Astronomy Dept., The Univ. of Texas, Austin, TX, 78712
                at&t:  [phone]

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

Date: Thu, 27 May 1993 14:18:05 GMT
From: Gary Coffman <ke4zv!gary>
Subject: Moon Base
Newsgroups: sci.space

In article <1u03e6$[e-mail]> [e-mail] (Pat) writes:
>
>Careful Gary,
>you are starting to sound like szabo :-)

I hope not. He's as fanatical as Sherzer. I don't expect costs to
come down nearly as far as either of them. And I don't see markets
anywhere as large, or as soon, as either of them. I do believe it's
in our best interests to aim for targets with the highest probable
return. Space is so much larger than anything we've dealt with
before that our sense of timescale is out of proportion. Political
funding doesn't have the necessary long term stability needed for
financing space exploration. And short term investors don't either.
Their timescales are sufficient for sure thing investments like
comsats, but when we move beyond LEO, selling services to Earth
no longer makes short term economic sense unless they are extremely
high value.

We've got to develop new mechanisms to fund space that aim for the
long pull. The only investment targets with sufficient return to
overcome the time cost of money for startup currently appear to be
in open space. We've got to move into the realm of selling things
from space for activities in space.

However, eventually all markets end with the consumer, and the
majority of consumers will remain on Earth for some time. Space
activity has to sell to that market. In the short term, most of
that product will remain information. In the longer term, there
may be a small flow of manufactured goods as well. In the much
longer term, if space is to prosper, customers will have to be
in space in large numbers. They won't be there unless there is
something profitable to do.

Gary
--
Gary Coffman KE4ZV          |    You make it,     | gatech!wa4mei!ke4zv!gary
Destructive Testing Systems |    we break it.     | uunet!rsiatl!ke4zv!gary
534 Shannon Way             |    Guaranteed!      | emory!kd4nc!ke4zv!gary
Lawrenceville, GA 30244     |                     |

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

Date: 27 May 93 13:03:04 GMT
From: Jim Hart <[e-mail]>
Subject: Moon vs. asteroids, Mars, comets
Newsgroups: sci.space

[e-mail] (Richard A. Schumacher) writes:

>Perhaps an illustration would help: if there were an
>asteroid of solid platinum in LEO right now, it would
>not pay (by a factor of 2 or so) to bring any of it back
>using the shuttle.
>(Assumptions: max shuttle landing payload weight = 20,000 lbs.
>Pt at $700 per oz. Shuttle flight costs >= US$350,000,000.)

You're amortizing the entire Shuttle cost to the return trip?

Which usually comes back mostly empty?  Wow.  Still, even if
we shave off an order of magnitude you still make the
point about just how much cost reduction needs to be done for
these kind of major projects.  (We might be able to afford
to bring platinum back but can we afford to launch the
platinum mine up?)

I wonder, if we designed a reentry vehicle for optimal
payload/vehicle mass ratio, either by modifying COMET or
starting from scratch, how good could we do?

The there vs. the other place controversy mostly depends on the quality
of ore.  There's a factor of 10^5 difference between the price of platinum
and the price of iron ore, for example.  This dwarfs the measly
5-15%/year cost of money and  factor of 2 differences in energy.
The mass of mining equipment, the nitty gritty details of how we're
extracting the stuff is also more important than mere distance or time,
and closely related to the ore quality.  Also, how much of the
working materials can be manufactured on-site, for example fuel,
water, oil, coolant, and spare parts beamed up to tiny 3d printers
and mills.  As for transport costs, the mass of a solar mirror or
array or nuclear reactor to drive a rocket scales with the power, not
the energy, which is a several-order-of-magnitude argument against
gravity wells.

Wherever we go, though, we have to miniaturize and automate big-time.
Does anybody expect any organization, government or commercial, is
willing to shell out in the $10's of billions for any of this stuff?
Get real.  We're talking $5 billion or less, maybe even <$1 billion, to
bring back some good paydirt or forget it.   The whole ball of wax
has to fit into two or three rocket payloads or forget it.  Since this
is aways off in the future, might as well bring advanced biotech, or
early nanotech, into the picture and have fun.   If we insist
on government research that's where it should be at, in the
big-payoff technology that makes the big breakthroughs in
automation, miniaturization, etc.  That kind of tech is
not as far off as you might think, and it looks like we'll need
it to make this stuff economical.    Also we'll get a lot
more "spinoffs" with big-breakthrough generic technology
(ie technology at a basic engineering level that applies to
many kinds of industries) then we will making the nth tiny
improvement in rocket technology, the nth spacesuit,
and other stuff special to space while more U.S. Earth-relevant
high tech moves to Asia, and your job, and any hope of a cheap
ride into space with it.

[e-mail]

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

Date: 27 May 1993 08:53:44 -0700
From: Nick Szabo <[e-mail]>
Subject: Moon vs. Mars vs. planetoids, etc.
Newsgroups: sci.space,sci.astro

It's good to seem Jim Bowery back givin' 'em hell, welcome
back Jim!  The "dark sky property  rights" stuff is also
quite interesting, a prelude to similar issues that will
arise over frequencies, orbital slots, and launch windows
as well as over physical resources in space in the future.
It seems improbable that we can solve this adsat problem
to everybody's satisfaction, but at least we can start thinking
about these issues in terms of free enterprise instead of
government planning bureaucracies; that's long overdue.
It's too bad some folks from APS express such fear of the
commercialization of space; it may be one of the few places left
where they can get a non-taxi-driving job after their hero
Clinton gets done slashing their budget. :-(

I see some posters who should know better continue to be
dogmatic about what we *MUST* do, "the next logical step",
etc., as if it's just such a crime that there are diverse
opinions on the matter.  I think some of these people will go to
their grave begging the U.S. government to do another Apollo.  Sad.
For the average amortized cost of five Shuttle launches,
$5 billion, we can explore Mars (MESUR), the moon (LPO,
Artemis), earth-crossing asteroids (NEAR), comets (Artemis-class
Rosetta), get tons of Keck and Hubble time do comet and
asteroid spectroscopy, build and launch an infrared telescope,
quadruple the asteroid discovery rate of Spacewatch,
and much more.  This will give us tons more information than we
have now -- answer crucial questions like, are there significant
accessible volatile deposits on the moon? (probably not, but
worth looking given the critical nature of volatiles to future
large-scale space industry).  Are there any uncollapsed lunar
lava tubes?  Are there significant patches of volatiles,
concentrated organics, concentrated platinum-group metals, concentrated
nanodiamond, or other interesting stuff in the earth-crossing asteroids?
Were there any interesting ore-forming processes on Mars?

The comet which passed within the Roche limit of Jupiter and
calved off pieces is quite exciting.  Let's get some scope time!
Spectroscopy with Keck!  We can get information from this as
important as we can get from a comet flyby, at a fraction of
the cost, all we need is good scope time and some grad students
to help out. It will be interesting and very informative to see how
long it takes for the pieces caught into heliocentric orbit to stop
outgassing.   I hope Galileo can get a look at pieces captured into
Jupiter orbit.  There is a large family of comets, the Jupiter family,
which have been caught by Jupiter into orbits that would resemble
Earth-Jupiter transfer orbits if the two planets were lined up.  These
are primo #1 fuel and feedstock dumps for future space industry.

Comet fragmentation is quite common, and it would be interesting to
get estimates of (a) the population of smaller fragments, (b)
their active lifetimes, and (c) how much ices are left trapped
in the inactive cinders.  Over a period somewhat longer than
a comet's active lifetime, objects in the Jupiter-family orbits
evolve into orbits indistinguishable from those of the earth-crossing
asteroids.  We've also recently discovered a much larger number
of smaller fragments in these near-earth orbits than is expected
from the asteroid size distribution.  Might these be millions
of old small comet fragments in earth-crossing orbits, with
round-trip delta-v's <= those from the lunar surface?  Might there
be ice left on any of them?  As we start looking at the "vermin
of the sky" with the big hardware like Keck, we get a chance
to look in much more detail.  We can do spectroscopy on dozens
of comets and asteroids, if we get the scope time.  Looking
at certain asteroids at perihelion, we may be able to see tiny
outgassings, little geysers far too small for the scopes traditionally
used to study asteroids and comets.  The line between asteroids
and comets may continue to blur.  The point being, telescopic
exploration costs orders of magnitude less than small spacecraft
probes, which in turn cost orders of magnitude less than actual
mining or manned missions.  We would be wise to look before we
leap, and the looking itself could be quite interesting!


--
Nick Szabo                     [e-mail]

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

Date: 27 May 1993 12:32:04 -0400
From: Pat <[e-mail]>
Subject: Philosophy Quest.  How Boldly?
Newsgroups: sci.space

I saw something that indicated our Big brain came in part from the
Desert environment of proto-humans.  High heat damaged brain cells.
a big brain  rode out the damage better,  somewhere along the
way we got a bunch of extra capability that snowballed enough.
Probably the first good idea was "This heat gives me a headache,
let's move someplace cooler" :-)

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

Date: 16 May 93 04:07:16 GMT
From: Roger Lewis <[e-mail]>
Subject: Space Marketing -- Boycott
Newsgroups: sci.environment,misc.consumers,misc.invest,sci.astro,talk.environment,talk.politics.space,sci.space,rec.backcountry,misc.rural,misc.headlines,k12.chat.teacher

The major danger of Space Marketing is all the bullets that will rain down
upon the earth from all the good ole boys firing at it when I buy the
message "No shooting allowed within sight of this sign". :)
--
[e-mail]    I'm the NRA *AND* the ACLU.   Power to the PEOPLE!

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

Date: 27 May 93 10:46:50 EDT
From: "John F. Woods" <[e-mail]>
Subject: The crew is toast
Newsgroups: sci.space

[e-mail] (Pat) writes:
>What they really needed were ejection seats.  According to henry,
>Martin baker had a design for seats for all STS occupants.

>Of course, that would require Nasa spending money on safety improvements as
>opposed to shuttle ops.  My opinion, here.

It would also require them reducing the payload capacity of the vehicle by
quite a lot in order to make it vague possible that the crew could survive
SOME accidents (note: there is only evidence that two astronauts remained
conscious AT ALL after the explosion, and because they had *air* packs and
not *oxygen* packs, they almost certainly did not remain conscious long --
the air is MIGHTY thin at that altitude[1]).  However, in other debates in this
newsgroup, a strong contingent has demonstrated that the shuttle doesn't NEED
any payload capacity in order to be valuable to *them*.

Note that the _astronauts_ for the British Hermes program vetoed ejection seats
as a pointless waste of mass.


[1] It's also worth considering that if the interior got bent at all (after the
shell was hammered by a high-Mach airstream?  Naaahhhhh...), the ejection seats
might wind up firing through structural supports instead of carefully placed
"soft" spots.  Ouch.

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

Date: Thu, 27 May 1993 14:42:51 GMT
From: Dillon Pyron <[e-mail]>
Subject: The crew is toast
Newsgroups: sci.space

In article <[e-mail]>, [e-mail] (Henry Spencer) writes:
>In article <1u0pnn$[e-mail]> [e-mail] (Pat) writes:
>>THe F-111,  and the B-1A?  had a crew ejection capsule that was
>>designed for such a similiar escape.  THe problem is, at least on STS,
>>a probable ejection occurs over water,  thus the crew compartment
>>must have a bouyant capcity.  A tough problem...
>
>Actually, both the F-111 and B-1A capsules were/are buoyant.  The real
>problem (and the reason why the production B-1 designs switched to
>ejection seats) is that those escape capsules simply don't work very
>well.  They land too hard, and tend to cause spinal injuries.

In fact, I remember one F-111 accident in which one crew member was killed by
the landing impact.  Can't remember any details, but some sort of training
changes were made.

I also remember that the first B-1B to go down killed a Rockwell tech who was
riding in the (non-ejecting)jump seat.
>--
>SVR4 resembles a high-speed collision   | Henry Spencer @ U of Toronto Zoology
>between SVR3 and SunOS.    - Dick Dunn  |  [e-mail]  utzoo!henry
What does that make Solaris 2.1?
--
Dillon Pyron                      | The opinions expressed are those of the
TI/DSEG Lewisville VAX Support    | sender unless otherwise stated.
[phone] (when I'm here)     |
[phone] (when I'm home)     |Compressed air is a drug, and I need a fix
[e-mail]          |
PADI DM-54909                     |

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

Date: 27 May 1993 12:55:21 -0400
From: Pat <[e-mail]>
Subject: The crew is toast
Newsgroups: sci.space

I guess I should have been more specific.  In order for the STS
crew compartment to act as a survival capsule, it would need a
bouyant capacity.  A large mass penalyty compared to Seats
and life vests.

Mercury, gemini, apollo's all had to pay that price because
the splashdown was the preferred end of flight.  For a
dry landing,  emergency flotation systems are a fairly big
weight penalty.  Note how few helicopters carry emergency
flotation gear.

I suppose, the STS crew compartment could be arranged with a
drogue chute for not a lot of penalty,  slow down witht he drogue
to appx 100 mph  and then the crew bail out individually,
or count on toughing out the impact and un-ass the sinking
vehicle at high speed.  But not my idea of fun.

I think early WW2 fighters, counted on  ditching  and then swimming
for it,  but i dounbt it was considered survivable.  any one know?

pat

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

Date: 27 May 1993 15:41 UT
From: Ron Baalke <[e-mail]>
Subject: Voyager Discovers the First Direct Evidence of the Heliopause
Newsgroups: sci.space

In article <1u2281$[e-mail]>, [e-mail] writes...
>
>Thus the voyagers are 15 to 30 years away from crossing the heleopause.
>Thus it does not sound like their power will hold out that long :-(
>How much longer do they have?

Provided there is no major breakdown on the spacecrafts due to old age, we
should be able to track them to at least to the year 2019.  Voyager 1 will
pass the 100 AU mark in 2010.  It is estimated that the hydrazine will
last until 2040 for Voyager 1 and 2034 for Voyager 2, so the fuel is not
a concern.  As the spacecraft move farther away, their signal becomes
weaker and fainter.  With current DSN capabilities, we can receive
the signals from both spacecraft at 46.6 bps in the year 2037 using the
70 meter antennas.  The DSN currently undergoing an upgrade, so this number
will be improved.  The power level from the RTGs is slowly dwindling, so some
of the instruments will have to turned off eventually.  The Ultraviolet
Spectrometer is scheduled to be turned off in 2000.  All of the fields and
particles instruments should have full power until around 2010.  After
that the instruments can still be used, it just that they all can't be
turned on at the same time.

>What other evidence (short of crossing it) can the voyagers provide to "find"
>the heliopause?

Voyager carries five instruments that will measure the bow shock of the
heliopause when it crosses it.
     ___    _____     ___
    /_ /|  /____/ \  /_ /|     Ron Baalke         | [e-mail]
    | | | |  __ \ /| | | |     Jet Propulsion Lab |
 ___| | | | |__) |/  | | |__   M/S 525-3684 Telos | Never laugh at anyone's
/___| | | |  ___/    | |/__ /| Pasadena, CA 91109 | dreams.
|_____|/  |_|/       |_____|/                     |

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Date: 27 May 1993 12:28:31 -0400
From: Pat <[e-mail]>
Subject: Voyager Discovers the First Direct Evidence of the Heliopause
Newsgroups: sci.space

I saw something that indicated that HST data showed the
Heliopause at 100 AU.  Some sort of faint Hydrogen activity
at that distance.

So  we should have something to check it out against.

pat

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Date: Thu, 27 May 1993 13:41:35 GMT
From: Gary Coffman <ke4zv!gary>
Subject: Why a far side Science station.
Newsgroups: sci.space

In article <1u0354$[e-mail]> [e-mail] (Pat) writes:
>
>I hate to ask this,  but
>
>Everytime someone talks about a lunar science base,  they say
>"Far side,  Radio dead,  no Light glare".
>
>Am i missing something, or could some sort of reasonably
>directional radio antenna  or optical scope avoid picking
>up earth scatter?  Sure,  you have a big black out zone in the
>center of the sky where you can't observe,  but you'd get
>a lot of operational advantages from being on the near side,
>even if you were close to the edges.

Having the Earth in the sky is a nuisance to optical astronomers
tracking an object on the ecliptic, but it's tragedy for radio
astronomers. Typical multi-element arrays have a front to back
ratio of 20 to 30 db, and sidelobes that are worse. Solid dish
antennas have much better front to back ratios, but side spill
and scatter over the dish edge still limits rejection to 50 to
60 db at best. Receiver sensitivity is on the order of -145 dbm.
With multi-megawatt emitters like TV and radar on Earth, the
directional abilities of the antennas just aren't good enough
to avoid saturating the receiver from spill. For Earthbound
scopes, or those in view of Earth, this means vast regions of
the spectrum are effectively off limits to the astronomers.
That's why the farside looks so attractive to them. And it
really has to be the farside, diffraction will carry radio
signals a ways around the curve of the Moon before the levels
drop to indetectability.

Gary
--
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End of Space Digest Volume 16 : Issue 639
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