Space & Astronomy/Space and Astronomy (October 1993).iso/mac/TEXT/SPACEDIG/V10_0/V10_005.TXT

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Subject: SPACE Digest V10 #5

SPACE Digest                                       Volume 10 : Issue 5

Today's Topics:
            Re: deep space dishes
            Voyager Neptune update (long)
             `Radio eclipses' of Voyager?
            Re: Direct Information
         Re: Sunspots of the Future? (was Sun Spots)
----------------------------------------------------------------------

Date: 24 Aug 89 21:34:45 GMT
From: usc!henry.jpl.nasa.gov!elroy.jpl.nasa.gov!jpl-devvax![e-mail]  (Lee Mellinger)
Subject: Re: deep space dishes

In article <[e-mail]> [e-mail] (Clayton Cramer) writes:
:In article <[e-mail]>, [e-mail] (James A. Markevitch) writes:
:> Let's see... from some computations I did a few years ago the power for
:#
:#     BW 20kHz                 -43 dB

Bandwidth is twice the data rate e.g., 21.6kBPS is 43.2kHz.

:#
:#     S/N for a single 70m antenna          -5 dB
:#
:# This sounds a little low, even given the arrays being used so maybe the
:# data rate is lower or there is a little slop in some of the above
:# numbers.
:#
:# Jamie
:
:The data rate is wrong, I think.  My copy of _Mariner_Jupiter_Saturn_
:77_Mission_Test_And_Telemetry_System_Software_Planning_Document_
:(before they changed the name to Voyager) dated May 18, 1976, shows:
:
:    Three high rate streams:
:
:        one at 57.6 KBPS, &
:        two at 1200 BPS, &
:        ESP input at 16 BPS.
:
:    One low rate stream at 40 bps, &
:    two high rate streams:
:
:        one at 57.6 KBPS, &
:        one at 67.2 KBPS, &
:        ESP input at 16 bps.
:
:My vague recollection was that the 1200 bps stream was engineering
:and general science data, and the 57.6 kbps stream was general science
:and imaging data.  (Everything was mixed together in the most peculiar
:arrangements, which required software to separate the various types
:of data out -- which is what I did -- badly -- on that project).
:
:--
:Clayton E. Cramer {pyramid,pixar,tekbspa}!optilink!cramer

Actually it is more complicated than this, but suffice it to say there
are 256 different data rates possible and 256 different frame sizes.
During cruise, 40 bps is used for engineering data and sometimes 1200BPS
for general science (not imaging) and engineering.  Currently, there
is 21.6kBPS for imaging and 40 BPS for engineering.

Uplink rate is 16BPS only.

Lee

"I'm the NRA"

"They that can give up essential liberty to obtain a little temporary
safety deserve neither liberty nor safety." -- Benjamin Franklin 1759

|Lee F. Mellinger                 Caltech/Jet Propulsion Laboratory - NASA
|4800 Oak Grove Drive, Pasadena, CA 91109 818/393-0516  FTS 977-0516
|{ames!cit-vax,}!elroy!jpl-devvax!leem  [e-mail]

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

Date: Thu, 24 Aug 89 11:34:54 PST
From: Peter Scott <[e-mail]>
Subject: Voyager Neptune update (long)
X-Vms-Mail-To: EXOS%"[e-mail]"
Lines:  202

Extracted without permission from NASA's _Voyager Bulletin_, Mission Status
Report No. 91, August 17:

[...] Bright, wispy "cirrus-type" clouds overlie the Great Dark Spot (GDS)
at its southern margin and over its northwest boundary.  This is the first
evidence that the GDS lies lower in the atmosphere than these bright clouds,
which have remained in its vicinity for several months.  [...]

[...] Neptune's coordinates on August 24 will be [R.A.] 18h 42m, [DEC]
-22 deg 11 min, magnitude 7.9.


Highlights of the Near-Encounter Phase
--------------------------------------
Most of the high-value science Voyager 2 will gather during the entire 4-month
encounter period will come during a 53-hour period spanning August 24, 25,
and 26.

By then, Neptune will completely fill the wide-angle camera's field of view
(55.6 x 55.6 milliradians), which looks at fifty times more viewing area
than the narrow-angle camera (7.5 x 7.5 mrads).  Triton [...] will fill
half the narrow-angle camera's field of view.

Near the start of the near-encounter sequence, the 70m antenna in Canberra
will transmit to the spacecraft a precise tone at the X-band frequency (about
8400 MHz).  The tracking stations near Madrid will then listen to Voyager's
return signal more than 8 hours later [...].  [Doppler shift will yield
Neptune's gravity.]

Every 6 minutes, the low-energy charged partice detectors will collect
high-rate samples of the flow directions of charged particles in Neptune's
(expected) magnetosphere.

About 11 hours before Neptune closest approach (N-11h), Voyager 2 will take
its best picture of Nereid, which will span less than 20 pixels in the
narrow-angle frame (Neptune was this size in January 1989).

From N-10h to N-8h, the infrared instrument will be trained on a spot in
Neptune's atmosphere at -40.4 deg south latitude.  This is the latitude
Voyager's radio signal will pass through as the spacecraft reappears rfom
behind the planet at the end of its Neptune Earth-occultation experiment,
55 min after Neptune closest approach.  Using this data, scientists can
later determine the helium abundance at this occultation egress point, as
it is called.  [...]

After imaging, infrared, and photopolarimetric observations of Neptune's
sunlit limb (edge), Voyager will next train its cameras on the ring-arc
region.  Between N-7h 17m and N-6h 22m, two retargetable ring-arc observations
will employ for the first time a clever technique called Nodding Image Motion
Compensation (NIMC) to "freeze" the motion of selected clumps of orbiting
ring-arc material.  (NIMC "nods" the spacecraft just enough to track the
target but not enough to break the antenna's line of sight to Earth, thus
allowing the data to be returned to Earth as it is taken, rather than recorded
onboard the spacecraft for later playback to Earth.)  Between the two ring
observations, Voyager has been reprogrammed to shutter four images of teh
recently-discovered moon 1989N2.

By N-5h 18m, a photopolarimetric and ultraviolet scan of Neptune's bright
limb will b completed.  Ring observations will continue for almost 2 more
hours.  Between N-4h 55m and N-3h 3m, the sensitive detectors in the
photopolarimeter and ultraviolet spectrometer will gaze at the star Sigma
Sagittarii (also known as Nunki) as it appears to drift behind the right-hand
half of the ring-arc system as a result of Voyager's motion.  This stellar
occultation may provide detailed ring-arc region structural and orbital data.

While the bright limb scans and stellar occultations are taking place, Voyager
2 will be receiving updated instructions from Earth.  All of the science
observations between about N-3.5h and N+9h are sequenced in three separate
movable blocks that can be shifted in time.  The Neptune Movable Block (NMB)
contains the spacecraft's instructions for all activities around Neptune
closest approach from N-3h 20m to N+1h 46m; the Triton Movable Block (TMB)
contains the observations around Triton closest approach from N+1h 50m to
N+8h 38m; and the Vernier Movable Block (VMB) encompasses the critical sequence
for controlling the Neptune radio science occultation from N-5m to N+56m.
The VMB overlies the NMB.

By allowing the entire block of activities in each block to shift, timing
updates can be applied to the whole set in one simple step, instead of changing
individual timing parameters in each observation.  Shifts in multiples of
48 seconds are possible for the NMB and TMB; for the VMB, a special technique
will allow shifts in radio science occultation events of a little as one
second, independent of how much the NMB is shifted.  The success of the
radio science measurements is dependent upon the Navigation Team's ability
to estimate the time of closest approach to within one second.  For everything
except the critical radio science occultation, 48 seconds would be good enough.

[...]

By N-3h, another retargetable ring-arc observation will be finished.  The
best image of Triton before Neptune closest approach will be taken; Triton
will subsequently be eclipsed by Neptune's southern limb, and won't be visible
again until the spacecraft arcs over Neptune's pole.  The scan platform
will shift back to Neptune for some imaging, infrared, and photometry
measurements.  The Low-Energy Charged Particle (LECP) instrument will switch
into a higher-energy sampling mode as Voyager 2 penetrates the deepest part
of Neptune's magnetic field and radiation belts.  [...]

At N-1h 41m, the sensitive optics of the instruments on the scan platform
wil be pointed away from Neptune -- towards deep space -- to protect them
from possible pitting during the inbound ring-plane crossing.  Then, one
hour from its aiming point, Voyager 2 will configure its radio transmitter
for the ring-arc system and Neptune occultations, calibrate its antenna,
and gather baseline pre-occultation data until N-20m.

For about 10 minutes centered around N-56m, the spacecraft will cross the
ring plane just outside the ring-arc region.  The plasma wave instrument
should pick up the sounds of microscopic (harmless) ring particles vaporizing
as they hit the spacecraft.

Immediately after the ring-plane crossing, the spacecraft will roll 61 degrees
from the lock star Canopus to orient the fields and particles instruments
for measurements of the charged particles that should be raining into Neptune's
north pole along the magnetic field lines, perhaps causing auroral activity.
At the end of this roll, the spacecraft's attitude will be under the control
of the onboard gyroscopes.

Last-minute "shoehorning" has enabled the flight team to insert an instruction
to Voyager 2 to shutter a high-resolution image of the recently-discovered
moon 1989N1 about 45 min before the closest approach to Neptune.  By a stroke
of luck, the image can be taken during a radio science antenna pointing
maneuver, which provides almost perfect image motion compensation.  Details
as small as 2.5km across should be visible [...].

[...]

At N-5m, the duration of each of Voyager's thruster pulses will be increased
from .004s to .010s, just in case Neptune's atmosphere applies some unexpected
drag on the vehicle, and also to provide quicker response to maneuver commands
needed for the occultation experiment.  This special provision will remain
in place for the next hour.  The shift of the VMB will precisely control
the timing for all occultation activities for the next hour.  Since the
telemetry stream will have been turned off an hour earlier to concentrate
power in the pure radio signal, all spacecraft telemetry during this time
will be routed to the tape recorder for later playback.

Voyager 2's speed relative to Neptune is expected to peak at an impressive
98,350 km/h (60,980 mph) [at closest approach] a mere 4400km (2730mi) about
Neptune's sensible atmosphere, and only 4900km (3000mi) about the methane
cloudtops below.  As it arcs over 77 degrees north latitude, the spacecraft
will start to slow down, and begin its permanent journey down and out of
the ecliptic plane.

[...]

With its pure-tone transmissions still turned on -- and while completely
out of view from the Earth -- the automated spacecraft will perform an amazing
string of 24 maneuvers, collectively known as the "limbtrack" maneuver,
to precisely point the boresight of the spacecraft's high-gain antenna along
Neptune's limb, starting with the ingress point in Neptune's northern
hemisphere, then around the left limb (as viewed from Earth), and ending
with the egress point at -40.4 deg south.  The limbtrack maneuever will
take about 48 min.  The radio signals will be refracted as they pass through
Neptune's atmosphere, and the limbtrack maneuver will control the pointing
of the antenna to ensure that these signals are bent so that they hit the
Earth and, thus, the waiting antennas in Australia and Usuda, Japan.  [Yields
info on atmosphere.]

[At the same time it will] take a series of three wide-angle images of the
ring-arc system in forward-scattered sunlight.  [This] will employ a new
image smear reduction ploy called Maneuverless IMC.  Instead of moving the
entire spacecraft smoothly to track the target, only the scan platform will
be moved.  [Interesting -- I thought that it was virtually crippled after
Saturn.]  Although the platform's motion is somewhat jerky, this technique
will still afford clearer images than if no attempt were made to track the
target.

As the spacecraft emerges from behind Neptune at N+55m 8s -- again watching
with the ultraviolet instrument -- it will see the Earth first, followed
by the Sun 49 seconds later.  Voyager 2 will continue to point its antenna
at Earth for the outbound ring occultation, and will take an edge-on shot
of the ring-arc system as the spacecraft descends across the ring-plane
at N+1.5h.  [...]

[...]  About two hours past Neptune, the spacecraft will roll to a new
lockstar, Alkaid, primarily to orient the charged-particle instruments for
magnetospheric measurements between Neptune and Triton while, at the same
time, preserving good viewing of Triton [...].

For the next 8 hours, Voyager will train its infrared, ultraviolet,
photopolarimetric, and imaging instruments on Triton.  The 3 highest-value
imaging observations from this period promise to be among the sharpest set
of pictures Voyager 2 has ever returned.  Features as small as 1km (0.62mi)
across are expected to be resolved near the time of closest approach to
Triton (N+5h15m)

By this time, Triton's small gravitational tug will be felt by Voyager,
allowing scientists on Earth to measure the gravitational effects by observing
changes in the radio signal.  Voyager will next train its photopolarimetric
and ultraviolet sensors on the star Beta Canis Majoris for about 20 min,
watching its brightness change as it [passes behind Triton and its atmosphere].

[40-min observation of Triton occulting Earth, Sun for about 3 min.]

[Re-acquire Canopus and observe Triton for 2 hrs until tape recorder nearly
full; look back at Neptune.]

[...]
--------------------------
Apologies for the length of this posting to those whose eyes are tired by
now (so are my fingers); I've done my best to edit, but still have left
out a wealth of information that seems just as appropriate to this newsgroup.
Hope this helps out some of you watching NASA Select.

Peter Scott ([e-mail])

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

Date: 24 Aug 89 17:54:37 GMT
From: mcsun!ukc!inmos![e-mail]  (Conor O'Neill)
Subject: `Radio eclipses' of Voyager?


Presumably, since the planets all lie roughly in the same plane,
every month the moon eclipses Voyager.
Is this taken into account when the trajectory is planned, or is
it simply luck that the moon isn't in the way at the interesting bits?

Another question - is Neptune currently on the same side of the
sun as we are, and at what angle (relative to the sun)?

--
Conor O'Neill, Software Group, INMOS Ltd. UK: [e-mail]
Disclaimer: All views are my own,         US: @col.hp.com:conor@inmos-c
            not those of INMOS.
"It's state-of-the-art" "But it doesn't work!" "That is the state-of-the-art".

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

Date: 25 Aug 89 00:55:55 GMT
From: bfmny0![e-mail]  (Tom Neff)
Subject: Re: Direct Information

In article <[e-mail]> [e-mail] writes:
>Is there an electronic publication that contains up-to-date information,
>without being colored by opinion?

That's a matter of opinion. :-)

Actually the NRAO has a 1200bps dialup service transmitting Coordinated
Universal Time (CUT) once per second.  That electronic service could be
said to be uncolored by opinion.  Everything else is tainted. :-)
--
"We walked on the moon --    ((    Tom Neff
    you be polite"         ))     [e-mail]

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

Date: 23 Aug 89 21:17:06 GMT
From: pacbell!osc![e-mail]  (Tim Atkins)
Subject: Re: Sunspots of the Future? (was Sun Spots)

In article <[e-mail]> [e-mail] (James N. Price) writes:
>
>-------
>I was at a recent, informal gathering of local (S. Calif) DXers at
>which it was mentioned that the sun might be in turmoil (i.e. good
>DX conditions) for the next 10 years or so.  Specifically, a
>recent Scientific American article was "quoted" as saying the current
>thinking is that there will be no sunspot minimum per se in the
>90s since the sun is changing magnetic poles and will be "upset"
>for quite a while.  Anyone have more info on this?  Or was the
>source of this info (our local ham radio store manager) trying to
>encourage sales??
>
>--Jim, K6ZH, ARPANET: [e-mail]

Please forgive me if these are a silly set of questions BUT:

    1) What correlation is there between increased solar turbulence
       and increased UV and skin cancer incidence on earth?

    2) What correlation with global warming trends?

    3) What if any correlation with ozone layer changes?

Thanks for your patience.

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

End of SPACE Digest V10 #5
*******************