Space & Astronomy/Space and Astronomy (October 1993).iso/mac/TEXT/SPACEDIG/V10_0/V10_003.TXT

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Date: Wed, 30 Aug 89 00:34:55 -0400 (EDT)
Subject: SPACE Digest V10 #3

SPACE Digest                                       Volume 10 : Issue 3

Today's Topics:
              Voyager link calculations
             Re: Galileo's RTG's.
         Voyager Disc (was Re: voyager audio)
               Re: SPACE Digest V9 #616
            Re: deep space dishes
        Re: Hipparchos (Was Re: European Space Agency)
         STS-34 background briefings set (Forwarded)
            Re: NSS Hotline Update
----------------------------------------------------------------------

Date: 24 Aug 89 03:33:46 GMT
From: ka9q.bellcore.com![e-mail]  (Phil Karn)
Subject: Voyager link calculations


Here's another link calculation for Voyager 2 at Neptune. I got some more
precise figures, and the result looks pretty reasonable. My references to
"Yuen" are to the book "Deep Space Telecommunications Systems Engineering",
edited by Joseph H. Yuen and published by Plenum (ISBN 0-306-41489-9).

8415 MHz transmitter power        +11.04 dBW
   (12.7 W - low power mode ref Yuen):
3.7 m spacecraft antenna gain
   (ref Yuen p 4):            +48.13 dB
EIRP:                    +59.17 dBW

Path loss, 4.416e9 km, 8415 MHz:    303.85 dB
   = 20 log10(4*pi*d*f/c)

Receive signal flux:               -244.68 dBW

70m receive antenna gain:        +73.8 dB
   = 10 log(4*pi*A/lambda^2) - N
   lambda = C/8415e6 = 3.56cm
   (assuming N = 2 dB illum loss)

Receive signal power:            -170.88 dBW = 8.16e-18 W
                            = 8.16 attowatts
                            = 8.16 nano nano watts

Received energy per bit (Eb):        -214.22 dBJ = 3.78e-22 J
   at 21.6 kb/s (43.34 dB-b/s)                = .000378 attojoules
                            = 0.378 piconanojoules

Receive noise density (N0):        -218.60 dBW-Hz
   = 10 log10(kT)
   T = 10 Kelvin (ref USENET)

Eb/N0 ratio:                4.38 dB

This is quite consistent with the performance of the concatenated rate 1/2
Reed Solomon + rate 1/2 convolutional coder, which according to Yuen (p 255)
has a very steep "wall" or threshold just below 3 dB.

However, this figure does not take into account miscellaneous losses
(connectors, feedlines, etc) on board Voyager or at the receiving site, nor
does it allow for atmospheric absorption or transmitter degradation below
the nominal 12.7 watt figure.

According to an interview carried tonight on NASA select, the arraying of
the VLA to Goldstone effectively doubles the aperture of the receiver, so
this should give another 3 dB of margin to compensate for these factors.

As you can see, attention to detail is all-important here!

Phil

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

Date: 23 Aug 89 15:46:04 GMT
From: mailrus!jarvis.csri.toronto.edu!utgpu!utzoo![e-mail]  (Henry Spencer)
Subject: Re: Galileo's RTG's.

In article <[e-mail]> [e-mail] (Hiram Clawson) writes:
>Why can't fuel cells be used for power generation in deep space?
>I assume there is a good reason they can't.

No, they were, on Project Apollo.  The trouble with fuel cells is that
they run out of fuel when you start talking about missions lasting years.
Getting even a modest power output that lasts years requires either an
outside source -- which means sunlight (assuming that it is bright enough
where the mission is going), since a space probe can't trail an extension
cord behind it -- or an *extremely* high energy density in a self-contained
power supply.  The energy density of chemical fuels is just too low; nuclear
power sources are the only viable method.
--
V7 /bin/mail source: 554 lines.|     Henry Spencer at U of Toronto Zoology
1989 X.400 specs: 2200+ pages. | uunet!attcan!utzoo!henry [e-mail]

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

Date: 23 Aug 89 16:17:04 GMT
From: ncspm![e-mail]  (Jay C. Smith)
Subject: Voyager Disc (was Re: voyager audio)

In article <[e-mail]> [e-mail] (Adam Glass)
writes:
>I would like to get a copy of the audio from the voyager's gold LP (you know,
>the one with the pictures of the man and woman, and the sounds of earth?)
>Where can I get a tape (preferred medium) of the "sondes of earth"?

Actually the entire contents of the discs sent with the Voyager spacecraft
seem like a good commercial laser videodisc release.  Has this been done?

--
"Good.  For a minute I thought we were in trouble."
---------------------------------------------------------------------
Jay C. Smith                      uucp:     ...!mcnc!ncsuvx!ncspm!jay
Domain: [e-mail]        internet: [e-mail]

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

Date:         Wed, 23 Aug 89 09:57:44 EDT
From: Leonard Abbey <[e-mail]>
Subject:      Re: SPACE Digest V9 #616
To: Henry Spencer <[e-mail]>

Mr. Spencer, we could do it again.  You couldn't.

Leonard Abbey
Georgia Tech
Research Institute
[e-mail]

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

Date: 23 Aug 89 17:09:30 GMT
From: tekbspa!optilink![e-mail]  (Clayton Cramer)
Subject: Re: deep space dishes

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
# Voyager's signal is as follows:
#
#     22W transmitter @ 8.5GHz          43 dBm
#     3.7m parabolic antenna 55% efficient      38 dBi
#     free space path loss (29.6 AU)        -303 dB
#     70m antenna gain              73 dBi
#                         --------
#                         -149 dBm
#
#     15 degree K receiver            -187 dBm/Hz
#
#     S/N                      38 dB/Hz
#
# I can't remember, offhand, what the data rate from Voyager is, but 20kHz
# comes to mind, so:
#
#     BW 20kHz                 -43 dB
#
#     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
A pacifist who calls the police isn't one; hired violence is still violence.
----------------------------------------------------------------------------
Disclaimer?  You must be kidding!  No company would hold opinions like mine!

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

Date: 23 Aug 89 13:41:46 GMT
From: stsci![e-mail]  (Giggles Gonzaga -- Prophetess of Wisdom and Truth)
Subject: Re: Hipparchos (Was Re: European Space Agency)

From article <[e-mail]>, by [e-mail] (Bob Gray):
>
> Does anyone have more information about what orbit Hipparcos
> is actualy in, and how long it is going to last there?
>     Bob.

A guy named Peter Bunclark has been posting some very interesting
information on HIPPARCOS in our local Space Telescope Science Institute
bulletin board. Here are excerpts from his articles --
------------------------------------------------------------------------
Date: 14 Aug 89 10:20:05 EDT

   "Hipparcos was successfully launched just after midnight on the 8/9 August.
   This placed the satellite into a transfer orbit with a perigee height of
   800 km and an apogee height of 41,000 km. The satellite was successfully
   spun up and all systems were described as nominal. On Thursday 10 August at
   1420 the apogee boost motor was supposed to fire and place Hipparcos into a
   geostationary orbit. It didn't. This was at the 4th apogee of the
   satellite. At the 6th apogee (Friday 11th 0930) another unsuccessful
   attempt occurred. Technical evaluations were being carried out."

Date: 17 Aug 89 12:26:40 EDT

   "The cause of the problem that has led to the failure
   of the apogee boost motors has been traced to a short circuit.
   The spin rate of the satellite was halved to see if this would
   have any affect on the short circuit. A further attempt at
   firing the motors was tried at 1300 (BST) today (17th). This
   was unsuccessful. The next attempt will be on Monday 21st at
   1110 (BST).

   If all attempts are unsuccessful the planned revised mission will
   take place in the current highly elliptical orbit (210km-36000km).
   It is possible that the perigee will be raised several hundred kms
   by using the hydrazine boosters. There are fears now that even
   this mission will not be as successful as first thought. Originally
   it should have lasted 6 months or more. Now the timescale is
   thought to be 3 to 4 months. This will mean that we will not even
   be able to get full sky coverage."

Date: 21 Aug 89 10:27:16 EDT

   "It would seem that there are 2 faults in the firing systems
   of the satellite. With the 2nd firing system it seems that the
   first stage of the circuitry is working fine but it's not
   proceeding to the second stage. In addition to the 1110 attempt
   on Monday to fire the motor there will also be one on Tuesday.

   There are also more problems with the alternative observing
   programme than first thought. Due to the lack of continuous
   contact with the ground stations it makes it very difficult to
   work out the attitude of the satellite (needed to better than
   1" accuracy) if it observes in a manner similar to the original
   mission. An alternative is that the spin axis points towards
   the Sun all the time. This leads to problems with the Solar
   panels overheating. Even if the ground station at Kourou is
   used we would only get ~70% coverage. There is also the problem
   that the detectors must be switched off when the satellite is
   below 10,000km. This is for about 2 hours every orbit.

   Another problem is that the satellite will spend longer stretches
   of time in the Earth's shadow due to it being in the current orbit.
   These periods will be longer than the backup batteries can cope
   with, so that during the March/April eclipse season the satellite
   will have to be placed in a dormant state. It could be that the
   satellite will not recover from this.

   There will also be a delay of 2 months (plus) before this alternative
   mission gets started while ESOC ground control carrys out various
   reprogramming that has to be done."

--
______________________________________________________________________________
Shireen Gonzaga/Space Telescope Science Inst./3700 San Martin Dr., Baltimore,
MD21218/tel[phone]/ARPA [e-mail]/SPAN SCIVAX::GONZAGA/sometimes
you just have to give in to the absurd -- Picard in ST-TNG "Up the Long Ladder"

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

Date: 24 Aug 89 22:43:02 GMT
From: trident.arc.nasa.gov![e-mail]  (Peter E. Yee)
Subject: STS-34 background briefings set (Forwarded)

Sarah Keegan
Headquarters, Washington, D.C.                    August 24, 1989

Steve Nesbitt
Johnson Space Center, Houston


N89-61

EDITORS NOTE:  STS-34 BACKGROUND BRIEFINGS SET

     The background briefings and astronaut press conference for
STS-34, the Oct. 12 flight of Space Shuttle Atlantis, are
scheduled for Sept. 5 and 6 at the Johnson Space Center, Houston.

     STS-34 will deploy the Galileo spacecraft to study the
planet Jupiter.

     A mission overview with the lead flight director and Galileo
spacecraft mission manager will begin at 1:30 p.m. EDT, Sept. 5,
followed at 3 p.m. by a briefing from the Galileo mission
scientist of the scientific observations to the made by the
planetary probe.  Briefings on other STS-34 payloads and
experiments will follow.

     The astronaut crew of STS-34 will hold a press conference at
11:15 a.m. EDT, Sept. 6.

     All briefings will be carried live on NASA Select television
via Satcom F2R, transponder 13, 72 degrees west longitude.  Two-
way question and answer capability will be available at NASA
Headquarters, Washington, D.C., the Jet Propulsion Laboratory,
Pasadena, Calif., the Kennedy Space Center, Fla., and the
Marshall Space Flight Center, Huntsville, Ala.

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

Date: 23 Aug 89 16:51:27 GMT
From: mcsun!ukc!icdoc!syma![e-mail]  (Nick Watkins)
Subject: Re: NSS Hotline Update

In article <[e-mail]> [e-mail] (Henry Spencer) writes:
>In article <246900031@cdp> [e-mail] writes:

>>A Soviet cosmonaut, Valeri Bykovsky, has written a book in which
>>he states that he was slated to pilot a spacecraft to the Moon
>>prior to the US Apollo 11, but that the death of a top Soviet
>>rocket designer slowed the lunar program.

 [Deleted stuff]

>Christ on a crutch!  What microcephalic ignoramus wrote this?!?  The
>Soviets said openly, explicitly, and repeatedly that they had a lunar
>program and that it was aimed at beating the US.  They've gone sort
>of quiet about it since it was cancelled, but it was never a secret,
>and there is plenty of corroborating evidence for its existence.

All true, BUT, official Soviet acknowledgements are useful, especially as
Bykovsky had been speculated on as a lunar flyby or orbit cosmonaut (see
e.g Phil Clark's "The Soviet Manned Space Programme"). The fact that the
lunar programme was delayed by Korolev's death is not surprising, but as
this was in 1966 one wonders how urgent the race was by 1969. Certainly
the original Soyuz designs (c.f. Clark's book) had been heavily amended.

>Incidentally, said ignoramus may also have jumped to incorrect conclusions.
>Note that Bykovsky is said to have referred to "a lunar mission", not
>necessarily a landing mission ... [stuff deleted] ...
> but a lunar
>flyby -- a la Apollo 8 -- was definitely possible and might have been
>practical before Apollo 8 if things had gone right.

The said Phil Clark is not sure about "definitely". He points out some
interesting counter arguments, but along with most observers feels that
the flurry of Zond activity before Apollo 8 did mean a lunar flyby was
imminent.
 On a related point the current issue of "Spaceflight" carries a letter
relating the disclosure by Cosmonaut Valentin Lebedev of the existence
of the G1 booster, confirmation of the conical 1st stage design, and
confirmation of the 3 launch failures.
 He then went on (in coversation with Mark Camp of Texas A&M) to deny
"the existence of a Soviet manned lunar landing programme in the 1960s".
Risking Henry's wrath I would say this is the first admission of the
existence of the G1 and near conclusive proof that there WAS a manned
lunar programme, unless the G1 was a long term space station related
project. This of course doesn't prove the Russians were in any shape to
land men on the moon though.






--
Nick Watkins, Space & Plasma Physics Group, School of Mathematical
& Physical Sciences, Univ. of Sussex, Brighton, E.Sussex, BN1 9QH, ENGLAND
JANET: [e-mail]   BITNET: [e-mail]
Voice: [phone]

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

End of SPACE Digest V10 #3
*******************