Space & Astronomy/Space and Astronomy (October 1993).iso/mac/TEXT/SPACEDIG/V15_5/V15NO539.TXT

Internet Message Format | 1993-07-13 | 40KB

Date: Sun, 13 Dec 92 05:00:10
From: Space Digest maintainer <[e-mail]>
Reply-To: [e-mail]
Subject: Space Digest V15 #539
To: Space Digest Readers
Precedence: bulk


Space Digest                Sun, 13 Dec 92       Volume 15 : Issue 539

Today's Topics:
              Cassini Undergoes Intensive Design Review
                      DC vs Shuttle capabilities
                     Mariner 2's 30th Anniversary
                 Mariner 2 Radio Tracking - 12/28/92
              Mariner 2 Venus Flyby - 12/14/62 (2 msgs)
              New Moon race (was Re: NASA town meetings)
                                Titan
                   what the little bird told Henry

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Date: 12 Dec 92 00:34:16 GMT
From: Ron Baalke <[e-mail]>
Subject: Cassini Undergoes Intensive Design Review
Newsgroups: sci.space

In article <[e-mail]>, [e-mail] (Hayim Hendeles) writes...
>In article <[e-mail]> [e-mail] writes:
>> ...
>>     After flybys of Venus (twice), Earth and Jupiter as it loops
>>around the sun to pick up energy, Cassini will arrive at Saturn
>>in November 2004, beginning a four-year orbital tour of the
>>ringed planet and its 18 moons. The Huygens probe will descend to
>>the surface of Titan in June 2005.
>
>Pardon my asking an ignorant question, but I can't understand why it
>should take 7 years to get to Saturn. When Voyager went to Jupiter and
>Saturn, it took (if I recall correctly) 4 years and a Jupiter flyby to
>make it to Saturn. Here, you are using 4 flybys, and it's taking you 7
>years! I would think that if you were to adjust the launch date so that
>Jupiter and Saturn were in the same relative positions as they were in
>1977 (when Voyager was launched), you could do the same trick again (in
>the same 4 years).

Inherently, orbiters will take longer to get to their destination than
flybyers.  Spacecraft that will orbit a planet (like Cassini) tend to be
bigger than spacecraft that are on flyby missions because they have to
carry additional propellant that will be used for orbit insertion.
Cassini is also carrying a Titan probe which adds additional mass to the
spacecraft.  The orbital mechanics are more constrained for an orbiting
mission because the approach speed to the planet has to be less, where
this was not much of a concern with Voyager.  To
further complicate the situation, the U.S. do not have any launch vehicles
that are powerful enough to send Cassini on a direct trajectory to the
outer planets.  To make up for this, the spacecraft has to circle around
the inner solar system for gravity assists from Venus and Earth
to pick up enough momentum to reach Jupiter, and then slingshot to Saturn.
These additional gravity assists add years to the mission.
     ___    _____     ___
    /_ /|  /____/ \  /_ /|     Ron Baalke         | [e-mail]
    | | | |  __ \ /| | | |     Jet Propulsion Lab |
 ___| | | | |__) |/  | | |__   M/S 525-3684 Telos | The 3 things that children
/___| | | |  ___/    | |/__ /| Pasadena, CA 91109 | find the most fascinating:
|_____|/  |_|/       |_____|/                     | space, dinosaurs and ghosts.

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

Date: 12 Dec 92 18:44:09 GMT
From: Greg Moore <[e-mail]>
Subject: DC vs Shuttle capabilities
Newsgroups: sci.space

In article <[e-mail]> [e-mail] (Allen W. Sherzer) writes:
>In article <[e-mail]> [e-mail] (Greg Moore) writes:
>
>>    1) Won't teh crew compartment take up part of the cargo bay?
>
>Of course. On the other hand the standard interface which makes you do
>this reduces integration time which keeps flight rate up and costs down.
>
    You missed my point.  If your crew compartment is in the cargo
bay, where do you put the satellite?

>In the longer run, you may be right. Plumeting launch costs will cause
>payload prices to fall since there will be more and cheaper launches
>plus the opportunity for on site repair.
>
    I eliminated some stuff above, but wanted to add some stuff here.
Actually, plummeting launch costs may contribute to lower payload costs
since people will be willing to build a less fault tolerant system
knowing that if it fails, they can launch another cheaply.
As for on-site repair, for now DC-? fails for the same reason that
the Shuttle normally does, it can't get up to GEO, you need a
OTV... in which case it doesn't matter in the long run how you get
into orbit, as long as it is cheap enough.

>>    Also, as for retrieval, the Shuttle has shown that it ain't
>>easy to do.  Will a two day on-orbit time be enough?
>
>It may take modifications to the DC. At the very least you need to add
>a robot arm and an airlock.
>
    Granted, but that's not what I meant.  Will you have enough time
to rendevous and capture the satelite?  It took what 3 days for the
shuttle to capture Intelsat VI? That's aday more than DC-?.
Also, what type of fuel margin would DC-1 have for IN-orbit
manevours? (I realize it has enough for landing, and of course
you don't wnt to cut into that for safety reasons.)

>>    Let's not try to have DC-1 do everything... remember that is
>>where the shuttle went wrong.
>
>But let's use it for what we can. The way to bring costs down fast with
>this concept is to use it.
>
    Use it yes, but use it for what it can be used for economically.
Let's see, we've added an airlock, an arm, additional on-orbit capacity.
Hmm, that adds up, and add complexity.  Yes, let's ok at possibilities,
but not claim t they are definites.

>My view is that we use the basic DC as a 'bus' which can be modified in
>small ways to meet diverse missions. Costs are cut because the same assembly
>lines are used to make DC1-EOT (Earth orbit transfer), DC1-OMV, and DC1-LM.
>
    I have a question about this.  EOT and LM should require roughly
the same amount of fuel, no? (as I recall, the energy to get into lunar
orbit is about the same as GEO? I'm ignoring landing here).  But how
economical is it to transport that fuel TO orbit?  Am I correct in
remembering you saying about 10 DC-1 flights?

    Also, does it make sense for the DC1-EOT and OMV and LM the same.
The requirements for landing gear are different.  The requirements for
fuel transfer MAY be different.  What about thermal protection.  LM
won't require any to land on the moon, but what about reentering earth
orbit or earth landing?


>This makes the basid DC a building block of a more extensive space
>infrastructure.
>
    Granted.  And that is attractive.

>  Allen
>
>--
>+---------------------------------------------------------------------------+
>| Allen W. Sherzer | "A great man is one who does nothing but leaves        |
>|  [e-mail]     |  nothing undone"                                       |
>+----------------------134 DAYS TO FIRST FLIGHT OF DCX----------------------+

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

Date: 12 Dec 92 01:03:41 GMT
From: Ron Baalke <[e-mail]>
Subject: Mariner 2's 30th Anniversary
Newsgroups: sci.space,sci.astro,alt.sci.planetary

PUBLIC INFORMATION OFFICE
JET PROPULSION LABORATORY
CALIFORNIA INSTITUTE OF TECHNOLOGY
NATIONAL AERONAUTICS AND SPACE ADMINISTRATION
PASADENA, CALIF. 91109.  TELEPHONE [phone]

Contact: James H. Wilson

FOR IMMEDIATE RELEASE                   December 9, 1992

     Thirty years ago, Dec. 14, 1962, the first successful
interplanetary traveler reached Venus after a 108-day journey
from Earth.  Named Mariner 2, it was a 200-kilogram (450-pound)
machine carrying six scientific instruments, a two-way radio, a
solar power system and assorted electronic and mechanical
devices.  Its crew, numbering roughly 75, stayed behind at NASA's
Jet Propulsion Laboratory.

     The Mariner planetary spacecraft series began in 1960 as a
group of mission studies at JPL; by 1975 there had been 10
Mariner flights, seven of them successful explorations of the
inner Solar System.  Mariner 2 became the model for planetary
space flights,  one that emphasized good and copious scientific
data collection, utilizing remote sensing of planets and in-situ
measurement of the space environment; all of is this supported by
high-quality engineering.

     The resulting program eventually led to close observation of
all the planets but Pluto, planetary orbiters and landers,
international cooperative missions and flights right out of the
Solar System.  What became the Mariner 2 mission was
authorized by NASA in August 1961, less than a year before the
first launch window.  The limited capacity of Atlas/Agena, the
largest available launch vehicle, severely restricted launch
opportunities and spacecraft size.  The first launch, Mariner 1,
was aborted when its launch vehicle strayed from the safe flight
corridor and was destroyed by the Range Safety Officer.

     Mariner 2 was successful, however; since that trailblazer
mission, there have been about four dozen U.S., Soviet and other
flights -- the majority successful -- reaching every planet from
Mercury to Neptune, plus comets and an asteroid, and one joint
U.S.-European mission (still underway) to the poles of the Sun.
These are in addition to dozens of lunar spacecraft and the
manned lunar flights of Project Apollo.

                             Liftoff

     A few minutes before 2 a.m. on Aug. 27, 1962, Mariner 2
lifted off the pad at Cape Canaveral aboard its Atlas-Agena
rocket.  It was nearly as much an experiment for the rocket and
spacecraft engineers as for the space scientists intent on
observing interplanetary space and the planet Venus.

     During its three-and-a-half-month odyssey of some 290
million kilometers (180 million miles), reaching a third of the
way around the Sun to Venus, Mariner 2 transmitted coded signals
continuously to the Earth, mixing scientific measurements of
interplanetary dust, magnetism, cosmic rays and solar plasma with
engineering data on the health and performance of the spacecraft.

     As Earth turned beneath the feeble radio transmissions,
three great steerable antennas (now the Deep Space Network)
captured Mariner's signals in turn, first in California, then
Australia, Africa and California again.

     Mariner 2 suffered and survived a number of unanticipated
events during the flight.  It lost its attitude orientation; one
of the solar panels failed; many temperature readings rose
ominously as Mariner approached Venus; and, just before the Venus
encounter, the computer/sequencer became erratic.  But Mariner
automatically recovered its orientation, survived solar heating,
and, as sunlight grew more intense, one solar panel did the work
of two.  When the flight engineers saw the sequencer faltering,
they started the encounter sequence by radio commands from Earth.

     On Dec. 14, 1962, Mariner's infrared and microwave
radiometers scanned back and forth across the planet, capturing
data that would prove Venus's surface to be fire-hot -- about 425
degrees Celsius or 800 Fahrenheit -- warmed in part by a runaway
greenhouse effect in the thick carbon dioxide atmosphere.  About
three weeks after its historic Venus flyby, Mariner 2 went off
the air.  Its signal was last received on Jan. 3, 1963.

     The ability of Mariner's crew and equipment to overcome in-
flight problems, and simply to complete the flight to the planet
Venus, constituted major technical advances in addition to the
scientists' discoveries about Venus and the Solar System.  The
spacecraft design proved robust, and the attitude-stabilized
spacecraft concept feasible for long-term exploration.

                             To Mars

     Two years later -- Nov. 28, 1964 -- a second-generation
Mariner set forth -- this time on an eight-month journey to Mars.
Mariner 4, like its predecessor, survived the loss of a twin and
the rigors of an alien environment.  Also like the earlier
Mariner it was extremely light in weight, solar-powered, fully
stabilized, automated, in constant contact with a team of
engineers and scientists back on Earth and bristling with
instruments.

     Unlike Mariner 2, this machine could see: a TV camera and
tape recorder caught the first close-up pictures of the surface
of Mars, revealing moon-like craters, some of them topped with
frost.  The navigators sent Mariner 4 behind Mars, letting the
radio link with Earth serve as a probe of the atmospheric density
and revealing a surface pressure less than 1 percent of Earth's.

     Following the pattern set by Mariner 2 and Mariner 4,
NASA/JPL sent spacecraft back to Venus and Mars, into Mars orbit
and to Mercury.  The latter flight, made by Mariner 10 in 1973-
74, used the gravitational field of Venus to boost it inward to
the orbit of Mercury.  In the 1970s, various USSR spacecraft
orbited Venus, entered its thick atmosphere, even landed.

     In 1976, two NASA scientific stations landed on Mars,
remaining in operation for several years. This Viking mission,
encompassing two large Mars-orbiting spacecraft as well as the
two landers, conducted a comprehensive, long-term mapping survey
of the entire planet, spot investigations of special areas
(including the moons Phobos and Deimos), and atmospheric studies.
Viking also produced biological, chemical, meteorological,
physical and image data collected at the landing sites.

                          A Grand Tour

     A year later two spacecraft were launched on what became the
grand tour of the outer planets: the Voyager mission to Jupiter,
Saturn, Uranus, Neptune and -- still going -- beyond the Solar
System to interstellar space.  Voyager 1 used Jupiter's
gravitational field to speed it on to Saturn and then, after tens
of thousands of images of the two planets and their many
satellites, it left the plane of the ecliptic.  Voyager 2 also
flew past Jupiter (1979) and Saturn (1981), but its path was
designed to use additional gravity assists to sling it onward to
Uranus (1986) and Neptune (1989).

     The two Voyagers took a total of well over 100,000 images of
the outer planets, rings and satellites, as well as millions of
chemical spectra, magnetic and radiation measurements.  They
discovered rings around Jupiter, volcanoes on Io, shepherding
satellites in Saturn's rings, new moons around Uranus and
Neptune, geysers on Triton.  The last imaging sequence was
Voyager 1's portrait of the Solar System, showing Earth and six
other planets as sparks in a dark sky lit by a single bright
star, the Sun.

     Two spin-stabilized Pioneer spacecraft had preceded the
Voyagers to Jupiter, and one of them went on to Saturn, before
heading out of the System.  Thus, four NASA spacecraft are now
actively searching, in different directions, for the frontier
between solar and interstellar space; at least one is expected to
detect it in the next quarter-century.

                             New Era

     Shortly before Voyager 2's Neptune encounter, a new
generation of planetary exploration began.  Magellan set out for
Venus in 1989 to map the surface from orbit using imaging radar.
A Pioneer spinning spacecraft had been orbiting Venus for more
than a decade, completing a low-resolution radar topographic map
and many other planetary and solar studies; the Soviets compiled
radar images of the northern part of Venus, landed more cameras
and deployed balloons into the atmosphere.  Magellan mapped 99
percent of the surface at high resolution, parts of it in stereo,
and is presently mapping the gravitational field.

     In October 1989, NASA/JPL's Galileo spacecraft began a
gravity-assisted journey to Jupiter, where it will place a probe
in the atmosphere and observe planet and satellites from orbit
for two years.  On the way, Galileo performed gravity-assist
encounters with Venus and the Earth and made the first close
flyby of asteroid Gaspra in 1991.

     In a joint mission with the European Space Agency, NASA
launched the Ulysses spacecraft in 1990 on a flight over the
poles of the Sun.  To achieve high orbital inclination, the
spacecraft did a gravity-assist flyby of Jupiter, measuring the
magnetosphere as it did so.

     In September 1992, Mars Observer was launched to Mars.  It
is scheduled to go into orbit around the planet in August 1993
and make many observations during a period of one Martian year.

     As 1992 rounded out three decades of scientific growth and
achievement in observing and understanding the Solar System and
the development of highly sophisticated spacecraft and missions,
NASA began to look anew to the small, purposeful, higher-risk
kind of mission represented by Mariner 2 thirty years ago.

                              #####
     ___    _____     ___
    /_ /|  /____/ \  /_ /|     Ron Baalke         | [e-mail]
    | | | |  __ \ /| | | |     Jet Propulsion Lab |
 ___| | | | |__) |/  | | |__   M/S 525-3684 Telos | The 3 things that children
/___| | | |  ___/    | |/__ /| Pasadena, CA 91109 | find the most fascinating:
|_____|/  |_|/       |_____|/                     | space, dinosaurs and ghosts.

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

Date: 12 Dec 92 01:47:15 GMT
From: Ron Baalke <[e-mail]>
Subject: Mariner 2 Radio Tracking - 12/28/92
Newsgroups: sci.space,sci.astro,alt.sci.planetary

OFFICE OF PUBLIC EDUCATION AND INFORMATION
CALIFORNIA INSTITUTE OF TECHNOLOGY
JET PROPULSION LABORATORY
NATIONAL AERONAUTICS AND SPACE ADMINISTRATION
PASADENA, CALIFORNIA.

FOR RELEASE:  P.M.'s of Friday, December 28, 1962
   RADIO TRACKING OF MARINER II AND ITS SCIENTIFIC IMPLICATIONS

          Mariner II's fly-by of Venus on December 14 has produced
the most accurate estimate yet of the mass of our sister planet,
two scientists from the California Institute of Technology Jet
Propulsion Laboratory reported today.  This information was re-
vealed at a meeting of the American Geophysical Union at Stanford
University, in a paper by John D. Anderson and George Null,
describing their preliminary analysis of the trajectory data
obtained during the 109-day flight of Mariner II from earth to
Venus.  According to Anderson, who presented the paper, they find
the mass of Venus a value of 0.81485 times the mass of the earth,
with a probable error of 0.015 percent.  They said that their
analysis is continuing, using additional data obtained before and
after the encounter with Venus, and that their final result will
probably alter the quoted value slightly and still further reduce
the probable error.  For comparison, the mass of the earth is
known to be approximately 13,173,000,000,000,000,000,000,000
pounds (about 13 septillion pounds).
          The only method known to astronomers for determining
the mass of other planets is through the observation of their
gravitational effects on other bodies in the solar system.  Thus,
for planets having satellites (moons), the determination can be
made with considerable accuracy.
          In the case of Venus, which has no known satellites, no
natural object has ever been observed to pass close to it, and
hence all estimates of its mass made before 1940 were both
inaccurate and erroneous.
          Two more recent determinations are in agreement with
the new Mariner value, but have much less precision.  In 1943, G.
M. Clemence published a value equivalent to 0.813 times the
earth's mass, with a probable error of 0.34 percent, based upon
his study of the astronomical records of the observations of the
motions of the planet Mercury through the year 1767 to 1937.
          In 1954, E. W. Rabe obtained a value equivalent to
0.8148, with a probable error of 0.05 percent, from records of
the motion of the minor planet, Eros, over two decades.
          In contrast, the data required to deduce the new more
accurate mass of Venus were obtained by the Jet Propulsion
Laboratory's Goldstone Tracking Station during two 10-hour
observations of Mariner, on the day of its passage of Venus and
the previous day.
          The data obtained was a so-called "two-way Doppler"
measurement, involving a round trip by a radio signal.  A signal
at a frequency of approximately 960 megacycles per second was
sent from Goldstone and was received by Mariner, 3 minutes 12.5
seconds later.  The spacecraft then shifted the frequency of the
signal slightly and sent it back to Goldstone, where it was
compared to the original signal.
          From this comparison the spacecraft velocity relative
to the earth, approximately 40,000 miles per hour, can be
calculated within about 0.01 miles per hour, and it was the
change in this velocity amounting to approximately 3,000 miles
per hour, produced by the gravitational field of Venus which gave
the scientists the necessary data to determine the mass of the
planet.
          Anderson also said that further analysis of the data
will probably refine our knowledge of another particularly
important astronomical constant, the Astronomical Unit--the mean
distance between the sun and the earth.
          At present, the measurement of this unit by a variety
of conventional astronomical techniques are slightly in disagree-
ment with those obtained by bouncing radar beams off of Venus, as
has recently been done again by the Goldstone station.  The two-
way Doppler measurement is an independent measurement, and may
help to resolve the inconsistency.

224-12/62
     ___    _____     ___
    /_ /|  /____/ \  /_ /|     Ron Baalke         | [e-mail]
    | | | |  __ \ /| | | |     Jet Propulsion Lab |
 ___| | | | |__) |/  | | |__   M/S 525-3684 Telos | The 3 things that children
/___| | | |  ___/    | |/__ /| Pasadena, CA 91109 | find the most fascinating:
|_____|/  |_|/       |_____|/                     | space, dinosaurs and ghosts.

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

Date: 12 Dec 92 01:35:15 GMT
From: Ron Baalke <[e-mail]>
Subject: Mariner 2 Venus Flyby - 12/14/62
Newsgroups: sci.space,sci.astro,alt.sci.planetary

In honor of the 30th anniversary of Mariner 2's flyby of
Venus, I am posting three of the Mariner 2 press releases
from 1962.

Ron Baalke

OFFICE OF PUBLIC EDUCATION AND INFORMATION
CALIFORNIA INSTITUTE OF TECHNOLOGY
JET PROPULSION LABORATORY
NATIONAL AERONAUTICS AND SPACE ADMINISTRATION
PASADENA, CALIFORNIA

FOR RELEASE:  To A.M.'s of Friday, December 14, 1962

                           MARINER II
                         VENUS ENCOUNTER

         Man's first chance to obtain information from another
planet will come on December 14 when the Mariner II spacecraft
passes approximately 21,000 miles from Venus.
          Mariner's radiometers will pierce the cloud cover to
determine surface temperature and temperatures in the atmosphere.
Instruments will determine the strength of the magnetic field and
nature of the radiation belts.  The entire spacecraft will measure
the strength of the gravitational field as it speeds and slows on
its curving path near Venus.
          The 447-pound spacecraft was launched by the National
Aeronautics and Space Administration on August 27, 1962, at 1:53
a.m. from the Atlantic Missile Range, Cape Canaveral, Florida.
It was built, and is now being tracked, by the California
Institute of Technology Jet Propulsion Laboratory.  The launch
vehicle was the Atlas-Agena B.
          When the Mariner arrives at Venus it will have traveled
182,000,000 miles during its 109-day journey through space.
During its long cruise, that extended almost halfway around the
Sun, the spacecraft set a long distance communication record of
36,000,000 miles, and performed the first successful guidance
maneuver in space.
          The Mariner II carries six scientific experiments.  Four
of these, turned on by ground command two days after launch, are:
a magnetometer, an ion chamber and particle flux detector, a solar
plasma detector, and a cosmic dust counter.  They have been making
invaluable measurements during Mariner's curving trip towards
Venus and when the spacecraft arrives will measure magnetic
fields, radiations and dust particles around the planet.
          Two other experiments--a microwave radiometer and an
infrared radiometer--will scan the surface and the atmosphere of
Venus for 42 minutes as Mariner rushes by.
          All telemetry information gathered during Mariner's
voyage is transmitted by Mariner to a network of ground receiving
stations called the Deep Space Instrumentation Facility (DSIF)
which are located in Goldstone, California, Woomera, Australia,
and Johannesburg, South Africa.
          Mariner was launched in a way that would cause it to
fall inward toward the Sun.  This was accomplished by timing the
injection so that the spacecraft would leave earth in a direction
opposite from that of the Earth in its orbit around the Sun.
Since Mariner's speed around the Sun was less than that of the
Earth, it could not maintain a circular orbit like Earth and the
Sun's gravity caused it to be drawn inward so that it would
eventually intercept the trajectory of Venus.
          By nine days after launch, DSIF tracking data processed
at JPL's Space Flight Operations Center in Pasadena, showed that
Mariner would arrive at a rendezvous ahead of Venus, missing the
planet by 233,000 miles.  This launch dispersion was well within
the correction capability of the 50-pound-thrust rocket motor
aboard the spacecraft.  During the midcourse maneuver, the motor
was fired for 27 seconds affecting a slight decrease in velocity.
This guidance correction will bring Mariner to a point 21,000
miles from the planet.  This point is well within the original
target area, a pie-shaped region extending between 8000 to 40,000
miles from Venus.
          Before Mariner passes Venus a sequence of events will
begin.  The first of these will be the activation of a stored
command in the spacecraft's central computing and sequencing
system that turns on the radiometer scan device.  If for some
reason this command is not initiated by the spacecraft, it will
be sent by the DSIF Goldstone station.
          The radiometers, located on the hexagonal deck of the
spacecraft, are 20 inches in diameter and five inches deep.  They
are mounted on a swivel and are driven by an electric motor in a
120 degree scanning motion.  During the pass by Venus, the
microwave and infrared energy will be collected and transmitted
to Earth.
          Prior to activation of the radiometers, the Mariner was
in a "cruise mode."  In this mode, it was continuously telemeter-
ing the first 20 seconds of information provided by its four
interplanetary scientific instruments, and then 16 seconds of
engineering data.  Engineering data is concerned with the condi-
tions aboard the spacecraft and include temperatures, pressures,
voltages and angular positions.
          During the fly-by, the data format changes from "cruise
mode" to "encounter mode" and Mariner devotes itself exclusively
to gathering and sending scientific data.
          At the time that the radiometer's scan mechanism is
turned on, Mariner will be approaching the planet from the dark
side and moving in a downward direction.  As seen from Venus, the
spacecraft will be moving in a direction to the right and below
the Sun.
          As Mariner cruises past Venus its solar panels will
remain locked on the Sun to obtain electrical power, as they did
throughout the long mission.  The radiometers point in a direction
perpendicular to the roll axis of the spacecraft and move in a
nodding motion across the surface of Venus at a rate of one-tenth
of a degree per minute.  As Mariner passes Venus, the radiometers
will first scan the dark side and then the sunlit side.
          This planetary scanning period will last for 42 minutes.
During this time, the findings of all sox scientific experiments
will be transmitted to the Woomera and Goldstone DSIF stations.
          At 66 minutes before the point of closest approach, or
10:55 a.m., December 14, Mariner will be 25,262 miles from Venus.
At that time its velocity will have increased to approximately
87,000 mph due to the gravitational pull of the planet.  At this
time the radiometers should detect the planet's surface for the
first time.
          At 44 minutes before the point of closest approach, or
11:17 a.m., Mariner will pass the planet's terminator, or
dividing line between light and darkness.  It will still be moving
downward and picking up speed.
          Drawn by the gravitational field of Venus the spacecraft
continues to accelerate.  By 11:37 a.m. the scanning period ends
as Venus moves out of sight of the radiometers.  At that point in
time, Mariner will be going approximately 87,000 mph.  Venus will
be approximately 21,700 miles away while the Earth is about
36,000,000 miles away.
          Twenty-three minutes later, at 12:01 p.m., Mariner will
reach the position of closest approach, approximately 21,000 miles
from Venus.  It will be traveling approximately 88,400 mph.
          The gravitational attraction of Venus will have
increased Mariner's velocity by 1400 mph in one hour.  As the
spacecraft starts moving away from Venus, gravity reverses its
effect and starts slowing the spacecraft down.  In addition to
changing the speed of the spacecraft, the gravitational field also
will bend Mariner's trajectory by about 25 degrees during
encounter.
          After closest approach Mariner will be instructed to
turn off its radiometers and return to the cruise mode.  When the
command is obeyed the spacecraft will resume the sending of
engineering data and will continue to take measurements with its
interplanetary instruments.
          It will continue in this mode until the mission is
completed.
          On December 27, it will reach its closest point to the
Sun, 65,539,000 miles.  At this time, its velocity will be
approximately 85,300 mph.  It will be 2,700,000 miles from Venus
and Mariner then will be 44,213,000 miles from Earth in a helio-
centric orbit around the Sun.
          Uncertainties in Mariner's trajectory resulted from:
the effect of solar pressure, the mass and gravitational fields
of the Earth and Venus, the exact location of ground tracking
stations and the astronomical unit.
          Refinements in these uncertainties will be achieved by
analysis of the tracking and doppler data collected during
Mariner's trip and during the encounter phase when Mariner's
trajectory is perturbed by Venus gravity.
          The doppler effect is a principle of physics in which
the frequency of radio waves appear to increase when a transmitter
and receiver are approaching each other, and to decrease when they
are moving apart.  The speed of Mariner is determined by analysis
of the frequency of its signals.

219-12/62
     ___    _____     ___
    /_ /|  /____/ \  /_ /|     Ron Baalke         | [e-mail]
    | | | |  __ \ /| | | |     Jet Propulsion Lab |
 ___| | | | |__) |/  | | |__   M/S 525-3684 Telos | The 3 things that children
/___| | | |  ___/    | |/__ /| Pasadena, CA 91109 | find the most fascinating:
|_____|/  |_|/       |_____|/                     | space, dinosaurs and ghosts.

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

Date: 11 Dec 92 17:55:50 GMT
From: Lord Vader <[e-mail]>
Subject: Mariner 2 Venus Flyby - 12/14/62
Newsgroups: sci.space,sci.astro,alt.sci.planetary

In honor of the achievements of the Mariner 2 mission, we
should take this time to contemplate the significance of
the planned shutdown of the operational Magellan spacecraft
scheduled for mid 1993.

We have only made a limited number of interplanetary spacecraft
and thus it seems almost criminal to shut off a spacecraft
that is for the most part fully operational.

Keep Magellan Alive.

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

Date: Sat, 12 Dec 92 12:11:31 -0600
From: [e-mail] (Phil G. Fraering)
Subject: New Moon race (was Re: NASA town meetings)
Newsgroups: talk.politics.space

In talk.politics.space you write:


>You missed the point, or ignored the question. Unless you think
>we have unlimited resources to do everything we'd like to do
>(and we don't), we have to prioritize, doing some things now and
>some later.  If you think returning to the moon is the thing
>to do NOW, fine. Present a convincing argument for it.  I'd like
>to see us return to the moon.  But NASA nad the space community
>has never done a convincing job of telling me why we should spend
>several billion on that instead of on a number of other alternatives.

You're missing the point. A 50 million dollar lunar probe won't
be the mission that killed DC-X and DC-Y; NASA is likely
to try to kill those programs, though, in order to feed
another year of designing the space station and flying the
space shuttle.

Look at the cost figures for :



1) Doing DC-X, DC-Y...

2) Flying the lunar resource probe

3) One year's worth of shuttle operations,

4) The Space Station's budget overruns, which are basically caused
   by the shuttle's shrinking capabilities...

The main obstacle to developing a cheap launcher is the conception
that the launcher needs to be expensive, i.e. cost billions upon
billions of dollars, to begin with.

>The US made a mistake in the 60s. We should have developed a better
>space infrastructure (shuttle, station) before going to the moon.
>Then going to the moon wouldn't have been such a one-shot thing.
>We'd have placed ourselves permanently in space, and not so subject
>to every Congressional budget whim.

Go over and read sci.space and the ongoing discussion of new launcher
technology. Please.

I'm cross-posting this to sci.space. I think it needs to be done,
since 1) I can't post to talk.politics.space, and 2) So many people
_can't_ get talk.pol.space that I'm beginning to think the group
creation was just done to stifle dissent.

>I do to. I'd like to see us on the moon and Mars and farther before
>I die.  But that alone is not a good enough reason to justify
>doing it now and not in 10 or 20 years.  I'd like to see NASA
>make a case for going to the moon soon.  But if they can't convince
>me (and I'm an easy sell, since I want to see this happen) how
>are they going to convince the person in the street (who is
>paying the bill) that it's a good idea to do now. (Note that I
>don't question that, medium and long term, that it is a very good
>idea. I've just yet to be convinced that we should take resources
>away from the space station and launcer improvements at this
>time.)

Putting the money towards a lunar program would probably be
the only way to _get_ launcher improvements because otherwise
it's just going to go to Scuttle operations...

>The mission is to make use of near-Earth space. We have a good
>consensus in the country now that this is a good idea. NASA
>should use this support to improve how well we can get into
>near-Earth space, as well as improve the ways human beings can
>work in near-Earth space.  Then, when this is such an integral
>part of our lives that Congress, on a whim, can't pull the plug,
>we can start moving outward.

There is no real consensus of that sort in this country.
Other than materials science and MTPE, leo is only good as
a staging area. And some of us see MTPE as killing the space
program rather than helping it, and materials science as being
much more cheaply done than the way NASA wants to do it.

>Then it's up to NASA to make a case for them. Among other things,
>I think space station work should justify some of this.  I also
>think once a station is built, it will justify better ways to
>get to it, and bigger launch systems to make it easier to add
>bigger expansion sections to it.

The station isn't that expandable, and is so expensive that
1) it isn't going to create a launch market and 2) When cheaper
launchers come along, it'll be cheaper for people who need a
station to build their own small ones from scratch.


>I think it's some of both. I also think I'm defining infrastructure
>more broadly than you are. I don't think we have a good enough
>infra-structure yet.  We, maybe, now have the equivalent of paved
>roads, but we need the equivalent of interstates, at least into
>orbit.  Or, to use another analogy, when the Europeans settled
>North America, they start in New York and settle California. Bit
>by bit, the developed a system of roads, cities, and outposts
>that helped them farther and farther along the way.  Wagon trains
>for California left from Kansas City and St. Louis, not from
>New York and Boston.  Similarly, I think we have to return to
>the moon and beyond in such steps. We need our St. Louis in
>space: a good, permanent space station, from which we can take
>the next step.

These aren't roads. Here's a different analogy, since paving
space would be very hard:

We have Langley's aerodrome. We need Wright flyers.

>Jim Mann
>Stratus Computer   [e-mail]

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

Date: Sat, 12 Dec 92 11:31:53 EST
From: John Roberts <[e-mail]>
Subject: Titan

-From: [e-mail] (Zdzislaw Meglicki)
-Subject: Re: Cassini Undergoes Intensive Design Review
-Date: 12 Dec 92 04:28:51 GMT
-Organization: Centre for Information Science Research, ANU, Canberra, Australia

-Could anyone sum up at this stage what is known about Titan and especially
-about the question of a possible ocean there. I vaguely recall that some
-time ago radio-ranging of Titan returned somewhat mixed signals in this
-matter.

Recent radar mapping of Titan indicates that it does *not* have large oceans,
though there may be smaller bodies of liquid. I don't remember where I read
that - probably either Science News or sci.space.

-|> To
-|> further complicate the situation, the U.S. do not have any launch vehicles
-|> that are powerful enough to send Cassini on a direct trajectory to the
-|> outer planets.
-Right, can't the US build such a vehicle by then? Clearly, if any serious
-space exploration is to continue a powerful vehicle like that will be
-needed sooner or later anyway. What happened to the idea of nuclear
-propulsion?

It's the classic "big science" problem - it doesn't make sense to risk a
$4 billion mission on an unproven technology, when you can try it on a
~$100 million spacecraft going somewhere else. (Let's hope they try a small
nuclear spacecraft sometime soon - but even if they do, the technology is
unlikely to be ready in time for Titan, unless they delay it considerably.)

John Roberts
[e-mail]

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

Date: 11 Dec 92 17:56:29 GMT
From: "Edward V. Wright" <[e-mail]>
Subject: what the little bird told Henry
Newsgroups: sci.space

In <[e-mail]> [e-mail] (Gary Coffman) writes:

>They're also heavy as I recall, something you don't need in a SSTO.
>I appreciated the summary you gave earlier, Henry. It looks like they
>have a better test program planned than what has been outlined here
>before. I still think their schedule is extremely optimistic and
>success oriented, but we'll see.

I'd be curious to know the exact date, sometime in the last 20 years,
when "success oriented" became a pejorative phrase.  Yeah, the project
is success oriented.  Just like Project Apollo.  The alternative, I
guess, is for a project to be "failure oriented."  I like success better.

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

End of Space Digest Volume 15 : Issue 539
------------------------------