Space & Astronomy/Space and Astronomy (October 1993).iso/mac/TEXT/JPLNEWS1/0341.PR

Text File | 1993-04-21 | 6KB | 116 lines

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

FOR RELEASE: Monday P.M.'s, June 28, 1965

          The National Aeronautics and Space Administration is
making final plans for processing the pictures Mariner IV will
take of Mars as it flys within 5600 miles of the planet on July
14.
          The processing of the 20 photographs of Mars taken by
Mariner will be many times more complex and difficult than the
processing of the photographs of the Moon taken by the Ranger
spacecraft.
          Mariner will radio its "pictures" back to Earth from
more than 134 million miles away as contrasted with Ranger's
250,0 miles - more than 500 times the distance.
          As with two people trying to shout to each other the
length of a football field, there will be some difficulty in
understanding all of what Mariner is trying to say.  As a result,
the tape on which Mariner records the pictures it takes will be
transmitted at least twice to Earth tracking stations.
          A data analysis system has been set up at the Jet
Propulsion Laboratory, Pasadena, California, which will compare
the two playbacks and eliminate errors.  Here is how Mars
pictures will be taken and returned to Earth:
          Mariner will take some 20 photographs of Mars in about
24 minutes.  These will be recorded on magnetic tape.  After
Mariner has passed behind Mars and has re-established radio
contact with Earth, it will start scanning the picture tape,

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converting the pictures into digital data (a series of 0's and
1's), and radioing the data to the stations of the NASA/JPL Deep
Space Network.
          Mariner has a 10-watt radio transmitter on board but by
the time its signal is gathered by an 85-foot diameter dish and
focused on to the antenna's receiver, the signal will be
extremely weak - about 1/10th of a billionth of a billionth of a
watt or a little less than 1-quintillionth (.00000000000000000001)
of one watt.
          For this reason, Mariner will "speak" very slowly.  A
picture which was taken in less than a minute, will take more
than 8 hours to radio to Earth.  Mariner will transmit only 8-1/3
bits of data each second.
          Because Mariner will be sending the pictures in digital
form, the stream of digits must be turned back into pictures
after they reach Earth.  Thus, each picture frame of Mars will be
made up of some 40 thousand dots or elements.  Each element is
made up of 6 bits of data.
          Each of the elements can be any one of 64 shades of
gray ranging from white to black.
          To complicate the job of understanding Mariner's picture
message is the fact that engineers want to keep track of the
spacecraft's condition during the picture transmission sequence
so, mixed in with the digitized pictures will be other digit
reporting on Mariner's temperature, its battery voltages, and
other engineerng performance data.  There also will be time
reports, picture synchronization and other information.

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          And because it takes so long to playback each picture,
two Deep Space Network stations may receive parts of one picture.
For instance, Mariner may be passing over the DSN station at
Johannesburg, South Africa, when it starts playing back one
picture and be over Goldstone, California, when that picture is
completed.
          Once a DSN station has received Mariner's message, the
magnetic tape on which it is printed will be sent to Pasadena by
courier or mail and the same message will be relayed by teletype.
          At Pasadena, in JPL's Space Flight Operations Facility,
the job of converting the teletype tapes into picture form begins.
Computers and a device called a digital photographic processor
will do the work.
          If a picture is split, computers will take teletype
messages or magnetic tapes from two DSN stations and form one
picture message from them.  They will then analyze the tapes and
separate from them all spacecraft performance and other informa-
tion leaving a tape of picture data only.
          This tape then will be fed into the digital
photographic processor.  This device converts each digit into its
proper shade of gray and electronically projects it on to a
precisely controlled and very accurate cathode ray tube - a
complex version of the picture tube in a home television set.  As
the dots are projected on the screen, they are photographed and
the picture is then developed and printed.
          Project officials at JPL plan to immediately release to
the public the first pictures after they have gone through this

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process.  If all goes well, this could be within 36 to 48 hours
after Mariner begins taking the pictures at about 8:00 p.m. EDT
July 14.
          The remaining pictures will undergo further processing
to improve their accuracy before they are released.
          For instance there may be some errors in the electronic
transmission or in the intricate processing equipment in the early
pictures from 134 million miles away.  Project engineers hope to
correct these errors by comparing two and possibly three playback
tapes.  Computers will compare the tapes and select the correct
elements if one is missing or is in error on one tape.  After the
pictures are finally processed, they will be released to the
public as scientists continue their intensive investigation of
what can be learned from man's first close-up look at Mars.

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