Suzy B Software 2/Suzy B Software CD-ROM 2 (1994).iso/nasa/mag41791/mag41791.txt

Text File | 1995-05-02 | 13KB | 303 lines

Magellan Status 4/17/91










                     MAGELLAN STATUS REPORT
                         April 17, 1991


     The Magellan spacecraft and its radar system are performing
well. Five star calibrations Tuesday were fully successful, with
two partially successful. The attitude updates still average
less than .02 degree. The spacecraft is now performing momentum
wheel desaturations on every other orbit and star calibrations
every orbit.

     The weekly command sequence was successfully set to
Magellan late Tuesday and is now being executed. This new mapping
sequence includes two eight-minute "hide" periods in each three
hour and 15-minute orbit. During that period the spacecraft is
shaded by the high-gain antenna for thermal control. The maneuver
is necessary because the geometry of the planets in relation to
the sun places the spacecraft in direct sunlight for too long a
period of time.

     As of this report, there has only been one orbit with the
hide sequences and there appears to be a cooling trend.

     The hide periods will increase from now through the end of
the primary mission May 15. Next week, for example, there will be
two 12-minute hide periods in each orbit which will cut the 37.2-
minute mapping swath by 4.5 minutes.

     In the following weeks, the hide periods increase to 23
minutes, which will cut mapping by 10 minutes, and then 36
minutes of hide period which will cut mapping by 15 minutes.



                              _____




                                                       AJS
                                                       4-17-91
                                                       9:00 AM



                    MAGELLAN STATUS REPORT



1.  The Magellan spacecraft and its radar system are
    performing nominally.

2.  Five the STARCALS yesterday were fully successful, with
    two partially successful.  The attitude updates still
    average less than .02 degree.   The spacecraft is now
    performing DESATS on every other orbit and STARCALS every
    orbit.

3.  The weekly command sequence M1107 was successfully sent
    to Magellan along with the radar control parameter and
    mapping quaternion files, and is now executing.  As of
    this report time, we have seen only one orbit of the "Two-
    Hide" sequence, and there appears to be a definite cooling
    trend.


                         ___________________

                                                  AJS (pca)
                                                  4/17/91


                 MAGELLAN SPECIAL REPORT

                  SCIENCE DATA PRODUCTS


During the primary mission, the Project has frequently
reported on the number of mapping orbits completed and the
orbits for which data was successfully transmitted to the
earth.  The ultimate measure of mission success, however, is
the production and distribution of final scientific data
products.

End-to-End Data Flow

The flow of data from the radar sensor onto the spacecraft
tape recorder, its transmission to Earth where it is again
recorded on tape as Original Data Records (ODRs), the
conversion of ODRs to Experiment Data Records (EDRs), then
into Full-Resolution Basic Image Data Records (F-BIDR's) and
various mosaics (F-MIDRs, C1-MIDRs, etc) is one of the major
challenges of the Magellan mission.

1.  The radar sensor transmits bursts of radar pulses toward
    the surface of Venus.  A portion of each radar echo is
    quantized to generate 16-bit data samples at a rate pf
    2.26 x 106 samples per second.  These are compressed by
    the Block Adaptive Quantizer to reduce the bits-per-sample
    from 16 to 4. The data acquired during each burst of
    pulses is stored in a buffer memory and then sent to the
    spacecraft tape recorder at a uniform rate of 800 kbps for
    each 37.2 minute mapping pass.  Thus, Magellan produces
    1.8 x 109 bits per orbit.

2.  The spacecraft tape recorder is played back at a 268.8
    kbps rate and transmitted via an X-band communication link
    to the Deep Space Tracking stations, where the data is
    recorded on standard computer-compatible, 3/4 inch
    magnetic tapes at a recording density of 6,250 bytes/inch.
    The data from each orbit normally requires two 2400 foot
    reels of tape.  These tapes are called Original Data
    Records (ODRs).

3.  During the first mission cycle, the ODRs from Goldstone
    are driven into JPL daily.  ODRs at the Madrid and
    Canberra stations are collected for one week then flown to
    JPL.  Although these ODRs can take as much as 21 days to
    reach JPL, the current backlog is about 12 days.

4.  Processing of data tapes is coordinated by Magellan's Data
    Management and Archive Team (DMAT) which schedules each
    stage of data processing from ODRs to EDRs to various
    image products.  DMAT also catalogs and stores the data
    tapes.

5.  ODR tapes are logged by DMAT and delivered to the Magellan
    High Rate (MHR) processor where the station overlap is
    removed, and ancillary data needed for further processing
    and user information is added to produce the Experiment
    Data Records (EDRs).

6.  EDRs are then logged by DMAT and forwarded to the SAR Data
    Processing Subsystem (SDPS) in Building 300.  SDPS
    operates on a two eight hour shift basis, Monday through
    Friday.  Here the 1.8 x 109 bits per orbit of raw radar
    data from each SARvEDR is converted into 0.8 x 109 bits of
    image data for each orbit and combined with ancillary data
    to form Full Resolution Basic Image Data Record tapes (F-
    BIDRs).  F-BIDRs contain the long thin strips of orbit
    image data which cover an area on Venus approximately 12
    miles wide and 10,000 miles long (20 by 17,000 KM).
    Understandably, these are called "radar noodles".

7.  As a check of the data quality and interpretability, the
    F-BIDRs are also delivered as long thermal prints to the
    science work area.  On each print the "noodle" is
    presented in four parallel pieces approximately 1 inch
    wide by 15 feet long.

8.  The F-BIDRs are transmitted electronically to the Image
    Data Processing Subsystem, (IDPS) in Building 168 to
    connect the digital form of these thin image strips into
    Mosaicked Image Data Record (MIDR) products:

    a.  F-MIDRs: The highest resolution image mosaics are the
    Full-resolution MIDRs.  These are images of 300 x 340 mile
    (500 x 532 KM) areas of the Venus surface with a pixel
    spacing of 75 meters.  F-MIDRs will be produced for about
    15% of the total surface area.

    b.  C1-MIDRs: These mosaicked products compress the full
    resolution pixel data by averaging each 3 x 3 array into a
    single pixel value.  Each frame covers an area on Venus
    measuring approximately 900 x 1000 miles (1450 x 1600 KM).

    c.  C2 & C3-MIDRs:  These products further compress the
    pixel arrays by averaging 9 x 9 and 27 x 27 arrays of full
    resolution data.  The C2 frames cover 45 degrees of
    latitude, and 45 to 72 degrees of longitude.  The C3
    frames cover 80 degrees of latitude by 120 degrees of
    longitude.  All of the surface of Venus can be displayed
    in six C3MIDRs.

    d. PIDRs: These are Polar Image Data Records, specifically
    designed for the polar areas of the planet. They contain
    portions of adjacent F-BIDRs covering the area from 80x
    latitude to the North Pole.

9.  In addition to the image data record products, altimetry
    and radiometry data products are being produced by
    investigators at the Massachusetts Institute of
    Technology. These include:

    a. ARCDRs - Altimeter/Radiometer Composite Data Records
    b. GTDRs  - Global Topographic Data Records
    c. GSDRs  - Global Slope Data Records
    d. GEDRs  - Global Emissivity Data Records
    e. GREDRs - Global Reflectivity Data Records

10. CD-ROMs: Many science data products end up as images,
    either printed as photos or distributed as digital
    records.  Many of the science investigators need the
    digital records because there are many analysis tools
    which can be applied to this computer-readable form of the
    images.  It is the Project's plan to distribute the images
    to the science community in the form of

CD-ROM = Compact Disk - Read Only Memory compact disks (CD-
         ROMs).  The first of these CD-ROMs was made available
         on March 8, 1991, and contained ten full resolution
         mosaicks from the first 24 orbits, i.e. the first 3
         days of mapping.

    The second CD-ROM includes mosaicks from the first 21 days
    of mapping is scheduled for release to the science
    community on April 19, 1991.

    The third CD-ROM, containing full resolution mosaicks
    beyond the first 21 days, is being used to test the
    production system for CD-ROMs and will not be distributed
    until about mid-summer.  Work is proceeding, however, on
    CD-ROMs 4, 5 and 6, containing images from the first 21
    days of mapping.  The goal is to release these about May
    17.  The Project is preparing for the production of 50-60
    CD-ROMs in the remainder of calendar 1991, including
    images from all of Cycle 1, on a schedule of about two per
    week.

    CD-ROMs will also be used to distribute these other
    science data records.  The first Altimeter/Radiometer
    Composite Data Record disk is scheduled for production,
    starting in late April, with release to the science
    community in June.

11. Perhaps the most striking visual form of the data are the
    simulated flights over the surface of Venus produced frame
    by frame by combining the Magellan image and altimeter
    data.  Videos of 2,000 to 5,000 mile flights over and
    around significant surface features will be produced every
    three months.  (This process is itself a unique story and
    will be described in a future special report.)

Development of the Magellan Data Processing System

Due to budget constraints, the completion of Magellan
processing system was deferred until after launch.  Throughout
cruise, final software development and test and system
integration and test were accomplished, targeted for
completion by May 1990.  This represented a major development
challenge in addition to operating the Spacecraft.  While most
of the system was in place by May 1991, certain software
builds took most of the summer to complete, but were ready for
mapping operations prior to arrival at Venus.

The Magellan processing challenge for a planetary mission is
unique and quite large.  The Magellan system is required to
process one week of acquired data in one week --- the highest
rate and the longest duration for any planetary mission.
Previous planetary encounters consisted of intense near
encounter phases lasting for a few months, over which large
volumes of data are collected, followed by many months of
quieter cruise activities.

Magellan's "Near Encounter"

Magellan continues in an intensive "near encounter" phase for
243 days, the time it takes the planet to rotate once
underneath the spacecraft.  During this time, data are
collected on each 3.25 hour orbit, 24 hours a day, 7 days a
week.  In seven months Magellan collected more data bits than
all the Mariners, Vikings and Voyagers.  At the end of the
primary mission, the "near encounter" continues into the next
243-day cycle, then the next and the next.

At the start of mapping on 15 September, the data processing
system began to immediately produce high quality data
products.  The first three weeks of radar data processing
operations concentrated on engineering refinements,
performance tests, and special product generation to support
initial press conferences.  The standard data processing
activity started on October 9th.  Several refinements were
made to correct problems that have been discovered during
operations.

The malfunction of one of the spacecraft tape recorders
resulted in several modifications to data processing to
alleviate the effects of the resulting damage in the received
radar data.  The recent experience indicates that the planned
Cycle 1 data products will all be completed by the original
schedule date of June 28, 1991.



SPACELINK NOTE:  For information on obtaining the CD-ROM disk, contact:

National Space Science Data Center
NASA/Goddard Space Flight Center
Code 633
Greenbelt, MD  20771
301/286-6695