[sci.astro] ESA-brief summary of activity

zmapj36@sund.cc.ic.ac.uk (M.S.Bennett Supvs= Prof Pendry) (06/26/90)

IN BRIEF-(taken from the ESA bulletin No.62 May 1990)


                         ESA/USSR Cooperative Agreement
                         ==============================


     An agreement  on cooperation  in  the exploration  and  use of  sapce  for
peaceful purposes between the Goverment of the Soviet Union and ESA was  signed
on 25 April at ESA Headquarters in Paris, by the Soviet Union's Ambassador, His
Excellency Iakov Riabov, and the Agency's Director General, Prof. Reimar Lust.

     The Agreement is  for an initial  period of  ten years and  covers a  wide
range of space activities,  including: exploration of  the Solar System,  space
astronomy  and  astrophysics,  Earth  observation  and  meteorology  and   life
sciences. Working groups will be esablished  for each of these disciplines,  to
investigate and recommend potential cooperative projects.

     ESA has a long  history of scientific cooperation  with the Soviet  Union,
the formal basis of which has until now been an Exchange of Letters between the
Soviet Academy  of  Sciences  and  ESRO (one  of  ESA's  forerunners),  largely
concerned with  the  exchange  of  scientific  information.  One  of  the  most
spectacular of past cooperative ventures was the encounter with Halley's  Comet
in 1986 by ESA's Giotto, two Soviet  spacecraft, Vega-1 and -2, as well as  two
Japanese spacecraft. Amongst other joint  projects, ESA experiments were  flown
aboard the Soviet space biology missions, Biokosmos-8 and -9 in 1987 and 1989.

     In February this year an International Workshop was held in Graz, Austria,
to discuss the scientific aspects of cooperation between ESA's Cluster  project
and the Soviet Regatta mission.


                                     ******


                        Hipparcos Survives Solar Eclipse
                        ================================


     Soon after Hipparcos became  trapped in its  highly elliptical orbit,  the
operations team realised that a critical  test of the satellite's power  system
would occur around mid-March, when the satellite would have to endure  extended
periods of solar eclipse.

     For three weeks the solar arrays were  in shadow for a much longer  period
each day than  the 72 minutes  foreseen in the  nominal circular orbit.  During
these eclipses, the spacecraft had to rely soley on battery power.

     Prior to  the maximum  eclipse  period, about  105  minutes on  16  March,
contingency plans were put  into action at  ESOC to shut  down elements of  the
payload to  limit the  drain  on the  batteries.  The satellite  survived  this
critical event  with a  power  margin of  barely  five minutes  and  scientific
measurments were able to proceed without interruption.

     The fourth ground station, the NASA Goldstone station in Mohave desert  in
California, is now on line, increasing the amont of scientific data that can be
retrieved from the satellite.

                                     ******

                               Giotto Reactivated
                               ==================


     On 19 Febuary 1990  a faintly whispered radio  signal was received at  the
Madrid tracking  station of  NASA's Deep  Space Network.  The signal  was  from
Giotto, the  ESA  probe that  has  been hibernating  in  deep space  since  its
spectacular encounter with Halley's comet in March 1986.

     Preperations have been underway since May 1988 at the Agency's  Operations
Center (ESOC) in Darmstadt, Germany, to reactivate the spacecraft. Beginning on
19 February, a series of telecommands was transmitted to Giotto via the  Madrid
tracking station, using a 70m antenna and a 100000 W transmitter, many thousand
times the  power  of a  TV  broadcasting station.  The  first faint  reply  was
received when Giotto was about a hundred million km from Earth

     The mission  control team  at  ESOC then  performed  a series  of  complex
manoeuvers to point Giotto's  high-gain antenna towards the  Earth in order  to
increase the  strength of  the signals,  so that  a complete  check-out of  the
spacecraft could be performed.

     The first of a series of manoeuvres to target Giotto for its new  mission,
an encounter with  comet Grigg-Skjellerup, was  performed in mid-March.  Giotto
was then 75 million km from Earth. The temperature of the spacecraft was  found
to be  too  high, because  of  damage to  the  thermal insulation  and  thermal
surfaces during the Halley encounter. However, as Giotto moves further from the
Sun, the  spacecraft  should cool  down,  and checking-out  of  the  scientific
instruments can begin, from end-April  onwards. (NOW) In the meantime  periodic
orbit control manoeuvres are being performed.

     On 2 July 1990 Giotto will pass within 23000 km of Earth, and the  Earth's
gravitational field  will  be  used  as  a  'slingshot'  force  to  propel  the
spacecraft on towards its new target.

                                     ******



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dieter@rwthinf.UUCP (Dieter Kreuer) (06/26/90)

In article <1990Jun25.175946.20917@cc.ic.ac.uk>, zmapj36@sund.cc.ic.ac.uk (M.S.Bennett  Supvs= Prof Pendry) writes:

>                                      ******
> 
>                                Giotto Reactivated
>                                ==================
>  
> 
> On 2 July 1990 Giotto will pass within 23000 km of Earth, and the  Earth's
> gravitational field will be  used  as  a  'slingshot'  force  to  propel  the
> spacecraft on towards its new target.
> 

A friend of mine uses to watch geostationary satellites with a C8 and has 
written a program for determining equatorial coordinates when geocentric
elements for the satellite are provided. He uses stars as a guide to direct
the scope to the desired position and switches off the drive when the
satellite crosses the field of view.
Is the Giotto probe also visible with an 8 inch as it passes Earth, though
it has no large solar panels? How fast will it move (angular velocity)?
Can anybody provide geocentric elements or even a table of guide stars
for 50.8 deg N, 6.5 deg E (if the event does not take place by daylight)?
URGENTLY, this net can be quite slow sometimes!

------------------------------------------------------------------------------
     Dieter Kreuer, Lehrstuhl Informatik IV, RWTH Aachen, Ahornstr. 55,
    D-5100 Aachen; dieter@informatik.rwth-aachen.de; dieter@rwthinf.uucp
------------------------------------------------------------------------------

dmc@videovax.tv.tek.com (Donald M. Craig) (06/26/90)

In <1990Jun25.175946.20917@cc.ic.ac.uk> seds@cc.ic.ac.uk (M.sean Bennett)
writes: "Beginning on
19 February, a series of telecommands was transmitted to Giotto via the Madrid
tracking station, using a 70m antenna and a 100000 W transmitter, many thousand
times the power of a TV broadcasting station."
Reaching for my trusty Television and Cable Factbook, which lists in gory
detail facts about all US television stations, I extracted the following:
KNLC, Channel 24 (530 - 536 MHz), St. Louis, MO, Authorized power: 3090-kw
max. visual, 309-kw max.aural.
WTZA, Channel 62 (758 - 764 Mhz), Poughkeepsie, NY, Authorized power: 5000-kw
max. visual, 500-kw max. aural.
KICU, Channel 36 (602 - 608 MHz), San Jose, CA, Authorized power: 4098-kw
max. visual, 410-kw max. aural.
That's 3 million watts, 5 million watts, and 4 million watts.  Perhaps the
100000 W number was a typo?
cheers,
Don Craig
Tektronix Television Division, dmc@tv.tv.tek.com