The specific scientific objectives of the Giotto Extended Mission can      be summarised as follows:      -  characterisation of the changing features of the solar-wind flow         and observations of cometary pick-up ions and anomalous accelerati      -  determination of electron densities      -  observation of upstream waves, and determination of the locations         the various boundaries (bow shock, ionopause, etc.)      -  observation of the magnetic pile-up region and cavity      -  determination of dust spatial density and size distribution, and t         optical properties of the dust grains      -  discrete gaseous emissions      -  combined dust and gas densities.        Status of the Giotto Payload for the Comet Grigg-Skjellerup Encounter        =====================================================================      Instrument                      Status                  Active During                                                              G-S Encounter      =====================================================================       Halley Multicolor Camera        aperture blocked;       no                                      baffle missing; blind       Neutral Mass Spectrometer       detectors dead          no       Ion Mass Spectrometer           HERS: high-voltage      no                                      damage,                                       HIS: no damage          yes       Particulate Impact Analyzer     mass spectrum slightly 	no                                     	degraded       Dust Impact Detection System    some detectors showing  yes                                      increased noise       Optical Probe Experiment        no damage               yes       Magnetometer                    no damage               yes       Johnstone Plasma Analyzer       high-voltage problems   yes                                      on one sensor       Reme Plasma Analyzer            cold ion composition:   no                                      high-voltage damage                                       damage to electron      yes                                      electrostatic analyzer       Energetic Particle Analyzer     no damage               yes       Giotto Radioscience Experiment  not applicable          yes       =====================================================================         The functioning payload complement listed in the table above shows tw      main scientific areas that can be addressed during the Grigg-Skjeller      encounter: the particle and field instruments have the potential to      provide significant new results pertaining to the field of cometary      plasma physics. The Optical Probe Experiment and the Dust-Impact      Detection System (DID) will complement our knowledge of dust-producti      rates and size distributions for a low-activity comet.       The dust measurements can also provide important data to support futu      European and international space programmes. Future missions to comet      for example, will need engineering models of the cometary dust      environment for low-activity comets, which the GEM mission should hel      to improve.       Cometary plasma physics is part of a broader domain of space plasma      physics dealing with the interaction between a planetary atmosphere      and a flow of magnetised plasma. Examples include comets, Venus, the      Saturnian satellite Titan in the solar wind, and Io, Titan and Triton      in their planetary magnetospheres. Physically, comets are distinguish      from the other planetary bodies by their characteristic of possessing      non-gravitationally-bound atmosphere.       Three instruments that will be especially useful for the      Grigg-Skjellerup encounter survived the dust impacts unscathed during      Giotto's encounter with Comet Halley. Of these, the Implanted Ion      Sensor (IIS) of the Johnstone Plasma Analyser (JPA) provides the full      pitch-angle distribution for each chemical species in a range of      energies from 100 eV/q to 86 keV/q. Its time resolution is rather goo      with just 128 s required for a full set of observations. This      corresponds to a spatial resolution of approx. 14 km/s x 128s =      +/-1700 km in the cometary frame of reference.       The Magnetometer (MAG) is also fully operational with 35.4 ms      resolution, corresponding to 0.5 km spatial resolution. The      Magnetometer results can be processed and evaluated much more easily      for Comet Grigg-Skjellerup than for Halley because of the absence of      magnetic disturbances produced by the motors of the Halley Multicolou      Camera (HMC), which is no longer functioning.       In addition, the fully operational Energetic Particle Analyser (EPA)      contains three semiconductor telescopes, each incorporating two total      depleted silicon surface barrier detectors.  Electrons, protons, alph      particles and heavier ions can be measured in eight channels covering      an energy range extending from approximately 30 keV to several tens o      MeV.  High spatial and temporal (0.5 s) resolution is available.       Finally, although the Reme Plasma Analyser (RPA) is severely crippled      by dust damage, it may still provide some information on low-energy      electrons.