PDS_VERSION_ID = PDS3 RECORD_TYPE = STREAM LABEL_REVISION_NOTE = "2003-04-24 A.C.Raugh Minor editing to conform to current standards" OBJECT = INSTRUMENT_HOST INSTRUMENT_HOST_ID = "GIO" OBJECT = INSTRUMENT_HOST_INFORMATION INSTRUMENT_HOST_NAME = "GIOTTO" INSTRUMENT_HOST_TYPE = "SPACECRAFT" INSTRUMENT_HOST_DESC = " Instrument Host Overview ======================== The Giotto spacecraft design was derived from the Geos concept. In 1978, ESA was invited by NASA to plan a joint mission consisting of a comet Halley fly-by in November 1985 and a rendezvous with comet Tempel 2 in 1988. The mission comprised an American main spacecraft which would carry a European probe. The main spacecraft, with its array of sophisticated cameras and experiments, would complete a fly-by of comet Halley at a safe distance. Shortly before fly-by, the probe would be released towards the nucleus to make detailed in-situ observations in the innermost coma. In January 1980, however, it became clear that financial support for the Halley Fly-by/Tempel 2 Rendezvous mission could not be secured in the USA. By that time the interest of European scientists had built up such momentum that ESA considered the possibility of a purely European mission. The support for a fly-by mission was strong in Europe and went far beyond the small section of scientists specialised in cometary research. A fly-by of comet Halley was suggested to ESA by the scientific community in February 1980. Rather than having the American spacecraft deliver the probe to the comet as in the earlier concept, the Europeans proposed that the capabilities of the small probe be increased by building an independent, self- sufficient spacecraft to be launched using the European Ariane rocket. The limited time available for development and the small financial resources made it advisable to use a spin-stabilised spacecraft derived from the European Earth orbiting spacecraft Geos. This proposal was studied by ESA in the first half of 1980. Details of the selected experiments are shown in the Table below. The Giotto spacecraft carried 10 instruments to carry out the scientific objectives. In addition, it was intended to extract from the radio signal information on the columnar electron content of comet Halley's ionosphere and the mass fluence of the cometary atmosphere. The mass and power allocations to the Halley Multicolour Camera (HMC) were similar to those of several other experiments. Half of the total data transmission rate of 40 kbit/s was allocated to HMC. The spin of the spacecraft had some advantages. The stability of the orientation (attitude) of the spacecraft was based on its angular momentum and was not so sensitive to the inevitable impacts by dust grains. This concept is also more compact than a three-axis stabilised spacecraft (such as the Vega and Voyager spacecraft) and, therefore, it was easier to protect the spacecraft. The high fly-by velocity caused by the combination of the retrograde orbit of comet Halley and the direct orbit of the Giotto spacecraft was almost 100 times higher than the speed of material leaving the cometary nucleus. This implied that the velocity of the dust and gas relative to the spacecraft would hardly change during the fly-by. The experiments measuring cometary species in-situ only had to look in the forward (ram) direction along which the symmetry (spin) axis of the spacecraft was oriented. Most of the experiments were situated on the experiment platform near the front end of the spacecraft and directly behind the dust shield. The communications link between the spacecraft and Earth was supported by a despun high gain dish antenna which was kept pointing towards Earth throughout the mission. The angle (135.7 degrees) between the antenna beam and the spin axis of the spacecraft was determined by the geometry of the fly-by and was fixed during the mission design phase. A unique feature of the Giotto spacecraft was its dust shield which was used to protect Giotto from the high velocity dust particle impacts. A 1mm thick plate of aluminium was mounted 23cm in front of the main body of the spacecraft and covered the full cross-section of the cylindrical body. Particles of mass >10**-6 g that penetrated this aluminium plate disintegrated and vaporised. A cloud of vapour (neutral and ionised gas) then hit the thick rear shield (made mostly of Kevlar) with a much larger cross-section than the original particle, thereby reducing the pressure. Only masses >/= 1 g were expected to penetrate the Kevlar shield. However, it had been calculated that smaller dust particles could already perturb the spacecraft attitude so severely that the communications link to Earth could be lost. The most realistic dust models led to the prediction that the probability of such an attitude perturbation was considerably higher than that of spacecraft destruction. Summary of Giotto experiments, as well as the Radio Science Experiment: HMC --- The Halley Multicolor Camera is a CCD narrow-angle camera used for imaging the inner coma and nucleus with high resolution (11m at a close approach of 500 km). The camera baffle was eroded during the encounter and the camera is no longer operational. The HMC successfully imaged the nucleus up to 10 s before closest approach. NMS --- Neutral Mass Spectrometer consists of a mass analyzer and energy analyzer that seeks to determine the neutral gas composition. Both CCDs of the detectors ceased operation during the dust episode that disabled the HMC. IMS/HIS ------- The Ion Mass Spectrometer has two sensors optimized to different parts of the coma. For the inner coma, the HIS (High Intensity Spectrometer) measures the relative abundance of ions in the energy range 300 to 1400 eV/e. This instrument remains functional. IMS/HERS -------- The Ion Mass Spectrometer sensor optimized for the outer coma is called HERS (High Energy Range Spectrometer). It measures the relative abundance of ions from 10 eV/e to 2.0 (or 4.5) keV/e depending on the M/Q ratio. There was high voltage damage to this isntrument and it is no longer useable. PIA --- The Particle Imapct Analyzer measures dust particle flux and composition between 1-110 AMU. Although the instrument recevied no damage in the encounter, it was turned off. DID/MSM ------- The Dust Impact Detector is used to determine the dust particle flux and mass distribution. It consists of three sensors one of which is the meteroid shield momentum sensor (MSM) that can be used to sample a large or small shield sector. No damage was sustained during encounter. DID/RSM ------- A similar type of DID measurement to determine dust particle flux and mass distribution is possible by using the rear momentum shield (RSM). No damage to this sensor was detected post encounter. DID/CIS ------- The second type of sensor used in DID is the capacitor impact sensor (CIS) which is sensitive to particles in the 1-5 micron range. The sensor is still operational. DID/IPM ------- The final type of DID sensor is for impact plasma and momentum (IPM) determination of the dust particle flux and mass distribution. The sensor consists of either an impact ionization detector (IPM-P) or a piezoelectric detector (IPM- M). This instrument shows some anomalous behavior. JPA/FIS ------- The Johnstone Particle Analyzer measures the 3-dimesnional velocity distribution of positive ions near the comet. The Fast Ion Sensor (FIS) ristricts the energy range to 10 eV/q to 20 KeV/q for all directions, once every rotation of the spacecraft. The high voltage to this sensor stopped working 1.5 hours from encounter. JPA/IIS ------- The JPA also consists of an Implanted Ion Sensor (IIS) which measures the energy per charge distribution from 90 eV/q to 90 KeV/q with discrimination into five mass groups. No damage to this instrument was detected post encounter. RPA/EESA -------- The RPA-Copernic plasma experiment for the Giotto mission seeks to measure the 3-dimensional distributions of electrons and thermal positive ions near the comet. The spectrometer sensor (EESA) measures both the flux and energy spectra of electrons from 10 eV to 30 KeV in 4 pi directions. Some damage to the sensor was detected post encounter. RPA/PICCA --------- In the plasma experiment, the electrostatic mass analyzer (PICCA) is designed to measure the thermal positive ions in the mass range 10-203 AMU near the comet. The high voltage damage sustained by this instrument makes it unuseable. EPA --- The Energetic Particle Analyzer (EPA) determines the flux of particle with energy greater than 20 KeV, thus including both electrons and accelerated ions. This instrument has been operating in the cruise phase and sustained no damage in the encounter. MAG --- The Magnetometer consists of a triaxial and separate biaxial system of fluxgate sensors of the ring-core type. This instrument was also switched-on during the cruise phase and continues to operate flawlessly post encounter. OPE --- The Optical Probe Experiment measures the flux and polarized brightness in various colors in the direction opposite to the direction of motion of the spacecraft through the comet's coma. This instrument sustained no damage in the encounter. GRE --- The Giotto Radio Experiment takes the measurements of the phase (Doppler) shifts of the downlink carrier, e.g. X-band, as a function of time to infer the total mass content along the trajectory. This experiment continues to function. Launch Date: 1985-07-02" END_OBJECT = INSTRUMENT_HOST_INFORMATION OBJECT = INSTRUMENT_HOST_REFERENCE_INFO REFERENCE_KEY_ID = "ESA-SP1077" END_OBJECT = INSTRUMENT_HOST_REFERENCE_INFO END_OBJECT = INSTRUMENT_HOST END