KEY QUESTIONS The UVS and EUV satellite observations during the Jupiter tour will answer several key questions related to the state of evolution and the surface composition of the Jovian satellites. The observational goals and strategies detailed below, combined with the Galileo's capabilities based upon the Phase II flight software, will permit observations which can answer these questions. The UVS and EUV satellite observations will determine the composition, or upper limits to the number density, of the neutral atmosphere of the Galilean satellites and the Io neutral cloud. The UVS observations will also determine the excitation mechanisms and escape rates of the satellite atmospheres. In addition, the UV albedo, when combined with the visible and infrared spectra, will determine surface composition and particle size. Observation Goals The UVS and EUV satellite observations will be conducted during each Jovian orbit with the exception of the non-targeted fifth-orbit (J5). The principal goal of these observations will be to answer these key scientific questions as well as to support the Satellite Working Group observations where possible. Observation Strategy Observations which will address the science questions are based upon the detailed observation descriptions below. UVS and EUV observations can be grouped into two general science area categories. These are 1) Volitile Escape; and 2) Surface Albedo and Composition observations. The categories are described below where the capitalized acronyms are the six-character observation names. 1) Volitile Escape observations will search for atomic spectral lines (H,O,C,N), molecular bands (OH,CO,CO2+), and neutral clouds (SO2,SO,O,S,K,Na) to determine the altitude near the Jovian satellites. These measurements will enable an understanding of the excitation mechanisms and the escape rates to determine the state of evolution of the Jovian satellites. The measurement set used to obtain this information consists of the BRTLMB, DRKLMB, ECLIPS, NRLCLD and SPNSCN observations. 2) Surface Albedo and composition observations will extend the surface scattering property measurements into the ultraviolet (1600A - 3200A) and extreme ultrviolet (500A-1300A) wavelengths. The data retrieved will provide information about particle size and absorption properties of the surface materials at resolutions and phase angles which cannot be obtained from Earth. The data will also be used to supplement and complement the NIMS surface property measurements. The measurement set used to obtain this information consist of the GLOBAL, MAPPNG, PHASE and SPNSCN observations. 3) Additional data is required through AACS-provided pointing information for all realtime and recorded observations. These data are provided through the realtime science formats and the recorded low-rate science ancillary data packets. SWG Measurement Set Priorities The UVS and EUV measurment sets are listed by acronym and fully described below. The recorded observations reflect the agreements made between discipline working groups as to the bits-to-ground and tape track allocations. The realtime observations include high priority UVS activities (designed to minimize the bits-to-ground and tape track allocation resources) and will use realtime bits-to-ground during the encounter period. Orbit JA/J0: No UVS or EUV satellite observations are planned. Orbits G1-E11: BRTLMB - UVS Satellite Bright Limb Drift Observations DRKLMB - UVS Satellite Dark Limb Drift Observations ECLIPS - UVS Satellite Eclipse Observations GLOBAL - UVS Satellite Global Observations (ride-along with NIMS team) MAPPNG - UVS Satellite Mapping Observations (ride-along with NIMS team) NRLCLD - UVS Io Neutral Cloud Observations PHASE - UVS Satellite Phase Coverage Observations SPNSCN - EUV Callisto Spin Scan Image Observations Recorded: 1) BRTLMB Objective: Measure the altitude distribution of the volatiles near the sub-solar point to determine the escape rates from the Jovian satellites when the atmosphere is in full solar illumination. Strategy: Near the satellite closest-approach, position the UVS field-of-view (FOV) approximately 1 satellite-radius off the satellite sub-solar point and allow the spacecraft motion to carry the FOV onto the body surface. Once this has completed, reposition the UVS FOV to ~1000 Km off the satellite sub-solar point and allow the spacecraft motion to carry the FOV onto the body surface. Orbits: Ganymede - G1, G2; Callisto - C3, C10; Europa - E11. 2) DRKLMB Objective: Measure the altitude distribution of volatiles off the dark limb to determine the particle impact excitation emission rates from the Jovian satellites. Strategy: Near the satellite closest-approach, position the UVS field-of-view (FOV) on the surface of the dark limb and allow the spacecraft motion to carry the FOV to approximately 1 satellite-radius off the satellite surface. Orbits: Ganymede - G1, G2; Callisto - C3, C10; Europa - E11. 3) GLOBAL Objective: Extend the surface scattering property measurements into the UV (1600A - 3200A) in concert with the NIMS measurements to infer information about particle size, and refractive and absorption properties of the surface materials. Strategy: Ride-along with the NIMS Ganymede and Callisto global observations. Cover the satellite surface at the highest resolution available within the allocated downlink bits and tape. Orbits: Ganymede - G1, G7; Callisto - C3, C9, C10. 4) MAPPNG Objective: Extend the surface scattering property measurements into the UV (1600A - 3200A) in concert with the NIMS measurements to infer information about particle size, and refractive and absorption properties of the surface materials. Strategy: Ride-along with several NIMS Ganymede and Callisto high resolution observations. Cover the satellite surface at the highest resolution available within the allocated downlink bits and tape. Orbits: Ganymede - G1, G8; Callisto - C9. 5) SPNSCN Objective: Characterize Callisto's surface and aeronomic properties by measuring the EUV surface albedo (He,O2,H) and local atmospheric resonance line wavelengths (H,He,O,Ar,S,C). Strategy: Record EUV data for approximately 15 RIMS centered on the time when Callisto will cross the EUV FOV at 90 deg. cone. Orbits: Callisto - C3, C10. Realtime 6) ECLIPS Objective: Characterize the change in the lower atmospheric UV airglow emissions as Io and Europa enter and exit eclipse. Determine if the source of the change is due to: 1) a change in the lower atmospheric composition as it cools (ie. SO2 condesation); or 2) a potential change in the excitation mechanism if solar excitation is dominant over particle impact. strategy: Monitor the satellite for one hour prior to ingress, one hour after ingress, one hour before egress, and one hour after egress utilizing the UVS 10bps realtime capacity. Orbits: Io - all, Europa - all. 7) NRLCLD Objective: Determine the composition and time variation of the ionized Io neutral cloud (SO2,SO,O,S,K,Na) to assist in the modeling of the Io plasma torus and Io's atmosphere. Strategy: Monitor the emissions from the Io at various distances from the satellite for a total of four hours per orbit. Orbits: Io - all. 8) PHASE Objective: Observe Io and Europa in the 1600A to 3200A wavelength regions at phase angles not obtainable from the Earth to supplement and complement the NIMS surface property measurements. Strategy: Observe Io and Europa at various phase angles throughout the tour utilizing the UVS 10bps realtime capability. Orbits: Io - all, Europa - all.