Spacecraft Instruments

► Spacecraft instrument selection begins with the mission description and the selected primary and secondary mission objectives  Available instruments and detectors may have minor influence on the mission objectives ► Budget and resources (communications, launcher, etc.) often have a dramatic impact on the mission objectives ► Power limitations may also impact the instrument selection

Spacecraft Instruments ► Data types, data processing, data communications, and data analysis can also influence criteria used for instrument selection

Spacecraft Instruments ► A list of a typical set of instruments and systems is not an accurate representation of any exploration spacecraft since every space exploration mission is unique ► Nevertheless, a list can help illustrate the selection process ► A more useful exercise begins with identifying the mission type before compiling a list of “typical” instruments and systems

Spacecraft Instruments Spacecraft mission types ► 1. Planetary/solar system exploration examples  Flyby (examples include Mariner series, Voyager, Pioneer series)  Orbiter (Explorer series, Magellan, Galileo)  Lander (Surveyor, Viking, Venera series)  Rover (Apollo, Luna series, Mars Pathfinder)  Atmospheric probe (Venera series, Galileo, Cassini) ► 2. Astronomical observation (COBE, HST, IRAS) ► 3. Communications (INTELSAT, TDRSS, INMARSAT) ► 4. Survey & remote sensing  Earth observation (LANDSAT series, SPOT)  Meteorological (GOES series, MEOSAT) ► 5. Reconnaissance (DoD satellites) ► 6. Technology advancement (ASAT)

Spacecraft Instruments Mission – Planetary/Moon Orbiter ► A spacecraft designed for travel to a distant planet and orbital operations must include a substantial propulsive capability for orbit insertion and orbit operations ► Orbital missions will expose the spacecraft to solar occultations (planet or moon shadows the spacecraft)  Interruption of solar panels' production of electrical power  Subjects the vehicle to extreme thermal variation ► Orbital missions will also produce Earth occultations  Interrupts uplink and downlink communications with Earth ► Orbital missions are used to follow up initial reconnaissance mission(s) with in-depth study of the planet/moon

Spacecraft Instruments - Orbiter Mission Spacecraft systems ► Structures - similar or the same as other mission types ► Electrical Power Systems  Must have a secondary power supply system if inside 2 AU  Must be a nuclear thermal (or reactor) system beyond 2 AU ► Propulsion  Orbit insertion  Orbital operations ► Telecommunications – Deep Space Network (DSN ) link ► Thermal Control  Extreme temperature environments in space are even more extreme beyond Mars and inside to orbit of Venus  Additional heating/cooling system considerations in these environments ► Guidance, Navigation & Control - similar or the same as other mission types ► Computer & Data Handling Systems - similar or the same as other mission types

Spacecraft Instruments - Orbiter Mission Experiments and instruments ► Imaging  Visible – geological features  IR imaging spectrometers ► Heat flow and composition  Microwave ► Synthetic aperture radar (SAR) ► Used to penetrate thick atmospheres for surface imaging ► Spectral analysis  IR spectrometer ► Surface composition and heat flow  IR imaging spectrometers ► Heat flow and composition  UV spectrometers ► Surface and atmospheric composition

Spacecraft Instruments - Orbiter Mission Experiments and instruments ► Spectral analysis  IR radiometer/bolometer ► Measures net heat flow over a broad frequency range and usually over a large area  X-ray spectrometer ► Used for mapping surface element distributions such as ice, iron, etc.  Gamma-ray spectrometer ► Also used for mapping surface element distributions  Neutron spectrometer ► Requires low orbit altitude ► Used recently for mapping hydrogen (Lunar Prospector)

Spacecraft Instruments - Orbiter Mission Experiments and instruments ► Radio Science  Uses communications link between the spacecraft and the DSN to measure Doppler shift acceleration, atmospheric gases, and plasma interference  Mass and density measurements ► Doppler shift anomalies in spacecraft signal and celestial mechanics used to measure mass distributions in planets/moons  Occultations ► Used to measure ring systems, atmospheres (even trace gases), and planet/moon diameters  Gravity fields Doppler shift anomalies in spacecraft signal and celestial mechanics used to measure and map gravity fields of planets/moonsDoppler shift anomalies in spacecraft signal and celestial mechanics used to measure and map gravity fields of planets/moons

Spacecraft Instruments - Orbiter Mission Experiments and instruments ► Magnetic fields  Magnetic field measurements are used to determine internal activity of the planet/moon and the differences in ancient and current fields  Measurements made using sensitive magnetometers  Triaxial fluxgate magnetometer ► Most common type used for planetary exploration  Proton precession magnetometer Uses hydrogen/proton nuclear resonance to couple with magnetic fieldUses hydrogen/proton nuclear resonance to couple with magnetic field

Spacecraft Instruments - Orbiter Mission Experiments and instruments ► Particle detectors  Particle detectors are employed in the analysis of low-energy and high-energy particles coming from the Sun, and trapped in the magnetic fields associates with the target planet/moon  High-energy particle detectors ► Used to measure the energy spectra of trapped energetic electrons, and the energy and composition of atomic nuclei  Low-energy particle detectors Used to characterize the composition, energies, and angular distributions of charged particles in interplanetary space and within planetary systemsUsed to characterize the composition, energies, and angular distributions of charged particles in interplanetary space and within planetary systems

Spacecraft Instruments - Orbiter Mission Experiments and instruments ► Particle detectors  Dust detectors ► Used to measure the number, velocity, mass, charge, and flight direction of dust particles striking the instrument ► Used to measure the energy spectra of trapped energetic electrons, and the energy and composition of atomic nuclei  Plasma detectors ► Designed for analyzing the lowest particle energies ► Used to measure the density, composition, temperature, velocity and three-dimensional distribution of plasmas in interplanetary regions and within planetary magnetospheres ► Plasma detectors are sensitive to solar and planetary plasmas ► Used to measure the solar wind and its interaction with a planetary system