Key Recommendations for SMART-1
1 March 1999The period January-February has been a busy one for the SMART-1 project, with a succession of key science, technical and management meetings, culminating in a number of recommendations concerning the launcher, electric propulsion system and payload, presented to ESA's Science Programme Committee (SPC) on 17 February.
The SPC took note of the following recommendations:
- a launch on Ariane as a secondary passenger (using the Cyclade configuration)
- the Stationary Plasma Thruster as the electric propulsion system
- the payload as recommended by the SMART-1 peer review committee, keeping within a mass budget of 15 kg, which is possible with the above launcher and propulsion.
The use of solar electric propulsion as primary drive mechanism on SMART-1 will be a first for Europe and is essential in paving the way for future ESA projects with large velocity requirements, such as the Mercury cornerstone mission. Stationary plasma thrusters belong to the category of so-called 'hall-effect thrusters'. Electrons from an external cathode enter a ceramic discharge chamber, attracted by an anode. On their way to the anode, the electrons encounter a radial magnetic field created between inner and outer coils, causing cyclotron montion around the magnetic field lines. Collisions between drifting electrons and xenon propellant create the plasma. The ions created are then accelerated by the negative potential existing near the exit of the chamber due to the Hall effect. The external cathode acts also as a neutraliser, injecting electrons into the thrust beam to maintain zero-charge equilibrium both in the beam and on the spacecraft. This type of thruster can provide a nominal thrust of 70 mN at 1640 s specific impulse and 1350 W of nominal input power.
SMART-1 model payload
The recommended payload is the result of a careful trade-off between the best possible science return and the technology demonstration needs of the mission. The model payload is targeted to lunar geo-chemistry observations and testing of the proposed solar electric propulsion system.
D-CIXS is a Compact X-ray Spectrometer providing high throughput fluorescence X-ray spectroscopy and imaging of the moon. It provides mapping of the main lunar rock-forming elements and at the same time demonstrates a technology applicable to the Mercury cornerstone missions and other future planetary missions. It includes a solar X-ray monitor for absolute calibration but also for continuous solar monitoring. It can be used in cruise phase to monitor X-ray variability of several cosmic sources. It can also be used for cometary detection, auroral X-ray monitoring on both hemispheres of the Earth, and for observing magnetospheric boundaries (in conjunction with Cluster II observations). In lunar orbit it can observe the main rock-forming elements with a sensitivity much higher than that of the Apollo orbiters. D-CIXS makes use of novel Swept Charge Device (SCD) detectors, less sensitive to radiation environment and able to operate at higher temperatures, and relies on a micro-structure collimating X-ray optics.
AMIE is a Micro-imager based on ongoing development work within ESA's Technology Research Programme, that helps to correlate surface mineralogy data and geology at medium scales. It is also able to monitor variations in light intensity in the moon's polar regions. It includes a CCD camera, an optical head and control electronics, plus a low-power micro-DPU (digital processing unit), highly integrated by means of 3-D MCM (Multi-Chip Module) technology of major interest for future missions.
AMIE will also possibly support the test of the laser link with the ESA Optical Ground Station, to verify the link acquisition from different distances and to evaluate the performance of the telescope sub-apertures system, designed to mitigate the effect of the atmospheric turbulence on the laser beam propagation. This experiment will open up an innovative technique for future deep-space communications.
SIR, the SMART-1 visible/infrared (0.9 to 2.4 microns) spectrometer is primarily a low-mass technology experiment to space-qualify a very low mass monolithic grating spectrometer. This geological instrument is able to discriminate between different minerals on the moon (pyroxenes, olivines and feldspars), and would be the first of its kind in lunar orbit. As such it is a key preparation for the forthcoming Mercury mission.
SPEDE is the Spacecraft Potential, Electron and Dust Experiment that complements the EPDP diagnostic package below in monitoring the solar electric propulsion, by measuring potential and induced currents by means of two Langmuir probes accommodated on the tips of two 0.5 m thin booms. It will also perform cruise science and lunar orbit science by monitoring the space - time variations of the plasma and electron environment.
The Electric Propulsion Diagnostic Package is a technology payload to study the plasma environment around the SMART-1 spacecraft when the electric propulsion system is both on and off. The package is composed by a suite of sensors, comprising a proximity Langmuir probe, a Retarding Potential Analyser and Deposition sensors (a Solar cell and a Quartz Crystal Micro-balance). EPDP performs key measurements to characterise the electric propulsion system and its influence on the spacecraft environment.
KATE is a Deep-Space Telemetry and Telecommand technology experiment, operating in Ka and X bands - suited for needs of future deep space missions and inner solar system missions such as the Mercury mission. The KATE transponder will also allow the testing of novel coding techniques (Turbo-codes) and possibly the high-accuracy tracking in VLBI operation (Very-Large Baseline Interferometry), both techniques aiming at enhancing the communications and radio-tracking in deep-space missions.
RSIS is a series of Radio Science Investigations which will allow during the cruise phase to monitor the dynamic performances of the electric propulsion system and during the lunar observation phase to test the method of measuring planetary bodies libration, in order to assess the mass distribution and the rotational properties of the target body. The testing of this technique on a well-known planetary body such as the Moon is a preparatory step towards its exploitation in future planetary explorations such as the Mercury mission.
SMART-1 is the first of the Small Missons for Advanced Research in Technology within ESA's Mandatory Science Programme. The mission is intended to demonstrate innovative and key technologies for deep-space scientific missions. Prime Contractor for defining the mission is the Swedish Space Corporation.