Computer Science – Performance
Scientific paper
Jan 2006
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2006aipc..813..982w&link_type=abstract
SPACE TECH.& APPLIC.INT.FORUM-STAIF 2006: 10th Conf Thermophys Applic Microgravity; 23rd Symp Space Nucl Pwr & Propulsion; 4th C
Computer Science
Performance
Spaceborne And Space Research Instruments, Apparatus, And Components, Photoelectric Conversion: Solar Cells And Arrays
Scientific paper
A modular design for a solar-electric tug was analyzed to establish flight control requirements and methods. Thrusters are distributed around the periphery of the solar array. This design enables modules to be berthed together to create a larger system from smaller modules. It requires a different flight mode than traditional design and a different thrust direction scheme, to achieve net thrust in the desired direction, observe thruster pointing constraints that avoid plume impingement on the tug, and balance moments. The array is perpendicular to the Sun vector for maximum electric power. The tug may maintain a constant inertial attitude or rotate around the Sun vector once per orbit. Either non-rotating or constant angular velocity rotation offers advantages over the conventional flight mode, which has highly variable roll rates. The baseline single module has 12 thrusters: two 2-axis gimbaling main thrusters, one at each ``end'', and two back-to-back Z axis thrusters at each corner of the array. Thruster pointing and throttling were optimized to maximize net thrust effectiveness while observing constraints. Control design used a spread sheet with Excel Solver to calculate nominal thruster pointing and throttling. These results are used to create lookup tables. A conventional control system generates a thruster pointing and throttling overlay on the nominals to maintain active attitude control. Gravity gradients can cause major attitude perturbations during occultation periods if thrust is off during these periods. Thrust required to maintain attitude is about 4% of system rated power. This amount of power can be delivered by a battery system, avoiding the performance penalty if chemical propulsion thrusters were used to maintain attitude.
Wingo Dennis
Woodcock Gordon
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