Development of a Cold Gas Propulsion System for the ... - SSL - MIT
Development of a Cold Gas Propulsion System for the ... - SSL - MIT Development of a Cold Gas Propulsion System for the ... - SSL - MIT
Figure 7-2. CGSE 3-DOF horizontal traverse and roll testing on air bearing. With the air bearing shown in Figure 7-2, the TALARIS hopper hovered about an inch off the floor on a cushion of air, so friction was greatly reduced. The air bearing also freed two degrees of freedom which had been constrained by the wheels, allowing the hopper to roll about its X axis and travel across the entire 2D plane of the floor. Furthermore, although the TALARIS hopper did not have any thrusters aligned with its Y axis, the air bearing did not prevent it from drifting in that direction, so it provided an opportunity to test software compensation for thruster misalignment. Thus, the air bearing allowed for 3-DOF testing, such as the roll and traverse test illustrated in Figure 7-3 below. 108
Figure 7-3. GNC data from 3-DOF test of TALARIS hopper, with 45° roll and horizontal traverse. (a) Angular position. (b) Linear traverse velocity. Figure 7-3 was created with data collected from the hopper’s inertial measurement unit, or IMU. Before the depicted test began, the hopper was placed on the air bearing and set at about a 45° angle to the intended direction of travel. Then during the test, after a calibration period, the vehicle fired its horizontal thrusters in pairs to roll to the desired heading. This maneuver can be seen from about 54 to 61 s in Figure 7-3(a). The hopper then held its new position briefly before performing a horizontal traverse, as shown from about 74 to 78 s in Figure 7-3(b). During the traverse, the hopper drifted slightly off course, probably due to thruster misalignments; however, as shown in Figure 7-3(a), the GNC algorithm executed small roll maneuvers to correct the heading. With a series of tests such as the one illustrated in Figure 7-3, TALARIS horizontal thruster control was successfully validated. The next step was to continue on to validation testing involving the vertical CGSE thrusters. 109
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Figure 7-2. CGSE 3-DOF horizontal traverse and roll testing on air bearing.<br />
With <strong>the</strong> air bearing shown in Figure 7-2, <strong>the</strong> TALARIS hopper hovered about an inch <strong>of</strong>f <strong>the</strong> floor on a<br />
cushion <strong>of</strong> air, so friction was greatly reduced. The air bearing also freed two degrees <strong>of</strong> freedom which<br />
had been constrained by <strong>the</strong> wheels, allowing <strong>the</strong> hopper to roll about its X axis and travel across <strong>the</strong><br />
entire 2D plane <strong>of</strong> <strong>the</strong> floor. Fur<strong>the</strong>rmore, although <strong>the</strong> TALARIS hopper did not have any thrusters<br />
aligned with its Y axis, <strong>the</strong> air bearing did not prevent it from drifting in that direction, so it provided an<br />
opportunity to test s<strong>of</strong>tware compensation <strong>for</strong> thruster misalignment. Thus, <strong>the</strong> air bearing allowed <strong>for</strong><br />
3-DOF testing, such as <strong>the</strong> roll and traverse test illustrated in Figure 7-3 below.<br />
108
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