The Deep Space 1 (DSl) spare flight thruster (FT2) was operated for 30,352 hours during the extended life test (ELT). The test was performed to validate the service life of the thruster, study known and identify unknown life limiting modes. Several of the known life limiting modes involve the ion optics system. These include loss of structural integrity for either the screen grid or accelerator grid due to sputter erosion from energetic ions striking the grid, sputter erosion enlargement of the accelerator grid apertures to the point where the accelerator grid power supply can no longer prevent electron backstreaming, unclearable shorting between the grids causes by flakes of sputtered material, and rouge hole formation due to flakes of material defocusing t he ion beam. Grid g ap decrease, which increases the probability of electron backstreaming and of arcing between the grids, was identified as an additional life limiting mechanism after the test. A combination of accelerator grid aperture enlargement and grid gap decrease resulted in the inability to prevent electron backstreaming at full power at 26,000 hours of the ELT. Through pits had eroded through the accelerator grid webbing and grooves had penetrated through 45% of the grid thickness in the center of the grid. The upstream surface of the screen grid eroded in a chamfered pattern around the holes in the central portion of the grid. Sputter deposited material, from the accelerator grid, adhered to the downstream surface of the screen grid and did not spall to form flakes. Although a small amount of sputter deposited material protruded into the screen grid apertures, no rouge holes were found after the ELT.
Supersonic wind tunnel testing of 0.813 m diameter Disk-Gap-Band parachutes is being conducted in the NASA Glenn Research Center (GRC) 10'x10' wind-tunnel. The tests are conducted in support of the Mars Science Laboratory Parachute Decelerator System development and qualification. Four percent of full-scale parachutes were constructed similarly to the flight-article in material and construction techniques. The parachutes are attached to a 4% scale MSL entry-vehicle to simulate the free-flight configuration. The parachutes are tested from Mach 2 to 2.5 over a Reynolds number (Re) range of 1 to 3 x 10 6 , representative of the MSL deployment envelope. Constrained and unconstrained test configurations are investigated to quantify the effects of parachute trim, suspension line interaction, and alignment with the capsule wake. The parachute is constrained horizontally through the vent region, to measure canopy breathing and wake interaction for fixed trim angles of 0 and 10 degrees from the velocity vector. In the unconstrained configuration the parachute is permitted to trim and cone, similar to the free-flight varying its alignment relative to the entry-vehicle wake. Test diagnostics were chosen to quantify parachute performance and to provide insight into the flow field structure. An in-line load cell provided measurement of unsteady and mean drag as a function of Mach and Re. Highspeed shadowgraph video of the upstream parachute flow field was used to capture bowshock motion and stand of distance. Particle image velocimetry of the upstream parachute flow field provides spatially and temporally resolved measurement velocity and turbulent statistics. Multiple high speed video views of targets placed in the interior of the canopy enable photo-grammetric measurement of the fabric motion in time and space from reflective. High speed video is also used to document the supersonic inflation and measure trim angle, projected area, and frequency of area oscillations.
Supersonic wind-tunnel tests of 0.813 m disk-gap-band parachutes were conducted in a 10 10 ft cross section of a closed-loop wind tunnel. Four-percent-scale parachutes were attached to a 4%-scale Mars Science Laboratory (Viking-type) entry vehicle to simulate the free-flight configuration. The parachutes were tested from Mach 2 to 2.5 over a Reynolds number Re range of 2 10 5 to 1:3 10 6 , representative of the Mars flight deployment envelope. A constrained parachute configuration was investigated to quantify the effect of parachute trim angle with respect to alignment with the entry-vehicle wake. In the constrained configuration, the parachutes were supported at the vent, using a rod that restricted parachute translation along a single axis. This was investigated for fixed trim angles of 0 and 10 degrees from the velocity vector. In the unconstrained configuration, the parachute was permitted to translate as well as trim and cone, in a manner similar to free flight. Nonintrusive test diagnostics were selected. An in-line load cell provided measurement of unsteady and mean parachute normal force. High-speed shadowgraph video of the upstream parachute flowfield was used to capture bow-shock motion and standoff distance. Stereo particle image velocimetry of the flowfield upstream of the parachute provided spatially resolved measurements of all three velocity components. Multiple high-speed-video views were used to document the supersonic inflation, parachute trim angle, projected area, and frequency of area oscillations. In addition, reflective targets placed in the interior of the canopy enabled photogrammetric reconstruction of the canopy-fabric motion (in both time and space) from the high-speedvideo data.
Nomenclatureor constructed diameter D p = projected diameter d = entry-vehicle diameter F D = axial drag force F D;RMS = axial rms drag M = Mach number m p = parachute mass q = freestream dynamic pressure Re = Reynolds number t = time t FI = time to full inflation t = nondimensional inflation time x=d = nondimensional trailing distance v = freestream velocity p = mass ratio ! AO = area oscillation frequency
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