NASA’s latest mission to Mars in November 2011 sent the Mars Science Laboratory rover “Curiosity” to assess whether Mars ever had, or still has, an environment able to support life. While on Mars, Curiosity will collect soil and environmental samples, and analyze the samples on location. Preventing contamination of the rover is critical to ensure that Curiosity’s data collection and analysis yields accurate results. Thus, engineering models and flight models are tested separately to validate design requirements of the various systems aboard the rover.
The inlets for the Chemistry and Mineralogy X-Ray Diffraction/X-Ray Fluorescence Instrument (CheMin) and Sample Analysis on Mars Instrument Suite (SAM) utilize piezodriven actuators at the base of the funnels to shake and sift soil from Mars’ surface into the spectrometers for analysis. Previously tested models using accelerometers produced inaccurate data due to the mass loading effects of attaching the transducers to the test article and limiting the amount of measurement locations possible. Scientists at NASA’s Jet Propulsion Laboratory (JPL) have developed a method of non-contact dynamic performance testing to measure the vibration levels of the spectrometer inlet funnels for design validation.
The first step in the validation process was to dynamically characterize the engineering models that have proven to effectively move soil through the funnel. By characterizing vibration levels at various locations on the inlet funnel, this data can be compared to the predicted results from the Finite Element Model (FEM), and provides a benchmark to be later compared with measurements on the flight model, which cannot be tested with soil.
The engineering model testing was performed, with excitation to the actuators, using a 100-500 Hz sweep over 15 seconds for the SAM and a 10.5-12.5 kHz sweep over 5 seconds for the CheMin. The plan called for testing each of the three actuators separately, then together in groups of two actuators exciting, and all three actuators exciting. The Polytec PSV-400-3D was used to measure vibrations in 3D on the engineering model. The engineering model was oriented in several positions to allow line-of-sight access from the sensor heads to the CheMin inlet (inside and outside), the CheMin funnel, the CheMin collection screen, and the SAM inlets. The measurement locations consisted of approximately 20 to 30 measurement points on the inlets, as well as a few locations on the collection screen and funnel.
To validate its functionality, the flight hardware had to be compared to the engineering models tested. The rover was assembled in a cleanroom, so to prevent damage to the rover and its components, access was limited to one meter away from the rover. The vibrometer was thoroughly cleaned and brought into the SAF to a distance in front of the rover with a direct line of sight to the CheMin and SAM inlets. Measurements were taken with the same excitation and acquisition settings from the engineering model tests on the outside and inside rim of the CheMin and SAM inlets.