Huygens HASI servo accelerometer: A review and lessons learned

Hathi, B.; Ball, Andrew; Colombatti, Giacomo; Ferri, F.; Leese, M. R.; Towner, M. C.; Withers, Paul; Fulchigioni, M.; Zarnecki, J. C.

doi:10.1016/j.pss.2009.06.023

Cited by 15 publications

(8 citation statements)

References 23 publications

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“…This means that DISR was looking up by 3.2 • ± 0.5 • with respect to a horizontal attitude. This angle is consistent with the HASI servo acceleration of 1.34300±0.00034 m s −2 (Hathi et al, 2009) when combined with the Titan reference gravity of 1.345 m s −2 (Lebreton and Matson, 2002). Even though no uncertainty was given for the reference gravity, radar topography data show that Titan's radius at the landing site is within 0.02% of the assumed 2575 km (Zebker et al, 2009), and thus the gravity should be within 0.04% of the reference value.…”

Section: Downward-looking Violet Photometer (Dlv)supporting

confidence: 79%

Bouncing on Titan: Motion of the Huygens probe in the seconds after landing

Schröder¹,

Karkoschka²,

Lorenz³

2012

Planetary and Space Science

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While landing on Titan, several instruments onboard Huygens acquired measurements that indicate the probe did not immediately come to rest. Detailed knowledge of the probe's motion can provide insight into the nature of Titan's surface. Combining accelerometer data from the Huygens Atmospheric Structure Instrument (HASI) and the Surface Science Package (SSP) with photometry data from the Descent Imager/Spectral Radiometer (DISR) we develop a quantitative model to describe motion of the probe, and its interaction with the surface. The most likely scenario is the following. Upon impact, Huygens created a 12 cm deep hole in the surface of Titan. It bounced back, out of the hole onto the flat surface, after which it commenced a 30-40 cm long slide in the southward direction. The slide ended with the probe out of balance, tilted in the direction of DISR by around 10 • . The probe then wobbled back and forth five times in the north-south direction, during which it probably encountered a 1-2 cm sized pebble. The SSP provides evidence for movement up to 10 s after impact. This scenario puts the following constraints on the physical properties of the surface. For the slide over the surface we determine a friction coefficient of 0.4. While this value is not necessarily representative for the surface itself due to the presence of protruding structures on the bottom of the probe, the dynamics appear to be consistent with a surface consistency of damp sand. Additionally, we find that spectral changes observed in the first four seconds after landing are consistent with a transient dust cloud, created by the impact of the turbulent wake behind the probe on the surface. The optical properties of the dust particles are consistent with those of Titan aerosols from Tomasko et al. (P&SS 56, 669). We suggest that the surface at the landing site was covered by a dust layer, possibly the 7 mm layer of fluffy material identified by Atkinson et al. (Icarus 210, 843). The presence of a dust layer contrasts with the dampness measured just centimeters below the surface, and suggests a recent spell of dry weather at the landing site.2005; Karkoschka et al., 2007). The surface itself appears fine-grained, damp, and relatively soft (Zarnecki et al., 2005;Niemann et al., 2005;Lorenz et al., 2006;Karkoschka et al., 2007), and may be covered by a 7 mm thick fluffy layer (Atkinson et al., 2010). The motion of Huygens during atmospheric entry and descent has been studied well (Bird et al., 2005;Karkoschka et al., 2007;Lorenz et al., 2007), but its motion during and directly following landing has not. In the last phase of the descent a stabilizer parachute restricted the vertical speed to 4.5 m s −1 , ensuring a relatively soft landing. The horizontal speed was then only around 1 m s −1 . It is clear that, upon impact, the 200 kg probe could not immediately have come to rest. Indeed, evidence for continued motion exists. Schröder (2007) noticed that DISR measurements were variable for several seconds after impact, and suspected that motion and/or du...

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Section: Downward-looking Violet Photometer (Dlv)supporting

confidence: 79%

Bouncing on Titan: Motion of the Huygens probe in the seconds after landing

Schröder¹,

Karkoschka²,

Lorenz³

2012

Planetary and Space Science

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“…one in every four of the original samples was stored) because of data volume issues. This sensor was the most sensitive accelerometer ever flown in a planetary entry probe Hathi et al 2009); accelerometers included in the Inertial Measurement Unit (IMU) used in the Guidance, Navigation and Control (GNC) system of an entry vehicle [e.g. Mars Phoenix, MER Spirit and Opportunity, Curiosity, ExoMars Schiaparelli, InSight], could reach such sensitivity, but generally the raw data are not transmitted, with only processed attitude measurements (e.g.…”

Section: Accelerometer (Acc)mentioning

confidence: 99%

“…Assuming the HASI ACC Servo performance at Titan (Hathi et al 2009), a noise of 0.3 µg (∼ 3 × 10 −5 m/s 2 ) is expected. The exact performance achievable, in terms of the accuracy of the derived atmospheric density will also depend on the probe ballistic coefficients, entry speed and drag coefficient and their associated uncertainties.…”

Section: Accelerometer (Acc)mentioning

confidence: 99%

The Atmospheric Structure of the Ice Giant Planets from In Situ Measurements by Entry Probes

et al. 2020

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In situ measurements by an atmospheric entry probe allow for sounding and investigating atmospheric composition, structure and dynamics deep into the atmosphere of a Giant planet. In this paper, we describe an Atmospheric Structure Instrument (ASI) for an entry probe at Uranus and/or Neptune. The scientific objectives, the measurements and the expected results are discussed in the framework of a future opportunity for an NASA-ESA joint mission to the Ice Giant planets.

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“…The Huygens probe contained a suite of accelerometers to monitor its path through the atmosphere of Titan and to record the touchdown shock. Although not intended to conduct a surface seismic experiment, the HASI accelerometer onboard the Huygens probe continued to record data for approximately 30 min after touchdown (Hathi et al, 2009). A network of three triaxial accelerometers was deployed on comet 67P/Churuyomov-Gerasimenko within the landing gear of Rosetta's lander Philae, resulting in a network aperture of about 2.5 m (Knapmeyer et al, 2016).…”

Section: Introductionmentioning

confidence: 99%

Estimation of the Seismic Moment Rate from an Incomplete Seismicity Catalog, in the Context of the InSight Mission to Mars

Knapmeyer¹,

Knapmeyer‐Endrun

Plesa³

et al. 2019

Bulletin of the Seismological Society of America

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We evaluate methods to estimate the global seismic moment rate of a planet from the ≥ 1 largest events observed during a limited and possibly short time span, as can be expected e.g. for lander missions to Mars. The feasibility of the approach is demonstrated with a temporary broadband seismometer that was recording in the Mojave Desert, California, for 86 days in 2014, and by application to the Global Centroid Moment Tensor catalog, subsets thereof, and a catalog of stable continental regions seismicity. From the largest event observed at Goldstone alone (≈ 7.9) we estimate the Earth's global moment rate to be 1.03 × 10 22 ⁄ , while an estimation based on the 10 strongest events yields a rate of 5.79 × 10 21 ⁄. Summation of 42 years of GCMT solutions result in an average of 7.61 × 10 21 ⁄. In general, a two years interval of GCMT solutions is sufficient to estimate the Earth's annual moment rate to within a factor 5 or better. A series of numerical experiments with more than 560 million synthetic catalogs based on the Tapered Gutenberg-Richter distribution shows that the estimation is rather insensitive against an unknown slope of the distribution, and that bias and variance of the estimator depend on the ratio between moment rate and corner moment of the size frequency distribution. Moment rates of published Mars models differ by a factor 1000 or more. Tests with simulated catalogs show that it will be possible to reject some of these models with data returned by NASA's InSight mission after two years of nominal mission life time.

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Huygens HASI servo accelerometer: A review and lessons learned

Cited by 15 publications

References 23 publications

Bouncing on Titan: Motion of the Huygens probe in the seconds after landing

Bouncing on Titan: Motion of the Huygens probe in the seconds after landing

The Atmospheric Structure of the Ice Giant Planets from In Situ Measurements by Entry Probes

Estimation of the Seismic Moment Rate from an Incomplete Seismicity Catalog, in the Context of the InSight Mission to Mars

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