Development of software for analysing entry accelerometer data in preparation for the Beagle 2 mission to Mars: towards a publicly available toolkit

We have tested techniques for turning Beagle 2’s entry accelerometer data into a T(z) profile. We reproduced the PDS results for Pathfinder. The PDS trajectory for Pathfinder appears inconsistent with its entry state. Our code is available online

Silence on Shangri-La: attenuation of Huygens acoustic signals suggests surface volatiles

Objective: Characterize and understand acoustic instrument performance on the surface of Titan. Methods: The Huygens probe measured the speed of sound in Titan's atmosphere with a 1 MHz pulse time-of-flight transducer pair near the bottom of the vehicle. We examine the fraction of pulses correctly received as af unction of time. Results: This system returned good data from about 11 km altitude, where the atmosphere became thick enough to effectively transmit the sound, down to the surface just before landing: these data have been analyzed previously. After an initial transient at landing, the instrument operated nominally for about 10 min, recording pulses much as during descent. The fraction of pulses detected then declined and the transmitted sound ceased to be detected altogether, despite no indication of instrument or probe configuration changes. Conclusions: The most likely explanation appears to be absorption of the signal by polyatomic gases with relaxation losses at the instrument frequency, such as ethane, acetylene and carbon dioxide. These vapors, detected independently by the GCMS instrument, were evolved from the surface material by the warmth leaking from the probe, and confirm the nature of the surface materials as ‘damp’ with a cocktail of volatile compounds. Some suggestions for future missions are considered. Practice implications: None

Removal of straylight from ExoMars NOMAD-UVIS observations

We present an in-flight straylight removal method for the Ultraviolet and Visible Spectrometer (UVIS) channel of the Nadir and Occultation for Mars Discovery (NOMAD) instrument aboard the ExoMars Trace Gas Orbiter (TGO). The presence of a ‘red-leak’ straylight signal in the UVIS instrument was discovered post-launch in ground calibration measurements of spectral lamps; UVIS observations of lamps with negligible UV light emission (RS12) showed a significant signal at UV wavelengths. Subsequent analyses of nadir observations of the martian atmosphere revealed that at UV wavelengths the red-leak straylight was in excess of 300% of the true UV signal, jeopardising the primary science observations of the instrument (retrievals of atmospheric ozone). By modifying the UVIS readout method to obtain a region of interest around the illuminated region on the Charge-Coupled Device (CCD) detector, instead of a binned one-dimensional spectrum, and utilising straylight profiles derived from measurements of the RS12 calibration lamp we show that the majority of the straylight at UV wavelengths can be successfully removed for the nadir channel in a self-consistent manner. The corrected UVIS radiances are compared to coincident Mars Color Imager (MARCI) instrument observations with residuals between the two instruments generally remaining within 15%

In-flight performance of the HASI servo accelerometer and implications for results at Titan

The Huygens Atmospheric Structure Instrument (HASI) includes a high sensitive servo accelerometer to sense deceleration of the probe in the direction of the probe trajectory. These data will be used to determine the atmospheric density profile in the upper reaches of the atmosphere where it is least well constrained. Results will be presented of the performance of this sub-system during the in-flight checkouts performed to date. In particular, the noise performance will be assessed. This is especially important as it limits the resolution and therefore performance of the sensor at the very top of Titan's atmosphere. Implication for the results expected at Titan will be presented

In-flight performance of the HASI servo accelerometer and implications for results at Titan

International audienc

Descent motions of the Huygens probe as measured by the Surface Science Package (SSP): Turbulent evidence for a cloud layer

The Huygens probe underwent vigorous short-period motions during its parachute descent through the atmosphere of Saturn's moon Titan in January 2005, at least some of which were excited by the Titan environment. Several sensors in the Huygens Surface Science Package (SSP) detect these motions, indicating the transition to the smaller stabilizer parachute, the changing probe spin rate, aerodynamic buffeting, and pendulum motions. Notably, in an altitude range of about 20–30 km where methane drops will freeze, the frequency content and statistical kurtosis of the tilt data indicate excitation by turbulent air motions like those observed in freezing clouds on Earth, supporting the suggestion of Tokano et al. [Tokano, T., McKay, C.P., Neubauer, F.M., Atreya, S.K., Ferri, F., Fulchignoni, M., Niemann, H.B. (2006a). Methane drizzle on Titan. Nature 442, 432–435] that the probe passed through such a cloud layer. Motions are weak below 20 km, suggesting a quiescent lower atmosphere with turbulent fluctuations of nominally <0.15 m/s (to within a factor of 2) but more violent motions in the upper troposphere may have been excited by turbulent winds with amplitudes of 1–2 m/s. Descent in part of the stratosphere (150–120 km) was smooth despite strong ambient wind (100 m/s), but known anomalies in the probe spin prevent investigation of turbulence in the known wind-shear layer from 60 to 100 km

In-flight performance of the HASI servo accelerometer and implications for results at Titan

International audienc

In-flight performance of the HASI servo accelerometer and implications for results at Titan

International audienc

Stratospheric balloon flight experiment campaign for the simulation of the Huygens probe mission: verification of HASI (Huygens Atmospheric Structure Instrument) performance in terrestrial atmosphere

International audienc

Stratospheric balloon flight experiment campaign for the simulation of the Huygens probe mission: verification of HASI (Huygens Atmospheric Structure Instrument) performance in terrestrial atmosphere

International audienc