Instruments
HASI: Huygens Atmosphere Structure Instrument
The Huygens Atmospheric Structure Instrument is a multi-sensor package designed to measure the physical properties of Titan's atmosphere. HASI will measure the temperature, the pressure, the turbulence, the atmospheric conductivity and will search for lightning. HASI will also address questions regarding the surface topography and dielectric properties. The scientific objectives of the Huygens atmospheric Structure Instrument (HASI) are: - Determine the density, pressure and temperature conditions corresponding to the higher part of the atmosphere during the entry phase. Of particular interest is the determination of the physical condition in this region where the "detached" haze, observed by Voyager, is formed.
- Measure the stratospheric density, T, P profile of the stratosphere during the descent phase and identify the composition in these layers in terms of trace constituents which condense in this part of the atmosphere. Interpret any data which may suggest the existence of clouds in the upper troposphere.
- Measure P,T in the lower troposphere and determine the existence and extent of a convective zone.
- Determine (in case of survival after impact) the nature of the surface.
- Determine the atmospheric electric conductivity and investigate ionisation processes, wave electric fields and atmospheric lightning. Detect acoustic noise due to turbulence and thunders. Characterise electric properties, conductivity and permittivity of the surface material.
- Determine the surface large scale and small scale topography, the surface dielectric properties and in particular to be able to remotely distinguish between a liquid or a solid surface before impact. If the surface is liquid, information on surface winds may be obtained. All data are measured along the ground track of the descending probe due to horizontal winds during the last 30 km.
| HASI Sensor Packages | | Sensor package | Sensor type | Accu-
racy | Resolution | Measured parameter | | Accelerometers (ACC) | 3-axis accelerometer | 1% | < 1 µg | Atmospheric deceleration,
Descent monitoring,
Response to impact | | Pressure Profile Instrument (PPI) | Kiel probe, capacitive gauges | 1% | 0.01 hPa | Atmospheric pressure | | Temperature Sensors (TEM) | 2 dual element Pt thermometers | 0.5 K | 0.02 K | Atmospheric temperature | | Permittivity, Wave & Altimetry (PWA) | Mutual impedance | 10% | 10-11(Ωm)-1
| Atmospheric electric conductivity,
Wave electric fields &
Lightning | | AC field measurement | 2 µVm-1 (threshold) | | Relaxation probe | 10% | 1 min
25 ms - 2 s
1 mV
(threshold) | Ion conductivity and DC electric field | | Acoustic sensor | 5% | 10 mPa
(threshold) | Acoustic noise due to turbulence of storms | | Radar signal processing (FFT) | 1.5 dB | 40 m
at 24 km | Radar echoes below 60 km altitude |
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GCMS: Gas Chromatograph and Mass Spectrometer |
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SSP: Surface Science Package |
Last Update: 07 Dec 2005
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