Instruments

Instruments in Brief

ACP

ACP (Aerosol Collector and Pyrolyser) will collect aerosols that will be analysed by the Gas Chromatograph and Mass Spectrometer experiment. It is equipped with a deployable sampling device that will be operated twice during the descent. The first sample will be taken from the top of the atmosphere down to an altitude of about 40 km. The second sample will be collected in the cloud layer, between altitudes of about 23 km and 17 km. After extension of the sampling device, a pump draws the atmosphere and its aerosols through a filter in order to capture the aerosols. At the end of each collection period, the filter is retracted into a pyrolysis furnace where the material from the captured aerosols is analysed, first at ambient temperature (about 0°C), then while heated to 250 °C and then to 600 °C in order to conduct a multi-step pyrolysis. The pyrolysed products are flushed into GCMS for analysis.

ACP Measurements
Sampling altitudes	150 - 45 km, 22 - 15 km
Pyrolysis temperatures	~275 K, 525 K, 875 K

DISR

DISR (Descent Imager and Spectral Radiometer) is an optical remote sensing instrument. It includes a set of upward and downward looking photometers, visible and infrared spectrometers, a solar aureole sensor, a side-looking imager, and two down-looking imagers - one providing medium resolution and the other high resolution. There is also a sun sensor that will measure the spin rate of the probe. DISR will make measurements in the 0.3 to 1.7 µm range.

DISR Measurements
Upward and downward looking photometer	Violet light
Spectrometers	Visible (480 - 960 nm) Infrared (0.87 - 1 µm)
Downward and side-looking imagers	0.66 - 1 µm
Solar aureole photometer	550 nm, 939 nm

DWE

DWE (Doppler Wind Experiment) is designed to determine the direction and strengh of Titan's zonal winds. A height profile of wind velocity will be derived from the residual Doppler shift of Huygens radio relay signal as received by Cassini. This will be corrected for all known probe and orbiter motions and signal propagation effects. Wind-induced motion of the probe will be measured with a precision better than 1 ms^-1 starting when the parachute deploys at an altitude of about 165 km and continuing down to the surface. The secondary objectives are to investigate the probe dynamics (spin rate, spin phase) during the descent and the to determine the probe's location and orientation up to and after landing.

DWE Measurements
(Allen variance)1/2	10-11 (in 1 s), 5 x 10-12 (in 10 s), 10-12 (in 100 s)
Corresponding wind velocities	2 ms-1 to 200 ms-1

GCMS

GCMS (Gas Chromatograph and Mass Spectrometer) is designed to measure the chemical composition of Titan's atmosphere from 170 km to the surface and determine the isotope ratios of the major gaseous constituents. It will also analyse gas samples from the ACP experiment and will investigate the composition of several candidate surface materials.

GCMS Measurements
Mass range	2 - 146 Dalton
Dynamic range	> 108
Sensitivity	10-12 mixing ratio
Mass resolution	10-6 at 60 Dalton

HASI

HASI (Huygens Atmospheric Structure Instrument) is a multi-sensor instrument that will measure the physical and electrical properties of Titan's atmosphere. Its sensors suite consists of a 3-axis accelerometer, a temperature sensor, a multi-range pressure sensor, a microphone and a electric field sensor array. The set of accelerometers is specifically optimised to measure entry deceleration for the purpose of inferring the atmosphere structure during the entry. The electric field sensor consists of a relaxation probe to measure the atmosphere's ionic conductivity and a quadripole array of electrodes fpr measuring the permittivity of both the atmosphere and of the surface. The sensor will also be used to detect atmospheric electromagnetic waves. In order to obtain information about the surface, HASI will also process the reflected signal of the radar altimeter.

HASI Measurements
Temperature	50 - 300 K
Pressure	0 - 2000 mbar
Gravity	1 µg - 10 mg
AC E-field (0 - 10 kHz)	80 dB at 2 µV m-1 Hz-1/2
DC E-field	50 dB at 40 V m-1
Electrical conductivity	10-15Ω m-1 - ∞
Relative permittivity	1 - ∞
Acoustic properties (0 - 5 kHz)	90 dB at 5 mPa

SSP

SSP (Surface Science Package) is a suite of sensors for determining the physical properties of the surface at the landing site and for providing information on the composition of the surface material. The instrument includes a force transducer for measuring the impact deceleration and sensors to measure the refraction index, temperature, thermal conductivity, heat capacity, speed of sound and dielectric constant of the surface material. The instrument suite includes an acoustic sounder for sounding the bottom layer of the atmosphere and the physical properties of the surface prior to landing. If the Probe lands in a liquid, the sounder will be used to probe the liquid depth. A tilt sensor is included to indicate the Probe's attitude after landing.

SSP Measurements
Gravity	0 - 100 g
Tilt	±  60°
Temperature	65 - 100 K
Thermal conductivity	0 - 400 mW m-1 K-1
Speed of sound	150 - 2000 m s-1
Liquid density	400 - 700 kg m-3
Refractive index	1.25 - 1.45
Acoustic sounder	0 - 500 m

Last Update: 07 December 2005

Related Articles

• Introduction (http://sci.esa.int/science-e/www/object/index.cfm?fobjectid=31193&fbodylongid=733)
• Instruments in Brief (http://sci.esa.int/science-e/www/object/index.cfm?fobjectid=31193&fbodylongid=1604)
• ACP: Aerosol Collector and Pyrolyser (http://sci.esa.int/science-e/www/object/index.cfm?fobjectid=31193&fbodylongid=1605)
• DISR: Descent Imager/Spectral Radiometer (http://sci.esa.int/science-e/www/object/index.cfm?fobjectid=31193&fbodylongid=734)
• DWE: Doppler Wind Experiment (http://sci.esa.int/science-e/www/object/index.cfm?fobjectid=31193&fbodylongid=735)
• GCMS: Gas Chromatograph and Mass Spectrometer (http://sci.esa.int/science-e/www/object/index.cfm?fobjectid=31193&fbodylongid=736)
• HASI: Huygens Atmosphere Structure Instrument (http://sci.esa.int/science-e/www/object/index.cfm?fobjectid=31193&fbodylongid=737)
• SSP: Surface Science Package (http://sci.esa.int/science-e/www/object/index.cfm?fobjectid=31193&fbodylongid=740)

Related Links

• ACP: Aerosol Collector and Pyrolyser (http://www.aero.jussieu.fr/experience/ACP/)
• DISR: Descent Imager / Spectral Radiometer (http://www.lpl.arizona.edu/~kholso/)
• DWE: Doppler Wind Experiment (http://www.astro.uni-bonn.de/%7Edwe/)
• HASI: Huygens Atmospheric Instrument (http://cisas.unipd.it/gen_HASI.php)
• SSP: Surface Science Package (http://pssri.open.ac.uk/missions/mis-cas.htm)