NSSDCA ID: 1997-061C-06
Mission Name: HuygensThe Surface Science Package (SSP) is designed to ascertain the composition and physical properties of Titan's surface at the impact site. To achieve this, the SSP consists of a suite of sensors including an accelerometer, tilt sensors, a thermal properties assembly, acoustic properties sensors, and instrumentation to measure fluid permittivity, density, and refractive index. An aperture (called a "top hat") in the foredome of the probe, with a vent extending upward along the probe axis and up to the experiment platform, will admit fluid, providing direct access to surface materials and mounting for several of the sensors. Although the SSP is primarily designed to investigate Titan's surface, several of its sensors are expected to contribute significantly to the study of atmospheric properties during the descent phase of the mission.
The accelerometer subsystem consists of two piezoelectric sensors, one (ACC-I) mounted on the SSP electronics on the probe's experiment platform, the other (ACC-E) on a spear which extends below the probe's foredome and is located next to the top hat aperture. ACC-E will provide information only on impact, but ACC-I will also measure atmospheric and surface accelerations.
The tilt sensors work on an electrolytic principle. They are comprised of sealed glass tubes which contain a methanol-based liquid and platinum electrodes. Each sensor is small and measures the local vertical about a single axis. Both sensors will be used to give the tilt angle in any plane and both are mounted on the SSP electronics box (on the top of the probe experiment platform). One axis of the tilt sensors is aligned (to within one degree) along the radius extending from the platform/probe central axis. The tilt sensors will measure any pendulum motion during descent as well as determining the probe attitude after landing (including any motion due to waves).
The thermal properties sensor assembly consists of platinum wires 5 cm in length and 10 and 25 micrometers in diameter mounted in the top hat. A current is passed through the wires to heat them and the surrounding medium. A series of resistance measurements (taken approximately every 0.1 s) measures the rate of heating of the wires and detects the onset of convection. In this manner, the temperature and thermal conductivity of the surface and lower atmosphere as well as the heat capacity of the surface can be determined.
The acoustic properties sensors are small piezoelectric ceramic devices similar to those used in marine applications. Two of the transducers (API-V) are mounted facing each other across the top hat, alternating between transmitting and receiving a 1.0 MHz acoustic signal. The third transducer (API-S) points vertically downward emitting a 15 kHz signal and will be used for sounding the depth of the ocean (after landing) as well as to Titan's surface (during descent). API-S may also be capable of atmospheric sounding.
The fluid permittivity sensor consists of electrodes placed within the top hat. The capacitance between the electrodes will vary with the permittivity of the substance between them. A measurement of the resistance between the electrodes will also yield the conductivity of the material and may provide information on the presence of polar molecules.
The density of any fluid entering the top hat will be measured using an Archimedes buoyancy sensor. Fluid entering the aperture will displace the float and be measured by four strain gauges in a bridge arrangement.
Finally, the refractive index sensor is a prism with a curved surface, two LED light sources, and a linear photodiode detector array. The LEDs provide internal or external illumination to the curved surface of the prism via light guides. Light passes through the prism surface onto the photodiode array and the refractive index is determined by the position of the transition from light to dark on the array.
Mass: 4.2 kg
Power (avg): 15 W
Bit rate (avg): 0.66 kbps
Questions and comments about this experiment can be directed to: Dr. Edwin V. Bell, II
Name | Role | Original Affiliation | |
---|---|---|---|
Prof. John C. Zarnecki | Principal Investigator | University of Kent, Canterbury | j.c.zarnecki@ukc.ac.uk |