Gianandrea Bianchini

VIRTIS: Visible Infrared Thermal Imaging Spectrometer for the Rosetta mission

The visible infrared thermal imaging spectrometer (VIRTIS) is one of the principal payloads to be launched in 2003 on ESAs Rosetta spacecraft. Its primary scientific objective s are to map the surface of the comet Wirtanen, monitor its temperature, and identify the solids and gaseous species on the nucleus and in the coma. VIRTIS will also collet data on two asteroids, one of which has been identified as Mimistrobell. The data is collected remotely using a mapping spectrometer co-boresighted with a high spectral resolution spectrometer. The mapper consists of a Shafer telescope matched to an Offner grating spectrometer capable of gathering high spatial, medium spectral resolution image cubes in the 0.25 to 5 micrometers waveband. The high spectral resolution spectrometer uses an echelle grating and a cross dispersing prism to achieve resolving powers of 1200 to 300 in the 1.9 to 5 micrometers band. Both sub-systems are passively cooled to 130 K and use two Sterling cycle coolers to enable two HgCdTe detector arrays to operate at 70 K. The mapper also uses a silicon back-side illuminated detector array to cover the ultra-violet to near-infrared optical band.

First results of performance test of temperature sensors of HASI instrument on Cassini/Huygens mission

First results about the performance of the temperature sensors (TEM) of Huygens Atmospheric Structure Instrument (HASI) obtained during Flight Model test campaign are presented and discussed. TEM belongs to the STUB subsystem of HASI, which is a multidisciplinary experiment package dedicated to the investigation of Titan atmosphere during the descent of the Huygens probe. TEM sensors are described, their characteristics and performances discussed and the data of thermal tests carried out at subsystem level and at probe level evaluated. From this preliminary analysis it seems that the sensors are suited to achieve the scientific objective of HASI experiment if post flight data correction is appropriately done.

On-line measurements to control the forming process of glass vials

The most relevant parameters to control the quality of glass vials are the internal and external diameters of the mouth and the height of the rim. A low cost vision system based on a 486 PC, a frame grabber, 4 CCD cameras (768 X 512 pixels) and I/O device to control the production of vials, by adjusting the flames temperature in the moulding section of the machine, has been developed and tested. A 24 mandrel machine rotating at about 300 rpm with a production capability of about 4200 pieces/hour had to be monitored with an accuracy of +/- 0.02 mm in the measure of the mouth diameters and +/- 0.04 mm on the rim height. In order to minimize the time delay required for the machine temperature compensation, the measurements had to be taken during the forming process. The system must be fast enough to follow the process, able to take into account the temperature variation of different classes of vials and far enough from the high temperature of the flames. A direct calibration procedure, using a reference vial, and a pyrometer to check the temperature range was derived. A long focus lens coupled with a bellow to put the system away from the flames was adopted. The algorithm implemented for the measurements and the machine temperature control is presented.

Thermomechanical design and optimization and acceptance of the Wide-Angle Camera for the Rosetta mission

The WAC is a telescope developed by University of Padova for the OSIRIS experiment, mainly composed by two instruments, Narrow Angle Camera and Wide Angle Camera, and the related electronics. The payload will fly on board of the Rosetta ESA scientific mission, that will be flown to encounter Comet Wirtanen after about 10 years of flight in 2013. WAC main scientific objectives are to follow structure evolution in the coma and monitor their dynamics. To fulfill scientific requirements, the optical characteristics of the WAC telescope may be summarized as follows: wide field of view of 12° X 12°, focal length of 140 mm, operate in the wave-length range 240-1000nm after 10 years in space, Encircled Energy greater than 70% over the entire FoV, contrast ratio of 10-4 to detect coma activities against a bright nucleus, minimum exposure time of 10 msec with a repeatability better than 1/500, scattered light rejection for sources inside and outside FoV. This paper deals with the design optimization of critical parts and acceptance test campaign performed to validate the thermo-structural behavior of the WAC. The functional and performance tests carried out at experiment and system level demonstrated the overall capability of the telescope to satisfy the system and scientific requirements.

Thermomechanical design optimization and acceptance of the Wide-Angle Camera for the Rosetta mission

The WAC is a telescope developed by University of Padova for the OSIRIS experiment, mainly composed by two instruments, Narrow Angle Camera and Wide Angle Camera, and the related electronics. The payload will fly on board of the Rosetta ESA scientific mission, that will be flown to encounter Comet Wirtanen after about 10 years of flight in 2013. WAC main scientific objectives are to follow structure evolution in the coma and monitor their dynamics. To fulfill scientific requirements, the optical characteristics of the WAC telescope may be summarized as follows: wide field of view of 12° X 12°, focal length of 140 mm, operate in the wave-length range 240-1000nm after 10 years in space, Encircled Energy greater than 70% over the entire FoV, contrast ratio of 10-4 to detect coma activities against a bright nucleus, minimum exposure time of 10 msec with a repeatability better than 1/500, scattered light rejection for sources inside and outside FoV. This paper deals with the design optimization of critical parts and acceptance test campaign performed to validate the thermo-structural behavior of the WAC. The functional and performance tests carried out at experiment and system level demonstrated the overall capability of the telescope to satisfy the system and scientific requirements.

Laser vision system to measure and track the attitude of a tether‐stabilized satellite system in a laboratory simulator

A bidimensional laboratory simulator to measure and control the attitude of a tether-stabilized platform for orbiting telescopes is presented and discussed. Yaw and libration angles are measured by plane tracking of the image of a laser spot, reflected on a screen by a mirror fixed to a floating platform. A multiple-reflection optical lever enables amplification of platform motion. The libration and yaw angles are related to the coordinates of the spot projected on the screen. Disturbances due to overall tether dynamics and telescope slewing are both reproduced and accounted for. Attitude control is achieved by moving the attachment point of the tether on the platform. Displacements are computed and commands are sent to a dc servo-motor via a PC. This measurement system allows platform libration ? and yaw ? angles to be measured to an accuracy of 0.06×10-3 rad; an accuracy of 0.4×10-3 rad in 10 s is reached in attitude control.

Accuracy improvement in the attitude control of an experimental system on tether-stabilized platform

This paper deals with some improvements on the accuracy of the laboratory model, presented in a previous work, for the simulation of the attitude control and pointing of an optical instrument connected to the Space Station, or other space facility, via a tether (2 to 10 Km long), mounted on a platform. The bidimensional model of this system was realized using a small platform equipped with a DC servo-motor and a screw bearing, floating with a small inclination angle, on an air table, and connected, like a pendulum, through a tether, to a second servo-motor on the wall. In the previous work the attitude control was based on the tracking of two points fixed on the model of the platform with one CCD camera and moving the attachment point on it. The new experimental apparatus, based on two CCD cameras, an optical system of mirrors and a He-Ne laser beam, has been assembled in order to better simulate the control system for a telescope mounted on the platform. The tracking is realized via a computer based vision system which acquires and locks a laser spot projected onto a screen representing the field of view of the telescope. The control loop has been optimized taking into account the disturbances produced by the simulation of the effect of the tether dynamics by means of a second motor which moves the wall tether end with a proper law, and reproducing the slewing manoeuvre effect of the telescope, on the dynamics of the system.

Multiple degree-of-freedom tracking for attitude control of an experimental system on tether-stabilized platform

A study has been conducted about attitude control and pointing of an optical instrument (a Schmidt-type telescope) connected to the space station via a tether 2 to 10 km long, mounted on a platform. The tether plays a multifunctional role, including elastic suspension and data and power transmission. It will insulate the platform from dynamic noise, light, and other pollution from the space station. Furthermore, stabilization and active attitude control will be achieved by moving the attachment point of the tether with respect to the platform itself. A bi- dimensional model of this system has been realized and tested in the laboratory. The measurement and control concept that works on the basis of a computer vision system is discussed. The system is used to stabilize a platform floating on an air table attached to a fixed point through a tether, via a closed loop position control circuit. This is achieved through a CCD camera (768 X 512 pixels), an image processing software, and a dc motor with encoder which controls the attitude of the platform moving its attachment point. The tracking function is realized via a multiple windows technique using an algorithm based on the linearized equations of motion of the platform. The performance of the overall system is presented. An analysis of system characteristics with respect to a real application is carried out. In particular, the possibility of achieving stabilization and active attitude control of such a system by moving the attach point of the tether has been investigated.