March 1999

GERB CalibrationImage of the upper portion of the Warm Blackbody (WBB) showing the rectangular shroud aperture with the warmer WBB flange behind. The WBB flange becomes warmer towards the centre and the WBB aperture itself is within the white spot centred in the shroud aperture. The dark patches on the flange are bolt holes. The vertical stripes are bad pixels on this detector, the darker right half of the image is caused by missing data from every other pixel due to a missing ASIC in the front end electronics.

On January 20th the GERB instrument was brought to ICSTM for calibration in the Earth Observation Characterisation Facility (EOCF). For five days Steve Kellock, Ray Wrigley, Justin Ashmall, Neil Foster worked shifts to keep the instrument running 24 hours per day. The calibration facility contains a visible source and cold and warm blackbodies, these are used to characterise the performance of the instrument. GERB is a broadband imaging instrument, a series of measurements were taken which will give, for the first time, its prime performance parameters and yielded some impressive images of each of the sources, examples of which are shown on the right and described below.

This was the second of three calibration sessions planned for the instrument – the first was in December last year. These first two sessions are mainly to exercise andrefine procedures and equipment. The instrument at this stage is flight-like but does not contain flight versions of all of its component parts. After the calibration session it was returned to RAL, who do the assembly of the instrument, and from there went on to the European Space Research and Technology Centre ESTEC for EMC testing. After return to RAL for final assembly with all flight parts it will be delivered once again to Imperial College, on March 8th, for the full flight model calibration.

Images Obtained with GERB at IC, 20th - 25th Jan 1999

Image of the Cold Blackbody (CBB) showing the rectangular aperture in the -28 degC shroud, patches of the warmer chamber wall (approx 18 degC) showing in the corners of the aperture, and the CBB at 77K as the dark spot in the centre of the aperture. All images are rotated by 90° so that the vacuum chamber vertical axis is across the page. They are obtained by scanning the instrument 18° vertical field of view horizontally across each source in 1° steps. The horizontal axis in each image contains the 256 pixels of the linear detector array, the vertical axis of the image is time so that each new line contains a new output from the detector as the instrument is being rotated in front of the source The dark vertical bands are caused by detector pixels that are not functioning correctly in this non-flight detector. The darker right hand side of each image is caused by the fact the on this side of the detector only every other pixel is connected – again this is a non-flight configuration.

1. Image of the Visible Calibration Source (VISCS), showing the rectangular shroud aperture (in grey) and structure on the flange surrounding the VISCS optical window.Image of the upper portion of the Warm Blackbody (WBB) showing the rectangular shroud aperture with the warmer WBB flange behind. The WBB flange becomes warmer towards the centre and the WBB aperture itself is within the white spot centred in the shroud aperture. The dark patches on the flange are bolt holes. The vertical stripes are bad pixels on this detector, the darker right half of the image is caused by missing data from every other pixel due to a missing ASIC in the front end electronics.

  1. Image of the Cold Blackbody (CBB) showing the rectangular aperture in the -28 degC shroud, patches of the warmer chamber wall (approx 18 degC) showing in the corners of the aperture, and the CBB at 77K as the dark spot in the centre of the aperture.

  2. Image of the Visible Calibration Source (VISCS), showing the rectangular shroud aperture (in grey) and structure on the flange surrounding the VISCS optical window.

Steve Kellock 1st March 1999

Rosetta Plasma Interface Unit: Progress Meeting held in ESTEC

Rosetta Plasma Interface Unit: Progress Meeting held in ESTEC At a Progress Meeting held at the end of February in the European Space Technology Centre (ESTEC) in Noordwijk, the Netherlands, the Imperial College Rosetta team was represented by Chris Gee-Yin Lee to present our progress in the design of the Plasma Interface Unit (PIU), the heart of a five-sensor group of instruments designed to measure the plasma environment of a comet. This meeting was an important milestone, intended to take stock of the status of the complex set of instruments which make up the Rosetta Plasma Consortium. The Imperial College team (Chris Carr, Chris Lee, Trevor Beek and Andre Balogh) is responsible for the provision of the central Data Processor Unit, the Spacecraft Interface, the Digital Links to the five sensors, and the Power Supply and Management Units of the whole Plasma Consortium Package. Chris Carr, PIU Technical Manager said that the schedule to develop the instrument is a real challenge, with the Structural Thermal Model of the instrument to be delivered this summer, and with the electrical integration of the whole instrument scheduled shortly afterwards.

Good progress is nevertheless being made on all fronts. This includes the electronics box design and manufacture in the Physics Department's Mechanical Workshop. A cutaway computer diagram of the box is shown in the illustration.

About Rosetta: A rendezvous with Comet Wirtanen is the destination of ESA's Rosetta mission. Comets are believed to be the most primitive objects in the Solar System, and are particularly interesting to scientists because they hold many clues about our Sun and its planets. Rosetta will study the fabric of the comet and land a small probe (Rosetta Lander) on its surface. The data expected from Rosetta will provide a vital insight into the origins of the Solar System itself.

Andre Balogh 3rd march 1999