TAUVEX

The Tel Aviv University Ultraviolet Explorer, or TAUVEX, is a space telescope array designed and constructed in Israel by El-Op [http://www.el-op.co.il/] , Electro-Optical Industries, Ltd. (a division of Elbit systems), for the exploration of the ultraviolet (UV) sky. TAUVEX was selected in 1988 by the Israel Space Agency (ISA) as its first priority scientific payload. Although originally slated to fly on a national Israeli satellite of the Ofeq series, TAUVEX was shifted to fly as part of the Spectrum Roentgen-Gamma (SRG) international observatory, a collaboration of a large number of countries with the Soviet Union (Space Research Institute) leading.

Due to repeated delays of the SRG project, caused by the economic situation in the post-Soviet Russia, ISA decided to shift TAUVEX to a different satellite. In early-2004 ISA signed an agreement with the Indian Space Research Organization (ISRO) to launch TAUVEX on board the Indian technology demonstrator satellite GSAT-4. TAUVEX is a scientific collaboration between Tel Aviv University and the Indian Institute of Astrophysics in Bangalore. Its Principal Investigators are [http://wise-obs.tau.ac.il/institute.html#noah Noah Brosch] at Tel Aviv University and [http://www.iiap.res.in/personnel/murthy/index.htm Jayant Murthy] at the Indian Institute of Astrophysics. TAUVEX is scheduled to be launched in 2008. [cite news | url=http://www.hindu.com/2007/11/16/stories/2007111654451300.htm | title=Space launches and the cost factor | publisher=The Hindu | first=T.S. | last=Subramanian | date=16 November 2007 | accessdate=2008-02-25]

Instrumentation

TAUVEX consists of three bore-sighted 20cm diameter telescopes on a single bezel called A, B, and C. Each telescope images the same sky area of 0.9 degree, with an angular resolution of 7-11 arcseconds. The imaging is onto position-sensitive detectors (CsTe cathodes on calcium fluoride windows) equipped with multi-channel plate electron intensifiers. The detectors oversample the point-spread-function by a factor of approximately three. The output is detected by position-sensitive anodes (wedge-and-strip) and is digitized to 12 bits. The full image of each telescope has about 300 resolution elements across its diameter.

The type of cathode (CsTe) assures sensitivity from longward of Lyman α to the atmospheric limit with a peak quantum efficiency of approximately 10%. The operating spectral range is separated in a number of segments selectable with filters. Each telescope [T] is equipped with a four-position filter wheel. Each wheel contains one blocked position (shutter) and three band-selection filters [Fn] . The filter complement, and its distribution among the three telescopes, is as follows:

The approximate characteristics of each filter type are summarized below:

TAUVEX is mounted to the spacecraft on a plate that can rotate around its axis (the MDP), enabling to point the telescopes' line-of-sight to any desired declination. Being on a geostationary satellite, the observation is therefore of a scanning type. A 'ribbon' of a constant declination, 0.9 degree wide, is scanned as time advances, completing an entire 360 degree circuit during one sidereal day. The dwell time of a source within the detector field of view is a function of the pointing declination and of the exact location in the FOV relative to the detector diameter. The closer a source is to one of the celestial poles, the longer it will reside in the TAUVEX field of view during a single scan. The longest theoretically-possible exposure is for sources at |δ|>89°30'; these will be observed all day.

Each photon event hitting the detectors is transmitted to the ground in real time and processed in a near-real-time pipeline. In-between the photon events a time tag is added every 128 ms. The time between the adjacent time tags is sufficiently short so that the orbital motion of the nadir-pointing platform is much smaller than the TAUVEX virtual pixel.

Given that TAUVEX operates from a geo-synchronous platform that is, essentially, a telecommunications satellite, it is clear that up and downlink telemetry are much less problematic that with other astronomical satellites. In fact, TAUVEX enjoys a dedicated 1 Mbit/s downlink to the ISRO control station near Bangalore. Command sequences will be uplinked after being generated by IIA and ISRO and the downlink will be analyzed on-line to monitor the payload state of health.

In most situations, TAUVEX will be able to download all the detected photon events. However, in case of strong straylight or of many bright sources in the field of view, the collected event rate may overload the capacity of the telemetry link. In this case, TAUVEX stores the photon events in a solid state memory module (4 GB), from which the events are transmitted at the nominal 1 Mbit/s rate.

cience with TAUVEX

The science of TAUVEX is based on its unique characteristics: three bore-sighted and independent telescopes able to operate independently, with different filters but measuring the same sources, and reasonably fine time resolution as every detected photon is time-tagged. A unique possibility allows the study of the interstellar dust band at 217.4 nm; the two TAUVEX filters SF2 and NBF3 are centered on this wavelength but have different widths. As the filters are located on different telescopes, it is possible to measure the same sky region with both filters simultaneously, deriving the equivalent width of the band for every star in the field of view [http://www.ncra.tifr.res.in/~basi/07June/352332007.PDF] . The use of TAUVEX as a scientific instrument is the result of calibration on the ground [http://www.ncra.tifr.res.in/~basi/07June/351872007.PDF] .

References

External links

Official

* [http://tauvex.iiap.res.in/ TAUVEX Project webpage (India)]
* [http://tauvex.tau.ac.il/TAUVEX1.html History]
* [http://www.isro.org/pressrelease/Dec25_2003.htm ISRO Press release on MoU]
* [http://www.ncra.tifr.res.in/~basi/toc07june.htm Proceedings of the TAUVEX Science Meeting 2006]