TAUVEX
Encyclopedia
The Tel Aviv University Ultraviolet Explorer, or TAUVEX, is a space telescope array designed and constructed in Israel
for Tel Aviv University
by El-Op, Electro-Optical Industries, Ltd. (a division of Elbit systems) acting as Prime Contractor, 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 in 1991 to fly as part of a Spektr-RG
international observatory, a collaboration of a large number of countries with the Soviet Union
(Space Research Institute
) leading.
Due to repeated delays of the Spektr 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 India
n technology demonstrator satellite GSAT-4
. The launch vehicle
slated to be used is the GSLV with a new, cryogenic, upper stage. TAUVEX is a scientific collaboration between Tel Aviv University
and the Indian Institute of Astrophysics
in Bangalore
. Its Principal Investigators were Noah Brosch at Tel Aviv University and Jayant Murthy at the Indian Institute of Astrophysics. Originally, TAUVEX was scheduled to be launched in 2008. but various delays caused the integration with GSAT-4
to take place only in November 2009 for a launch the following year. ISRO decided in January 2010 to remove TAUVEX from the satellite since the Indian-built cryogenic upper stage for GSLV was deemed under-powered to bring GSAT-4
to a geosynchronous orbit. GSAT-4
was subsequently lost in the 15 April 2010 launch failure of GSLV. On 13 March 2011 TAUVEX was returned to Israel and was stored at the Prime Contractor facility pending an ISA decision about its future.
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 was mounted to the GSAT-4 spacecraft on a plate that could 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 would therefore have been of a scanning type. A 'ribbon' of a constant declination, 0.9 degree wide, would have been scanned as time advanced, completing an entire 360 degree circuit during one sidereal day. In this mode of operation, 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 resides in the TAUVEX field of view during a single scan. The longest theoretically-possible exposure is for sources at |δ|>89°30'; these could be observed all day.
The interface with GSAT-4 ensured that each photon event hitting the detectors would have been 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 on GSAT-4 was planned to operate 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 was allowed a dedicated 1 Mbit/s downlink to the ISRO Master Control Facility (MCF) at Hassan, near Bangalore
. Command sequences were planned to be uplinked after being generated by IIA and ISRO and the downlink to be analyzed on-line to monitor the payload state of health.
In most situations, TAUVEX would have been 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 could overload the capacity of the telemetry link. In this case, TAUVEX would have stored the photon events in a solid state memory module (4 GB
), from which the events are transmitted at the nominal 1 Mbit/s rate.
; 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. The use of TAUVEX as a scientific instrument is the result of calibration on the ground
.This calibration was very difficult and produced unreliable results possibly indicating a significantly reduced performance. Given the uncertain results, the Principal Investigators planned to repeat and improve the calibration in space, in the months following the launch.
Israel
The State of Israel is a parliamentary republic located in the Middle East, along the eastern shore of the Mediterranean Sea...
for Tel Aviv University
Tel Aviv University
Tel Aviv University is a public university located in Ramat Aviv, Tel Aviv, Israel. With nearly 30,000 students, TAU is Israel's largest university.-History:...
by El-Op, Electro-Optical Industries, Ltd. (a division of Elbit systems) acting as Prime Contractor, for the exploration of the ultraviolet
Ultraviolet
Ultraviolet light is electromagnetic radiation with a wavelength shorter than that of visible light, but longer than X-rays, in the range 10 nm to 400 nm, and energies from 3 eV to 124 eV...
(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
Ofeq
Ofeq, also spelled Offek or Ofek is the designation of a series of Israeli reconnaissance satellites first launched in 1988. All Ofeq satellites have been carried on top of Shavit rockets from Palmachim Airbase in Israel, on the Mediterranean coast. The Low Earth Orbit satellites complete one...
series, TAUVEX was shifted in 1991 to fly as part of a Spektr-RG
Spektr-RG
Spektr-RG is a series of satellites carrying scientific instruments developed in international co-operation led by the Russian Federal Space Agency....
international observatory, a collaboration of a large number of countries with the Soviet Union
Soviet Union
The Soviet Union , officially the Union of Soviet Socialist Republics , was a constitutionally socialist state that existed in Eurasia between 1922 and 1991....
(Space Research Institute
Russian Space Research Institute
The Russian Space Research Institute is the leading organization of the Russian Academy of Sciences on space exploration to benefit fundamental science....
) leading.
Due to repeated delays of the Spektr 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 India
India
India , officially the Republic of India , is a country in South Asia. It is the seventh-largest country by geographical area, the second-most populous country with over 1.2 billion people, and the most populous democracy in the world...
n technology demonstrator satellite GSAT-4
GSAT-4
GSAT-4, also known as HealthSat, was an experimental communication and navigation satellite launched in April 2010 by the Indian Space Research Organisation on the maiden flight of the Geosynchronous Satellite Launch Vehicle Mk.II rocket. It failed to reach orbit after the rocket's third stage...
. The launch vehicle
Launch vehicle
In spaceflight, a launch vehicle or carrier rocket is a rocket used to carry a payload from the Earth's surface into outer space. A launch system includes the launch vehicle, the launch pad and other infrastructure....
slated to be used is the GSLV with a new, cryogenic, upper stage. TAUVEX is a scientific collaboration between Tel Aviv University
Tel Aviv University
Tel Aviv University is a public university located in Ramat Aviv, Tel Aviv, Israel. With nearly 30,000 students, TAU is Israel's largest university.-History:...
and the Indian Institute of Astrophysics
Indian Institute of Astrophysics
The Indian Institute of Astrophysics , with its headquarters in Bangalore , India, is a premier national institute of India for the study of and research into topics pertaining to astronomy, astrophysics and related subjects....
in Bangalore
Bangalore
Bengaluru , formerly called Bengaluru is the capital of the Indian state of Karnataka. Bangalore is nicknamed the Garden City and was once called a pensioner's paradise. Located on the Deccan Plateau in the south-eastern part of Karnataka, Bangalore is India's third most populous city and...
. Its Principal Investigators were Noah Brosch at Tel Aviv University and Jayant Murthy at the Indian Institute of Astrophysics. Originally, TAUVEX was scheduled to be launched in 2008. but various delays caused the integration with GSAT-4
GSAT-4
GSAT-4, also known as HealthSat, was an experimental communication and navigation satellite launched in April 2010 by the Indian Space Research Organisation on the maiden flight of the Geosynchronous Satellite Launch Vehicle Mk.II rocket. It failed to reach orbit after the rocket's third stage...
to take place only in November 2009 for a launch the following year. ISRO decided in January 2010 to remove TAUVEX from the satellite since the Indian-built cryogenic upper stage for GSLV was deemed under-powered to bring GSAT-4
GSAT-4
GSAT-4, also known as HealthSat, was an experimental communication and navigation satellite launched in April 2010 by the Indian Space Research Organisation on the maiden flight of the Geosynchronous Satellite Launch Vehicle Mk.II rocket. It failed to reach orbit after the rocket's third stage...
to a geosynchronous orbit. GSAT-4
GSAT-4
GSAT-4, also known as HealthSat, was an experimental communication and navigation satellite launched in April 2010 by the Indian Space Research Organisation on the maiden flight of the Geosynchronous Satellite Launch Vehicle Mk.II rocket. It failed to reach orbit after the rocket's third stage...
was subsequently lost in the 15 April 2010 launch failure of GSLV. On 13 March 2011 TAUVEX was returned to Israel and was stored at the Prime Contractor facility pending an ISA decision about its future.
Instrumentation
TAUVEX consists of three bore-sighted 20 cm diameter telescopes on a single bezel, called telescopes A, B, and C. Each telescope images the same sky area of 0.9 degree, with an angular resolutionAngular resolution
Angular resolution, or spatial resolution, describes the ability of any image-forming device such as an optical or radio telescope, a microscope, a camera, or an eye, to distinguish small details of an object...
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
Cathode
A cathode is an electrode through which electric current flows out of a polarized electrical device. Mnemonic: CCD .Cathode polarity is not always negative...
(CsTe) assures sensitivity from longward of Lyman
Lyman series
In physics and chemistry, the Lyman series is the series of transitions and resulting ultraviolet emission lines of the hydrogen atom as an electron goes from n ≥ 2 to n = 1...
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:
| T | F1 | F2 | F3 | F4 |
| A | BBF | SF1 | SF2 | Shutter |
| B | Shutter | SF1 | NBF3 | SF3 |
| C | BBF | Shutter | SF2 | SF3 |
The approximate characteristics of each filter type are summarized below:
| Filter | Wavelength | Width | Normalized transmission |
|---|---|---|---|
| BBF | 2300 Å Ångström The angstrom or ångström, is a unit of length equal to 1/10,000,000,000 of a meter . Its symbol is the Swedish letter Å.... (230 nm) |
1000 Å (100 nm) | 80% |
| SF1 | 1750 Å (175 nm) | 400 Å (40 nm) | 20% |
| SF2 | 2200 Å (200 nm) | 400 Å (40 nm) | 45% |
| SF3 | 2600 Å (260 nm) | 500 Å (50 nm) | 40% |
| NBF3 | 2200 Å (220 nm) | 200 Å (20 nm) | 30% |
TAUVEX was mounted to the GSAT-4 spacecraft on a plate that could 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 would therefore have been of a scanning type. A 'ribbon' of a constant declination, 0.9 degree wide, would have been scanned as time advanced, completing an entire 360 degree circuit during one sidereal day. In this mode of operation, 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 resides in the TAUVEX field of view during a single scan. The longest theoretically-possible exposure is for sources at |δ|>89°30'; these could be observed all day.
The interface with GSAT-4 ensured that each photon event hitting the detectors would have been 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 on GSAT-4 was planned to operate 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 was allowed a dedicated 1 Mbit/s downlink to the ISRO Master Control Facility (MCF) at Hassan, near Bangalore
Bangalore
Bengaluru , formerly called Bengaluru is the capital of the Indian state of Karnataka. Bangalore is nicknamed the Garden City and was once called a pensioner's paradise. Located on the Deccan Plateau in the south-eastern part of Karnataka, Bangalore is India's third most populous city and...
. Command sequences were planned to be uplinked after being generated by IIA and ISRO and the downlink to be analyzed on-line to monitor the payload state of health.
In most situations, TAUVEX would have been 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 could overload the capacity of the telemetry link. In this case, TAUVEX would have stored the photon events in a solid state memory module (4 GB
Gigabyte
The gigabyte is a multiple of the unit byte for digital information storage. The prefix giga means 109 in the International System of Units , therefore 1 gigabyte is...
), from which the events are transmitted at the nominal 1 Mbit/s rate.
Science 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 nmNanometre
A nanometre is a unit of length in the metric system, equal to one billionth of a metre. The name combines the SI prefix nano- with the parent unit name metre .The nanometre is often used to express dimensions on the atomic scale: the diameter...
; 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
Equivalent width
The equivalent width of a spectral line is a measure of the area of the line on a plot of intensity versus wavelength. It is found by forming a rectangle with a height equal to that of continuum emission, and finding the width such that the area of the rectangle is equal to the area in the spectral...
of the band for every star in the field of view. The use of TAUVEX as a scientific instrument is the result of calibration on the ground
.This calibration was very difficult and produced unreliable results possibly indicating a significantly reduced performance. Given the uncertain results, the Principal Investigators planned to repeat and improve the calibration in space, in the months following the launch.