The Tel Aviv University Ultraviolet Explorer, or TAUVEX (), is a space telescope array conceived by

Noah Brosch Noah Brosch (Hebrew: נח ברוש; born 1948) is an Israeli astronomer, astrophysicist and space researcher. Biography Noah Brosch was born in Bucharest (Romania) in 1948 and immigrated with his family to Israel in 1963. Brosch studied at T ...

Tel Aviv University Tel Aviv University (TAU) is a Public university, public research university in Tel Aviv, Israel. With over 30,000 students, it is the largest university in the country. Located in northwest Tel Aviv, the university is the center of teaching and ...

and designed and constructed in

Israel Israel, officially the State of Israel, is a country in West Asia. It Borders of Israel, shares borders with Lebanon to the north, Syria to the north-east, Jordan to the east, Egypt to the south-west, and the Mediterranean Sea to the west. Isr ...

for

by El-Op, Electro-Optical Industries, Ltd. (a division of Elbit systems) acting as Prime Contractor, for the exploration of the

ultraviolet Ultraviolet radiation, also known as simply UV, is electromagnetic radiation of wavelengths of 10–400 nanometers, shorter than that of visible light, but longer than X-rays. UV radiation is present in sunlight and constitutes about 10% of ...

(UV) sky. TAUVEX was selected in 1988 by the

Israel Space Agency The Israel Space Agency (ISA; , ''Sokhnut heKhalal haYisraelit'') is a governmental body, a part of Israel's Ministry of Science and Technology, that coordinates all Israeli space research programs with scientific and commercial goals. The ag ...

(ISA) as its first priority scientific payload. Although originally slated to fly on a national Israeli satellite of the

Ofeq Ofeq, also spelled Offek or Ofek (, ''lit.'' Horizon) is the designation of a series of Israeli reconnaissance satellites first launched in 1988. Most Ofeq satellites have been carried on top of Shavit launch vehicles from Palmachim Airbase i ...

series, TAUVEX was shifted in 1991 to fly as part of a

Spektr-RG Spektr-RG ( Russian: Спектр-РГ, ''Spectrum'' + '' Röntgen'' + ''Gamma''; also called Spectrum-X-Gamma, SRG, SXG) is a Russian–German high-energy astrophysics space observatory which was launched on 13 July 2019. It follows on from t ...

international observatory, a collaboration of many countries with the

Soviet Union The Union of Soviet Socialist Republics. (USSR), commonly known as the Soviet Union, was a List of former transcontinental countries#Since 1700, transcontinental country that spanned much of Eurasia from 1922 until Dissolution of the Soviet ...

(

Space Research Institute The Russian Space Research Institute (; SRI RAS, Russian abbreviation: ИКИ РАН, IKI RAN) is the leading organization of the Russian Academy of Sciences on space exploration to benefit fundamental science. It was formerly known as the Space ...

) 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 Organisation The Indian Space Research Organisation (ISRO ) is India's national List of government space agencies, space agency, headquartered in Bengaluru, Karnataka. It serves as the principal research and development arm of the Department of Space (DoS), ...

(ISRO) to launch TAUVEX on board the

India India, officially the Republic of India, is a country in South Asia. It is the List of countries and dependencies by area, seventh-largest country by area; the List of countries by population (United Nations), most populous country since ...

n technology demonstrator satellite

GSAT-4 GSAT-4, also known as HealthSat, was an experimental communication satellite, communication and navigation satellite, navigation satellite launched in April 2010 by the Indian Space Research Organisation on the maiden flight of the Geosynchronous ...

. The

launch vehicle A launch vehicle is typically a rocket-powered vehicle designed to carry a payload (a crewed spacecraft or satellites) from Earth's surface or lower atmosphere to outer space. The most common form is the ballistic missile-shaped multistage ...

slated to be used was the

GSLV Geosynchronous Satellite Launch Vehicle (GSLV) is a class of expendable launch systems operated by the Indian Space Research Organisation (ISRO). GSLV has been used in fifteen launches since 2001. History The Geosynchronous Satellite Launch ...

with a new, cryogenic, upper stage. TAUVEX was a scientific collaboration between

and the

Indian Institute of Astrophysics The Indian Institute of Astrophysics (IIA), with its headquarters in Bengaluru, is an autonomous research institute wholly funded by the Department of Science and Technology, Government of India. IIA conducts research primarily in the areas of ...

Bangalore Bengaluru, also known as Bangalore (List of renamed places in India#Karnataka, its official name until 1 November 2014), is the Capital city, capital and largest city of the southern States and union territories of India, Indian state of Kar ...

. 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

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

was deemed under-powered to bring

to a geosynchronous orbit.

was subsequently lost in the 15 April 2010 launch failure of

. On 13 March 2011 TAUVEX was returned to Israel and was stored at the Prime Contractor facility pending an ISA decision about its future. In 2012 ISA decided to terminate the TAUVEX project, against the recommendation of a committee it formed to consider its future that recommended its release for a high-altitude balloon flight.

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 resolution Angular resolution describes the ability of any image-forming device such as an Optical telescope, optical or radio telescope, a microscope, a camera, or an Human eye, eye, to distinguish small details of an object, thereby making it a major det ...

of 7-11

arcseconds A minute of arc, arcminute (abbreviated as arcmin), arc minute, or minute arc, denoted by the symbol , is a unit of angular measurement equal to of a degree. Since one degree is of a turn, or complete rotation, one arcminute is of a tu ...

. The imaging is onto position-sensitive detectors (CsTe cathodes on

calcium fluoride Calcium fluoride is the inorganic compound of the elements calcium and fluorine with the formula CaF2. It is a white solid that is practically insoluble in water. It occurs as the mineral fluorite (also called fluorspar), which is often deeply col ...

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 An anode usually is an electrode of a polarized electrical device through which conventional current enters the device. This contrasts with a cathode, which is usually an electrode of the device through which conventional current leaves the devi ...

(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 A cathode is the electrode from which a conventional current leaves a polarized electrical device such as a lead-acid battery. This definition can be recalled by using the mnemonic ''CCD'' for ''Cathode Current Departs''. Conventional curren ...

(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 is equipped with a four-position filter wheel. Each wheel contains one blocked position (shutter) and three band-selection filters n 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 A geostationary orbit, also referred to as a geosynchronous equatorial orbit''Geostationary orbit'' and ''Geosynchronous (equatorial) orbit'' are used somewhat interchangeably in sources. (GEO), is a circular geosynchronous orbit in altitud ...

, 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 Sidereal time ("sidereal" pronounced ) is a system of timekeeping used especially by astronomers. Using sidereal time and the celestial coordinate system, it is easy to locate the positions of celestial objects in the night sky. Sidereal t ...

. 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 Hassan, Hasan, Hassane, Haasana, Hassaan, Asan, Hassun, Hasun, Hassen, Hasson or Hasani may refer to: People *Hassan (given name), Arabic given name and a list of people with that given name *Hassan (surname), Arabic, Jewish, Irish, and Scotti ...

, near

. 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.

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 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 The equivalent width of a spectral line is a measure of the area of the line on a plot of intensity versus wavelength in relation to underlying continuum level. It is found by forming a rectangle with a height equal to that of continuum emission, ...

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 resultsAlmoznino, E., Brosch, N., Finkelman, I., Netzer, H., Yacoby, E.~R., Topaz, J., Saar, N. 2009. Ground-based calibration of the TAUVEX flight model. Astrophysics and Space Science 320, 321-341. 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.

References

External links

TAUVEX Project webpage (India)

{{DEFAULTSORT:Tauvex Space telescopes Ultraviolet telescopes Space program of Israel

Instrumentation

Science with TAUVEX

See also

References

External links