XTE

X-ray Timing Explorer, Also called RXTE (Bruno B. Rossi X-ray Timing Explorer)

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General

Designation	23757 / 95074A
Launch date	30 Dec 1995 13:48 UT
Country of origin	United States
Mission	Scientific: X-ray astronomy
Perigee/Apogee	565/583 km
Inclination	23°
Period	96.1 min
Launch vehicle	Delta 2 #230

Cost: $195 million, Launched under the MELVS contract

Delta's new avionics system will use an array of redundant laser gyros and accelerometers to sense the vehicle's velocity and attitude movement, which includes its angular position and direction. The avionics system feeds data to onboard computers which control Delta 2's engines and power, engine start, main engine cutoff, staging and payload separation. The avionics system now has two power sources and is completely redundant. If one data system is lost, the other will complete the mission.

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External resources

http://heasarc.gsfc.nasa.gov/docs/xte/

sat-index articles

Technical data

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Specifications

Built under coordination of NASA-Goddard Space Flight Center. It includes two high gain antennae, allowing an almost continuous telemetry stream using TDRS's Multiple Access mode.

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Proportional Counter Array (PCE)

Instrument with large collecting area but low spatial resolution, for accurate timing and spectral measurements of bright X-ray sources. Built by the LHEA at GSFC

The PCA is an array of five proportional counters with a total collecting area of 6500 square cm. The instrumental properties are:

Energy range	2 - 60 keV
Energy resolution	&< 18% at 6 keV
Time resolution	1 microsec
Spatial resolution	collimator with 1 degree FWHM
Detectors	5 proportional counters
Collecting area	6500 square cm
Layers	1 Propane veto; 3 Xenon, each split into two; 1 Xenon veto layer
Sensitivity	0.1 mCrab
Background	2 mCrab

Events detected by the PCA will be processed on board by the EDS before insertion into the telemetry stream.

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High Energy X-ray Timing Experiment (HEXTE)

Intrument built by CASS at UCSD which will study X-rays. HEXTE consists of two clusters each containing four phoswich scintillation counters. The clusters can rock at right angles to each other, with amplitudes of 1.5 or 3 degrees, to provide accurate background measurements. The total collecting area is 1600 square cm. The instrumental properties are:

Energy range	20 - 250 keV
Energy resolution	&< 18% at 60 keV
Time resolution	10 microsec
Spatial resolution	collimator with 1 degree FWHM
Detectors	2 times 4 scintillation counters
Collecting area	1600 square cm
Phoswich	NaI / CsI
Sensitivity	10 mCrab
Background	100 mCrab

Events detected by HEXTE will be processed on board by its own data system before insertion into the telemetry stream. It will allow event mode, histogram binned mode, multiscalar mode, PHA/PSA spectral mode, and burst mode formats.

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All-Sky Monitor (ASM)

ASM, built by the CSR at MIT, will spot X-ray flare stars and burst sources. It consists of three wide-angle shadow cameras equipped with proportional counters with a total collecting area of 90 square cm. The instrumental properties are:

Energy range	2 - 10 keV
Time resolution	80% of the sky every 90 minutes
Spatial resolution	3' x 15'
Number of shadow cameras	3, each with 6 x 90 degrees FOV
Collecting area	90 square cm
Detector	Xenon proportional counter, position-sensitive
Sensitivity	30 mCrab

Events detected by the ASM will be processed on board by the EDS before insertion into the telemetry stream.

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Experiment Data System (EDS)

The EDS consists of eight Event Analyzers (EA), of which two are dedicated to the PCA and six to the ASM. Each EA contains an Intel 80286 processor and associated memory. The EAs can be programmed independently to process incoming events from the instruments in any of the following modes:

Transparent mode, using 1, 2, or 3 EAs
Event mode, using 1 or 2 EAs
Binned mode (time and/or energy)
Burst catcher mode
Fourier transform mode
Pulsar fold mode
Autocorrelation mode
Arrival time differences histogram mode

It is being built by the CSR at MIT.

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Downlink frequency

Telemetry: 2287.5 MHz (realtime: 16/32 kbps, playback: upto 1024 kbps)
Command: 2106.4 MHz (1/0.125 kbps)

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