The Rossi X-ray Timing Explorer (RXTE) was a

NASA The National Aeronautics and Space Administration (NASA ) is an independent agencies of the United States government, independent agency of the US federal government responsible for the civil List of government space agencies, space program ...

satellite that observed the time variation of astronomical X-ray sources, named after physicist Bruno Rossi. The RXTE had three instruments — an All Sky Monitor, the High-Energy X-ray Timing Experiment (HEXTE) and the Proportional Counter Array. The RXTE observed X-rays from black holes,

neutron stars A neutron star is the collapsed core of a massive supergiant star, which had a total mass of between 10 and 25 solar masses, possibly more if the star was especially metal-rich. Except for black holes and some hypothetical objects (e.g. white ...

, X-ray pulsars and

X-ray bursts X-ray bursters are one class of X-ray binary stars exhibiting X-ray bursts, periodic and rapid increases in luminosity (typically a factor of 10 or greater) that peak in the X-ray region of the electromagnetic spectrum. These astrophysical sys ...

. It was funded as part of the

Explorer program The Explorers program is a NASA exploration program that provides flight opportunities for physics, geophysics, heliophysics, and astrophysics investigations from space. Launched in 1958, Explorer 1 was the first spacecraft of the United Stat ...

, and was also called Explorer 69. RXTE had a mass of and was launched from Cape Canaveral on 30 December 1995, at 13:48:00 UTC, on a

Delta II Delta II was an expendable launch system, originally designed and built by McDonnell Douglas. Delta II was part of the Delta rocket family and entered service in 1989. Delta II vehicles included the Delta 6000, and the two later Delta 7000 ...

launch vehicle A launch vehicle or carrier rocket is a rocket designed to carry a payload ( spacecraft or satellites) from the Earth's surface to outer space. Most launch vehicles operate from a launch pads, supported by a launch control center and ...

. Its

International Designator The International Designator, also known as COSPAR ID, is an international identifier assigned to artificial objects in space. It consists of the launch year, a three-digit incrementing launch number of that year and up to a three-letter code repr ...

is 1995-074A.

Mission

The X-Ray Timing Explorer (XTE) mission has the primary objective to study the temporal and broad-band spectral phenomena associated with stellar and galactic systems containing compact objects in the energy range 2--200 KeV, and in time scales from microseconds to years. The scientific instruments consists of two pointed instruments, the Proportional Counter Array (PCA) and the High-Energy X-ray Timing Experiment (HEXTE), and the All Sky Monitor (ASM), which scans over 70% of the sky each orbit. All of the XTE observing time were available to the international scientific community through a peer review of submitted proposals. XTE used a new spacecraft design that allows flexible operations through rapid pointing, high data rates, and nearly continuous receipt of data at the Science Operations Center (SOC) at Goddard Space Flight Center via a Multiple Access link to the

Tracking and Data Relay Satellite System The U.S. Tracking and Data Relay Satellite System (TDRSS) is a network of American communications satellites (each called a tracking and data relay satellite, TDRS) and ground stations used by NASA for space communications. The system was desig ...

(TDRSS). XTE was highly maneuverable with a slew rate of greater than 6° per minute. The PCA/HEXTE could be pointed anywhere in the sky to an accuracy of less than 0.1°, with an aspect knowledge of around 1

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

. Rotatable solar panels enable anti-sunward pointing to coordinate with ground-based night-time observations. Two pointable high gain antennas maintain nearly continuous communication with the TDRSS. This, together with 1 GB (approximately four orbits) of on-board solid-state data storage, give added flexibility in scheduling observations.

Telecommunications

* Required continuous TDRSS Multiple Access (MA) return link coverage except for zone of exclusion: Real time and playback of engineering/housekeeping data at 16 or 32 kbs - Playback of science data at 48 or 64 kbs. * Requires 20 minutes of SSA contacts with alternating TDRSS per orbit: Real time and playback of engineering/housekeeping data at 32 kbs - Playback of science data at 512 or 1024 kbs. * For launch and contingency, required TDRSS MA/SSA real time engineering and housekeeping at 1 kbs. * The bit error rate shall be less than 1 in 10E8 for at least 95% of the orbits.

Instruments

All-Sky Monitor (ASM)

The All-Sky Monitor (ASM) provided all-sky X-ray coverage, to a sensitivity of a few percent of the Crab Nebula intensity in one day, in order to provide both flare alarms and long-term intensity records of celestial X-ray sources. The ASM consisted of three wide-angle shadow cameras equipped with proportional counters with a total collecting area of . The instrumental properties were: * Energy range: 2–12-keV * Time resolution: observes 80% of the sky every 90 minutes * Spatial resolution: 3' × 15' * Number of shadow cameras: 3, each with 6° × 90° FoV * Collecting area: * Detector:

Xenon Xenon is a chemical element with the symbol Xe and atomic number 54. It is a dense, colorless, odorless noble gas found in Earth's atmosphere in trace amounts. Although generally unreactive, it can undergo a few chemical reactions such as the ...

proportional counter, position-sensitive * Sensitivity: 30 mCrab It was built by the CSR at

Massachusetts Institute of Technology The Massachusetts Institute of Technology (MIT) is a private land-grant research university in Cambridge, Massachusetts. Established in 1861, MIT has played a key role in the development of modern technology and science, and is one of the ...

. The

principal investigator In many countries, the term principal investigator (PI) refers to the holder of an independent grant and the lead researcher for the grant project, usually in the sciences, such as a laboratory study or a clinical trial. The phrase is also often us ...

wa
Dr. Hale Bradt

High Energy X-ray Timing Experiment (HEXTE)

The High-Energy X-ray Timing Experiment (HEXTE) is a scintillator array for the study of temporal and temporal/spectral effects of the hard X-ray (20 to 200 keV) emission from galactic and extragalactic sources. The HEXTE consisted of two clusters each containing four phoswich scintillation detectors. Each cluster could "rock" (beamswitch) along mutually orthogonal directions to provide background measurements 1.5° or 3.0° away from the source every 16 to 128 seconds. In addition, the input was sampled at 8

microsecond A microsecond is a unit of time in the International System of Units (SI) equal to one millionth (0.000001 or 10−6 or ) of a second. Its symbol is μs, sometimes simplified to us when Unicode is not available. A microsecond is equal to 1000 ...

s so as to detect time varying phenomena. Automatic gain control was provided by using an radioactive source mounted in each detector's field of view. The HEXTE's basic properties were: * Energy range: 15–250-keV * Energy resolution: 15% at 60-keV * Time sampling: 8 microseconds * Field of view: 1° FWHM * Detectors: 2 clusters of 4 NaI/CsI scintillation counters * Collecting area: 2 × * Sensitivity: 1-Crab = 360 count/second per HEXTE cluster * Background: 50 count/second per HEXTE cluster The HEXTE was designed and built by th
Center for Astrophysics & Space Sciences (CASS)
at the

University of California, San Diego The University of California, San Diego (UC San Diego or colloquially, UCSD) is a public land-grant research university in San Diego, California. Established in 1960 near the pre-existing Scripps Institution of Oceanography, UC San Diego is t ...

. The HEXTE principal investigator wa
Dr. Richard E. Rothschild

Proportional Counter Array (PCA)

The Proportional Counter Array (PCA) provides approximately of X-ray detector area, in the energy range 2 to 60 keV, for the study of temporal/spectral effects in the X-ray emission from galactic and extragalactic sources. The PCA was an array of five proportional counters with a total collecting area of . The instrumental properties were: * Energy range: 2–60-keV * Energy resolution: <18% at 6-keV * Time resolution: 1-μs * Spatial resolution: collimator with 1°

Full width at half maximum In a distribution, full width at half maximum (FWHM) is the difference between the two values of the independent variable at which the dependent variable is equal to half of its maximum value. In other words, it is the width of a spectrum curve mea ...

(FWHM) * Detectors: 5 proportional counters * Collecting area: * Layers: 1 propane veto; 3

, each split into two; 1 Xenon veto layer * Sensitivity: 0.1-mCrab * Background: 90-mCrab The PCA is being built by the Laboratory for High Energy Astrophysics (LHEA) at Goddard Space Flight Center. The principal investigator was Dr. Jean H. Swank.

Results

Observations from the Rossi X-ray Timing Explorer have been used as evidence for the existence of the

frame-dragging Frame-dragging is an effect on spacetime, predicted by Albert Einstein's general theory of relativity, that is due to non-static stationary distributions of mass–energy. A stationary field is one that is in a steady state, but the masses ca ...

effect predicted by the theory of

general relativity General relativity, also known as the general theory of relativity and Einstein's theory of gravity, is the geometric theory of gravitation published by Albert Einstein in 1915 and is the current description of gravitation in modern physics ...

of Einstein. RXTE results have, as of late 2007, been used in more than 1400 scientific papers. In January 2006, it was announced that Rossi had been used to locate a candidate

intermediate-mass black hole An intermediate-mass black hole (IMBH) is a class of black hole with mass in the range 102–105 solar masses: significantly more than stellar black holes but less than the 105–109 solar mass supermassive black holes. Several IMBH candidate obje ...

named M82 X-1. In February 2006, data from RXTE was used to prove that the diffuse background X-ray glow in our galaxy comes from innumerable, previously undetected

white dwarf A white dwarf is a stellar core remnant composed mostly of electron-degenerate matter. A white dwarf is very dense: its mass is comparable to the Sun's, while its volume is comparable to the Earth's. A white dwarf's faint luminosity comes ...

s and from other stars' coronae. In April 2008, RXTE data was used to infer the size of the smallest known black hole. RXTE ceased science operations on 12 January 2012.

Atmospheric entry

NASA scientists said that the decommissioned RXTE would re-enter the Earth's atmosphere "between 2014 and 2023". Later, it became clear that the satellite would re-enter in late April or early May 2018, and the spacecraft fell out of orbit on 30 April 2018.

References

External links

MIT's Rossi X-Ray Timing Explorer Project

Video documentary

RXTE Reveals the Cloudy Cores of Active Galaxies
{{Space observatories Spacecraft launched in 1995 Spacecraft which reentered in 2018 Explorers Program Space telescopes X-ray telescopes