View source for Rossi X-ray Timing Explorer

{{Short description|NASA satellite of the Explorer program}}
{{Use American English|date=November 2021}}
{{Use dmy dates|date=November 2021}}
{{Infobox spaceflight
| name              = Rossi X-ray Timing Explorer
| names_list        = Explorer 69<br/>RXTE<br/>XTE
| image             = Rxte.jpg
| image_caption     = Rossi X-ray Timing Explorer satellite
| image_alt         = RXTE 3D Model
| image_size        = 300px

| mission_type      = [[Space observatory|Astronomy]]
| operator          = [[NASA]]
| COSPAR_ID         = 1995-074A
| SATCAT            = 23757
| website           = [http://heasarc.gsfc.nasa.gov/docs/xte/xte_1st.html RXTE home page]
| mission_duration  = 16 years (achieved)

| spacecraft        = Explorer LXVIX
| spacecraft_type   = Rossi X-ray Timing Explorer
| spacecraft_bus    = X-ray Timing Explorer
| manufacturer      = [[Goddard Space Flight Center]]
| launch_mass       = {{cvt|3200|kg}}
| dimensions        = 
| power             = 800 [[watt]]s

| launch_date       = 30 December 1995, 13:48:00 [[Coordinated Universal Time|UTC]]
| launch_rocket     = [[Delta II|Delta II 7920-10]] (Delta 230)
| launch_site       = [[Cape Canaveral Space Force Station|Cape Canaveral]], [[Cape Canaveral Space Launch Complex 17|SLC-17A]]
| launch_contractor = [[McDonnell Douglas|McDonnell Douglas Astronautics Company]]

| entered_service   = 30 December 1995
| last_contact      = 
| deactivated       = 12 January 2012
| decay_date        = 30 April 2018 <ref>{{cite web |title=NASA's Rossi X-ray Timing Explorer Leaves Scientific "Treasure Trove" |date=May 2018 |url=https://www.nasa.gov/feature/goddard/2018/nasas-rossi-x-ray-timing-explorer-leaves-scientific-treasure-trove |publisher=NASA |access-date=3 May 2018}} {{PD-notice}}</ref>

| orbit_reference   = [[Geocentric orbit]]<ref name="Trajectory">{{cite web |url=https://nssdc.gsfc.nasa.gov/nmc/spacecraft/displayTrajectory.action?id=1995-074A |title=Trajectory: X-Ray Timing Explorer (1995-074A) Explorer 69 |publisher=NASA |date=28 October 2021 |access-date=28 November 2021}} {{PD-notice}}</ref>
| orbit_regime      = [[Low Earth orbit]]
| orbit_periapsis   = {{cvt|409|km}}
| orbit_apoapsis    = {{cvt|409|km}}
| orbit_inclination = 28.50°
| orbit_period      = 92.60 minutes
| apsis             = gee

| instruments       = {{aligned table|fullwidth=y|style=text-align: left; font-size: 100%;
   |'''ASM'''  | All Sky Monitor (ASM)
   |'''HEXTE'''| High-Energy X-ray Timing Experiment (HEXTE)
   |'''PCA'''  | Proportional Counter Array (PCA)
  }}

| programme         = [[Explorer program]]
| previous_mission  = [[Solar Anomalous and Magnetospheric Particle Explorer]] (Explorer 68)
| next_mission      = [[Fast Auroral SnapshoT Explorer]] (Explorer 70)
}}

The '''Rossi X-ray Timing Explorer''' ('''RXTE''') was a [[NASA]] 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]], [[X-ray pulsars]] and [[X-ray bursts]]. It was funded as part of the [[Explorer program]] and was also called '''Explorer 69'''.

RXTE had a mass of {{cvt|3200|kg}} and was launched from [[Cape Canaveral Space Force Station|Cape Canaveral]] on 30 December 1995, at 13:48:00 [[Coordinated Universal Time|UTC]], on a [[Delta II]] [[launch vehicle]]. Its [[International Designator]] is 1995-074A.<ref name="Display">{{cite web |url=https://nssdc.gsfc.nasa.gov/nmc/spacecraft/display.action?id=1995-074A |title=Display: X-Ray Timing Explorer (1995-074A) Explorer 69 |publisher=NASA |date=28 October 2021 |access-date=28 November 2021}} {{PD-notice}}</ref>

== 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]] (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 [[Minute and second of arc|arcminute]]. 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 [[Gigabit|GB]] (approximately four orbits) of on-board solid-state data storage, give added flexibility in scheduling observations.<ref name="Display"/>

== 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.<ref name="Telecommunications">{{cite web |url=https://nssdc.gsfc.nasa.gov/nmc/spacecraft/displayTelemetry.action?id=1995-074A |title=Telecommunications Description |publisher=NASA |date=28 October 2021 |access-date=28 November 2021}} {{PD-notice}}</ref>
* 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 ==
[[File:XTE launch.gif|thumb|upright=1.0|right|XTE launch]]
[[File:RXTE preparations.jpg|thumb|upright=1.0|right|RXTE preparations in 1995]]

=== 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.<ref name="Experiment1">{{cite web |url=https://nssdc.gsfc.nasa.gov/nmc/experiment/display.action?id=1995-074A-01 |title=Experiment: All-Sky Monitor (ASM) |publisher=NASA |date=28 October 2021 |access-date=28 November 2021}} {{PD-notice}}</ref> The ASM consisted of three wide-angle shadow cameras equipped with proportional counters with a total collecting area of {{cvt|90|cm2}}. The instrumental properties were:<ref>{{cite web |url=http://heasarc.gsfc.nasa.gov/docs/xte/ASM.html |title=All-Sky Monitor (ASM) |publisher=Heasarc.gsfc.nasa.gov |date=2002-02-04 |access-date=2012-02-03}} {{PD-notice}}</ref><ref name="ASM">{{cite web |url=https://heasarc.gsfc.nasa.gov/docs/xte/asm_products_guide.html |title=The RXTE All Sky Monitor Data Products |publisher=NASA |date=26 August 1997 |access-date=28 November 2021}} {{PD-notice}}</ref>

* 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: {{cvt|90|cm2}};
* Detector: [[Xenon]] proportional counter, position-sensitive;
* Sensitivity: 30 [[Crab (unit)|mCrab]].

It was built by the CSR at [[Massachusetts Institute of Technology]]. The [[principal investigator]] was [http://web.mit.edu/physics/people/faculty/bradt_hale.html 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.<ref name="Experiment3">{{cite web |url=https://nssdc.gsfc.nasa.gov/nmc/experiment/display.action?id=1995-074A-03 |title=Experiment: High Energy X-ray Timing Experiment (HEXTE) |publisher=NASA |date=28 October 2021 |access-date=28 November 2021}} {{PD-notice}}</ref> The HEXTE consisted of two clusters each containing four [[phoswich detector|phoswich scintillation detectors]]. Each cluster could "rock" (beam switch) 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]]s so as to detect time-varying phenomena. Automatic gain control was provided by using an {{SimpleNuclide|americium|241|link=yes}} radioactive source mounted in each detector's field of view. The HEXTE's basic properties were:<ref>{{cite web |url=http://heasarc.gsfc.nasa.gov/docs/xte/HEXTE.html |title=High Energy X-ray Timing Experiment (HEXTE) |publisher=NASA |date=1999-09-14 |access-date=2012-02-03}} {{PD-notice}}</ref>

* Energy range: 15–250 keV;
* Energy resolution: 15% at 60 keV;
* Time sampling: 8 microseconds;
* Field of view: 1° [[Full width at half maximum|FWHM]];
* Detectors: 2 clusters of 4 NaI/CsI [[scintillation counter]]s;
* Collecting area: 2 × {{cvt|800|cm2}};
* Sensitivity: 1-Crab = 360 count/second per HEXTE cluster;
* Background: 50 count/second per HEXTE cluster.

The HEXTE was designed and built by the [http://cass.ucsd.edu Center for Astrophysics & Space Sciences (CASS)] at the [[University of California, San Diego]]. The HEXTE principal investigator was [https://web.archive.org/web/20081229041202/http://mamacass.ucsd.edu/people/rrothschild.html Dr. Richard E. Rothschild].

=== Proportional Counter Array (PCA) ===
The Proportional Counter Array (PCA) provides approximately {{cvt|6500|cm2}} 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.<ref name="Experiment2">{{cite web |url=https://nssdc.gsfc.nasa.gov/nmc/experiment/display.action?id=1995-074A-02 |title=Experiment: Proportional Counter Array (PCA) |publisher=NASA |date=28 October 2021 |access-date=28 November 2021}} {{PD-notice}}</ref> The PCA was an array of five proportional counters with a total collecting area of {{cvt|6500|cm2}}. The instrumental properties were:<ref name="HEASARC">{{cite web |url=https://heasarc.gsfc.nasa.gov/docs/xte/learning_center/pca.html |title=Proportional Counter Array (PCA) |publisher=NASA |date=2011-12-06 |access-date=2018-10-05}}</ref>

* Energy range: 2–60 keV;
* Energy resolution: <18% at 6 keV;
* Time resolution: 1 μs
* Spatial resolution: collimator with 1° (FWHM);
* Detectors: 5 proportional counters;
* Collecting area: {{cvt|6500|cm2}};
* Layers: 1 [[propane]] veto; 3 [[Xenon]], 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 [[Jean Swank]].<ref name="HEASARC"/>

== Results ==
Observations from the Rossi X-ray Timing Explorer have been used as evidence for the existence of the [[frame-dragging]] effect predicted by the theory of [[general relativity]] of [[Albert Einstein|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]] named [[M82 X-1]].<ref>{{cite news |url=http://www.scienceblog.com/cms/dying_star_reveals_more_evidence_for_new_kind_of_black_hole_9685 |title=Dying Star Reveals More Evidence for New Kind of Black Hole |newspaper=Scienceblog.com |date=8 January 2006 |publisher=Science Blog |access-date=2012-02-03 |last1=Com |first1=Scienceblog}}</ref> 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]]s and from other stars' [[Stellar corona|coronae]].<ref>{{cite web |url=http://skyandtelescope.com/news/article_1681_1.asp |title=Galactic Glow Gleaned}}</ref> In April 2008, RXTE data was used to infer the size of the smallest known black hole.<ref>{{cite web |title=NASA Scientists Identify Smallest Known Black Hole |url=http://www.nasa.gov/centers/goddard/news/topstory/2008/smallest_blackhole.html |date=2008-04-01}} {{PD-notice}}</ref>

RXTE ceased science operations on 12 January 2012.<ref>{{cite web |title=The RXTE Mission is Approaching the End of Science Operations |url=http://heasarc.nasa.gov/docs/xte/xhp_new.html#endofoperations |archive-url=https://web.archive.org/web/20040107162230/http://heasarc.nasa.gov/docs/xte/xhp_new.html#endofoperations |url-status=dead |archive-date=2004-01-07 |date=2012-01-04}} {{PD-notice}}</ref>

== Atmospheric entry ==
NASA scientists said that the decommissioned RXTE would re-enter the Earth's atmosphere "between 2014 and 2023" (30 April 2018).<ref name="Register">{{cite web |url=https://www.theregister.co.uk/2012/01/11/rxte_satellite/ |title=NASA's aging black hole-stalking probe switched off |website=theregister.co.uk |date=11 January 2012 |access-date=28 November 2021}}</ref> Later, it became clear that the satellite would re-enter in late April or early May 2018,<ref name="NASA20180425">{{cite web |title=NASA Frequently Asked Questions: RXTE Spacecraft Re-entry |url=https://www.nasa.gov/feature/goddard/2018/nasa-frequently-asked-questions-rxte-spacecraft-re-entry |publisher=NASA |date=25 April 2018 |access-date=28 November 2021}}</ref> and the spacecraft fell out of orbit on 30 April 2018.<ref name="SC20180515">{{cite web |url=https://www.space.com/40592-nasa-rxte-satellite-falls-to-earth.html |title=A Pioneering NASA Satellite Just Fell to Earth After 2 Decades in Space |publisher=Space.com |date=15 May 2018 |access-date=28 November 2021}}</ref>

== See also ==
{{Portal|Spaceflight}}
* [[List of X-ray space telescopes]]
* [[Neutron Star Interior Composition Explorer]] (NICER, launched in June 2017 and attached to ISS)

== References ==
{{Reflist|30em}}

== External links ==
{{Commons category|RXTE}}
* [http://xte.mit.edu/ MIT's Rossi X-Ray Timing Explorer Project]
* [http://heasarc.gsfc.nasa.gov/docs/xte/xte_1st.html NASA RXTE Mission Site]
* [https://web.archive.org/web/20060102023814/http://www.ucsd.tv/search-details.asp?showID=1713 Video documentary]
* [https://web.archive.org/web/20061001024105/http://heasarc.nasa.gov/docs/objects/heapow/archive/transients/asm_movie.html Variations in the X-ray Sky by RXTE (1997)]
* [http://www.nasa.gov/content/goddard/rxte-reveals-the-cloudy-cores-of-active-galaxies/ RXTE Reveals the Cloudy Cores of Active Galaxies]

{{Explorer program}}
{{Orbital launches in 1995}}
{{Space observatories}}

[[Category:Spacecraft launched in 1995]]
[[Category:Spacecraft which reentered in 2018]]
[[Category:Explorers Program]]
[[Category:Space telescopes]]
[[Category:X-ray telescopes]]