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Uhuru was the first satellite launched specifically for the purpose of X-ray astronomy. It was also known as the X-ray Explorer Satellite, SAS-A (for Small Astronomy Satellite A, being first of the three-spacecraft SAS series), SAS 1, or Explorer 42. The observatory was launched on December 12, 1970 into an initial orbit of about 560 km apogee, 520 km perigee, 3 degrees inclination, with a period of 96 minutes. The mission ended in March 1973. Uhuru was a scanning mission, with a spin period of ~12 minutes. It performed the first comprehensive survey of the entire sky for X-ray sources, with a sensitivity of about 0.001 times the intensity of the Crab nebula.

Uhuru

Uhuru (X-ray Explorer Satellite)
Mission type	Astronomy
Operator	NASA
COSPAR ID	1970-107A
SATCAT no.	4797
Website	heasarc.gsfc.nasa.gov/docs/uhuru/uhuru.html
Mission duration	3 years
Spacecraft properties
Dry mass	141.5 kilograms (312 lb)
Start of mission
Launch date	December 12, 1970, 10:53:50 (1970-12-12UTC10:53:50Z) UTC
Rocket	Scout B S175C
Launch site	San Marco
End of mission
Last contact	March 1973 (1973-04)
Decay date	April 5, 1979
Orbital parameters
Reference system	Geocentric
Regime	Low Earth
Eccentricity	0.002956
Perigee altitude	520.0 kilometers (323.1 mi)
Apogee altitude	560.0 kilometers (348.0 mi)
Inclination	3.0 degrees
Period	95.70 minutes
Epoch	December 12, 1970, 05:54:00 UTC[1]
Instruments
All-Sky X-Ray Survey
Explorers ← Explorer 41 Explorer 43 →

Objectives

The main objectives of the mission were:[2]

• To survey the sky for cosmic X-ray sources in the 2–20 keV range to a limiting sensitivity of 1.5 × 10⁻¹⁸ joule/(cm²-sec), 5 × 10⁻⁴ the flux from the Crab Nebula
• To determine discrete source locations with a precision of a few square minutes of arc for strong sources and a few tenths of a square degree at the sensitivity limit
• To study the structure of extended sources or complex regions with a resolution of about 30 arc minutes
• To determine gross spectral features and variability of X-ray sources
• To perform, wherever possible, coordinated and/or simultaneous observations of X-ray objects with other observers.

Instrumentation

The payload consisted of two sets of proportional counters, each with ~0.084 m² effective area. The counters were sensitive with more than 10% efficiency to X-ray photons in the ~2–20 keV range. The lower energy limit was determined by the attenuation of the beryllium windows of the counter plus a thin thermal shroud that was needed to maintain temperature stability of the spacecraft. The upper energy limit was determined by the transmission properties of the counter filling gas. Pulse-shape discrimination and anticoincidence techniques were used to filter out emissions of particles and undesirable high-energy photons in the background. Pulse-height analysis in eight energy channels was used to obtain information on the energy spectrum of the incident photons. The two sets of counters were placed back to back and were collimated to 0.52° × 0.52° and 5.2° × 5.2° (full width at half maximum) respectively. While the 0.52° detector gave finer angular resolution, the 5.2° detector had higher sensitivity for isolated sources.[2]

Results

Uhuru achieved several outstanding scientific advances, including the discovery and detailed study of the pulsing accretion-powered binary X-Ray sources such as Cen X-3, Vela X-1, and Her X-1, the identification of Cygnus X-1, the first strong candidate for an astrophysical black hole, and many important extragalactic sources. The Uhuru Catalog, issued in four successive versions, the last being the 4U catalog, was the first comprehensive X-ray catalog, contains 339 objects and covers the whole sky in the 2–6 keV band.[3] The final version of the source catalog is known as the 4U Catalog;[4] earlier versions were the 2U and 3U catalogs. Sources are referenced as, e.g., "4U 1700-37".

Naming

The satellite's name, "Uhuru", is the Swahili word for "freedom". It was named in recognition of the hospitality of Kenya from where it was launched, from the Italian San Marco launch platform near Mombasa.

See also

• Timeline of artificial satellites and space probes
• Small Astronomy Satellite 2
• Small Astronomy Satellite 3

References

External links

• SAS-A (Explorer 42) Press Kit
• Uhuru Satellite at (GSFC. NASA)
• NSSDC Master Catalog: Uhuru

На других языках

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[de] Uhuru (Satellit)

Uhuru (Swahili für Freiheit), auch als Explorer 42, SAS A (Small Astronomical Satellite A) und SAS-1 bezeichnet, war der erste Satellit, der den Himmel vollständig nach Röntgenquellen durchmusterte. Er wurde am 12. Dezember 1970 mit einer Scout-Rakete von der vor der Küste Kenias befindlichen Plattform San Marco gestartet und gelangte in eine Umlaufbahn um die Erde zwischen 531 und 572 km Höhe. Dadurch war dies die erste Satellitenmission der NASA, die nicht vom Gebiet der USA gestartet wurde. Ein Start von Cape Canaveral z. B. hätte eine stärkere Trägerrakete erforderlich gemacht, da eine Inklination von 3,0 ° vorgesehen war.

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- [en] Uhuru (satellite)

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[es] Uhuru

Uhuru, lanzado por la NASA fue el primer satélite lanzado específicamente para el estudio de la astronomía de rayos-X. También es conocido como Small Astronomical Satellite 1 (SAS-1)

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[ru] Uhuru

Спутник UHURU (Ухуру) — первая орбитальная рентгеновская обсерватория. Впервые спутниковая миссия была полностью посвящена изучению небесных источников рентгеновского излучения. Предыдущие эксперименты по исследованию рентгеновского излучения небесных источников проводились исключительно на суборбитальных ракетах, что значительно ограничивало полезное время работы их инструментов.

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