Yohkoh (, ''Sunbeam'' in
Japanese
Japanese may refer to:
* Something from or related to Japan, an island country in East Asia
* Japanese language, spoken mainly in Japan
* Japanese people, the ethnic group that identifies with Japan through ancestry or culture
** Japanese diaspor ...
), known before launch as Solar-A, was a
Solar observatory spacecraft of the
Institute of Space and Astronautical Science
(ISAS) is a Japanese national research organization of astrophysics using rockets, astronomical satellites and interplanetary probes which played a major role in Japan's space development. Since 2003, it is a division of Japan Aerospace E ...
(Japan), in collaboration with space agencies in the
United States
The United States of America (U.S.A. or USA), commonly known as the United States (U.S. or US) or America, is a country primarily located in North America. It consists of 50 states, a federal district, five major unincorporated territori ...
and the
United Kingdom
The United Kingdom of Great Britain and Northern Ireland, commonly known as the United Kingdom (UK) or Britain, is a country in Europe, off the north-western coast of the European mainland, continental mainland. It comprises England, Scotlan ...
. It was launched into
Earth
Earth is the third planet from the Sun and the only astronomical object known to harbor life. While large volumes of water can be found throughout the Solar System, only Earth sustains liquid surface water. About 71% of Earth's surfa ...
orbit
In celestial mechanics, an orbit is the curved trajectory of an object such as the trajectory of a planet around a star, or of a natural satellite around a planet, or of an artificial satellite around an object or position in space such as ...
on August 30, 1991 by the
M-3SII
The Mu, also known as M, was a series of Japanese solid-fueled carrier rockets, which were launched from Uchinoura between 1966 and 2006. Originally developed by Japan's Institute of Space and Astronautical Science, Mu rockets were later operated ...
rocket from
Kagoshima Space Center
The is a space launch facility in the Japanese town of Kimotsuki, Kagoshima Prefecture. Before the establishment of the JAXA space agency in 2003, it was simply called the (KSC). All of Japan's scientific satellites were launched from Uchino ...
. It took its first soft X-ray image on September 13, 1991, 21:53:40, and movie representations of the X-ray corona over 1991-2001 are available at th
Yohkoh Legacy site
Description
The satellite was three-axis stabilized and in a near-circular orbit. It carried four instruments: a Soft X-ray Telescope (SXT), a Hard X-ray Telescope (HXT), a Bragg Crystal Spectrometer (BCS), and a Wide Band Spectrometer (WBS). About 50
MB were generated each day and stored on board by a 10.5 MB
bubble memory
Bubble memory is a type of non-volatile computer memory that uses a thin film of a magnetic material to hold small magnetized areas, known as ''bubbles'' or ''domains'', each storing one bit of data. The material is arranged to form a series o ...
recorder.
Because SXT utilized a
charge-coupled device
A charge-coupled device (CCD) is an integrated circuit containing an array of linked, or coupled, capacitors. Under the control of an external circuit, each capacitor can transfer its electric charge to a neighboring capacitor. CCD sensors are a ...
(CCD) as its readout device, perhaps being the first X-ray astronomical telescope to do so, its "data cube" of images was both extensive and convenient, and it revealed much interesting detail about the behavior of the solar corona.
Previous solar soft X-ray observations, such as those of
Skylab
Skylab was the first United States space station, launched by NASA, occupied for about 24 weeks between May 1973 and February 1974. It was operated by three separate three-astronaut crews: Skylab 2, Skylab 3, and Skylab 4. Major operations ...
, had been restricted to film as a readout device.
Yohkoh therefore returned many novel scientific results, especially regarding solar flares and other forms of magnetic activity.
The mission ended after more than ten years of successful observation when it went into its "safehold" mode during an annular eclipse on December 14, 2001, 20:58:33 and the spacecraft lost lock on the sun. Operational mistakes and other flaws combined in such a way that its solar panels could no longer charge the batteries, which drained irreversibly; several other solar eclipses had successfully been observed.
On September 12, 2005, the spacecraft burned up during reentry over South Asia. The time of reentry, as provided by the
U.S. Space Surveillance Network, was 6:16 pm
Japan Standard Time
, or , is the standard time zone in Japan, 9 hours ahead of UTC ( UTC+09:00). Japan does not observe daylight saving time, though its introduction has been debated on several occasions. During World War II, the time zone was often referred to ...
(JST).
Instruments
''Yohkoh'' carried four instruments :
* The Soft X-ray Telescope (SXT) was an X-ray telescope with glancing incidence X-ray mirror and a CCD sensor. There was also a co-aligned optical telescope using the same CCD, but after the failure of the entrance filter in November 1992 it became unusable.
The CCD was 1024×1024 pixels with pixel angular size of 2.45″×2.45″, a point-spread function (core width
FWHM
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 me ...
) of about 1.5 pixels (i.e. 3.7″), a field of view of 42′×42′, which was a little larger than the whole solar disk. Typical time resolution was 2 s in flare mode and 8 s in quiet (no flare) mode, the maximum time resolution in 0.5 s.
For spectral discrimination, SXT employed wide-band filters installed on a filter wheel. There were five usable filter positions: 1265 Å-thick Al filter (2.5 Å–36 Å pass band), Al/Mg/Mn filter (2.4 Å–32 Å), 2.52 μm Mg filter (2.4 Å–23 Å), 11.6 μm Al filter (2.4 Å–13 Å), 119 μm Be filter (2.3 Å–10 Å). Before the entrance filter failure in November 1992 three more filter positions were available: no analysis filter (2.5 Å–46 Å), Wide band optical filter (4600 Å–4800 Å), Narrow band optical filter (4290 Å–4320 Å).
* The Hard X-ray Telescope (HXT)
was a Fourier-synthesis X-ray imager with 64 bigrid collimators sparsely sampling the (u,v) plane and feeding individual scintillation-counter detectors. HXT was sensitive to photons with energies from 14 keV to 93 keV, this range was divided into four energy bands (called L, M1, M2, H). The angular resolution was about 5″, image synthesis field of view is 2′×2′, maximum time resolution was 0.5 s.
* Bragg Crystal Spectrometer (BCS) was two bent crystal
spectrometer
A spectrometer () is a scientific instrument used to separate and measure spectral components of a physical phenomenon. Spectrometer is a broad term often used to describe instruments that measure a continuous variable of a phenomenon where the ...
s sensitive in four spectral lines: the line of ion Fe XXVI (1.76 Å–1.81 Å), ion Fe XXV (1.83 Å–1.90 Å), ion Ca XIX (3.16 Å–3.19 Å), and ion S XV (5.02 Å–5.11 Å). Spectral resolution varied in the range of λ/Δλ=3000–8000, typical time resolution in flare mode was 8 s, maximum is 0.125 s. BCS integrates radiation over the whole solar disc.
* Wide Band Spectrometer (WBS) had spectroscopic capabilities in a wide energy band from 3 keV to 100 MeV. WBS was a set of four subinstruments, eаch of them outputs Pulse Count (PC) corresponding to intensity integrated over a band, and Pulse Height (PH) profile which corresponded to spectrum. Time resolution for PC (0.125 s–4 s for different subinstruments and modes) was 8–16 times better than for PH (1 s–32 s). WBS integrated radiation over the whole Sun and did not resolve source position.
** Soft X-ray Spectrometer (SXS) consisted of two
proportional gas counters with nominal energy band 5 keV–40 keV, which was divided into two PC channels and 128 PH channels. It was found after the launch that PH to energy relationship was distorted. No energy calibration for WBS PH data was available in 1999.
** Hard X-ray Spectrometer (HXS) was a NaI(Tl)
scintillator. The energy band after June 1992 was 24 keV–830 keV. It was divided into 2 PC channels and 32 PH channels.
** Gamma-ray Spectrometer (GRS) consisted of two identical bismuth germanate oxide scintillators. It covered energy range 0.3 MeV–100 MeV, which was divided into 6 PC channels and 128+16 PH channels.
** Radiation Belt Monitor (RBM) unlike the other three was not aimed at solar flare observations and served to sound the alarm for
radiation belt passage.
References
External links
JAXA/ISAS overview of mission at the
Wayback Machine
The Wayback Machine is a digital archive of the World Wide Web founded by the Internet Archive, a nonprofit based in San Francisco, California. Created in 1996 and launched to the public in 2001, it allows the user to go "back in time" and see ...
JAXA/ISAS Yohkoh legacy home page(Japanese)
(English)
Encyclopædia Britannica, YohkohHXT project pageNASA/NSSDC information on YohkohU.S.-European-Japanese Workshop on Space Cooperation: Summary Report 1999
Yohkoh Science Nuggets
{{Japanese space program
1991 in spaceflight
Satellites formerly orbiting Earth
Satellites of Japan
Solar telescopes
Space telescopes
X-ray telescopes
Spacecraft which reentered in 2005
1991 in Japan