Yohkoh

• Name — Yohkoh • Names List — Solar-A (before launch • Mission Type — Heliophysics • Operator — ISAS / NASA / PPARC • Cospar Id — 1991-062A • Satcat — 21694 • Website — Yohkoh home page • Mission Duration — (achieved) • Launch Mass — 390 kg • Dimensions — 2 m x 2 m x 4 m • Launch Date — 1991 08 30 02 30 7=Z • Launch Rocket — Mu-3S-II • Launch Site — Kagoshima M1 • Disposal Type — Spacecraft lost accidentally • Last Contact — 14 December 2001 • Decay Date — 12 September 2005 • Orbit Reference — Geocentric • Orbit Periapsis — 516 km • Orbit Apoapsis — 754 km • Orbit Inclination — 31.3° • Orbit Period — 97.4 min • Apsis — gee

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) 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 spectrometers 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.