Editing Einstein Observatory (section)

==Instrumentation==
[[File:HEAO-2-Configuration.png|thumb|HEAO 2 diagram: B-1: Gas proportional counter, B-2: High definition camera detector, B-3: Crystal spectrometer, B-4: Gas proportional counter, B-5: Gas spectrometer solid detector, 1: Platform/bus, 2: Solar panel, 3: Optical bench, 4: Rear pre-collimator, 5: Wolter optics, 6: Front pre-collimator, 7: Sun visor, 8: Filters and spectrometer grids, 9: Star finders, 10: Locations reserved for experiments, 11: Central electronics, 12: Focal plane]]

Einstein carried a single large [[Wolter telescope|grazing-incidence]] focusing X-ray telescope that provided unprecedented levels of sensitivity. It had instruments sensitive in the 0.15 to 4.5 [[electronvolt|keV]] energy range. Four instruments were installed in the satellite, mounted on a carousel arrangement that could be rotated into the focal plane of the telescope:<ref name=adsabs-harvard>{{cite journal |title=The Einstein /HEAO 2/ X-ray Observatory |publisher=adsabs.harvard.edu |bibcode=1979ApJ...230..540G |last1=Giacconi |first1=R. |last2=Branduardi |first2=G. |last3=Briel |first3=U. |last4=Epstein |first4=A. |last5=Fabricant |first5=D. |last6=Feigelson |first6=E. |last7=Forman |first7=W. |last8=Gorenstein |first8=P. |last9=Grindlay |first9=J. |last10=Gursky |first10=H. |last11=Harnden |first11=F. R. |last12=Henry |first12=J. P. |last13=Jones |first13=C. |last14=Kellogg |first14=E. |last15=Koch |first15=D. |last16=Murray |first16=S. |last17=Schreier |first17=E. |last18=Seward |first18=F. |last19=Tananbaum |first19=H. |last20=Topka |first20=K. |last21=Van Speybroeck |first21=L. |last22=Holt |first22=S. S. |last23=Becker |first23=R. H. |last24=Boldt |first24=E. A. |last25=Serlemitsos |first25=P. J. |last26=Clark |first26=G. |last27=Canizares |first27=C. |last28=Markert |first28=T. |last29=Novick |first29=R. |last30=Helfand |first30=D. |journal=The Astrophysical Journal |year=1979 |volume=230 |page=540 |display-authors=5 |doi=10.1086/157110 |doi-access=free|s2cid=120943949 }}</ref>
* The High Resolution Imaging camera (HRI) was a digital x-ray camera covering the central 25 arcmin of the focal plane. The HRI was sensitive to x-ray emissions between 0.15 and 3 keV and capable of ~2 arcsec spatial resolution.
* The Imaging Proportional Counter (IPC) was a proportional counter covering the entire focal plane. The IPC was sensitive to x-ray emissions between 0.4 and 4 keV and capable of ~1 arcmin spatial resolution.
* The Solid State Spectrometer (SSS) was a cryogenically cooled [[silicon drift detector]]. The SSS was sensitive to x-ray emissions between 0.5 and 4.5 keV. The cryogen keeping the SSS at its operational temperature ran out, as expected, in October 1979.
* Bragg Focal Plane Crystal Spectrometer (FPCS) was a Bragg crystal spectrometer. The FPCS was sensitive to x-ray emissions between 0.42 and 2.6 keV.

Additionally, the Monitor Proportional Counter (MPC) was a non-focal plane, coaxially-mounted [[proportional counter]] that monitored the x-ray flux of the source being observed by the active focal plane instrument.

Two filters could be used with the imaging detectors:

* The Broad Band Filter Spectrometer consisted of [[aluminum]] and [[beryllium]] filters than could be placed into the x-ray beam to change the spectral sensitivity.
* The Objective Grating Spectrometer [[diffraction grating|transmission gratings]].

[[Riccardo Giacconi]] was the principal investigator for all of the experiments on board Einstein.<ref name=investigator>{{cite web |title=HEAO-2 Experiments |publisher=nssdc.gsfc.nasa.gov/ |url=https://nssdc.gsfc.nasa.gov/nmc/spacecraft/displayExperiment.action?spacecraftId=1978-103A |access-date=14 July 2021}}</ref>

<gallery mode=packed heights=180>
File:HEAO-2_Assembly_of_the_High_Energy_Astronomy_Observatory_8005694.jpg|Assembly of the HEAO-2 at TRW, Inc., the prime contractor for the HEAOs
File:HEAO-2_Testing_the_High_Energy_Astronomy_Observatory_(HEAO)-2.jpg|HEAO-2 checked at the X-Ray Calibration Facility at the Marshall Space Flight Center
File:HEAO-2_Testing_of_the_High_Energy_Astronomy_Observatory_(HEAO)-2_2.jpg|HEAO-2 experiment level testing after integration at TRW, Inc.
</gallery>