[3] HEAO-2 was constructed by TRW Inc. and shipped to Marshall Space Flight Center in Huntsville, AL for testing in 1977.

Einstein ceased operations on April 26 1981, when the exhaustion of the satellite's thruster fuel supply rendered the telescope inoperable.

[7] Einstein carried a single large grazing-incidence focusing X-ray telescope that provided unprecedented levels of sensitivity.

[11] Einstein data also indicated that coronal x-ray emissions in main sequence stars are stronger than was expected at the time.

[13] The Uhuru satellite discovered x-ray emissions from a hot, thin gas pervading distant clusters of galaxies.