Editing Marshall Space Flight Center (section)

====Post-Apollo science====
The [[HEAO Program|High Energy Astronomy Observatory]] (HEAO) Program involved three missions of large spacecraft in [[low Earth orbit]]. Each spacecraft was about {{cvt|18|ft|m}} in length, massed between {{cvt|6000|and|7000|lb|kg}}, and carried some {{cvt|3000|lb|kg}} of experiments for [[X-ray astronomy|X-ray]] and [[gamma-ray astronomy|gamma-ray]] astronomy and [[Cosmic ray|cosmic-ray]] investigations. The project provided insights into celestial objects by studying their high-energy radiation from space. Scientists from across the US served as [[principal investigator]]s.{{citation_needed|date=July 2019}}

The HEAO spacecraft concept originated in the late 1960s, but funding did not become available for some time. Using [[Atlas-Centaur]] launch vehicles, three highly successful missions were flown: HEAO 1 in August 1977, HEAO 2 (also called the Einstein Observatory) in November 1978, and HEAO 3 in September 1979. Fred A. Speer was the HEAO project manager for MSFC.<ref>Tucker, Wallace H.; [https://history.nasa.gov/SP-466/sp466.htm "The Star Splitters: The High Energy Astronomy Observatories"] {{Webarchive|url=https://web.archive.org/web/20171225231009/https://history.nasa.gov/SP-466/sp466.htm |date=2017-12-25 }} NASA, SP-466, 1984;</ref>

Other MSFC-managed space science projects in the 1970s included the [[LAGEOS|Laser Geodynamics Satellite]] (LAGEOS) and [[Gravity Probe A]]. In LAGEOS, laser beams from 35 ground stations are reflected by 422 prismatic mirrors on the satellite to track movements in the Earth's crust. The measurement accuracy is a few centimeters and it tracks the movement of [[tectonic plates]] with comparable accuracy. Conceived and built at MSFC, the LAGEOS was launched by a [[Delta (rocket family)|Delta]] rocket in May 1976.<ref>[https://nssdc.gsfc.nasa.gov/nmc/experiment/display.action?id=1976-039A-01 "Laser Tracking Reflector"] {{Webarchive|url=https://web.archive.org/web/20200803162713/https://nssdc.gsfc.nasa.gov/nmc/experiment/display.action?id=1976-039A-01 |date=2020-08-03 }}, NASA Tech Data</ref>

Gravity Probe A, also called the Redshift Experiment, used an extremely precise [[hydrogen maser]] clock to confirm part of Einstein's [[general relativity|general theory of relativity]]. The probe was launched in June 1976, by a [[Scout (rocket family)|Scout]] rocket, and remained in space for near two hours, as intended.<ref>Vessot, R.F.C. et al. (1980). "Test of Relativistic Gravitation with a Space-Borne Hydrogen Maser" ''. Rev. Ltrs.'', vol. 45, no 26 (1980), pp. 2081–2084</ref>