For solar cells, the relevant design problem was exposure to sunlight and atmospheric conditions resembling those outside Earth’s atmosphere. Beginning in 1963, Glenn used specially modified aircraft, including Learjets, to recreate some of those conditions. NASA says the calibration program continued for decades, using high-altitude flights and adapting to newer aircraft over time. [S1]
For microgravity experiments, the flight maneuver supplied the test condition. Specially modified aircraft such as Glenn’s DC-9 flew parabolic maneuvers to create short periods of weightlessness. Researchers could study fluids, combustion, materials and experimental equipment in near-zero gravity before conducting experiments in space. The useful comparison is the condition each approach supplied: selected sunlight and atmospheric conditions for solar-cell calibration, brief weightlessness for experiments sensitive to gravity. [S1]
Source documents
- NASA Glenn’s Legacy Forged Through Decades of Flight Researchhttps://www.nasa.gov/general/nasa-glenn-inflight-research/