Mary Helen Johnston was born in West Palm Beach, Florida, and grew up in the nearby Fort Pierce.

[2] In 1974, she worked with Doris Chandler, Carolyn S. Griner and Ann Whitaker on the simulation of a space mission at the General Purpose Laboratory (GPL) of MSFC.

The team of four women, all scientists, conducted eleven experiments to test their feasibility before they were carried out in the Spacelab of the Space Shuttle.

[5][6][7] These tests included some in the neutral buoyancy simulator, itself a mock-up of one to be built in Europe to provide training for future astronauts.

"[8] In 1976, Johnston worked with Griner on MSFC experiments testing space-like conditions with Space Processing Applications Rocket (SPAR) launched objects, particularly involving "dendrite remelting and macrosegregation".

[1] On June 5, 1983,[10] she was selected as one of the four payload specialists for the STS-51-B Spacelab mission (Spacelab-3 group) as part of the reserve crew,[11][12] not flying – she never went to space.

[14] Of her selection, mission manager Joseph Cremin wrote: "The job ahead is difficult and the time is short which makes this assignment a significant challenge that will require the utmost dedication and perseverance of Dr. Johnston.

To me, being a researcher, scientist, and engineer, the best way to do that was to get up there with a bunch of equipment and find out what worked, because it's almost impossible to imagine what some things will do where there is absolutely no gravity.