STS-57 (Endeavour, 21 Jun 93 - 01 Jul 93):

Astroculture™ Lighting System Development

The second subsystem of the Astroculture (ASC-GC) hardware to be developed was the plant lighting system. The lighting system needs to be as energy-efficient as possible because electrical power is of limited availability on a space flight, typically no more that 150 W for a middeck locker sized payload. Much of the power is also rejected as waste heat, an important factor in keeping the plant chamber temperature suitable for plant growth. Yet, despite this, there must be sufficient light to meet the requirements of the plants.

Pilot Brian Duffy monitors the Astroculture payload on board the space shuttle Endeavor.

The solution used in Astroculture is lighting provided by high intensity light emitting diodes (LEDs) (U.S. Patent 5,012,609). To make the lighting as energy-efficient as possible, only the wavelengths needed by the plants are incorporated into the LED light caps. Plants require light at about 670 nm (red) for photosynthesis and a small amount at about 470 nm (blue) for development and for proper orientation in the absence of gravity. The intensity of the photon flux and the ratio of red to blue light may be continuously varied. Total photon flux of the light cap may be as great as several times full sunlight.

The purpose of the STS-57 activity was to verify proper operation of the LED light cap in microgravity. It was critical to observe the removal of waste heat from the light cap in microgravity, where forced convection must be used for cooling, due to the absence of natural convection. Additionally, the light cap was operated at the same time as the water delivery system, testing Astroculture's ability to manage two separate subsystems at the same time.

STS-50 - STS-57 - STS-60 - STS-63 - STS-73 - STS-95 - STS-101 - STS-107  /  STS-89/91 - Inc 2 - Inc 4 - Inc 5