Protein Crystal Growth - Single Locker Thermal Enclosure System (PCG-STES) - 07.19.17

Summary | Overview | Operations | Results | Publications | Imagery

ISS Science for Everyone

Science Objectives for Everyone
Protein Crystal Growth - Single Locker Thermal Enclosure System (PCG-STES) supports a series of investigations to grow protein crystals in microgravity. Multiple independent and collaborating principal investigators contributed samples and evaluated the technology for crystal growth in space.
Science Results for Everyone
Information Pending

The following content was provided by Teresa Miller, and is maintained in a database by the ISS Program Science Office.
Facility Details


Facility Manager(s)
Teresa Miller, Marshall Space Flight Center, Huntsville, AL, United States

Facility Representative(s)
Todd Holloway, Marshall Space Flight Center, Huntsville, AL, United States

NASA Marshall Space Flight Center, Huntsville, AL, United States

Sponsoring Space Agency
National Aeronautics and Space Administration (NASA)

Sponsoring Organization
Human Exploration and Operations Mission Directorate (HEOMD)

ISS Expedition Duration
March 2001 - August 2001; December 2001 - December 2002; November 2002 - May 2003; April 2003 - October 2005

Expeditions Assigned

Previous Missions
Information Pending


  • Retired/Returned/Disposed
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    Facility Description

    Facility Overview

    • The Protein Crystal Growth - Single Thermal Locker System (PCG-STES) has been designed to crystallize macromolecules in microgravity.

    • The PCG-STES is very autonomous, minimal crew time is required for activation, deactivation and periodic status checks of the hardware.
    The Protein Crystal Growth - Single-Locker Thermal Enclosure System (PCG-STES) provides a controlled-temperature environment between 1 and 40 degrees C to grow large, high-quality crystals. Its thermal control system (TCS) regulates the temperature inside the payload chamber. A fan pulls cabin air through an intake on the front panel causing the air to flow across the heat exchanger fans, and then out the rear left side of the unit. Push buttons and an LCD display on the front panel allow the crew to command the unit. STES can also be commanded from the ground.

    Samples were housed in the PCG-STES and within two different types of crystallization hardware: the Protein Crystallization Apparatus for Microgravity (PCAM) or the Diffusion-Controlled Crystallization Apparatus for Microgravity (DCAM).

    PCAMs consist of nine trays, each containing seven vapor-equilibration wells. The nine trays are sealed inside a cylinder. Crystals are formed by the "sitting drop" method of vapor diffusion. Each sample well holds a drop of protein solution and precipitant (salts or organic solvents, which draw water away from the protein solution) mixed together. A surrounding moat holds a reservoir, filled with an absorbent fluid, that draws moisture away from the mixed solution. Crystals form as the moisture is absorbed. A rubber seal pressed into the lip of the reservoir keeps crystals from forming on Earth or from bouncing out of their wells during transport. Each cylinder holds 63 experiments for a total of 378 experiments inside the Single-locker Thermal Enclosure System (STES).

    DCAMs, which are slightly smaller than a 35-mm film canister, each contained two cylindrical chambers that are connected by a tunnel. One chamber holds the precipitant solution and the other contains the protein sample. A thin semipermeable membrane covers the protein sample that allowed the precipitant to pass through at a controlled rate. The rate of diffusion was controlled by a porous plug that separates the two chambers. This is referred to as the liquid-liquid diffusion method. Crewmembers transferred the experiment hardware, PCG-STES (containing the DCAM and PCAM chambers with the experiment samples) from the Space Shuttle Middeck to the ISS EXPRESS Rack. The experiment was activated on Earth where the sample and precipitant were added to their chambers.

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    Facility Operations

    • Samples were pre-loaded in the PCG-STES prior to launch. The PCG-STES unit was transferred from the Shuttle to the ISS EXPRESS Rack.

    • Following installation into the EXPRESS Rack the PCG-STES unit was activated by the crew.

    • The crew monitored the PCG-STES on daily basis. In addition, the crew also performed regular cleaning of the fan inlet.

    • Prior to the return to Earth, the PCG-STES unit was deactivated and transferred to the Space Shuttle. Following landing the samples were returned to the respective investigators for analysis.

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    Decadal Survey Recommendations

    Information Pending

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    Results/More Information

    The PCG-STES hardware has supported nine experiments onboard the ISS, with additional shared samples for associated investigators. Samples were taken to and from station five times for crystallization during Expeditions 2, 4, 5, and 6. PCG-STES samples in DCAM were on orbit prior to the space shuttle Columbia accident, and then spent an unprecedented 981 days (November 2002 - August 2005) on ISS before being returned on STS-114/LF1(Kundrot 2002).

    Results Publications

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    Ground Based Results Publications

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    ISS Patents

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    Related Publications

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    Related Websites

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    image Protein Crystallization Apparatus for Microgravity (PCAM). Image Courtesy of NASA, Marshall Space Flight Center.
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    image Diffusion-Controlled Crystallization Apparatus for Microgravity (DCAMs). Image Courtesy of NASA, Marshall Space Flight Center.
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    image NASA Image: ISS005E21531 - Astronaut Peggy A. Whitson, Expedition Five science officer, works the PCG-STES hardware on board the International Space Station.
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