January 07, 2025
Growing plants from seed in space under micro gravity is an important milestone for space biological research, to produce food in space and as an engaging activity for the astronauts in space during long duration manned missions.
CROPS stands for Compact Research Module for Orbital Plant Studies which is an unmanned experimental module designed to develop ISRO’s capabilities for growing and sustaining plants in space. CROPS first mission (CROPS – 1) is designed to demonstrate germination of a seed and growth of plant up to two leaves stage in space. It is an airtight container of diameter 300mm and height 450mm simulating earth like environment in space except gravity.
Conceptual image of CROPS Module and Electronics assembly
A neutral clay soil medium in pellet form having high porosity to absorb and retain water is used in CROPS – 1 for the seed to spread its roots. The soil medium can be sterilized by heating at high temperature to neutralize microbes, fungus, spores etc. without losing any of its functional properties. The soil is premixed with a slow release fertilizer (activated by water) in a measured quantity to provide nutrients to the plant in a controlled manner over a period of time. The soil is tightly packed in four chambers (with two seeds each) covered by a silicon foam layer followed by a cover plate on the top to provide sufficient compression to the soil. Each seed is pasted on to a polypropylene tissue and glued together using an organic gum. This gum holds the seed rigidly in position until it is wetted by water. The seed also has to be thoroughly sterilized using ethanol before pasting to avoid contamination. The pasted tissue strip is inserted into the soil medium through a slit in the silicon foam and the cover plate. This mechanism of seed fixing helps the seed to survive the high vibrations and shock levels experienced during launch. In addition, CROPS – 1 also has vibration isolators to protect the module from vibration and shock felt during launch.
The CROPS - 1 container is sealed in a clean room environment after inserting the tissue strips, and the chamber will have earth like atmospheric composition with 20.9% oxygen, 400 - 600 ppm of carbon dioxide, 50 to 60% humidity and temperature of 25 to 30 degree Celsius. Practically in this chamber, the seed has all constituents for germination except water. Pure filtered drinking water is stored in small pressurized tank under the CROPS -1 module and water is isolated from the soil medium using an electric valve. From the valve, water is carried in small metallic tubes, which comes out through the perforations all around the tubes. The water coming out of the tubes is absorbed by the porous soil medium due to capillary action. Once in orbit, the experiment starts through a telecommand issued from ground, which opens an electric valve thereby admitting water to soil.
The tissue strips also absorbs water by capillary action from the soil, the seed gets soaked and germination starts. During germination, based on ground trials, carbon dioxide levels start to increase and oxygen levels start to decrease during the process. After the development of the first green leaves, photosynthesis starts and carbon dioxide levels start to decrease and oxygen levels will start to increase. The plants will stop growing once the available carbon dioxide levels in sealed chamber goes very low. There are sensors with in the module to measure the concentration of carbon dioxide & oxygen, pressure, temperature, relative humidity and soil moisture. These sensors are powered by an electronics module and the data is acquired and sent to ground by telemetry during visible orbits. A high resolution camera with associated electronics is provide inside at the top of the module to observe the continuous growth of the plant and capture images at periodic intervals. During photosynthesis, plants require sufficient illumination mostly in the Photosynthetically Active Radiation (PAR) spectrum (400 to 700 nm). Four warm LEDs and four cool LEDs are provided at the top of the chamber to provide the necessary PAR and also illumination during image capture. The lights are programmed to be ON for 16 hours and OFF for 8 hours simulating day and night conditions for the plant. Light duration can be changed based on various requirements.
Every seed has an ideal temperature for germination and growth and this has to be maintained in the CROPS module. In space, since the external temperature is 4 kelvin the temperature inside the module is maintained within 20 to 30 deg Celsius by using tape type heaters temperature sensors, and multi-layer insulation (MLI) to prevent heat loss from the module. The electronics module will switch on the heater when the lower temperature limit is reached and the temperature will slowly start to increase. The heater is switched off automatically when the upper temperature limit is reached. The temperature limits and sensors can be used in various configurations as per the specific experiment requirement.
CROPS – 1 was flown in PSLV C60 mission in POEM 4 payload to demonstrate germination of a seed and sustenance up to two leaves stage in space for 5 to 7 days. Cowpea (Scientific name: Vigna Unguiculata) was chosen based on ground trials on a variety of seeds due to its shorter germination time. After launch and main satellite separation, POEM platform was lowered to 350 km orbit and CROPS – 1 payload was switched on. All system parameters were found normal and the temperature was regulated precisely between 20 to 30 deg Celsius. Approximately after 90 minutes, water was injected successfully into the soil medium by operating the electric valve from ground. Data was acquired during subsequent orbits, which indicated carbon dioxide levels rising indicating germination of the seeds. On the fourth day, seeds sprouting out from the enclosed tissue strips was observed. On the fifth day, two leaves were visible on spouted seeds indicating successful accomplishment of the objectives.
CROPS Module flown in POEM-4
The next phase of CROPS will be for longer duration (30 to 45 days) envisaging plant growth beyond two leaves stage with active control system to regulate percentage of carbon dioxide, oxygen, relative humidity, soil moisture and temperature for sustained growth of plants in space.
CROPS image from orbit on 30th Dec. 2024
CROPS image from orbit on 4th Jan. 2025
(sprouting of first seed)
CROPS image from orbit on 5th Jan. 2025
(two leaves stage)
CROPS image from orbit on 6th Jan. 2025
Description: CROPS: A Leap in Space Biological Experiments Format : webm File Size : 949 KB Duration : 00:00:48 Plugin : NA