The Spacelab-Mir-1 "Greenhouse-2" experiment.

The Spacelab-Mir-1 (SLM-1) mission is the first docking of the Space Shuttle Atlantis (STS-71) with the Orbital Station Mir in June 1995. The SLM-1 "Greenhouse-2" experiment will utilize the Russian-Bulgarian-developed plant growth unit (Svet). "Greenhouse-2" will include two plantings (1) designed to test the capability of Svet to grow a crop of Superdwarf wheat from seed to seed, and (2) to provide green plant material for post-flight analysis. Protocols, procedures, and equipment for the experiment have been developed by the US-Russian science team. "Greenhouse-2" will also provide the first orbital test of a new Svet Instrumentation System (SIS) developed by Utah State University to provide near real time data on plant environmental parameters and gas-exchange rates. SIS supplements the Svet control and monitoring system with additional sensors for substrate moisture, air temperature, IR leaf temperature, light, oxygen, pressure, humidity, and carbon-dioxide. SIS provides the capability to monitor canopy transpiration and net assimilation of the plants growing in each vegetation unit (root zone) by enclosing the canopy in separate, retractable, ventilated leaf chambers. Six times during the seed-to-seed experiment, plant samples will be collected, leaf area measured, and plant parts fixed and/or dried for ground analysis. A second planting initiated 30 days before the arrival of a U.S. Shuttle [originally planned to be STS-71] is designed to provide green material at the vegetative development stage for ground analysis. [As this paper is being edited, the experiment has been delayed until after the arrival of STS-71.]     

Induced abnormality in Mir- and Earth grown Super Dwarf wheat.

Super-dwarf wheat grown on the Mir space station using the Svet "Greenhouse" exhibited morphological, metabolic and reproductive abnormalities compared with Earth-grown wheat. Of prominent importance were the abnormalities associated with reproductive ontogeny and the total absence of seed formation on Mir. Changes in the apical meristem associated with transition from the vegetative phase to floral initiation and development of the reproductive spike were all typical of 'Super-Dwarf' wheat up to the point of anthesis. Observation of ruptured anthers from the Mir-grown plants revealed what appeared to be normally developed pollen. These pollen gains, however, contained only one nuclei, while normal viable pollen is tri-nucleate. A potentially important difference in the flight experiment, compared with ground reference studies, was the presence of a high level of atmospheric ethylene (1,200 ppb). Ground studies conducted by exposing 'Super-Dwarf' wheat to ethylene just prior to anthesis resulted in manifestation of the same abnormalities observed in the space flight samples.     

Airdrop ballistic winds operationally capable lidar

The Airdrop Ballistic Winds (ABW) team at Wright-Patterson AFB, Ohio, conducted flight tests of its 2 μm laser radar (lidar). This system, called the Operationally Capable Lidar (OCL), was installed in a modified C-130 fuel pod. The OCL was designed to: (1) provide real-time, 3-D maps of wind fields between the aircraft and the ground; and (2) significantly improve airdrop accuracy from high altitudes. This paper briefly describes the OCL, the Precision Airdrop simulation (PADS) tool, and flight test activities, including the Precision Airdrop Integrated Demonstration     

Six-month space greenhouse experiments--a step to creation of future biological life support systems

SVET Space Greenhouse (SG)--the first automated facility for growing of higher plants in microgravity was designed in the eighty years to be used for the future BLSS. The first successful experiment with vegetables was carried out in 1990 on the MIR Space Station (SS). The experiments in SVET SG were resumed in 1995, when an American Gas Exchange Measurement System (GEMS) was added. A three-month wheat experiment was carried out as part of MIR-SHUTTLE'95 program. SVET-2 SG Bulgarian equipment of a new generation with optimised characteristics was developed (financed by NASA). The new SVET-GEMS equipment was launched on board the MIR SS and a successful six-month experiments for growing up of two crops of wheat were conducted in 1996 - 97 as part of MIR-NASA-3 program. The first of these "Greenhouse" experiments (123 days) with the goal to grow wheat through a complete life cycle is described. Nearly 300 heads developed but no seeds were produced. A second crop of wheat was planted and after 42 days the plants were frozen for biochemical investigations. The main environmental parameters during the six-month experiments in SVET (substrate moisture and lighting period) are given. The results and the contribution to BLSS are discussed.     

Current and potential productivity of wheat for a Controlled Environment Life Support System.

The productivity of higher plants is determined by the incident photosynthetic photon flux (PPF) and the efficiency of the following four physiological processes: absorption of PPF by photosynthetic tissue, carbon fixation (photosynthesis), carbon use (respiration), and carbon partitioning (harvest index). These constituent processes are analyzed to determine theoretical and potentially achievable productivity. The effects of optimal environmental and cultural factors on each of these four factors is also analyzed. Results indicate that an increase in the percentage of absorbed photons is responsible for most of the improvement in wheat yields in an optimal controlled environment. Several trials confirm that there is an almost linear increase in wheat yields with increasing PPF. An integrated PPF of 150 mol m-2 d-1 (2.5 times summer sunlight) has produced 60 g m-2 d-1 of grain. Apparently, yield would continue to increase with even higher PPF's. Energy efficiency increased with PPF to about 600 micromoles m-2 s-1, then slowly decreased. We are now seeking to improve efficiency at intermediate PPF levels (1000 micromoles m-2 s-1) before further exploring potential productivity. At intermediate and equal integrated daily PPF levels, photoperiod had little effect on yield per day or energy efficiency. Decreasing temperature from 23 degrees to 17 degrees increased yield per day by 20% but increased the life cycle from 62 to 89 days. We hope to achieve both high productivity and energy efficiency.     

Wheat production in controlled environments.

Our goal is to optimize conditions for maximum yield and quality of wheat to be used in a controlled-environment, life-support system (CELSS) in a Lunar or Martian base or perhaps in a space craft. With yields of 23 to 57 g m-2 d-1 of edible biomass, a minimum size for a CELSS would be between 12 and 30 m2 per person, utilizing about 600 W m-2 of electrical energy for artificial light. Temperature, irradiance, photoperiod, carbon-dioxide levels, humidity, and wind velocity are controlled in state-of-the-art growth chambers. Nutrient solutions (adjusted for wheat) are supplied to the roots via a recirculating system that controls pH by adding HNO3 and controlling the NO3/NH4 ratio in solution. A rock-wool plant support allows direct seeding and densities up to 10,000 plants per meter2. Densities up to 2000 plants m-2 appear to increase seed yield. Biomass production increases almost linearly with increasing irradiance from 400 to 1700 micromoles m-2 s-1 of photosynthetic photon flux (PPF), but the efficiency of light utilization decreases over this range. Photoperiod and temperature both have a profound influence on floral initiation, spikelet formation, stem elongation, and fertilization. High temperatures (25 to 27 degrees C) and long days shorten the life cycle and promote rapid growth, but cooler temperatures (20 degrees C) and shorter days greatly increase seed number per head and thus yield (g m-2). The life cycle is lengthened in these conditions but yield per day (g m-2 d-1) is still increased. We have evaluated about 600 cultivars from around the world and have developed several breeding lines for our controlled conditions. Some of our ultra-dwarf lines (30 to 50 cm tall) look especially promising with high yields and high harvest indices (percent edible biomass).     

Canopy photosynthesis and transpiration in microgravity: gas exchange measurements aboard Mir.

The SVET Greenhouse on-board the Orbital Station Mir was used to measure canopy photosynthesis and transpiration rates for the first time in space. During the Greenhouse IIB experiment on Mir (June-January 1997), carbon and water vapor fluxes from two wheat (cv. Superdwarf) canopies were measured using the US developed Gas Exchange Measurement System (GEMS). Gas analyzers capable of resolving CO2 concentration differences of 5 micromoles mol-1 against a background of 0.9% CO2, are necessary to measure photosynthetic and respiratory rates on Mir. The ability of the GEMS gas analyzers to measure these CO2 concentration differences was determined during extensive ground calibrations. Similarly, the sensitivity of the analyzers to water vapor was sufficient to accurately measure canopy evapotranspiration. Evapotranspiration, which accounted for over 90% of the water added to the root zone, was estimated using gas exchange and used to estimate substrate moisture content. This paper presents canopy photosynthesis and transpiration data during the peak vegetative phase of development in microgravity.     

Preparations for CELSS flight experiments with wheat.

We are planning a short-term experiment with Superdwarf wheat on the U.S. Space Shuttle and a seed-to-seed experiment on the Russian Space Station Mir. The goals of both experiments are to observe effects of microgravity on developmental steps in the life cycle and to measure photosynthesis, respiration, and transpiration by monitoring gas exchange. This requires somewhat different hardware development for the two experiments. Ground-based research aims to understand plant responses to the environments in the space growth chambers that we will use (after some modification): the Plant Growth Unit (PGU) on the shuttle and units called Svet, Svetoblock 2, or Oasis on Mir. Low irradiance levels (100 to 250 micromoles m-2 s-1 at best) pose a particular problem. Water and nutrient supply are also potentially limiting factors, especially in the long-term experiment. Our ground-based studies emphasize responses to low light levels (50 to 400 micromoles m-2 s-1); results show that all developmental steps are delayed by low light compared with plants at 400 micromoles m-2 s-1. We are also testing various rooting substrates for the shuttle experiment. A 1:1:1 mixture of peat:perlite:vermiculite appears to be the best choice.     

"From seed-to-seed" experiment with wheat plants under space-flight conditions.

An important goal with plant experiments in microgravity is to achieve a complete life cycle, the "seed-to-seed experiment." Some Soviet attempts to reach this goal are described, notably an experiment with the tiny mustard, Arabidopsis thaliana, in the Phyton 3 device on Salyut 7. Normal seeds were produced although yields were reduced and development was delayed. Several other experiments have shown abnormalities in plants grown in space. In recent work, plants of wheat (Triticum aestivum) were studied on the ground and then in a preliminary experiment in space. Biometric indices of vegetative space plants were 2 to 2.5 times lower than those of controls, levels of chlorophyll a and b were reduced (no change in the ratio of the two pigments), carotenoids were reduced, there was a serious imbalance in major minerals, and membrane lipids were reduced (no obvious change in lipid patterns). Following the preliminary studies, an attempt was made with the Svetoblock-M growth unit to grow a super-dwarf wheat cultivar through a life cycle. The experiment lasted 167 d on Mir. Growth halted from about day 40 to day 100, when new shoots appeared. Three heads had appeared in the boot (surrounded by leaves) when plants were returned to earth. One head was sterile, but 28 seeds matured on earth, and most of these have since produced normal plants and seeds. In principle, a seed-to-seed experiment with wheat should be successful in microgravity.