Does gravity play a role in your chemistry? A call for ideas.
Have you ever wished that a solid you were working with stayed in suspension instead of settling to the bottom of your reaction vessel? Do changes in density of the fluids you are working with affect your results? Does convection or buoyancy play a role in the efficiency of your reactions? These are just examples of questions I would like the Canadian chemistry community to consider while reading this article.
We tend to think of gravity as an unavoidable, ever-present force when in fact, we can cancel out its effects. Doing experiments and carrying out sample processing in the apparent absence of gravity is more accessible to the Canadian researcher than ever, thanks to the efforts of the Canadian Space Agency. I feel, however, that this is a resource which is under-used by the chemists and biochemists of Canada and this community may want to consider the possibilities and implications of doing more chemistry in microgravity.
Anywhere near the Earth, including in orbit, we cannot actually escape its gravitational attraction. However, when we create a free-falling environment, where an object falls at the same acceleration as the acceleration due to gravity, the effects due to gravity can be virtually eliminated.
Drop towers, usually built in mine shafts or in tall above-ground towers, allow samples to be dropped under controlled conditions. The dropped equipment can often be monitored by telemetry or on-board recording of data and the drop shaft is usually evacuated to minimize drag due to air resistance. In fact, some drop capsules have an on-board propulsion system to compensate for drag. Drop towers usually deliver microgravity conditions on the order of 5 seconds or less.
Some aircraft are capable of parabolic profile flight. In this case, an aircraft will fly on a roller-coaster style flight path, entering into a ballistic trajectory at the top of the parabola and into the dive. The engines are used to compensate for drag. This results in all contents of the aircraft (crew and experiments) to experience microgravity for periods of 20 to 25 seconds at a time, with a typical 2-hour flight carrying out 40 such parabolas. This aircraft has been nicknamed "the vomit comet" for obvious reasons, once you've had a flight.
Sounding rockets launch payloads high above the atmosphere where drag caused by air pressure is less significant. The payload falls toward the Earth after deployment from the launcher and microgravity conditions can be generated for periods of time on the order of 5 minutes. The experiment is monitored by on-board recording or telemetry, usually followed by retrieval of the payload.
The US Space Shuttle, the Russian Space Station Mir, and the future International Space Station provide microgravity conditions for periods of days to months. Experiments can be in the form of automated setups in canisters in the payload bay of the Space Shuttle or some experiments may need crew interaction for extended periods of time. All of these microgravity platforms are accessible to the Canadian Space Agency through its ties to the microgravity community in Canada and around the world.
The Microgravity Sciences Program has been responsible for several major space missions in the past two years. In May, 1996, the US Space Shuttle Endeavour on mission STS-77 carried Canadian mission specialist Marc Garneau into orbit with a major payload called the Commercial Float Zone Furnace, CFZF. This was a joint project between Canada, the United States, and Germany which studied containerless processing of semiconductor materials using the float zone technique. The QUELD II (Queen's University Experiment in Liquid Diffusion) Microgravity Furnace provides an experimental method of measuring the diffusion coefficients and solidification properties in material samples (for example, ternary Cd-In-Sn systems) under microgravity conditions. This experiment is presently on Mir.
STS-85 in August, 1997 saw Canadian payload specialist Bjarni Tryggvason flying on the US Space Shuttle Discovery with the Microgravity Vibration Isolation Mount (MIM) which helps to isolate experiments from the vibrations associated with perturbations while on orbit such as crew activity and thruster firings. On MIM, a fluid physics experiment called FLEX was performed studying five different aspects of fluid physics from Brownian motion to the study of liquid/gas interfaces.
Presently flying on the Mir space station is CAPE, the Canadian Protein Crystallisation Experiment. This is a large project involving 15 different researchers from across Canada, including some experiments proposed and being flown by students. CAPE carries on the order of 700 different samples to be crystallised on orbit and returned to Earth for analysis.
There is no doubt that carrying out experiments under these conditions is much more involved than on a lab bench. In fact, cost and schedule implications are often very limiting. Experiments can take years of painstaking qualification and safety certification before they ever fly. However, the objective of this article is to get the Canadian chemist and biochemist to consider the effect of gravity on their chemistry and to possibly generate new ideas and new avenues of research.
The Canadian Space Agency has issued a Request for Proposals to carry out ground-based research in microgravity sciences. This is a good opportunity for the Canadian chemistry community to get involved and propose new ideas and applications. The deadline for responses to the RFP is December 1.
For more information on our program, please consult our web site at http://www.space.gc.ca. I can be reached by e-mail at Alain.Berinstain@space.gc.ca.
Alain Berinstain, MCIC is a Project Manager in the Microgravity Sciences Program at the Canadian Space Agency in St. Hubert, QC. He holds a PhD in physical organic chemistry from the University of Ottawa and a Master of Space Studies from the International Space University in Strasbourg, France.
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|Publication:||Canadian Chemical News|
|Date:||Nov 1, 1997|
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