Dancing fireballs of microgravity

On the experiments carried out by the astronauts, who lived and died in the cause of science.

A candle flame on Earth is shaped like a teardrop because of the effect of gravity on the rising air molecules. But what would a flame look like in outer space, in the absence of gravity? Ya. B. Zeldovich, the great Russian physicist had predicted in 1944 that in the absence of gravity flames should curl up into fireballs. In one of the experiments done aboard Columbia, flame balls dancing around in space were indeed seen and photographed. The Columbia mission, STS-107, was to gather data on this and other phenomena to find answers to a whole range of questions in physics, chemistry, biology and in commercial technology, especially in relation to spacecraft navigation devices. (STS stands for `Space Transportation System' - the space shuttle - and `107' is the "flight tail number", or the 107th flight of the space shuttle, although the order of missions may have changed after assignment of the flight number.)

Launched on January 16, STS-107 was on a dedicated 16-day scientific mission, carrying a new research module called Spacehab Research Double Module (RDM). The mission was conducted at an altitude of 274 km and an inclination of 39o. It was not a mission to the International Space Station (ISS) to whose ongoing assembly the shuttle launches in recent years had been largely dedicated. It was an autonomous mission with no docking with the ISS, no extra vehicular activity (EVA) and no crew exchange as had become the pattern with most of the recent shuttle launches.

Although the mission was primarily that of the United States, the multi-disciplinary experiments on-board STS-107 involved international participation. The experiments, dedicated to scientific and commercial research under microgravity, included the study of Xenon in its liquid state, sleeping astronauts, kidney stones, ant-colony behaviour and sponge-like rocks.

Mandated by the U.S. Congress and recommended by the U.S. National Research Council (NRC), mission STS-107 was intended to serve as a link between microgravity research conducted aboard the shuttle in the 1980s and 1990s as part of the Spacelab mission and the long-term research programme planned for the ISS when it is completed.

What is microgravity? There is not a single aspect of terrestrial life and events that is not influenced by the Earth's gravity. To understand in full the role played by gravity in our lives and the physical world, scientists would have to study physical, chemical and biological processes in conditions not influenced by gravity. Such a condition obtains in outer space as also in a free-fall in a gravitational field. Microgravity is a term applied to describe a condition of free fall within a gravitational field, in which the weight of an object is reduced greatly compared with its weight at rest on Earth.

As the shuttle is in free-fall around the Earth, a microgravity environment - with one-thousandth to one-millionth of the earth's normal gravitational pull - is established. This microgravity, or `weightless' environment, gives researchers a unique opportunity to study the fundamental states of matter (solids, liquids, and gases) and the forces that affect them. In microgravity, researchers can isolate and control these forces.

From the scientific results of the microgravity experiments, researchers can study the influence of gravity on physical processes as well as other phenomena that are normally masked by the influence of Earth's gravity. In the near absence of gravity, changes to fluid dynamics and combustion can be studied. For example, surface tension becomes more pronounced while convection-related processes are minimised.

The seven-member crew, divided into two teams - Red and Blue - performed round-the-clock research inside the RDM, which was carried in the shuttle's cargo bay. The Spacehab research module is actually a commercial spaceflight module designed and produced by SpaceHab Inc., U.S., the only private enterprise to have developed such a system. The company was originally formed to develop a 5,000-kg pressurised module, derived from the Spacelab of the European Space Agency (ESA), which flew aboard the shuttle between 1983 and 1997. In its original design it was 3 metres long and provided 28.3 cubic metres (cu m) of space to carry out experiments in conditions of microgravity.

The RDM aboard STS-107 is like two single modules brought together with a common bulkhead that lets astronauts work between the two modules. It is twice the original size - 6.1 m long, 4.3 m wide and 3.4 m high - and has the capability to house twice the number of experiments. Outfitted as a state-of-the-art laboratory, the RDM has a pressurised volume of 62.3 cu m and a payload capacity of 4,082 kg. The STS-107 carried about 3,400 kg of research equipment and an additional 363 kg of spacehab-integrated payloads, which were flown in the middle deck of the shuttle. The aft module of the RDM was designed and developed recently to enable a new interface with the orbiter uplink/downlink system, which allows for commanding from the ground and for data to flow real-time down to the experimenters. This was a feature that the Spacehab modules, including double modules of 15 earlier launches did not have.

Under the contract between SpaceHab Inc., and NASA, the company is permitted to sell 12 per cent of the payload capacity to commercial customers on STS-107.

AMONG the experiments aboard Columbia (see table), there were quite a few commercial microgravity experiments. Given the wide array of experiments, STS-107 was the most varied research mission ever planned aboard a shuttle flight and the 16-day research period was the longest ever on a solo shuttle mission. The 16-day mission was made possible by the inclusion of an Extended Duration Orbiter (EDO) kit carrying additional hydrogen and oxygen for use by the Orbiter's fuel-cell system and life-support system.

Besides the primary payload, the RDM, and the experiments located in the middle deck, Columbia's payload bay was equipped with Fast Reaction Experiment Enabling Science, Technology, Applications and Research (FREESTAR) - a hitch-hiker payload managed by the NASA-Goddard Space Flight Centre. It comprised six experiments, one of which included 11 educational experiments involving an ant-colony, spiders, bees and the Medaka fish for school students from Australia, China, Israel, Japan, Liechtenstein and the U.S. The payload also included 13 rats in an animal enclosure.

The seven experimental facilities of the ESA accounted for nearly a quarter of the shuttle's payload. In particular, the Advanced Respiratory Monitoring System (ARMS), in which the Canadian and German space agencies were also collaborating, itself consisted of seven experiments to look for changes in the heart, lungs or metabolism. Of the 30-odd experiments, involving a total of nearly 80 experiments, 25 were located in the RDM, three were on the rooftop, directly exposed to space and six were located in the middle deck. The pressurised environment of the payload was accessible to the crew through a tunnel from the shuttle's middle deck.

Eighteen of the shuttle's payloads were related to or involved biology and biotechnology, using living organisms ranging from viruses, bacteria and fungi to rats and the astronauts themselves. As many as 15 investigations were slated to focus on the effects of microgravity on the basic body systems, including cardiovascular and skeletomuscular functions. A NASA biospecimen-sharing plan would have provided 36 types of tissues to 15 investigators from NASA, ESA, the Canadian Space Agency and the Japanese National Space Development Agency (NASDA). Several studies, for example, were designed to grow pure protein crystals, without structural defects, considered important to enhance drug efficacy and reduce side-effects. A commercially sponsored facility had housed two experiments aboard STS-107 to grow protein crystals. This single commercial payload had carried more than 500 protein samples to be crystallised. Another commercially sponsored NASA payload was intended for investigations in drug delivery technique.

Some experiments were meant to study the mechanisms involved in gene transfer and gene expression. A set of medical experiments (some to be conducted in orbit and some on landing) was intended to throw light on how calcium is added to and removed from bones. Two studies were to look at how viruses spread and are shared within closed environments. A rotating bioreactor, the Biotechnology Demonstration System (BDS), would have gathered data on the three-dimensional growth process of suspended cells under conditions impossible to obtain on Earth.

Astronauts aboard STS-107 had volunteered as test subjects for the sleep study. Each of them wore a watch-sized `actigraph', which is essentially a computerised accelerometer, to track disturbed sleep-wake patterns. Increased wrist activity indicates that the individual is awake. Scientists believe that the study of the sleep-wake patterns would provide leads to minimise sleep disruption on Earth and in space. Rapid day/night cycles due to the occurrence of sunrise and sunset every 90 minutes or so of orbiting the Earth can have a telling effect on the circadian rhythm (biological processes that take 24 hours to complete) of the human system.

One of the physical science payloads was a rugged chamber to conduct studies that would have provided insights into the physics of combustion, soot production and fire-quenching processes for fire suppression technology. Kalpana Chawla was the one who carried out these combustion experiments aboard Columbia. Another experiment involved the compression of granular materials to help understand soil behaviour and improve Earth movements in areas where earthquakes, floods and landslides are common.

Vascular health in space was the concern of experimenters from Texas A&M University who had designed an experiment to measure blood vessel response to the near absence of gravity. Because the human cardiovascular system is well adapted to the constant gravitational pull of the Earth - vessels in the legs, for instance, constrict to prevent blood from clotting in the lower regions - its absence causes physiological dysfunction. The smooth muscles of blood vessels atrophy unless they are challenged by the constant gravitational pull and they lose their capacity to dilate or constrict. Long exposure to gravity-less conditions will weaken the circulatory system.

Microgravity also lowers the head-to-foot blood pressure gradient. By the time astronauts return to Earth they would have been deconditioned for living under gravity and their blood vessels cannot push blood to the brain against gravity. As a result, after a space mission of a few days, most astronauts feel dizzy while standing up and cannot stand upright for even 10 minutes without becoming unconscious - a condition known as orthostatic intolerance.

The rats on board were meant to aid in this study; their hind leg tissues were to be examined for the effects of microgravity. According to researchers, rats respond quickly to microgravity-induced physical change - 16 days of space flight by a rat is equivalent to several months of space mission by a human.

The experiment aimed at using the data on the basic response of rats to pressure changes and chemical signals to evolve methods of treatment to improve the health of the crew and its performance on returning to Earth.

Since the conditions obtaining in old age and microgravity are similar, these studies should help in treating orthostatic intolerance that occurs in old age.

THE dancing flame balls. What are they? Compared to the wide-ranging experiments in the applied sciences, the phenomenon of the dancing flame balls might appear somewhat different. The objective of Paul Ronney of the University of Southern California in his experiment called SOFBALL - Structure of Flame Balls At Low Lewis number - was to study weakly burning flames in hydrogen-oxygen-inert and methane-oxygen-inert mixtures in a configuration called `flame balls'. These had been predicted nearly 60 years ago but were only fleetingly in 1984 by Ronney.

In the absence of gravity, flames in space break up into spheres that are a few millimetres in diameter. They drift about as they move towards regions of fuel after exhausting it in their vicinity. A typical floating flame ball produces 1-2 watts of thermal power as against 50 watts of a candle. Flame balls are "lean" burners and do not need much fuel to keep going. According to Ronney if one understood how these mini balls of fire worked, that knowledge could be used to improve the efficiency of automobile engines. Flame balls are steady, convection-free and spherically symmetric, and occur in fuels with simple chemistry, and represent the simplest possible interaction of chemistry and transport in flames. A total of 39 tests were performed aboard the shuttle with 15 different fuel mixtures, resulting in 55 flame balls of sizes ranging from 2mm to 15 mm.

The experiment produced the weakest flame burned either in space or on the ground, with just 0.5 watts of thermal power. It also produced the leanest flame ever produced in space or on the ground. The leanest hydrogen-air mixture in these tests contained about 8 per cent of the chemically balanced mixture.

By comparison, the lean limit for the gasoline-air mixture in an internal combustion engine is about 70 per cent of the chemically balanced mixture. The importance of Zeldovich's flame balls is in combustion research to develop cleaner, fuel-efficient engines. The shuttle experiment also produced the longest-lived flame that ever burned in space, lasting 81 minutes.

According to both NASA and the ESA, the telemetry data and pictures from these experiments over the two-week period indicate that all the experiments had gone well. Although experiments that required samples to be analysed on the ground have been lost with the shuttle, other experiments have provided a whole lot of data to researchers on the ground.

As the economist Paul Krugman observed in a recent article in The New York Times, the debate on whether human beings are required to do experiments in space and whether they could not be done by robots will go on. The debate is mainly because of the prohibitive costs involved.

Indeed, but for the issue of lives at risk, the same argument can be made for mega science projects on Earth. But, as astrophysicist and space expert Jonathan McDowell of Harvard University puts it, humans will be required as long as methods of science require making mistakes, correcting them, repeating them and tinkering with parameters.