Science Correspondent

Expert says materials processing in space can be a promising area of research

Till date, 44 microgravity experiments in 42 missions have been conducted

Self-organisation of hydroxyapatite found to be better in space

UDHAGAMANDALAM: The first results from the microgravity experiments on board the space capsule that was successfully launched and recovered (after its re-entry into the atmosphere) last year were presented at the ongoing 15th National Space Science Symposium (NSSS-2008) on Wednesday.

The results from the two experiments that were carried out in the maiden flight are highly encouraging — and even somewhat unexpected — said Kamanio Chattopadhyay of the Indian Institute of Science (IISc), the National Coordinator of the Indian Microgravity Programme. The success of these experiments seems to suggest that materials processing in space, in particular biomaterials, could be a promising area to be pursued in the future microgravity platforms.

Microgravity refers to the condition of “weightlessness” that one obtains in a spacecraft, which, while in orbit around the Earth, is in a state of “free fall” under Earth’s gravity. Both the spacecraft and the objects in it are experiencing the same amount of gravitational pull of the Earth with no counter reaction force (due to, say, an anchored floor) that gives the feeling of “weight” to the objects. Till date, 44 microgravity experiments in 42 missions by 15 countries and the European Space Agency (ESA) have been conducted.

Unique in execution

According to Prof. Chattopadhyay, the Indian experiments were unique in their conceptualisation and execution. As a consequence, the results are absolutely new in the field of materials processing in space, he added.

Called the Space capsule Recovery Experiment (SRE-1), ISRO’s first microgravity platform was launched aboard the PSLV-C7 on January 10, 2007, in a circular polar orbit at an altitude of 635 km and was recovered after its splashdown 150 km east of Sriharikota in the Bay of Bengal on January 22, 2007. SRE-1 was launched along with three other satellites: ISRO’s Cartosat-1, LAPAN-TUBSAT of Indonesia and PEHUENSAT of Argentina.

Experiments

The two experiments on this scientific mission were:

Biomimetic synthesis of the particles of the inorganic chemical hydroxyapatite (a calcium-nitrate based substance). (Biomimetics refers to mimicking biological systems in nature for designing engineering systems and applications in modern technology.)

Growth of magnesium-zing-gallium (Mg-Zn-Ga) quasicrystals in an isothermal heating furnace (IHF) through a ‘peritectic’ reaction. (Quasicrystals have the unusual five-fold symmetry, like the icosahedral patches on the surface of a traditional leather football. A ‘peritectic’ solution is a mixture of substances in different phases, like a mixture of a solid and a liquid, and the mixture has the lowest melting point. During crystallisation, the two phases crystallise simultaneously from the molten solution.)

Bones and hard tissues in mammals, in particular the enamel of teeth, are made predominantly of hydroxyapatite (HAP), whose chemical formula is Ca10 (PO4)6(OH)2. The self-assembly of HAP rods in the teeth, for example, occurs in a matrix of the body protein collagen. Scientists have tried to grow this in large molecules in the laboratory (under normal gravity conditions) but have been unsuccessful, said Prof. Mukhopadhyay. The idea was to see if this biological process could be reproduced in the microgravity environment of a spacecraft. Instead of a collagen matrix, for making HAP in space, the scientists brought the appropriate chemicals to combine in a gel matrix of the polymer polyvinyl acetate (PVA), which resulted in the successful self-assembly of the molecules into the typical rod-like structures. “Initially I was sceptical, but contrary to intuition the self-organisation of HAP in the presence of large molecules is better in space,” Prof. Chattopadhyay said.

Cause rock formation

Speaking about the second experiment, Prof. Chattopadhyay said, “It is peritectic reactions that result in the formation of rocks, materials in asteroids etc. But in the presence of Earth’s gravity, these reactions rarely go to completion because sedimentation of one of the substances due to gravity cannot be prevented.” On the Earth the crystallisation of an Mg-Zn-Ga peritectic mixture was found to result in a mixture of structures with Mg-Zn crystals, Mg-Zn quasi crystals and the original peritectic solution coexisting. “The peritectic reaction could not be completed,” he observed.

Increase in crystal spacing

“But in space,” Prof. Chattopadhyay said, “the pathways of solidification seem to be different. The significant thing here is the crystallization of gallium from the solution. Electron microscopic images have clearly revealed the formation of magnesium-zinc-gallium quasicrystals. The morphology of the crystals is also different in space where the crystal spacing shows an increase.” According to him, only a French group studying aluminium-nickel peritectic mixture had earlier observed such an increase in crystal spacing while others had found a decrease. The reasons for this need to be studied, he said.

Next platform in 2009?

The next microgravity platform SRE-2 may be flown next year, Prof. Chattopadhyay said. This is likely to be bigger than the SRE-1 platform to include slightly scaled-up versions of the earlier experiments as well a new biomaterials experiment in collaboration with the Japanese Aerospace Exploration Agency (JAXA). Scientists of JAXA are currently in India to discuss the possibility of such a payload on SRE-2.

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