November 23, 1997
United States Microgravity Payload-4 - Flight Day 4

continued from France active in microgravity sciences

The fluid program largely comprises experiments aboard Russia's Mir space station.

The materials sciences cover MEPHISTO, which developed under a memorandum of understanding with NASA. Part of the agreement includes having U.S. investigators use the facility in exchange for NASA flying the facility aboard the Space Shuttle.

"As we don't have manned access to space in the national space program," Zappoli explained, "our policy in this field is to build collaborations with agencies that have access to space. Within that framework, we build the facility and the agency pays the flight ticket. MEPHISTO is a good example of that."

While CNES is a major participant in the Ariane launch vehicle program, Ariane is unmanned and offers no capability to return samples from space. Thus, CNES uses the U.S. Space Shuttle or Russia's vehicles for experiments requiring the human support or a return to Earth.

CNES will be active aboard the International Space Station where Zappoli hopes that MEPHISTO will continue its investigations.

"MEPHISTO has produced good science," Zappoli said. "It has been possible to check theories that have never been checked previously because of the physical impossibility to check this on the ground. It has also been possible to understand the origin of the instability of the growth interface [between solid and liquid] on which the structure and thus the properties of the materials strongly depend."

MEPHISTO has made four flights. The agreement with NASA calls for six: "Everybody feels that it's worth continuing that kind of research aboard the space station."

He also looks forward to DECLIC, an investigation of combustion phenomena under water. Fire under water sounds like a contradiction in terms, but it can be done under the right conditions, Zappoli said: around 400 deg. C (752 deg. F) and 370 times sea level pressure. (DECLIC is the acronym, in French, for Apparatus for the Study of Growth in Critical Liquids.)

"In these conditions, water becomes 10,000 times more compressible than a perfect gas," he explained, "and you can burn, completely, at very low temperature, wastes. So this is a very interesting topic."

Because the combustion would be underwater and contained, emissions would be trapped in the water, and a failure would quickly extinguish the flames. Studying this phenomenon in microgravity will help define the optimum conditions for using this process on Earth.

Keeping things as still as possible is the objective of a different experiment, PHARAO, the Atomic Clock Project by Atom Cooling in Orbit. Advanced electronic devices use the vibration of atoms to keep time. Their accuracy is limited by the width of the radio pulse given off by the atoms.

PHARAO, Zappoli explained, will use lasers to trap and contain atoms in a vacuum chamber. This technique is used on Earth to cool atoms in some physics experiments. The atoms eventually settle to the bottom, but could be positioned and kept cold in microgravity.

Collisions between atoms broadens their natural radio emissions. Keeping them cold will make the emissions much sharper, Zappoli said, like the difference between an electronic beep and the gradual click of a mechanical clock.

"This would be very useful for tracking, for localization by navigational satellites and for deep space navigation," he said. Navigation by satellite works by measuring the differences between time broadcast by clocks at different locations.

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Author: Dave Dooling
Curator: Linda Porter
NASA Official: Gregory S. Wilson