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Sunday, July 13, 1997, 7 a.m. CDT
STS-94 Mission Science Report # 20s

During the past 24 hours, researchers aboard Columbia have gained yet a better understanding of what makes certain types of heat transfer devices fail in space. They also pushed the envelope of knowledge of combustion by setting a fire at the lowest atmospheric pressure yet this mission and “giving birth to twin droplets of flame in an unplanned experiment. Meanwhile, researchers in the Spacelab Mission Operations Control Center set an all-time record for the number of commands issued to experiments aboard a Spacelab mission.

At 5:25 p.m. CDT Saturday night, the 25,838th science command was sent to the shuttle breaking a 1994 record and demonstrating the high pace of research activities aboard Columbia.

Saturday morning, Payload Specialist Dr. Gregory Linteris resumed work on the Droplet Combustion Experiment, burning a drop of heptane fuel at one-quarter of the atmospheric pressure on Earth. It left scientists ecstatic.

“It was a superior burn,” said Dr. Fred Dryer of Princeton University in Princeton, N.J.. “This is the first time we’ve been successful with a quarter-atmosphere burn. It is the most difficult condition (to achieve a burn) -- the lowest pressure of this kind that we’ve been trying to obtain science for. It’s always hard to do science at extremities. It was very gratifying.”

So successful was the experiment run that two additional tests were dropped from the schedule. “The one run defined all the science we needed,” said Dryer. “Additional experiments this morning just are not necessary. We will conserve fuel for future runs.”

The Droplet Combustion Experiment is providing researchers with fundamental knowledge of the burning process and may provide a method for verifying which complex, chemical model accurately describes the process. It may also lead to cleaner and safer ways to burn fuels.

Later Saturday, Mission Specialist Janice Voss again set up the Droplet Combustion Experiment for three more runs by igniting a 3-millimeter fuel droplet in the chamber filled with normal air.

“On the ground, there have been a lot of studies on heptane. But all have been less than 2 millimeters in diameter,” said the study’s lead investigator, Dr. Forman Williams of the University of California at San Diego. “This is the first complete burn of a 3-millimeter diameter heptane droplet.” Forman was also excited “because in the atmosphere of normal air, we were able to observe a fuel droplet that burns for a longer period of time.” Additionally, as a fuel droplet burned in a spherical shape, the heat dissipated outward, and actually extinguished the flame before all the fuel vapor was completely burned away. This gave researchers a very pure look at the combustion process.

Also Saturday, Mission Specialist Dr. Donald Thomas began what would be eight hours of highly successful combustion tests in the Middeck Glovebox -- a facility that allows the crew to handle, transfer and manipulate experiment hardware and materials not approved for use in the open Spacelab. The Spacelab crew has now performed more than 100 tests runs in the Glovebox -- twice as many as expected.

In a novel twist to this experiment, scientists decided to run a test using two droplets instead of one. This provided a bonus to researchers as they observed the interaction of the droplets. Dr. Williams, the experiment’s principal investigator, called the view of the two droplets “the most beautiful set of twins I’ve ever seen.” Information from the study is expected to help improve theoretical models of combustion.

Saturday evening and Sunday morning, Mission Specialist Voss set up the flame ball -- or Structure of Flame Balls at Low Lewis-number -- experiment for another series of test in the Combustion Module. She used a fuel mixture of hydrogen, oxygen and sulfur hexafluoride at one atmospheric pressure. Voss sparked the fuel mixture in the test chamber, producing a burning ball of flame. Upon a reburn attempt, another flame ball was ignited.

The flame ball study, led by Dr. Paul Ronney of the University of Southern California in Los Angeles, is designed to show under what conditions a stable flame ball can exist and if heat loss is responsible for the stabilization of the flame ball during burning. The experiment also examines how various mixture properties, such as fuel/oxidizer concentrations and temperature, affect the flame-ball's stability and existence.

Ronney said that from this experiment, “we can learn the burning limits of fuel mixtures. It gives us an idea of just how lean a fuel can be -- and still burn.” He said the results of this experiment may lead to leaner-burning fuel on Earth. “That would mean better gas mileage and less auto emissions,” said Ronney. Other benefits include improved fire safety for future spacecraft.

Saturday afternoon, Payload Specialist Dr. Roger Crouch set up the Capillary-driven Heat Transfer Device in the Middeck Glovebox. The study examines the device’s ability to transfer heat away from a particular location. In the future, these devices may be used to transfer heat from electrical equipment to radiators on spacecraft. The benefits of these systems are that they weigh less than conventional units because they operate on evaporation and condensation, and are more economical because they do not require power. This study has already provided insight into how these devices work and is offering explanations as to why they occasionally fail in spacecraft applications.

The experiment’s lead investigator, Dr. Kevin Hallinan of the University of Dayton, Ohio, said, “As a result of today’s tests, we’ve been able to characterize boundaries of what we call unstable operations which accelerates this transition to this failed -- or disrupted state.”

“We’ve seen the same failure mechanism that we’ve also seen previously. But today we were able to characterize the conditions that cause a violent instability in the evaporator portion of the device. This instability immediately causes the entire device to fail. So we now effectively understand another ‘failure mechanism’ and are closer to our goal of understanding why the Capillary-driven Heat Transfer devices have failed in space yet succeed in 1-G (on the ground). We are confident new designs can be rendered that will work.”

Coming up later today, Payload Specialist Dr. Gregory Linteris will continue combustion test runs -- observing the structure of flame balls -- as other members of Columbia’s crew start the Coarsening in Solid-Liquid Mixtures experiment. The goal of this investigation is to examine the solidification process for the development of stronger alloys and new manufacturing processes.

The next scheduled Public Affairs status report will be issued at approximately 6 a.m., July 14.


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