STS-107 CM-2 / SOFBALL science summary

Paul D. Ronney, Principal Investigator

University of Southern California


This summary was written before the loss of Columbia.


Click here to read about my perspective on the loss of Columbia and its crew


Click on a link below to view crew tribute produced by NASA-Glenn: 

Low resolution (33 MB)      High resolution (72 MB)


1 flame ball moving in corkscrew pattern

Another corkscrew test

2 large flame balls

3 flame balls

9-ball test

(Camera 1 view)

Only first 15 minutes of test shown; we won’t know which one is Kelly until post-mission.

9-ball test

(Camera 2 view)

Only first 15 minutes of test shown; we won’t know which one is Kelly until post-mission.


Click on image to view movie




The objective of the SOFBALL experiment was to study weakly burning flames in hydrogen-oxygen-inert and methane-oxygen-inert mixtures in a configuration called “flame balls” that were originally predicted by the Russian physicist Ya. B. Zeldovich in 1944 but not seen experimentally until 1984 in short-duration drop tower experiments conducted by Prof. Ronney.  Because flame balls are steady, convection-free, spherically symmetric and occur in fuels with simple chemistry, they represent the simplest possible interaction of chemistry and transport in flames.  In this sense flame balls bear a similar relationship to combustion research that the fruit fly does to genetics research.


Summary of results


A total of 39 tests were performed in 15 different mixtures, resulting in a total of 55 flame balls, of which 33 were named by the crew.  The total burn time for all flames was 6 1/4 hours.  Since flame balls are extremely sensitive to gravitational acceleration, all tests were conducted during orbiter free drift periods.  Microgravity levels were measured using OARE.  The quality of the microgravity was found to be excellent (average accelerations less than 1 micro-g for most tests).


Among the accomplishments of the experiment were



Several totally new results were found, for example


The data obtained during the mission will keep combustion scientists busy for many years to come and will help lead to the development of cleaner, more fuel-efficient engines as well as improved methods for spacecraft fire safety assurance.


Parting notes


  1. When the Gods want to punish you they answer your prayers.  It will take me years to analyze all of the data obtained on STS-107.
  2. Flame balls live by the old stage performer motto – “leave ‘em wanting more…”  Several tests were expected to last for more than an hour, but (until the last test) none lasted more than 25 minutes because of the mysterious drift.  The very last test produced 9 flame balls initially (below right) (a large number of balls was expected from this test) that extinguished one by one until only one flame ball, named “Kelly” by the crew, remained.  Unexpectedly, Kelly survived an astounding 81 minutes, seemingly immune to drift, until the test was extinguished due to operational reasons (it was still burning at the time). 
  3. Kelly could be nicknamed “Magellan,” who also set out to circumnavigate the globe but was extinguished before completing the journey.  (It takes 90 minutes to orbit the earth).




Radiometer signal showing flame ball oscillations

Image of flame balls in a hydrogen-oxygen-sulfur hexafluoride mixture at 3 atmospheres pressure.  Click here to see video.