By Susan Killenberg McGinn
November 30, 2001
Around Antarctica in 30 days.
 Members of the TIGER mission in Antarctica unload the 1,200-lb. instrument that was built by faculty, staff and students to measure the elemental abundances of galactic cosmic rays. The instrument will be attached to a high-altitude balloon and launched sometime in December. |
That's what University cosmic ray researchers are hoping their experiment aboard a high-altitude balloon will be able to accomplish when it launches from McMurdo Station in Antarctica. The launch ready date is Dec. 5.
The Trans-Iron Galactic Element Recorder, better known as TIGER, is a balloon-borne instrument built by faculty, staff and students in the cosmic ray astrophysics group in the McDonnell Center for the Space Sciences and the Department of Physics in Arts & Sciences.
TIGER, which is about half the size of a pingpong table, will be hooked up to an unmanned helium balloon about the size of a football field and sent some 125,000 feet into the atmosphere. There it will measure the elemental abundances of galactic cosmic rays (GCRs), high-energy particles that travel very close to the speed of light and originate from outside our solar system. TIGER will measure the abundance in the GCRs of each element from sulfur (atomic number, Z=16) through zirconium (Z=40).
Astrophysicists are particularly interested in GCRs because they are one of only two types of matter from outside the solar system that can be directly sampled. (The other type is interstellar dust grains from meteorites, the study of which was pioneered in the McDonnell Center by Robert M. Walker, the McDonnell Professor in physics, and his colleagues.)
The study of GCRs will lead to a better understanding of their origin and the explosive processes in our galaxy that are responsible for giving the nuclei such enormous energy.
The University crew in Antarctica preparing TIGER for the launch, as well as those working on the project at home in Compton Laboratory, have their fingers crossed that TIGER's ride will be the longest high-altitude scientific balloon flight yet.
"The longer it's up there, the more particles we can collect and identify," said W. Robert Binns, Ph.D., research professor of physics and principal investigator on the project. "We plan to measure for the first time all elemental abundances between charge 30, which is zinc, and charge 40, which is zirconium.
"We really want to measure nuclei all the way up to uranium (Z=92) and beyond. But the higher the atomic number, the more rare the elements are. To collect much above atomic number 40, we need a bigger instrument and longer time aloft. TIGER is a prototype of an instrument we are proposing for a three-year mission on a spacecraft in Earth orbit."
Antarctica in the summer is the ideal launch location because the sun never sets, therefore the balloon doesn't have the nighttime cooling that causes it to drop in altitude, requiring daily release of ballast to bring it back up. The balloon can only carry enough ballast for one or two nights, not nearly enough for a 30-day flight.
And the Antarctic high-altitude summer winds set up a vortex around the pole that will carry the balloon in a circle, coming back around to the launch area some 10 to 15 days later. While high-altitude balloons have launched from the Antarctic base before and made the loop, none have completed the trip twice.
Balloon flights are not new to TIGER. In September 1997, TIGER launched from Fort Sumner, N.M., and landed 23 hours later in a Kansas cornfield, after floating at altitudes between 115,000 and 133,000 feet.
That mission, which led to a doctoral thesis for former physics graduate student Stephanie Sposato, was considered a great success.
"While you can't collect enough particles of the very high atomic number during such a short flight, we were able to demonstrate that our instrument has the kind of charge resolution and other characteristics that we need to measure the heavier nuclei," said Martin H. Israel, Ph.D., professor of physics and a co-investigator on TIGER.
Based on the collecting power that TIGER demonstrated on the 1997 flight, NASA selected the instrument to be the payload on its first Ultra-Long Duration Balloon (ULDB) flight slated for about this time. Unfortunately, two ULDB test balloons have failed, resulting in a two-year delay for the approximately 100-day mission.
So the hoped-for two revolutions around the Antarctic could be considered a consolation prize from NASA, which conducts the balloon launches through its National Scientific Balloon Facility (NSBF).
In addition to the Washington University cosmic ray group, researchers from the Goddard Space Flight Center in Greenbelt, Md., the California Institute of Technology in Pasadena, Calif., and the University of Minnesota are collaborating on TIGER's flight.
No one is more anxious for TIGER to complete two circumpolar flights than Jason Link, a physics graduate student whose doctoral thesis will be based on this mission. He has been in Antarctica since Oct. 31, preparing TIGER for launch.
"To accomplish our primary scientific objective --measuring the elemental abundance of galactic cosmic rays with a Z between 30 and 40 --we need to be aloft for at least 30 days," said Link, who has worked on TIGER for the past four years. "The individual elemental abundances of bromine (Z=35), rubidium (Z=37) and yttrium (Z=39) have never been measured before. TIGER will be the first instrument to provide such a measurement.
"By measuring these elements, we hope to be able to better understand the origin of the material that is accelerated to become cosmic rays."
Others from the cosmic ray group who have joined Link in Antarctica are Binns; John Epstein, mechanical engineer; Paul Dowkontt, electrical engineer; Garry Simburger, electrical technician; Dana Braun, mechanical technician; and Lauren Scott, a physics graduate student.
Once TIGER is airborne, among those who will monitor the data as it is transmitted by radio telemetry to Compton Laboratory are Israel; Jay Cummings, senior research associate; and Martin Olevitch, computer programmer/analyst.
TIGER's traveling days won't be over with this mission. If all goes as planned, TIGER will have a smooth landing, permitting its recovery by Epstein and a member of the NSBF crew, and it will be ready to fly again in two years for another 30-day Antarctic whirl.
"If TIGER is successful, it will give NASA all the more confidence to fund us for a premier spacecraft mission that we hope to put into orbit in 2005," Binns said. "We'll have an instrument four times larger with three years' exposure on the spacecraft. With a larger instrument and longer exposure, we should be able to extend our reach to the heaviest elements in the periodic table."
For more information on the TIGER flight, log onto cosray2. wustl.edu/tiger.
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