Dark matter experiment is space shuttle's 'last hurrah'
BY STEPHEN CLARK
Posted: August 24, 2010
After a late magnet switch forced NASA to order a six-month deferment of the final planned space shuttle flight, the Kennedy Space Center is preparing to receive a $1.5 billion physics experiment Thursday to seek out the cosmic signature of enigmatic, ubiquitous dark matter.
"If we see a deviation, then this would be new physics - a new contribution," said Roberto Battiston, the experiment's deputy principal investigator. "The first candidate that comes to mind would be dark matter."
Researchers say less than 5 percent of the universe is made of matter - stuff we can see and touch.
"Everything else is something else," Battiston tells Spaceflight Now.
About 23 percent of the universe is made of something called dark matter. Scientists know this because they can't account for all the gravity affecting distant stars and galaxies.
The search for antimatter and the characteristics of cosmic rays themselves are also objectives of the AMS mission.
The payload is ultimately bound for the International Space Station, but researchers must first ship AMS from Switzerland to Florida for final assembly and testing before launch aboard the shuttle Endeavour in February.
The shipment is running a few months late after the AMS science team, led by Samuel Ting of the Massachusetts Institute of Technology, elected to swap the instrument's powerful helium-cooled superconducting magnet for a permanent device with a longer lifetime.
The frigid superfluid helium would gradually boil off in space, leaving the cryogenic magnet useless after two or three years, scientists say, while the permanent magnet could support observations for more than a decade.
"Even though the permanent magnet has a lower field, we can operate an unlimited amount of time," Battiston said. "In the end, this configuration is much more suited for very long exposures at the space station."
The outpost's pending life extension through at least 2020 played into the AMS team's decision, according to Battiston, a professor at the University of Perugia and the National Institute of Nuclear Physics in Italy.
About 600 physicists from 56 institutions in 16 countries are contributing to the AMS project.
The magnet replacement prompted NASA to flip-flop the last two planned shuttle flights and shove Endeavour's AMS delivery mission to February 2011.
Workers switched the magnets in June at CERN, the European Organization for Nuclear Research. The spectrometer was put back together in July and exposed to a high-energy beam of particles last week in a final check of its sensitivity, according to updates on the mission website.
Scientists have since packaged the nearly 16,000-pound platform and other support equipment for loading inside a U.S. Air Force C-5 Galaxy cargo plane Wednesday in Geneva.
A cadre of KSC engineers will take responsibility of the sophisticated experiment for final assembly, testing and launch preparations this fall and early next year.
"To work on a payload that's going to to take a look at the Big Bang theory and take a look at antimatter and dark matter and dark energy...I'm astounded," said Joe Delai, the KSC payload processing manager for Endeavour's STS-134 mission.
The spectrometer will be stored inside the Space Station Processing Facility for a series of functional tests and sensor calibrations, according to Delai.
After a break for the winter holidays, Delai's team will place AMS and an unpressurized logistics carrier inside Endeavour's cargo bay on the launch pad.
"Then we'll do some final closeouts and get ready for the February launch," Delai said.
For many KSC workers, the AMS experiment is a fitting punctuation for the shuttle program.
"Most of the folks that I know working on it look at this as one big last hurrah for the program," said Ralph Fritsche, the AMS element test lead at the space center.
Congress ordered the addition of the STS-134 mission to the shuttle manifest in 2008 to deliver the AMS experiment and spare parts to the space station.
Fritsche said the AMS team in Florida has a rich background, including experience preparing interplanetary probes launched by the space shuttle two decades ago.
"Working on AMS has some of the old interfaces for testing we used to do with the space shuttle, as well as the work that we've become more accustomed to with the station," Fritsche said. "It's a really complex mission for us to work. It takes the best from all the things we've done in the past and combines it into one mission."
For Jack Keifenheim, a mission project engineer, the arrival of AMS will conclude years of preparatory work by scores of officials.
"We've been associated with the AMS payload at KSC for a full decade," Keifenheim said. "It's been very inspirational for us to see the resilience in this payload getting themselves ready."
Some KSC engineers were also around when a similar predecessor experiment flew on the space shuttle in 1998, Keifenheim said.
Once Endeavour arrives at the space station, two robot arms will pull AMS out of the shuttle's payload bay and attach the package to outpost's starboard truss.
The spectrometer's magnetic field will bend incoming energetic particles, shedding light on the properties of the cosmic rays. A suite of detectors will determine the energy, velocity and charge of each particle, Battiston said.
How do scientists know there is something called dark matter?
"There is a violation of Newton's laws in the sense that the stars or the galaxies are behaving as if there is much more mass than the visible matter," Battiston said. "The universe is like a big web of strings and chunks of dark matter to which small visible, shiny galaxies and clusters of galaxies are attached."
Gravity from the unseen material is the best evidence of dark matter's existence so far, but AMS will conduct an indirect search for the fingerprint of dark matter.
A leading candidate for dark matter is called the neutralino, a hypothetical particle predicted by an exotic theory known as supersymmetry, in which standard particles like electrons and quarks have a more massive counterpart.
Some scientists believe the neutralino the lightest of the supersymmetric particles, making it relatively stable until two neutralinos collide in a process called annihilation that produces a burst of radiation.
If neutralino annihilation is occurring, AMS should detect the cosmic rays triggered by the weak collisions and analyze their spectra for tiny fluctuations that would signal the presence of neutralinos.
Astrophysicists believe this is a well-conceived theory, but it's still just that - a theory.
And AMS will put it to the test.
"Ultimately, it is not a guarantee that this exists," Battiston said. "Supersymmetry has not been discovered yet. It is a very nice fascinating theory, but so far, we don't have any evidence of the existence of supersymmetric particles."
While AMS is searching for indirect evidence of dark matter, underground laboratories around the world are seeking the direct detection of the supersymmetric particles. Other facilities like the Large Hadron Collider are attempting to create supersymmetric particles in high-energy collisions, but even its capabilities are limited in the hunt for dark matter, according to Battiston.
"When you look at the indirect process of annihilation in space, you will have a reach to all possible types of particles, even with very large mass," Battiston said.
Tests on the ground could be more constrained, but AMS and LHC studies are both interconnected and complementary.
"This dark matter can be searched for everywhere," Battiston said.
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