Volume 2, Issue 15 October 2005
Astrophysics Via Helium Balloon
On June 1, UC Berkeley astrophysicist Steve Boggs and a team of graduate students and postdocs gazed into the sky as three years of research vanished into thin air. They were watching a prototype telescope they built ascend into the atmosphere on its maiden voyage. It took a long time before the craft carrying their instrument was out of sight. That's because the telescope wasn't stowed inside a rocket, but rather hanging in the canopy of a massive unmanned helium balloon slowly ascending to the edge of space.
Steven Boggs polishes a thermal shield for the Nuclear Compton Telescope.
"Launching a small satellite carrying a telescope into orbit costs around $100 million," says Boggs, an assistant professor in the Department of Physics. "But for about $1 million, a balloon can get you above 99 percent of the atmosphere. So balloon flights are great for testing out new instruments that may eventually go up in space."
The telescope was built at UC Berkeley's Space Sciences Laboratory where Boggs specializes in gamma ray astronomy. The rays are of such high energy that they can travel incredibly long distances to give us glimpses of phenomena in the deepest regions of space.
"Gamma ray astrophysics is the study of some of the most exotic things our universe has to offer, like matter falling into the edge of a black hole or the surface of neutron stars," Boggs says.
For example, late last year the Reuven Ramaty High-Energy Solar Spectroscopic Imager (RHESSI), a satellite launched by UC Berkeley and NASA in 2002, captured the brightest gamma ray explosion ever observed. The giant gamma ray that burst from the other side of our galaxy was powerful enough to affect the Earth's atmosphere.
The Nuclear Compton Telescope hangs from a crane awaiting attachment to the balloon at the Fort Sumner launch site.
"Gamma ray bursts are explosions that, in a fraction of a second emit, almost the entire energy of the sun in gamma rays," says Boggs, a collaborator on the RHESSI project.
The telescopes that Boggs and his team build and use are odd in that they have no optics. That's because the gamma rays are so high energy that they pass right through the lenses or mirrors of traditional telescopes.
As a result, gamma ray telescopes must gather data more indirectly. The prototype Nuclear Compton Telescope that flew aboard the balloon employs a physics principle called Compton Scattering. The instrument's detectors calculate the arrival direction and energy of the incoming gamma photons. This particular telescope is designed, Boggs says, to "witness the fires of creation."
The NASA balloon is inflated in preparation for launch.
In the earliest moments of the universe, the Big Bang produced helium, hydrogen, and small amounts of other elements. The rest of what surrounds us was created in the meantime, Boggs explains. One of the best ways to understand how these elements are produced is to examine their radioactive decay, he says. Frequently, the instability of an element's nucleus causes it to decay, resulting in another element. The Nuclear Compton Telescope seeks out particular gamma rays that correspond to specific radioactive decays.
"That way, we know that these atoms were just created on the scale of hundreds to millions of years ago," Boggs says. "By studying them, we can better understand how elements are forming today."
Even on its first balloon trip, the Nuclear Compton Telescope likely gathered valuable scientific data. Launched in collaboration with NASA, the balloon the size of a football field carried the telescope in a canopy about as bulky as a small truck. The instrument itself is the size of a shoebox but the support electronics filled the canopy to capacity. After departing at sunrise from Fort Sumner in eastern New Mexico, the balloon spent the entire afternoon at altitudes of 35 to 40 kilometers. It finally touched down at sunset in southwestern New Mexico right in the middle of an outdoor art installation called the Lightning Field.
NASA illustration from 2003 depicting the RHESSI satellite capturing a gamma-ray burst flashing just off the limb of the sun, measuring for the first time the polarization of these gamma rays.
The flight was a success, Boggs says, save for a few dents suffered on landing. In the months since, they've begun to analyze the scientific data collected during the flight while simultaneously preparing the instrument for a two or three week flight in 2007, when they'll launch from Australia and hopefully fly the instrument around the world.
"You really have to be in the southern hemisphere to see the bulk of our galaxy," Boggs says.
While this prototype contained just two gamma ray detectors, the next generation will carry twelve. Once the advanced model proves itself, Boggs hopes to work with NASA or a foreign collaborator to launch the instrument into orbit on a satellite.
"These instruments enable us to study matter in very extreme environments that are far more exotic than what we can create in laboratories on Earth," Boggs says.