Fri, 10 Dec 2010 10:50 UTC
For decades, the U.S. Department of Defense has operated classified spacecraft loaded with high-tech gear to carry out a range of reconnaissance duties. But the satellites have also spotted the high-altitude explosions of natural fireballs that routinely dive into the Earth's atmosphere, and talks are under way to offer scientists access to that data.
In the past, the data on the fireballs, caused by small asteroids called bolides, was shared with the near-Earth object (NEO) science community, information deemed ideal for understanding the size of small NEOs and the hazard they pose.
From space scientists, they stress that such data sharing is also important for validating airburst simulations, characterizing the physical properties of small NEOs - such as their strength - and assisting in the recovery of meteorites.
On the other hand, the message from U.S. military and intelligence officials is that they worry about release of sensitive data gleaned by secret satellites.
'The bolide thing'
A delicate dance is under way between the U.S. military and scientists to put in place a partnership focused on fireballs - but there are a number of thorny issues on the table.
"We are working it," said Robert Rego, now chief of Space and Cyberspace Operational Integration at Peterson Air Force Base in Colorado Springs, home of the Air Force Space Command.
"I would say that we're working it, not from the perspective of 'no and how we can't do it'...but from 'yes, and how we can do it' and make it beneficial while still protecting a space capability," Rego told SPACE.com in an exclusive interview.
A former brigadier general, Rego transitioned last October to a U.S. Air Force civilian position. Since that time, "we've re-energized what we're thinking here," Rego said, noting that it's still referred to "as the bolide thing."
Rego said that from the sensor development community perspective, "there's a wide variety of folks that play in that ... some that we can talk about, some that we can't."
The thinking today centers on figuring out the what, in terms of data release, Rego said. "That's been a tad contentious," he said, "but we think we've got a data set now that's valuable, as well as agreed upon in terms of releasability."
Following an observed incoming bolide by a space-based asset, date and time of the event, location, altitude, the estimated velocity of the object, as well as the approximate total radiated energy would be made available, Rego said.
Furthermore, an assessment of the type of event - whether or not the activity is based upon a comet or an asteroid - can be provided, he said.
"We think that [these factors] give a good balance between what's valuable for the researchers and what protects the capability of our space systems," Rego added. This policy would be put in place, he said, from a U.S. Air Force perspective.
Fireball data dictionary
But still to be settled is the how the military will distribute the data.
"Sort of who does it, how do we do it?" Rego pointed out. "How do you make data available for a variety of users, for a variety of reasons? That data exposure is something that we're wrestling with here."
Rego said that a "data dictionary" - agreement on terms, methods, the meaning of words - is also part of the dialogue on data exposure.
In looking for models to push forward on bolide data-sharing with scientists, Rego pointed to the government's Space Situational Awareness Sharing Program. It provides tracking data on the whereabouts of space objects with various entities - including commercial space players - to help prevent satellite collisions and from trashing the Earth's orbit even more.
Another possible model, Rego said, is the Civil Applications Committee (CAC), an interagency committee that coordinates and oversees the federal use of classified collections.
In recent years, CAC activities have expanded beyond traditional mapping applications to a broad range of environmental and remote sensing applications central to federal agency missions.
Examples include monitoring volcanoes; detecting wildland fires; coordinating emergency response to natural disasters, such as hurricanes, earthquakes, and floods; monitoring ecosystems, and mapping wetlands.
"So we're looking there," Rego said. "I'd be the last guy on the planet to put a clock on this thing," admitting that he was "dramatically optimistic" when interviewed last year for SPACE.com.
Migration to newer systems
Yet another piece of Rego's on-going look into bolide data-sharing is resources.
"This would be a new effort," he said, although not likely something that breaks the bank.
"But it will take an amount of resources, either dollars or people to set it up and make sure that the outcome is not unduly biased by a poor set-up," Rego said.
Given that space-based assets used to support scientific bolide investigations are aging, is migration of this data sharing to newer space systems in the cards?
"The fundamental answer is yes, Rego said. "We don't anticipate putting this effort in place and then have it dwindle to nothing as vehicles age out."
Study recommends NEO data dumps
Mark Boslough, a physicist at Sandia National Laboratories in Albuquerque, N. M., served on the mitigation panel of a National Research Council committee that reviewed NEO surveys and hazard mitigation strategies.
The NRC report, called "Defending Planet Earth: Near-Earth Object Surveys and Hazard Mitigation Strategies," was issued last January. It outlined options NASA could follow to detect more NEOs, asteroids and comets that could pose a hazard if they cross Earth's orbit.
That NRC assessment made a number of high-level recommendations.
"Data from NEO airburst events observed by the U.S. Department of Defense satellites should be made available to the scientific community to allow it to improve understanding of the NEO hazards to Earth," the report stated.
Boslough said that being a member of the scientific and national security communities, he felt he could offer both perspectives, as he views them.
Impact risk to Earth
"There are legitimate national security reasons for some restrictions on data release, but these data are extremely valuable to the scientific community in our effort to understand and quantify the impact risk and to develop the most effective mitigation plan against airbursts," Boslough told SPACE.com.
Boslough said that another airburst like the 1908 Tunguska event is, by far, the most likely threat from asteroids in our lifetimes.
"Satellite-based observations allow us to better understand the physics and damage potential of dangerous airbursts, and to better estimate their likelihood and risk," Boslough said. "Even if the raw data remain classified at a higher level than scientists want, I hope that there will be a mechanism that will allow us to release other information based on the classified data."
Longer observation times will provide more statistics, Boslough added, allowing researchers to refine the power-law size distribution - which by itself is immensely useful for both risk assessment and basic science, he said, but doesn't necessarily require open release of the raw data for every bolide detection.
"It is always better for science when data are openly available for independent scrutiny, but sometimes a balance must be struck between openness and security. I would like to see the balance account for the scientific value of the data," Boslough concluded.
Unmatched data source
Bolide experts also covet the sheer wealth of data on NEO airbursts that are routinely recorded by military assets in orbit.
"From past experience working with U.S. government satellite data, the information provided is unmatched by any other data source and allows scientific analyses which are otherwise impossible," said Peter Brown, a research scientist specializing in meteors, meteorites, meteoroids and asteroids at the University of Western Ontario in London, Ontario, Canada.
Brown is also a core faculty member of the university's meteor physics group within the department of physics and astronomy. On the group's website there's an archive of past fireball measurements with sources to the U.S. Department of Defense, the U.S. Air Force and Sandia National Laboratories - data derived from optical and infrared sensors aboard U.S. satellites.
But the list ends with a U.S. report of a bolide detonating at 23 statute miles (37 kilometers) over Africa on Oct. 7, 2008.
"The science community remains eager to get this information," Brown told SPACE.com.
With NEO airburst data, he said, it allows scientists to advance the understanding of NEO hazards to our planet.