Sentinel: A Plan to Save Earth

A 17-meter-wide asteroid that no one saw coming exploded in February near Chelyabinsk, Russia, blazing across the sky and television screens world wide. Efforts have been made to identify asteroids larger than a kilometer—objects large enough to threaten life on Earth. Hollywood has cranked out dozens of cheesy asteroid collision movies, some bad and others worse, but none capture the magnitude of the actual threat from near Earth objects (NEOs). There may be a million asteroids with masses greater than ocean liners in Earth-approaching orbits, nearly all of which remain undiscovered and their courses uncharted. Now, a private foundation wants to build Sentinel, a satellite containing an infrared telescope that would be able to detect a half-million orbiting objects from a vantage point near Venus. Is this a project too important to trust to government agencies like NASA and the ESA?

A kilometer-wide asteroid could devastate part of a continent and shroud the planet in dust, perhaps triggering a new ice age. Recognizing the threat, NASA-sponsored searches have identified most of the kilometer-size and larger near Earth objects (NEOs). What is normally not discussed are smaller asteroids that are not world threatening but still dangerous—an asteroid only 40 meters across could wipe out a city like New York or London. While the large, potentially civilization-threatening, NEOs are kept under observation few of the smaller, but still dangerous, objects have been identified. Some experts say as few as 1% have been spotted.

“Planetary scientists agree that a full inventory of NEOs will require a dedicated space observatory—at least a half-billion-dollar proposition,” says an news article in Science. In an era of shrinking budgets, NASA has fallen behind on its current assignment, a 2005 mandate from Congress. Ordered to identify 90% of NEOs 140 meters wide and larger by 2020, NASA has only found an estimated 10% of them have.


Orbits of potentially hazardous asteroids from NASA.

While it now seems feasible to deflect an incoming asteroid, scientists would need many years of advance warning to mount such an effort. Waiting until the last minute to discover an impending collision is not a viable option. “I believe the agency has ducked its responsibility a little bit,” says Lindley Johnson, NASA's program executive for NEO Observations. “I never dreamed it would take as long as it has to develop a robust capacity.”

Now, a private foundation led by several former astronauts is taking up the challenge of protecting human civilization from the space born threat. Named B612 after the asteroid in Antoine de Saint-Exupéry's The Little Prince, it has set its sights on launching a $450 million mission by July 2018. The infrared telescope, called Sentinel, could identify a half-million NEOs from a vantage point near Venus. The public faces of B612 are two astronauts from different generations: CEO Edward “Ed” Lu, 50, and Russell “Rusty” Schweickart, 77, chair emeritus of the board of directors. Their celebrity has helped keep the philanthropic dollars flowing. Here is the mission statement from their website:

The B612 Foundation is a nonprofit 501(c) 3 organization dedicated to opening up the frontier of space exploration and protecting humanity from asteroid impacts. On June 28, 2012, the Foundation announced its plans to build and operate the first privately funded, launched, and operated interplanetary mission – an infrared space telescope to be placed in orbit around the Sun to discover, map, and track asteroids whose orbits approach Earth and threaten humanity.

Everyone in this day and age has heard the story of the asteroid that killed the dinosaurs. As noted on the foundation's website: “The dinosaurs didn’t have a space program. An asteroid caused the extinction of the dinosaurs and most of life on Earth during the Cretaceous period. But they had no way of preventing their demise. Humans do...”

Schweickart, an Apollo 9 astronaut, had seen Earth from orbit and recognized the faint outlines of ancient impacts on its surface. But it wasn't until 1998, when he heard Stanford University geophysicist Norman Sleep speak about Earth's impact history, that the immediacy of the collision threat became a concern for him. “The incredible energies blew my mind,” he says.

The energies involved can, indeed, be mind blowing. In my latest science fiction novel, Peggy Sue, aliens wishing to destroy life on Earth bombard our planet with asteroids. Though the asteroids in the book arrive at higher velocities than typically found in NEOs, the resulting impacts are in the same general range. The energy released can be in the millions of megatons, larger than any of humanity's puny atomic bombs. Science fiction aside, the threat of asteroid impact is frighteningly real.

Lu, an astrophysicist and solar scientist who flew on two space shuttle missions before spending 6 months on the International Space Station, became aware of the cosmic threat through personal observation. “You see shooting stars below you,” he says. “You know where the impact craters are. It's a constant reminder.”

Together, Lu and Schweickart founded the B612 Foundation in 2002, along with astrophysicist Piet Hut of the Institute for Advanced Study in Princeton and planetary scientist Clark Chapman of the Southwest Research Institute in Boulder. At first they studied ways of deflecting an asteroid from a collision course—at the time scientists were not sure such a feat could be accomplished with present day technology. Lu and fellow astronaut Stanley Love devised the "gravity tractor," a spacecraft hovering near an NEO to alter its orbit slightly, but enough to avoid an impact. Another concept, ramming a projectile into an asteroid, could also do the trick if done far enough in advance. They came to realize that they would need ten or more years warning to be sure of success.

In light of their findings, B612 changed its focus. As Lu put it, “we came to the conclusion that deflection was doable. Finding the other 99% [of NEOs] is the entire problem.” Now B612 has a team of veteran planetary scientists and a fixed-price contract with Ball Aerospace & Technologies to build and operate the Sentinel. The technology for the new satellite comes from proven systems used in earlier space probes that Ball Aerospace had a hand in. B612 lists the following design highlights:

  • Provides highly specialized design specifically optimized for NEO detection and discovery.
  • NEO detection efficiency increased using IR-detector (5 to 10.4 microns). Venus-like orbit.
  • Provides an astrometric accuracy of 0.2-arcseconds for any detected NEOs (typical); NEO orbits determined in as few as two detections, with multiple visits to each region of the sky.
  • On board detection processing reduces data downlink volume, minimizes contact requirements.
  • Provides a targeted follow-up observation capability, enabling time-critical revisit of high-priority targets.
  • Heritage draws lineage from great observatories and pioneering scientific missions: Kepler, Spitzer, Deep Impact.

Perhaps the most notable aspect of Sentinel's design is its planned orbit in a path similar to that of Venus. This vantage point will allow Sentinel to view fully illuminated asteroids as it looks out toward Earth's orbit. Sentinel's half-meter-wide telescope will hunt for NEOs with new infrared detectors sensitive to 10 microns. At that wavelength asteroids warmed by the Sun stand out clearly against the cold backdrop of space. Designed for highly autonomous operation, the spacecraft will require only weekly ground contact. Still, any mission design is a compromise and the B612 team knows Sentinel won't catch everything. They are hoping for a 90% identification rate over the six and a half year life of the mission.


Sentinel will look outward from an orbit similar to Venus.

The foundation's immediate goal is $20 million in donations by the new year, followed by at least $40 million each year for a decade. While the amount of money involved may seem daunting it is on a scale familiar to those in astronomy. Before World War II, astronomical observatories were built almost entirely with private money. The amounts involved in building the Mount Wilson Observatory in California and Yerkes Observatory in Wisconsin are in the same range, when adjusted for inflation.

It is nice to know in this day of false crises, like energy shortages and global warming, that there are real scientists working to solve real problems that actually threaten our world. I have written about the extraterrestrial threat before and how it is a much greater hazard than climate change. Can you help? Donate online or, for more information regarding partnerships, education projects, corporate donations, or media queries, contact Diane Murphy, CapComm, B612 Foundation (diane@b612foundation.org).

Be safe, enjoy the interglacial and stay skeptical.