Richard A Lovett
Deadly asteroid strikes have long been a staple of science fiction. But last week, NASA used an international conference to war-game a scenario in which a “newly discovered” asteroid moved from having a 1% chance of striking the Earth to obliterating a big chunk of New York City.
The exercise was conducted as a way of exploring possible responses to a situation that, should it ever arise, will be of global, and perhaps existential, import.
The scenario was played out over the course of five days at the International Academy of Astronautics’ 2019 Planetary Defence Conference in College Park, Maryland.
Each day, participants were presented with fictional press releases that tracked crucial steps in a developing emergency. The bulletins covered a period of eight years.
“We’re scientists pretending that we are actors playing scientists who happen to be ourselves,” joked Mark Boslough, a physicist at Sandia National Laboratories, New Mexico.
The exercise began with the announcement that an asteroid had been spotted on potential collision course with Earth, but that the odds of impact were only one in 100.
On the second day of the conference, the scientists were told that the astronomers had refined their calculations of the object’s orbit by enough to raise its impact probability to 10%.
These same hypothetical observations also found that the asteroid’s size was somewhere between 140 and 260 metres – too small to be a dino-killer, but big enough to pack a serous wallop if it hit.
At this point, the assembled scientists concluded that it was time to start taking action, with an eye to deflecting the asteroid. There were two possible courses of action: hitting it with a fast-moving rocket at a crucial point in its orbit or exploding a nuclear device close above its surface. (However, the latter strategy is currently prohibited by international law.)
“You only need a few centimetres per second [change in velocity] to move it thousands of kilometres [by the time it reaches the Earth],” explained Paul Chodas, of NASA’s Centre for Near Earth Object Studies in Pasadena, California.
That said, you can’t deflect an asteroid if you don’t know the proper direction in which to move it, or even if it really is on collision course.
To resolve that, the scientists concluded that the first step had to be to build and launch a reconnaissance mission as quickly as possible to do a flyby of the asteroid. This was seen as a useful step in gathering more information.
Meanwhile, additional spacecraft, ranging from a reconnaissance mission capable of rendezvousing with the asteroid to a fleet of asteroid-deflection spacecraft, also needed to be rapidly pressed into development. {%recommended 8960%}
“We are looking at one to 10 Falcon Heavy impactors,” said Brent Barbee of NASA’s Goddard Space Flight Centre, Greenbelt, Maryland.
Falcons are a family of rockets built by the private company Space Exploration Technologies, or SpaceX. The Falcon Heavy is the biggest of the bunch, capable of carrying the biggest payload of any currently operable launch vehicle.
Unfortunately the precise number of such rockets wouldn’t be known until the flyby satellite gets to the asteroid, but, added Barbee, “we have to begin construction of whatever vehicles we are going to commit to, right now. And spacecraft could fail, so we need to include that in our thinking.”
Fast forward to December 2021.
In the third press release, data from the flyby mission revealed that the asteroid was heading for somewhere near Denver, Colorado.
“The obvious thing to do is to deflect this thing,” Boslough noted on receiving the news. “We still have five years.”
The next update, dated September 2024, revealed that a fleet of six Falcon Heavy rockets had been built, but only three found their target. One was lost to a launch failure, while the other two experienced systems failures en route. Nuclear devices were not deployed.
The surviving three rockets, Barbee explained, would still have been enough to deflect the asteroid, but there was a problem. One hit hard enough to break it into two pieces.
The larger fragment was deflected away from Earth, but the smaller one, about 60 metres across, was merely nudged hard enough to deflect it away from Denver. Instead, it wound up on course for an indeterminate location on the eastern half of the US, or maybe in the Atlantic Ocean.
Worse, Barbee said, the reconnaissance satellite observing the deflection attempt was hit by debris and knocked offline, making it impossible to calculate exactly where the fragment would hit.
It was still possible, he added, to launch a nuclear-equipped mission capable of either deflecting the asteroid fragment or breaking it up into tinier fragments that, if they reached Earth at all, would burn up harmlessly in the upper atmosphere.
But such a mission had to be approved, built, and launched within the next six to 12 months.
“Whether people would do it, I can’t say,” he said. “What I can say is that as an engineer, we can do this.”
Fast-forward one final time, to the last day of the exercise, just 10 days before the impact.
Blowing the thing up, like Bruce Willis did in the 1998 film Armageddon, was an idea that never got off the ground, the war-gaming team decreed, either due to lack of time, or lack of political will.
As a result, the asteroid fragment had got close enough for Earth-based radar to track its course with high precision. It was headed directly for the heart of New York City, which it would hit with the force of a 15-megatonne bomb. (To compare: the atomic bomb that levelled Hiroshima in 1945 had a yield of just 15-kilotonnes.)
New Yorkers would have been well aware that they might be in the asteroid’s cross-hairs, Chodas’s team said, but now that the scientists knew exactly where the asteroid would hit, and emergency managers had 10 days to evacuate 10 million people.
All of this, of course, was simply a hypothetical scenario, akin to a science fiction story, but it was played out with excruciating attention to detail.
Conference organisers stressed that the exercise was not designed to represent a truly likely real-world scenario. Rather, it was designed to highlight ways in which things might go wrong.
“One of the things I take away from this is we probably should have been planning the back-up options from the beginning, just in case,” Barbee said afterwards.
Chodas added that there wasn’t much value in war-gaming a scenario in which the asteroid either misses or is easily deflected.
“We learn by studying these what-ifs,” he concluded.
