Raumfahrt - NASAs asteroid defense program aiming for more impact Its planning the first-ever demonstration to knock one off course but the funding is in limbo



The Trump administration has proposed increasing the budget for NASA's Planetary Defense Coordination Office by three-fold -- from some $60 million to $150 million -- amid growing concerns that humanity is utterly unprepared for the unlikely but still unthinkable: an asteroid strike of calamitous proportions.


Lindley Johnson, a former Air Force officer who serves as the space agency's planetary defense officer, is at the center of these efforts, which include plans for the first-ever demonstration to knock an asteroid off course should any of the more than 25,000 estimated asteroids that are 140 meters in size or greater prove to be a real threat.

But that test, which is planned for 2022, is at risk of being delayed if NASA appropriations for fiscal year 2019 get included, as expected, in a continuing resolution -- meaning the agency will have to operate at current spending levels until Congress passes a new NASA budget.

Johnson, who first published a paper on the asteroid threat as an Air Force major in 1994, called a recent two-kiloton meteor strike in Greenland a "cosmic wake-up call."

He laid out for POLITICO how the planetary defense mission has evolved; how much more NASA has learned; and the various ways a sizable near-Earth asteroid might theoretically be deflected if it were heading our way -- that is, if we had enough advance notice it was coming.

This transcript has been edited for length and clarity.

NASA has been looking at this for two decades. What’s different now?

I think one of the reasons that you see more interest and activity here is due to NASA’s efforts over the last two decades of better understanding what is out there – asteroids and comets in our solar system that can come through and pass close to the earth and on occasion impact. Thirty years ago, there were maybe only a handful of astronomers that thought there was any danger. It is because nobody had really looked at what is out there. As there became a dawn in people’s minds : 'well, you know, there is still a lot of stuff left over from the formation of the solar system and a lot of asteroids and comets that could come into the inner solar system within the orbit of Mars and still impact the Earth.'

There is nothing preventing that from happening and if there is a sizable population of asteroids that do come interior to Mars' orbit there could still be a significant potential for an impact to occur [here] in the future.

Tell us how this mission began some two decades ago.

The original charge was to try to find any asteroid larger than a kilometer – two-thirds of a mile in size – to see how many of those did come into near-Earth orbits around the sun.

The projections back 20 years ago were there might be as many as 2,000 out there. And our survey work we did through the early 2000s determined that number is only about half that. There is somewhat less than 1,000 near-Earth asteroids that we have discovered in our surveys -- and believe we are about 96 or 97 percent complete in discovering the population of one-kilometer asteroids. Of course that is something we would not want to get hit with. An impact by a kilometer or larger object would have significant global effects and be a global disaster.


So if 140 meters in size is the threshold I imagine it increases the population of these asteroids?

There is almost 950 objects larger than a kilometer in size in near-Earth orbits and we believe the population of [asteroids] 140 meters or larger is about 25,000. To date, we have found 8,303 asteroids larger than 140 meters in size that are now in our catalog. But based upon what we have found and statistical studies, we believe the overall number approaches 25,000. How bad the effects could be from an impact of even a relatively small, 100-meter size object has led to the increased interest and the drive to ‘well, let’s find out what’s really out there and figure out what we would do about one if it was on an impact trajectory.'

Those are all asteroids that come within about 30,000 million miles of Earth’s orbit. That’s a relatively small distance when you are thinking on a scale of solar system. We have got to find them first before we can do anything about them. If we don’t know they are coming there is no chance to be able to prevent an impact. And the more time between detection and impact the better our chances of being able to do something about it.

How is NASA building this picture?

None of the observatories we use to try to detect these things are actually NASA observatories. Our program funds observatories that are actually run and operated by universities and space institutes within the U.S. The University of Arizona is one of the big ones, the other is the University of Hawaii. We also work with the U.S. Air Force. We have also set up an International Asteroid Warning Network with counterparts in Europe, the Japanese, even assets in Russia and China. They contribute observations to the Minor Planet Center, which is the International Astronomical Union’s central node for observations from around the world on asteroids and comets.

What would be the options be to deflect one deemed a threat?

There have been several studies of what we can do for mitigation. The most reliable methods are based upon basically one simple principle. We just need to change the velocity of the asteroid by a fraction of a percent. If we do that far enough ahead of time, the orbital mechanics of an asteroid orbiting the sun will change its orbit from a hazardous orbit to one that is benign. So we need to either add or trim a few inches per second of speed off the asteroid.

A National Research Council study in 2010 took pretty hard look at this and given current technology there are at least three techniques that appear viable to do that. Some are very simple in principle. The first one is just a kinetic impact. Just ram a spacecraft into it at the right speed and angle to impart that force to cause a velocity change of an inch per second or so.

So we have embarked on a mission to demonstrate that technique and determine if we really understand everything we think we do about that to make sure it would be a viable response to finding an asteroid on an impact trajectory. The Double Asteroid Redirect Test is in our budget request for fiscal year 2019 – a significant increase on the planetary defense program. A good part of that is to get the redirect test on its way to the launch pad in summer of 2021 to encounter the double asteroid system in October 2022. We are going to show the capability that a kinetic impactor would have to change the orbit of that moon around the primary asteroid.

How much of a budget increase are we talking about?

For the overall proposed Planetary Defense Program the budget is $150 million for FY19 -- $98 million of it is for the Double Asteroid Redirect Test.
The entire program increases from about $60 million to $150 million. It allows us to embark on space capabilities and demonstration of deflection techniques and to start work on space-based detection and characterization capabilities.

What are the other potentially viable means to address a threatening asteroid?

The second one is what is called a gravity tractor. The principle of it is that you station a spacecraft alongside an asteroid and the mutual gravity attraction between the spacecraft and the asteroid will slowly tug that asteroid off its impact trajectory. If it is a large asteroid the relative mass of the asteroid to the spacecraft is an important factor here. If it is a very large, kilometer-size asteroid this is not going to have much effect. But the more frequent impactors are going to be those that are 100 meters or maybe less in size. So now the mass of the spacecraft becomes more of a factor and can have more effect on gradually tugging on that asteroid and changing its velocity.

Another idea that came along as we were looking at this was ‘well, what if you could increase the mass of the spacecraft after it got there – i.e. go down and pick up a large, tens-of-tons boulder off the surface of the asteroid and put that in the arms of the spacecraft. It was going to be part of the asteroid redirect mission back in the last administration but that program didn’t make it through the transition. So now we don’t have that in our program yet. We are still interested in that technique and perhaps a future demonstration for the planetary defense program could be demonstration of a gravity tractor.

The other viable option?


The third one, of course, if the one everybody likes to talk about and that is the nuclear option. Not like in the movies 'Armageddon' or 'Deep Impact.' The most effective technique, we think, would be to have an explosion of a nuclear device several hundred meters from the surface of the asteroid. The nuclear radiation causes super heating of the asteroid surface and imparts a force on the asteroid in the opposite direction.

So nuking the asteroid itself wouldn't work.

Blow it up into bitty pieces and then you have a bunch of buckshot headed at you. You haven’t changed the direction of it. You have just broken it up into pieces, some of which the Earth’s atmosphere may take care of but maybe not all.

How important is the recent strategy and action plan?

it makes all the agencies that have a piece of the pie aware of what is the problem, what can be done about it does their particular agency have that can contribute to the nation’s capability to dealing with this issue. NASA, of course, has been working this for 20 years now and we have been working with the Federal Emergency Management Agency for about the last eight years on emergency response preparations if NASA were to find an asteroid on an impact trajectory for U.S. territory. How would we work together to protect as many citizens and infrastructure as we could.

What agencies could do more?

The Air Force certainly is doing some but could possibly do more. They certainly have a role on the detection, tracking and characterization -- building a more complete space situational awareness picture to take onto account not only man-made but natural objects. If we get into a scenario where we need space lift and rapid development capabilities we would need to call upon the resources of the Air Force to help us.

So which what is the best asteroid movie?

I'm the real Bruce Willis. Don't look so disappointed.

Hollywood is entertainment and fantasy. I'd have to say the movie 'Deep Impact' is probably better than 'Armageddon.' 'Deep Impact' actually had some science in it. 'Armageddon' was pure fantasy. My favorite asteroid impact disaster movie is 'Meteor," from back in the 70s. It starred Natalie Wood and Sean Connery played me. That's why it's my favorite movie.