An Asteroid's Greatest Threat to Earth? Human Nature

The scoop: Asteroid Apophis will swing by Earth in 20 years. When it loops back around in 2036, there may be a slim chance it could whack us.

We chat with former astronaut Rusty Schweickart about the dangers of near-Earth asteroids and humanity's danger to itself in stopping them.

Dave Mosher: Hi Rusty!

Rusty Schweickart: Hi Dave... all set.

Dave: Let's get started since you don't have too much time:
The word on the street is that you're pretty concerned about near-Earth asteroids/objects... how did that come about?

Rusty: Well, back in the mid 1990's I became interested NASA's astrobiology program.
When you look at the formation of life on Earth, asteroid and comet impacts played a BIG role in it.
So that's when my interest began.

Dave: Thanks.
Now if you don't mind my asking flat-out: What's the chance we'll see an impact in my lifetime?

Rusty: Well, let's give that a try.
First I'll say in the next 100 years (that's an optimistic lifetime for someone of your generation) since it's a nice round number.

Dave: Hey, we'll all be half-robots by then. I'd expect longevity to increase a bit :)

Rusty: Perhaps!
Next I'll assume that by impact you mean one that could create some damage on the ground. Those are about 145 feet in diameter and larger.
On average, these guys come around once per 300 to 500 years... let's go with the 500 year figure.
Therefore, within the next 100 years, the probability is about 20 percent.

Dave: So one in five? Wow.

Rusty: HOWEVER... the real issue is how many such objects *look* like they're going to hit.
It looks as though we'll end up having to make a decision of whether or not to "act" against a potential impact once every 10 years or so.
In other words:
We'll need to make decisions about whether or not to act when objects reach a probability of impact of say 1 in 50, or 1 in 100.

Dave: Any ideas from your end about what we should do if the odds get that frightening?

Rusty: Generally... Each of these things pose unique issues.
The first thing to do when one *looks* threatening is to send up a spacecraft with a transponder on it.
That could give us much more accurate information on its orbit than ground telescopes can manage.
The robot would also have a gravity tractor capability, i.e. a weak but precise capability to slightly change the orbit of an asteroid via gravity.
So: The transponder would answer the question "is it really headed for us?" and -- if so -- the spacecraft could provide the capability to adjust its orbit to cause a miss vs. a hit.

Dave: How much notice would we need to get a spacecraft out to a threatening object?
And do we have the technology to do that yet?

Rusty: The answer to the latter is yes.
As to the former? Several components there.
First, working back from an impact date, you need to allow time for a deflection it to take adequate effect. In general that might be 3 to 10 years...
So the deflection maneuver should be completed, say, 10 years ahead of impact.

Dave: What about everything before the deflection?

Rusty: Right. You need to factor in:
1. the decision to deflect
2. a spacecraft design
3. manufacture and test the spacecraft
4. launch it
5. rendezvous with the asteroid
6. and, finally, the deflection maneuver
All in all, something no shorter than 7 years.  So the overall time would be 15 to 25 years prior to an impact.
And the toughest element of that sequence, FRANKLY, is getting the planet to make a decision to act!
That's the really tough element of it.  The technology is a piece of cake by comparison.

Dave: Good point... Do you think it's possible for the human race to pull it together that quickly?
I know asteroid Apophis is making a very close swing by Earth 20 years from the day today. And it doesn't sound like we've done anything at all about it.
Have we?