We’re NASA experts who are getting ready to change the course of an asteroid. Ask us anything about NASA’s DART test mission!

You guys decided to call the program DART first and then came up with words to fit as an acronym after, didn't you?

Guilty! We had a whiteboard with a bunch of words related to the mission and basically played a game of word scramble.

DART came out as the top choice, though I also advocated for RAD - Redirection of the Asteroid Didymos. -ZF

Are you worried that you'll miscalculate and send the asteroid straight to downtown Dallas?

No, I'm not worried about an asteroid hitting Dallas (or anywhere else on Earth).

NASA and the DART team did a detailed study to make sure that the DART test would not cause the asteroid to hit the Earth. -T.D.

What's the minimum time it'll take to notice an asteroid heading towards earth?

For example, if you guys are keeping track of asteroids, what are the chances of spotting one within a week of impact.

We're trying to find asteroids with years to decades of advance notice, although there are also regular searches for objects on possible impact trajectories.

So far, the only ones that hit that were seen first were tiny--generally less than 10 feet in diameter—and did no damage. Larger objects are regularly discovered at many times the distance of the Moon. --LB

Besides earth, which planet would you want to crash this asteroid into and why?

Well, there is no need for anything so dramatic when the solar system has its own "giant attractor" of asteroids and comets -- Jupiter.

In 1994, we had an opportunity to observe a spectacular impact on Jupiter by comet Shoemaker-Levy 9 (or rather its fragments). This was not the only event since then. We have noticed several other impacts (likely small asteroids). The last two were reported just this September and October. -MB

Hi, if is successful , how quickly would you be able to launch and send another mission up if someone finds a new NEO and is on a collision course with Earth?

The main strategy for Planetary Defense is to find any asteroid that is a significant impact threat years to decades in advance. This is possible with current technology, so we'll have years to select the right way to deflect an asteroid—more than enough time to build and launch a DART successor. - LJ

Nukes. Nukes.

We've got a bit more on this further down in the AMA: https://reddit.com/r/IAmA/comments/qw7ijh/were_nasa_experts_who_are_getting_ready_to_change/hl14t2j/

Thanks for your reply, but with objects like Oumuamua getting to 33 million miles of Earth before detection, don’t we need a fast reaction force too? With redundancy being a huge NASA thing, is there an option to how multiple DARTS to act as a rapid deployment system in case of a similar object being detected only when it’s relatively close to earth?

33 million miles is a long ways away, even in space terms. That's over 125 times the distance to our Moon.

O'umuamua was never a concern for Earth, but rather an exciting discovery of something coming through from outside of our solar system.

No, we have the technology to find any real threat to Earth years in advance. We just need to apply it in a more focused program to find them early. That is the Planetary Defense program's main task. - LJ

How can this system be scaled up? Imagine a 500m asteroid that is going to hit the earth, is there any current launch vehicle that would be able to launch the redirect system for such a big asteroid on a short notice? How long before impact would you need to be notified of the asteroid to be able to successfully redirect it? What is the maximum diameter the asteroid can have that we would be able to redirect with current technology?

The more notice we have, the better. The more warning we have, the bigger the asteroid we can deflect.

If we have 10 or more years of warning, a mission like DART could deflect an asteroid up to a few hundred meters in size. Asteroids of that size are large enough to cause regional devastation. Currently, we know of no asteroids that pose an impact threat for the next 100 years. But, we actually haven't yet found most of the asteroids that could destroy a city or metropolitan area. NASA is looking for them 24/7/365.

Finding the asteroids is critical--as is having the technology in place to deflect them, like DART. It's a puzzle, and we need both pieces! -T.D.

How did you feel about Didymos's moonlet being called "Didymoon"? Why is it called Didymorphos instead?

Didymoon is such a great nickname for the smaller of the two asteroids!

I think the new name is also quite meaningful since it means “having two forms”: one before the impact and one after the impact! -LW

Does planetary defense include the use of explosive missiles or even nuclear-capable missiles for destruction of asteroids?

We wouldn't want to destroy the asteroid - just move it into a non-hazardous orbit. How we would do that would depend on several factors, but the size of the asteroid and the time we would have to do it are two major ones.

What we'd use would then depend on the energy required. But our strategy is to find them years in advance, so methods like the kinetic impactor being demonstrated by DART will be sufficient. - LJ

I visited JPL during a highschool trip 4 years ago and I was fascinated by the work you guys do! My question is: How long has the DART mission been in development, and why did you specifically choose Dimorphos?

The earliest concept studies have been in development for about 10 years! We looked for well-observed binary asteroids, roughly 150m (450 ft) in diameter that are easy to get to.

Dimorphos topped that list, and there really weren't any other very good options. - ZF

Will you be playing Aerosmith during the mission?

Dream On! - LB

Heard about the DART mission on Science Vs. I can't thank you enough for putting this forward and caring about this defense project.

What is the probability (mathematical) of a moderate size asteroid impact in the next 100 years?

I', eagerly expecting the development of this project, lets see if you can change the moonlet orbit!

Our current knowledge of the impact statistics is the following:

1. Tunguska-type of event, an asteroid a few tens of meters in size, hundreds of years;
2. An asteroid several hundred meters in size -- hundreds of thousands to millions of years,
3. >1 km asteroid - several million to tens of millions of years.

We do not currently know of any object of "moderate" size which has a chance of impact in the next 100 years. By moderate, I will assume you mean several hundred meters.

Please keep in mind that anything smaller than about 30 meters in size will have an airburst and is unlikely to reach ground (excluding metallic NEAs). Our atmosphere is very efficient at protecting us from small impacts. -MB

What's the day-to-day like at the Planetary Defense Coordination Office?

Not all that exciting, I'm afraid. The usual meetings and phone calls and paperwork involved in managing any large program.

But every few weeks we find something "interesting" out there, and we work with our observation projects to learn all we can about it so that we can assess the hazard to Earth and determine what, if anything, should be done about it. - LJ

What material is the DART made from?

The DART spacecraft's main structure is made from aluminum honeycomb.

There are many components inside and out such as batteries, solar arrays, propellant tanks, thrusters, and more—all made up of various materials. We even have some parts made of 3D-printed metal! -LW

Will this technology help pave the way for us to get asteroids on the earth orbit and mine them?

This is something that I am very interested in.

Both NASA and JAXA had a number of successful asteroid missions in the past. OSIRIS-REx at near-Earth asteroid 11195 Bennu and Hayabusa 2 at NEA 162173 Ryugu are just the two most recent ones that come in mind.

All this knowledge that we gain when a spacecraft rendezvous with an asteroid, or interacts with it by taking a sample or impacting it, is an incredible opportunity to learn. This should be very valuable knowledge for any future mining operations. -LB

How exactly does it work? Is this a one time explosion or is the spacecraft going to attempt to push the asteroid long term?

The spacecraft will slam into the asteroid one time and be smashed to smithereens. However, that one-time DART impact will permanently change the asteroid's orbit. -T.D.

What happened to using laser ablation?

This is a method that could be used to deflect asteroids, and there is plenty of scientific literature on the topic of methods of deflection, including things like laser ablation and even painting an asteroid!

That said, a kinetic impactor like DART is a much simpler solution and more feasible on shorter time scales. -ZF

Will you be using the sound effects from the Asteroids video game during the mission?

Hah! I used to play that game a lot when I was in school. I was the only person who could beat my girlfriend's brother. --LB

Hi, is there any way you can send the asteroid towards earth?

No. DART doesn't have enough mass or velocity (i.e., momentum) to cause Dimorphos to leave orbit around Didymos. --LB

Was there a particular reason you chose this asteroid? Does it align with characteristics of an asteroid with a probably impact percentage or was it just an easy target to hit and gain data from?

Yes!

We chose Dimorphos carefully. We needed a binary asteroid system (i.e., an asteroid with a moon) for this test.

We also selected an asteroid that was representative of the size we might need to deflect, if we one day found an asteroid that could hit the Earth.

Lastly, we needed an asteroid system that was easy to get to with a spacecraft and came close enough to Earth for the necessary ground-based observations. The Didymos system fits that bill perfectly and is not a threat to the Earth. - TD

Is Bruce Willis helping with this?

I think he retired from saving the Earth from asteroids in 1998. But his spirit still inspires us! -ZF

DART went from proposal to flight ready in about 6 years, which is pretty fast for any space project.

What did it take to make DART happen, both in terms of resolving engineering challenges and getting it funded?

Well, the concept of using a kinetic impactor to deflect an asteroid has been discussed for decades.

It was assessed as being the most viable method from a technology already available standpoint, so it was the easiest to get approval to proceed for this test. It is also a relatively economic space mission to perform. - LJ

How would you describe an asteroid to a lay person?

Edit: second part removed for clarity.

Asteroids are predominantly rocky and sometimes metallic objects (or the mix of the two) and they are the remanents of the solar system formation. Like "the left-over building blocks for the planets". Many of them contain water and organic molecules, so they are also considered (together with comets), "builders" of the oceans and life on Earth. – MB

What kind of impact or detonation size are we talking about here? Maybe I missed it in the tech specs, but in layman's terms? Like a nuke? Car crash?

For perspective, the DART spacecraft is roughly the size of a smart car, and Dimorphos is roughly the size of the Great Pyramid in Egypt.

The DART spacecraft will be going ~15,000mph (~6.65km/s) into the asteroid… so yes, basically a very very VERY fast car crash! -LW

How will you get data from spacecraft that is going to crash?

During its approach, DART will send back pictures as fast as it can until its impact with Dimorphos.

LICIAcube, a CubeSat provided by the Italian Space Agency, will ride along with DART and deploy prior to impact to capture and send back pictures as it flies by. -LB

What can we expect to happen in the boundary cases of the regolith properties? I.e., how much impact energy could the asteroid absorb and disperse seismically?

@Lance, what is your favorite fact about owls that you would like to share?

This is part of what we're trying to measure with the DART impact. We know the impact will be complicated but we're expecting the orbital period to change by at least 1%, which should be straightforward to measure with telescopes on the ground. But if Dimorphos has an extremely porous interior (say, like Mathilde), then things could surprise us.

Owls: They can adjust muscles in their faces and on their ears, so in a real sense, they have adaptive optics systems on their heads. They evolved this millions of years before astronomers invented it. - LB

Is the reactionary debris a concern?

Assuming by "reactionary debris" you mean asteroid material ejected by the impact, the likely amount and trajectory it could achieve from the impact was researched and assessed and determined not to be any issue.

Almost all will be reaccumulated by the Didymos asteroids within days to weeks. - LJ

Hello! About the DRACO and SMART Nav I've got two questions:

1) At which "T- Impact" time does DART start making use of it's navigation and optical systems to fine tune it's trajectory to make sure it's on a precise intercept trajectory for Dimorphos?

2) How fast is DART able to modify it's attitude for corrections during the time window since it acquires visual of Dimorphos? Does it use a set of gyros, reaction control...?

Thanks <3

We switch over to our autonomous "terminal" mode at about T-4 hours from impact. Before that, we're still imaging the target to get better estimates of its trajectory, but that processing is being done on Earth.

DART has plenty of divert capability using its thrusters and can correct much much faster than needed. Most of the time it is waiting for uncertainty of the target trajectory to decrease enough that it makes sense to do a new movement. -ZF

How do you balance the need for the craft to have significant enough mass to move an asteroid versus the low mass requirement for general space flight?

DART doesn't have extra mass added in order to deflect the asteroid. Because we're impacting the asteroid at such a high velocity (6.6 km/s), the mass needed to build a spacecraft that can navigate to and impact an asteroid, which is about 610 kg, is enough to measurably change the orbit of Dimorphos! -ZF

That’s actually pretty dope!

1) ‘any future planetary defense missions’, like as in, if anything SHOULD be headed towards earth?

2) Do you guys work with ‘Space Force’? (Is that still a thing?

3) is Bruce Willis aware of this project?

1. That is correct! Right now, there are no potentially hazardous asteroids coming our way in the next 100 years, so we are in the clear, but it is always good to be prepared!
2. We are actually launching from the Vandenberg ‘Space Force’ Base!
3. I hope Bruce Willis is aware! DART is such a cool mission! -LW

How big does DART need to be relative to the target asteroid? Is it common for asteroids to exist above a certain size threshold that hitting it with a spacecraft won't bend it's trajectory enough? Is there a distance threshold that an asteroid must be beyond in order for DART to turn it far enough off course?

The DART spacecraft is about 2.5 m in diameter (not including solar panels). Its target, Dimorphos, is about 160 meters in diameter. DART has a mass of about 650 kg and will impact at about 6 km/s. Extensive calculations indicated that DART has enough momentum (mass x velocity) to nudge Dimorphos enough to see the change. But if DART hit a much larger asteroid, the nudge would be too small to detect. That's what happened when NASA's Deep Impact spacecraft hit comet Tempel 1 in 2005: the nudge on the comet was too small for us to see it. --LB

Any chance you can just let it hit us?

Nope. The asteroid is not on a collison course with Earth--that's why "test" is part of DART's name. Right now we know of no asteroids that pose an impact threat to the Earth for the next 100 years. – TD

What does your job look like on a day to day basis? Do you do a bunch of calculations for 8 hours a day? Do you guys work 40 hour work weeks?

As a mechanical engineer, I am actually not at my desk very often. Usually a typical day for me is in the cleanroom installing various components on the spacecraft, designing parts using CAD (computer aided design) and getting assemblies ready for the next big operation! It is really cool to get to work with flight hardware everyday! -LW

Is there a good way to calculate what the new asteroids path would be? Do you guys have any guesses?

We're aiming for Dimorphos, the smaller of the binary asteroids, which has an orbital period of ~12hrs.

Our prediction, based on our velocity and mass, is to hit it and change the orbital period by ~10mins. -LW

Is there a list of asteroids that might need to be redirected?

No. There aren't any asteroids known with impact probabilities large enough to worry about. --LB

Q: Where was your starting point, if you had one? Did you start from scratch? Did you start with a call for papers? And what collaboration/influence surprised you the most that moved the project most ahead. (if you can disclose)[1]

[1] I can imagine theoretical technology developed/on paper during the cold war for the national missile defence system to intercept nukes from orbit could have been used as starting point. Although on second thought, space is a different beast than orbital mechanics (math) and supersonic physics problems.

We actually had a collaboration with the European Space Agency, who had formerly conducted a similar study, Don Quijote, except that it was targeting a non-binary asteroid.

DART was born when Andy Cheng, our principal investigator, came up with the idea to target a binary asteroid system instead, which would allow measurements of deflection to made from ground-based telescopes. -ZF

What's the expected deviation from the original trajectory? Is it enough to escape Didymos' orbit?

I'm mostly thinking of it from a conservation of momentum point of view and can't help but think that a spaceship is much lighter than a 160m-wide ball of rock.

The orbital period, which is 11.9 hours, is expected to change by more than 1%.

DART cannot change the orbit enough for Dimorphus to escape and become a threat to Earth. --LB

How did you account for local tidal forces on your spacecraft for the duration of the redirect mission?

Tidal forces on the spacecraft will be negligible. The spacecraft impacts at 6 km/s, and Dimorphos and Didymos are only 160 m and 800 m in diameter, so their tidal forces are very, very small. Dimorphos and Didymos will experience complicated tidal interactions _after_ the impact, though, and this is something we hope to study with groundbased telescopes and with ESA's Hera mission a few years later. -LB

Are there any plans to see if a non-kinetic solution (like a gravity tractor) might be effective?

A gravity tractor is an excellent idea! Both kinetic impactors and gravity tractors would be effective solutions to deflect an incoming asteroid assuming we have some reasonable (years or decades) warning time. – MB

Hello.

1 – If I understand it, this mission to move a random asteroid is to collect data and see what happens. What data are you going to collect and how will you use them?

2 – Is your team or NASA pursuing other methods of changing planetary course then sending missiles/spacecrafts? Are there any other possible methods, then to just hit it?

Thank you very much and big love and respect for your work, must be very exciting to be the first people moving asteroids:)

Great questions! Let's take 'em one at a time...

1. We are collecting data to measure how much the DART impact changes the orbit of Dimorphos. Those data include images taken by the spacecraft and its companion CubeSat and observations by telescopes on Earth. The pictures will show us where we hit and what happened afterward. The telescopes will measure the change in the asteroid's orbital period. These data will be used to help the world be ready to deflect an asteroid, should we discover one. This test prepares us to deflect an asteroid "for real", if we were to one day find an asteroid on a collision course with Earth.
2. The three main ways of deflecting an asteroid all involve spacecraft (kinetic impact, like DART; gravity tractor; nuclear device). -TD

So this is a pretty morbid question, but what's the minimum size an asteroid, comet etc has to be in order to cause extinction?

Not saying you guys couldn't successfully divert the apocalypse, but just in case it would be nice knowing whether or not a bunker would be of any use haha.

Thanks so much for doing this and all the awesome work you guys do!

The Chicxulub asteroid (also known as asteroid that killed the dinosaurs) was estimated to be 10km (~6.2mi) in diameter. -LW

Are you at all worried that the collision will cause pieces of the asteroid to break off and disperse into the atmosphere and create new hazards?

No. The impact will occur when Didymos and Dimorphos are nearly 11 million km (6.7 million miles) from Earth. The ejecta will disperse harmlessly. –LB

Greetings!

Planetary defense sounds like something out of sci-fi! I think its great that people are thinking about these types of problems!

My questions:

• Will the NEXT-C propulsion system be the primary method to generate the impact velocity?
• If so, how long will the acceleration period take?
• After the impact, what is the fate of the space craft? Is it designed to break apart into smaller (less harmful) space debris?

The NEXT-C thrust isn't the primary propulsion system on the spacecraft. So, no. The collision (at a speed of ~15,000 miles per hour) will break the spacecraft into lots of small pieces of debris. The debris isn't expected to be harmful in any way. -T.D.

I understand you will release a cubesat. Are you expecting photos or video from the impact?

Yes! I'm so excited for DART selfies from the cubesat. -LW

What exactly is being tested here? It seems like the question of will crashing a spacecraft into an asteroid change its momentum is just basic physics right? Is there reason to think it wouldn't work as well as it should? Or is this more of a test to see if you're able to hit an asteroid at high speed in the first place? And what will the closing speed be? Thanks!

The closing speed will be ~15,000 miles per hour. The spacecraft is guiding itself autonomously to the asteroid during the last four hours (i.e., it's a self-driving spacecraft during the last four hours). That's one big piece of technoloigy that we're testing.

We're also going to find out how the asteroid responds to the impact. The impact will excavate ejecta, and that should enhance the momentum transfer. We want to figure out how much of added "oomph" we get from that ejecta. Right now, all we have are best guesses! - T.D.

What are you all going to do to celebrate after?

I'll have the movie Armageddon playing on repeat in the background for at least a few days. -ZF

I assume you can't leave anything to luck in such experiments, but are there factors outside of your control you hope don't happen ?

One of the biggest challenges we face is that we don't have any resolved images of Dimorphos, so we don't know what shape the asteroid is until we get there. There are certainly some shapes the asteroid could be that would make impacting very challenging, a donut for example, that I hope don't happen. That said, we simulate all kinds of possible shapes, textures and brightnesses of Dimorphos and are robust to nearly every feasible combination. -ZF

Why do you need a binary set?

A binary system was chosen as the target partly because the impact will simply change the orbit of Dimorphos around Didymos. The impact does not provide enough energy for Dimorphos to leave orbit around Didymos, so Dimorphos cannot hit Earth.

Didymos also makes relatively close approaches to Earth every two years, and the delta-V to reach it is the smallest for any binary asteroid system currently known. --LB

What other projects are happening related to planetary defence? Are you looking into other options in case the DART results aren’t what you are hoping for? I’ve heard of some solar sale techniques or even some type of laxer array? Also do you still smile to yourself when you realise you are literally defenders of the planet ?

Check out https://www.nasa.gov/planetarydefense/! NASA is working on a lot of different areas related to planetary defense!

And of course! My resume even says “saving the world from future asteroids” :) -LW

Will DART be looking for molecules and small life forms, in an attempt to gain more data on the panspermia theory?

No; the spacecraft is not designed for that. --LB

How long will the spacecraft travel to the asteroid? How far is it?

The DART spacecraft will take about ten months to reach its target. The asteroid's distance from Earth at the time of impact will be about 0.072 astronomical units (6.7 million miles or about 11 million kilometers). --LB

What are you looking forward to? What is something you want us to know? What question are you hoping for?

Every time we try something new with a spacecraft mission we find something nobody expected. It seems very likely that something about the DART impact will surprise us and that we'll learn many new things.

We're particularly interested in how much the impact nudges Dimorphos and thus how accurate the predictions are. --LB

I just listened to the recent Planetary Radio podcast where they interviewed Lindley Johnson... fascinating stuff! I'm a high school physics teacher who is looking forward to sharing more of this mission with my students. Here are my questions:

1. Are there any features that you really hoped to include in/on this mission that did not make the cut this time around, or was just about everything funded/functional by the end?
2. I'm reading that you want to crash into the asteroid at 6.6km/s. At that speed, you probably won't be making too many last-minute course corrections (hopefully!). But, I'm curious... given that your main power is from solar arrays, how exactly would a course-correction be made if it is deemed necessary in the weeks prior to impact? This might best be served by an ELI5 (explain it like I'm 5) of the electric propulsion system.
3. What types of secondary data be collected prior to impact?

THe DART spacecraft was designed to be simple and focused to accomplish its mission - impact the moonlet of Didymos. So it has what it needs to do that. Flight path corrections are made by pressurized gas jets arranged around the spacecraft, that are fired in response to inputs needed determined by its autonomous SMART Nav guidance system. – LJ

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No.

The DART spacecraft can't change the orbit enough to make Dimorphos leave orbit around Didymos. The spacecraft doesn't have enough momentum. --LB

Wouldn't it be easier to just drill into the asteroid and place a nuke in the center like a firecracker in a closed fist?

No, not really. A few different options exist for deflecting asteroids, including use of a nuclear device, a "gravity tractor," and kinetic impact (the technique that DART is demonstrating).

The technique DART will demonstrate is the method that is the most technologically mature. So, that's the technology that what we're testing right now. -T.D.

Have there been any situations where a DART plan would’ve been beneficial to us before?

The dinosaurs probably wished they'd had something like DART!

But seriously, significant asteroid impacts happen on timescales of many decades to centuries, so we've not needed a DART in the time period we've known about asteroids - only about 220 years.

But we are just learning what is out there, and someday Earth will again need something like DART to protect life here. -LJ

How long will the course be changed? Is it temporary until gravity reassert the object's trajectory or will this cause a permanent change?

We're expecting a permanent change to the orbital period, but theorists expect some damping between Dimorphos and Didymos after impact. This is something we are eager to investigate. --LB

Hi NASA peeps! How are you guys today? And how many women on your team?

Doing great!

I would say our team is roughly half women (me being one of them!). It is a great group of folks, with many women in lead roles such as lead mission systems engineer, lead mechanical, lead structural, and more! -LW