Monday, September 26, 2022

NASA's DART Mission Sticks the Impact

NASA's DART mission - the Dual Asteroid Redirection Test - successfully concluded this evening at 7:14PM (Eastern time) by crashing the vehicle into the smaller of the two dual asteroids it has been targeting since last November.  The smaller is Dimorphos, which orbits the larger asteroid,  Didymos.  Being billed as the World's First Planetary Defense Test, the purpose of hitting the smaller body is to change its orbit and measure how much velocity change there is.

A screen capture from the replay with the last full frame of the surface of Dimorphos. 

The DART mission began in the late evening California time of November 23, 2021, with its launch from Vandenberg Space Force Base's SLC-4E.  It's ride into space came atop a Falcon 9, marking the first interplanetary NASA mission launched on a flight-proven commercial rocket and the Falcon 9 family’s first interplanetary launch.  

As it's full name implies, the goal of DART (NASA's mission page) has been to practice all of the steps necessary to rendezvous with a moving body in space, impact it and then verify that its trajectory change matches theory.  Why shouldn't the change match the prediction?  The problem isn't just hitting Dimorphos, but hitting it squarely, over its center of gravity and not imparting forces in directions other than what you've assumed.  Considering that no one has ever seen the two of them, it's hard to conclusively know what Dimorphos is shaped like and therefore where that center of gravity is to hit.  By the time that information can be obtained, it's too late to do the mission.  

Basically, it's the movie Armageddon turning into reality, except for the mission being unmanned, so no Bruce Willis equivalent and no live video as it's going on.  Well, it's a test of the concept; Dimorphos and Didymos are no threat to Earth.  

It always seemed to me that if one wanted to do a test like this, they'd better be pretty sure there's no way they can make a non-threatening asteroid into one that will threaten us.  

At the time of the launch, one of my sources said, “... the mission is going to complete between September 26 and October 1, 2022; under one year from launch.”  With the impact at 7:14PM EDT, that's 2314 UTC on September 26.  Pretty good prediction. 

Yes, I watched it live.  How often do you get to watch something that has never been done in all human history? 


  1. Watched video replay of the live feed. They nailed it dead center. Great job!

  2. O, if only someone in the government had already perfected hitting one moving target with another moving body, like, oh, I AMRAAM, a Patriot missile, an ABM, a moon landing...

    I guess hitting Mach 2 targets with Mach 6 missiles, or anything even more delicate, doesn't scale up at all, because math and physics are weird like that...?

    It's a pity there wasn't 70 years of institutional knowledge somewhere paid for by taxpayer dollars on doing something eerily similar to this. Pretty much every day since the 1950s.

    Oh, wait, it's NASA we're talking about. Re-inventing the wheel is their entire raison d'etre. Never mind.
    They should live broadcast hitting the urinal successfully from 2' away.
    They need the views to justify institutional existence.

    Next week the Mars Rover wheel design will go from hexagonal to octagonal. Film at 11. :)

    1. Big difference hitting known mass targets and hitting an unknown mass target. What if Dimorphos was hollow, or made of low density crud mixed with higher density blobs, or if the center-of-mass was very off center?

      Lots of variables. Much easier to hit a nuclear re-entry vehicle with an ABM, either slow and way downfield (like the Spartan ABM) or fast and close (like the Sprint ABM, and, yes, got to see both in play as a kid, fascinating.) Much easier to hit a maneuvering vehicle going fast when you have multiple targeting locks on it (like the AEGIS system) and multiple launchers/weapon systems to target said maneuvering vehicle.

      Trying to do this way out in the deep black where speed-of-light affects any Earth or Earth Orbit targeting systems and you have to rely, in the final terminal state, upon the attack vehicle's systems only, and that ups the complexity. Just look at all the attempts to land or sample comets and asteroids, let alone moons and planets, which are, in comparison to Dimorphos, huge gigantic sides of barns versus that sugar ant (one of the smalles ants around) moving over that black asphalt driveway that's 500 yards away.

      That's the complexity of the issue. Identify target, calculate the trajectory of said target using assumptions of mass, COG, density, surface area, solar winds, composition, yada yada yada, and then actually maneuver and hit that small (in solar system terms, a specific grain of sand on a beach) target.

      A lot of number crunching. A lot of guess-work and assumption-work.

      The neat thing is, with all the data from this mission, it makes hitting nearer in-space objects a lot easier. And hitting space objects is a lot harder than whacking atmospheric objects.

      Good Job!!! Go, NASA, Go!

      This is NASA doing the job that NASA was created to do. To do the not-impossible but highly, highly improbable thing. Not the NASA-as-welfare that we have come to know and despise.

    2. "Big difference hitting known mass targets and hitting an unknown mass target. What if Dimorphos was hollow, or made of low density crud mixed with higher density blobs, or if the center-of-mass was very off center?"

      Horsefeathers, Beans.

      Impact is impact. Period.

      If I'm dropping a baseball from a blimp at 50,000', what the target is made of - cream pie or slab of rock - means nothing whatsoever to impact or no impact.
      Ditto for intercepting an object in space.

      You're trying to hit it, not build a nest on it.

      Whether it did, in fact, hit center of gravity, and how much (if any) orbital deflection it achieves, will be determined by future observations, and is exactly the point under investigation.

      One of us read the homework assignment.
      Less NASA fanboy, more physics.

    3. Okay, smart guy.

      What about all the various layers of winds, often going counter to each other? Said baseball ain't exactly a guided missile.

      Now put a guidance package on said baseball. Chance of hitting target increases greatly.

      Now put a 3-4 second delay on any guidance from said blimp. Chance of hitting target drops greatly.

      Now, in order to add some more complexity, raise said blimp up to 150,000 feet. Have the target moving. Increase delay from controls up to 3-4 minutes.

      Because that is what is going on with the DART mission. Firing at a target far far far out there, faaaaar out there, with everything subject to solar winds, space radiation (yes, that does matter) and a huge transmission delay from ground station to DART.

      I have read the homework assignment. And I am not a fanboy of NASA.

      Perhaps you need to re-read the homework assignment.

    4. Evidently you didn't. Now you're just moving the goalposts.

      First you argued they were trying for precise target placement.
      The problem is, they have no idea if they placed it precisely, nor correctly, nor had any way to find out any of the things you mentioned beforehand. Only the results of the impact - if any - will determine if all the things you thought they were doing beforehand actually happened, afterwards. Or, not. They can then try another shot.
      The technical term for that is "Kentucky windage."

      So now you want to misuse the baseball analogy, when the point of the example is that this was simply an impact calculation based on physics, and a baseball, unlike the DART, is completely stupid unguided the minute you drop it.

      Putting a "guidance package" on the object in question is a problem science solved in 1904, and applied to moving payloads into targets as early as the 1950s. It's called radar. Perhaps you've heard of it.

      That, coupled with control thrusters, a space technology only 60 years old, makes hitting an asteroid completely independent of "transmission delay", and throwing that into the equation was another pointless exercise, simply because its existence is a deal-breaking given.

      It's simply a question of putting the payload in a basket within which it can self-guide onto a moving but non-maneuvering and braindead inert target.
      This is about as complicated as penguins hitting an ice floe, something they've managed to do with a walnut-sized guidance package for some 50 million years.

      This would only be something hard, in absolute terms, if you were trying to do it in 1905, with steampunk levels of technology.
      Dimorphos was 6.8M miles away, at impact.
      Mars, by contrast, averages 140M miles distance, and the closest it's ever been in recorded history is 35 million miles (5 times farther than Dimorphos), and yet we've been sending things there since 1965.

      What's questionable in the extreme is whether DART is even worth bothering about - let alone paying for - to begin with.

      Which explains entirely why NASA is all agog over it.

      (For bonus points, dollars to donuts they demanded the project be conducted by the Diversity Dream Team. If NASA could get actual hoodrats to study enough STEM to pull it off, that would be the project's only notable achievement. But if they missed, they'd claim systemic racism in space, and go back to dealing dope and collecting outright welfare.)

      Frankly, they should have tried to land on Dimorphos, and then just hired the same geniusii formerly in charge of the Mars Climate Orbiter mission, thus making a crash impact with it a dead-on certainty.

      50:50 NASA induces Dimorphos into some catastrophic result anyways, just based on their recent track record. But if it lands on the set of The View while they're taping a show, I'll take it all back.

  3. I saw a link, clicked on it, and saw the last 30 seconds before impact. Yes, I'm lucky that way . . .

  4. It was fun to watch in Real Time, the Guidance people did a great job of identifying and locking on to the target. In spite of what Aesop says, it is NOT a trivial problem, you can't just throw a spacecraft "thataway" and expect to hit it precisely, if at all! I can't wait to see the hi-res images from the little cubesat that followed it and took the pictures of before/during/after the impact (Italian Space Agency’s LICIACube satellite) . A lot of good science there. Waytogo, APL!!

    1. Trivial?

      Relatively easy, given that we've done all that and much more, with vacuum tube technology, time after time, using multiple mature technologies older than most people on the internet?
      Absolutely yes.

      The only thing less spectacular than NASA hitting Dimorphos, given their competence the last 30 years, would have been NASA missing the target entirely. They'd have had to work to be that stupid, but I have the utmost confidence in their incompetence, and I think we've barely plumbed those depths.

      NASA should rename the whole program "Observation and Obstruction of Planetoid Structures". No other acronym could be so apt for any government agency from now until the end of time.

  5. The last full frame is reported to show an area 100 meters on a side.