DART mission successfully altered asteroid's orbit | Hacker News Reader

DART mission successfully altered asteroid's orbit

nasa.gov

37 pointslqet14 comments

"Prior to DART’s impact, it took Dimorphos 11 hours and 55 minutes to orbit its larger parent asteroid, Didymos. Since DART’s intentional collision with Dimorphos on Sept. 26, astronomers have been using telescopes on Earth to measure how much that time has changed. Now, the investigation team has confirmed the spacecraft’s impact altered Dimorphos’ orbit around Didymos by 32 minutes, shortening the 11 hour and 55-minute orbit to 11 hours and 23 minutes. This measurement has a margin of uncertainty of approximately plus or minus 2 minutes."

Saw this quote in the WSJ[1]:

> Alan Fitzsimmons, a DART investigation team member and astronomy professor at Queen’s University Belfast, said he would like the gravity tractor technique tested next, “because it’s actually very difficult to accurately guide and maneuver spacecraft in very close proximity to an asteroid.”

For the gravity tractor technique, I’m curious whether any experts here could explain just how challenging it would be to have a spacecraft match the speed and path of an asteroid headed to Earth. Could you take an elliptical path, and how much fuel would you need to match the asteroid’s velocity? How would that compare with past missions with a return component (e.g. the moon)?

As a layperson, just smashing into an asteroid seems like much simpler technique, if admittedly less elegant.

[1] https://archive.ph/20221011184904/https://www.wsj.com/articl...

The thing with the gravity tractor is that all the energy needs to come from the spacecraft itself. Whereas with impactor design you can use energy from the Earth's relative motion to the incoming object.

The solar system has had 4.6 billion years to settle. To me, being ignorant of the field, it seems dangerous to artificially nudge asteroids like this. Who knows what butterfly wings will do when small gravitational effects begin to cascade. That said, there is a lot of space out there and the probability of disrupting the equilibrium is probably very low.

This is why we nudged the moon in this asteroid pair. Overall the change in the entire system is much smaller and less of an effect on the overall solar orbit of the pair.

This was effectively a nearly perfect opportunity to, safely without the risks your mentioning, test the concept before we need it for real in an emergency.

Thank you for this insight. I had no idea that was the reason.

The good news was it was successful. The bad news is they way under predicted the amount of redirection. Back to the physics drawing board to understand this.

Did they? Article says mission had a minimum successful change but it says nothing on whether the actual change was successfully predicted.

NASA's press conference said the result was in the upper end of the predicted range, which was between "a few minutes and several tens of minutes" depending on the (unknown) physical makeup of Dimorphos.

Studying the impact and debris plumes is expected to help scientists learn more about Dimorphos.

I linked the press conference as primary source in my sibling comment if you're curious, although it didn't go into much more detail: https://news.ycombinator.com/item?id=33169879

During the press conference [1], they stated that there was a variety of models that depended on the physical properties of Dimorphos, which were not well known.

The estimated range by which the orbital period would be shortened was between "a few minutes and several tens of minutes" and that 32 minutes is "consistent with the estimates but at the upper end of that range".

They also showed a pretty fresh Hubble image of debris plumes from this past Saturday and mentioned that teams are working to use the data and imagery to better understand the composition of Dimorphos.

[1] Discussion starts around 11:25 in this video: https://www.youtube.com/watch?v=Zhzn0U2m5wQ&t=685s

That's not what they said though. It was within the 3 sigma error bars of the amount of deflection, if at the edge of them.

At least having an asteroid falling on our heads will be one less thing to worry about destroying us.

A little less, but this was a small asteroid. Dimorphos is 170-ish meters in diameter. The asteroid that made the Chicxulub crater (the accused dino-killer) is thought to have been 10 kilometers in diameter.

Yes but an asteroid that large can be detected and deflected much further away such that even a “nudge” such as this test can avoid earth impact.

Reply on news.ycombinator.com