cant-login-to-main t1_jatda8r wrote
Reply to comment by Ouatcheur in NASA’s DART data validates kinetic impact as planetary defense method | DART altered the orbit of the asteroid moonlet Dimorphos by 33 minutes by mepper
Bruh, go read up on orbital mechanics or something. You really think you know better than the scientists that worked on this mission?
Ouatcheur t1_jautk5r wrote
No I don't I never said or even implied it, it's you projecting something on me that just ain't there. I think you deeply misread me anbd my intent. Of course such an experiment is a vital one. But all media even NASA website definitely focus only on the half hour differential over the previous 11 hours orbit, and very hard to find data on the actual resulting delta V.
It is cherry picked information to make it seems as if it was a huge effect, but while it is indeed a huge accomplishment, in terms of actual delta V this is a tiny effect.
It is way too easy to just say "Go learn this!" in a condescending and dismissive way. While without correcting anything.
Well, I checked my numbers. Did you? I dare you to do the same computations yourself. And yeah when just trying to get a ball park figure, you are allowed to use simplified formulas, as long as they don't introduce "orders of magnitude" errors. No need to be a "scientist", kinetic energy formulas are simple.
And for tiny angles, sin (angle) is proportional to the angle.
Inverse proportional relationship: Mass <===> Resulting Delta V.
Inverse square proportional relationship: Speed <===> Kinetic energy ==> Resulting angle differential (for small angles) obtained from applying some force.
It's not rocket science. Orbital speed of dimorphos around it's primary is one thing, and it is super slow. Overall speed of a typical asteroid is over ten thousand times higher.
So with DART we got a resulting Delta V of 1 of a centimeter per second.
Over a year, that is approx less than 300 kilometers of deviation. This is only an order of magnitude value here as of couse orbital mechanics mean curved, not straight, trajectories. But the deviation remains a small one. The compounding effects won't magically stack up to somehow give superbly different total values for the final asteroid's position.
But here we want to deflect an asteroid so that it "misses Earth". This means we have to (at most) speed it up or slow it down or deviate it by approx 6500 kilometers (half the Earth's width). So you have to catch the asteroid really early on, or apply way more force than DART did, to succeed. Or preferably, both.
The media is all gloating about the "huge feat" without also talking about how you'd need scores and scores of DARTs to do the ACTUAL job of deviating an actual asteroid successfully, not just apply a super tiny actual delta V to it's orbital period. Something beyond our capabilities. "Just send a more massive DART that moves faster, and/or send a lot of DARTS", that means requiring a LOT more fuel.
We are still far from having a valid asteroid planetary shield defense. Very far. It doesn't take "top scientists" to see that, just checking the numbers at a very basic level and yet at a little bit more depth than just the surface evaluation of "Oh wow half an hour of an 11 orbit that is like about 1/20 of the job done!" when the ACTUAL job isn't changing a slow orbital speed by 1 centimeter per second, but changing a way faster collision vector speed by a whopping lot more.
DART is cool and all, but it fails to properly show how huge the task really is.
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