Ouatcheur t1_jall102 wrote
Orbit duration is a zilch-usefulness information.
What we need to know is by how much would an actual asteroid deflected (angle), and that is determine by the inverse square of it's speed.
i.e. an asteroid twice as masssive need a blast twice as big to be deflected by the same total angle. But an asteroid twice as fast, needs a blast FOUR TIMES as big. Kinetic Energy is proportional to square of speed after all.
I searched everywhere, found that pre-impact orbital velopcity was either 0.174 or 0.177 m/s. No word on the post-impact orbital velocity.
The about 11 hours orbit was lengthened by about half an hour. Supposedly, this means if you slowed down the thing by about 1/22 of it's pre-impact speed, then it's post impact speed would give just about that time interval for it's new post-impact orbit.
Going from 0.177 m/s to 0.167 m/s is a measly 1 *centimeter* per second speed vector change, in this case here a reduction, but it could be in any direction, really.
Also, found zero data on actual angular effects, too.
A real, typical asteroid moves at what, 18 km/s, average?
Does this mean that for this "planetary defense" thing to work, we'd have to scale it up by a factor of about 1 800 000 ? Just to get the same amount of angular deflection?
Good luck with that, I guess.
I think they focus only on giving the "whopping" 32 minutes orbital revolution slowdown change, because if they told the entire story clearly, that the dimorphos asteroid was deflected only by a measly 1 centimeter per second, then everybody would immediately see that this "solution" is laughably NEVER going to successfully "defend" us vs an actual asteroid coming for us.
Accelelolita t1_jam5av4 wrote
> typical asteroid moves at what, 18 km/s, average?
Get off wikipedia and go hit the astrophysics books lmao.
Ouatcheur t1_jauvidx wrote
Get off your dusty old books dating from before relativity explained Mercury's recession, and just put a bit more faith in actually fact checking reliable sources directly yourself?
Also, please get off your high horse. When you come with such an agressive attitude, the impetus is on you to prove your point, instead of just doing nothing more useful than throwing the cheap blow of an Ad Hominem without any extra substance to it than that.
That 18 km/s figure comes from the Lunar and Planetary Institute.
https://www.psi.edu/epo/ktimpact/ktimpact.html says :
Asteroids hit Earth typically at high speeds of 16 to 32 km/sec
Some move way faster and those are the really most dangerous ones. The 18 km/s is just some average, the reality is of course a spectrum.
That one is said to move "at warp speed" but it is moving at about "only" 6 km/hour. STILL at about twice the size of dimorphos it remains a super dangerous potential extinction event.
Still, the overall logic remains true within an order of magnitude for more or less similarly sized, similar speed asteroids.
Keep on laughing your ass off and judging others while actually contributing absolutely nothing that would be actually useful to the discussion. Congratulations!
cant-login-to-main t1_jatda8r wrote
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.
Viewing a single comment thread. View all comments