Recent comments in /f/space

Ouatcheur t1_jalot2h wrote

Reply to comment by SirLauncelot 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

Nope. The energy that is trsnsferred from the DART to the asteroid CANNOT be higher than the initial kinetic energy it has initially, no matter the way it penetrates the asteroids.

You don't get energy out of nothing!

But people often ignnore that the total enerrgy before must equal the totlal enerrgy after.

And before it is:

DART + ASTEROID.

And after is is:

now-a-bit-saller-ASTEROID + its-EJECTA

People just tend to ignore the ejecta.

so in their minds it is

DART + ASTEROID(before) = ASTEROID(after)

or even worse it is:

DART + ASTEROID(before) + magicalwaytheimpacthappened = ASTEROID(after).

Like in "Oh it hit the dense core so it transferred MORE energy". Morer energy than what exactly? The DART fully crasthe asteroid, its, so it's gonna give 100% of it's kinetic energy no matter what. No "it transfers more than 100% because it hit something more solid". Duuh huuh huuh.

Sp, always remember the ejecta. And note that the ejecta is mostly ejected in the OTHER direction.

So the *only* way for the kinetic equations to balance out is for the asteroid to move faster once accounting for its ejecta (faster than if there hadn't been any ejecta at all).

The solidity of the "central" core part is irrelevant.

As the DART experiment proved, the amount of ejecta gives a MAJOR effect to the results.

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Ouatcheur t1_jalmnj2 wrote

Reply to comment by kmaxile 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

Moving fast doesn't screw radio signals up. Not unless you move at relativistic speeds in which case all it does is change the speed (the frequency and the data rate) of the signal. Not "jumble it out".

But 6 km/s while it sewsmc fast for us at ground level, it pitifullly slow when comparing to light speed. the relativistic Lorentz transformation effect aat such relative speeds is so tiny as to be completely ignorable.

And there is no atmosphere in space, either, so moving fast won't shake you around like a plane flying too fast beyond it's structural limits and being destroyed by air turbulences. There is no "wall of air" in front of you to constantly apply friction and slow you down: there is (next to) nothing! Basically, ideal conditions for moving around.

It is not the engine's power and speed that gives off that 6 km/s. It is the slow ACCUMULATION of speed by the engines. Forget Hollywood sci-fi when they nearly instantly reachh full speed when they lit the engines, then magicallly slow down to a stop when they turn the engines off. Things don't work like that in reality. At all. Think more like this: your spaceship has a speed vector. Each time unit, you move by that speed vector. It doesn't matter if you rotate where your ship is pointing at, it moves in the same direction of that vector. That is called inertia: things tend to keep on moving the same way unless a force is applied to them to counteract that. Now, you have engines, but all they do is, each time unit, add a TINY speed vector. Say, after accelerating for one hour, you are now moving 5 km/s from bottom to top. You could turn the ship sideways to turn to the "right" and lit your engines for say another hour. Then you'd be moving the same 5 km/s from bottom to top PLUS 5 km/s from left to right, thus now your speed vector is about 7.4 km/s going "top and right".

It takes a long time to accelerate something to 5 km/s. For comparison the fastest hypersonic jet known movves at Mach 6.72 = 4520 mph = just about 2 km/s. And that is with a jet with a superbly monstrous and HEAVY engine, that can use the abundant "thick" air it travels through as for it's oxygen for nburning it's fuel much hotter. Not the measly "built to work in space" engine of a little very fragile satellite. These two things can't even be compared.

Presumably, DART's propulsion systems were turned off for its very final segment, letting DART final closing in "sail through" mode, without any engines vibrations in other to get the best images. No atmosphere, means no vibrations and no friction. And very clear images, too. Once you turn the engines off, you just keep on moving inertially at the same speed.

From the point of view of DART, once itS' engines are off, it is immobile and it is Dimorphos that is closing towards it at 6 km/s. Not the other way around.

Because Special Relativity, ya know.

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space-ModTeam t1_jall3b1 wrote

Reply to Theoretically, could we see another giant galaxy in our sky if… by Careful_Swordfish742

Hello u/Careful_Swordfish742, your submission "Theoretically, could we see another giant galaxy in our sky if…" has been removed from r/space because:

  • Such questions should be asked in the "All space questions" thread stickied at the top of the sub.

Please read the rules in the sidebar and check r/space for duplicate submissions before posting. If you have any questions about this removal please message the r/space moderators. Thank you.

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Ouatcheur t1_jall102 wrote

Reply to 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

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.

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learntospellffs t1_jalky47 wrote

Reply to Your Questions for an Astronaut by DerVodkaOtta

I asked another astronaut on here this question a few months ago, but didn't get an answer (not blaming him, I squandered my first contact with him by gushing over the fact that a person on the edge of space was talking to me, and he was swamped with many questions)

So my question is, how hard/easy is it to fall asleep in zero G? And are dreams affected in any way?

And if I may be so cheeky, I'd also love to know if anyone has experienced the effects of THC in zero G. For uh, research purposes, y'know?

Thanks!

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