coriolis7
coriolis7 t1_jajr75p wrote
Reply to comment by Kear_Bear_3747 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
Not exactly. Momentum is always conserved, but the kinetic energy is not. A fully elastic collision preserves kinetic energy, while a partially inelastic collision does not.
In both cases m1 x v1(initial) + m2 x v2(initial) = m1 x v1(final) + m2 x v2(final).
However, only in the fully elastic collision does the following hold: [m1 x v1(initial) + m2 x v2(initial)] / 2 = [m1 x v1(final) + m2 x v2(final)] / 2
It doesn’t matter if it’s in space, in a lab, or wherever.
I think what the above redditor was saying is that because the outer material was more loosely held, more of the material could be ejected. That ejected material has additional momentum. Even though the probe never bounced off (ie elastic collision) the ejected material made the collision act as partially elastic.
coriolis7 t1_j1skhk9 wrote
Reply to comment by Commies4Lyfe in Meet the amateur astronomer who found a lost NASA satellite by jarvedttudd
They design everything to have an extremely high chance of surviving the mission life at full operational capability. If they design each system to have a 50% chance of surviving 2 years, and there are 5 systems, then there’s only a 3% chance the mission will actually make it to 2 years.
Even then, if NASA wants 2 full years, then they’ll shoot for a high likelihood of meeting it, like 95+%. That means there’s a decent chance it’ll make it well past 2 years.
coriolis7 t1_iqxlvrt wrote
Reply to comment by JagerBaBomb in After DART: Using the first full-scale test of a kinetic impactor to inform a future planetary defense mission by EricFromOuterSpace
No, because the impact is not an ideal collision. There is material ejected, which influences how much the momentum of the body changes. We have a rough idea of how much the velocity should change, but it’s still unknown how much, like on the order of tens of percent compared to theoretical.
If we underestimate how much of an effect an impactor has, we may expend far more resources or take more risks than are necessary to avoid a collision with Earth. Overestimate and we either get hit, or we have to send a second mission which may require an even larger deflection than the original mission (due to a shorter amount of time for the velocity variations to add up to a planetary miss).
coriolis7 t1_jak3dle wrote
Reply to comment by workingdad83 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
Sorry about the formatting, it makes a lot more sense when you see it properly formatted. The unformatted above is kinda dry to the eye.