Science: asteroid vs. hero physics

[Tonguez]

So could the pico-gel be used to collect up all the space debris in orbit and use that as her bullet?

Of course there’s the power of narrativium which would allow cool effects like having the asteroid graze the atmosphere until her suit channels te increase energy to expel the asteroid in fiery aurora explosion the lights up the sky around the world (ie every thing works through the power of cool)

 

[tomBitonti]

so are you saying, speeding up the asteroid might actually work?

And you raise the other elephant in the room, if the asteroid doesn't hit the earth (she wins), it's still out there, ready to be a problem again...

Any other solutions to that, besides let it hit the earth? Or is there a way to hit the earth safely? Or build a parachute for it? or wings to land it like a shuttle?

I don't think she can drill it fast enough or disolve it with her pico-printer-gel (think my version of nano-tech, but smaller)

Yes to speeding up the asteroid ... in very specific initial conditions. (Think of a putt that grazes the cup going too fast.)

Yup, it's not just enough to perturb the initial trajectory. Unless the asteroid is booted out of orbit entirely, it either needs to get into a stable orbit, or it will hit earth anyways, say, after looping away for a short bit.

A solution might be to dissolve the asteroid into a dispersed mist (or maybe a very fine gravel?). I'm not sure what will happen in those cases. Say, have the pico-gel go van-neumann (start self replicating, by doing an ultra dangerous removal of safeguards against such,"But the manual said never every enable full self replication!") and have it burrow through the asteroid and break it into millions of fragments.

Thx!
TomB

 

[Nagol]

Yes to speeding up the asteroid ... in very specific initial conditions. (Think of a putt that grazes the cup going too fast.)

Yup, it's not just enough to perturb the initial trajectory. Unless the asteroid is booted out of orbit entirely, it either needs to get into a stable orbit, or it will hit earth anyways, say, after looping away for a short bit.

A solution might be to dissolve the asteroid into a dispersed mist (or maybe a very fine gravel?). I'm not sure what will happen in those cases. Say, have the pico-gel go van-neumann (start self replicating, by doing an ultra dangerous removal of safeguards against such,"But the manual said never every enable full self replication!") and have it burrow through the asteroid and break it into millions of fragments.

Thx!
TomB

Considering the thing is in a century orbit, the perturbation is likely to be insufficient to yank it into a secondary pass. It's more likely to fly away and become a threat again in a few thousand years (maybe). If the hero is a particularly lucky math genius then the perturbation could either (a) reduce eccentricity and keep the asteroid outside Earth orbit or (b) have it hit the moon as it moves away from the Earth.

Converting the asteroid to dust would have potential if there was time for the dust to start to disperse. Dust or a single solid lump, it contains the same kinetic energy -- dust would just tend to release it faster as it hit the atmosphere. More *boom* less splat.

 

[Ovinomancer]

Hmm. Earth is moving pretty quickly in space, so, depending on approach vectors, speeding the asteroid up or slowing it down a bit should generate enough 'miss' if you're far enough out.

For example, if the asteroid is crossing the orbit of Earth perpendicularly, the window to strike Earth is only 13,000 km / 30 km/s or about 435 seconds (about 7 and a quarter minutes). Assuming the asteroid aimed precisely at the center of Earth, you'd need to speed up or slow down the approach by half that 7 minute time, or about 4 minutes to be safe (240 seconds). A 4 minute delta in arrival time depends on the velocity of the asteroid and how long you take to start the acceleration. Assuming a 50 km/s speed on the asteroid, 4 minutes at 1 hour distance is a ratio: needed speed over current speed = needed time over original time. Or needed speed = original speed x (new time/old time). In this case, needed speed = 50km/s x (56 minutes/60 minutes) = 50 km/s x (.933) = 46.67 km/s. You'd need to generate a delta-v of 3.33 km/s at exactly 1 hour out (or earlier) to cause a complete miss. I think this is lower than the necessary delta-v to accelerate the mass sideways 6500 km over an hour (6500km/360 seconds = 18 km/s, so, yep, 6 times less).

Now, if your geometry has the asteroid coming in much closer to the orbital direction, this changes, as earth's relative movement is much less with respect to the path of the asteroid. However, a rock launched from the asteroid belt some time in the past should have a high angle of intercept to Earth's orbit, as it would be on a steep elliptical around the Sun. But, assuming a near head on collision, say at about a 20 degree approach, combined delta-v would be 30km/s (Earth) plus cosine(20)x50km/s or about 77 km/s. Earth relative speed on the perpendicular would be sin(20)x30km/s or about 10km/s. This puts a Earth on-target time window of 1300 seconds or 21.7 minutes. Again assuming a center strike, that's a time window of 11 minutes you have to modify. Needed speed up/slow down delta-v at 1 hour would be 14.7 km/s. This is still less than the needed perpendicular delta-v to cause a miss, although not much.

Orbital mechanics are funny. Often speeding up or slowing down along your path causes huge changes in orbit, while orthogonal thrusts change orbits more slowly. For the purposes of your story, gathering up a bunch of debris and smacking the asteroid just enough to slow it down would be sufficient for a high angle of intercept. This is the most likely scenario given the orbital geometries of a rock launched from the belt that's coming around again.

A neat way to tell this story might be that the angle of impact is such that meeting the asteroid and speeding it up is the right call (this would be the case if the asteroid was going to hit on the forward half of the Earth). Timing could be such that the push means the ateroid scrapes the atmo and skips, causing an awesome light show and placing the heroine at risk.

 

[Janx]

So could the pico-gel be used to collect up all the space debris in orbit and use that as her bullet?

Of course there’s the power of narrativium which would allow cool effects like having the asteroid graze the atmosphere until her suit channels te increase energy to expel the asteroid in fiery aurora explosion the lights up the sky around the world (ie every thing works through the power of cool)

adding more details (ain't like y'all are gonna spoil it for readers). The suit is a Vid Liv Kostym, a swedish acronym I made up with Google Translate to spell VLK which thus smells like Valkyrie. It's got mass driver bracelet/anklets, solar panel wings bonded to the back and a happy coat of pico-printer-gel for general protection and utility. Plus BalDR, the Ballistic Defense Ring, satellites hosting an AI that does all the heavy lifting, math-wise.

So the mass drivers can move matter around up to some range and weight limit. They'd be how she scoops up space debris to make a shield or something. The pico-printer-gel does the fine detail work of re-organizing that matter when it's brought into range to make electronics, repairs, heal injuries by re-organizing atoms (hence why I went tinier than nano-tech).

All of it limited by the power of narrativium as Tonquez surmises. Basically if it sounds good or plausible within what I described above, but not too powerful. Much like Umbran asking if she could kill the planet. I guess, but I already got an asteroid on the way to do that so it ain't OP right now...


Tom's idea to replicate the pico-gel is good. I had similar thoughts but ruled them out for purposes of just dissolving the asteroid to save the day was "too easy" Presumably, something about the total mass vs. time isn't possible.

Now I could have it that Mars has been sending these every year or something, rather than looping around a century later. Mars doesn't play directly into the story, it's just the big final reveal of how nobody understood what really happened to Earth.


So to recap the ideas:
perpendicular attack to deflect
speedup to skip might work
dissolve it - not allowed per original restriction of too easy unless we think of some complication
put a rocket on it and push (hauling a rocket up might be too heavy or slow)
build a mass-driver on it and move itself (variant of rocket idea)


Did I get everything? There's a lot of posts since I got back, sorry if I missed something. I'll be re-reading these after I finish my night-shift of work...

I'm hoping for one that is risky to her, and being non-obvious. Extra points for if its something a sniper would think of OR if it required her to get close and personal (the opposite of a sniper's mentality). Also, in the current draft, I only have 300 words left in my 6K budget.

BTW, thanks to all of you for participating. Good ideas from everybody. I had a hunch that whatever I thought of might have a hole that y'all would find, which would ruin the story for some. Plus, hopefully this is fun.

 

[Umbran]

Orbital mechanics are funny.

Yes, they are. But in this situation, those are not so telling, unless you have much longer timescales to work on. The lightsail idea mentioned upthread can work on these premises - much lower thrust applied over days, months, or even years, to subtly change orbits.

Over the course of minutes as given in this scenario it is somewhat easier (and more understandable to an audience that isn't made of rocket scientists) to take this from the point of view of the Earth as the center of the coordinate system. In that, we simply have a target (the Earth) and a projectile (the asteroid).

 

[Ovinomancer]

Yes, they are. But in this situation, those are not so telling, unless you have much longer timescales to work on. The lightsail idea mentioned upthread can work on these premises - much lower thrust applied over days, months, or even years, to subtly change orbits.

Over the course of minutes as given in this scenario it is somewhat easier (and more understandable to an audience that isn't made of rocket scientists) to take this from the point of view of the Earth as the center of the coordinate system. In that, we simply have a target (the Earth) and a projectile (the asteroid).

Treating Earth as a fixed point completely ignores the geometry of the problem. The asteroid is essentially a bullet fired leading Earth, on a rendevous to meet it, not a bullet fired directly at a stationary Earth.

There's a 6x difference in needed delta-v 1 hour out by treating the problem as an orbital one rather than a fixed Earth one (3.3 km/s vs 18 km/s). This was calculated as instantaneous delta-v at one hour out, so I have no idea where light sails come into that. Heck, at 5 mins out, ypu need to slow the object by 40km/s (80% of it's 50km/s speed!) to cause a miss, but you'd need 108km/s (216%!!) to generate the same miss by perpendicular thrust. Ignoring Earth's 30km/s speed and the fact this is a rendezvous problem not a fixed target problem is the oversight, here.

The acceleration needed will vary by object mass, but the delta-v doesn't care. For the 1 hour out case, and assuming a 1EE14 kg mass at 50km/s (roughly the same as the Chicxulbub impact), let's look at a 10 minute burn application centered at 1 hour out. The needed delta-v to slow or speed the stroid is 3.3km/s. Over 10 minutes, the a is 5.5m/(s x s). The F needed is 5.5EE14 N. The lateral shove needs an a of 30m/(ss), and an F of 3EE15 N. An order of magnitude more force!

So, no, no lightsails or slow accelerations here.

 

[Janx]

Treating Earth as a fixed point completely ignores the geometry of the problem. The asteroid is essentially a bullet fired leading Earth, on a rendevous to meet it, not a bullet fired directly at a stationary Earth.

There's a 6x difference in needed delta-v 1 hour out by treating the problem as an orbital one rather than a fixed Earth one (3.3 km/s vs 18 km/s). This was calculated as instantaneous delta-v at one hour out, so I have no idea where light sails come into that. Heck, at 5 mins out, ypu need to slow the object by 40km/s (80% of it's 50km/s speed!) to cause a miss, but you'd need 108km/s (216%!!) to generate the same miss by perpendicular thrust. Ignoring Earth's 30km/s speed and the fact this is a rendezvous problem not a fixed target problem is the oversight, here.

The acceleration needed will vary by object mass, but the delta-v doesn't care. For the 1 hour out case, and assuming a 1EE14 kg mass at 50km/s (roughly the same as the Chicxulbub impact), let's look at a 10 minute burn application centered at 1 hour out. The needed delta-v to slow or speed the stroid is 3.3km/s. Over 10 minutes, the a is 5.5m/(s x s). The F needed is 5.5EE14 N. The lateral shove needs an a of 30m/(ss), and an F of 3EE15 N. An order of magnitude more force!

So, no, no lightsails or slow accelerations here.

so to recap this (which tests my rudimentary understanding as I digest and keep it simple in the story):

the planet-killer asteroid has a mass of 1EE14 kg and is traveling at 50km/s (same size as Chicxulb)

by realizing that the rock is leading the moving target of Earth (a sniper thing to do), messing up that timing will save the day

If she can get behind it and speed the rock up, it takes less force than a pushing from the side, which is something she might be able to do

I can make it scrape the atmosphere for a lightshow and heat up, since she's personally pushing this thing, thus creating the danger through art of wordsmithing. To solve the repeat-performance problem, I can have her set the pico-printer-gel to chewing away at it, which in another hundred years, probably wouldn't be a problem. I'll come up with something to explain how she got so much force, but it's easy to justify in words that this is more feasible than pushing from the side once I throw in "order of magnitude"

I don't know how much techno-babble I'll put in, but y'all have given enough detail that if this version of the plan is plausible, I can take it from here.

Thanks!

 

[Eltab]

Larry Niven's novel The Smoke Ring has a poem (6 lines or so) about what direction a thing in orbit will really move when you push on it, compared to the things around it. It might help you visualize the changing situation as Our Heroine is working on the problem.

Once in a while, borrowing everything I read from the library has a downside: I can't just copy the poem here.

 

[Janx]

another wrinkle in the heroics is catching up to this thing and matching speed to then get behind it to push.

that seems like it could be action packed, but also complicated. unlike superman, where smashing headlong into it would be easy, if she flies toward it, she's got momentum in the wrong direction once she gets there. I assume she could zip out to some midpoint, then reverse direction and bring herself back up to speed as the asteroid catches up

I'm sure the mass-driver system she uses defies conventional physics, but...