Asteroids and space physics

efreysson

Closer than ever
Super Member
Registered
Joined
Jan 23, 2007
Messages
1,618
Reaction score
101
Location
Iceland
I'm working on the outline for my new space opera WIP, and I want the climax to be about a terrorist group directing an asteroid towards an inhabited planet.

I need to somehow justify the good guys not simply blasting it into oblivion with their massive warship, so the idea is by the time they arrive it is already so close that blowing it up would result in a shotgun blast hitting the planet, rather than a cannonball. So they have to land on the asteroid themselves, and redirect it away.

Can someone help me with making the physics of this somewhat plausible? My initial idea was that the terrorists install a gravity generator (my handwave-y excuse for ships having on-board gravity) on the asteroid, but would giving it increased mass change its trajectory? That also leaves me with the problem of directing the asteroid away from the planet.

Installing starship engines on the asteroids kind of goes against my vision for the climax, but is that my only option?
 

waylander

Who's going for a beer?
Super Member
Registered
Joined
Oct 24, 2005
Messages
8,263
Reaction score
1,560
Age
65
Location
London, UK
Can they run the ship's engines while it is firmly attached to the asteroid?
 

efreysson

Closer than ever
Super Member
Registered
Joined
Jan 23, 2007
Messages
1,618
Reaction score
101
Location
Iceland
Can they run the ship's engines while it is firmly attached to the asteroid?

Ah, now there's an idea. But that still leaves me with directing the asteroid at the planet.
 

waylander

Who's going for a beer?
Super Member
Registered
Joined
Oct 24, 2005
Messages
8,263
Reaction score
1,560
Age
65
Location
London, UK
Depends on the orientation of the ship. If they deliberately land it with this in mind then no problem
 

L.E.N. Andov

Super Member
Registered
Joined
Mar 4, 2017
Messages
59
Reaction score
3
Location
Charlotte area, East Coast U.S.A.
If I place a bowling ball on the beach it will sink slightly. I can move that bowling ball by removing sand. I don't think I could ever raise the bowling ball by digging under it but I can make it move. If the bowling ball "wants" to move in a straight line toward the earth's center of gravity, then I can alter its course by providing a path of lesser resistance.

I think you have two choices here. First, you could divert the asteroid. Second, you could move the planet.

Do any of your ships use a mobility tech that warps space? Would arriving or departing bend space? I just had an idea that your hero could look like cowards escaping but actually turns out they were diverting the asteroid.

Lemme know whatcha end up using

(A)
 

efreysson

Closer than ever
Super Member
Registered
Joined
Jan 23, 2007
Messages
1,618
Reaction score
101
Location
Iceland
Can someone chime in on my whole "gravity generator" idea, and whether it would work? I realise it's probably bullshit, but I would prefer to confirm it before moving on to other ideas.

Also, any idea on how close an asteroid has to be to a planet that blowing it up actually wouldn't prevent a disaster? Ie, how much time the heroes have to deal with it?
 

blacbird

Super Member
Registered
Joined
Mar 21, 2005
Messages
36,987
Reaction score
6,158
Location
The right earlobe of North America
Can someone chime in on my whole "gravity generator" idea, and whether it would work? I realise it's probably bullshit, but I would prefer to confirm it before moving on to other ideas.

It's no greater bullshit than faster-than-light travel or time-travel or teleportation. Or, God knows, dilithium crystals and "replicators", standard fare for Star Trek stories. You're writing SF. SF aficionados are accustomed to accepting impossible physics that make a good story work. Don't over think it. Just . . .

"Make it so." -- Star Trek Enterprise Captain Jean-Luc Picard.

caw
 
Last edited:

Techs Walker

Super Member
Registered
Joined
Jan 23, 2017
Messages
244
Reaction score
87
Location
Out walkin'
Howdy efreysson,

I'm kind of with the bird on this one, but here's a question that only you can answer: How far along the technology fantasy spectrum are you willing to go for your story? You say 'space opera', so perhaps you're fairly tolerant, and that's fine. But here's a possibly related question: Are you willing (or perhaps even eager) to have a constraint imposed by currently known physics be a plot element? For example, there was a very plausible discussion upthread about using thrust from a spaceship in contact with the asteroid. Here, the constraint is the need for the spaceship to be in contact, but that could be part of the plot complication. FWIW, there are also non-contact methods of applying thrust, if you want to relax the need-for-contact constraint.

It's no greater bullshit than faster-than-light travel or time-travel or teleportation. Or, God knows, dilithium crystals and "replicators", standard fare for Star Trek stories. You're writing SF. SF aficionados are accustomed to accepting impossible physics that make a good story work. Don't over think it. Just . . .

"Make it so." -- Star Trek Enterprise Captain Jean-Luc Picard.

caw

Like the bird said, story first, but do you want technological constraints to play a role in your plot? Or would you rather avoid 'pesky details'?

Techs
 

L.E.N. Andov

Super Member
Registered
Joined
Mar 4, 2017
Messages
59
Reaction score
3
Location
Charlotte area, East Coast U.S.A.
..."gravity generator" idea, and whether it would work?..how close an asteroid has to be to a planet that blowing it up actually wouldn't prevent a disaster? Ie, how much time the heroes have to deal with it?..

Yes, it will work, as long as your characters must do certain things to accomplish it. There must be a risk that they overtighten a screw or forget to plug something in. The risk of failure doesn't come from "is this possible?" Fail would be because it wasn't done correctly. And of course, theres always the aftermath and unforeseen consquences. Write it in such a way that the goal is clear to the reader and they will engage with the journey instead of the destination.

Gravity is a trait or condition that physical matter has. The more massive an object is, the stronger the effect of gravity is associated with it; felt near it. Any other force is different from gravity. A gravity generator would have to either bring massive (dense not necessarily big) materials into the area or else tunnel thru space in such a way that gravity from the distant massive object could tug on your asteroid. This wouldn't be hard to write and it would be fun to ponder. Ditto SF fans are willing to accept fancy things. Maybe less is better here. Let your reader's imagination do the work rather than writing pages of supporting information.

The "how close" question is easy to answer. You need to think about the size of the pieces. The danger factor is the kinetic (motion energy) math. Tiny pieces can burn up in the planet's atmosphere. Big pieces will make it the surface. That's where craters and tsunamis come from. The energy is transferred from the ball to the glove.

If you blow it up you are spreading the mass across multiple fragments. But the total energy is still (mostly) retained. The pieces could drift apart or they could hang out, depending on what they are made of and how they were smashed. If they spread out your planet is in a better position. A sock full of wet sand smacking you in the face hurts just as bad as a softball even though its a bunch of tiny pieces.

Don't get bogged down in the materials analysis or the math behind the bomb tho. If you can dustify the asteroid far enough out, problem solved. Most of it will blow past the edges without hitting the planet. If your bomb only turned a baseball into a sand-sock, well...

The amount of time is easy also. Once you decide "what" will hit the planet (leftovers or none at all), then you decide how long it would take to put the intervention in place. Make sure you weave rising tension into this. Your reader probably thinks the planet will survive, but they keep reading to see how close a call it will be. Put the asteroid far enough away and make it go a reasonable speed and make it detectable that far away.

If you did use some kind of tunneling, either for gravity or as a portal to capture the asteroid, you provide yourself with a couple threads to pick up on later. In the sequel perhaps. Bombing an asteroid is kinda lame to me(I think Bruce Willis did it). What would really make me keep reading is if Bruce Willis blew up on the Launchpad along with the bomb and now we only have (doomed time frame). But this is a darkest hour and more than you were asking for.

Sorry I got diarrhea of the keyboard on you

(A)