Jump to content

What I learned from ARM


Monger
 Share

Recommended Posts

And even if you do, the maneuver node system might not indicate an intercept until separation is only a few km.

The maneuver node system changed with the ARM; I can see "closest"-approaches out to hundreds of thousands of kilometers not just for planets but also targets like asteroids. Much, much easier to make solar-orbit rendezvous now. (Note that "easier" does not mean "easy".)

-- Steve

Link to comment
Share on other sites

PS My issue in Armageddon is wouldn't it be easier to teach astronauts how to deep drill, rather than teach deep drillers how to be astronauts? (answer: Micheal Bay film)

Also, there's the fact that people like to think that a blue-color everyman could save the day, instead of an Astronaut with a PhD.

Link to comment
Share on other sites

I just caught my first class D asteroid which was on direct collision course to Kerbin. Things I learned from that mission:

  • "Deep Impact" was pretty stupid. You don't need nuclear bombs to move asteroids, you just have to catch them early enough and give them a little nudge.
  • "Armageddon" was insanely stupid. For several obvious reasons, but especially that if the Earth vista is already filling the Asteroid's horizon, you are WAY too late.
  • kind of shocking: even if you discover an Asteroid really early on (say, a year before impact), it might be practically impossible to find a Rendez-Vous point. My class D asteroid had a really benign orbit (same orientation as Kerbin's orbit, only slightly crossed), and still I just caught it like 40 days earlier (of 170 days discovered before impact)
  • Generally speaking: finding a proper interception path is not simple. I am so used to more or less planar orbits, and that I can choose where to intercept my target, I really had to rethink how and where to intercept.

Also, ARM taught you that these movies were stupid!? Armageddon and Deep Impact taught me that Armageddon and Deep Impact were moronic 15 years ago.

Link to comment
Share on other sites

Also, ARM taught you that these movies were stupid!? Armageddon and Deep Impact taught me that Armageddon and Deep Impact were moronic 15 years ago.

I justed wanted a frame of reference. I would have mentioned "Gravity", but none of its logical loopholes had anything to do with asteroids.

Link to comment
Share on other sites

I don't think real object can be spinning around more than one axis, physics laws don't allow that IMO - unless the spin is forced. Yes, real asteroids are spinning and the axis may be random. But there's just one axis for each.

Meet (4179) Toutatis. It has a principal axis of rotation, but that axis is precessing so fiercely that the effect is that even if you want to argue that it has only one axis of rotation, that axis is not fixed.

http://echo.jpl.nasa.gov/asteroids/4179_Toutatis/toutatis.html

Link to comment
Share on other sites

I justed wanted a frame of reference. I would have mentioned "Gravity", but none of its logical loopholes had anything to do with asteroids.

Gravity has its problems, but they went to much greater lengths to get a lot of things right, or reasonably right.

Link to comment
Share on other sites

I don't think real object can be spinning around more than one axis, physics laws don't allow that IMO - unless the spin is forced. Yes, real asteroids are spinning and the axis may be random. But there's just one axis for each.

You got something wrong there. Think pitch, roll, yaw. You can hold both Q and D at the same time, right? :)

Link to comment
Share on other sites

You got something wrong there. Think pitch, roll, yaw. You can hold both Q and D at the same time, right? :)

Nikolai above has a point, but in this case ... usual objects settle on single-axis rotation quite fast after you stop applying forces on them.

Take this experiment, for example. Note the rotating wheel is trying to prevent any other rotation. There is precession on the axis caused by the force of gravity pulling one end of the axis down while the rope holds the other end up and this precession is slowing down the rotation of the wheel. If you forced the axis into another rotation like what the guy did at the start, the wheel would slow down rather fast and eventually stop. You can do such experiment at home.

Link to comment
Share on other sites

PS My issue in Armageddon is wouldn't it be easier to teach astronauts how to deep drill, rather than teach deep drillers how to be astronauts? (answer: Micheal Bay film)

well they had 2? proper astronauts in that, for the others, do it kerbal style, put them in a space suit and strap 'em in!

Link to comment
Share on other sites

Right, an object will only spin around one axis when free floating. That axis may or may not be aligned with one of the cardinal axes (that is, it could be a diagonal axis, compared to the spacecraft's pitch/yaw/roll, for instance).

Link to comment
Share on other sites

Right, an object will only spin around one axis when free floating. That axis may or may not be aligned with one of the cardinal axes (that is, it could be a diagonal axis, compared to the spacecraft's pitch/yaw/roll, for instance).

I don't believe that's true (I just tried it out with my mouse). An object can spin along all three axes at once. Take this plane (it doesn't look much like an asteroid, but use your imagination):

3axis.gif

It can spin along any and all of its three axes independently; you can't just generalize it to a single rotational motion.

Link to comment
Share on other sites

Did you know NASA actually train their employees using this movie, by have them point out every scientific mistake that's made? There's a lot of them.

Oh? *every* mistake? wow.

So THAT must be why astronaut training takes so many years.

i mean, just this one requirement would keep me busy for a great many months, and use up a small forest of paper.

I once started a list like this for myself, quit after 40 pages of 1-line-per-error.

Even "independence day" is not as bad. Heck, "Mars Attacks" is almost a documentary, in comparison!

Link to comment
Share on other sites

I don't think real object can be spinning around more than one axis, physics laws don't allow that IMO - unless the spin is forced. Yes, real asteroids are spinning and the axis may be random. But there's just one axis for each.

The *only* sort of real-life object that spins on one axis only, is an infinitely rigid body, with perfect radial symmetry, rotating on the axis of this symmetry.

*all* others will tumble, to a greater or lesser extent. (usually, the ratio is very very small though)

Any extent of flexibility within the object, expecially non-elastic motion(fluids, friction between parts, etc), will rapidly damp out the rotation about other axes, but *not* *ever* stop them completely.

Link to comment
Share on other sites

I don't believe that's true (I just tried it out with my mouse). An object can spin along all three axes at once. Take this plane (it doesn't look much like an asteroid, but use your imagination):

http://virtualskies.arc.nasa.gov/aeronautics/images/3axis.gif

It can spin along any and all of its three axes independently; you can't just generalize it to a single rotational motion.

I think it works a bit like adding vectors to get a single vector, you can add the spins on each axis to make a single spin along a new, non-cardinal axis.

Link to comment
Share on other sites

True. Still: if you are able to reach the asteroid, you should have enough time on the Asteroid's surface. Not only a few hours, but rather weeks. Attaching a few nuclear drives that continuously nudge it out of harm's way should be much more efficient than a single undirected nuclear blow. It is no fair comparison, but I needed to move my asteroid about 10 m/s to move it away from a center hit to a near miss (i.e. Periapsis at 400km). Of course, this will get increasingly more difficult with bigger objects, but you don't have to knock it around like a bowling pin. Getting there is probably the hard part.
On the other hand, humanity doesn't have any nuclear rockets at the moment. We have loads of nuclear bombs. Sending up a rocket with a few nukes to give an asteroid a shove would be relatively simple and relatively safe. The main concern is to actually push it rather than just turning it to gravel, but that's a concern with any method.

And now I'm wondering if KSP's physics permit shoving an asteroid with an explosion. Anyone tried yet?

Link to comment
Share on other sites

I don't believe that's true (I just tried it out with my mouse). An object can spin along all three axes at once. Take this plane (it doesn't look much like an asteroid, but use your imagination):

http://virtualskies.arc.nasa.gov/aeronautics/images/3axis.gif

It can spin along any and all of its three axes independently; you can't just generalize it to a single rotational motion.

Yes, that's just another way of visualizing it. But even if it's spinning on all three cardinal axes at once, the object still has a single line/axis through it at some diagonal angle that it is spinning around, unless it is under an applied force.

I think it works a bit like adding vectors to get a single vector, you can add the spins on each axis to make a single spin along a new, non-cardinal axis.

Precisely.

Link to comment
Share on other sites

On the other hand, humanity doesn't have any nuclear rockets at the moment. We have loads of nuclear bombs. Sending up a rocket with a few nukes to give an asteroid a shove would be relatively simple and relatively safe. The main concern is to actually push it rather than just turning it to gravel, but that's a concern with any method.

Turning it to gravel is not bad option. It would burn in atmosphere instead of making large crater on surface.

I don't think, though, that a nuclear explosion is very useful at redirecting an asteroid.

What exactly happens? The explosion produces large amount of radiation which heats up the surface of the asteroid. The depth directly affected by this depends on type of the radiation and the material of the asteroid. Up to certain depth, the matter changes to gas which expands at speed corresponding to temperature it acquired.

In effect we created a large but rather ineffective rocket engine which expels material in one direction and pushes the payload (rest of the asteroid) in another direction. Neither the mass of the "fuel" nor its speed are substantial as there is not much space for pressure to build up (no nozzle). Most of the energy released by the explosion would go either to open space (half of it) or to heating up mass of the asteroid with no direct effect (mass which stays solid or only liquifies does not count as it stays with the asteroid).

Better effect can be expected on icy bodies with larger evaporation potential.

Link to comment
Share on other sites

The idea of using nukes is based on the fact that nuclear warheads are small, cheap, and powerful. The physics package of a B61 nuclear bomb weights around 130 kg, yet it's capable of producing a 340-kiloton explosion. That's around 1013 J/kg, so you can afford being quite inefficient when using it.

By "cheap" I mean that it's much cheaper to build the warhead than to deliver it to the asteroid.

Edited by Jouni
Link to comment
Share on other sites

I don't think, though, that a nuclear explosion is very useful at redirecting an asteroid.

What exactly happens? The explosion produces large amount of radiation which heats up the surface of the asteroid. The depth directly affected by this depends on type of the radiation and the material of the asteroid. Up to certain depth, the matter changes to gas which expands at speed corresponding to temperature it acquired.

In effect we created a large but rather ineffective rocket engine which expels material in one direction and pushes the payload (rest of the asteroid) in another direction. Neither the mass of the "fuel" nor its speed are substantial as there is not much space for pressure to build up (no nozzle). Most of the energy released by the explosion would go either to open space (half of it) or to heating up mass of the asteroid with no direct effect (mass which stays solid or only liquifies does not count as it stays with the asteroid).

Better effect can be expected on icy bodies with larger evaporation potential.

What if you were to use a "bunker buster" bomb that penetrates the surface before detonating?

Link to comment
Share on other sites

Agreed, the sheer power of a nuke more than offsets concerns about wasted energy.

After all, as I think someone else said, deflecting an asteroid with a nuke amounts to an informal Orion drive. Orion drive's performance is reasonably well established.

Link to comment
Share on other sites

After all, as I think someone else said, deflecting an asteroid with a nuke amounts to an informal Orion drive. Orion drive's performance is reasonably well established.

The Orion drive is based on a proper deflector shield, and small, well timed nuclear explosions. Unless you install a deflector shield on the asteroid and launch multiple nuclear warheads, their efficiency is not really comparable.

Link to comment
Share on other sites

This thread is quite old. Please consider starting a new thread rather than reviving this one.

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.
Note: Your post will require moderator approval before it will be visible.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

 Share

×
×
  • Create New...