View Full Version : Interstellar space travel

2012-Apr-14, 11:37 PM
Our interstellar space craft is traveling 1/2 c = 150,000 kilometers per second, and is about to enter an area of space with lots of one cubic millimeter particles. At this speed they have enough kinetic energy for one of them to total the manned space craft. We have 33 robot space craft about 1500 kilometers ahead of the manned craft which can detect slightly larger particles, which can be vaporized with 13 laser canons (500 to 1000 kilometers ahead of the manned space craft) a few micro seconds before they hit our manned craft, but the radars can't detect one cubic millimeter particles, except at very short range. How can we design to save our space craft? We have several other systems which protect from smaller than one cubic millimeter particles, but the one cubic millimeter particles have the kinetic energy of an H bomb when they hit anything due to the relative speed of about 1/2 c. It appears we were imprudent to go that fast. Design a system that can save the space craft without magic. 330 robot space craft, perhaps? Something else is possibly more cost effective and safer as a disabled/malfunctioned robot space craft (or laser cannon kinetic energy) could total the manned space craft. Nearly all the particles that are a threat are within plus or minus one degree of arc from straight ahead of the space craft at 1500 kilometers ahead where we need to find all of them within a few hundred micro seconds.
In case you didn't do the arithmetic, the 1/2 c is already marginal or worse: After the radar pulse reflects off the several cubic millimeter particle it takes up to 100 microsecond to reach the radar receiver antenna, another microsecond to get though the stages of the receiver and calculate the aiming instruction for the laser canons; another microsecond to get though the data link transmitter stages and be radiated by the data link antenna, another 100 micro seconds to travel at c to the closer laser cannons, another ten microsecond to aim and fire the laser cannon; another 100 micro seconds for the laser beam to reach the one cubic millimeter particle; another ten micro second for the plasma to spread out sufficiently that it is no longer a serious threat to the manned space craft. Possibly some of those microsecond delays can be reduced, but others are over optimistic. We are all ready using coded pulses so we can transmit a million radar pulses per second, and receive them at multiple radar receivers up to 10,000 micro seconds later, with only rare multiple range results. The laser canons can fire at occasional false targets, but they need to avoid shooting at the manned space craft, the robot space craft and the other laser canons so one micro second computing time may be very optimistic. Our technology isn't there yet, but is it within grasp? Please suggest alternative ways to save the manned space craft, refute, or embellish the problem. Neil

2012-Apr-15, 12:48 AM
What about setting up some kind of shield in front of the ship? Either a generated field of some type (have no idea what would work), or something that takes the impacts, like an ablative shield that can be replenished.

Or the opposite of a ram scoop, using EM fields far in front to move anything out of the way. Would this work on non-charged particles though?

2012-Apr-15, 12:53 AM
What sort of engine does the ship have? Would it be practical to fly backwards and fire a focused stream of exhaust from the engine at the larger impactors?

2012-Apr-15, 03:12 AM
perhaps aerogel? or some gelatin-like substance.

2012-Apr-15, 05:20 AM
Project Daedalus (http://www.daviddarling.info/encyclopedia/D/Daedalus.html)would have used a mass of beryllium as well as an artificially generated cloud of dust ahead of the main body for shielding.

2012-Apr-15, 08:58 PM
Two spacecraft one ahead of the other might help. One to act as a dustbreaker to establish a lane?

2012-Apr-16, 03:14 PM
Eh, the wall of text is too dense for me to feel like reading. But anyway, I've posted straightforward solutions before, and I'll summarize again:

You just use passive magnetic shielding, combined with an extremely low mass shield. This shield may be a simple puff of gas or thin foil or a cloud of dust or some combination. It only needs a sectional density on the order of atoms.

The purpose of the shield is to ionize the incoming objects. Since the shield material is slamming into the incoming objects at relativistic speeds, it really doesn't take much to strip electrons from the incoming.

Thus, the threat to the starship is converted from a solid object into a spray of charged particles. This can then be deflected by a magnetic field. Conveniently, this magnetic field is also inherently useful as a main component of a practical relativistic propulsion system (relativistic kinetic impact powered rocket).

Anyway, the basic starship configuration is for it to be a large diameter superconducting magnetic loop, and to string two or three mission modules along this loop--like necklace beads. This places the mission modules in the regions most heavily protected by the magnetic field.

The basic requirement is that the magnetic field energy of the magloop's magnetic field must exceed the kinetic energy of the incoming object. That's why a large diameter is required--the energy stored is proportional to the cube of the diameter.

If you use relativistic kinetic impact powered rocket propulsion, then the relevant "incoming object" is not actually any naturally occuring object. Rather, it is the kinetic impactor drones used for propulsion in the first place. Unless you're talking about some sort of fancy nanotechnology, each kinetic impactor drone will be far more massive than anything the starship could be expected to naturally encounter. Interstellar space is just incredibly incredibly empty. (If it weren't, then trying to see even the closest star systems would be like looking through pea soup.)

If you are really so paranoid that you are worried about larger objects, then you can upscale the protection factor simply by using a larger shield placed further ahead of the starship. When the incoming object hits this shield, the incredible violence of the collision will convert it into a conical spray of plasma. Only a fraction of this spray will encounter the starship. Thus, the starship's magnetic field only needs to deflect a tiny fraction of the incoming threat, and only needs a tiny fraction of its kinetic energy. For example, if the diameter of the spray is 100 times the diameter of the ship, then the magnetic field only needs to have 1/10,000 of the energy of the incoming threat.

The bottom line is that it is easy to protect against natural interstellar debris at relativistic speeds.

2012-Apr-16, 05:41 PM
To add to what Isaackuo says, apparently it's best to have a really thin (nanometers), low atomic number, shield.

Interstellar dust particles will then punch a neat hole through this shield. Crucially, very little of the kinetic energy is deposited in the shield material itself, as long as it is thin enough. But enough energy is transferred to the particle itself to turn it into plasma.

Because it is electrically charged, this plasma can be deflected electromagnetically.


2012-Apr-20, 09:21 PM
For the breakthrough physics crowd:
Crap--taken down--it was from Page 26 of the Feb 2012 AIAA HORIZONS


2012-May-04, 10:43 AM
What about something like tanks have to protect against rocket strikes, explosive-reactive-armour its called, the problem I can see with this is you would have to be replacing it quite frequently.

2012-May-30, 11:34 AM
Interstellar dust particles will then punch a neat hole through this shield.


What stops the second dust particle?

2012-May-30, 11:54 AM
What stops the second dust particle?
Probability of it's path not being directly through the hole.

2012-May-30, 11:55 AM
What stops the second dust particle?

Do you mean dust generated in the impact, or do you mean another dust particle that happens to find the hole punched by the first particle?

If the former, I don't think there is any such secondary dust. It's all vapourised and turned into plasma. That's what they say anyhow.

As for second particles going through pre-punched holes, I don't know what the chances of that are. The holes are microscopic. I guess you'd have to work out how many impacts per unit area you expect on a certain journey, and see what proportion of the shield area that is. My guess is very small.

If comes down to it, it'd probably be practical to carry spare shielding film so it could be replaced periodically. It's very low in mass as I said, only nanometers thick. Probably some automated sail-rigging set up could be built, that deploys fresh film in front of the vessel.

2012-May-30, 06:51 PM
There are also simple ways to essentially heal any holes. For example, you could have two or more layers, rotating with respect to each other. An impact could create holes which are momentarily aligned, but then the rotation brings them out of alignment.

Or the sheet could actually be a very low density foam, so it naturally closes in on any holes.

Or the shield could actually be a low density cloud of charged dust particles, constrained by a magnetic field. This sort of solution naturally heals any holes and is easy to deploy and maintain.

And of course, there's always the possibility of active repair. Cameras can visually inspect a shield for any damage, and patches can be applied (spray on foam, or adhesive patches, or whatever).

2012-May-30, 08:38 PM
There are also simple ways to essentially heal any holes. ...
Or the film could be made of lots of little nanobots that know to fill the hole back in if it gets created.