6
$\begingroup$

Of course, there are a lot of different kinds of ITV's (Interstellar Transport Vehicles). Some only fly at 0.05c and some quiet a lot faster. Today, I would like to ask what kind of Protection against Radiation and Debris would be in use if we had to protect an ITV flying at 0.8c. So around 239833 km/s. I don't want to assume any flat out impossible ideas, it is suppose to be somewhat realistic.

A few of my own thoughts: At 0.8c we travel such a long distance in a single second, that any sort of meaningful Point Defense System just doesn't work. A Laser is barely faster than the ITV itself (Which is kind of insane to think about). Not to mention that by the time a Computer sees, locks on and shoots at a Target this said target is probably behind you. So my thought is that we need a passive protection. In other words, why avoid debris when you can fly through them ?

The first idea was to use a Normal Layered Shield. So you don't stop anything coming at you with the first layer, but like 20 maybe do the trick. This has the problem though that your shield wears down. And if it is hit twice at the same spot, well that ain't too good.

So the next idea was some sort of Plasma shield. Which is great, in theory. This Plasma shield would have to be a few Million degrees hot at best, just to be able to Vaporize big chunks of debris. I could easily see such a shield being as hot as the core of the sun or a Fusion reactor, which sort of raises 3 problems.

  1. Where is all the heat going ?
  2. Where is all the matter coming from ?
  3. Where is all the energy coming from ?

To the first, into space ? I would assume you need a stupid long ship to have this sun more or less be far enough away from the main body. And you could not run it at 100% all the time as your ship would just sort of melt.

I thought that maybe you could try to recycle most of the Shield´s Plasma and then fill the rest up with the debris your run over.

Since we need Fusion for such a shield anyways, I would guess Fusion would provide the Energy. Maybe the Shield itself is just some kind of Fusion reactor where the Fusion product is propelled outwards and shaped into a cone that protects the ship.

So yeah, this is how far I got. I would guess a Plasma shield is the only really option you have at this speed but I could very well be wrong.

Anyways, thank you for reading !

$\endgroup$
7
  • 2
    $\begingroup$ "A laser is barely faster than the ITV itself" - from the perspective of an outside observer, yes. From someone onboard the ITV, they see the laser beam shoot off at speed c, the same as if they're not moving at all. $\endgroup$ Aug 7 '20 at 17:25
  • $\begingroup$ @Nuclear Wang the real problem here is not the speed of the laser beam, but the problem of detecting and reacting to objects coming at you at 0.8c $\endgroup$
    – Alexander
    Aug 7 '20 at 17:28
  • $\begingroup$ One helpful resource: Shielding the Starship $\endgroup$
    – Alexander
    Aug 7 '20 at 17:35
  • $\begingroup$ @NuclearWang You are of course correct. My point was more that there is no way for a detection / Point defense system to lock on and fire at a Target with those speeds. For a Grain sized object, we have trouble seeing it a few km out. Not to mention 200.000. $\endgroup$
    – Erik Hall
    Aug 7 '20 at 18:13
  • $\begingroup$ You could probably set up an automatic detection system with drones or a large "shield" as far in front as you can to run into/record the location of objects. Send that info back to your deflection array (guns) to shoot stuff out of your way. Your "cannonballs" don't have to move much faster than you are, as long as they don't go slower. $\endgroup$
    – Leviathann
    Aug 7 '20 at 18:27
5
$\begingroup$

I don't want to assume any flat out impossible ideas, it is supposed to be somewhat realistic.

The issue of inertia

Most Sci-fi either hand waves in some variation of inertia dampener or non-newtonian drive, neither of which have any scientific basis. When you accelerate a crew in the real world, they experience inertial forces similar to gravity; so, if you want to accelerate a person over a long period of time, you want to stay somewhere in the range of Earth's gravity (9.8m/s^2). At this acceleration it will take you about 283 Earth days to reach a speed of 239,833 km/sec.

The issue of conservation of mass and energy

Another issue you will run into for realism is the conservation of mass and energy. For a ship to both speed up to and stop from 0.8c under its own power your ship will need a LOT of fuel. Anti-matter specifically since nuclear fuel can't get you going that fast. To reach that speed you need need 40% of your mass to be antimatter and 40% expendable normal matter assuming you have a 100% efficient engine which you generally don't get in real life. Then the remaining capsule will need to also be 80% matter/antimatter fuel. This means that your ship would have to be made of 96% fuel before you even start to consider powering a plasma shield or anything fancy like this.

Using ground-based-laser accelerated sails, you would not need nearly so much fuel, but you'll still need to slow yourself down meaning you are looking at 80% anti-matter.

To complicate this, anti-matter is REALLY hard to contain; so, keeping it contained for such a long trip with so little mass to expend on a containment systems will be nearly impossible as well.

How to achieve those speeds

The most realistic solution IMO to this problem is the use of a bussard collector, a magnetic field device that scoops up all the hydrogen from space within several km of your ship to use as fuel. It's definitely not doable with today's technology, but at least the theoretical science for one already exists. So, you only need to accelerate your ship under its own power up to a small fraction of light speed until you can start gathering enough hydrogen to run a fusion reactor to keep yourself going. While a bussard collector will not protect you from an enemy torpedo, it will protect you from the thin atmosphere of space while simultaneously cheating the conservation of mass and energy dilemma.

What about combat?

Just because you can get going at 0.8c does not mean you can fight at those speeds at all. It's not just a matter of seeing your enemy. Since any significant course correction would take months, there is no real way to intentionally put yourself in the path of an enemy ship you are trying to intercept at those speeds. This means you need to predict where an enemy ship will want to go by fortifying planets and other places of tactical and economic interest. So, while an enemy ship might travel between stars as 0.8C, it will begin slowing down hundreds of days before it arrives at you planet so that it can effectively stop at it. So when it arrives, it will be moving at the much more sane speeds of just a few km/s. At these speeds, ships will be able to maneuver enough to engage each other and traditional thoughts regarding detection, interception, etc. will all apply.

$\endgroup$
5
  • $\begingroup$ Firstly, thanks for the answer ! I think i should expand the setting a bit more. I want to make a CGI short film for my Portfolio with such a ITV. The Internal setting is simple, a ship going to a fictional Binary Planet System. So no combat. For now, the Ship is acc- and decelerated by a set of Lasers. One at Earth and one at the Destination. So the ship really has no way of slowing down on its own. $\endgroup$
    – Erik Hall
    Aug 7 '20 at 20:13
  • $\begingroup$ If you are using the laser to laser route, your ship will need a giant light sail that could definitely not survive the trip at those speeds because they by thier very purpose have to be so thin and light weight to be effective. For that, I'd either consider bringing your max speed waydown or add something akin to a bussard collector to either scoop or deflect the atmosphere of space. Or use the sail to get up to a speed where a bussard collector would be useful, then pack up the sail and fly by fusion powered ion thruster until you are moving slow enough to need it for the final approach. $\endgroup$
    – Nosajimiki
    Aug 7 '20 at 21:24
  • $\begingroup$ Its not a Light Sail in the traditional sense. I am sure you know the idea of Mirrors around the Sun focusing light on a Ship. Its pretty much that. I mean the Ship is 3113,6 Meters long after all and i suppose to carry around 2,3 Megatons of Cargo. (For Context, there are 3 Ships in the story. One crashed into the star, the 2nd one sets up a Base and the 3rd one brings in the Party) And it is kind of a Plot point that the 3rd ship is so much faster then the other 2. (1st = 0.5c, 2nd = .65c) The idea is that the sail can be retracted so it dosnt break the ship to much ... $\endgroup$
    – Erik Hall
    Aug 7 '20 at 22:07
  • $\begingroup$ The issue with the light sail is not about the how the light striking it affects it but how the ever so slightly not vacuum of space would tear it apart as you get up to speed. If the ship has no crew you could possible accelerate it in a much shorter distance and maybe mitigate that a bit, but then you need to worry about it crushing/splitting itself from acceleration. Even at 1G of acceleration, a freighter that size runs into some serious engineering issues, worldbuilding.stackexchange.com/a/179662/57832 $\endgroup$
    – Nosajimiki
    Aug 8 '20 at 0:56
  • $\begingroup$ Can you say more about the purpose of "… a CGI short film"? If your portfolio about CGI or most other creative courses, why does this need to approach scientific reality? Isn't CGI rather about realism? If it's centred on anything technical and the CGI is simply a presentation medium, why is it so speculative? $\endgroup$ Aug 9 '20 at 18:12
2
$\begingroup$

Needle ship.

  1. The most relevant impactors are those encountered in the direction of travel, directly ahead of the ship. Mostly the ship will be ramming slower things in the way because it is so fast.

  2. The smaller the forward profile of the ship, the less things it will ram. The ship is thus maximally long and thin, a flying needle.

  3. The ship tapers to a molecularly sharp point in front, which can be regenerated. The idea is not to ram into things ahead, but divert them so that they change course with a minimum of kinetic energy exchanged. Hopefully this is mostly hydrogen molecules.

  4. Lasers can fire forward from the shop. There are many and they illuminate what is ahead. With increased energy, the lasers themselves might be able to deal with smaller objects.

  5. More massive objects detected in the path can be met with projectiles. A regular railgun projectile will suffice because at a speed of 0.8c it will convert whatever it hits to plasma. The needle tip can traverse hot plasma.

$\endgroup$
1
$\begingroup$

The ship needs a small fleet of small sensors flying ahead of it to detect any potentially problematic objects as they fly past and help deal with them. The main ship could be fed data concerning speed and direction at the speed of light so would get advanced warning of approaching objects at 0.8c and could have time to activate high powered lasers to destroy the approaching object.

The sensor fleet would be small, have redundancy and be capable of replacement from the mother ship to a limited extent. The sensors would fly ahead and in a ring around the main ship so that if any sensor was hit the debris would not hit the main ship.

$\endgroup$
1
  • $\begingroup$ While this could be helpful with resolution, you'll want to bare in mind that it would take a signal at least as long to reach your ship from a sensor drone as a signal emanating from the target; so, an object 10 light seconds ahead of you still won't been known to you until it is 2 light seconds away. $\endgroup$
    – Nosajimiki
    Aug 7 '20 at 19:21
1
$\begingroup$

Isaac Arthur's "Interstellar Challenges" video raises the same concerns, namely that, after a certain speed, point defenses are just not reliable. A laser-driven ship has the advantage that the laser can fire before the ship gets in the beam, which could somewhat clear the path, but you'll need something more , especially if you're going somewhere without a huge relay of lasers from both ends.

In addition to Wilk's needle-ship design, a couple other things are mentionned:

  • Hydrogen fuel tanks could be put on a conveyer belt, since they also make decent shielding. If one gets damaged, convey it out of the way for repairs, while another takes its place.
  • You don't have just one light sail; you have as many as you have room for materials. Throw some spares out in front of your ship, perhaps pushed farther ahead by your own lasers, and let those serve as shields. The farther ahead they are, the better, as any debris that penetrates them will be slightly deflected. The drag from small impacts will cause the sails to fall back toward the ship, where you can pick them up to be recycled and replaced.
$\endgroup$
1
  • $\begingroup$ I saw the episode but always thought that the Hydrogen idea is kind of pointless for most ITV´s. At 0.8c, it takes around 7 Years to get from earth to the fictional destination. And as the ship(s) themself have no way of slowing down, why carry all the extra Hydrogen ? I guess protection. But i think i now know who to protect the ship. A giant Main shield far ahead and a smaller Internal shield on the ship itself. $\endgroup$
    – Erik Hall
    Aug 8 '20 at 14:44
0
$\begingroup$

Leaving all fancy yet-to-be-invented physics aside, one plausible method would be pushing large chunk of ice in front of the ship. The ice can be used as reaction mass for fusion engine, works as a shield and is useful resource anyway. The ship simply hides behind the iceberg in the acceleration and cruise phase.

When decelerating, the whole setup gets turned upside down, so the fusion torch of the ship blows obstacles away from its path. Collision with large asteroids remains a risk factor which makes the story more interesting. Nobody actually knows how many rocks there are flying between stars. There definitely are few, as astronomers have recently discovered.

$\endgroup$
1
  • 1
    $\begingroup$ Thats the thing, you could just not put a shield on there and pray nothing happens. And tbh, the ship will probably still arrive with a Shield that can just take punches from like 1cm stuff. But i hardly belive anyone would do that. And in the context of the story, you really dont want to have a 2nd ship slamming into a star because of a faulty shield. For context, its CGI Short in which the first ship crashed, the 2nd made it and the 3rd is on its way. $\endgroup$
    – Erik Hall
    Aug 7 '20 at 20:27
0
$\begingroup$

My completely unrealistic idea- have an atomic diverter, a device that takes objects in front and reconstructs them behind the ship in mostly the same way.

My more realistic idea- have a suicide ship in front, basically a big metal wall with rocket boosters(or whatever your propulsion system is) to block all the debris. Of course, you shouldn't fly through any huge asteroid fields, but it should help a lot with random space debris.

probably not much help, but that's my 2 cents.

Honestly surprised nobody downvoted this answer, so I guess I'll add a bit more.

The Atomic Diverter(4th sentence of the 3rd paragraph) was something I made up to solve this problem, but with advanced technology and FTL travel. I do not go into how it works, so I have no idea if it is possible.

Your suicide ship would need to be at least as wide as your other ship, with a way to correct itself on at least 2 axis (X and Y, viewing from the front. Y isn't as important, but you might want it) either using engines or these reaction wheels I've recently learned about. Please note I am not a physicist or anything, so they might not reset the ship fast enough or be too small for your suicide ship.

$\endgroup$
3
  • $\begingroup$ I love it. I forgot to add this to my question but this is for a CGI Short film (Portfolio stuff) and my god this sounds like a Visual impressiv idea. You got this Ship just fly through a Protoplanet or something... The main Concern is about stuff that is big, but to small to see ahead of time. So idk a 5meter asteroid will nuke the ship a few thousand times over but is hard to see. So having a big shield way ahead of the Ship should work... $\endgroup$
    – Erik Hall
    Aug 7 '20 at 18:46
  • $\begingroup$ Large asteroids are so few and far between, that even if you fly between stars, the likelihood of hitting one is next to nil, but if you did, a suicide ship hitting a 5m round asteroid of average density at those speeds would be like setting off a 14 billion megaton nuke right in your path; so... it will have to be pretty far in front of you... $\endgroup$
    – Nosajimiki
    Aug 7 '20 at 19:14
  • $\begingroup$ In one of the Culture novels by Iain M Banks a drone makes rapid decent from orbit by displacing atmosphere in front to the empty space behind itself. So if your universe has a matter displacer, this unrealstic part may be applicable. $\endgroup$ Aug 7 '20 at 19:19
0
$\begingroup$

**A detached shield or series of shields ** made of harvested matter traveling in front of the spacecraft. (Plus magnetic shielding for charged particles.)

Basically you would have to accelerate properly shaped impact shield/s to the same speed you wish to travel at and then travel in the 'shadow' of that shield all the way to your destination.

The shield/s don't decelerate at the end of the journey but the ship does.

One serious problem will be the 'flip' for the deceleration phase of the journey. Unless you install two drives (front and rear) your ship has to expose its longitudinal axis before it can start slowing down. So either you build an unrealistically huge (wide) shield or you make the turnover as fast as possible with fingers crossed.

$\endgroup$

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.