Designing Spacecraft for Hard SF Battles & Piracy

[GTOM]

I'm going to write a (semi) hard SF. I wonder whether i left out something from spacecraft design, or got something wrong?Armed cargo ship (used for piracy/commerce raid also)

At the back of the ship, a large block contains the fusion reactor, the main ion thruster, the manuevering ion thrusters, and also the command computers. It is the realm of the engineers, due to sensitive electronics, cables, magnetic boots are not allowed here.
After that, a long cylinder contains the heavy hydrogen fuel. It has got large radiator wings, and also a row of chemical thrusters meant for rapid dodge.
The cargo block is a big cube, it has got a small living container with life support. They hide the fighters in it also.
At the front of the ship, a hollow pyramid, meant to protect frontal sensors from high speed collision with micrometeors, when it is closed. Its opened when the frontal sensors are really needed, like landing on an asteroid mine, or combat.
Since the ship is armed, the lasers are also hid in this pyramid.Battleship

Looks like a giant icicle (with large radiator wings), almost a km long. In the middle of it, a dreaded spine weapon, a huge coilgun that launches missiles with 100 km/s. A missile shatters into a dozen smaller warhead in order to get through point range defence.
The ship has got another spine weapon also, a free electron laser in order to defend itself. Together with smaller coilguns firing tiny unguided slugs, the ship is almost unkillable with a frontal attack.
However it has two weakness : simultaneous attacks from different directions, and low acceleration.Fighter

Since an asteroid mine offers cover from missiles (and the goal of wars is to capture them), and nuclear hardware isn't cheap (reusablity is good), instead of regular missiles, smaller than battleship warcraft and motherships like to use spacecraft originally developed for orbital combat. Since they are unmanned most times, they can be still expended like missiles.
It has an egg like shape, with pointy nose to help landing on the surface of a planet, if that is needed. It has got high thrust low specific impulse nuclear thermo engines, thrusters facing in every direction.
It is armed with a coilgun firing tiny unguided slugs with 100 km/s in order to deal with other fighters and attack point range defence from a distance. It also has got laser jammers and small shield like interceptor missiles.

 

[mfb]

Spacecrafts do not have a "back". They have one or more directions of acceleration. If your fusion reactors are at one side, I assume your exhaust is always at that side as well. If you want to approach any object in space, for example, this side would look like the "front" as seen from this object.

the ship is almost unkillable with a frontal attack.

What does it do against small, cold, massive objects approaching it at high speed? And why would you want to attack it from the front anyway? An object that size is highly visibie over huge distances.

 

[GTOM]

What do you suggest instead of "back"? Well, in case of acceleration it is the bottom of the ship to the crew. Should i call it that, since it is also similar to present day spacecraft launched by a big rocket on the bottom?

"What does it do against small, cold, massive objects approaching it at high speed?"

It can have active sensors as well (maybe the laser in small energy continuous stream can count as one), and spread out the beam in order to burn a number of shrapnels. Of course it is not unkillable, but pretty resistant.

Detection and interception are different things, one has to build up proper interception courses, in order to attack with high speed from multiple directions.

 

[mfb]

Bottom, engine side, whatever.

Small, cold, black massive objects are hard to track, especially if you coat them like modern stealth airplanes to avoid radar detection.

 

[GTOM]

Bottom, engine side, whatever.

Small, cold, black massive objects are hard to track, especially if you coat them like modern stealth airplanes to avoid radar detection.

Thanks, i think bottom side will be good, proper terminology isn't marginal.

But swallowing the microwaves heates up the object, also small cold stuff are unguided, with the sizes of space, even a battleship isn't easy to hit.
Anyway, spacecraft has to be well prepared for encounters with small meteors, maybe statistically there isn't much chance even in the asteroid belt, but still.

 

[TrueGormagon]

Bottom, engine side, whatever.

Small, cold, black massive objects are hard to track, especially if you coat them like modern stealth airplanes to avoid radar detection.

Sorry, stealth in space is impossible without' magic' technology.

 

[phinds]

Sorry, stealth in space is impossible without' magic' technology.

This makes no sense to me. Can you substantiate your statement in any way? Why would stealth technology care whether it's in an atmosphere or not?

 

[GTOM]

Depends on how you define stealth. You can't become invisible in air neither. A plane can reduce its radar cross section.
In space the main problem is that you can't hide the flames of the thrusters, and it can be detected from very far.
Then they will know where to search for you, and find you with active radars and lidars, even if one can reduce IR cross section with liquid helium, heat sinks, radiate heat toward the opposite direction, or outside the elliptic plane.
At this point i assume that even small cold shrapnels can be detected from a distance, that one can still dodge or burn them. But i also employ the constraint (for epic reasons), that defence can be still overloaded with a kinetic swarm, and attack rockets have a superior range compared to lasers..

 

[TrueGormagon]

This makes no sense to me. Can you substantiate your statement in any way? Why would stealth technology care whether it's in an atmosphere or not?

I started typing all the reasons why I could remember, but it would save me about an hour of typing just to post this article I found instead.

http://www.projectrho.com/public_html/rocket/spacewardetect.php

 

[GTOM]

Since we couldn't detect a kilotons meteor before it hit Earth, i have doubts whether that article isn't underestimate difficulties, however the basic assumptions are right, a dense recon network is much cheaper than spaceships.

 

[vemvare]

We have satellites with telescopes designed to look at giga-lightyear distant galaxies, we weren't trying to guard the Earth against incoming objects.

An active-LIDAR system using a short, intense broadband burst of say, visible light to IR should be very hard for anything to completely absorb. Then the object will be visible even if it is at 3K.

 

[phinds]

I started typing all the reasons why I could remember, but it would save me about an hour of typing just to post this article I found instead.

http://www.projectrho.com/public_html/rocket/spacewardetect.php

Which simply states, as the opinion of one poster, that stealth technology does not work in space. This is a useless reference. How about you spend just a minute or two posted even one valid reason why stealth technology would not work in space?

I do understand that if you are firing chemical rockets out the back of your fighter, unless they are in a tight beam and you are masking them by heading straight for the target, they will be detectable but the exact same thing is true in the atmosphere. This is not a distinction of space-based detection.

 

[mfb]

Sorry, stealth in space is impossible without' magic' technology.

For spacecraft s. We were not discussing spacecraft s at that point.

 

[GTOM]

Which simply states, as the opinion of one poster, that stealth technology does not work in space. This is a useless reference. How about you spend just a minute or two posted even one valid reason why stealth technology would not work in space?

I do understand that if you are firing chemical rockets out the back of your fighter, unless they are in a tight beam and you are masking them by heading straight for the target, they will be detectable but the exact same thing is true in the atmosphere. This is not a distinction of space-based detection.

But in space, from a range that is much beyond interception range unless they are using relativistic projectiles...

 

[phinds]

But in space, from a range that is much beyond interception range unless they are using relativistic projectiles...

I have no idea what the intent of that statement is.

 

[russ_watters]

So, to put a finer point on things:
1. The "stealth" used by the stealth fighter and bomber is invisibility to radar (primarily). Since it is determined soley by materials type and shape, it will work exactly the same in space as on earth/in the atmosphere. A steath fighter in space would be just as invisible to radar as on earth.

2. The arguments against are focused on other potential detection methods besides radar. And while it is true that they may still theoretically work, radar is primarily used for a reason: it is the best.

The biggest problem for any detection method in space is the distances involved. If it were as simple as just pointing a SPY-1 radar out into space, we'd already have detected every asteroid in the solar system. A similar problem applies to IR: one way to defeat a heat seeking missile is to put yourself between the missile and the sun. In space, with much weaker heat sigatures, picking a spaceship out of the background of stars would be difficult.

 

[GTOM]

In space, with much weaker heat sigatures, picking a spaceship out of the background of stars would be difficult.

Yes, however the main point is that thrusters emit lots of heat, background clutter is much lesser than air, so a network of telescopes and recon probes can track the ship based on that trail. To achieve a big travel speed, the thrusters needs to be fired for a long time. While drifting slowly can reduce the spot distance, but also result in very long travel time, and during that, one recon craft might still spot the ship.

 

[TrueGormagon]

My main point was, regarding stealth in space is that besides radar there are so many ways to detect a vessel easily that you mineaswell not bother making it undetectable to radar and put your resources into more propellant and/or payload.

Its not the authors opinion in the article, besides him being an engineer, he merely points out known fact and common sense along with the hard data.

Assuming their is a space war, and you take the time make your ships undetectable to radar, any military organization worth anything would guard against this and employ a wide variety of detection systems, passive and active.

So essentially, without 'magic' tech, such as the 'cloaking device', total and plausible stealth is virtually unachievable in space. Trust me, I hated it to. I fought it. Then I came to accept it. Once you do, you can move on and look for other ways to make your spacecraft design hobby, novel, screenplay, fanfic or role playing more interesting.

Your best stealth attack would be via infiltration, sabotage, and long range attack with relativistic weapons. Space pirates, or more accurately privateers, might be able to succeed to a degree in orbit above a planet or station with high traffic, where they can escape into sovereign space.

 

[mfb]

Payload? We were discussing the detection of (unguided) bullets.

 

[TrueGormagon]

Payload? We were discussing the detection of (unguided) bullets.

Those could be considered a payload.

You could still detect these however. Granted, it would be more difficult, and it would depend on how they were launched as to the ease of detection. Assuming you want them to reach the target within any reasonable period of time, you need to accelerate them. There are a few ways to do this.

1. You accelerate the inert projectiles via conventional means, a gun turret for example. This means chemical or electromagnetic propulsion. These would create heat from the firing/power plant, EMR in the form in IR. This heat could be detected, but of course assuming your ship is maneuvering so could the propellant exhaust. In addition, residual heat would be present on the projectiles. Seeing as space has no temperature, these would show up like little beacons. Whether or not the target your firing at could do anything about it is another matter.
2. Ok, you say i'll fire them more slowly but cold... but how? I'll keep them exposed to space to keep them chilled and not use a gun. Well then you have other problems, if you open up your 'bay' to space well moving, aiming is more difficult. If your stationary, your a nice target. In addition, your payload is going to bloom like crazy over distance and slower moving projectiles can be easier to avoid.
3. The final point however, what are your targets defenses? Does it have a space age Trophy type active defense system? CIWS? Mag/plas shields? Heavy armor? Is it even military? If not, there would be easier ways to destroy the target then via stealth. Detection does not necessarily mean defense.

 

[dbmorpher]

Seeing as most of you have read the atomic rockets website I would like to say something about the "fighters". OP describes them as having omnidirectional nuclear fission propulsion systems. I would say use of fission energy is over powered in this respect due to the excessive shielding systems required and the complexity of systems. Most likely the mass of the extra propellant needed to get the same delta v as a nuclear system would be less than the necessary auxiliary systems needed to support a reactor. Basically what I'm saying is that fission is not worth it's weight as a system for fighters that do not require excessive amounts of delta v in the first place.

 

[russ_watters]

Yes, however the main point is that thrusters emit lots of heat, background clutter is much lesser than air, so a network of telescopes and recon probes can track the ship based on that trail. To achieve a big travel speed, the thrusters needs to be fired for a long time. While drifting slowly can reduce the spot distance, but also result in very long travel time, and during that, one recon craft might still spot the ship.

I guess it depends on the specifics of the motion -- probes launched these days go months or years between engine burns.

 

[russ_watters]

My main point was, regarding stealth in space is that besides radar there are so many ways to detect a vessel easily that you mineaswell not bother making it undetectable to radar and put your resources into more propellant and/or payload.

"Easily"? No. Again, if such other methods worked well, we would already have found every asteroid in our vicinity instead of being surprised when mountain-sized asteroids pass nearby. Not to mention our stealth bombers and fighters would be a waste of money.

Assuming their is a space war, and you take the time make your ships undetectable to radar, any military organization worth anything would guard against this and employ a wide variety of detection systems, passive and active.

Like they've done against stealth in the atmosphere...?

Its not the authors opinion in the article, besides him being an engineer, he merely points out known fact and common sense along with the hard data.

I see a lot of problems with the article. One glaring example:

As of 2013, the Voyager 1 space probe is about 18 billion kilometers away from Terra and its radio signal is a pathetic 20 watts (or about as dim as the light bulb in your refrigerator). But as faint as it is, the Green Bank telescope can pick it out from the background noise in one second flat.

Our stealth aircraft have an ingenious method of making their radios undetectable: they turn them off.

 

[Evo]

What does this have to do with science fiction writing and our rules?

There can be no speculation about the real world and about known science. Rather, all speculative theories must be about a world which is different (although similar) from our own. Writers must give some kind of indication in what way their world is different from our world.

https://www.physicsforums.com/threads/expectations-in-using-the-writers-forum.631327/

I'm going to make an exception for this thread to remain open as it is productive, but others, please remember to follow the above rules in other threads, real science needs to go into the appropriate science forum.

 

[mfb]

Those could be considered a payload.

Yes but they do not have payload on their own.

In addition, residual heat would be present on the projectiles.

What would heat them? On earth, friction, but without an atmosphere that is not relevant.

Seeing as space has no temperature

It has one: 3K.

and slower moving projectiles can be easier to avoid.

Slower relative to what? There are no absolute speeds in space. A slow projectile relative to its source can be fast relative to its target.

Detection does not necessarily mean defense.

Right, but we were discussing detection to defend against it.

 

[GTOM]

Ok, so there are two issues that has some connection.

OP describes them as having omnidirectional nuclear fission propulsion systems. I would say use of fission energy is over powered in this respect due to the excessive shielding systems required and the complexity of systems.

Wiki suggested that nuclear thermo propulsion can be twice as efficient as chem fuel, however it might be best if I don't go into much details, fighters have high thrust low specific impluse drives.

Using cold small projectiles, i see a number of problems with it.

1. If they launched from a coilgun with high speed, i think it will heat them up.
2. If they launched with a lower speed, that gives more time to absorb radar and lidar beams, and that will heat them up.
3. With the distances in space, even a battleship or mothership not so likely to get hit with unguided projectiles, and i expect them to withstand the hit of a smaller projectile.

The more general issue of detection :

I guess it depends on the specifics of the motion -- probes launched these days go months or years between engine burns.

My constraints are the following : Fusion power increased travel speed of ships to the scale of 100 km/s.
That requires expending lots of energy, resulting in a bright trail.
If something drifts slowly, it can't intercept a fast ship before it finishes its course, unless they know exactly when will it start, and where it will go.
An asteroid mine has a fixed course, but also a very dense surveillance network, and a battleship is much bigger than a stealth bomber. So I see, base an attack on stealth is risky at best.

I expect small probes can be still spotted only with luck.

 

[TrueGormagon]

To firstly respond to Evo, it does have to do with scifi writing, specifically accurate depiction of events and sciences in space as regards to how they would be presented in a book or some such written work whether with scientific accuracy or not, so as to present information to potential writers as to what is real science and not and give them the personal choice to follow it or not, to make their world different, or to not. However, since addressing inconsistencies or inaccuracies regarding scifi writing on this (For some reason) thread does not seem to be approved of, even though discussions akin to it were being held previously as to radar detection and semi hardcore spacecraft design in this persons universe, (And they were asking about design) I will move this discussion to a different thread.

https://www.physicsforums.com/threads/stealth-and-detection-in-space-continued.783912/

(Formatting edited by moderator)

 

[Khashishi]

Why is the missile launcher so large? You seem to indicate it is 1km long? Surely several smaller launchers can achieve greater destructive potential.

 

[GTOM]

Why is the missile launcher so large? You seem to indicate it is 1km long? Surely several smaller launchers can achieve greater destructive potential.

The battleship's spine weapon meant to boost missiles to 100 km/s. Length is needed, so the missile can withstand acceleration, and the cannon could withstand expending about a TJ energy.
Fighters also launch slugs with 100 km/s. but they are tiny unguided projectiles, launched from 200km at most, and only used against other fighters and the sensor arrays and lasers of point range defence.

 

[vemvare]

To firstly respond to Evo, it does have to do with scifi writing, specifically accurate depiction of events and sciences in space as regards to how they would be presented in a book or some such written work whether with scientific accuracy or not, so as to present information to potential writers as to what is real science and not and give them the personal choice to follow it or not, to make their world different, or to not. However, since addressing inconsistencies or inaccuracies regarding scifi writing on this (For some reason) thread does not seem to be approved of, even though discussions akin to it were being held previously as to radar detection and semi hardcore spacecraft design in this persons universe, (And they were asking about design) I will move this discussion to a different thread.

https://www.physicsforums.com/threads/stealth-and-detection-in-space-continued.783912/

(Formatting edited by moderator)

I have started a stand-alone thread in the astronomy forum.

 

[GTOM]

I thought about two manuevers, i wonder whether they make any sense?
A: connect two fighters with carbon nanotube cables, and rotate that squadron around its new centre of gravity.
So with tether propulsion, they can change position without using thrusters, that can't be hid.

B: Position two ships into vicinity, fire their thrusters at once, so it won't be obvious, whether ship A fired with 100%, ship A fired with 50% and ship B also fired with 50%. So it would be hard to calculate their acceleration based on the flames of thrusters.