Are laser-stars the better missile carriers in space warfare?

Question

Laser-stars are war-spacecraft optimized to accommodate a huge laser weapon capable of eliminating an enemy thousands of kilometers away. They will usually have enormous radiators to deal with the waste-heat of their lasers and to cool the lasers further to reduce thermal lensing to keep the beam quality high. During an attack-run, they will use pulsed-beam lasers, but many laser designs can be switched between pulsed- beam and continuous-wave mode.

Missile Carriers are war-spacecraft optimized to shoot missiles at the enemy to kill them. The Rocinante from The Expanse could be considered a moderate missile carrier. An extreme missile carrier would be a propulsion bus whose only payload is hundreds or dozens of missiles.

With the relevant terms cleared up, on to the issue. Lasers have, unlike missiles (and kinetics, but the lines between those two are blurry at best in my setting), a limited range due to diffraction while missiles can just shut of their engines and go into cruise mode, possibly for centuries. This means that laser-stars will spend a long time on the approach doing nothing with their amazing lasers (they could threaten the enemy in Morse code with them, but that doesn't seem to be an effective use of a billion-dollar weapon system). Missile carriers likewise have their problems, or rather their missiles have. Unless you can install small, ridiculously efficient and powerful drives on the missiles, you either have to use humongous swarms to get through the point-defense grid (laser-star lasers, PDS-lasers, PDS-guns and defensive wide-angle-casaba-howitzers) our your attack won't be effective. Additionally, the enemy will know where the missiles will come from due to their very detectable drives. And all of this assumes that the missile carriers can get effective launches of before the laser-stars vaporize them. So essentially laser-stars will have a lot of ineffective downtime and missile carriers will be countered by point defense and the rocket equation.

My solution to these issues is based on the assumption that stealth in space is in fact possible (the links provide equations) (I know that a lot depends on the sensor nets available, but I assume that those will become worse as the war carries on as sensor hunters, x-ray fluorescent illumination searches, laser scans, and sandstorm kinetics will take their toll on them). I don't mean tactical Star Trek stealth but strategic detection lowering stealth. True, one can't hide a departure or launch burn but one can cool oneself down close to the temperature of the CMB with evaporative cooling and use metamaterials to make visible light and radio detection harder. If the cold missiles use serpentine rocket nozzles to strategically dump coolant to maneuver, the enemy will know only that there is a missile coming in and that it is somewhere in a 10 million square-kilometer zone. Useful information to be sure, but virtually useless to the point-defense effort. When the missiles will inevitably be detected they might have gotten into the range where they could effectively deploy their payload, say a nuclear-pumped x-ray laser.

My solution to the issues of laser-stars and missile carriers is to use the laser-stars laser to accelerate missiles until it can effectively fire at the enemy. This is the concept of laser propulsion. I could either use laser sails or laser thermal rockets. The delta-v budget of the laser-boosted stage of the is given by:

$$v = sqrt(d / 0.5 * a) * a$$

$v$ = change of missile velocity relative to laser-star

$d$ = distance over which the missile is accelerated (effective range of laser)

$a$ = acceleration of missile

According to my research $a$ will be several G's or even several tens of G's and $d$ will be in the hundreds or thousands of kilometers, resulting in delta-v budgets of several tens of kilometers per second. After the laser burn, the hot propulsion stage is ditched and broken up in a wide field shrapnel storm meant to harass the enemy. The cold and stealthy missile continues to cool itself and uses the coolant to increase the volume of space where it could be.

The warhead the missile will carry if they are used in an anti-spacecraft capacity are very diverse.

• kinetic impactors (nuclear gun, kinetic missile, cold bullet)
• sandstorm kinetics (small particles meant to damage surface structures)
• directed energy (casaba howitzers and bomb pumped lasers)
• virus bots (micro-machines meant to land and hack into enemy computers)
• combat drone (the closest thing to a space-fighter in my universe, various applications)

In the end, assuming that my assumptions about warheads and the nature of stealth in space are correct, is it thus reasonable to conclude that a laser dominated battlefield will automatically lead to a missile dominated one?

Answer 1

The conclusion I had gotten from sources like Atomic Rockets and Rocketpunk Manifeto is that the Laserstar is one component of a combat system, much like an aircraft carrier is one component of a naval task force or battle group.

Luke Campbell RBoD. The liniac is @ 500m long

Rocketpunk Manifesto in particular had lots of discussions about laser warfare, expecially using Ravening Beam of Death lasers (RBoDs) which would have an effective kill range of a light second (mostly in order to minimize the target cycle - there is only a two second delay from shot to seeing the effect). RBoDs were considered to be effective at vapourizing metals, ceramics and carbon fiber in milliseconds at that range, but Rick Robinson pointed out that massive weapons like that could engage far beyond, delivering "scorching" damage at a light minute and even appreciable energy on target at a light hour.

This suggests that the laserstar would work as a searchlight, illuminating potential targets with high energy beams and the sensor cloud surrounding the constellation of warships would be looking for reflections, heat energy or other tell tale signs of enemy activity. A spaceship cooled by evaporation of liquid hydrogen or helium would be suddenly discovered by the appearance of ionized gas molecules from the evaporative cooling cloud, for example. When that happens, the RBoD simply refocuses the beam, and starts to sweep up and down the trail of ionized gas to find the source.

Given your fleet mirrors many of the assumptions from Rocketpunk, Atomic Rockets and Tough SF, then you already are aware that the constellations suggested by these sources could be deployed in a disc or sphere about a light second in diameter, with multiple laserstars, kinetic platforms and other weapons and sensors. The inputs from so many different sensors (tuned to multiple different wavelengths) will provide a fairly detailed 3 dimensional picture of the space surrounding the constellation, and multiple RBoD's illuminating the space around them for light hours will give them more opportunities to discover stealth spacecraft and prepare countermeasures to deal with them.

The other issue is that stealth spacecraft as described seem to be fairly low performance vehicles, so the defending commander can likely be able to look at potential launch sites and work out transfer orbits to search, cutting down on the need to observe the entire volume of space surrounding the constellation.

I might also observe that in this environment, there will be a push to create more and less expensive lasers. Replacing the RBoD's 500m long liniac with a Plasma Wakefield Accelerator brings the entire apparatus down to the size of a kitchen table, allowing the constellation to have hundreds of mini RBoDs rather than a few stately kilometer long vessels. If the giant ones are used as illumination search lights, the oncoming stealth spacecraft might not even be able to determine where the multitude of "fighter" RBoDs actually are, meaning it can be skewered by many unexpected laser beams once its position and orbit are tracked.

Visualization of the Plasma Wakefield in action

Answer 2

They will see the missiles coming no matter what.

Your giant laser ships have a giant laser that they are not doing very much with. They have a lot of empty space. They can power the laser down, broaden the beam and swing it around and around, lighting up the emptiness with the laser. As the beam scatters with distance, it will remain effective at illumination. If something interrupts the beam, that something will reflect the laser back, and the doppler shift of the reflected light will tell you the speed of the object. If the obstacle is nonreflective it will still prevent sparkle from dust further down the path of the laser and so give away its position.

The laser then swings back for another more sustained look on what that thing was that got in the way. If it could be a missile, the laser delivers additional energy until something happens - either destruction of the thing or it is going the other way.

Given that a push by a laser was what got your missiles going in the first place, this offers the awesome possibility of laser missile ping pong. But otherwise I think missiles in space are a hard sell. Space is big and light is fast.

Answer 3

There's no comparison... if you had your laserstar mount a whole bunch of lasers, a few really, really big, and the rest relatively small, the small lasers could act as point defence.

The point defence lasers could kill any missile before it could reach effective detonation range, yet a powerful laser can be lethal at a range of several light seconds with dispersion.

The only way a missile ship might be able to compete with a laser ship is if the missiles carry atomic-bomb-pumped rod lasers that are aimed at the target ship before detonation - effectively becoming shrapnel for an atomic-scale weapon.

Consider the mathematical relationship between energy density and distance: Energy per square meter at the target varies proportionally to the square of the distance.

However, the energy released from a bomb is released in all directions, so for a bomb to be maximally effective - to deliver the greatest amount of energy to its target - it needs to be in contact with - or better, inside - the target.

Compare that with a laser: its energy is released unidirectionally with only a small dispersal, so a distance at which it delivers only a quarter of the energy per square meter is very much longer than for a bomb, and it may still deliver all of its energy to the target.

Answer 4

Whilst your assertion that stealth may be possible in space is reasonable (and the links you've provided give reasonable arguments in its favour), it does not play well with this second assertion:

According to my research a will be several G's or even several tens of G's and d will be in the hundreds or thousands of kilometers, resulting in delta-v budgets of several tens of kilometers per second

Energetic reaction engines, regardless of their mode of operation, cannot be stealthy. The launch of your salvo of missile busses cannot go unremarked, even if the missiles themselves immediately become invisible. Once you've revealed your location, you can be observed via occultation. Your metamaterials can't help but be imperfect due to distorting light sources behind them, especially when faced with a broad-baseline sensor array. You'll also have problems with a coating that works equally well from mm-wave to sub-nanometre x-rays. Once spotted, a retaliatory missile strike can be launched against you.

If your missiles are as dangerous as you imply, what you end up with is mutually-assured destruction all over again... you can't launch, because their relatiatory strike will annihilate you, even if you achieve total destruction of your targets (which is one of the reasons I'm finding "realistic" spaceship combat a bit uninteresting, these days).

is it thus reasonable to conclude that a laser dominated battlefield will automatically lead to a missile dominated one?

Given the assumptions you're operating under, it seems reasonable enough. Your missile dominated battlefield will then immediately turn into a stealth-dominated one, because as soon as anyone gets spotted then there's a good chance that everyone gets killed.

Answer 5

You are right to think that the battlefield is not static.
Even when the battlefield appears to stick to the same concept and strategies for an extended period of time it continues to evolve.

If the current state of the battle field is dominated by lasers alone, then that leaves all those who believe it will stay as such vulnerable to even the mildest amount of creativity.
The weakness of lasers is dissipation, so imagine if someone decided to store a missile with a substance that expands rapidly and dissipates light effectively when introduced to heat? Long range, and perhaps even point defense, would be rendered useless.
Of course, this veil could become a disadvantage too if the only issue for defense is heat build up.
My point is, you need to be flexible in battle to be able to survive. If the only defense you have is lasers and they've become useless, it doesn't matter if you can see the missiles coming or not.

Making your laser specialized ship adapt and carry missiles that utilize the ship's strengths to enhance their effectiveness is perfectly natural, especially if your ship sails alone and not in a pack. Specialized ships only make sense when they are in a group, so when they are countered they are not completely vulnerable to obliteration.