Attacking Darius:

Relax wrote: For super close in shots, Initial velocity is just as important as high acceleration in terms of distance. So, if super worried about close in shots, seems increasing Initial Velocity from your missile tube is very important. Since we have all been looking at MDM combat, initial velocity as a requirement of ship design has disappeared, but in the age of Spider ships, and close in combat, or at least the prospect of close in combat, initial velocity once again becomes VERY important. Of course acceleration is ultra important for vector control of said missiles. We have to assume a missile cannot be fired off vector of pure broadside. Maybe one can change orientation from pure normal/perpendicular to broadside by a couple degrees, but more than this? Seems improbable.

Unless it's a spinal rail launcher, physics are going to get in the way. Even if your rail launcher could impart 10 million gravities of acceleration and your broadside launchers were 100 m in length, the missile would come out of the tube at a mere 140 km/s. Even one billion gravities would only bring it up to 1400 km/s.

140 km/s plus 10 seconds of one million gravities of acceleration results in a delta-v of 98207 km/s (0.32c) and a range of 491732 km. That means the launching ship can't fire if the target is over 520,000 km away.

The only way to make this work is if the launching ship's base velocity towards the target is already very high. If said ship has a radial velocity vector towards its targets of 0.1c, the range increases to 790,332 km, which starts to put it outside of energy range. Except that it's moving towards the target at 0.1c, so it will be in energy range in 3 to 5 seconds... so why fire missiles 3 seconds early and advertise you're there?

Another simple calculation: for regular anti-ship missiles, their two modes have an easy relationship: double the acceleration and it lasts one third of the time. A CM lasts 75 seconds, so if we get a third of a third of that time (8⅓ seconds), we should see the acceleration maybe quadruple. The Cataphract CM stage is said to have an acceleration of under 100,000 gravities, so quadrupling it only puts at 400,000. They'd need to start with a CM that already has a quarter million gravity of acceleration to get there.

EDIT: fixed "tangential" with "radial"

ThinksMarkedly wrote:Another aspect that David is VERY good at (possibly the best at) is figuring out the other consequences this technology would have, militarily as well as not.

He missed a big one in Apocalypse Troll. He correctly saw the symbioite could be used as a last-resort medical treatment. What he missed is that there would be a lot of people who would take the chance as death approached. Look at places where euthanasia is accepted--a fair number of people choose not to fight death to the bitter end. I see no reason to think that will change--but in a world with the symbioite I would expect that most people that have reached that point would choose sedate and infect instead. (There would be some with genetic issues that couldn't be saved, thus it wouldn't be 100%.)

kzt wrote:You want a breakthrough?

Liquid immersion with liquid breathing. According to an old NASA study that should get you to about 40G tolerance. I forget the multiple that David was using, but it's a LOT of delta V.

Big practical problem: The human body isn't capable of actually breathing liquid. There are liquids that probably could provide the O2/CO2 exchange, but the lungs aren't strong enough to pump it. I haven't heard whether the lungs could survive it being pumped in and out but I certainly wouldn't want to count on that being survivable.

On the other hand, they are exploring using the rectum for gas exchange--it definitely works to some degree, they don't know how far it can go. It's being studied as a safer alternative to a ventilator.

If that pans out, fill the lungs (and all other body cavities) with fluid and you get the same acceleration tolerance.

There's also the possibility of using ECMO combined with filling the body cavities with fluid.

cthia wrote:Even the acceleration of GA missiles is talked about in this light. Paraphrasing "Sir, if their current acceleration holds up, yatta yatta yatta." Like a prize fighter, the missiles have to pace themselves. If maximum range is your objective, you are going to have to scale back on the design in maximum acceleration. You don't want the missile (or long distance runner) to shoot its wad too quickly having to go ballistic too soon. But there is no navy to date that has had a reason to look at it from the other side, because of a ship that can launch from such a close range.

Necessity really is the mother of invention.

The GA would have paid attention.

1) Countermissiles.

2) LACs aren't purely defense weapons.

3) Mistletoe.

RFC already addressed this initial velocity via acceleration of launcher problem everyone and their mother(myself included, like you) have brought up. He did so waaaaaaayyyyy back at the beginning when he brought up wedge smoke, fratricide and the fact the sidewall is 10km from ship and edge of wedge is ~150km from the ship. The distance is between the launcher and the sidewall for acceleration profile and initial imparted velocity. Not the physical launcher itself. With the miracle of handwavium this is true...

PS: Oh yea, regarding range/acceleration; it has been a few years since ran calc, but a DDM with 225s burn running at 65,000g has more range than a MDM. Or saying a CM who has 75s burn and 130,000g is "stepped down".

One wonders what is limitation on acceleration as theoretically RFC said accel is infinite? Pure power throughput? Heat buildup before failure? All of the above and since RFC is not publishing engineering treatises, but rather space opera.

ThinksMarkedly wrote:

Relax wrote: For super close in shots, Initial velocity is just as important as high acceleration in terms of distance. So, if super worried about close in shots, seems increasing Initial Velocity from your missile tube is very important. Since we have all been looking at MDM combat, initial velocity as a requirement of ship design has disappeared, but in the age of Spider ships, and close in combat, or at least the prospect of close in combat, initial velocity once again becomes VERY important. Of course acceleration is ultra important for vector control of said missiles. We have to assume a missile cannot be fired off vector of pure broadside. Maybe one can change orientation from pure normal/perpendicular to broadside by a couple degrees, but more than this? Seems improbable.

Unless it's a spinal rail launcher, physics are going to get in the way. Even if your rail launcher could impart 10 million gravities of acceleration and your broadside launchers were 100 m in length, the missile would come out of the tube at a mere 140 km/s. Even one billion gravities would only bring it up to 1400 km/s.

140 km/s plus 10 seconds of one million gravities of acceleration results in a delta-v of 98207 km/s (0.32c) and a range of 491732 km. That means the launching ship can't fire if the target is over 520,000 km away.

The only way to make this work is if the launching ship's base velocity towards the target is already very high. If said ship has a tangential velocity vector towards its targets of 0.1c, the range increases to 790,332 km, which starts to put it outside of energy range. Except that it's moving towards the target at 0.1c, so it will be in energy range in 3 to 5 seconds... so why fire missiles 3 seconds early and advertise you're there?

Another simple calculation: for regular anti-ship missiles, their two modes have an easy relationship: double the acceleration and it lasts one third of the time. A CM lasts 75 seconds, so if we get a third of a third of that time (8⅓ seconds), we should see the acceleration maybe quadruple. The Cataphract CM stage is said to have an acceleration of under 100,000 gravities, so quadrupling it only puts at 400,000. They'd need to start with a CM that already has a quarter million gravity of acceleration to get there.

Loren Pechtel wrote:

kzt wrote:You want a breakthrough?

Liquid immersion with liquid breathing. According to an old NASA study that should get you to about 40G tolerance. I forget the multiple that David was using, but it's a LOT of delta V.

Big practical problem: The human body isn't capable of actually breathing liquid. There are liquids that probably could provide the O2/CO2 exchange, but the lungs aren't strong enough to pump it.

There's also the possibility of using ECMO combined with filling the body cavities with fluid.

Yes, would have to use ECMO... battle damage in ECMO or springs a leak...

Relax wrote:NIT: MK16 with micro fusion reactor was powered up before it entered the launch chamber. Why it had to be placed in a hull beam with double length effective chamber and only the SAG-C would do and why a smaller ship did not have enough beam width for it.

No, it needed to be powered up in the tube. David discussed this a little here. Older missiles are powered up in the magazine, the Mk16 needs a plasma feed in the tube to power up the reactor because reasons.

On a BC there is extensive reinforcing around the tube, which can, in theory, absorb the megaton scale explosion of a reactor failing for some reason as it powers up. It's a little unclear how effectively a supersized DD can handle that.

Relax wrote:RFC already addressed this initial velocity via acceleration of launcher problem everyone and their mother(myself included, like you) have brought up. He did so waaaaaaayyyyy back at the beginning when he brought up wedge smoke, fratricide and the fact the sidewall is 10km from ship and edge of wedge is ~150km from the ship. The distance is between the launcher and the sidewall for acceleration profile and initial imparted velocity. Not the physical launcher itself. With the miracle of handwavium this is true...

Oh, indeed. The missiles need to get half a wedge length past the sidewall before they can bring their wedge up and accelerate away. If the launcher can do one million gravities and an SD's launcher is one eighth of the SD's beam, it's only 25 metres long. That gives a launch time of 2.25 ms for a final speed at the end of the launcher of 22.1 km/s. That means it'll clear 15 km (sidewall distance + half a 10 km wedge) in 677 ms. At one tenth that acceleration, the time increases by the square root of 10, to 2.14 s. Those are reasonable values by themselves.

But I think this needs to add one aspect of handwavium: a pressor beam from the launch tube. Because the length is no longer a limitation, the acceleration can be lower. Say the beam pushes at only 10,000 gravities: over 10 km, that adds a delta-v of 44.2 km/s. There's also no reason the beam needs to stop at the sidewall, so it can add 54.2 km/s over 15 km. With the base velocity of the launcher (7 km/s for 100,000 G @ 25 m), the missile clears the half-wedge in 460 milliseconds.

An addition is for the missile to be pitched up or down. So long as it avoids the launching ship's roof or floor (respectively), that manoeuvre can shorten the distance to wedge activation.

CMs make it harder, because they have oversized wedges, so they need to be pushed further out. But if they apply the pitch manoeuvre, they have an added benefit: they are now completely blocking the aspect of the ship with an impenetrable wedge. That's the Travis Manoeuvre.

Anyway, none of this helps save the idea. The acceleration to get a meaningful base velocity needs to be ludicrous. It requires that the ship carry those missiles, which occupy space that could be dedicated to regular missile pods or torpedoes. It requires a sufficient quantity of missile tubes on the broadside, instead of graser mounts. And it may not serve to kill anything bigger than a light-cruiser.

Loren Pechtel wrote:Big practical problem: The human body isn't capable of actually breathing liquid. There are liquids that probably could provide the O2/CO2 exchange, but the lungs aren't strong enough to pump it. I haven't heard whether the lungs could survive it being pumped in and out but I certainly wouldn't want to count on that being survivable.

On the other hand, they are exploring using the rectum for gas exchange--it definitely works to some degree, they don't know how far it can go. It's being studied as a safer alternative to a ventilator.

If that pans out, fill the lungs (and all other body cavities) with fluid and you get the same acceleration tolerance.

There's also the possibility of using ECMO combined with filling the body cavities with fluid.

The USN Experimental Diving Unit ran tests on oxygenated prefluorocarbons. It worked (as in the divers survived), it was distinctly not fun and had problems with removing CO2 and with the exertion required. And if you don't get all the fluid out you got pneumonia. So not practical.

It's also apparently used, with lots of medical support, for life support with premature infants.
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3191624/

So it's just a matter of maturing the tech over the next few thousand years.

kzt wrote:

Relax wrote:NIT: MK16 with micro fusion reactor was powered up before it entered the launch chamber. Why it had to be placed in a hull beam with double length effective chamber and only the SAG-C would do and why a smaller ship did not have enough beam width for it.

No, it needed to be powered up in the tube. David discussed this a little here. Older missiles are powered up in the magazine, the Mk16 needs a plasma feed in the tube to power up the reactor because reasons.

On a BC there is extensive reinforcing around the tube, which can, in theory, absorb the megaton scale explosion of a reactor failing for some reason as it powers up. It's a little unclear how effectively a supersized DD can handle that.

Nyet. Power up time of micro fusion reactor as stated by DW is ~30s. Cycle rate is 18s. Why the beam of required ship is so great. He has another tube section which is armored for a micro fusion device blowing up behind the missile tube