Landing Atmo capable ships

[aramis]

the 33 cm of steel was picked, and the OTU is stuck with it. 100 diams of the largest generatable worlds in T5 is only 15,000,000 miles (240,000,000 km or so).. So let's do the math for a 1G going 2.5E11 m... in to a size F planet.

D=0.5AT²
2.5E11=0.5•10•T²
5E11=10•T²
5E12=T^2
2.236E6=T
621:07:48 = T
25d 21:07:48

V_peak= 2.236E7 m/s or about 0.1.5 PSL

A 1 gram object is going to have around 2 Megajoules - and focus it on about 0.01 cm². BSD or not, that's quite a bang. Like a semi or a tac-nuke.

Now, given that those size occur about 1 per cubic km... a square meter of surface goes 1 million meters between such hits... actually, due to accel/decell, about 2 million m, or 2000km... 2.5E11/2E6=1.25E5... 12,500 impacts, with the peaks at nuke level, PER SQUARE METER of cross-sectional area.

33 cm of steel or equivalent simply is NOT going to stop these at the high end.

Note that superterestrials (size >10) are long travel times... which also means high velocities. The realization of this is probably why Beltstrike added repulsors as standard - Me, I don't until TL12... but that's IMTU.

 

[Timerover51]

That is why I prefer the boost and cruise method of getting to 100 diameters. It takes a little longer, which oddly enough makes pirates more possible, but reduces the impact speed of undesirable particles. I see no sense building up a massive velocity vector, simply to brake to a stop again. I understand that is not canon.

 

[shaunhilburn]

Such large micrometeoroids are rare, but even a 10 g fragment would hit with the energy of a tonne of TNT.
.

That's what repulsors are for.

 

[Carlobrand]

the 33 cm of steel was picked, and the OTU is stuck with it. ...

Well, part of it is. I imagine there's the odd group here and there who don't frequent this group and haven't bought Striker or MegaTrav, who haven't encountered anything but those thousand-point-hull adventures. One of those "ignorance is bliss" things.

As a matter of curiosity, what's GURPS got to say on the issue?

...A 1 gram object is going to have around 2 Megajoules - and focus it on about 0.01 cm². BSD or not, that's quite a bang. Like a semi or a tac-nuke. ...

I'd point out that a lot of those are hitting at sharp angles rather than dead on - except of course that the energy involved makes that a moot point. I don't think we're dealing with tac-nuke bangs. I think it's more of a superheated rapier thrust that goes all the way through the ship and out the other side, which really doesn't make things better since there's a good chance that rapier thrust is going to kill some important piece of equipment, or even a crewman. Of course, I'm an amateur at such things.

That is why I prefer the boost and cruise method of getting to 100 diameters. It takes a little longer, which oddly enough makes pirates more possible, but reduces the impact speed of undesirable particles. I see no sense building up a massive velocity vector, simply to brake to a stop again. I understand that is not canon.

It's a pretty good idea. Set some upper speed limit, coast ... simplifies combat to some extent. Someone trying to run away could find themselves in as much danger from the odd mote in front of them as from the pirate behind them.

Occurs to me that "1 million meters between such hits" also affects missile combat. Well, maybe 56.6 million meters - their cross-section area's quite a bit less than a square meter. Still enough to limit the effective range of missiles, or at least have you rolling dice to see if they didn't get taken out by the odd dust mote before they reach the target. That 5G missile's doing over 30 kps after just 10,000 km flight, and it just gets worse from there. Missile's taking needlepoint superheated through-and-throughs that are bound to affect something.

 

[kilemall]

I'd point out that a lot of those are hitting at sharp angles rather than dead on - except of course that the energy involved makes that a moot point. I don't think we're dealing with tac-nuke bangs. I think it's more of a superheated rapier thrust that goes all the way through the ship and out the other side, which really doesn't make things better since there's a good chance that rapier thrust is going to kill some important piece of equipment, or even a crewman. Of course, I'm an amateur at such things.

I think more like the impact would create a plasma stream turning the fragment into something more like a plasma gun hit tearing through the ship, with heat and splash damage setting off fires to the side of whatever now has a hole through it.

Then around the edges of the impact , you would have spall, bits of metal or whatever material now embued with a fraction of the kinetic enemy imparted by the hit and firing like a claymore mine into the compartment the fragment breached and possibly the one behind it.

 

[kilemall]

Semi-agreed. More likely kinetic than anything else. Book 2 gives you the 1-6 with potential to damage the power plant, jump drive, maneuver drive, computer, and so forth, but Book 5 only gives you a single weaker impact - you could damage the maneuver drive, but the plant, jump drive, and computer are out of reach. Clearly there's some degree of divergence.

Hmm, but the nature of most targets is different too. The LBB2 missile is a little thing hitting little ships, and note the HG critical hit rule treats ACS harshly.

Most HG warships are going to be 3000-ton plus scaling all the way up, and consider how little impact most LBB2 missile hits would be against a 3000 ton ship even in LBB2.

The main flaw IMO is how a surface hit does damage to the maneuver drive whether it is 10 tons or 10,000 tons. That's a system simplification for game effect divergence, and clearly one done for ease of damage notation for a game of 100+ ship battles, rather then logic or consistency.

 

[Brandon C]

Well, part of it is. I imagine there's the odd group here and there who don't frequent this group and haven't bought Striker or MegaTrav, who haven't encountered anything but those thousand-point-hull adventures. One of those "ignorance is bliss" things.

As a matter of curiosity, what's GURPS got to say on the issue?

In GT (not GT:IW) most non-warships hulls have the equivalent of 35mm or 70mm steel armor. The SDB comes in ~400mm equivalent. I'll have dig around for bulkheads.

 

[aramis]

Well, part of it is. I imagine there's the odd group here and there who don't frequent this group and haven't bought Striker or MegaTrav, who haven't encountered anything but those thousand-point-hull adventures. One of those "ignorance is bliss" things.

As a matter of curiosity, what's GURPS got to say on the issue?



I'd point out that a lot of those are hitting at sharp angles rather than dead on - except of course that the energy involved makes that a moot point. I don't think we're dealing with tac-nuke bangs. I think it's more of a superheated rapier thrust that goes all the way through the ship and out the other side, which really doesn't make things better since there's a good chance that rapier thrust is going to kill some important piece of equipment, or even a crewman. Of course, I'm an amateur at such things.



It's a pretty good idea. Set some upper speed limit, coast ... simplifies combat to some extent. Someone trying to run away could find themselves in as much danger from the odd mote in front of them as from the pirate behind them.

Occurs to me that "1 million meters between such hits" also affects missile combat. Well, maybe 56.6 million meters - their cross-section area's quite a bit less than a square meter. Still enough to limit the effective range of missiles, or at least have you rolling dice to see if they didn't get taken out by the odd dust mote before they reach the target. That 5G missile's doing over 30 kps after just 10,000 km flight, and it just gets worse from there. Missile's taking needlepoint superheated through-and-throughs that are bound to affect something.

Actually, once you get to megajoules per gram ranges, you've got instant vaporization and the sudden plasma expansion from that...

The angle of incidence is not going to cancel much, as the acceleration needed on the particle is sufficient to vaporize it with the horizontal anyway. And the 9x30 m cross-section of a scout ship (I forget which version) is 135 such hits per trip.
the median hit is 1/4 that energy, but that's still carving chunks from the armor

Without some deflector, as TR notes, coasting is much safer.

 

[Blue Duke]

cant the Type S and the far trader land in the water ? and also wouldnt their materials science in the far future be MUCH better then ours ? maybe they've got stuff that can support the weight that we cant even dream of or use Grav plates or what ever to counter the weight some what.

 

[Timerover51]

cant the Type S and the far trader land in the water ? and also wouldnt their materials science in the far future be MUCH better then ours ? maybe they've got stuff that can support the weight that we cant even dream of or use Grav plates or what ever to counter the weight some what.

Using the grav lifters or what I call contra-gravity plates to partially cancel out the weight ot the ship to allow them to float would work okay. I just tend to use naval architectural designs because I have some knowledge of that, so I am biased to ships that will float without assistance.

I am not sure about advanced materials, as the future will still be working with the same periodic table. Developing new ways to use the existing materials will likely occur, Kevlar being one example. I am looking at how to do it with what we know now.

Jetty Pournelle once made a comment that if the Dean Drive actually worked, a nuclear submarine would make a great spaceship. I am just following up on that.

 

[Carlobrand]

Actually, once you get to megajoules per gram ranges, you've got instant vaporization and the sudden plasma expansion from that...

How sudden? That's well beyond my limited knowledge of physics, but with the ship moving at speeds measured in tens and hundreds of kilometers per second, that would seem to be a big factor in how much damage is done.

I think we're a zero off in that equation. 15 million miles went to 240 million kilometers. Still big numbers. That 15 million is for a super-Jovian, if I have it right - something 150,000 miles in diameter, yes? Looking at terrestrial worlds, CT's top was a C, 12,000 miles diameter. Figuring from that, the 100-diameter limit's at 1,920,000 km. Peak velocity at 960,000 km is 138.564 kps. Energy in a 1 gram particle impacting at that velocity is 9.6 megajoules. 340 kilojoules vaporizes about 56 grams of iron so figure enough to vaporize about 1.6 kilograms. Certainly enough to get through the little bit of hull on the classic ships, maybe enough to get through that 33 cm hull too, but I don't know enough to figure that one out.

So, relying on that sudden expansion, we put a shell around the ship. Whipple shield. The particle hits the shield, vaporizes, penetrates, expands, hits the hull as a puff of superheated expanding plasma. Effectiveness depends on how fast the particle is going relative to the ship, how fast it expands, and how far out the shell is from the hull. So, since we're dealing with stuff coming from in front, have a shell that fits tight around the front of the ship but can be pushed forward a few meters in space, a sort of thin bulldozer blade.

 

[aramis]

The numbers I picked were for Size 15 - the largest terrestrial size in T5.

In rock, let's see, specific heat of between 0.84 and 3.5 for typical rock minerals...let's use the high ends for both density and specific heat, of about 5 g/cc and 3.5 J/g per 1°C (or K) so a 1 g particle is about 6mm diameter, and 2 megajoules heats it 0.5 million degrees in under a second. BANG!nearly half the trip it will be 1 g plasma pellets in a rate of one or two an hour.

The issue isn't the hit - the plasmafication really does make the damage less... but...the hit steel will take half the energy, and be sever cm thick melted away to vapor.

Further, not all will be at relative rest, so some will be hotter.

The other issue is that the energy is sufficient to cause atomic level damage - creating secondary radiation. Which can affect the metal just as badly. I don't know where that line is...but ISTR it being about 100 kJ/g

 

[Carlobrand]

The numbers I picked were for Size 15 - the largest terrestrial size in T5.

In rock, let's see, specific heat of between 0.84 and 3.5 for typical rock minerals...let's use the high ends for both density and specific heat, of about 5 g/cc and 3.5 J/g per 1°C (or K) so a 1 g particle is about 6mm diameter, and 2 megajoules heats it 0.5 million degrees in under a second. BANG!nearly half the trip it will be 1 g plasma pellets in a rate of one or two an hour.

The issue isn't the hit - the plasmafication really does make the damage less... but...the hit steel will take half the energy, and be sever cm thick melted away to vapor.

Further, not all will be at relative rest, so some will be hotter.

The other issue is that the energy is sufficient to cause atomic level damage - creating secondary radiation. Which can affect the metal just as badly. I don't know where that line is...but ISTR it being about 100 kJ/g

Away for a bit, sorry.

The whipple shield addresses some of those points. Part of the engineering of the design will be in deciding how far ahead the shield needs to be for the plasmafied particle to spread adequately enough that the hull can take the damage without compromising the vulnerable stuff, and that would also set the ship's upper speed limit. Hull design would also need to have some way of keeping that secondary radiation from becoming a threat to the crew or equipment. Looks like the hull would take gradual erosion along the leading and trailing surfaces regardless, not to mention becoming gradually more radioactive, and of course the whipple shield itself is getting swiss-cheesed, so those repairs would have to be dealt with periodically at the starport. Ablative layer? Second or third layer whipple to slow the plasma?