Pushing the Speed of Light (not too hard, but pushing it...)

The effective speed limit in both hyper and real space has been limited by the open wedge and the need for particle shielding and the danger of micrometeoroids. So far, it's not been mentioned, but the speed limit in real space and all accessible bands of hyper should be much higher now, unless I'm missing something.

Ships can accelerate with the bow wall "Buckler" up--so could they keep that up as they push closer to the speed of light. TextEv puts hyper speeds at close to 50%C, and, IIRC, 80% in normal space. So--how fast now? Perhaps ships so equipped can beat the Mesan dispatch boats--even before Manticore discovers how to get into the higher bands...

ZOOM!

NHBL wrote:Ships can accelerate with the bow wall "Buckler" up--so could they keep that up as they push closer to the speed of light. TextEv puts hyper speeds at close to 50%C, and, IIRC, 80% in normal space.

I don't think there is any textev to say one way or the other, but I suspect a bow or stern buckler does limit top speed to ofset improved shielding effects. If there isn't a speed penalty imposed by having the buckler up, you may well be on to something.

One question: what do you do if you need the stern buckler while over the top speed allowed by normal particle shielding?

NHBL wrote:So--how fast now? Perhaps ships so equipped can beat the Mesan dispatch boats--even before Manticore discovers how to get into the higher bands...

ZOOM!

Beating a MAlign streak drive isn't going to happen until ships can reach the same hyper bands as the streak drive reaches. (I don't remember what thee multiplier is, but for the sake of argument call it double the previous hyper band.) If you managed to reach light-speed without killing yourself, you will only have reached 100% of light-speed. If you're in the maximum pre-streak band, a MAlign dispatch boat will travel 200% of your maximum speed in the next higher band and 400% of your maximum speed in its max band. (it's actually closer to 600100% but who cares about minor details like that. )

Weird Harold wrote:One question: what do you do if you need the stern buckler while over the top speed allowed by normal particle shielding?

You just bring it up. Bucklers don't affect acceleration - you're thinking of the full bow-wall and stern-wall, which merely cuts acceleration to zero.

munroburton wrote:

Weird Harold wrote:One question: what do you do if you need the stern buckler while over the top speed allowed by normal particle shielding?

You just bring it up. Bucklers don't affect acceleration - you're thinking of the full bow-wall and stern-wall, which merely cuts acceleration to zero.

No, I'm well aware of the difference between a bow-wall and a "buckler." I'm also aware that you can't have BOTH bucklers at the same time -- which is also true of bow and stern walls with the added complication that you can neither accelerate or decelerate, nor can you steer with the Wedge.

The Question posed presumes you would lose the protection of the bow-buckler being used as a rad-screen. Another way of wording the question is, "How do you survive if the Buckler fails or has to be taken down for any reason?"

Weird Harold wrote:No, I'm well aware of the difference between a bow-wall and a "buckler." I'm also aware that you can't have BOTH bucklers at the same time -- which is also true of bow and stern walls with the added complication that you can neither accelerate or decelerate, nor can you steer with the Wedge.

The Question posed presumes you would lose the protection of the bow-buckler being used as a rad-screen. Another way of wording the question is, "How do you survive if the Buckler fails or has to be taken down for any reason?"

Same as if the rad-screens, or any of a dozen critical systems aboard a starship failed - I'm thinking of compensators going down during maximum acceleration. You don't survive. Oh, maybe you could turn the wedge perpendicular towards the direction of travel and hide from the particles behind it. But you'd have no way to decelerate until you got one of the bucklers back up, unless you are in hyperspace and able to perform downward translations to bleed the velocity off.

I think the problem with this is that you still need the wedge up to make the buckler work, and you can't raise the wedge in a grav wave, severely limiting a ships opportunity to actually utilise it.

This is a fairly straightforward exercise in fluid dynamics: that buckler is not a cookie-cutter in space. Assuming, and it is almost certainly _not_ a valid assumption, that nothing can actually diffuse through the buckler field, all the material swept up by it will flow across to the nearest edge [well, as a first approximation, anyway], at which point it interacts with the edge and the medium that hasn't been swept up, and very likely with the insides of the wedge as well, and you end up with a very turbulent wake streaming back towards the ship. How dense it will be depends on velocity, diameter, density and viscosity of the various elements involved, but, IIRC, in air it's back to the average density by something like the diameter of the disk or sqrt(2) x the diameter behind the disk. With the added complication that the turbulence means that locally the density can be much higher than average. I believe that the velocity of the flow in the turbulent region will now be sub-sonic, but that just guarantees that the ship will ram into it.

IOW, turning on a buckler does little good, and could even make things worse

NHBL wrote:The effective speed limit in both hyper and real space has been limited by the open wedge and the need for particle shielding and the danger of micrometeoroids. So far, it's not been mentioned, but the speed limit in real space and all accessible bands of hyper should be much higher now, unless I'm missing something.

Ships can accelerate with the bow wall "Buckler" up--so could they keep that up as they push closer to the speed of light. TextEv puts hyper speeds at close to 50%C, and, IIRC, 80% in normal space. So--how fast now? Perhaps ships so equipped can beat the Mesan dispatch boats--even before Manticore discovers how to get into the higher bands...

ZOOM!

Louis R wrote:This is a fairly straightforward exercise in fluid dynamics...

You are correct that you can in some cases apply fluid dynamics to the interstellar medium, but I think you're being mislead by the scales involved here. The ISM is *so* incredibly rarefied that any traditional fluid dynamics intuition is going to be very misleading on the size scale of a starship.

The first basic problem is that the mean free path for a particle at the densities of the ISM is on the order of *at least* tens of thousands of km even for denser regions (interaction cross sections of ~10^-16, particle densities lower than 1000/cm^3). And that means that any behavior which relies on particles interacting with each other (i.e. fluid dynamics) will not be apparent on any scales less than that - the ISM only acts like a fluid on scales of tens of thousands (if not millions) of km. The particles deflected by the buckler will proceed radially outwards for thousands of KM before they have any realistic chance of hitting any other particle which could redirect their motion back inwards. (Well, assuming they didn't hit the wedge, anyway, but I very highly doubt the wedge would push them *inwards*, otherwise the wedge itself would be dangerous to the ship as it swept up the ISM as it passed through.) So while yes, normally a flow around a moving disk will fill back in within a short distance relative to the size of the disk, that's only valid when the size of the disk is not many orders of magnitude smaller than the mean free path of the medium. That doesn't mean that the hollow behind the disk won't be filled up pretty rapidly in an *absolute* sense (by particles that were not hit by the buckler diffusing back into the channel), but you can't relate the depth of the hollow to the size of the disk itself.

The other main problem is that this is an *incredibly* hypersonic flow. Even in the higher temperature regions of the ISM the speed of sound isn't much above ~10 km/s (T~10,000K), meaning that a ship moving at 0.8c is travelling at something like mach 24,000! Even if the medium was dense enough for the mean free path to be comparable to the scales involved, the sheer blazing *speed* with which the buckler sweeps out its channel is going to make it very hard for any material to actually physically move back inwards in time for it to hit the ship. Sidewalls are ~10km from the ship. A ship moving at 0.8c covers 10km in ~4e-5s! In that time, those particles moving at ~10km/s cover a whopping 0.4m. Even if you assume the shock of the impact results in them moving an order of magnitude faster (i.e. a 100-fold increase in temperature), they're still not spreading more than a few meters back inward before the ship is far, far past.

The real problem with the buckler acting as a particle shield at speeds where normal particle shields would fail is that it only will work as long as the ship's orientation *exactly* matches its vector - as soon as the ship rotates to accelerate in a different direction than the one it's currently moving, the buckler swings out of line with the flow and all those particles start smashing right through your regular particle shielding. Given that you can't maneuver at all (or even slow down!) without changing heading, it would be impossible in a practical sense to actually safely use a buckler as a shield even if it might be theoretically possible. (Barring, as munroburton mentions, the possibility of making a downwards hyper translation to bleed off speed, but even then the inability to do anything other than go in straight lines would be crippling.)

So, simplisticly, any particles that are near the centerline of the ship are going to be obliterated because they can't move out of the way of the buckler in time?

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MuonNeutrino wrote:

Louis R wrote:This is a fairly straightforward exercise in fluid dynamics...

You are correct that you can in some cases apply fluid dynamics to the interstellar medium, but I think you're being mislead by the scales involved here. The ISM is *so* incredibly rarefied that any traditional fluid dynamics intuition is going to be very misleading on the size scale of a starship.

The first basic problem is that the mean free path for a particle at the densities of the ISM is on the order of *at least* tens of thousands of km even for denser regions (interaction cross sections of ~10^-16, particle densities lower than 1000/cm^3). And that means that any behavior which relies on particles interacting with each other (i.e. fluid dynamics) will not be apparent on any scales less than that - the ISM only acts like a fluid on scales of tens of thousands (if not millions) of km. The particles deflected by the buckler will proceed radially outwards for thousands of KM before they have any realistic chance of hitting any other particle which could redirect their motion back inwards. (Well, assuming they didn't hit the wedge, anyway, but I very highly doubt the wedge would push them *inwards*, otherwise the wedge itself would be dangerous to the ship as it swept up the ISM as it passed through.) So while yes, normally a flow around a moving disk will fill back in within a short distance relative to the size of the disk, that's only valid when the size of the disk is not many orders of magnitude smaller than the mean free path of the medium. That doesn't mean that the hollow behind the disk won't be filled up pretty rapidly in an *absolute* sense (by particles that were not hit by the buckler diffusing back into the channel), but you can't relate the depth of the hollow to the size of the disk itself.

The other main problem is that this is an *incredibly* hypersonic flow. Even in the higher temperature regions of the ISM the speed of sound isn't much above ~10 km/s (T~10,000K), meaning that a ship moving at 0.8c is travelling at something like mach 24,000! Even if the medium was dense enough for the mean free path to be comparable to the scales involved, the sheer blazing *speed* with which the buckler sweeps out its channel is going to make it very hard for any material to actually physically move back inwards in time for it to hit the ship. Sidewalls are ~10km from the ship. A ship moving at 0.8c covers 10km in ~4e-5s! In that time, those particles moving at ~10km/s cover a whopping 0.4m. Even if you assume the shock of the impact results in them moving an order of magnitude faster (i.e. a 100-fold increase in temperature), they're still not spreading more than a few meters back inward before the ship is far, far past.

The real problem with the buckler acting as a particle shield at speeds where normal particle shields would fail is that it only will work as long as the ship's orientation *exactly* matches its vector - as soon as the ship rotates to accelerate in a different direction than the one it's currently moving, the buckler swings out of line with the flow and all those particles start smashing right through your regular particle shielding. Given that you can't maneuver at all (or even slow down!) without changing heading, it would be impossible in a practical sense to actually safely use a buckler as a shield even if it might be theoretically possible. (Barring, as munroburton mentions, the possibility of making a downwards hyper translation to bleed off speed, but even then the inability to do anything other than go in straight lines would be crippling.)

Besides making an upward or downward hyper translation* (most likely downward) to bleed off speed, the other option to reduce speed is to simply stop accelerating with the wedge. The impact of the particles hitting buckler then would produce a (probably slow) braking action.

* Assumes the ship is in hyper-space, since you can't make an upwards translation from normal space to hyper-space above .3c without destroying the ship.