Navigation lasers and other ideas

[Carlobrand]

Aramis pointed out an issue: a ship traveling under acceleration toward a target a week away (presumably 3 1/2 days accelerating, 3 1/2 days decelerating) reaches speeds at which a mote of dust can penetrate through the hull of a ship - and right out the other side. Not on the list of healthy things if you or some vital electronic component or some such item happen to be in the mote's flight path.

Question then becomes: how do you prevent that? The obvious way is to slow down, but that has a pretty severe impact on canon. Safe speeds could leave you either spending weeks to get to the gas giant or having to jump to go get the fuel to jump.

Well, one good thing is that space is pretty empty. One estimate puts the amount of space dust out there at around 30 to 40 trillion tons - in a region of space measuring in the tens or hundreds of sextillions of kilometers. Odds of encountering something are very low. Still, what are the odds of lightning striking you? Given enough opportunity, the bad thing happens somewhere.

What is needed then is the ability A) to detect something as small as a mote of dust at ranges where you can do something about it, and/or B) to do something about it.

One thought is a navigation laser. Shine a beacon-size laser forward in an effort to illuminate tiny motes that might be in the flight path, either with the intent of spotting the things with enough time to maneuver around them or with the intent of targeting them with a second laser strong enough to vaporize the mote, so that instead of a dust mote the ship runs into a thin and expanding gas. The other thought is to make the beacon-laser strong enough to vaporize the mote itself, and then let it play across the ship's flight path. It depends on how much energy is needed to vaporize a mote: the object is to protect the ship without introducing an undocumented weapon.

What other ideas might be developed to protect the ship?

 

[aramis]

Carlo, part of the problem is that, at those speeds, even the routine gas is a major issue, in that it abrades and irradiates the hull.

Also, at 3.5G-days..., you're moving 3 million meters per second. The Interplanetary medium is about 5 atoms per CC, or 5,000 atoms per square meter. this has a mass of roughly 8.3e-24 g/cubic meter. And you're crossing 3 million cubic meters per second per square meter of frontage. So, 2.49e-17g, at 3e6m/s, or about 0.2mJ per second per square meter. Not a lot... but it adds up. Worse, it occasionally results in atomic change, and cascade decay.

At a week, you're doubling the mass and quadrupling the impact energy per unit mass, and thus getting about 1.6mJ per square meter per second. Note that background gamma radiation for an SG 35 1cm BSD hull is 1µR/h... 560µR/s or about 2 rads per hour... 2 million times the background on planet.

 

[Carlobrand]

Carlo, part of the problem is that, at those speeds, even the routine gas is a major issue, in that it abrades and irradiates the hull.

Also, at 3.5G-days..., you're moving 3 million meters per second. The Interplanetary medium is about 5 atoms per CC, or 5,000 atoms per square meter. this has a mass of roughly 8.3e-24 g/cubic meter. And you're crossing 3 million cubic meters per second per square meter of frontage. So, 2.49e-17g, at 3e6m/s, or about 0.2mJ per second per square meter. Not a lot... but it adds up. Worse, it occasionally results in atomic change, and cascade decay.

At a week, you're doubling the mass and quadrupling the impact energy per unit mass, and thus getting about 1.6mJ per square meter per second. Note that background gamma radiation for an SG 35 1cm BSD hull is 1µR/h... 560µR/s or about 2 rads per hour... 2 million times the background on planet.

Abrading the hull is a question of extent. Might be an immediate hazard, might not be an immediate problem but lead to expensive repairs and a once-over with an n-damper at the next stop, might just be an issue for annual maintenance. 0.2 mJ per square meter doesn't melt the hull - immediately - but it does add to the burden of heat removal, lest the hull quickly reach a melting point.

Radiation: I show the standard thickness armor able to reduce incoming radiation by about a factor of 11,000. 2 million divided by 11 thousand equals dead people, I think. Is all this gamma secondary to proton impacts on the hull? Is that going to set a hard upper limit on maximum velocity, or is there some way to mitigate the problem?

Point of the thread is mitigation: how does one address the problem? Is a magnetic field of any possible use in slowing down the incoming protons a bit, or are the velocities and energy requirements too extreme? Is a deployable "umbrella" of any value to "pre-impact" the proton field at a safe distance, and if so then how thick does this shield need to be? Should we put a layer of disposable material over the armor? Is the hull threaded through with a cooling system that takes heat to whatever form of heat exchanger the ship uses? (That creates another interesting engineering challenge, since the part of the ship in shadow on the acceleration leg is the leading edge on the deceleration leg.)

Let's be clear that we're talking about a week stop to stop, highest speed at midpoint 3.5 days into it?

Does make the point that a ship trying the "ultimate weapon" gambit is going to be giving off a lot of infrared long before it reaches dangerous velocities - and those velocities are going to have a definite upper limit.

What is an "SG 35 1cm BSD hull"? I'm guessing BSD is bonded superdense. What is the rest?

 

[mike wightman]

Hmm, :CoW: time...

Navigational repulsor technology?

Nuclear damper fields reinforcing the structural integrity of your hull preventing the radioactive decay Aramis postulates.

The magic manoeuvre drive screen that deals with micrometeorites and radiation.

Plasma armour held in place by magnetic, static electrical or gravitic fields?

 

[aramis]

Abrading the hull is a question of extent. Might be an immediate hazard, might not be an immediate problem but lead to expensive repairs and a once-over with an n-damper at the next stop, might just be an issue for annual maintenance. 0.2 mJ per square meter doesn't melt the hull - immediately - but it does add to the burden of heat removal, lest the hull quickly reach a melting point.

Radiation: I show the standard thickness armor able to reduce incoming radiation by about a factor of 11,000. 2 million divided by 11 thousand equals dead people, I think. Is all this gamma secondary to proton impacts on the hull? Is that going to set a hard upper limit on maximum velocity, or is there some way to mitigate the problem?

Point of the thread is mitigation: how does one address the problem? Is a magnetic field of any possible use in slowing down the incoming protons a bit, or are the velocities and energy requirements too extreme? Is a deployable "umbrella" of any value to "pre-impact" the proton field at a safe distance, and if so then how thick does this shield need to be? Should we put a layer of disposable material over the armor? Is the hull threaded through with a cooling system that takes heat to whatever form of heat exchanger the ship uses? (That creates another interesting engineering challenge, since the part of the ship in shadow on the acceleration leg is the leading edge on the deceleration leg.)

Let's be clear that we're talking about a week stop to stop, highest speed at midpoint 3.5 days into it?

Does make the point that a ship trying the "ultimate weapon" gambit is going to be giving off a lot of infrared long before it reaches dangerous velocities - and those velocities are going to have a definite upper limit.

What is an "SG 35 1cm BSD hull"? I'm guessing BSD is bonded superdense. What is the rest?

SG is standard abbreviation for specific gravity; water at 4°C and 1 Bar is SG1. Note that rads is a function of J/kg, and is 100x that ratio.

Any time you hit stuff at relativistic velocities, you get secondary EMR (electromagnetic radiation).

Note that in addition to heating, that drag adds up.

That's also completely ignoring the 1g/km^3 of rock/dust/sand in the Interplanetary medium. Which is still hitting with canonfire imacts at half a week peak velocity for 1G. 9.1e10 J (that's 91 gigajoules) on an area half a cm across. Which should penetrate several dozen meters.

 

[Carlobrand]

SG is standard abbreviation for specific gravity; water at 4°C and 1 Bar is SG1. Note that rads is a function of J/kg, and is 100x that ratio.

Any time you hit stuff at relativistic velocities, you get secondary EMR (electromagnetic radiation).

Note that in addition to heating, that drag adds up.

That's also completely ignoring the 1g/km^3 of rock/dust/sand in the Interplanetary medium. Which is still hitting with canonfire imacts at half a week peak velocity for 1G. 9.1e10 J (that's 91 gigajoules) on an area half a cm across. Which should penetrate several dozen meters.

I always learn something when I talk with you.

We're completely ignoring the rock/dust/sand because we're operating on the assumption that we can vaporize that with lasers at a safe distance, or spot it far enough off that we can detour slightly to avoid it. That last assumption implies some incredible sensor equipment, but I haven't gotten that far yet. First problem is, as you pointed out, that the vaporized gas left by the laser is triggering lethal gamma through the ship. No point in solving other problems if the crew is being killed by the first problem.

Drag, similar: no problem in running the equations yet if the ship is a gamma ray coffin. I'm not even sure I can save the computer under such circumstances.

So, "SG 35 1cm BSD hull" translates as, "Specific Gravity of 35, 1 cm thickness bonded superdense hull"? I thought Bonded Superdense had a specific gravity of 15. And, I'm getting 2.4 cm for hull thickness. Not that it helps any - I think that cancels out to mean about the same thing.

Hmm, :CoW: time...

Navigational repulsor technology?

Nuclear damper fields reinforcing the structural integrity of your hull preventing the radioactive decay Aramis postulates.

The magic manoeuvre drive screen that deals with micrometeorites and radiation.

Plasma armour held in place by magnetic, static electrical or gravitic fields?

And this is what I'm looking for, and this is where things get nasty. As you mention, :CoW:

We clearly need to get the mass out of the way. If it hits the hull, we get lethal gamma unless we armor up the hull beyond what even a dreadnought can manage. However, whatever magic physics we dream up, we have to obey the most basic rules. We can't spend more energy shielding the ship than the ship makes, and the more energy we spend shielding, the less energy we have for drives.

The worse problem: unintended consequences. What we dream up as a field to deflect matter inbound at fractions of C will also make a field against missiles. I'd considered lasers, but that still leaves me with the vapor problem, and lasers strong enough to vaporize and then move all that vapor and associated free-floating protons and whatnot out of the way would also be one wicked powerful antiship weapon. My best solution seems to be a spinal mount laser of fantastic power, firing along the ship's path to drive everything out of the way for a light-second or more - which means I've left the realm of Traveller and gone into Larry Niven's universe.

What is needed is something that can move protons and dust motes and such laterally out of the way - at ranges of tens of thousands of kilometers, so that the acceleration needed is not too ludicrous. Or, something that can move them out of the way closer - but with ludicrous levels of acceleration that imply major amounts of power used. That one is taxing my imagination.

Makes the Island Clusters colony ships a real challenge. With speeds several times higher than we're discussing, only way I can see it is for them to put the whole blessed asteroid between them and the oncoming matter, site the living structure in the asteroid's shadow rather than inside it. And it would still be a big mucking asteroid, and I don't for the life of me know how they'd fuel that kind of a trip. Maybe an ice asteroid, but that's scary: living in the shadow of your fuel and having your shield get smaller and smaller as you went faster and faster.

 

[aramis]

The small rocks being vaporized isn't going to make all that much difference. When you're doing 3000km/s, if you vaporize said rock at 10 km, you've impacted a plasma cloud at 3km/s rather than a rock.

And the laser is going to need to be pretty big.

asteroids work out to between 6.3MJ/kg and 10MJ/kg to vaporize; cometary items about 2.25MJ/kg.†

they will still expand at fairly low velocities after...

Given a focal length of 30,000km, as is common in TNE/T4, and a spread of 0° 1', that's a L*2.91e-4 spread, or 8km spread, of a 1m beam. Given a 5" of arc... L*2.42e-5 spread, or 720m... and we know the focal mirror is about 1.5m or smaller. So, given that, we can get that we need about 230K x the energy.

We need to deliver that before impact... so let's say at least one second out.

So, we need 3 seconds at about 10 MJ accumulated. so, divide by 3. 3.3 MJ per 0.25cm^2... x10,000 cm/m^2, * π * 720^2... we need to deliver 2.15e11 J to the beam. 215 GJ, continuous - 215 GW.

Well beyond the capabilities. Oh, and you STILL hit that bit. Just as a 1-2m cloud of gaseous silicon and iron. Which, now, rather than penetrating, just impacted and generates a widespread gamma and x-ray cascade.


Forget your freaking "navigational laser" - it's not going to work. Not without redefining the units of available energy and assuming a level of reliability.

Given that most of the rock isn't in pebbles, but sand grains of milligram size, you can't even dodge them. if we take a 10m cylinder, that's needing 2G-seconds to clear. you have to detect that at about 2.5 seconds, for safety.

2.5 x 3,000km = 7,500 km. at 5" collimation, you're still 1/(182^2) the energy, or needing to put 33,000 times the detectable energy density on the stupid thing. Oh, and then double the range, aka quadruple the energy, since the return energy also has to travel the distance. so, if you need a 1 W return to spot, you still need to use a 132 kW laser.

a 132kW laser is a noticeable weapon - it's "kill a man" kind of strong.

† someone else did this math, working out the energy of a Star Wars turbolaser...

 

[Carlobrand]

The small rocks being vaporized isn't going to make all that much difference. ...

Yeah, we've seen that. Death by gamma, or maybe some lucky fellow gets to turn into the Incredible Hulk.

...And the laser is going to need to be pretty big. ...

Yeah, I see that now. I'm not using TNE/T4, sticking to the flawed CT convention of long-range lasers - since I'm predicating this on a CT setting - and thinking I could vaporize a dust mote with a laser carbine, which I think hits in the 75 Kw range, but that's not doing the job even by Striker rules: range is too short even in vacuum. It's looking like CT would need a tank laser or a turret-mounted ship laser to hit the thing with enough distance to make any difference, and at ranges where it'd be just as easy to avoid it - and sensors of incredible sensitivity, far, far more sensitive than are described in canon to be able to see the things that far out, without which avoiding it is a pipe dream - and an accuracy to the lasers that would make killing missiles child's play. Levels of technology far beyond what the game implies.

We are still left with a fundamental conflict. Players routinely fly out to the gas giant for refueling, yet our discussion suggests a top speed well below any that would make it practical. We've discussed the worst case scenarios, but a trip to a "close neighbor world" yields a top speed of 670 kps, about 8.8% of your projected top speed: that milligram grain you mentioned in the other post still packs around a thousand times as much energy as that 20mm APDS, which at half a millimeter width still seems quite adequate to punch lengthwise through the ship and out the back end. That tiny spec of dust isn't near as potent, but it's still enough to punch through the hull and deep into the ship. My best guess on safe speed with the current hull puts it under 480 kps and makes it a two week flight to the near gas giant - and still requires you to be able to detect grains of sand at ranges of a couple thousand kilometers. That grain of sand, he out to get us!

Which still leaves us the question: what clever rabbit can we pull out of the hat that can allow Trav ships to do what canon says Trav ships do with the energy budget and resources available to the typical ship, without inadvertently creating a black hole and without inventing something that doesn't torpedo some other detail of canon?

 

[aramis]

The only extant Traveller tech that does the task is the repulsor... and those are pretty damned big. 50Td for the smallest canonical ones. And there's little evidence they can "sweep" the path ahead...

 

[whulorigan]

The only extant Traveller tech that does the task is the repulsor... and those are pretty damned big. 50Td for the smallest canonical ones. And there's little evidence they can "sweep" the path ahead...

Yes, but remember that those repulsors are specifically "weaponized" versions for tactical use, and are designed to act on a much larger mass that is under thrust. A "Navigational Deflector" need only have enough force to nudge/deflect tiny masses slightly from their relative course, and in fact might be specifically designed to sweep ahead.

If the CT: Beltstrike reference is to be considered, then one can assume that the mechanism is already installed and powered as an integral component of the M-Drives/Astrionics. (Of course, this would not help for HEPlaR and/or Fusion Torch Drives).

Also, in TNE, T4, and/or T5, aren't there provisions for Barbette-mount Repulsors (or at least the rule-specs to build ones of that size - don't have the books in front of me at the moment)?

 

[Ulsyus]

How hard does the science in this sci-fi game have to be? I recall in another post mentioning that if we try to justify solutions based on our current understanding of technology, we're just like that statistician (I heard this story years ago, pre-internet) who in the 19C determined that society would collapse by the 1950s because it'd need so many horses by then for transport and industry that we couldn't grow enough food for them as well as the rest of society concurrently...

Navigational repulsor technology?

The magic manoeuvre drive screen that deals with micrometeorites and radiation.

Those two make the most sense WRT the setting.

Yes, but remember that those repulsors are specifically "weaponized" versions for tactical use, and are designed to act on a much larger mass that is under thrust. A "Navigational Deflector" need only have enough force to nudge/deflect tiny masses slightly from their relative course, and in fact might be specifically designed to sweep ahead.

If the CT: Beltstrike reference is to be considered, then one can assume that the mechanism is already installed and powered as an integral component of the M-Drives/Astrionics. (Of course, this would not help for HEPlaR and/or Fusion Torch Drives).

Also, in TNE, T4, and/or T5, aren't there provisions for Barbette-mount Repulsors (or at least the rule-specs to build ones of that size - don't have the books in front of me at the moment)?

That's a logical explanation for the idea of using deflectors, as well as including it as part of the M-drive. If someone's using TNE, then while the vessel may be driven by HEPLaR or fusion drives, the grav-based deflector could be generated by the contragrav lifter.

Aramis' calculations are still fascinating...

 

[Lycanorukke]

Yes, but remember that those repulsors are specifically "weaponized" versions for tactical use, and are designed to act on a much larger mass that is under thrust. A "Navigational Deflector" need only have enough force to nudge/deflect tiny masses slightly from their relative course, and in fact might be specifically designed to sweep ahead.

That is what I put it down for. A 'weak' anti-grav field forming a virtual 'bow' which deflects the tiny masses around the ship. It's no good against big masses (missiles) or even 'penny sized' rocks (that's what armour and whipple shields are for) but for light materials they are pushed aside like a wet ships wake. It also extends a fair distance in front of the ship, to give the materials sufficient time to be moved aside without colossal grav fields.

Of course this does nothing for EM radiation, but if you dont have charged particles hitting your hull, you dont get bremstrahlung in the first place. Supplement with magnetics and not much charged radiation would get through, though neutron radiation may be problematic - but you wont get that very much from natural sources (a nuke on the other hand....)

The 'weaponised' resulsor is highly focused and guzzles power - if you tried to do the same thing with a 'nav deflector' it wouldn't work for the same reason you can't use a cigarette lighter as a cutting torch.

 

[Carlobrand]

The only extant Traveller tech that does the task is the repulsor... and those are pretty damned big. 50Td for the smallest canonical ones. And there's little evidence they can "sweep" the path ahead...

Yes, but remember that those repulsors are specifically "weaponized" versions for tactical use, and are designed to act on a much larger mass that is under thrust. A "Navigational Deflector" need only have enough force to nudge/deflect tiny masses slightly from their relative course, and in fact might be specifically designed to sweep ahead.

If the CT: Beltstrike reference is to be considered, then one can assume that the mechanism is already installed and powered as an integral component of the M-Drives/Astrionics. (Of course, this would not help for HEPlaR and/or Fusion Torch Drives).

Also, in TNE, T4, and/or T5, aren't there provisions for Barbette-mount Repulsors (or at least the rule-specs to build ones of that size - don't have the books in front of me at the moment)?

So we're looking at a precursor to or weaker form of the TL10 deflector, or possibly an outgrowth or side effect of or something integrated into maneuver drive technology if we want to remain true to the Beltstrike reference. Kind of a huge diaphanous prow made of some force or another, capable of reaching ahead thousands or tens of thousands of kilometers with just enough strength to accelerate protons, atoms, dust motes and other small particles perpendicular to the ship's line of travel enough to get them out of the way before the ship arrives.

Whatever the nature of the field, it is in the nature of fields to treat those particles they affect without discrimination, if I understand such things correctly. That is to say, if gravity pulls a proton "downward" at 9.8 meters per second squared, it will do the same equally to all the protons, neutrons and electrons that make up a feather or a ball of lead. So, if we postulate a weak mystery field, say only able to shove something to right or left at 1 meter per second squared (~0.1 G), then it must be able to reach far ahead - perhaps 50,000 or 60,000 km or farther - to be able to push those particles out of the path of the ship. To reach so far ahead without a massive energy investment, it would most likely need to be directional. Stronger fields would probably be noticeable in roleplay terms.

I personally like the deflector. It's already doing the job in the game; we just need to speculate on a very, very weak variation of the theme, perhaps showing up at TL9 (though in High Guard this will leave TL7-8 ships unprotected). So - we postulate a navigational deflector?

How hard does the science in this sci-fi game have to be? I recall in another post mentioning that if we try to justify solutions based on our current understanding of technology, we're just like that statistician (I heard this story years ago, pre-internet) who in the 19C determined that society would collapse by the 1950s because it'd need so many horses by then for transport and industry that we couldn't grow enough food for them as well as the rest of society concurrently...

In this case, it's more like 19th century futurists speculating that the horse problem would be solved by everyone driving their own steam-powered carriages, followed by a detailed discussion about the problems involved in and possible solutions for the delivery of coal and water on the needed scale. However, as Rancke pointed out elsewhere, we're not trying to predict the future. We're trying to create a plausible sci-fi rationale to support one of the game's features. Aramis showed the ship's hulls were inadequate to the task at hand. My laser idea was likewise inadequate. This one might work, assuming there aren't hidden flaws or implications.

(Cue the hidden flaw or implication.)

An interesting thought is that if this field is having that effect on matter along the flight path, this would also apply in atmosphere. I think there'd be some push-back effect, so it's not a free ride for the ship to go as fast as it wants in atmosphere. I'm also not clear whether inducing a 1 meter per second squared outward acceleration on a medium as dense as a gas (with the molecules bumping into each other at around 300-500 meters per second and knocking each other back into the volume that the field tries to push them out of) is going to do more than thin the atmosphere ahead a very wee bit. However, it's something to think about.

 

[whulorigan]

An interesting thought is that if this field is having that effect on matter along the flight path, this would also apply in atmosphere. I think there'd be some push-back effect, so it's not a free ride for the ship to go as fast as it wants in atmosphere. I'm also not clear whether inducing a 1 meter per second squared outward acceleration on a medium as dense as a gas (with the molecules bumping into each other at around 300-500 meters per second and knocking each other back into the volume that the field tries to push them out of) is going to do more than thin the atmosphere ahead a very wee bit. However, it's something to think about.

Why not just shut it down when you are in atmosphere, as it is unnecessary there?

Alternately, thinning the atmosphere in front could actually increase the maximum speed and decrease atmospheric drag/reentry compression-heating, if the fluid dynamics is modulated correctly.

 

[Ulsyus]

Alternately, thinning the atmosphere in front could actually increase the maximum speed and decrease atmospheric drag/reentry compression-heating, if the fluid dynamics is modulated correctly.

Cue the Engineer speaking to the Captain over the intercom:

"Captain, she canna take much moore o' this, ye'll have tae slow it down or tha fluid dynamic modulator is gonna blow..."

 

[Lycanorukke]

Cue the Engineer speaking to the Captain over the intercom:

"Captain, she canna take much moore o' this, ye'll have tae slow it down or tha fluid dynamic modulator is gonna blow..."

Captain: Just throw some more Redshirts into the reactor then.
Engineer: I cannae do that Capt'n. We used them tae destroy the giant space wevils.
Captain: Oh all right... reverse the polarity then.

 

[Ulsyus]

Doesn't all of this though still come down to the need to be able to say that vessels using M-drive have a shield of sorts that deflects or similar particles in space? Otherwise there's going to be an awful lot of players very unhappy out there when their vessel gets holed by sand and grit a couple of days out from the world they're leaving...

 

[McPerth]

A "Navigational Deflector" need only have enough force to nudge/deflect tiny masses slightly from their relative course, and in fact might be specifically designed to sweep ahead.

That has always been my take in this. A repuslor field heading ahead that deflects any body (regardless the size) coming from this angle, being integral part of the MD.

Of course, that also meant no ship may dock another from straight ahead, unless those repulsors are turned off (usually, small crafts turn them off and dock another ship wither laterally or by its stern side).

 

[Carlobrand]

Doesn't all of this though still come down to the need to be able to say that vessels using M-drive have a shield of sorts that deflects or similar particles in space? Otherwise there's going to be an awful lot of players very unhappy out there when their vessel gets holed by sand and grit a couple of days out from the world they're leaving...

Pretty much, at least for the flight path. Whether it's in all directions or just in one direction is another question, although if it's unidirectional, you'd still need to be able to point it so you could handle turnaround and the deceleration leg. We've more or less come full circle, endorsing the Beltstrike view of things as a necessary component to making the ships capable of the velocities the game says they should be able to do. I'm gonna stick to calling it a navigational deflector, and I'm tending to think of it as long range and low power.