Regular travel KKMs

[TheEngineer]

Hi !

While messing around with the KKM topic I again stumbled about the enormous travel velocities a starship reaches in regular operation (travel to jump point etc.).
Here maximum velocity might be around several hundred km/s.
Thinking of in-system travel (to GGs for example) we easily reach several thousend km/s.
Space seems to be "full" (relative expression in space) of regular potential KKMs.

What measures would you use to secure a starships flight path ?
Would there be something like a "city limit" ?

Or is it just another regular risk of Travellers life ? Space lottery ?

GM:
Sorry, on the way to this systems gas giant your Free Trader collided with a dumped Hamburger. Thats really bad at 3000 km/s as the front is slightly damaged by a 250 t TNT explosion....

So, perhaps thats the reason, why waste dumping should happen at the starport

Regards,

Mert

 

[The Oz]

I did some calculations on this a =long= time ago, using STRIKER armor values to find the maximum energy impact that an unarmored starship hull (STRIKER armor 40) could withstand and then converting that to an impact velocity. The result was that even unarmored ships were safe from most impacts with interplanetary dust particles up to nearly 500 kilometers per second, or about 0.167 of lightspeed. A 1-G ship reaches this speed in about 14 hours of constant acceleration.

Admittedly, the mass of the dust particles I used in my calculations was only 0.0001 kilograms, so a hamburger would have considerably more impact.

 

[Scott Martin]

On the flip side, space is full of a lot of nothing, and anything the size of a Big Mac wrapper is going to be picked up on your PEMS arrays a LONG way out (probably on the order of a light second or more: I can track down the actual math if anyone cares)

Even with your sensors off ("blind") the chances of a colission are pretty insanely minute: Unless someone does the equivalent of dumping a gravel (sand?) truck into one of the most commonly used flight paths.

Due to the distances involved, this also means that folks will have a lot of warning if someone loses control. Those multi kps speeds tend to be out in the middle of nowhere (at least hours from "impact" on anything important) "Asteroid impact" scare movies to the contrary, the easy way to make sure that an out-of-control object doesn't hit anything valuable (or populated) is to give it a smack a long way out. I suspect that this is one of the duties for those 400T SDB's: match velocities and rescue the idiot who didn't have his regular maintenance done, or deal with the terrorist. I suspect that the fine for the former would be sufficient to discourace "skimping" on maintenance...

Your local laws (within 100 diameters) may specify that only police or military vessels are authorized to exceed 1G...

BTW the impact energies involved in kps collisions was why I laughed when I saw required hull armour based on *accelleration* in FF&S. I have hopes that this will be "revealed" as an "Imperial Convention" required to license a starship in an Imperial member system, and thus is always added by any Imperial naval architect. Non-Imperial states can build lightly armoured high-thrust platforms to their hearts content.

Scott Martin

 

[Fritz_Brown]

Dumping a gravel truck in the flight path.... hmmmmm.... seems I have seen that mentioned somewhere before.

 

[TheEngineer]

Yep, space is full of nothing

Taking planetary dust around earth the change to hit something > 1 mg is nearly impossible. Things are likely to be different in planetoid belt regions and may be completey different in other solar systems....
And I guess regular flight paths could be surveyed pretty well, at least if its about floating hamburger sized pieces.

At typical "travel to jump point" velocities this could work well.
I did some math, too and figured out, that 500 km/s really is a velocity, where smaller, hardly detectable particles can still be survived, though I am not satisfied with the penetration calculations I found in literature up to now.
So I found a Poncelet calculation, which results in 12 cm steel penetration for a 5 cm diameter projectile of 260 g (Ekin=32,7 GJ). Another way, which relates Ekin to the energy needed to evaporate target material, results in a surface crater of 1,6 m diameter and 80 cm penetration deepth
Any weapon geeks out here having knowledge about other impact calculation methods ?

Anyway, at "fancy velocity in system travels" to a gas giant, hardly detectable particles are able to hurt badly.
Perhaps this reduces frequent long range in-system travel to well equipped military or commercial/prirate vessels, which are able to use high resolution sensors and beam weapons to secure flight path. For other ones it might be a risky business.

Right here, I just collected some random thoughts:

- high velocity vectors must never direct to some special locations (inhabited planets, regions, space stations etc...), meaning even theoretical collisions have to be prevented
- I really like Scotts thought of SDBs and the job to prevent collisions
- your vessel must not loose any parts of itself during regular operations
- dump in jump
- space combat might result in highly dynamic travel/speed restricted areas (just think of sandcaster use..gravel again

)
- burning thru travel = catch objects via sensors and burn them with lasers
- preburner travel = regular low power (?) laser intervals to disperse solid particles in flight path
- I wonder about the situation, if really Heplar drives are used in a TU. Ok, not radioactive but still representing high velocity particle streams it might have some impact on space weather conditions

Someone on the TML or here in COTI once made a pretty details description of the "appearance" of the heplar drive, but I'm unable to find it anymore.

 

[The Oz]

According to my STRIKER calculations unarmored ships would have to coast when travelling long distances in normal space. They would reach what I calculated as the maximum safe speed in about 14 hours of 1-G acceleration (less for higher accelerations, of course) and then have to coast the rest of the way until they begin deceleration. This makes in-system jumps much more practical (if you have the fuel, of course).

Now, if you add High Guard factor-1 armor (STRIKER factor 60) the safe maximum speed jumps to 2.26% of lightspeed (6870 kps) which is more than enough to allow continuous acceleration/deceleration. Heck, it's high enough to allow a 6-G ship continuous acceleration/deceleration!

 

[aramis]

The risks of continuous burn in-system travel make jumping from 100D to 100D in system look like a good idea.

 

[Scott Martin]

I think that the "risk" in our solar system is somewhat lower probability than winning the local "Pick-7" Jackpot, and far, far lower than air or car travel.

Of course in systems with a lot of "rubble" drifting around (After the battle of the twin suns for example) or in really "dirty" systems (still in the planetary formation stages) the particle density might be significantly higher, and warrant "microjumps" to get around, but most parts of a system are "closer" than a week using M-Drives...

That said, the accident per year in the 3I probably gets a lot of press coverage

Scott Martin

 

[TheEngineer]

Hi !

Sadly we dont have much information about space dust concentrations. I only got a figures showing dust smples densities around earth, e.g. giving a matter flow for 1e-3 g particles of around 1e-14 particles per m2 per second.

My thought concentrated less on natural space dust but more on commlative space debris of several thousand years space travel

Guess there is a anime around dealing with space waste collectors....

 

[aramis]

a 1G continuous burn of 8LM =480LS = 14,400,000,000m, using Traveller standards, not real world, for C=300,000,000m/s and G=10m/s/s.

d=0/5AT²
14,400,000,000=0.5*10T²
28,800,000,000=10T²
2,880,000,000=T&sup2
53665.63146≅T
(14:54:25.631459995)

AT/2=Vmax
10*53665.63146/2=268328.1573m/s ≅0.00089442719PSL

given a mass of 1μg, at this speed, a standing particle gives
E=72000J
E=72kJ

Not bad...

But they add up.

Also, the impacting against the 5K particles (mostly alpha)/m³ of the local interplanetary medium generates some abrasive forces at this point.

Also, peak speed is comparable to 1/2 that of a CME, and likely to be close to 90° from course. This gives us a relative impact approaching 1.2x normal for coronal mass ejections.

at 6 G, same 1μg dust particle is doing 108kJ at median speed; 432kJ at peak.

I spent two hours looking for good estimates of the mass of interplanetary medium, but I recall some rules of thumb.
1μg object per cubic kilometer
5 molecules per cc of gas (multiple references, including NASA...)

 

[Scott Martin]

Hey aramis, you really want your distance to be 1/2 final (halfway point and turnover) and Vmax will be AT at that point. 37947=T, Vmax = 379.5 kps. your 1 microgram particle will have 144 Kj, 6 g burn has the same distance, in less time, so Vmax will only be root(6) times as fast at peak velocity.

a 1 mg micrometiorite at this speed will probably punch a hole through most hulls (even escorts) but the way traveller ships are designed it will probably hit fuel tankage, and be re-sealed without bothering the crew.

I wonder if the 3I has comprehensive glass coverage for the free, fat and far traders that seem to insist on having "glass" (or equivalent) "windshields" on the front of their ships

Mert
Most of the stuff chucked around in space combat is fairly high velocity, and will escape from the system into deep space. Fights in or near planetary orbit will be a bit more of an issue, but can probably be dealt with more readily (especially with Repulsor technology) since it will be in a confined area.

Perhaps outlawing sand?

I'm pretty sure that "sand" showed up because in the '70s and early '80s it was the proposed defence against "orbital lasers" of the time. Unfortunately, sand probably won't do much good against a high energy laser, since the laser will have more than enough beam energy to just vaporize the sand in its path and still hit the target.

If sand is so wonderful against lasers, why don't military starship hulls incorporate it

Scott Martin

 

[aramis]

I did. Average exposure speed, however, is half Vmax. I don't do calc, so I will not spend the time manually integrating on a spreadsheet to find total energy dump... but at the risk of sounding blasé, abrasive wear is a real concern at NASA, as well as solar pressure and interplanetary medium drag, in plotting long duration courses and designing craft.

I did the calcs for time
Vmax=A(Tt -Tf)/2
where Tt = Time of trip
Tf=Time to flip (abstracted to 0 for simplicity)

By the way, you need to bone up on your symbology for SI measure. The particle size I used was μg (Micrograms), not mg(milligrams); 3 orders smaller. This is a density I recall being substantiated by some astronomy document as 1 per cubic kilometer.

 

[Scott Martin]

My apologies Aramis, that post was not intended as an attack: I didn't understand what you were getting at, so I figured you'd either agree or clarify. I did the math with your microgram ("mike") but typed the wrong beastie. (I have trouble tracking down the appropriate symbol set, especially in UBB.)

To me it looked like you were trying a shortcut I have seen many times before: calculate the burn on the full distance and divide the resultant velocity by 2: that must be the "turnover" velocity right?

The reason that I looked at peak velocity was because that's where the scarey bogey-men live. If you take a hit at turnover (nasty even in the microgram range, dangerous in the milligram+ range, lethal in the "hamburger" range) you have troubles. I suspect that average exposure is probably more in the (1/root(2)) range (0.707-ish, and yes I have spent WAY too much time doing math without a spreadsheet) because that's where the energy mean will be. This makes your point more rather than less cogent, since abrasive wear will be significantly higher. Perhaps this is why "merchant" ships carry such crappy passive sensors: less area to degrade (and need replacement)

That said, I suspect that a metal hull gets a lot of polished patches from spot melts due to impacts of this kind: not an issue unless they penetrate, or melt a chunk off your sensor array.

The Traveller universe is a lot easier than the Real World(tm) because the vessels have power to burn and then some (even the "slow" merchants) and they're insanely tough (and don't have multi-year maintenance-free mission envelopes) I don't think that we currently have anything with close to a "G-Turn" of boost: the Saturn-V rockets were in that range, but I think that they were stilll less than 2 G-turns: your info is probably less memory-mangled than mine though.

And can you imagine the reaction of someone at NASA proposed the minimum thickness of the ISS being 5 cm of steel?!


Scott Martin

 

[aramis]

the DS1 probe approaches a G-hour.

I don't have the formula to go from molecules of H2 to mass to throw into the Ek=mv² polishing figures. I suspect at turn-around, it accounts for some noticeable heating, polishing and pitting.

And yes, I *CAN* imagine NASA's reaction. "How in the EXPLETIVE do we launch that much steel?!?!?" Of course, NASA used 6 layers of copper to protect a leading surface on one of the unmanned missions recently.

BTW, to get the μ, the following (delete the spaces) & m u ; will produce it.
² is & s u p 2 ;
³ is & s u p 3 ;
√ is & r a d i c ;

If you use the straight key-stroke versions, you'll get funky results. (these are from the HTML Character Entity Refs list from W3C.org, and ignore encoding.)

 

[Scott Martin]

Hi

Avogadro's number = 6.02214199 × 10&sup2&sup3 used to convert AMU to grams (and back) a single hydrogen molecule would be about 2.02 g/mol x 6.02214199 × 10-&sup2&sup3. You probably won't have a significant increase in background from years of HEPLAR use, since reaction mass tends to be chucked out the backs of HEPLAR rockets at significant percentages of C (my current WAG is around 4% C: 2% C looks like it was low)

Good thing I'm not a rocket scientist (and not one of those scary physical chemists like Ptah )

Ctrl-C
Ctrl-V
(del-fwd-del-fwd-del-fwd)
Hey wait, UBB is just using standard HTML conversion ? (Scott feels dumb...)

Looks like you can't superscript a minus though..

Thanks Aramis

 

[aramis]

cranking the math in the spreadsheet, I get, at peak Vmax for a 1AU burn 11J/m²/sec from normal interplanetary medium. Lots of drag there... using my prior calcs for Vmax. Some heating effects, and each molecule hit is around 2.2J/sec/m²

heating, pitting, and possibly even noise . Quadruple the distance, double the velocity, and quadruple the energy.

The numbers feel right, but I'm damned sure not sure.

 

[Scott Martin]

Hey Aramis

Remember that *thrust* is probably well into the 100's of megajoules, so that amount of "drag" probably isn't noticable to a Traveller starship, although it's a huge amount of drag for something like a NASA probe.
<EDIT> 100's of MJ *per square meter* <\EDIT>

The extra heat wouldn't be a problem, but micro-penetrations might seriously chew into your sensor arrays and control runs: IMTU I have already added a company that sells interplanetary "Umbrellas" for visiting starships, due to a system with an unusually high interplanetary gas density. No issue with collisions on the "tail" (after the flip) since anything "behind" you will be swept away by your high energy exhaust. If you "coast" then you should probably keep the nose pointed in your direction of travel.

If you are using thruster plates, you could probably handwave a gravitic "prow" to redirect anything before it hits your ship...

I'd be interested in the energy per AMU (mass = 1/Avagadro's number) which would tell you what the real pitting / penetration was likely to be. (I *think* that may be the 2.2J/sec number but a single collision should just be joules) If it is above metallic bond strain energies you will be doing some nastiness, if below you're probably unlikely to do long-term damage (remember that you refit ships every year...)

Scott Martin

 

[Fritz_Brown]

Originally posted by Scott Martin:
(remember that you refit ships every year...)

And, this thread would be a good explanation as to why......

 

[aramis]

2.2j/m²/sec, yes, Joules per sec. But those are in lots of much smaller hits. It will, slowly, peel the paint. More important is that that's going to add up to a significant heating issue, based upon the low masses. A few odd penetrations, and some REALLY loud pings when you hit those microgram and milligram masses!

 

[TheEngineer]

Here's just another source about "dust in space".
Text is in german but you may have a look at the figure at the bottom of the page:

Just Dust