Fuel Skimming

[Condottiere]

I thought it was catastrophic reentry.

 

[mike wightman]

Here is the situation

The Haunting Thunder lies adrift, tail down, in an ammonia sea on the surface of
the gas giant, buoyed up by its empty fuel tanks and assumed destroyed beyond
chance of recovery by the Zhodani.

 

[kilemall]

[FONT=arial,helvetica] Skimming is not the same as loitering nor normal ops.

the info in A12 on local gravity is specific for Komesh. Altitude of 30,000 km from center is the actual 3G point, but surface G is apparently still over 2G... and the "quantization" of Traveller drives in CT was a near absolute for playability.

The limits are not on a table, but a paragraph on the tables page.
Commercial vessels: 1000 Atm, 1000° K
Military vessels: 2000 Atm, 1500° K
SDB's Designed for deep: 3000 Atm, 2500° K
Protective suit: 400 Atm, 1000° K

Overpressure: throw 2d each 15 min. On 10+, the drives fail.

For comparison, the bottom of the Marianas Trench is 1086 Bar...
Sea level mean pressure is 1 Bar, and is 1.01325 Bar. So commercial shipping can get VERY deep in CT.
[/FONT]

Hmm, our relatively low tech beats a LOT of that, at least for reentry heat.


Parts of the shuttle can handle 3000 F, which is equivalent to 1922 K. So almost as good as Traveller military vehicles.



https://en.wikipedia.org/wiki/Space_Shuttle_thermal_protection_system



Course, that is with a national asset level of support and cost, not a commercially viable routine entry, so a lot of the tech advance would be in having a ridiculously reliable tough and low maintenance reentry hull for streamline craft.


Nonetheless, it does paint a picture of Traveller commercial ships and small craft NEVER 'coming in hot'.


ICBM RVs are usually quoted as coming in at 7 km/s, which is not surprising given that they are ballistic in nature and not reentering under power. The fastest known human craft entry was the Stardust sample RV, at 12.9 km/s. That's a pretty hefty speed, but of course these are one-time use items, again not a commercially viable trading craft. Heat listed as 2900 C which is 3192 K, so we can already do specialized craft with that capability.



https://en.wikipedia.org/wiki/Stardust_(spacecraft)


Note that Stardust flight profile, especially the high speed decel, going from Mach 36 to subsonic in 110 seconds with a peak decel of 34Gs. Problem may not be the vehicle strength, but avoiding turning crew and cargo into paste.



Especially interesting to note for bombardment ortillery, higher tech levels may have missiles that can take multiples of 10 km/s reentry and still be functional, but atmosphere may still slow it down enough to be a functional PD target in atmo.


All in all, probably best to reenter below 10 km/s on a gentle entry curve and gracefully land on antigrav.



As for gas giants,definitely a more dangerous operation for non-specialized craft and you would want to stay out of the thicker parts of it's atmosphere, allowing life-preserving speed to make up for thinness.

 

[AnotherDilbert]

Hmm, our relatively low tech beats a LOT of that, at least for reentry heat.


Parts of the shuttle can handle 3000 F, which is equivalent to 1922 K. So almost as good as Traveller military vehicles.

The values given are for loitering in an atmosphere with that extreme pressure and temperature.

The Space Shuttle wouldn't last many milliseconds in a 2000 bar, 2000 K atmosphere.

 

[kilemall]

The values given are for loitering in an atmosphere with that extreme pressure and temperature.

The Space Shuttle wouldn't last many milliseconds in a 2000 bar, 2000 K atmosphere.

Well, ya.


My focus is on reentry, which coincidentally is a similar problem set to skimming.

 

[AnotherDilbert]

My focus is on reentry, which coincidentally is a similar problem set to skimming.

Agreed, but the CT A12 data does not say much about that.

T5 does discuss reentry, but not in exact temperatures.

MT describes reentry as a routine operation that takes minutes (MT IE p92).

 

[aramis]

Agreed, but the CT A12 data does not say much about that.

T5 does discuss reentry, but not in exact temperatures.

MT describes reentry as a routine operation that takes minutes (MT IE p92).

MT describes a gravitics based reentry with available thrust ≥ local gravity, and the ability to put at least 50% of thrust off the primary thrust axis...

Essentially, it's maneuvering like a helicopter. a fully powered descent. The temp issue is pretty low by comparison - pretty much just the reaction mass' temperature, or the general outside temp, whichever is warmer.

Resistance deceleration is where major heaps of heat happen.

One of the reasons I give for skimming being dangerous is that the scoops use the ram air effect to help liquify the atmospheric gasses. Which means it's also a hot process. You're balancing thrust, flight arc, forward speed, ram pressure, heat, and correct layer for the desired gasses.

Or, more likely, your computer is balancing all those factors and you're punching in the parameters ahead of time... the skill roll is getting them all in ahead of time.... and then posting the following on all conning and engineering positions...

ACHTUNG!!!

Das machine is nicht fur gefingerpoken und mittengrabben. Ist easy
schnappen der springenwerk, blowenfusen und corkenpoppen mit
spitzensparken. Ist nicht fur gewerken by das dummkopfen. Das
rubbernecken sightseeren keepen hands in das pockets. Relaxen und
vatch das blinkenlights!!!​

Source: motd.ambians.com html

 

[Blue Ghost]

I've been playing that reflec is not actually reflecting laser energy (which would involve having reflect that is 'tuned' to each major laser EM wavelength) but heat insulation. Very IMTU, but makes sense to me.

That's interesting. In all sessions I've been in reflec "splays" away energy at various angles upon impact. The beam hits the armor, and the materials used in the armor split and refract the beam. Hence the energy is reflected in various discreet beams and directions. Ablative, as expected, absorbs and either decays or falls apart.

 

[kilemall]

That's interesting. In all sessions I've been in reflec "splays" away energy at various angles upon impact. The beam hits the armor, and the materials used in the armor split and refract the beam. Hence the energy is reflected in various discreet beams and directions. Ablative, as expected, absorbs and either decays or falls apart.

Well good enough for unexamined lasers, but once you get into visible vs. IR/UV/X-ray/Gamma, you get into different wavelength issues where it's unlikely one material is going to deflect all of them.


So, I got a material that can be used at all TL for X amount of x-ASER protection, and a material that got made as a useful space material likely in every engineering suit for those less then fusion fireball heat events, and as a bonus a descriptive layer to explain away hot reentries/scooping.

 

[kilemall]

MT describes a gravitics based reentry with available thrust ≥ local gravity, and the ability to put at least 50% of thrust off the primary thrust axis...

Essentially, it's maneuvering like a helicopter. a fully powered descent. The temp issue is pretty low by comparison - pretty much just the reaction mass' temperature, or the general outside temp, whichever is warmer.

Resistance deceleration is where major heaps of heat happen.

One of the reasons I give for skimming being dangerous is that the scoops use the ram air effect to help liquify the atmospheric gasses. Which means it's also a hot process. You're balancing thrust, flight arc, forward speed, ram pressure, heat, and correct layer for the desired gasses.

Or, more likely, your computer is balancing all those factors and you're punching in the parameters ahead of time... the skill roll is getting them all in ahead of time.... and then posting the following on all conning and engineering positions...

ACHTUNG!!!

Das machine is nicht fur gefingerpoken und mittengrabben. Ist easy
schnappen der springenwerk, blowenfusen und corkenpoppen mit
spitzensparken. Ist nicht fur gewerken by das dummkopfen. Das
rubbernecken sightseeren keepen hands in das pockets. Relaxen und
vatch das blinkenlights!!!​

Source: motd.ambians.com html

Good POV, I had already determined you get into some serious issues once you go the slightest bit above 1G reentry speed.


Did determine a human HAS taken 46G decel, but I have to think he would not qualify as a typical Traveller passenger.


Video of max decels-
https://vimeo.com/292235615


Of course that's just a second, not sure what happens in say 10 seconds of same.


I still want to figure out what the criteria is for reentry and which yes should help with skimming. I've got a new damage system where I already worked out ship scuttling, itching to get it workable for 'unplanned reentry'.


While working this, it occurred to me that the partial streamlined hulls could conceivably land and take off under gravitic powered descent/ascent. It would just be VERY slow which chews up valuable airspace/time over down starports, so my rough ruling for now would be that only streamlined ships are allowed to land at A-C starports, and the partially streamlined can land at D, E and X ports. Unstreamlined can't land at all because they aren't structured to be weight bearing with a landing support.


One of the things this damage system will do is measure when hull damage takes a ship from streamlined to partially streamlined to unstreamlined, with obviously negative landing/skimming consequences. So fixing hull damage in orbit may be a priority just to get the beastie on the ground.

 

[Blue Ghost]

Well good enough for unexamined lasers, but once you get into visible vs. IR/UV/X-ray/Gamma, you get into different wavelength issues where it's unlikely one material is going to deflect all of them.


So, I got a material that can be used at all TL for X amount of x-ASER protection, and a material that got made as a useful space material likely in every engineering suit for those less then fusion fireball heat events, and as a bonus a descriptive layer to explain away hot reentries/scooping.

Well, it is a game. I don't think the rules extend to blue-green or X-band lasers. Maybe they do somewhere and I don't know, but I think for generic purposes reflec and ablat work as is. YTUMV and all that.

 

[kilemall]

Well, it is a game. I don't think the rules extend to blue-green or X-band lasers. Maybe they do somewhere and I don't know, but I think for generic purposes reflec and ablat work as is. YTUMV and all that.

Zactly. I have hardcore rules about things partially to assuage my annoyance points but mostly cause they can be player decision branches and/or glitter to show they aren't in Kansas anymore.


All the while I ignore horrible tech gaps in the stuff I AM using because it's more important to the game then simulation.


All very to taste, I just like sharing my 'seasonings' in case someone else can use them or trigger thoughts to go in their own directions.


Timerover51's point about space vs. atmo missiles set me off partially on this reentry tangent. While I don't have a big issue with the streamlined missile vs. boxy space missile, I do think ortillery is largely unexamined and is going to have to be conducted danger close to planets if it isn't a standoff meson bombardment.

 

[PVernon]

I take exception to "Unstreamlined can't land at all because they aren't structured to be weight bearing with a landing support". If the ship has enough maneuver drive of course it can land, take off in one peace may be an issue though.

 

[kilemall]

I take exception to "Unstreamlined can't land at all because they aren't structured to be weight bearing with a landing support". If the ship has enough maneuver drive of course it can land, take off in one peace may be an issue though.

Fair point, although I wouldn't quite use the word land, more 'soft crash'.