Re-Entry

[Licheking]

Right as written there are some problems i can see with the Re-Entry rules (P.364-365). We will take a standard Scout/Courier TL=11 (11AV) trough all the Re-Entry types.

Fast Boost/Re-Entry does 2000 Friction damage modified by the Friction value for the ship, in this case /5 for Lifting Body hull. This means that Heat-400 damage is done to the Scout even with minimum damage (400) the ship is wiped out. Everything over 11 points is damage to components going from compartment to compartment using up the points.

Slow Boost/Re-Entry does 200 Friction modified down to Heat-40 for the Scout and again we see that minimum damage would destroy our Scout ship.

Safe Boost/Re-Entry does no damage and is therefore completely safe, but does take 5x the World size to complete.

Now if the Scout had an Ablative Coating applied to the Hull then its AV=11 is now AV=1100 versus the Heat but it would still struggle to survive the Fast Boost/Re-Entry since average damage is likely 1200 from 400d6.

Now it has been mentioned several times on the forums that Starship armour is 10x more effective against damage than normal armour, and that seems fair, since if we look at combat armour and Battledress AV ratings why would you bother with hull armour at all you would make spaceships from Battedress and strap them to engines to move about which breaks the internal consistency of the setting, well in my opinion.

If we do that to the Previous Examples then the Fast Boost/Re-Entry is still out , the Slow Boost/Re-Entry is possibly survivable if you roll lowish on 40d6 (average 120 against AV=110).

So basically unless you have multiple layers of armour or the Ablative Coating applied the only Re-Entry type anyone can use without committing suicide is the Safe one. Now i actually like the concept of the Re-Entry doing possible damage but i think it should be influenced by pilot skill as well as the basic factors presented. The Task for Re-Entry/Boost is Difficult (3d), if the task is successful then double the Friction factor from the Hull and for every 1d you choose to make the task harder you may double it again giving the really good pilots a chance to land on world faster than not so good pilots without all the damage and flaming death.

This would then make, assuming the pilot made the basic roll, Fast Boost/Re-Entry doing Heat-200, Still unsurvivable without Ablative Coating. The Pilot would have to take a 2d penalty to make it possible to survive making the task 5d in total but providing /40 (/5 double to /10, then doubled for the first penalty die to /20 and then double to /40 for the 2nd penalty die) so Heat-50 from Re-Entry.

Slow Boost/Re-Entry doing Heat-20 for the Scout, now possible also assuming the 10x rule, which gets our Scout to World surface in World Size hours, more like the times presented in CT and MT.

What do you guys think.

 

[mike wightman]

Remember the personal re-entry kit?

A foam ablative heat shield in a can

Ships could be modified with ablative shielding dispensers to provide the ablative shielding they need for the fast re-entry.

Otherwise they have to take it slow.

Although why they don't just transfer all the heat to the magic heat sinks that keep the interior of the ship cool is beyond me...

 

[SpaceBadger]

Remember the personal re-entry kit?

A foam ablative heat shield in a can

Ships could be modified with ablative shielding dispensers to provide the ablative shielding they need for the fast re-entry.

Otherwise they have to take it slow.

Excellent suggestion. I can hardly wait for a copy of T5 to start mining for ideas like this to use in my game.

Although why they don't just transfer all the heat to the magic heat sinks that keep the interior of the ship cool is beyond me...

:file_21:

 

[selunatic2397]

Before the very smart people on this board informed me the room temperature super conductors in larry niven's books just would not work, my players would use that and the ice/freezer to hide heat signatures...

Now my lone player is just accepting the magic heat sinks of traveller and making no attempt to understand them!

 

[Vladika]

Hmmmm Here's a WAI...Use a small black globe. As in SMALL. Like small enough, while on, to fit in your engine room?

IIRC during the first experiments of Black Globes, a tester hit the switch and was cut in two. Another story was there was no way to turn off a Globe because the switch couldn't be reached. It overloaded and exploded.

ALL energy is absorbed into the black globe so, why not heat energy?

Store the excess energy in your capacitors, do your dirty work, go on your way and bleed off the capacitors through the power plant/ maneuver drives.

So, no heat signature? Also, you are invisible at just a few kilometers otherwise.

 

[selunatic2397]

Very Sneaky! I like it...my lone player is a scientist...I'll give him a few hints and see what he does.

Thanks for the idea.

 

[Spartan159]

The rules now allow for partial enclosure fields.

What's that box with the one black side in engineering?

Oh, that's where we dump all the ships heat. Converts it to usable energy. Also keeps the engine room beer supply cold.

 

[Reban]

Licheking I think you may be reading that wrong. Friction is given in Hits not Damage dice. So 2000 is the maximum Friction you will ever encounter.

All Armor is x100 vs. Heat and x10 vs. Pressure.

This is badly stated on p336. under Armor. The table makes it look like this is an effect of anti-Rad but in the Beta re-entry got a fuller explanation which explains how armor stands up against and sheds heat.

In addition look at p55 for Hot & Cold Benchmarks. You'll see that Heat is expressed in Hits and a number of damage dice for generating a random number Hits.

Your AV11 Scout is AV1100 vs Heat

 

[Reban]

For reference

In Atmosphere 2+


Fast Re-entry = Friction 2000 (= 3725C)
Fast Boost = Friction 1000 (= 1725C)

Slow Re-entry = Friction 200
Slow Boost = Friction 100 (= 275C)

Safe Re-entry = Friction 0
safe Boost = Friction 0

Friction is modified by Hull configuration from Cluster x2 to Lifting Body /5

 

[Licheking]

So Ablative armour coating would increase that by a further 100x then? (110000).

That was my thinking when i re-read it last night as well, that it actually represents hits not dice.

 

[Reban]

I was doing some re-reading as well and I can't find a clear reference to the inherent x100 against Friction. Possibly Table C on p336 should read vs. Friction x100 and not vs Heat which would give Ablat a clearer function. Ablat is supposed to be destroyed or removed as it counters Heat (ref p318).

I'll pop a note in the errata thread.

 

[HG_B]

So, no heat signature? Also, you are invisible at just a few kilometers otherwise.

You are still radiating at least at "room temp". Around 300 kelvin. VERY visible in the IR band in space.

 

[Licheking]

I have also now noticed, what is to me, a glaring discrepancy.

Take a Size 8 world (Earth) with atmosphere 6, Orbit is 500km or R-8.

Fast Re-Entry/Boost takes 8 minutes = 3750kph
Moderate Re-Entry/Boost takes 8 hours = 62.5kph
Slow Re-Entry/Boost takes 14 hours = 35.7kph

As a world gets smaller these speeds get higher and slower as the world gets bigger.

A flyer can cover 1 range band per personal combat round which means a flyer can reach R-8 in 8 minutes. NASA's Shuttle gets into earth orbit in 8.5 minutes and 45 minutes for it highest point, so the fast times sit well with me. Flyers with wings have to maintain Speed-6 (100kph) to remain flying but I'm going to assume that starships with maneuver drives don't have to worry about that. And i can buy that in a busy starport or world with heavy air traffic that it might take some time to be given a clear flight path to the landing site but that doesn't explain low traveled worlds or worlds with no population or little population.

As it stands the Shuttle must have Ar-20 (2000 vs friction) to be able to do the 8.5 minute boost. If it was designed as a vehicle it would require Ar-2000 or 20 with ablative shielding (acceptable in my eyes). Either way i cannot vindicate the exceptionally long travel times for the moderate and slow Re-entries/Boosts and will be looking at changing them to something more akin to MT travel time tables for different sized worlds.

 

[HG_B]

I have also now noticed, what is to me, a glaring discrepancy.

Take a Size 8 world (Earth) with atmosphere 6, Orbit is 500km or R-8.

Fast Re-Entry/Boost takes 8 minutes = 3750kph
Moderate Re-Entry/Boost takes 8 hours = 62.5kph
Slow Re-Entry/Boost takes 14 hours = 35.7kph

These figures make no sense. You could free fall from just outside the atmosphere to the ground, needing no real heat shielding MUCH faster than Moderate or Slow times listed...

 

[esampson]

I have also now noticed, what is to me, a glaring discrepancy.

Take a Size 8 world (Earth) with atmosphere 6, Orbit is 500km or R-8.

Fast Re-Entry/Boost takes 8 minutes = 3750kph
Moderate Re-Entry/Boost takes 8 hours = 62.5kph
Slow Re-Entry/Boost takes 14 hours = 35.7kph

As a world gets smaller these speeds get higher and slower as the world gets bigger.

A flyer can cover 1 range band per personal combat round which means a flyer can reach R-8 in 8 minutes. NASA's Shuttle gets into earth orbit in 8.5 minutes and 45 minutes for it highest point, so the fast times sit well with me. Flyers with wings have to maintain Speed-6 (100kph) to remain flying but I'm going to assume that starships with maneuver drives don't have to worry about that. And i can buy that in a busy starport or world with heavy air traffic that it might take some time to be given a clear flight path to the landing site but that doesn't explain low traveled worlds or worlds with no population or little population.

As it stands the Shuttle must have Ar-20 (2000 vs friction) to be able to do the 8.5 minute boost. If it was designed as a vehicle it would require Ar-2000 or 20 with ablative shielding (acceptable in my eyes). Either way i cannot vindicate the exceptionally long travel times for the moderate and slow Re-entries/Boosts and will be looking at changing them to something more akin to MT travel time tables for different sized worlds.

In the case of the shuttle you are forgetting to take into account its hull configuration. As an airframe configuration its friction mod is /4, which means during a fast boost it would take 2000/4 or 500 hits, divided by another 2 because it's a boost or 250 hits. With the x100 rule for friction that means it would only need an armor value of 2.5. TL-8 Early Shell is a 1 for a single layer so it is pretty conceivable that the space shuttle had 3 layers of shell (or alternately a single layer of Plate. The primary reason to use Shell seems to be because the ship is a lifting body which reduces friction even more).

Initially I thought that the boost/re-entry temperatures were completely wacky since a ship with lifters could just easily settle down through the atmosphere but what I've come to realize is that the main problem is simply the names. fast boot/re-entry is more or less what we do now IRL (re-entry is tricky. It is a good deal more than 8 minutes but a lot less than 8 hours. That's more a problem in granularity since friction also goes from 2000 to 200). Instead of 'fast, slow, and safe' they should probably have had names more along the lines of 'normal, slow, and extremely slow', possibly with a few other categories tossed in (something faster than normal and some that go in between normal and slow and slow and extremely slow).

 

[Murdoc]

No, these rules don't make any sense. Any ship with an M-drive or G-drive higher than the local planet's gravity, and/or lifters, can easily slow down to any speed they want (even zero; they can "hover" in space at any point over a world). If they slow down to sub-sonic speed, they will experience no friction at all, and don't need to to worry about hull configuration (except maybe cluster hulls, but they'd have to worry about wind pressure, not friction). At 1000 kph, you can travel "safely" from a height of 500 km in 30 minutes, so there is no reason for any normal Traveller ship really to experience friction or take longer than that to reach the ground. The only times they might would be for unpowered landings (like the space shuttle today, which can't slow down from orbital speed), or perhaps a chase in the atmosphere between two ships, in which case the ship with the highest friction tolerance more likely wins than the one with the best engines. But those are pretty fringe cases. This is why I rewrote the rules for this in my aerodynamics rules (link in sig).

 

[esampson]

. . .At 1000 kph, you can travel "safely" from a height of 500 km in 30 minutes, so there is no reason for any normal Traveller ship really to experience friction or take longer than that to reach the ground . . .

If you are using the 'slow re-entry' rules the friction would only be 200 points, which even cluster hulls have no problem with that unless they have lower than 4 points of armor, which would be practically impossible.

However 'slow re-entry' is still about 16 times longer than 30 minutes. Unfortunately 30 minutes is also about 4 times longer than 'fast re-entry', putting it in a bad spot. That's why I said there needs to be more granularity. Maybe something that is 5xSize minutes and generates 1500 friction. For a streamlined ship you would be looking at needing 5 points of armor, which nearly any ship would have (except maybe Lifting Body, but then they only need 3 points). Cluster and Braced would have trouble at those speeds needing 30 points of armor, but at 1000 kph that doesn't really seem unreasonable.

There could also be an increment for about 20xSize minutes that is somewhere in the neighborhood of 800 points of friction.

 

[esampson]

Just in the interest of doing the math I tried to figure out the simple geometric curve that would generate 2000 friction at 1 minute per size and 200 friction at 60 minutes per size. It is 2000/(10^((M-1)*1/59)) with M equaling the minutes.

For people who don't want to do the math this turns into (with a little rounding):

Minutes/Size point	Friction
1	2000
2	1925
3	1850
4	1775
5	1700
6	1650
7	1575
8	1525
9	1475
10	1400
11	1350
12	1300
13	1250
14	1200
15	1150
16	1125
17	1075
18	1025
19	1000
20	950

So a streamlined ship would only need 6 points of armor to make it from orbit to surface in 30 minutes (1775 Friction). It is far from perfect, but I think it should prove pretty useful as a rule of thumb.

 

[Murdoc]

If you are using the 'slow re-entry' rules the friction would only be 200 points, which even cluster hulls have no problem with that unless they have lower than 4 points of armor, which would be practically impossible.

Slow Re-entry is speed 13, which is about 5000 kph, or over Mach 4. No unstreamlined ship should be able to go that fast without breaking up. Hence my rules on break-up.

However 'slow re-entry' is still about 16 times longer than 30 minutes. Unfortunately 30 minutes is also about 4 times longer than 'fast re-entry', putting it in a bad spot. That's why I said there needs to be more granularity.

500 km is a pretty conservative number. The space shuttle usually orbits between 200-250 km, so you can halve the 30 minutes number to 12-15. Less for smaller worlds, or lesser atmospheres, which I also include rules for.

As for granularity, my rules do include a "Fast, Powered" option (the previous "safe" decent being called "Slow, Powered"), where you can just pick your speed, and the chart on page 3 of the aerodynamics rules tells you what the friction is, although you can figure it out since is it almost always twice the previous speed's value. So there's your granularity, nice and simple. There's also an "Fast, Unpowered" option, in case you want to simulate a decent like that of the current space shuttle.

One thing that really changed my views on all this was the realization that in this age of fusion-powered anti-gravity drives, there is really no reason to actually go into a real planetary orbit unless you are trying to dock with a space station that's in orbit. And while there are definitely many advantages to keeping a station in orbit, it is not actually strictly necessary, so you could in theory at least run into stations that use grav-drives to stay aloft. But that is veering off topic.

 

[Licheking]

I like your table esampson and will probably be implementing that for my games in the future.