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Old 05-22-2024, 02:45 PM   #11
David L Pulver
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Default Re: Starships as Giant Armored Air/Rafts

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Originally Posted by thrash View Post
Starships in CT don't have contragravity, as such. Maneuver drives produce acceleration; there is (so far as I know) no mention of hovering without thrust. Gravitic units neutralize gravity within their field of action (Supp. 12, pp. 16-17), but are otherwise also described as "lifting" or producing thrust (e.g., Striker 3, p. 8.)

Operationally, there is a very large difference between passive lift (e.g., a dirigible) and active lift (e.g., a helicopter or Harrier). If you have to actually fly the thing all the time to use it, it makes sense to ground the big, unwieldy starship and use auxiliary craft.
I agree that you can't hover without thrust in classic traveller, but after HG 2nd edition and Striker, I don't think there was any distinction between maneuver drive and gravitic thrusters. Anti-gravity in Traveller "produces both neutralization of weight and lateral thrust" to quote Striker, and given that a grav tank and air/raft can both hover, I can't see why a ship can't.
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Old 05-22-2024, 02:49 PM   #12
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Default Re: Starships as Giant Armored Air/Rafts

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Well, landing on paved concrete berth guided by the ports systems is something other than bringing the old bird down in jungle-covered swamp, but wouldn't legal stuff and (more important) money be more important?

So, if anything goes wrong, the star port authority can just shook its head. "Sorry, not our problem."

Will you really risk your ship (often your home, your whole existence) just because you want to avoid a few hours in a ground car or on horse back?

Yes, in the end, it is your Traveller Universe.

My own feeling is that player characters when surveying or crossing a hostile wilderness will generally say "okay, we can do it with are spaceship, and not be in real danger, or we can do it a foot/in an ATV, and possibly die..."
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Old 05-22-2024, 03:16 PM   #13
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Default Re: Starships as Giant Armored Air/Rafts

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Sorry, I'm mostly in th camp witht he peopel who think that the possessors of a fucntioning starship have little need to hike through the wilderness.

Working from a Spaceships defined setting where a reasonable "Scout Ship" can be a (probaly "Hot")reactionless thruster tailsitter without needing a Contragravity system.

If contragravity is available a dedicated "Rescue/Repair Ship" will have it and will hover where ever it needs to.
There is that. Whether the ships in Traveller logically should be hot thrusters (as per some artwork) or not (as per other artwork and gravitic vehicles) and whether grav vehicles and starships do or don't use the same drive is a much vexed question, presumably also within GDW (e.g., HEPLAR in TNE as a solution that didn't catch on). It's been discussed before many times, e.g.,

https://forums.sjgames.com/showthread.php?t=93906

Mongoose Traveller actually does provide some welcome game mechanics for landing a starship making it more difficult outside of a starport, but while this is welcome, doesn't really square the circle on the ability to use a starship as a big VTOL space plane. The question of whether or not starships and non starships (e.g. pinnaces) can maneuver like the Imperial Marine's 600-metric ton grav APC (if you believe striker) does seem to be rather significant from a play balance perspective.

I suppose one option that retains both grav vehicles and starships but maintains canon continuity with starports and art is to say the ships are vectored thrust "hot reactionless" drives and that while an air/raft with a couple of tons thrust is not very hot - like a jet engine - with a few dozen tons of thrust, a starship (assuming a rough 5 metric tons per dton) with 1000+ tons thrust is going to be setting forests alight and panicking wildlife if you drive if at treetop height, so best to set down in ocean, bedrock, or starship landing pads.

I do kind of think that a space opera game may work better if there were strict but simplified fuel constraints within a gravity well and you only had enough fuel for takeoff or landing, and there were no grav vehicles at all.
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Old 05-22-2024, 03:38 PM   #14
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Default Re: Starships as Giant Armored Air/Rafts

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I do kind of think that a space opera game may work better if there were strict but simplified fuel constraints within a gravity well and you only had enough fuel for takeoff or landing, and there were no grav vehicles at all.
Space opera's usual solution to this is pretty handwave-y. Maybe you crashed. Maybe there's some rule (prime directive, etc) that requires not letting the locals know that there's advanced aliens among them. Maybe there's a mysterious phenomenon that disables ships that try to pass over. Frequently, this isn't limited to ships, it applies to all kinds of advanced tech, with whatever gaps the author things gives a good story.

Honestly, Traveller works better if there's a mysterious field that means once you leave the spaceport no tech that's higher than the TL of the world works, at least not reliably; using something like TORG Eternity for Traveller might be amusing.
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Old 05-22-2024, 05:40 PM   #15
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Default Re: Starships as Giant Armored Air/Rafts

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... 1000+ tons thrust is going to be setting forests alight and panicking wildlife if you drive if at treetop height, so best to set down in ocean, bedrock, or starship landing pads.
Some of the math I did for GT Starports also points to ground pressure on landing feet as an issue. An air/raft or grav tank is designed to set down on its wide, flat belly. If something (e.g., heat dissipation) prevents starships from doing the same, it may required bedrock or landing-pad grade concrete to avoid the gear sinking in and getting stuck. (Naturally, water helps mitigate the heat issue if that's the limitation, so a full dunking is okay.)

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I do kind of think that a space opera game may work better if there were strict but simplified fuel constraints within a gravity well and you only had enough fuel for takeoff or landing, and there were no grav vehicles at all.
For my own games, I've split spacecraft into planes (belly landers, with <1g thrust and wings), boats (tail landers with ~1.5g thrust), and ships (unstreamlined and never land). All maneuver drives are rockets and there is no gravitic technology. Air/rafts and such are replaced by ducted fan flitters (cf. the coming generation of eVTOLs).
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Old 05-22-2024, 08:29 PM   #16
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Default Re: Starships as Giant Armored Air/Rafts

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The problem is that the sort of planet where you're likely to need to go tooling across the outback in an air/raft is also the sort of planet where that extraterritoriality is irrelevant.
It's coming up with that "need" that's the problem.
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Old 05-25-2024, 04:05 PM   #17
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In various Traveller adventures, starting with early GDW ones like Mission on Mithril but continuing the present day, there is often the assumption that their ship lands on an exotic world, and the crew exit to explore, map, hunt, or otherwise travel via ATV, open air/raft, or afoot across dangerous terrain
<snip>

So, which of the rule sets, if any, address this sort of thing, either by explicitly allowing it, or by setting specific limits on the safety, maneuverability or capabilities of standard M-drives in a planetary setting. I've seen some rules sets that seem to require landing rolls, at least in bad weather, but not much that takes into account the fact that the ship's power plant is usually good for 2 weeks to a month and the ship is seemingly a giant VTOL grav sled covered in pretty thick armor....
One element that no one seems to have brought up for non-gravitic maneuver drives is stall speed (the slowest speed that a ship can go and still remain airborne).

Let's take the 100-Ton Suleiman-class Scout/Courier (TL10) from GURPS Traveller (p. GT130) as our example. According to Modular Starship Design Statistics (p. GT157) "Calculate other useful aerial performance statistics with GURPS Vehicles." So, Stall Speed (p. VE133) is given by the formula [(Lwt-Static Lift)/Lift Area] x Sl x Rs. LMass is 346 tons which gives 692,000 lbs. for Lwt. Static Lift is 0. Lift Area can be approximated as 1/5 of the total surface area as is used in the Air Speed formula giving 10,000/5 = 2,000 sf. To make the stall speed as low as possible we will assume fair streamlining which makes Sl =1. We don't have a responsive structure, so Rs = 2.

Plugging the numbers into the formula we find that Stall Speed = [(692,000-0)/2,000] x 1 x 2 = 692,000/2,000 x 2 = 346 x 2 = 692 mph. By comparison an air raft has a top speed of 160 mph. So at least one of the reasons that no one travels along at "about treetop level at a walking pace" in their spaceship is because it isn't physically possible. To do decent detailed mapping/sensor readings on a planetary surface you have to use an air/raft or similar vehicle because your spaceship is just too blasted fast to do the job that's required.

With sufficiently sensitive sensors and enough processing power along with an anti-gravity drive something like you envisage is probably possible but for most Classic Traveller Starships, stall speed is generally going to rule it out.

I'm mildly surprised at catching you out on Stall Speed. You put it in Vehicles.
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Old 05-25-2024, 04:52 PM   #18
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Default Re: Starships as Giant Armored Air/Rafts

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Let's take the 100-Ton Suleiman-class Scout/Courier (TL10) from GURPS Traveller (p. GT130) as our example. According to Modular Starship Design Statistics (p. GT157) "Calculate other useful aerial performance statistics with GURPS Vehicles." So, Stall Speed (p. VE133) is given by the formula [(Lwt-Static Lift)/Lift Area] x Sl x Rs. LMass is 346 tons which gives 692,000 lbs. for Lwt. Static Lift is 0. Lift Area can be approximated as 1/5 of the total surface area as is used in the Air Speed formula giving 10,000/5 = 2,000 sf. To make the stall speed as low as possible we will assume fair streamlining which makes Sl =1. We don't have a responsive structure, so Rs = 2.

Pl.
No, Suleimans are built as Lifting Bodies w/Excellent Strealining. All Traveller "Streamlined" ships are. So the lift formula is 30% of total area rather than the 1/5 you're assuming for some reason not obvious to me.

This gives us 3333 sf and a multiple of 1.2 rather than 1.

I get a Stall speed of 498 which is still totally impractical. Even with a Thrust-to-weight ratio of 2-to-1 Suleimans would need extremely long runways if they had wheels but they don't.. They take off on vertical thrust or they don't take off at all. Landings too.

Stall speed would be relevant only for a Suleiman that had lost all engine power and was trying to glide in. I don't recommend such aproceedure.
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Old 05-25-2024, 09:04 PM   #19
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Default Re: Starships as Giant Armored Air/Rafts

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No, Suleimans are built as Lifting Bodies w/Excellent Strealining. All Traveller "Streamlined" ships are. So the lift formula is 30% of total area rather than the 1/5 you're assuming for some reason not obvious to me.

This gives us 3333 sf and a multiple of 1.2 rather than 1.

I get a Stall speed of 498 which is still totally impractical. Even with a Thrust-to-weight ratio of 2-to-1 Suleimans would need extremely long runways if they had wheels but they don't.. They take off on vertical thrust or they don't take off at all. Landings too.
I missed the Lifting Body with Excellent Streamlining part, which does change the Stall Speed, however your figure is not quite correct (and should according to Vehicles be rounded to 500 mph). Excellent streamlining makes Sl=1.2 instead of 1, which raises the stall speed and is why I went with Fair Streamlining initially as it was the lowest possible multiplier for Stall Speed. While I was probably wrong to use surface area/5 willy-nilly from the air speed calculation, thinking about it, it wasn't an unreasonable number. The calculation for a non-lifting body is 10% of surface area plus the surface area of the wings. Saying that the wings would contribute at least as much aerodynamic surface area as the non-aerodynamic body seems like a fairly safe, even conservative, bet.

The revised stall speeds would be 555 mph if using your brute force "lifting body with no wings" surface area of 30% and a stall speed of 415 mph if one assumes a somewhat more aerodynamic lifting body with wings that has 40% of the total surface area (4,000 sf).

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Stall speed would be relevant only for a Suleiman that had lost all engine power and was trying to glide in. I don't recommend such a procedure.
The scenario being addressed is one of using the spacecraft in atmosphere as a method of safe, due to the high DR, means of planetary travel from point A to point B. Since this is specifically called out by the OP as using the spacecraft as a substitute for an air/raft, stall speed is absolutely relevant as you have to be moving at stall speed or faster to keep the spacecraft in the air. Gliding might be an option for shorter hops that the OP seemed to be envisioning but we are talking about heavier-than-air atmospheric flight, not landing from orbit.
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Old 05-25-2024, 09:40 PM   #20
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Default Re: Starships as Giant Armored Air/Rafts

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My own feeling is that player characters when surveying or crossing a hostile wilderness will generally say "okay, we can do it with are spaceship, and not be in real danger, or we can do it a foot/in an ATV, and possibly die..."
Going back to the air/raft for a second, it should be pointed out that it is a TL12 vehicle, so not every character will have the chance to see one for sale. An air/raft isn't a tank by any means when it comes to protection but compared to a car (p. GT148) it is half the size, nearly twice as fast, and has more than five times the armor, so it's not an outrageously bad choice of vehicle.

It's possible that if you have a TL12 air/raft, you have a spaceship similar to the TL12 Lady of Shalott-class yacht, though the yacht uses the speedier Ship's Boat rather than an air/raft, and itself is not capable of entering the atmosphere, rendering the use of that particular spacecraft moot.

If it is the case, it's worth pointing out that in terms of taking a beating, a TL7 ATV, tracked (p. GT147) is just as armored as the Lady of Shalott herself and the only advantage a spacecraft would then offer is speed. Well, that and being bigger and thus soaking up more damage that does get through the armor.

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