[Ships] Atmospheric Speeds?
- Thread starter Kilgs
- Start date
drnuncheon
Mongoose
For what it's worth, GT used the following formula:
sqrt(15,000,000 x (thrust/drag))
where drag was (surface area in sq ft/1000) times 100 for airframe, 200 for streamlined, and 1000 for unstreamlined. SUrface area is calculated based on hull size & shape.
GT:IW caps airspeed at 740 mph for streamlined and 600 for unstreamlined, and noted that this was normal cruising velocity, not absolute top speed when trying to reach orbit. All the ships easily go above the cap so I'd just use those figures unless you had an airframe (which isn't in the MonT rules).
sqrt(15,000,000 x (thrust/drag))
where drag was (surface area in sq ft/1000) times 100 for airframe, 200 for streamlined, and 1000 for unstreamlined. SUrface area is calculated based on hull size & shape.
GT:IW caps airspeed at 740 mph for streamlined and 600 for unstreamlined, and noted that this was normal cruising velocity, not absolute top speed when trying to reach orbit. All the ships easily go above the cap so I'd just use those figures unless you had an airframe (which isn't in the MonT rules).
Commander Drax
Mongoose
Ishmael said:
That's what it says in the MegaTraveller rules, yet unstreamlined air/rafts and g-carriers were frequently cited as being able to reach orbit or be deployed to the surface from an orbiting ship. Hence max atmospheric speed was 300 kph for unstreamlined craft.
Also as vessels leave the surface and approach space they are free to exceed the atmospheric speeds given as the surrounding atmosphere will be constantly getting thinner hence less drag on the hull. Escape velocity is irrelevant to gravity suspended craft or those with thruster plates.
I always took the max speed in an atmosphere rules to mean at standard pressures fairly close to the ground if flying like a traditional aircraft, it stands to reason that thinner atmospheres will allow greater speeds to be reached whilst thicker ones might warrant slower speeds.
Commander Drax said:
MT specifically singles out spaceships and starships when considering unstreamlined craft inability to enter atmospheres... ordinary vehicles are not considered
Why?
Who knows?... yet another reason to forget those rules for top atmospheric speed.
I'll stick to my way which covers atmo density and size ( a spaceship will have much more drag than a small air-raft of similar shape anyways ).
And its another reason why I dislike Trav's magic grav tech... it makes things too easy and space opera-ey for my tastes ( if it takes less energy for an air-raft to reach orbit than the amount of potential energy gained from going so high, then I can make a perpetual motion machine despite lack of 100% efficiency ).
Air rafts and G-carriers are built to operate in an atmosphere whereas an unstreamlined ship is not. They are not making a re-entry as we currently understand it but just flying through the atmosphere, to (or from) where it is effectively non-existent (orbit [1]) to the surface. They are not moving quickly enough for frictional heating to be an issue. Indeed I am a little confused as to why people seem fixated on shuttle style re-entry, it just is not necessary in Traveller for ships.
I am trying to think of a good example of an unstreamlined ship and the Cosmonaut Alexei Leonov from 2010 seemed a good candidate - until I remembered the aerobreaking scene. I suppose the Earthforce ships in Babylon 5 are reasonable examples but I was trying to think of something even less streamlined without invoking Star Trek or Star Wars but sticking to more plausible designs.
If a ship is stressed to resist at least 1G acceleration as every ship in Traveller is they could in theory at least land on an airless planet (with a gravity of 1 G or less) though a lack of landing gear might be a problem. They just have to do so slowly. This might be a useful scenario hook involving a lost ship - she was hidden on a moon to be looted at leisure or for some other reason, I see big pools of microfine dust - anyone for A Fall of Moondust?
Notes
1. However not above orbit as, unlike starships, they are limited to working in a gravity well by their lift/propulsion system. Now there is an interesting question, could you make a cheap ground to orbit lifter using contra-grav plates (or whatever they are called) instead of more expensive thruster plates like a ahip?
I am trying to think of a good example of an unstreamlined ship and the Cosmonaut Alexei Leonov from 2010 seemed a good candidate - until I remembered the aerobreaking scene. I suppose the Earthforce ships in Babylon 5 are reasonable examples but I was trying to think of something even less streamlined without invoking Star Trek or Star Wars but sticking to more plausible designs.
If a ship is stressed to resist at least 1G acceleration as every ship in Traveller is they could in theory at least land on an airless planet (with a gravity of 1 G or less) though a lack of landing gear might be a problem. They just have to do so slowly. This might be a useful scenario hook involving a lost ship - she was hidden on a moon to be looted at leisure or for some other reason, I see big pools of microfine dust - anyone for A Fall of Moondust?
Notes
1. However not above orbit as, unlike starships, they are limited to working in a gravity well by their lift/propulsion system. Now there is an interesting question, could you make a cheap ground to orbit lifter using contra-grav plates (or whatever they are called) instead of more expensive thruster plates like a ahip?
I seem to be deviating from the original question. Anything flying in an atmosphere is going to have it speed limited by thrust, form and friction. I think we all agree on that even if I have not stated it well.
The more streamlined a ship is the faster it's potential top speed is - though this is also dependant on the density of the atmosphere so will vary with composition and altitude. This is also affected by the material the hull is made of, some materials resist heat and stress better than others but no modern ship (in Traveller terms) is going to have an ablative heatshield, it is a waste of money and mass [1] - but if the drives fail your ship will glide like a piano unless it has an expensive airframe hull form and even then I would not much for its chances [2].
A ship flying in an atmosphere will probably limit it's speed to below what it is theoretically capable of in any case for a variety of reasons including not wishing to stress the hull unnecessarily.
Notes
1. Well you might want it on a ship for some odd and very specialised reason but I find it hard to come up with one - sport?
2. I am thinking of the Harrier here. Later models dispensed with an emergancy generator thingy on the very reasonable grounds that if the engine failed it would glide like a piano.
The more streamlined a ship is the faster it's potential top speed is - though this is also dependant on the density of the atmosphere so will vary with composition and altitude. This is also affected by the material the hull is made of, some materials resist heat and stress better than others but no modern ship (in Traveller terms) is going to have an ablative heatshield, it is a waste of money and mass [1] - but if the drives fail your ship will glide like a piano unless it has an expensive airframe hull form and even then I would not much for its chances [2].
A ship flying in an atmosphere will probably limit it's speed to below what it is theoretically capable of in any case for a variety of reasons including not wishing to stress the hull unnecessarily.
Notes
1. Well you might want it on a ship for some odd and very specialised reason but I find it hard to come up with one - sport?
2. I am thinking of the Harrier here. Later models dispensed with an emergancy generator thingy on the very reasonable grounds that if the engine failed it would glide like a piano.
I think I forgot about something but it only occurred to me last night after I turned the computer off and went to bed.
I believe that a ship has it’s manoeuvre drive system which can generate thrust in microgravity conditions where a contragrav craft cannot operate. For some reason though I think a ship also has a contragrav system for use in a gravity well like a giant air raft – though actual thrust may still be provided by its manoeuvre drive.
I am not sure if this is ‘true’ as it is a good few years since I have looked at any of the relevant older Traveller books.
I think part of the reasoning behind this assumption is that a ships manoeuvre drive is often at right angles to the way it lands (aircraft like). I know the old DGP Starship Operators Guide had something to say about this – about briefly overloading or redirecting the drive but I was never really happy with that solution. Another argument in favour of tail sitters like the classic rocket ship designs or the Broadsword class.
I believe that a ship has it’s manoeuvre drive system which can generate thrust in microgravity conditions where a contragrav craft cannot operate. For some reason though I think a ship also has a contragrav system for use in a gravity well like a giant air raft – though actual thrust may still be provided by its manoeuvre drive.
I am not sure if this is ‘true’ as it is a good few years since I have looked at any of the relevant older Traveller books.
I think part of the reasoning behind this assumption is that a ships manoeuvre drive is often at right angles to the way it lands (aircraft like). I know the old DGP Starship Operators Guide had something to say about this – about briefly overloading or redirecting the drive but I was never really happy with that solution. Another argument in favour of tail sitters like the classic rocket ship designs or the Broadsword class.
A
Anonymous
Guest
yes, I am aware that air/rafts and g-carriers need a gravity well to operate in but there still is gravity in low planetary orbits. In the original traveller rules it definately stated that air/rafts could reach orbit. In other supplements and materials air/raft and g-carriers were often described as being able to enter planetary atmospheres from orbit.
Indeed in MegaTraveller, the universal craft design system failed to differentiate between an unstreamlined air/raft or an unstreamlined space ship, probably to minimise on complexity. The Donosev Class Scout Surveyor from World Builder's Handbook had a complement of either 3 hurricance class air/rafts or a single Kankurer (Spelling may be wrong) G Carrier to allow field expeditions for the scouts aboard. As the Donosev was unstreamlined the air/rafts or G Carrer had to be deployed from orbit.
My point is why state that starships/spacecrafts can't enter atmosphere if they are unstreamlined whilst Air/Rafts and G Carriers clearly can, even if they air unstreamlined like the Hurricane Class.
Nonsensical rules!
When entering atmosphere speed and drag are of limited concern to gravity suspended ships, hence no need for significant heat build up on the hull.
Indeed in MegaTraveller, the universal craft design system failed to differentiate between an unstreamlined air/raft or an unstreamlined space ship, probably to minimise on complexity. The Donosev Class Scout Surveyor from World Builder's Handbook had a complement of either 3 hurricance class air/rafts or a single Kankurer (Spelling may be wrong) G Carrier to allow field expeditions for the scouts aboard. As the Donosev was unstreamlined the air/rafts or G Carrer had to be deployed from orbit.
My point is why state that starships/spacecrafts can't enter atmosphere if they are unstreamlined whilst Air/Rafts and G Carriers clearly can, even if they air unstreamlined like the Hurricane Class.
Nonsensical rules!
When entering atmosphere speed and drag are of limited concern to gravity suspended ships, hence no need for significant heat build up on the hull.
Commander Drax
Mongoose
That was me by the way, I thought I was logged in...
Also the unstreamlined ship in 2010 that aerobraked was definately unstreamlined but deployed an inflatable cowling that served both as a heat shield and streamlining for the duration of the aerobrake.
Also the unstreamlined ship in 2010 that aerobraked was definately unstreamlined but deployed an inflatable cowling that served both as a heat shield and streamlining for the duration of the aerobrake.
The MGT rules don't state this - quite the contrary -Anonymous said:
Even distributed ships are allowed and provisions are made in both cases [see Core pg 106/137)[i said:
May not be a concern for significant heat (ala shuttle), but still an ongoing concern!Anonymous said:
The air/raft moves at 400 kph [Core pg 103 - not explicity max] and the atmosphere is not stationary while the planet spins beneath it, it moves (not to mention weather) - if a craft is not moving just as fast there is definitely going to be pressure and heat differences - not to say this is the same as say a space shuttle 'hurtling' from orbital speeds without any sustained lifting thrust...
The bigger issue of anti-grav lifting into an orbital altitude is that things in orbit (i.e. not expending thrust, but using their tangential velocity and gravitational acceleration to continue falling indefinitely) can definitely have an impact
If equivalent to a 'low earth orbit' - protection from radiation and space dust (and the planet's own trapped radiation belts - ala Van Allen Belts) should be adequate. Getting to higher orbits of highports should be an issue (at least for air/raft).
BTW: Didn't find specific mention that G/Carrier could reach orbit [Core pg 103/104]- but it seems even more reasonable that it could (faster, closed, sealed option, armoured) - IMHO.
dmccoy1693
Cosmic Mongoose
Truthfully, a simple way to handle it:
Streamlined configuration: normal thrust
Standard configuration: half thrust (Thrust 1 ships fall out of the sky)
Distributed hulls: 1/4 thrust (Thrust 1 and 2 ships fall out of the sky). Also takes Siz of the planet in damage every round it is in the atmosphere.
Edit: Granted everything (range, speed, etc) is reduced because you're in an atmosphere, but everyone is reduced by the same gravitational acceleration and same air friction. Why over complicate the math since that is going to be a constant for everyone in the fight. So use the same numbers as space combat but just know in your head that Long range in an atmosphere is probably closer to medium or short range in space.
Streamlined configuration: normal thrust
Standard configuration: half thrust (Thrust 1 ships fall out of the sky)
Distributed hulls: 1/4 thrust (Thrust 1 and 2 ships fall out of the sky). Also takes Siz of the planet in damage every round it is in the atmosphere.
Edit: Granted everything (range, speed, etc) is reduced because you're in an atmosphere, but everyone is reduced by the same gravitational acceleration and same air friction. Why over complicate the math since that is going to be a constant for everyone in the fight. So use the same numbers as space combat but just know in your head that Long range in an atmosphere is probably closer to medium or short range in space.
