Ship Design Philosophy

[phavoc]

Acceleration/thrust is a constant, regardless of the presence of an atmosphere. The issue you are referring to is drag. Drag decreases the efficiency of thrust, so more thrust is required to get the same performance if you are encountering drag.

As acceleration increases, and you have a denser atmosphere, you can get to a point where drag increases to the point where you are literally running into a brick wall. Plus you get increased thermal bloom as well as stress on your airframe. This is why Traveller gets it wrong showing ships that would work in a subsonic environment, but not in a supersonic one, let alone anything faster (at least at lower altitudes). Anything moving faster than Mach 1 is supersonic, and past Mach 5 is hypersonic.

The space shuttle converted it's speed into Mach numbers when it begins its descent. It starts out at roughly Mach 25 in the very upper levels (thermosphere), then does a braking maneuver over the Pacific as it transitions through the mesophere/stratosphere to bleed speed through drag. It's a very specific maneuver designed to take advantage of the properties of drag. While technically it doesn't have acceleration on the way down, it has a great deal of inertia that, combined with lift, its' able to do a controlled glide.

A Traveller ship, with antigrav for lift would not need to do any of that and would not have any of the thermal / hull stresses that the shuttle has. But it would still be subject to drag. Because it has antigravity it could do reentry at any angle and orbital speed, thus skirting the issue of lift vs drag. That also means it has no need for higher speed in an atmosphere (so the non-aerodynamic ships could literally float down to land quite efficiently at a measly few hundred Kph).

 

[k0k0pelli]

Acceleration/thrust is a constant, regardless of the presence of an atmosphere. The issue you are referring to is drag. Drag decreases the efficiency of thrust, so more thrust is required to get the same performance if you are encountering drag.

As acceleration increases, and you have a denser atmosphere, you can get to a point where drag increases to the point where you are literally running into a brick wall. Plus you get increased thermal bloom as well as stress on your airframe. This is why Traveller gets it wrong showing ships that would work in a subsonic environment, but not in a supersonic one, let alone anything faster (at least at lower altitudes). Anything moving faster than Mach 1 is supersonic, and past Mach 5 is hypersonic.

The space shuttle converted it's speed into Mach numbers when it begins its descent. It starts out at roughly Mach 25 in the very upper levels (thermosphere), then does a braking maneuver over the Pacific as it transitions through the mesophere/stratosphere to bleed speed through drag. It's a very specific maneuver designed to take advantage of the properties of drag. While technically it doesn't have acceleration on the way down, it has a great deal of inertia that, combined with lift, its' able to do a controlled glide.

A Traveller ship, with antigrav for lift would not need to do any of that and would not have any of the thermal / hull stresses that the shuttle has. But it would still be subject to drag. Because it has antigravity it could do reentry at any angle and orbital speed, thus skirting the issue of lift vs drag. That also means it has no need for higher speed in an atmosphere (so the non-aerodynamic ships could literally float down to land quite efficiently at a measly few hundred Kph).

By nature of continual thrust, drag is the limiting factor on velocity. `1/2 * density * velocity^2 * drag-coefficient * cross section in direction of travel` the velocity^2 is the important one since drag coefficient and cross section will mostly be constant. Density of travel medium will obviously vary by altitude but is not a square linear progression so is not as significant a factor as velocity.

The space shuttle has significantly higher thrust than is needed to match gravitational pull. I do not know the exact number but on takeoff but in excess of 2Gs at least. A M-Drive at 1G taking off from a planet with 1G of pull in effect cannot get off the ground in a vertical line, much less achieve orbit in the fashion that a rocket does. Where thrust cannot exceed gravitational pull the only way to achieve altitude would be to use aerodynamic lift. A current technology plane will never achieve orbit because it's thrust needs atmosphere. A traveler craft with m-drive does not have that limitation but it still would take a significantly longer to achieve orbit than on a vehicle going straight up with an acceleration of 9.8m/sec^2 (2 Gs when you account for baseline gravitational pull)

Traveller ignores gravity entirely when it comes to time to orbit based on g's of acceleration and personally I am fine with that, indeed even prefer it. In the grand scheme of things how a 1G craft gets to orbit on a 1G planet is not important most of the time. It may become a plot hook on high G planets but to make them struggle for the majority of planets in the galaxy seems counterproductive. I personally doubt a ship designer would make a streamlined ship without sufficient thrust to achieve orbit from the baseline gravity of the predominant race.

If you want to account for gravitational pull on a craft for purposes of achieving orbit though a craft with 1G of thrust will face significant challenges in the achievement of orbit and cannot be calculated as straight line movement as is done in the time to travel calculations in traveller.

 

[Condottiere]

Someone has to try this under water.

 

[Condottiere]

This bridge design can be ejected from the ship in an emergency to become a lifeboat for the command crew. The bridge has two weeks of life support and battery power, while emergency thrusters give it basic manoeuvring capabilities, equivalent to Thrust 0. A detachable bridge is even capable of soft-landing on a planetary surface.


Apparently, landing is a lot less dramatic with presumably manoeuvre drive facto zero, and let's assume, a streamlined hull at Terran norm gravity.

If you think about it, gravity based drive puts the control into crash.

Whether this is actually a realistic depiction of the capabilities of thrust zero. I couldn't say.

 

[phavoc]

By nature of continual thrust, drag is the limiting factor on velocity. `1/2 * density * velocity^2 * drag-coefficient * cross section in direction of travel` the velocity^2 is the important one since drag coefficient and cross section will mostly be constant. Density of travel medium will obviously vary by altitude but is not a square linear progression so is not as significant a factor as velocity.

The space shuttle has significantly higher thrust than is needed to match gravitational pull. I do not know the exact number but on takeoff but in excess of 2Gs at least. A M-Drive at 1G taking off from a planet with 1G of pull in effect cannot get off the ground in a vertical line, much less achieve orbit in the fashion that a rocket does. Where thrust cannot exceed gravitational pull the only way to achieve altitude would be to use aerodynamic lift. A current technology plane will never achieve orbit because it's thrust needs atmosphere. A traveler craft with m-drive does not have that limitation but it still would take a significantly longer to achieve orbit than on a vehicle going straight up with an acceleration of 9.8m/sec^2 (2 Gs when you account for baseline gravitational pull)

Traveller ignores gravity entirely when it comes to time to orbit based on g's of acceleration and personally I am fine with that, indeed even prefer it. In the grand scheme of things how a 1G craft gets to orbit on a 1G planet is not important most of the time. It may become a plot hook on high G planets but to make them struggle for the majority of planets in the galaxy seems counterproductive. I personally doubt a ship designer would make a streamlined ship without sufficient thrust to achieve orbit from the baseline gravity of the predominant race.

If you want to account for gravitational pull on a craft for purposes of achieving orbit though a craft with 1G of thrust will face significant challenges in the achievement of orbit and cannot be calculated as straight line movement as is done in the time to travel calculations in traveller.

Drag increases as the density of the fluid increases (air is considered a fluid, in this case aerodynamic vs hydrodynamic resistance. So the highest amount of drag is at the denser (lower) parts of the atmosphere. Depending on the flight path (vertical vs. angle or horizontal) you are correct, it will reduce as you gain altitude. The angle of your flight path, along with the density of the atmosphere, plays a huge role in drag calculations. And the less aerodynamic you are, the greater the drag forces. This also diverges based upon the specific shape of the craft, as you have to start thinking about the air vortices and movement around the craft and what it does to stabilization and adding to the drag coeffecient. Traveller just hand waves all that away, which isn't a bad thing since it's a game and not aerodynamics for RPG's.

The shuttle gets complicated. The SSME (3 on a shuttle) can each put out about 500,000 lbs of thrust in a vacuum and roughly 20% less at sea level. The output of the engines is throttled, depending on which stage of flight. At launch they are running at about 105%, then get throttled back as the shuttle passes through the max stress level, then ramp back up, then get throttled down again as it gets higher. At some point the SRB's have separated and it's just the SSME running on their external tank. Without the external tank they can't really run since they don't have an onboard fuel supply. But all that is by design.

It's about 9 min from ground to LEO for a shuttle. That's travelling more or less vertical, and also travelling at 3Gs. As we've both pointed out, Traveller just steps around some crucial aerodynamic things. Assuming you could counter gravity, all you need to do is have a method of propulsion that would 'fly' you up to LEO. In Traveller that's the magical M-drive. Even at a leisurely 500 kph, you'd make it in an hour. It gets more complicated if you start adding in G, though the above works at 1G and 1 atmosphere (ignoring all the issues related to drag, etc). In theory if your planetary grav field is 1.2 G's, a free trader wouldn't even be able to lift off the ground since it's systems are a theoretical 1G - but that's where more ignorance of physics in the game comes into play. MT SOM manual had the ships routinely redlining their thrusters at 400% to land, which is a terrible though process. However the shuttle routinely ran at 105% of thrust, but that, too, is a misnomer since it wasn't actually exceeding thrust - it was a convenient level the engineers set for 100% thrust. The engines were capable of more thrust, but that was set aside for emergencies (that never happened). This is where you'd need to do some hand-wavium again to get the ship off the ground using anti-gravity. That same force would allow you to escape the gravity well. CT and other versions really don't even go into this sort of detail. I think it was GURPS (or maybe TNE) that went into more detail. I don't recall SOM doing much in this arena though.

Overall there is some wiggle room because of lift - but there's a LOT of "but..." involved. Most Traveller ship designs don't have enough lift/mass ratio to even begin to address that equation. Ship hulls provide very little lift at ground level and the wing surfaces (via the illustrations at least) are far too thick to provide good aerodynamics. Which is why I've always assumed the whole lift concept was better left to discussion since the game mechanics and rules don't go into enough discussion about how it works and what the operational parameters might be.

 

[phavoc]

Someone has to try this under water.

Someone needs to build a working supercavitation submersible.

 

[Condottiere]

Speaking of bubbles, we could create an artificial one with deflector screens and energy shields; so it's a question of velocity times drag creates how much energy to be absorbed.

Though going by implication, deflector screens might actually be more efficient, since you could dictate the angle, crafting optimal streamlining.

 

[Condottiere]

Inspiration: Thrilling 3D Action Short: "Countdown" - by Andrew Klimov | TheCGBros

TheCGBros Presents "Countdown" - by Andrew Klimov - Deep space. An interstellar spaceship crashes. A crew of a small drop-ship have managed to miraculously survive in this disaster. Their ship is damaged and they have to land on an unexplored planet nearby. They steer the ship into an atmosphere without suspecting that a layer of impenetrable thunderclouds enveloping the planet hides something that will be even worse than their worst assumptions - an ocean of acid! For more information, please see the details and links below:

TEAM:
Director: Andrew Klimov
Compositor: Alexander Billione

And regarding landing and inertial compensation.

I'm not too sure what's going on, but it looks like a meteor assault.

I'm thinking that having oxygen masks as a drop down feature may actually have been a work of inspired genius.

 

[Condottiere]

Inspiration: Top Five Spookiest Sci-Fi Spaceships

This Halloween, Spacedock breaks down the spookiest sci-fi spaceship interiors that have made for great horror settings.

1. Power surges - reactor overload indication.

2.

3. Lighting.

 

[Condottiere]

Spaceships: Engineering, Batteried Thrusters versus Fueled Rockets and Comparison

1. Two percent factor one rocket, two hundred kilobux per tonne, and two and a half percent fuel per hour, one hundred fifty bux per tonne.

2. One percent factor thruster, two megabux per tonne, and two and a half percent battery pack per hour, one hundred kilobux per tonne.

3. Two percent factor one rocket, high technology, three hundred kilobux per tonne, and one percent fuel per hour, one hundred fifty bux per tonne.

4. One percent factor thruster, high technology triple energy efficiency, three megabux per tonne, and five twelfths of a percent battery pack per hour, two hundred kilobux per tonne.

5. One percent factor one thruster, high technology triple energy efficiency, three megabux per tonne, and one sixth percent standard fusion reactor, one megabux per tonne.

6. One percent factor one thruster, budget inefficient, one and a half megabux per tonne, and 1.5625 percent early fusion reactor, budget enlarged, three hundred kilobux per tonne.

7. One and a quarter percent factor one thruster, budget enlargement, one and one fifth megabux per tonne, and 1.5625 percent early fusion reactor, budget enlarged, three hundred kilobux per tonne.

 

[Condottiere]

Spaceships: Gliders

1. This process takes about 20 minutes. During this time, the orbiter is cooling and noxious gases, which were made during the heat of re-entry, blow away. Once the orbiter is powered down, the crew exits the vehicle.

2. So, the Shuttle has enough energy during re-entry to heat the average home in Colorado for 41 years! The Shuttle has kinetic energy due to its speed of 7700 m/s and potential energy due to its altitude. It must lose all this energy in only about one-half hour to come to a full stop on the runway (at Earth's surface).

3. As a spacecraft re-enters the earth's atmosphere, it is traveling very much faster than the speed of sound. The aircraft is said to be hypersonic. Typical low earth orbit re-entry speeds are near 17,500 mph and the Mach number M is nearly twenty five, M < 25.

4. Once you commit, say five rounds.

5. Streamlined hull, factor zero manoeuvre drive, soft landing.

6. Or, on consideration, maybe 5'775 metres per second and six to seven rounds?

7. What matters is that game says factor zero is a soft landing.

8. And likely for a planet with an atmosphere, the hull should be streamlined.

9. Partial might be considered default bumpy.

 

[Condottiere]

Spaceships: Heavy Fighters

1. The difference between medium and heavy fighters could well be a bridge and a stateroom.

2. Possibly, the tonnage range is between fifty and ninety nine tonnes.

3. That would give a very tiny window, still assuming cockpits are limited to fifty tonnes and under, for there to be a cockpit.

4. Going by the canonical example, it would seem it's meant for long range, long endurance, missions and deployment.

5. A week is mentioned, though Traveller default would allow four weeks of life support.

6. Interesting question would be if doctrine allows them to be alone.

7. Might indicate picket duty, using advanced sensors.

 

[Condottiere]

Inspiration: An Astronomer Ranks Fictional Spaceships

In this video, I rank 21 spaceships by not only scientific accuracy but how closely they adhere to the Rule of Cool.

Dirt and grease and broken parts.

 

[Condottiere]

Spaceships: Armaments and Firmpoints

1. You can convert hardpoints to three firmpoints.

2. The only real advantage to that is that you can split that into two mounted fixtures and a separate single turret.

3. Wouldn't have an affect on the range for sandcasters and missile launchers.

4. In theory, could have disposable missile/torpedo launcher, or torpedo grapple, per firmpoint; at least for the Confederation Navy.

5. Energy weapons are very limited in range, though the lasers could be dual purpose as weak point defence.

 

[Condottiere]

Spaceships: Light Fighters

1. The Imperium seems to think it's ten tonnes.

2. That depends on what you thought it should be able to perform.

3. If the idea was to give the pilot some form of protection, that would making it sixteen tonnes a better proposition.

4. Pilots tend to be rather expensive to acquire, so you'll want them to stay alive, at least long enough to make some impact in a conflict, as opposed to just a crater impact.

5. Acceleration tends to be a matter of what type of engine is available at a given technological level, though you can augment that with an afterburner.

6. Sixteen tonnes does give leeway for additional armour and propulsion.

7. Unlike medium or heavy fighters, range tends to be a lot short term so using up fuel for the afterburner is justified.

8. Armament options increase to having a single turret, or stock up on missiles.

 

[Condottiere]

Spaceships: UltraLite Fighters

1. Would in theory be anything below sixteen tonnes.

2. Pragmatically, ten tonnes and below.

3. High Guard two point five lists it at six tonnes, a legacy from Classic, and supposedly you can squish four of them into a thirty tonne volume.

4. Though I'm not too sure that doing so from a fifty tonne cutter is a great idea.

5. There's the Indigo class Pirate Carrier, being notorious skinflints, probably would switch from ten to six tonnes.

6. And the Centaur class Mercenary Carrier, with twenty ten tonne fighters.

7. Without armour, and default one tonne fuel, one tonne power plant, one and half tonne single cockpit, virtual mounted fixture, leaving one and a half tonnes from minimum five tonne hull.

8. Twenty percent thrusters; unlike jump drives, there's actually no minimum tonnage, limited more by technological level potential acceleration, so you could drop it to nine percent at technological level thirteen.

9. So now you're up to two and one twentieth of a tonne to spare.

 

[Condottiere]

Spaceships: UltraLite Fighters

A. You could, eh, sidestep the armour question by using a planetoid hull.

B. That's twenty percent for factor two armour, at four kilobux per tonne inclusive organic gravitation.

C. Twenty percent gets you factor two titanium steel, factor four crystaliron, factor sixish bonded superdense armour plating.

D. Remaining one and one twentieth of a tonne would be sufficient for the civilian one tonne sensors.

E. Streamlining is out, I wouldn't try reentry at speed, but manoeuvre drives would allow a dead slow descent.

F. Stealth, I assume, was added that with low tonnage it doesn't cost that much, and if you aren't protected, you would like to remain mostly undetected.

 

[Condottiere]

Spaceships: UltraLite Fighters

G. The minimum fuel tankage is a tonne.

H. However, there doesn't seem to be a minimum for the power plant, at least in the current High Guard.

I. Though I do believe it's supposed to be a volume capable of generating a minimum of one power point.

J. Basic systems for five tonnes is one power point, half would be half a point.

K. Laser is three power points, per acceleration factor half a power point, civilian sensors one power point.

 

[Condottiere]

Spaceships: UltraLite Fighters

L. Can you shrink the bunkerage?

M. That depends.

N. It's specifically mentioned in the new High Guard as having a minimum.

O. Which for larger spacecraft becomes a rounding error.

P. And only mentioned in a previous adventure as being able to be mostly ignored, so for all intents and purposes, you're stuck with it.

 

[Sigtrygg]

I think 'fighters' are better built using the Vehicles rules since they are better suited to that scale of things.