Ship Design Philosophy

Discuss the Traveller RPG and its many settings
Condottiere
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Re: Ship Design Philosophy

Postby Condottiere » Mon Dec 31, 2018 5:13 pm

Spaceships: Hulls and Heat Shields

Atmospheric entry is the movement of an object from outer space into and through the gases of an atmosphere of a planet, dwarf planet, or natural satellite. There are two main types of atmospheric entry: uncontrolled entry, such as the entry of astronomical objects, space debris, or bolides; and controlled entry (or reentry) of a spacecraft capable of being navigated or following a predetermined course. Technologies and procedures allowing the controlled atmospheric entry, descent, and landing of spacecraft are collectively termed as EDL.

Animated illustration of different phases as a meteoroid enters the Earth's atmosphere to become visible as a meteor and land as a meteorite
Atmospheric drag and aerodynamic heating can cause atmospheric breakup capable of completely disintegrating smaller objects. These forces may cause objects with lower compressive strength to explode.
Crewed space vehicles must be slowed to subsonic speeds before parachutes or air brakes may be deployed. Such vehicles have kinetic energies typically between 50 and 1,800 megajoules, and atmospheric dissipation is the only way of expending the kinetic energy. The amount of rocket fuel required to slow the vehicle would be nearly equal to the amount used to accelerate it initially, and it is thus highly impractical to use retro rockets for the entire Earth reentry procedure. While the high temperature generated at the surface of the heat shield is due to adiabatic compression, the vehicle's kinetic energy is ultimately lost to gas friction (viscosity) after the vehicle has passed by. Other smaller energy losses include black body radiation directly from the hot gases and chemical reactions between ionized gases.
Ballistic warheads and expendable vehicles do not require slowing at reentry, and in fact, are made streamlined so as to maintain their speed. Furthermore, slow-speed returns to Earth from near-space such as parachute jumps from balloons do not require heat shielding because the gravitational acceleration of an object starting at relative rest from within the atmosphere itself (or not far above it) cannot create enough velocity to cause significant atmospheric heating.
For Earth, atmospheric entry occurs at the Kármán line at an altitude of 100 km (62.14 mi / ~ 54 nautical mi) above the surface, while at Venus atmospheric entry occurs at 250 km (155.3 mi / ~ 135 nautical mi) and at Mars atmospheric entry at about 80 km (50 mi / ~ 43.2 nautical mi). Uncontrolled, objects reach high velocities while accelerating through space toward the Earth under the influence of Earth's gravity, and are slowed by friction upon encountering Earth's atmosphere. Meteors are also often travelling quite fast relative to the Earth simply because their own orbital path is different from that of the Earth before they encounter Earth's gravity well. Most controlled objects enter at hypersonic speeds due to their suborbital (e.g., intercontinental ballistic missile reentry vehicles), orbital (e.g., the Soyuz), or unbounded (e.g., meteors) trajectories. Various advanced technologies have been developed to enable atmospheric reentry and flight at extreme velocities. An alternative low velocity method of controlled atmospheric entry is buoyancy[1] which is suitable for planetary entry where thick atmospheres, strong gravity, or both factors complicate high-velocity hyperbolic entry, such as the atmospheres of Venus, Titan and the gas giants.[2]

The concept of the ablative heat shield was described as early as 1920 by Robert Goddard: "In the case of meteors, which enter the atmosphere with speeds as high as 30 miles (48 km) per second, the interior of the meteors remains cold, and the erosion is due, to a large extent, to chipping or cracking of the suddenly heated surface. For this reason, if the outer surface of the apparatus were to consist of layers of a very infusible hard substance with layers of a poor heat conductor between, the surface would not be eroded to any considerable extent, especially as the velocity of the apparatus would not be nearly so great as that of the average meteor."[3]
Practical development of reentry systems began as the range and reentry velocity of ballistic missiles increased. For early short-range missiles, like the V-2, stabilization and aerodynamic stress were important issues (many V-2s broke apart during reentry), but heating was not a serious problem. Medium-range missiles like the Soviet R-5, with a 1,200-kilometer (650-nautical-mile) range, required ceramic composite heat shielding on separable reentry vehicles (it was no longer possible for the entire rocket structure to survive reentry). The first ICBMs, with ranges of 8,000 to 12,000 kilometers (4,300 to 6,500 nmi), were only possible with the development of modern ablative heat shields and blunt-shaped vehicles.
In the United States, this technology was pioneered by H. Julian Allen and A. J. Eggers Jr. of the National Advisory Committee for Aeronautics (NACA) at Ames Research Center.[4] In 1951, they made the counterintuitive discovery that a blunt shape (high drag) made the most effective heat shield.[5] From simple engineering principles, Allen and Eggers showed that the heat load experienced by an entry vehicle was inversely proportional to the drag coefficient; i.e., the greater the drag, the less the heat load. If the reentry vehicle is made blunt, air cannot "get out of the way" quickly enough, and acts as an air cushion to push the shock wave and heated shock layer forward (away from the vehicle). Since most of the hot gases are no longer in direct contact with the vehicle, the heat energy would stay in the shocked gas and simply move around the vehicle to later dissipate into the atmosphere.
The Allen and Eggers discovery, though initially treated as a military secret, was eventually published in 1958.[6]
Condottiere
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Re: Ship Design Philosophy

Postby Condottiere » Wed Jan 02, 2019 6:12 pm

Spaceships: Hulls and Heat Shields

There are four critical parameters considered when designing a vehicle for atmospheric entry:
Peak heat flux
Heat load
Peak deceleration
Peak dynamic pressure
Peak heat flux and dynamic pressure selects the TPS material. Heat load selects the thickness of the TPS material stack. Peak deceleration is of major importance for manned missions. The upper limit for manned return to Earth from low Earth orbit (LEO) or lunar return is 10g.[52] For Martian atmospheric entry after long exposure to zero gravity, the upper limit is 4g.[52] Peak dynamic pressure can also influence the selection of the outermost TPS material if spallation is an issue.
Starting from the principle of conservative design, the engineer typically considers two worst case trajectories, the undershoot and overshoot trajectories. The overshoot trajectory is typically defined as the shallowest allowable entry velocity angle prior to atmospheric skip-off. The overshoot trajectory has the highest heat load and sets the TPS thickness. The undershoot trajectory is defined by the steepest allowable trajectory. For manned missions the steepest entry angle is limited by the peak deceleration. The undershoot trajectory also has the highest peak heat flux and dynamic pressure. Consequently, the undershoot trajectory is the basis for selecting the TPS material. There is no "one size fits all" TPS material. A TPS material that is ideal for high heat flux may be too conductive (too dense) for a long duration heat load. A low density TPS material might lack the tensile strength to resist spallation if the dynamic pressure is too high. A TPS material can perform well for a specific peak heat flux, but fail catastrophically for the same peak heat flux if the wall pressure is significantly increased (this happened with NASA's R-4 test spacecraft).[52] Older TPS materials tend to be more labor-intensive and expensive to manufacture compared to modern materials. However, modern TPS materials often lack the flight history of the older materials (an important consideration for a risk-averse designer).
Based upon Allen and Eggers discovery, maximum aeroshell bluntness (maximum drag) yields minimum TPS mass. Maximum bluntness (minimum ballistic coefficient) also yields a minimal terminal velocity at maximum altitude (very important for Mars EDL, but detrimental for military RVs). However, there is an upper limit to bluntness imposed by aerodynamic stability considerations based upon shock wave detachment. A shock wave will remain attached to the tip of a sharp cone if the cone's half-angle is below a critical value. This critical half-angle can be estimated using perfect gas theory (this specific aerodynamic instability occurs below hypersonic speeds). For a nitrogen atmosphere (Earth or Titan), the maximum allowed half-angle is approximately 60°. For a carbon dioxide atmosphere (Mars or Venus), the maximum allowed half-angle is approximately 70°. After shock wave detachment, an entry vehicle must carry significantly more shocklayer gas around the leading edge stagnation point (the subsonic cap). Consequently, the aerodynamic center moves upstream thus causing aerodynamic instability. It is incorrect to reapply an aeroshell design intended for Titan entry (Huygens probe in a nitrogen atmosphere) for Mars entry (Beagle-2 in a carbon dioxide atmosphere).[citation needed][original research?] Prior to being abandoned, the Soviet Mars lander program achieved one successful landing (Mars 3), on the second of three entry attempts (the others were Mars 2 and Mars 6). The Soviet Mars landers were based upon a 60° half-angle aeroshell design.
A 45° half-angle sphere-cone is typically used for atmospheric probes (surface landing not intended) even though TPS mass is not minimized. The rationale for a 45° half-angle is to have either aerodynamic stability from entry-to-impact (the heat shield is not jettisoned) or a short-and-sharp heat pulse followed by prompt heat shield jettison. A 45° sphere-cone design was used with the DS/2 Mars impactor and Pioneer Venus Probes.

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Condottiere
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Re: Ship Design Philosophy

Postby Condottiere » Thu Jan 03, 2019 9:54 pm

Inspiration: Flash Gordon 1936 serial, fan edit - 2 hour movie

Fan edit of the first Flash Gordon sci fi serial from 1936. 13 episodes (4 hours of footage) edited down to a 2 hour movie. Gets kind of janky when they're escaping from the palace after rescuing Dale from marrying Ming, but other than that I think it turned out good.

https://www.youtube.com/watch?v=Jc3n7sMHsnM
Condottiere
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Re: Ship Design Philosophy

Postby Condottiere » Sat Jan 05, 2019 12:31 am

Starships: Engineering, Jump Drives and Capacitation

So, twenty percent of the volume of a jump drive consists of capacitors, holding the charge necessary to push a starship into the rabbit hole.

Now, my calculations are not and probably never be verified by official sources, but not counting the five tonne overhead, that's enough capacity to take two and a half times the default energy charge necessary to max out any jump drive.

Any commercial organization would probably cut some corners, and capacitors, since capacitors are actually the most expensive part of the jump drive ship system; the reason it hasn't been done might be OSHA regulations. Essentially, jump drive are actually military grade equipment.

Considering the risk of misjumps if the stars don't align, and the possibility of overloading capacitors, incurring a catastrophic explosion, who could argue with that?
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Re: Ship Design Philosophy

Postby Condottiere » Sat Jan 05, 2019 5:49 pm

Spaceships: Starship Hopper and What's Going On With SpaceX's Stainless Steel Starship?

They're working around the clock building this thing, and while it doesn't look like something that would fly, Elon Musk keeps telling us it will.
Which leads to questions as to why it's designed the way it is, why the team seem to be working so hard, whether the engine nozzles we can see are attached to real engines?

https://www.youtube.com/watch?v=XVgEKBwE2RM

1. Stainless steel hull option

2. Kink in the nozzle

3. Carbon fibre tanks

4. Solar cells stuck on the outside.
Condottiere
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Re: Ship Design Philosophy

Postby Condottiere » Sun Jan 06, 2019 7:05 pm

Spaceships: Hulls, Planetoids and Breakaways

Since it's not explicitly forbidden, you have to wonder if planetoid configurations can be configured with breakaway sections.

Planetoids don't have to look like potatoes, they could be sculpted in Borg cubes; buffered planetoids with their advantages against meson bombardment would be a different issue, planetoids are just lumps of nickel iron that get cored out, and need twenty percent of shell to maintain structural integrity, I would assume, since you'll need some room for error, overcompensated to the point you get two factors of armour protection.

Take a large enough laser, and start slicing off sections, and then add two percent of clamps that will hold them together; true, you probably have to carefully design the interior so that at the connecting sections you have that twenty percent as buffer. Or you could take two lumps of nickel iron and shave the connecting areas to get a tight fit, then add the connecting clamps.

What are the advantages: beyond the basic five thousand schmucker per tonne for a gravitated hull, which is ten times cheaper than the default. The two percent for breakaway is net total, which means you could slice up a hull like salami, since it's not per, but a set overhead.

To a certain extent, making this about planetoids is more of a diversion, but the concept itself holds potential, and you have to set up the fact that a nicely salamied nickel iron hull can be added to another material, as long as the connecting clamps correspond.
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Re: Ship Design Philosophy

Postby Old School » Sun Jan 06, 2019 7:43 pm

Anything that has a cost based on a percentage of hull cost is going to be cheesy when applied to planetoids due to their low hull cost. Breakaway hulls and armor come to mind. You can conjure up a justification for the low cost if you like, but its still cheese.
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Re: Ship Design Philosophy

Postby AnotherDilbert » Sun Jan 06, 2019 8:30 pm

Old School wrote:
Sun Jan 06, 2019 7:43 pm
Anything that has a cost based on a percentage of hull cost is going to be cheesy when applied to planetoids due to their low hull cost. Breakaway hulls and armor come to mind.
No cheese with breakaway; cost isn't proportional to hull cost.

Low cost of armoured planetoids is intended, unfortunately.
AndrewW wrote:
Tue Mar 01, 2016 5:25 am
AnotherDilbert wrote:Armour for planetoid hulls cost very little since the armour cost is based on hull cost. I guess that is not intended.
Think of it this way, you can hollow out less and use the planetoid for part of the armour. (Not that that actually covers the different armour types).
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Re: Ship Design Philosophy

Postby AndrewW » Sun Jan 06, 2019 9:00 pm

AnotherDilbert wrote:
Sun Jan 06, 2019 8:30 pm
Old School wrote:
Sun Jan 06, 2019 7:43 pm
Anything that has a cost based on a percentage of hull cost is going to be cheesy when applied to planetoids due to their low hull cost. Breakaway hulls and armor come to mind.
No cheese with breakaway; cost isn't proportional to hull cost.

Low cost of armoured planetoids is intended, unfortunately.
Not really, just a consequence of using the existing system.
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Re: Ship Design Philosophy

Postby Condottiere » Sun Jan 06, 2019 11:53 pm

Armour plating should be by tonne, modified only in the quantity required by the type of hull configuration, spherical should be minimal.

For planetoids, quantity based on usable volume.
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Re: Ship Design Philosophy

Postby Old School » Sun Jan 06, 2019 11:56 pm

I can see a discount for certain shapes based on ease of construction, same as the hull, but you can put 14 points of bonded superdense armor on a planetoid really cheap. I could see it being cheaper than the others, but its too cheap. I’d probably use the same cost as armor for a sphere if it ever came up in my game.
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Re: Ship Design Philosophy

Postby dragoner » Mon Jan 07, 2019 5:41 pm

I found with 1e that the easiest way to fix the system was to eliminate armor, and just use the core rules. It was quick, easy, and logical; made combat faster.
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Re: Ship Design Philosophy

Postby Condottiere » Mon Jan 07, 2019 11:01 pm

Deflector screens and force fields require juice, probably a more logical calculation.
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Re: Ship Design Philosophy

Postby dragoner » Tue Jan 08, 2019 1:30 am

The simpler solution would be to not have them; there are point defense and ECM as traditional trav systems.
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Re: Ship Design Philosophy

Postby Condottiere » Tue Jan 08, 2019 8:33 am

Armour is a relatively cheap form of protection, which besides the cost and volume usage, would still be used by those who believe it is an effective solution against some or most forms of damage delivery.
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Re: Ship Design Philosophy

Postby dragoner » Wed Jan 09, 2019 10:07 pm

Armor, while it's unrealistic for a variety of reasons, and it seems that it's mostly represented as "material thickness" a design idea rendered obsolete by the British with their development of Chobham Armour; mostly it is passive. The main design philosophy focus should be how the player characters interact with the designs, and passivity is a poor choice, over something like taking M drive number, plus pilot skill, and comparing them to give a "parry bonus" to maneuvers to avoid getting hit. Then again, I have been playing a lot of M-Space currently in my face to face group. That passivity means it affects players, without them really being to interact with it, and in turn it sort of reduces the granularity of 2d6, which it sorely needs.
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Re: Ship Design Philosophy

Postby Condottiere » Thu Jan 10, 2019 12:41 pm

Tank design is a compromise of mobility, firepower and protection.

You can't outrun a missile or a cannon shell; you can try to see first, shoot first, hit first. Of course, if the enemy is moving around, and trying to do the same to you, that degrades accuracy. With modern ordnance, a direct hit should be fatal, but not necessarily for the crew, as protective measures, including a buffer of material thickness, using differing materials to deflect or mitigate various lethal effects.

That thickness could be the difference between life and death, or if hit at an angle, bounces off.

And of course, it's mosquito proof.
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Re: Ship Design Philosophy

Postby dragoner » Thu Jan 10, 2019 6:26 pm

Designing a spacecraft like a WW2 tank is weird. For material thickness, hitting a paint chip at orbital velocities and the resultant spalling sends fragments through the interior of the vehicle. Hit by a missile or beam, the material can explode into a cloud of plasma.
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Re: Ship Design Philosophy

Postby Condottiere » Thu Jan 10, 2019 9:57 pm

Tank construction and combat has been experienced, so we have a fair idea of what and what doesn't work.

Spaceship combat using a made up combat system and ship design system is pretty much hit and miss.

Tee Five allows composite armouring, and presumably a laser has a different effect from a nuclear missile.

All you can do is look at the damage tables and figure out the best way of protecting a specific ship design against the most likely threats.
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Re: Ship Design Philosophy

Postby dragoner » Fri Jan 11, 2019 1:23 am

"Game the rules."
-Eurisko

:wink:

Space combat could be not so exciting ...

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