Ship Design Philosophy

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

Postby Condottiere » Thu Feb 14, 2019 4:23 pm

Spaceships: Engineering, Escape Velocity, and Reactionary Rockets

Ascent G-Forces

The Apollo 11 AS-506 launcher flight report contains a nice graph of the G-force curve of that famous Saturn V launch:

Image

From this chart you can see that, off the pad, the Saturn V first stage is doing about 1.2g; this climbs rapidly as atmospheric drag falls and fuel mass is consumed. The center engine is intentionally shut down to limit acceleration, and the outboard four keep pushing to a max of about 3.9g. This is the highest acceleration in the mission until re-entry and landing.

The upper stages are less dramatic in their acceleration but follow similar increasing curves; the second stage curve steps down once for the center engine cutoff and once again when the fuel-to-oxidizer ratio is switched ("EMR Shift" on the graph, for Engine Mixture Ratio) -- this is done to optimize Isp in vacuum, with the timing dynamically chosen to ensure simultaneous depletion of fuel and oxidizer. The second stage center engine early cutoff is done to reduce longitudinal (pogo) vibrations rather than to limit acceleration; this was instituted starting with the Apollo 10 flight.

The third stage doesn't use all its fuel in this portion of the mission; most of the fuel load is for the later lunar injection burn, and that's why its acceleration curve is so flat in comparison to the others.

Mercury-Atlas missions were more dramatic: 1.35g off the pad, peaking around 7g just before the booster engines shut down and dropped away, climbing again to almost 8g before the sustainer ran out of fuel.

Image

Here's Mercury-Atlas 7: Acceleration time series plot from 1.4g at 0:00 to 2.1g at 0:55, then in a steepening curve up to 6.8g at booster cutoff at 2:10; rising again from 1.3g to 7.8g at sustainer cutoff at 5:10

Gemini-Titan peaked above 7g on the second stage. Here's a plot from the Gemini VIII mission report:

Image

g force time series plot, increasing from about 1.25 g at liftoff in an inverse-linear curve to booster cutoff at around 155 seconds, 5.5 g, rising again from 1.35 g at second stage ignition to nearly 7.5g at second stage cutoff at around 335 seconds

Both Atlas and Titan were designed as ICBMs, so not really optimized for human comfort.

The Space Shuttle was much more gentle in comparison; at solid booster burnout it reached the first peak of 2.5g, briefly falling a bit below 1g then slowly picked back up to 3g on the main engines; the mains were repeatedly throttled down to hold about 3g for a little over a minute.

I think Soyuz does under 4g on launch.

Other things being equal, a higher-g launch can be more fuel efficient, because less energy is lost to gravity by getting to orbit more quickly, and gravity losses normally dominate over drag losses. Keeping STS down to 3g was a challenging design goal - it's hard to build deep throttling capability into an engine, but the shuttle was designed to carry (relatively fragile) scientists rather than ex-military fighter jocks. Soyuz is a bit of a compromise there.

Falcon 9 starts at about 1.15g, and depending on payload would have a first-stage peak acceleration of around 4.5g, but it appears to throttle its engines back toward the end of the first-stage burn to maintain closer to 3.5g.

Re-entry and landing G-Forces

I haven't found a good time series graph of reentry force, but the peaks are relatively brief -- force increases as the capsule descends into denser air, but decreases as the capsule slows, so the higher the decelerating g-force, the shorter it's going to last.

Mercury astronauts took about 11g peak force on re-entry, Apollo about 6.5-7g, space shuttle about 3g.

Again, Soyuz does about 4g here, I think.

There may be a pretty good jolt at touchdown/splashdown, too. Some of the Apollos hit rising waves at the end of the ride for very brief 15g bump.

STS and Soyuz g-forces are necessarily low, again, because they carry civilian crews. In the case of the shuttle, again, it's a major design consideration: the gentle re-entry means the ship has to deal with a prolonged period of high thermal load, which requires fancy and vulnerable ceramic tiles rather than a simple ablative heat shield.

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edited Dec 14 '18 at 17:42
answered Jan 17 '15 at 0:21

Russell Borogove
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The center motor was not shut down to limit acceleration. It was shut down to limit Pogo-vibrations that could damage the ship. – Gunnar Øyro Aug 23 '17 at 19:51
The first stage center shutdown is for acceleration limiting according to the flight manual: "S-IC center engine cutoff occurs at 2 minutes 5.6 seconds after first motion, to limit the vehicle acceleration to a nominal 3.98 g." The second stage center shutdown is a pogo-control measure. history.nasa.gov/afj/ap08fj/pdf/sa503-flightmanual.pdf – Russell Borogove Aug 23 '17 at 21:34
"a higher-g launch can be more fuel efficient, because less energy is lost to drag and gravity by getting to orbit more quickly": Wouldn't higher-g launch mean MORE energy lost to drag? Higher acceleration means higher speed while low in the atmosphere and thus higher drag. Energy loss to drag is the same as its (negative) work, which is the integral of its force (or, rather, its projection on the velocity vector) over the path. The length of the path in the atmosphere doesn't depend on acceleration, but higher acceleration means higher force. – Litho Aug 24 '17 at 7:45
@Litho - whoops, good catch; I've corrected that. Note that gravity losses usually dominate over drag losses (by around 20:1 for Saturn V, for example), so the conclusion is the same. – Russell Borogove Aug 24 '17 at 16:10


To answer your second question on the astronauts' experience and how much thought went into adjusting the g-force profile of a launch, NASA published a document that contains information on the g-force survivability range of a human.

Here is the Paper, the relevant figure you want is Figure 5 which is about halfway down the page. The figure is a plot of g-forces in the y axis and time in the x axis with highlighted regions of survivability.

Image

Fig. 5 - Human time-tolerance: acceleration
Condottiere
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Re: Ship Design Philosophy

Postby Condottiere » Tue Mar 12, 2019 9:20 pm

Spaceships: Hulls and Bigelow Aerospace Is Building The World's First Space Hotel | Answers With Joe

Robert Bigelow became a billionaire as the owner of Budget Suites of America hotels. But now he wants to build hotels in space. And his company Bigelow Aerospace is getting closer with their inflatable habitats.

https://www.youtube.com/watch?v=5nE3UO1kqv0


Problem with using fabric based hulls is that volume counts more than mass.
Condottiere
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Re: Ship Design Philosophy

Postby Condottiere » Fri Mar 15, 2019 2:59 am

Starships: Engineering and the One Shot Jump Drive

Default at ten tonnes and fifteen megaschmuckers providing two hundred parsec tonnes.

Twenty percent decrease in tonnage gives four tonne overhead and four tonne core/capacitors at three and three quarters megaschmuckers.

Though if cost is calculated at de facto per tonne, three hundred and seventy five kay schmuckers, that's three megaschmuckers.

Minimum ten tonne jump drive, six tonne core/capacitors, that's a performance of three hundred parsec tonnes at a cost of three and a quarter megaschmuckers.

Make it a budget version with energy inefficiency, it costs 2'812'500.- Credite Imperiale and needs 39 energy points to transition three hundred parsec tonnes.
Condottiere
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Re: Ship Design Philosophy

Postby Condottiere » Fri Mar 15, 2019 8:47 pm

Starships: Engineering, Deconstruction, and the One Shot Jump Drive

For the default ten tonne jump drive, overhead/capacitors are five tonnes, and core/capacitors are another five tonnes; while you really don't have to worry that much of deterioration of the capacitors with extensive use, at seventy five percent discount, I certainly wouldn't mix them with default capacitors, not that it is clear that accelerated deterioration is part of the one shot process.

As such, you initially remove the capacitors, and are left with four tonnes each of overhead and core at nine megabux, which results in 1'125'000 CrImps per tonne, at seventy five discount 281'250 CrImps per tonne, with a further budgetted variant at 210'937.50 CrImps.

Bare overhead weighs in at 3.2 tonnes, budgetted capacitors have a 62.5 energy point capacity per tonne at 562'500 CrImps.

Target four hundred parsec tonnes.

Required would be double of initial core at 6.4 tonnes, plus overhead at 3.2 tonnes, equals 9.6 tonnes at 2'700'00 CrImps, budgetted 2'025'000 CrImps.

Minimum one shot capacitors for 52 energy points is 0.832 tonnes, round that off to 0.9 tonnes at 455'625 CrImps, budgetted 341'718.75 CrImps.

End result ten and a half tonne one shot jump drive rated for four hundred parsec tonnes, at 2'366'718.75 CrImps.
Condottiere
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Re: Ship Design Philosophy

Postby Condottiere » Tue Mar 19, 2019 11:04 pm

Spaceships: Engineering, Mechanics, and Why Machines That Bend Are Better

Compliant mechanisms have lots of advantages over traditional devices.

At the above link, you can download 3D-print files to make some of the objects in the video, plus learn more about compliant mechanisms.

What I learned about compliant mechanisms I summarize in the 8 P's of compliant mechanisms:

1. Part count (reduced by having flexible parts instead of springs, hinges)
2. Productions processes (many, new, different enabled by compliant designs)
3. Price (reduced by fewer parts and different production processes)
4. Precise Motion (no backlash, less wear, friction)
5. Performance (no outgassing, doesn't require lubricant)
6. Proportions (reduced through different production processes)
7. Portability (lightweight due to simpler, reduced part count designs)
8. Predictability (devices are reliable over a long period of time)

https://www.youtube.com/watch?v=97t7Xj_iBv0


And possibly, missile arming safety switch.
Condottiere
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Re: Ship Design Philosophy

Postby Condottiere » Thu Mar 21, 2019 12:04 am

Spaceships: Engineering, Power Plants, and Using nanotechnology to convert waste heat into electricity | Charles Stafford | TEDxTucsonSalon

Dr. Stafford's talk discusses his ideas of using nanotechnology to convert waste heat into electricity. In particular, he shows how we might take advantage of quantum oddities in the way heat is transferred across specific atomic structures, so that we could produce cost-effective, non-polluting electricity.

Dr. Stafford is a Professor of Physics at the University of Arizona. He is also Co-Director of the UA Chemical Physics Program. For over twenty-five years, Dr. Stafford has focused his research on the theory of charge and heat flow in quantum systems. He has published over seventy peer-reviewed scientific articles, and he holds three U.S. Patents for inventions in nanotechnology. In 2000, he received the ABB Prize of the Swiss Physical Society “for his outstanding contributions to research on Cohesion and Conductance of Disordered Metallic Contacts.”

https://www.youtube.com/watch?v=BG8LYEqNmqk
Condottiere
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Re: Ship Design Philosophy

Postby Condottiere » Thu Mar 21, 2019 12:07 am

Spaceships: Engineering, Power Plants, and Converting Heat Into Electricity

Humankind wastes a lot of energy, but thanks to new technologies, it is increasingly affordable to harvest and use it. At a recent energy summit in Washington, one of the participating commercial firms exhibited photovoltaic cells that turn waste heat into electricity.

https://www.youtube.com/watch?time_cont ... 5qCw5RIBc0
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Re: Ship Design Philosophy

Postby Sigtrygg » Thu Mar 21, 2019 6:38 pm

Here we go again.

You can not convert 'waste heat' into electricity. you can only convert a temperature gradient into electricity, which in turn generate waste heat.
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Re: Ship Design Philosophy

Postby Condottiere » Thu Mar 21, 2019 10:27 pm

I don't pretend to be a physicist either, but if you have to sink that heat any where, I'd dump it into the fusion reactor.

It seems pretty much equivalent to perpetual energy, if you use it to force a cycle through a steamish type turbine, whether the material is hydrogen, water or liquid metal.
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Re: Ship Design Philosophy

Postby Sigtrygg » Thu Mar 21, 2019 11:35 pm

The principles of the laws of thermodynamics are pretty easy to learn, but the most basic one is heat energy goes from where it is hot to where it is cold.

You can only have a temperature gradient going from hot to cold. You can not dump waste heat into your fusion reactor unless it is hotter than your reactor or you do work to shift the heat to your reactor. Doing so requires energy input to do the work, which generates yet more waste heat. Put another way, in a closed system like a spaceship if you try to move waste heat into your fusion reactor you will end up generating even more waste heat in the process - I am aware I am not explaining this very well but it is difficult without diagrams and equations :)

The laws of thermodynamics are very well understood and have yet to be contradicted by any observation or experiment.

Traveller has a magic heat sink technology that it has never revealed, I postulate it is based on that old chestnut gravitics...
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Re: Ship Design Philosophy

Postby Condottiere » Sat Mar 23, 2019 8:47 am

The other way to dump heat would be diverting it to plasma and fusion weapon systems, since the material gets expelled, and new material has to be heated up.
Condottiere
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Re: Ship Design Philosophy

Postby Condottiere » Sat Mar 30, 2019 9:06 am

Inspiration: Battle of the Dreadnoughts -- A Star Wars Short Film

Battle of the Dreadnoughts, A Star Wars Short Film, sees the Eclipse Super Star Destroyer -- one of the Empire's most devastating weapons -- face off against the New Republic's Viscount Class Star Defender in a Star Wars Legends space battle for the ages.

Thanks to EC Henry for all of his exceptional work, check out his behind the scenes video here:
youtu.be/VVdiY7W2B_M

https://www.youtube.com/watch?v=5Jlo081vSQQ
Condottiere
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Re: Ship Design Philosophy

Postby Condottiere » Mon Apr 01, 2019 6:46 am

Inspiration: Century 21 Tech Talk - Episode Four: Fireball XL5 | Hosted by Brains [Thunderbirds] and Prof Matic

Welcome to Century 21 Tech Talk, a brand new video series hosted by International Rescue's resident genius - Brains!

In this briefing, we'll be learning about Fireball XL5, the pride of the World Space Patrol!

https://www.youtube.com/watch?v=_3Jwe8s4Nww


Oxygen pills and surviving contact with vacuumed space.
Condottiere
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Re: Ship Design Philosophy

Postby Condottiere » Fri Apr 19, 2019 8:32 pm

Inspiration: Archer Season 10 Trailer (HD) Archer: 1999

Archer 1999 premieres this May on FXX.

https://www.youtube.com/watch?v=ILmMhNN0hZc


I kinda suspected that the next season would be futuristic; the other genres would have been Renaissance, Enlightenment, Regency, Victorian, Western, Civil War, Great War, Roaring Twenties, fantasy, ancient or medieval.

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