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Re: Ship Design Philosophy

Posted: Thu Feb 14, 2019 4:23 pm
by Condottiere
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:


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.


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:


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.

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

Russell Borogove
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. – 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.


Fig. 5 - Human time-tolerance: acceleration

Re: Ship Design Philosophy

Posted: Tue Mar 12, 2019 9:20 pm
by Condottiere
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.

Problem with using fabric based hulls is that volume counts more than mass.

Re: Ship Design Philosophy

Posted: Fri Mar 15, 2019 2:59 am
by Condottiere
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.

Re: Ship Design Philosophy

Posted: Fri Mar 15, 2019 8:47 pm
by Condottiere
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.

Re: Ship Design Philosophy

Posted: Tue Mar 19, 2019 11:04 pm
by Condottiere
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)

And possibly, missile arming safety switch.

Re: Ship Design Philosophy

Posted: Thu Mar 21, 2019 12:04 am
by Condottiere
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.”

Re: Ship Design Philosophy

Posted: Thu Mar 21, 2019 12:07 am
by Condottiere
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. ... 5qCw5RIBc0

Re: Ship Design Philosophy

Posted: Thu Mar 21, 2019 6:38 pm
by Sigtrygg
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.

Re: Ship Design Philosophy

Posted: Thu Mar 21, 2019 10:27 pm
by Condottiere
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.

Re: Ship Design Philosophy

Posted: Thu Mar 21, 2019 11:35 pm
by Sigtrygg
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...

Re: Ship Design Philosophy

Posted: Sat Mar 23, 2019 8:47 am
by Condottiere
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.

Re: Ship Design Philosophy

Posted: Sat Mar 30, 2019 9:06 am
by Condottiere
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:

Re: Ship Design Philosophy

Posted: Mon Apr 01, 2019 6:46 am
by Condottiere
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!

Oxygen pills and surviving contact with vacuumed space.

Re: Ship Design Philosophy

Posted: Fri Apr 19, 2019 8:32 pm
by Condottiere
Inspiration: Archer Season 10 Trailer (HD) Archer: 1999

Archer 1999 premieres this May on FXX.

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.

Re: Ship Design Philosophy

Posted: Tue Apr 23, 2019 9:36 pm
by Condottiere
Inspiration: USCM Tech: UD-4L "Cheyenne" Utility Dropship

A look at the USCM's UD-4L "Cheyenne" Utility Dropship, and the incredible detail put into it by James Cameron & Co, as shown in the Aliens: Colonial Marines Tech Manual.

The weapon pylons could act as aerofoils, properly configured and streamlined.

Re: Ship Design Philosophy

Posted: Thu Apr 25, 2019 7:39 am
by Condottiere
Inspiration: Anatomy of a Vessel: USCSS Nostromo - Registration 1809246(09)

An exploration of the USCSS Nostromo, the Weyland-Yutani-owned commercial towing vehicle that brought the company one step closer to attaining a Xenomorph specimen.

Streamlined (battle) tender, I'd speculate.

Re: Ship Design Philosophy

Posted: Fri Apr 26, 2019 4:48 am
by Condottiere
Spaceships: Engineering and Expander Cycle Rocket Engines - Using Waste Heat To Drive Your Rocket

Another installment of 'Things Kerbal Space Program Doesn't Teach' - explaining the expander cycle rocket engines in more detail. Expander cycles use the waste heat from the combustion chamber and nozzles to boil liquid hydrogen and power the turbines. The main advantages are cooler, less chemically active turbine environments, but if used in a closed cycle design the total thrust is limited.

Most of this material is at a pretty high level, I'm not a rocket scientist, I only play one on the internet.

1. Turbo pump.

2. Low boiling point of hydrogen.

3. Expander bleed cycle.

Re: Ship Design Philosophy

Posted: Sun May 19, 2019 2:38 pm
by Condottiere
Spaceships: Engineering and These Engineers Want to 3D Print an Entire Rocket in 60 Days

This team of engineers is using one of the world's largest 3D metal printers to build rockets, and it could shake up the space industry as we know it.

Read More:
Aerospace startup making 3D-printed rockets now has a launch site at America’s busiest spaceport
“America’s busiest spaceport in Cape Canaveral, Florida, is about to get a new tenant: a startup that shares SpaceX’s ambitious plans of turning humans into a multiplanetary species.”

NASA Tests First 3-D Printed Rocket Engine Part Made with Two Different Alloys
“Engineers at NASA's Marshall Space Flight Center in Huntsville, Alabama, tested NASA's first 3-D printed rocket engine prototype part made of two different metal alloys through an innovative advanced manufacturing process. NASA has been making and evaluating durable 3-D printed rocket parts made of one metal, but the technique of 3-D printing, or additive manufacturing, with more than one metal is more difficult.”

Relativity Space reveals its ambitions with big NASA deal
“Relativity announced Wednesday that it has signed a 20-year partnership with NASA's Stennis Space Center for an exclusive lease of the 25-acre E4 Test Complex in Southern Mississippi. The four test stands on the site will allow Relativity to develop and test enough engines to build 36 rockets a year, and the agreement includes an option for the company to eventually expand its footprint at the site to 250 acres.”

Re: Ship Design Philosophy

Posted: Sun May 26, 2019 7:18 pm
by Condottiere
Spaceships: Engineering and How NASA Mission Designers Invent Futuristic Spacecraft

From journeying to distant worlds to catching asteroids, this NASA conceptual design team turns the spacecraft of your dreams into reality.

Read More:
This Jumping Probe Might Explore Neptune’s Biggest Moon
“After the probe (called the Triton Hopper) lands on Triton, it would use radioactive isotopes to heat ice that it mined from the moon to drive rocket-powered jumps up to a kilometer high and five kilometers long. Steven Oleson, the principal investigator on the Triton Hopper, says the probe has the potential to explore a large portion of the moon's surface. "We want to go from the equator to the pole."”

A Nuclear Tunneling Worm Could Help Us Find Out What's Beneath Europa's Ice
“While the Europa Clipper's launch is TBD, scientists are already working on the big problem of getting through all that ice to see what's below. Working with NASA, a team of scientists have proposed a solution: a nuclear-powered tunneling robot.”

NASA Space Submarine Could Explore Titan's Methane Seas
“The extraterrestrial seas of Titan, Saturn's largest moon, provide an ideal world for a robotic submarine to explore, and a team of scientists is working on an innovative mission concept that could make that vision a reality.”

Maybe more, alternatives to All Terrain Vehicles.

Re: Ship Design Philosophy

Posted: Wed May 29, 2019 4:59 pm
by Condottiere
Spaceships: Hulls and Adam Savage's One Day Builds: Scratch-Built Spaceship!

One Day Builds are back! Adam takes us through another spaceship model build, this time utilizing his trusty vacuum former, sheet styrene, and years of experience from his special effects modelmaking days. As the spaceship takes shape, Adam introduces several new tools and tips for this kind of modelmaking, and shows the versatility of this kind of build.

Lots of vacuum in space.