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#1 2022-02-24 12:19:42

tahanson43206
Moderator
Registered: 2018-04-27
Posts: 18,143

Large Ship Momentum (Mass) Management

Large Ship Prime is: Large scale colonization ship by RobertDyck

This topic is offered to collect knowledge, insights and best practices for maintaining longitudinal stability of the vessel as it flies

"Large Ship" is (arbitrarily) defined as 5,000 metric tons, for the purposes of calculations to be posted in this topic.

Humans have learned how to build and deploy rotating devices for hundreds of years:

Per Google:

Barrel rifling was invented in Augsburg, Germany in 1498. In 1520 August Kotter, an armourer from Nuremberg, improved upon this work. Though true rifling dates from the mid-16th century, it did not become commonplace until the nineteenth century.
Rifling - Wikipedia
en.wikipedia.org › wiki › Rifling
About Featured Snippets

A characteristic of ** all ** rotating devices, from the first bullets to the latest NASA spacecraft (eg, deep space probes) is that mass is distributed inside the device so that momentum about the axis of rotation is even.

The Large Ships, regardless of design, will ** all ** be required by the Laws of Physics to maintain precise control of mass inside (and attached to) the vessel.

It is likely that humans will be able to move about in their cabins without disturbing the stability of the rotating vessel.  However, movements between cabins will (I suspect) need to be coordinated with a corresponding movement on the opposite side of the axis of rotation.

Since humans have no experience with this situation, it is understandable that everyone involved in thinking about it may be oblivious of this operational requirement.  This is just not something that readily comes to mind.

I asked Google if anyone has been thinking about this anywhere on Earth, and a preliminary result looks encouraging:

Spinning Brains - NASA
www.nasa.gov › vision › space › livinginspace › 23jul_spin
Jul 23, 2004 · Inside a spinning spaceship, on the other hand, there would be an ... In each case, your brain makes on-the-fly Coriolis adjustments.

I cannot see this reference from the machine in use at the moment, but I suspect it does ** not ** extend to planning for mass management in a large vessel.

Large aircraft, such as those used by the military to send tanks around the world, employ specialists called "Load Masters".  These are generally non-commissioned officers who are responsible for seeing to it that the load to be carried is placed so that the center of mass of the aircraft coincides with the center of mass of the load, so that the pilot can control the machine.  An example of an incorrectly positioned load is available in the not-too-distant historical record, when an aircraft took off from an Asian air field (probably Afghanistan) and the pilot was unable to achieve level flight.

The crew of Large Ship will most certainly include the celestial equivalent of the Load Master.  Depending upon the sensitivity of the vessel to individual mass movements, the Load Master may have control of movements of passengers and crew outside the cabin.

(th)

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#2 2022-02-24 14:51:32

Quaoar
Member
Registered: 2013-12-13
Posts: 652

Re: Large Ship Momentum (Mass) Management

tahanson43206 wrote:

Large Ship Prime is: Large scale colonization ship by RobertDyck

This topic is offered to collect knowledge, insights and best practices for maintaining longitudinal stability of the vessel as it flies

"Large Ship" is (arbitrarily) defined as 5,000 metric tons, for the purposes of calculations to be posted in this topic.

Humans have learned how to build and deploy rotating devices for hundreds of years:

Per Google:

Barrel rifling was invented in Augsburg, Germany in 1498. In 1520 August Kotter, an armourer from Nuremberg, improved upon this work. Though true rifling dates from the mid-16th century, it did not become commonplace until the nineteenth century.
Rifling - Wikipedia
en.wikipedia.org › wiki › Rifling
About Featured Snippets

A characteristic of ** all ** rotating devices, from the first bullets to the latest NASA spacecraft (eg, deep space probes) is that mass is distributed inside the device so that momentum about the axis of rotation is even.

The Large Ships, regardless of design, will ** all ** be required by the Laws of Physics to maintain precise control of mass inside (and attached to) the vessel.

It is likely that humans will be able to move about in their cabins without disturbing the stability of the rotating vessel.  However, movements between cabins will (I suspect) need to be coordinated with a corresponding movement on the opposite side of the axis of rotation.

Since humans have no experience with this situation, it is understandable that everyone involved in thinking about it may be oblivious of this operational requirement.  This is just not something that readily comes to mind.

I asked Google if anyone has been thinking about this anywhere on Earth, and a preliminary result looks encouraging:

Spinning Brains - NASA
www.nasa.gov › vision › space › livinginspace › 23jul_spin
Jul 23, 2004 · Inside a spinning spaceship, on the other hand, there would be an ... In each case, your brain makes on-the-fly Coriolis adjustments.

I cannot see this reference from the machine in use at the moment, but I suspect it does ** not ** extend to planning for mass management in a large vessel.

Large aircraft, such as those used by the military to send tanks around the world, employ specialists called "Load Masters".  These are generally non-commissioned officers who are responsible for seeing to it that the load to be carried is placed so that the center of mass of the aircraft coincides with the center of mass of the load, so that the pilot can control the machine.  An example of an incorrectly positioned load is available in the not-too-distant historical record, when an aircraft took off from an Asian air field (probably Afghanistan) and the pilot was unable to achieve level flight.

The crew of Large Ship will most certainly include the celestial equivalent of the Load Master.  Depending upon the sensitivity of the vessel to individual mass movements, the Load Master may have control of movements of passengers and crew outside the cabin.

(th)

If the masses of the passengers and crew is little respect the mass of the whole ship, their movements will have an imperceptible effect on the center of mass, otherwise the ship needs a liquid ballast system with sensors and fast acting pumps, for a real time compensation of the movement of people: in this case, the water ballast may also be used to screen the storm cellar from solar proton events.

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#3 2022-02-24 15:47:13

tahanson43206
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Registered: 2018-04-27
Posts: 18,143

Re: Large Ship Momentum (Mass) Management

For Quaoar re #2 .... Thank you for giving this new topic a robust push out of the cradle!

The mass of Large Ship is (arbitrarily) defined as 5000 metric tons, for the purposes of the various calculations that must be done as the concept develops.

The mass of a single human being is given (by Google) as 62 kg globally, and 80.7 kg in region called North America.

I expect that a member fluent in physics will be able to show the perturbation that ** will ** occur as 62 kg moves about in the interior of the periphery of Large Ship. The issue is not the disturbance caused by a single mass moving about, but instead, the very significant possibility of reinforcing perturbations on the interior of the vessel.

RobertDyck has previously published a suggestion that water might be moved about inside the vessel in response to disturbances of equilibrium, as you have done.  Your post includes the concept of "fast acting pumps", which was not included in the earlier post by RobertDyck (as I remember it).

Until a person with advanced physics skills shows up, I am going to assume the potential problems are non-trivial at minimum, and severe if unattended.

A strict discipline of planning coordinated movements of personnel and mass on opposite sides of the axis or rotation seems (to me at this point) to be a requirement for your science fiction novels which make use of rotation to achieve artificial gravity.

Since MOST science fiction writers are NOT physicists, or even familiar with science concepts beyond a single required class in high school, it is not surprising (to me for sure) that NOT one of them (that I have seen so far) has added momentum management into the story line.

You have an opportunity to break that mold, and to achieve some distinction if you explore this aspect of space flight in fiction.

(th)

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#4 2022-02-24 18:20:18

Quaoar
Member
Registered: 2013-12-13
Posts: 652

Re: Large Ship Momentum (Mass) Management

tahanson43206 wrote:

For Quaoar re #2 .... Thank you for giving this new topic a robust push out of the cradle!

The mass of Large Ship is (arbitrarily) defined as 5000 metric tons, for the purposes of the various calculations that must be done as the concept develops.

The mass of a single human being is given (by Google) as 62 kg globally, and 80.7 kg in region called North America.

I expect that a member fluent in physics will be able to show the perturbation that ** will ** occur as 62 kg moves about in the interior of the periphery of Large Ship. The issue is not the disturbance caused by a single mass moving about, but instead, the very significant possibility of reinforcing perturbations on the interior of the vessel.

RobertDyck has previously published a suggestion that water might be moved about inside the vessel in response to disturbances of equilibrium, as you have done.  Your post includes the concept of "fast acting pumps", which was not included in the earlier post by RobertDyck (as I remember it).

Until a person with advanced physics skills shows up, I am going to assume the potential problems are non-trivial at minimum, and severe if unattended.

A strict discipline of planning coordinated movements of personnel and mass on opposite sides of the axis or rotation seems (to me at this point) to be a requirement for your science fiction novels which make use of rotation to achieve artificial gravity.

Since MOST science fiction writers are NOT physicists, or even familiar with science concepts beyond a single required class in high school, it is not surprising (to me for sure) that NOT one of them (that I have seen so far) has added momentum management into the story line.

You have an opportunity to break that mold, and to achieve some distinction if you explore this aspect of space flight in fiction.

(th)

The problem of momentum management was also addressed by the project team of space habitat Kalpana One, who used long steel cables with weights at their extremity, extended outside the habitat, and fast acting electric motors for real time spin balancing.

https://space.nss.org/kalpana-one-space-settlement/

Last edited by Quaoar (2022-02-24 18:22:09)

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#5 2022-02-25 07:53:46

tahanson43206
Moderator
Registered: 2018-04-27
Posts: 18,143

Re: Large Ship Momentum (Mass) Management

For Quaoar re #4

Thank you (again) for posting the link to the Kalpana study.  The paper includes history that adds perspective on the subject.

The name Kalpana remembers an Indian who died in the Columbia Shuttle disaster.

I hope that every one in the Large Ship community takes the time needed to study this paper.

One benefit (for me for sure) was additional insight into the question of longitudinal stability.

This paper gives 1.3r as the maximum length before a cylinder becomes unstable.

I'd like to see more about this phenomena, because I find it counter intuitive.  I would expect a longer cylinder to be more stable than a shorter one, but this is the second paper that makes this assertion that has come to my attention.

the first was a video that (I think) Void brought to our attention.

In any case, the amount of radiation protection mass proposed for a living habitat is out of the question for Large Ship. The answer has to be dynamic shielding, which SpaceNut has bravely decided to investigate.

The problem to be solved is the arrival of iron nuclei traveling at 70% of the speed of light, and from any direction. 

The only tools that I know of to provide protection are the two electric fields: electrostatic force, and magnetic force.

The solution may well require clever deployment of both forces.

This topic is about instability due to movement of mass inside a rotating cylinder, and the paper addresses that factor. The deployment of weights on cables is innovative and it may be practical for a living habitat, but it is clearly not suitable for Large Ship.

(th)

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#6 2022-02-25 09:13:23

tahanson43206
Moderator
Registered: 2018-04-27
Posts: 18,143

Re: Large Ship Momentum (Mass) Management

Human beings have a great deal of experience rotating large masses at high velocity.

An example that comes to mind in the electric generation field is the generators driven by steam or hydropower.

Those devices are engineered to insure they are perfectly balanced.

Other examples include large propellers for aircraft, including those for helicopters, and propellers for wind turbines.

A Ferris wheel is another example of a large machine designed for rotation.  When a Ferris wheel is loaded or unloaded, the operator takes care to perform the mass transfers evenly.

It is possible that astronauts have experimented with rotational stability in microgravity, but at this point, I am not aware of any organized set of experiments to demonstrate the principles of rotation of objects in space.

I hauled out one of my physics books and reviewed the section on "Rotation, stability of" .... this section covered behavior of rotating objects in a gravitational field, and showed the concept of stability of the center of mass with respect to the center of gravity.  Helpful as this section might be for application on Earth, I found it unhelpful for understanding of stability (or instability) in space.

The one detail I ** did ** pick up was the concept of disturbance.

Large Ship may be configured by the Captain to be rotating smoothly at 3 RPM and a mass of 5000 tons.  The issue at hand is what happens when a disturbance occurs.  The disturbance can come from the outside, as in the physics book examples, or it might come from inside, as the paper Quaoar found discusses.  One outcome of a disturbance is chaotic tumbling.

There have been reports of observation of chaotic tumbling of asteroids in space.

It ** should ** be possible for members of the NewMars forum to run software that allows this interesting aspect of the natural Universe to be studied.

A few of us have Blender installed, and since Blender runs on Windows, Linux and Apple, it is a candidate for illustration of the physics of rotation.

Blender has a physics engine.  It can be configured to Earth normal, or it can be adjusted to meet special needs of a particular animation.

For the purposes of ** this ** topic, I would like to see a Blender application that allows demonstration of longitudinal stability of rotating objects, and in particular, why two sources have reported that longitudinal stability of a cylinder degrades when the length of the axis of rotation is greater than 1.3r.

An American football is proof that a rotating object with length greater than 1.3r is stable.

Perhaps the issue at hand is disturbance.  Since those who observe a football in motion do Not see disturbance, perhaps we are missing the opportunity to observe longitudinal instability due to a small disturbance.

The disturbance we usually see, in watching a football in flight, is a non-trivial disturbance.

Per Google:

American Football Dimensions & Drawings
www.dimensions.com › element › american-football
Dec 11, 2020 · American Footballs have a short diameter of 6.68”-6.76” (16.9-17.2 cm) and length of 11”-11.25” (28-29 cm), resulting in circumferences of 21”- ...

The radius of the diameter given above is 8.5 cm (taking a midpoint of the range)
The length is 28.5 (again taking the midpoint of the range)
The ratio of radius to length is: 3.35 and change

The Explorer satellite found the Van Allen belts.  It was given rotation during launch.
The dimensions of that satellite are given (by Google) as:

It made one orbit every 114.8 minutes, or a total of 12.54 orbits per day. The satellite itself was 203 centimeters (80 inches) long and 15.9 centimeters (6.25 inches) in diameter.
Aug 3, 2017

The ratio of radius to length of Explorer was: 1:25 and change
***
If anyone can find out where this meme of 1.3r is coming from, I'd sure appreciate a post about it.

(th)

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#7 2022-02-25 09:47:37

Quaoar
Member
Registered: 2013-12-13
Posts: 652

Re: Large Ship Momentum (Mass) Management

tahanson43206 wrote:

For Quaoar re #4

Thank you (again) for posting the link to the Kalpana study.  The paper includes history that adds perspective on the subject.

The name Kalpana remembers an Indian who died in the Columbia Shuttle disaster. (th)

In fact the space habitat was named after her.

tahanson43206 wrote:

I hope that every one in the Large Ship community takes the time needed to study this paper.

One benefit (for me for sure) was additional insight into the question of longitudinal stability.

This paper gives 1.3r as the maximum length before a cylinder becomes unstable.

I'd like to see more about this phenomena, because I find it counter intuitive.  I would expect a longer cylinder to be more stable than a shorter one, but this is the second paper that makes this assertion that has come to my attention.

the first was a video that (I think) Void brought to our attention.

In any case, the amount of radiation protection mass proposed for a living habitat is out of the question for Large Ship. The answer has to be dynamic shielding, which SpaceNut has bravely decided to investigate.

The problem to be solved is the arrival of iron nuclei traveling at 70% of the speed of light, and from any direction. 

The only tools that I know of to provide protection are the two electric fields: electrostatic force, and magnetic force.

The solution may well require clever deployment of both forces.

This topic is about instability due to movement of mass inside a rotating cylinder, and the paper addresses that factor. The deployment of weights on cables is innovative and it may be practical for a living habitat, but it is clearly not suitable for Large Ship.

(th)

To deflect the 2 GeV protons - the vast majority of GCR - you need a 20 Tesla field: if your habitat is a torus, you have to put the main coil along the outer circumference, plus a secondary coil along the inner one to cancel the field in the living quarters. With the new high temperature superconductors the mass penalty of the coils is not excessive on a 5000 ton spaceship and you can also enhance the effect inflating the field with small amount of plasma puffs.

You can build a toroidal habitat connected to the axis by four radii. Each radius has a cargo container mounted on a truck and an electric motor that move the container outside and inside to keep the center of mass on the axis, using your cargo as a ballast without extra mass penalty.

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#8 2022-02-25 19:59:11

SpaceNut
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From: New Hampshire
Registered: 2004-07-22
Posts: 29,310

Re: Large Ship Momentum (Mass) Management

The greater the mass is in the large ship design in the center the less effect is felt by things on the ring that circles it.

The central hub is quite heavy and is part of that 5,000 mT we are sending to mars.

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#9 2022-02-26 08:31:01

tahanson43206
Moderator
Registered: 2018-04-27
Posts: 18,143

Re: Large Ship Momentum (Mass) Management

For SpaceNut re #8

The source of all specifications for Large Ship (Prime) is the Large Colonization Ship topic of RobertDyck.

Please show a link to a post in that topic that supports your assertion in Post #8.

As I interpret the drawings and text of RobertDyck, the greater part of the mass of his design is in the ring.

You must (surely) have found something in the writings of RobertDyck that supports your assertion.

Please post a link to it.

(th)

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#10 2022-03-30 07:39:21

tahanson43206
Moderator
Registered: 2018-04-27
Posts: 18,143

Re: Large Ship Momentum (Mass) Management

Activity to design structures to be incorporated into Large Ship (Prime) is under way.

Some progress has been achieved in defining the elements of the 119 panels that together will comprise an air tight surface around the Habitat Ring.

So far, no asymmetry has emerged.  This post is a reminder that the end point is a massive rotating machine which must maintain mass symmetry to the nearest gram.  All components added to the design must preserve this principle.

A gram added anywhere must be matched by the same gram on the opposite side of the center line AND of the center of mass.

This principle can be observed by always planning for symmetrical modification of the design.

Only watch makers on Earth (and designers of large rotating machinery such as propellers) have had to deal with this, so the discipline is unfamiliar to most Earth dwellers.

We appear to be off to a good start.  We have decided upon 119 identical elements to be welded together to make a mass-symmetrical ring.

At manufacture time, the mass of each of the 119 panels MUST match all the others to the nearest gram.

At assembly time, the mass added by welding must be calibrated so it is equal for all panels.

There is no need for a human "enforcer".... Ma Nature will apply discipline as needed, so I recommend doing the job right the first time.

(th)

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#11 2022-03-30 17:03:42

SpaceNut
Administrator
From: New Hampshire
Registered: 2004-07-22
Posts: 29,310

Re: Large Ship Momentum (Mass) Management

The attached tug earth departure stage that will stay with the ship has the added mass that moves the center of balance back to the hub axis.

I gave an empty hull mass for the section and will re-post it here.

So materials for a solid stainless steel with inner hull plus.
480 mT Ring
120 mT Tunnels
+160 mT Hub
--------
760 mT Total less booster



66.8455 tonnes or 66,845.5 kg of water in the water wall.

Total ships air mass gives 16.5 mT of air but now you need the recycling and greenhouse aspects

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#12 2022-03-30 22:38:51

Calliban
Member
From: Northern England, UK
Registered: 2019-08-18
Posts: 3,573

Re: Large Ship Momentum (Mass) Management

If you are concerned with shifting mass distribution as people walk about the ship, then I would suggest a trimming system.  This would involve pumping water between ballast tanks located around the wheel.  Similar arrangements exist on ships and submarines, which need to maintain their centre of gravity to avoid unforseen changes in bow angle, which would generate dynamic lift effects.


"Plan and prepare for every possibility, and you will never act. It is nobler to have courage as we stumble into half the things we fear than to analyse every possible obstacle and begin nothing. Great things are achieved by embracing great dangers."

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#13 2022-03-31 05:56:29

tahanson43206
Moderator
Registered: 2018-04-27
Posts: 18,143

Re: Large Ship Momentum (Mass) Management

For Calliban re #12

Thank you for your contribution to this topic.  The idea of shifting water around has been proposed, without the detail of actual experience you have cited.  It is good to have this practical experience to add to the discussion.

My concern with water as a balancing mechanism is slow response.  If the system you have described is highly responsive, and the out-of-balance condition is nipped in the bud, then it may well find a place in the design.

However, the mass budget for the hardware portion of Large Ship is 2500 tons, and it remains to be seen how the existing requirements for cabins, atmosphere, power equipment, radiation protection, propulsion systems and all the other equipment needed will consume the available mass.

The water that is shifted from one location to another can be counted against the consumables budget, but pipes to every part of the ship whee mass compensation is needed are dead weight, as are the pumps and control equipment.

A countermeasure that does not require more mass is intelligent, coordinated movement.  This method would require self discipline of a high order, by both passengers and crew, but it would not require more mass beyond the electronics to coordinate movements.

Again, thank you for the practical example that can (hopefully) guide planners as we go along.

(th)

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#14 2022-04-01 17:45:09

SpaceNut
Administrator
From: New Hampshire
Registered: 2004-07-22
Posts: 29,310

Re: Large Ship Momentum (Mass) Management

I did a close look at the greenhouse ring section and its unable to provide air and food for the size of the crew onboard the large ship since the upper deck can only provide for 360 give or take crew members.

http://newmars.com/forums/viewtopic.php … 68#p192968


This means we are in need of a machinery deck to place all of the other stuff on moving outward and leaving the people deck sandwiched in between them.

The add reason is due to much needed tanks for sewage treatment, water processing and more that does not have enough room in the remaining portions of the large ship.

I would make it a 3 meter as well and keep the outer one meter open to the outside hull.

The increase would also allow for more solar panels to be placed onto the sun facing side of the ship increasing the available power for the trip.

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#15 2022-04-01 18:31:51

tahanson43206
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Registered: 2018-04-27
Posts: 18,143

Re: Large Ship Momentum (Mass) Management

For SpaceNut re Greenhouse capability on Large Ship ...

For reasons I don't (yet) understand, the vision for the greenhouse capability on Large Ship is quite limited.

From my point of view. the entire Sun facing side of the Ship is available for a combination of greenhouse facilities and solar panels.

The default configuration (visible in the Blender image created by RobertDyck) is to let all that useful real estate go to waste.

Hopefully the vision will change over time.

(th)

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#16 2022-04-01 19:14:38

SpaceNut
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From: New Hampshire
Registered: 2004-07-22
Posts: 29,310

Re: Large Ship Momentum (Mass) Management

The sun facing side of the image is the dark end of this image which has the engines pushing it from.

Uq9F6Sb.png

I think the layered glass is about a meter on that side but its that side which appears shaded as to if its all glass?

chloroplast life support oxygen

These require light pipes to bring the sun to these and these are in each cabin area

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#17 2022-04-01 19:35:24

RobertDyck
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From: Winnipeg, Canada
Registered: 2002-08-20
Posts: 7,852
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Re: Large Ship Momentum (Mass) Management

Primary oxygen is by chloroplast bags, enough in the life support wall of every cabin for passengers in that cabin. Crew cabins the same. So greenhouses provide extra oxygen. Some of that oxygen will be use by yeast to produce alcohol, or cooking oil, or raise bread. Metabolism of yeast is different, I could map it out, but long-story-short yeast produce CO2. I expect greenhouses will produce enough oxygen that some chloroplast bags will not be installed. But greenhouses are not the primary oxygen generator.

Food: entrées will be brought stored. Bread baked on the ship from flour, pasta cooked from dry, mashed potatoes from instant flakes, etc. Greenhouses are for the salad bar. So passengers have some fresh food.

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#18 2022-04-01 21:43:37

RobertDyck
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From: Winnipeg, Canada
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Posts: 7,852
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Re: Large Ship Momentum (Mass) Management

My skill with Blender is not that good. The top of this image is the forward end. The bottom is aft. During transit from Earth to Mars, the aft end will point to the Sun. I tried to add a second level to the image, and give it a texture for glass. Unfortunately what it did is depict the upper layer as solid glass, not windows. Windows will have minimum 2 layers of aluminum oxynitride, with argon gas between. Argon conducts heat less than air. And the gap will be pressurized less than internal pressure, but more than the vacuum of space. That way pressure of the gap can be monitored: a drop in pressure indicates a leak to the outside, while a rise in pressure indicates a leak to the inside. Windows will be sized so a single pane is sufficient to hold in ship air against hard vacuum. So there is redundancy. Greenhouses will have transparent roofs where plants grow, because mirrors will reflect sunlight through the roof. Observation rooms will have wide windows to look out, but greenhouses will not need windows on the forward side. We can debate whether windows on the aft (sunward) side are useful. Areas with work tables or vats to grow yeast or other microbes will not need sunlight, so won't have windows.

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#19 2022-04-02 06:44:04

tahanson43206
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Registered: 2018-04-27
Posts: 18,143

Re: Large Ship Momentum (Mass) Management

For everyone contributing to this topic ... Because this topic is dedicated to Mass Management, while all items (material objects) to be included in Large Ship are important to be included, I would appreciate everyone contributing to THIS topic making sure to add new mass in precise amounts on the opposite side of the center of mass of Large Ship.  The ship's crew will include a Load Master , comparable to the position in large military aircraft.

That person will have the authority to discipline any person who fails to adhere to mass discipline on a 5000 ton rotating vessel.  Such a vessel has never been built in human history, and no one in this forum, or on Earth for that matter, has any experience to prepare for the responsibility of crewing such a vessel.

However, we (humans) have centuries of experience building rotating objects, and those who were successful learned mass management.

This topic is available to help to insure that everyone contributing to the project understands that mass must be distributed evenly throughout the entire vessel, and the standard I am offering is the nearest gram.

If a bag of chloroplasts is to be installed in a cabin, an equal bag needs to be installed in the cabin opposite the center of Mass.

If a radiation protection coil is wound around the exterior of the Habitat Ring, it must be wound evenly in all locations.

GW Johnson has calculated that 6300 tons of propellant will be required to lift Large Ship to escape velocity after release by LEO Tug.  The tanks to hold that propellant will be rotating along with everything else on Large Ship.  The tanks have not been shown in the preliminary drawings of Large Ship we have seen to date, but the **real** Large Ship will have them, and the mass of the tanks and their contents **will** be distributed according to the rules Ma Nature has set down.  The mass of 6300 tons of propellant is in addition to the 5000 tons of Large Ship and it's contents, so the total mass released by the LEO tug is 11,300 tons.

These rules are imposed by Ma Nature, and they will be ignored by no one who actually flies on the vessel.

(th)

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#20 2022-04-02 07:52:22

SpaceNut
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From: New Hampshire
Registered: 2004-07-22
Posts: 29,310

Re: Large Ship Momentum (Mass) Management

Like the starship holds 1200 mt of fuel to take a trip anywhere the ship its self has a mass of 120 mt with the payload being added onto that for what we are trying to do going forth. The fuel sizing is about 5.25 starship amount with just as many engines to make it function.

So unless that structure is part of the 5000 dead mass its got to be included and that is 630mT to add to the total or remove as available out of its total.

The solar is increased by giving it more surface area to rest on but we are still in mass adding mode. If this is custom the surface area is the solving number but its much lower if these are square or rectangular panels.

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#21 2022-04-02 09:37:48

tahanson43206
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Re: Large Ship Momentum (Mass) Management

For SpaceNut  re #20

Thank you for your example of the Starship and it's propellant.

The 6300 tons proposed by GW Johnson is NOT part of the 5000 tons "dead" weight of Large Ship.

However, the tanks, and pipes, and shades (to keep them at 50 Kelvin) ARE included in the 5000 tons.  They always were, but no one seems to have started thinking about them until now.

Your mention of a Starship is helpful, because it is a candidate to be used for propulsion of Large Ship to reach Escape velocity.  That Starship would be built/secured to the central hub of Large Ship, so there is another 120 metric tons out of the 2500 structure mass budget.

The point of ** this ** topic is to keep everyone thinking about mass distribution as we proceed.

Many ideas will be proposed for equipment and structure in the weeks immediately ahead.  This topic is here to make sure that everyone plans for equal distribution of that mass around the Center of Mass / Center of Gravity of Large Ship.  This point will be the same, just as it is in an Americal football.

(th)

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#22 2022-04-02 10:25:56

RobertDyck
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From: Winnipeg, Canada
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Re: Large Ship Momentum (Mass) Management

th: In post #15 you stated an opinion that you have stated before...

tahanson43206 wrote:

For reasons I don't (yet) understand, the vision for the greenhouse capability on Large Ship is quite limited.

From my point of view. the entire Sun facing side of the Ship is available for a combination of greenhouse facilities and solar panels.

The default configuration (visible in the Blender image created by RobertDyck) is to let all that useful real estate go to waste.

First, do not "fill in" the space between the ring and the hub. We must keep the mass of the ship as low as possible. That's true for all spacecraft. More mass requires more propellant to move.  Just because the ship is shaped as a ring does not mean you have to "fill in" the space inside the ring. Quite the opposite. You want as much as possible to be empty space. That reduces mass. We already have a problem with propulsion to move the mass of this ship, we certainly don't need to increase the total mass 10 times.

Some of that space will have light-weight mirrors to reflect sunlight into greenhouses. There will also be solar panels to generate electricity. But we want as much as possible to be empty space, to avoid blocking the view of passengers in observation rooms. The purpose of the observation rooms are to serve as the deck of a ship. It's an open area where passengers can view outside. Observation rooms will have walls and ceiling that are all transparent window. Walls will be all window from waist height to ceiling. Or should it be from knee height? The idea is to give a clear view of the stars. There will be telescopes bolted to the floor with mounts that can counter the rotation of the ship so the telescope remains locked on a particular star. There will also be lounge chairs, and potted plants. But if the space within the ring is completely filled in, that would obstruct the view.

Regarding greenhouses: the idea is to provide some fresh food, and to reduce mass. If a particular food crop takes more time to harvest than the trip, then it's not worth growing on the ship. If greenhouse space requires more mass than carrying stored food, then it's not worth growing. Part of the purpose of the greenhouse is for emergency conditions. The ship will use a trajectory that takes 6 months to go to Mars. That means if an Apollo 13 style disaster happens and a free return is required, that means the ship won't stop in Mars orbit but simply pass by Mars at high speed, then the ship will take 18 months to return to Earth. During a normal trip, the ship will remain parked in Mars orbit until the planets are aligned for return, then 6 months to return to Earth. A free return will take much longer, but in an emergency will get you home. The ship will carry food for 6 months, not 24 months. So one purpose of the greenhouse is to provide food under emergency conditions for that additional 18 month return.

I have suggested developing a microbe that can be grown in a vat. This new microbe would produce wheat protein. That protein could be mixed with starch from chloroplast bags to form flour. If this can be done then we don't need to carry flour from Earth. It also means during an 18 month free return, there will be bread. If that can be done, than a second microbe could produce protein for semolina wheat. When mixed with starch that will produce semolina flour, which is used to make pasta. And I suggested producing margarine on the ship: posts #626 #625 and #620 in Life support systems / Crops. This also reduces mass by not bringing margarine from Earth. It also means margarine would be available during an emergency 18-month free return.

Greenhouse space must be used efficiently. We can grow lettuce with vertical farming. Not with artificial light, but with sunlight reflected with mirrors. Sunlight will enter the greenhouse through transparent roof, then be directed sideways into the lettuce. This provides limited light, so limits height the vertical farming system. I described an aeroponic system, using the design of an existing lettuce vertical farm in Minnesota. That company no longer grows lettuce, they had difficulty competing with lettuce from California, but the system is valid. Individual plants inserted into a growing rack, with roots dangling inside. A nozzle sprays water with nutrient solution onto plant roots, then drips down into a catch tray. A pump picks up the water from the collection tray, piping that water back to the spray nozzle. The system designed so water doesn't spray outside the rack. It's amazing how much can be produced in limited space.

I posted some ideas of what to include in a salad bar, in "Large scale colonization ship" post #601, of course we will need greenhouse space to grow these as well. Post #1052 lists some preserved food that can be brought from Earth (or Mars) to be added to the salad bar.

A lot of this is about mass allocation. For example, vanilla bean vines produce real vanilla bean. However, they take some time to grow. A greenhouse on Mars could grow them, but would not be worth growing on the ship because the vines take too long to produce. The ship will carry coffee grounds to make real coffee, but will not grow coffee trees on the ship. Whether the ship carries grounds or whole beans and grinds them fresh is a detail we can work out later, but that doesn't change mass. Cinnamon is the inner bark of two species of tree. The ship will carry cinnamon spice, but not grow cinnamon trees on the ship.

I had also posted about potatoes. Theoretically we could develop a cultivar of potato that could be grown on the ship. This would require a new cultivar (variety of plant) that requires bright sunlight 24/7, and grows much fewer leaves and stems. That's to reduce space required in the greenhouse. Also develop a durable glass bead that is light weight, opaque to visible and ultraviolet light but transparent to infrared. These beads would be used as growth medium for potatoes, used with IR cameras that can see the potato tuber under the beads. And develop a robot that can harvest potatoes when they are fully grown, without killing the plant. So we can harvest multiple potatoes from a crop of plants. Robots reduce crew required, and the rest greatly reduces greenhouse space. As they are grown now, potatoes require far too much space to be worth growing on the ship. Far better to carry instant potato flakes and dehydrated scalloped potatoes (eg Idahoan brand).

It's all about controlling mass.

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#23 2022-04-02 20:22:28

SpaceNut
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From: New Hampshire
Registered: 2004-07-22
Posts: 29,310

Re: Large Ship Momentum (Mass) Management

tahanson43206, The central hub is not a starship as RobertDyck has defined it as 9 meter diameter and is just from top to aft 28 meters.
It has a docking port on the top but that is all.

There is no engines or fuels tanks in this layout
Uq9F6Sb.png

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#24 2022-04-03 07:34:10

tahanson43206
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Registered: 2018-04-27
Posts: 18,143

Re: Large Ship Momentum (Mass) Management

For SpaceNut re #23

Thank you for bringing this terrific Blender image of the vision of RobertDyck for the general skeletal structure of Large Ship (Prime)

That image is comparable to the frame of a bike.  The typical frame of a bicycle looks like a trapazoid.  It does not include the wheels, the drive mechanism, the steering mechanism or countless other details that end up as a "real Universe" bicycle.

So it is with the wonderful starting image provided by RobertDyck.

GW Johnson has provided RobertDyck with something he could not have developed on his own ... an exact figure for the number of tons of propellant he must carry with him to achieve Escape velocity.

That number is 6300 tons, distributed beween liquid oxygen and liquefied methane.  RobertDyck **WILL** have to add those tanks to his skeleton design, and he **WILL** have to add the modular propulsion unit to the skeleton.

RobertDyck ** never ** said that the image you showed us in anything more than a starting point for development of a "Real Universe" space craft.

You can help (if you have time) by working out the volume of tankage that will be needed for 6300 tons of propellant.

This is the Mass Management topic.  As you work on the configuration of tanks, please be sure to plan for precise allocation of mass so that at all times, there is an equal distribution of mass before propulsion events, during and after them.

This should be an interesting exercise, and one that will be quite valuable, if you can find time for it.

(th)

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#25 2022-04-03 10:58:24

GW Johnson
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From: McGregor, Texas USA
Registered: 2011-12-04
Posts: 5,615
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Re: Large Ship Momentum (Mass) Management

If you look closely at the sketches I have been drawing when investigating propulsion needs,  I have been visualizing both Rob's spinning design,  and Kbd512's counter-rotating design,  as dead-head payload items to which I affix a propulsion stage.  That propulsion stage has the propellant tanks and insulation/sunshields/cryocoolers/whatever for containing propellant long term,  the engines,  the engine controls,  maneuvering thrusters,  and enough flight controls to allow the stage to maneuver independently as needed. 

For any elliptic capture orbit / space-tug operations,  the space tug itself is just another propulsion stage of a different size.  It is similarly equipped,  and capable of independent flight.  Because it needs to be. 

What I got for LOX-LCH4 chemical pushing 5000 metric tons of dead head,  with a space tug at Earth but not Mars,  was 6457 tons of propellant in a propulsion stage with an inert mass of about 200 tons.  This assembly goes 1-way to Mars and must be refilled on-orbit there in low circular orbit,  where ferries and tankers from the surface can reach it with significant payloads.  You cannot do that directly in the elliptic capture orbit,  because the dV required of the ferry increases by (at least) a factor of 1.41.  Payloads quickly become insignificant in size. True at both Earth and Mars.

This big ship/propulsion stage assembly has to be filled and loaded in low circular orbit at Earth,  where ferries and tankers can reach it with significant payloads,  but it uses an elliptic capture orbit for its departures and arrivals to significantly reduce the dV that sizes the propulsion stage.  The space tug that takes it from circular to elliptic periapsis speed is very much larger than the big ship propulsion stage.  It holds 16,326 metric tons of propellant in a stage with an inert mass of about 505 tons. 

That same tug only needs 7630 tons of propellant to bring the big ship from elliptic capture back to circular for arrival,  because the big ship is depleted of propellant,  after its arrival into the elliptic capture orbit,  and thus very much lighter.

But when you total up the big ship propulsion stage,  the tug departure,  and tug arrival quantities,  you have to put some 30,412 metric tons of propellant into low orbit at Earth,  and you still have to put some 6457 metric tons of propellant into low circular orbit at Mars,  to refill the big ship propulsion stage there.

It'll cost you about 26.9 tons of launch propellant for every ton of on-orbit propellant,  at Earth,  assuming my projected performance of Starship/Superheavy as a tanker vehicle (171 max tons useful payload to low circular eastward orbit).  It'll cost you about 6 tons of launch propellant for every ton of on-orbit propellant at Mars,  assuming my projected performance of Starship as a single-stage ferry at Mars (roughly 200 tons to low circular eastward orbit).

That's roughly 850,000 tons of propellant to manufacture per mission at Earth,  and about 49,000 tons of propellant to manufacture per mission at Mars.  Because the mission is a 30-month long Hohmann min-energy transfer (one way 8.6 months),  you can only fly a mission with the one big ship every other planetary line-up.  So you have 52 months to manufacture those enormous quantities of launch and on-orbit propellant.  That's a bit over 46,000 tons per month at Earth,  and almost 900 tons per month at Mars. 

All that to send 1000 folks orbit-to-orbit with chemical propulsion with the lowest possible propellant refill requirement at Mars.  You can zero the refill of the big ship propulsion at Mars,  but when you do,  the propulsion stage and Earth tug get very much larger,  and the Earth propellant quantities increase by a bit over a factor of 10.  You are then in the 9 million tons of propellant to be manufactured per mission class.

Which in turn is why I suggested we go with electric instead,  as a technology already flying,  just needing enormous scaleup to the size we are talking about here.  That went direct low circular to low circular,  unrefilled at Mars,  as a 2-way trip,  with around 6950 tons of propellant.  For that put on-orbit with the same chemiccal propulsion at about the same 26.9:1 ratio,  the total propellant manufacturing quantity per mission was down nearer 200,000 tons per mission,  every 52 months.  That's a whole lot more reasonable. 

And it is why I suggested getting gas core nuclear and the fission explosion technologies into serious development,  because they look even better!  That's what the numbers I have been running are really saying!

GW


GW Johnson
McGregor,  Texas

"There is nothing as expensive as a dead crew,  especially one dead from a bad management decision"

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