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As of 2022/01/10, the Large Ship topic created by RobertDyck has split into two, based upon physical differences.
The original Large Ship is defined as a Unitary Rotating Habitat able to carry 1000 passengers and 60 crew to Mars and back in a 2 year voyage.
The competitive Large Ship is defined as a Counter-Rotating pair of Habitats together able to carry passengers and crew.
The original design remains under the direction of RobertDyck.
The competitive design is sponsored by kbd512, under the title:
A More Practical Interplanetary Colonization Ship
Both versions of Large Ship must provide answers to questions about:
1) What the Large Ship is
2) What the Large Ship is not
3) Gravity Prescription (eg, Mars equivalent and 20 second rotation, or something else)
4) Atmosphere Prescription (eg, 3-5-8 rule, 431 rule, or something else)
5) Water - rationing procedure for passengers and crew, methods of preparation for various uses, procurement, disposition
6) Food - rationing procedure for passengers and crew, methods of preparation, storage, procurement, disposition
7) Radiation protection - Medical care
8) EVA - Life Support in emergency - Life boats made from cabins or clusters of cabins or something else
9) Propulsion/Navigation/System management
10) Psychological factors - activities - responsibilities of each person - education - amusement - exercise - discipline
11) Funding
12) Construction and maintenance in LEO, in flight, at Mars, and on long flights to other Solar System destinations.
SearchTerm:Large ship specifications
The Large Ship design in development by RobertDyck has a small number of distinguishing characteristics:
1) Rotation rate is 3 rpm (20 seconds per revolution)
2) Gravity prescription: Mars equivalent (ie, about 4/10ths Earth normal)
3) Atmosphere: 3-5-8 rule: 3 PSI Oxygen 5 PSI inert gas 8 PSI total
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tahanson43206,
A Ford Fiesta is not a competitor to a Rolls Royce Phantom. Both are motor vehicles that can take you from Point A to Point B, but all other similarities end there. If money were no object, then few people would choose a Fiesta over a Phantom, but money happens to be "a real thing", and a Rolls Royce is simply beyond the price range that most car buyers can afford. Ford didn't invent motor vehicles, nor were its models the most luxurious available by any stretch of the imagination, but they had a number of good qualities that made them very attractive to potential car buyers, which included remaining within the limited means of the majority of the consumer public. To colonize a planet tens of millions of miles from home, you need a lot of very affordable ships to increase the number of prospective colonists who can afford to make the trip. The ultra-wealthy alone will not be able to establish a colony on another planet. Opulent wealth follows ample opportunity and the means to capitalize on that opportunity. I want to make interplanetary transport a routine event for the middle class general public, which means we must build ships that are economical to own and operate. It's a different approach to solving the same problem. Robert's ideas are correct, but they're at the edge of feasibility without new propulsion and life support technologies that may require another decade of development and testing. I think it's worth it, but we need to establish a colony first, then concern ourselves about arriving there in style.
Cruise liners came about well after sailing ships, not before. Nobody could seriously argue that an all-steel cruise liner wasn't a much better ocean-going vessel than a wooden sailing ship, but it took multiple refinements and combinations of new and existing technology before cruise liners became the practical mass transports that they are today. We will get there eventually, because we must, but prior to that we're going to have to accept less capable vessels that still get the job done.
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The primary flaw in Elon Musk's plan for Mars was failure to work on an intermediary size system for the pioneering explorations of the landing zones. He needed to be doing this concurrently with Starship, and using a scaled up center core for Falcon Heavy. Falcon "Super Heavy" with a 17 foot diameter (5 meters) and using the expertise gained in the Falcon Heavy engineering work would have been feasible. This model would have used 4 Falcon 9 side boosters and a 15-17 Merlin engine central core. I recall suggesting something similar to this back in about 2016. This was to have been a bare bones, "survival and explore mission" flight vehicle, and a squadron of 4 of these for the mission. This would have enabled some significant progress on the ISRU fuel production facility and preparation of a larger and boulder free landing site for larger Starship missions. Even a Bobcat style tracked skid-steer unit could clear away some big boulders and use of explosives can render the large rocks to smaller rocks.
But hindsight is always better than 20-20. Just sayin'.
Last edited by Oldfart1939 (2022-01-10 14:53:23)
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Thanks to kbd512 and Oldfart1939 for adding to this new topic.
For kbd512 .... the distinctive feature of your competitive design is the counter-rotating habitats.
Everything else in your design appear to be in total flux. That is not a criticism at all. You are at the start of a two year journey that ** should ** resolve to a set of plans that someone will want to fund.
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Big difference is how many work versus not is why we are at a 2 design point.
The months of time getting there is not a free ride to do nothing to support your own butt's being there.
The same holds true on the surface as well as the trip back home.
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For SpaceNut re #5
It's easy for us to lose sight of what we're attempting to do .... this topic is dedicated to design of space vessels able to carry passengers and crew safely between planets in the Solar System. Discussion of the nature or activity of the passengers themselves would seem (to me at least) better suited for other topics than this one.
We have a concept for a particular design of rotating space vessel well along in the topic created by RobertDyck, and we have a concept for a competing design that was recently created by kbd512 in his "practical" topic.
It is entirely possible a third member may decide to enter the competition with another concept altogether, although what that would be I cannot imagine.
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Both kdb512 and Rob are thinking even LARGER than Elon. I'm striking out here as a pragmatic minimalist. Don't get me wrong,; what I'm suggesting is still bigger than anything other than Starship/Super Heavy Booster. I view the problems at hand kinda like eating an Elephant. We have to do it one bite at a time, but other's think it takes a bigger mouth and fewer bites.
I thought Elon had some great ideas earlier about Red Dragon, but abandoned those in favor of the Bigger is Better approach.
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tahanson43206,
I'm not fixated on a specific design or technology set, because fixating on favored ideas is not practical engineering. The counter-rotation concept was about at least partially counteracting the general instability issue caused by imbalance of an unbalanced spinning top, as well as gyroscopic precession, which presents a more intractable vehicle control problem. The instability effect is both simple and easy to demonstrate using a child's toy with a small weight inserted into a hole drilled into the edge of the top. A corollary counter-rotation experiment is only nominally more complex and costly to perform, but can also be done with some basic woodworking skills. If you lack the fabrication skills and tools, then simply purchase a gyroscopic and add a small weight to one of the spokes / arms attached to the flywheel mass before spinning it up, then watch what happens. If anyone thinks I'm wrong, then do the experiments yourself and prove me wrong. I've already done them and physics professors routinely provide the same or substantially similar demonstrations for their students to observe, using gyroscopes. It's not a made-up problem. It's real and can't be hand-waved away. If you have sufficient counter-balance mass to compensate for this issue, then you can use either design. I've stated that before.
However, that second problem that the simpler spinning top design creates is related to vehicle control. A spinning top design will experience gyroscopic precession. That is an even more problematic design feature of the simpler spinning top vehicle design. Fine control over the vehicle's attitude is necessary for maneuvering. If the vehicle is continuously doing 360s like a helicopter that's lost its tail rotor while generating artificial gravity, however slowly, then that is very problematic when attitude control and propulsion are taken into consideration, as they must be, in order for any ship to be navigable. Over significant distances, bullets fired through rifled barrels drift in the direction of rotation, absent any wind effects, specifically because of gyroscopic precession. Marksmen who shoot over extended distances are specifically taught to compensate for this effect. They frequently call it "spin drift", but in the texts used to teach them, it's frequently denoted by its proper name- gyroscopic precession. This is such basic stuff that it's difficult to imagine why it would be seriously debated or unaccounted for. The low rotational rate doesn't preclude experiencing the effect, either, especially given the component and consumable masses we're talking about using (hundreds to thousands of tons). Counter-rotation significantly reduces or eliminates the gyroscopic precession effects.
As a final example, the most powerful piston engines that came in towards the end of WWII were frequently so powerful that counter-rotating propellers were required, not only to provide much needed ground clearance while efficiently turning engine horsepower into thrust, but to counteract the massive torque / gyroscopic precession effects that such engines would create at high power output settings and low forward speed. The end result was a powerful plane that was easier to run up to full power without having to stomp on a rudder pedal to prevent the plane from sharply precessing from the powerful torque of a heavy paddle-bladed prop turning the bird into the direction of prop rotation. Purpose-built twins like the Lockheed P-38 had counter-rotating props so that loss of an engine on take-off would not make the plane uncontrollable. Every time I take off in the Cessna 172s that I fly, this is something I have to initially counter-act when starting my takeoff roll by using rudder deflection. The more powerful the engine and/or the heavier the prop, the worse the effect becomes. It's noticeable but still relatively mild in a 172. When flying a much lighter Cub tail dragger with the same engine power (same 180hp Lycoming IO-360 hanging off the nose), and you'd better be ready for it or it will quickly swing the nose around if it's not counter-acted with rudder.
Anyway, I think that's enough different examples of gyroscopic precession. If the concept still isn't understood and accepted, then it's not due to lack of explanation or real world examples being provided.
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For kbd512 .... Thanks for your post about the ship design you're developing.
That post belongs in the "practical" topic.
In this topic, I intend to try to track the progress of the two competing designs as they diverge.
The competition involves achieving the same goals.
The ship you design needs to carry 1000 passengers and 60 crew to Mars from LEO, using whatever technology you consider suitable.
To the best of my knowledge, you have not yet decided what lubricant you intend to employ for your very large slip joint.
In a recent Zoom session (available to all as a link to the saved recording) you explained that a slip joint is used in a crankshaft connection to the piston arm in an internal combustion engine. I then asked what lubricant you would use in space, and if you replied I missed it.
Please compose a post in "Practical" topic and show what lubricant you think would work in space.
You have indicated you might depart from the gravity prescription of Large Ship. That is fine, as long as your design covers the Mars equivalent gravity and 20 second rotation of Large Ship.
If your design fails to meet that requirement, then this is not a competition.
RobertDyck is committed to his Unitary Rotation concept, and I would like to see that work.
He avoids the serious and possibly fatal slip joint problem you must solve, and accepts the gyroscopic instability challenge you've identified.
Each of you need to start producing drawings that can pass muster with professional engineers.
We have been issuing reams of text in this forum for 20+ years. It is past time to start producing real-world results.
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I was a preschool child during the space race of the 1960s. I had hoped when I grew up I could be an aerospace engineer. I wanted to design the spacecraft for the first human mission to Mars. Looks like I'm too late for that, SpaceX Starship will get there first. But the Large Ship project was started as an alternative to the next thing after Starship, something 8 times as large.
My ideal would be to start with something about the size of Mars Direct. Instead of 4 crew, it's not hard to modify for 6. MDRS has 6 bunks. I designed a Moon mission that uses 2 Falcon Heavy rockets for the first mission, one for each subsequent mission. It would require an additional upper stage but otherwise no modification to Falcon Heavy. But Elon wants to focus on Starship because it drives cost down so dramatically. Ok. Mars Direct can be sent with two launches of Starship. The second for either on-orbit refuelling or just to deliver the fully fuelled TMI stage. Could be done with one launch if the vehicle is small enough, but I don't think you would want it that small.
Overall I would like to see a crew of 12 build the first base. Then build habitation and life support for 100 before Starship shows up with 100 settlers. Then they build for 1,000 before the Large Ship arrives with 1,000 more settlers. You could add an intermediate of 12 more settlers after the first 12. If a Mars Direct hab accommodates 6 then just send two.
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tahanson43206,
If the ship carries 999 colonists and 61 crew members, is it no longer relevant to affordable transport to Mars? Arbitrary allocations of labor are not terribly useful. In my design concept, the colonists are also considered part of the crew, not luxury liner passengers being catered to by a comparatively tiny ship's company. Inclusivity is based upon being part of a team. If anything untoward happens, there can be none of this "it's not my job" silliness. Everybody has a vested interest in their own survival, which means thinking and acting as a team to do their utmost to assure their collective and individual survival. That is truly the essence of what the Navy teaches you, and something that civilians seem to not to know or respect, possibly because so few of them have been forced into "life-and-death" survival situations. The enemy doesn't particularly know or care if you're the ship's Captain or the ship's cook, they'll send you all to Davy Jones' locker just the same. Similarly, a hard vacuum does not "care" that it's "not your job" to evacuate the injured and repair your ship's hull. Vacuum does what it does to the human body, and nature is both unconcerned and totally oblivious to what you think your job should be. Humans, on the other hand, should care about what happens to their fellow humans and act accordingly. Giving everyone a job to do is an important aspect of teamwork, building trust, and fostering devotion to duty.
The lubricant for the slip joints will be a synthetic oil with good lubricity over a wide temperature range. There are literally hundreds of different gear oil type lubricants that would work. Heat can be applied to the joint prior to starting rotation, if need be.
I'm focused on supplying 1g, not 0.38g, because humans function best in 1g, according to all experimentation done to date. I never claimed that this was a competitor design, so if you feel that invalidates competition, that's fine, since competition was never one of my objectives.
This design concept's "serious and possibly fatal" slip joint problem is replaced with a "seriously baked-in" problem with propulsion and attitude control of a precessing spinning top that weighs thousands of tons (a ship that's constantly doing 360s in space). If you think that's not "serious and possibly fatal", then you might want to review the after-action assessment of the near-disaster associated with the Agena docking target artificial gravity experiments conducted during the Gemini Program. Despite that, I would also like to see Robert's "spinning top" design work. Everything is a trade-off, including these design features.
I seriously doubt that either of us will be able to produce "drawings that pass muster with professional engineers". To do that, we'd need a serious CAD tool like ANSYS that could determine whether or not our proposed designs account for all the forces they'll be subjected to, from launch to end-of-life operations, along with any transient events such as the extreme heating of aerobraking, if Robert is still insisting on slowing the ship by using that method of orbital insertion, which seems impractical given what we know about Mars' atmospheric variability and the gas temperatures that the ship will be subjected to at entry speeds of 7km/s+.
I have access to Dassault's CATIA through EAA, which is up to the design task in some respects- certainly not all, but since I am not a professional aerospace engineer and don't play one on TV (I guess there's not enough drama in structural analysis), I'm going to elect to use a different CAD tool that I think is sufficient for the task of illustrating the basic design concept and freely available. CATIA was used by Lockheed-Martin to help design the F-35, by Boeing to help design the 787 Dreamliner, and by Airbus to help design the A350, for example. As part of EAA, you can use Dassault's software for non-commercial purposes, which they have generously provided free of charge for aspiring aerospace engineers. I seem to have misplaced my team of aerospace engineers, along with all my electrical engineers, so I'm electing to use something that's a little simpler to work with. The analysis won't be quite as comprehensive, not that it ever could be if I was the sole person working on it, but this is just for funsies. It will ultimately go nowhere unless championed by private industry, much like the rest of our manned space program. If a real aerospace engineering outfit picks up my design concept, then they can spend the big bucks to hire the appropriate engineering staff to perform a comprehensive design analysis.
What different products would we need for an actual analysis (probably best done with ANSYS)?:
1. Structural strength and fatigue analyses (I could feasibly do this for a rigid structure made from a homogeneous material like a specific steel alloy, but don't know enough about flexible structures made from fabrics to know how applicable my results would be to a real world use case)
2. Thermal analysis (Josh would be a far better candidate for this type of work- I never learned the first thing about this in college, and then became interested after he changed my mind on global warming- IIRC, it took me a couple of months to work through the basic math to prove to myself that the effect was real through book learning and running numbers using simple models, which is why I stopped responding until I could do enough homework to recognize my error)
3. Vibration analysis (This is highly specialized work that requires a dedicated engineer, as well as real world testing in most cases to confirm that the computer simulation is accurate- singular components like crankshafts are subjected to rigorous analysis and testing for things like torsional vibration to assure that a destructive standing wave is not produced at the part's resonant frequency, and that appropriate dampening or tuning is applied to prevent said part from coming apart)
A Beginner's Guide to Torsional Vibration Analysis
Torsional Vibrations - a (twisted) Overview
Since my design concept requires electric motors to counter-rotate habitation rings, it requires a torsional vibration analysis. I won't be able to do this myself. I simply lack the knowledge required, which is why I reached out to a real aerospace structural design engineer for help with my personal aircraft design, which requires the use of a propeller shaft.
4. Impact analysis (Accurate analysis of the effects on layered fabrics is also very specialized work)
5. Radiation materials degradation and activation analyses (I can't begin to do this, though maybe Calliban or Antius could)
6. Design optimization analysis (to go through successive iterations of design permutations to optimize mass or other design characteristics; this would have to be a team effort because even if the entire model was parameterized, someone would have to do comparative analysis and then accept or reject those optimizations based upon their own experience / judgement of suitability for meeting minimum design criteria)
The notion that one person can do all of that over any reasonable time frame is, to be perfectly frank, a little absurd. From my attempt at designing my own airplane, I can personally attest to the difficulty of accounting for all of the design factors associated with that endeavor. I only know what I've learned, which isn't much. The more I learn, the more I realize there is to know, and the less confident I am in simply asserting that something will work as originally envisioned, without considerable design effort and realistic testing. There are gaps in my entirely self-taught engineering knowledge that you could drive a fleet of semi-trucks through. As I said before, the more I learn, the more there seems to be to know before stating with some confidence that a specific design will work acceptably well.
Yes, I agree that it's time to start producing real-world results. Now, we seemed to have misplaced our full time engineering staff, the tens of millions of dollars to pay them and purchase the computer assets for their use, the hundreds of millions to produce flight-quality hardware, and the billions for launch contracts... That's where all this talk about "real-world results" inevitably ends. It takes real money and real engineering effort. NASA seems to be supremely adept at consuming billions of tax dollars, doing whatever they do with it, but they've yet to produce any real-world results as it relates to beyond-LEO manned space exploration, at least within my lifetime (more than 40 years). They have a standing army of engineers working for them, every computer software and test apparatus known to man, and the industrial capabilities of the entirety of America's Military Industrial Complex. We keep funding them, so you might want to direct any questions to them, regarding why we've yet to produce any usable "real-world results".
If you think a couple of guys posting on the internet will accomplish what they've failed to do, with zero real-world spacecraft design experience, or money, then I happen to have a bridge in Brooklyn that I'd be willing to sell to you for a great price. All talk is quite cheap. Real engineering costs a small fortune, hence the admonishment that if you want to make a small fortune designing and building aircraft, then you should start with a large fortune.
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I am getting a clearer understanding of where this thread topic is heading, and it's a very constructive direction. My contribution has been something else--trying to facilitate the first "baby steps," so to speak. Trying to get there (Mars!) in one massive step is a commendable concept, but I'm a conservative and cautious planner. I would like to see some groundwork for landing and building ISRU facilities before making a high stakes throw of the dice, gambling on everything working all at one time.
The previously proposed--and subsequently cancelled--Red Dragon missions were not ambitious enough, but the concept is still viable on an enlarged scale, large enough to incorporate a decent sized nuclear reactor in one, and a rotary drilling rig in a second vehicle. These could be sent to a proposed first base camp landing zone to have immediately available power and some concept of whether or not any useable subsurface ice is at hand. I'm also a believer that solid experimental/exploratory data is necessary before landing Starships ANYWHERE other than back here on Earth or on the Lunar surface.
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For Oldfart1939 re #12
Your post offers hope that this topic might be headed somewhere....
I created this topic to try to encourage creative thinking by NewMars members, and to allow distinctly different design ideas to blossom on their own.
We've had a specific design idea under development for two years.
Introducing the Zoom meetings caused the pace of progress to accelerate, but it also revealed differences of opinion that I felt were counterproductive.
By separating the designs, I am hoping to encourage creative thinking by more than just the two present leaders.
The original Large Ship design is for a Unitary Rotating structure.
A competitive design will (if continued) feature counter-rotating habitats.
I am setting up the competition so that the two vessels will serve the same population.
What I want to see is continued, steady, resolute, implacable, reliable progress by the Large Ship initiative, while the competitive design goes through initial wild swings all over the compass in seeking its bearings.
I am of the opinion that RobertDyck has the steady, solid temperament to lead a development effort that will eventually employ thousands of people on a global enterprise.
We have already seen significant creative thinking by members of this forum who support the Large Ship vision, and who want to see it succeed.
For Oldfart1939 .... your vision of where this topic might go would be of interest to me, and perhaps to other forum members.
Thanks again for contrubuting.
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Getting with the kbd512 counterotational gravity plan, I would again suggest something I mentioned earlier in a post that I haven't looked for, but there should towards the end of the voyage to Mars--be a slow decrease on the gravity could be implemented so that once there, the astronauts would be accustomed to the exact gravity of the planet. It could also work in reverse, and on a return trip start at Mars gravity and over the 5-6 month return, restore a full 1 g onboard.
Last edited by Oldfart1939 (2022-01-12 10:31:06)
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Oldfart1939,
Since electric motors supply the artificial gravity to the counter-rotating habitation rings, rather than a spinning or tumbling motion of the entire ship, adjustment of the rotational rate of the habitation rings is a matter of supplying more or less electrical power to those motors. I suppose it could be done, if it proves useful. We still don't know what health effects 0.38g has on the human body, but could experiment with various different gravitational acceleration values until we discover the lowest gravitational acceleration value that does not result in unacceptable loss of muscle mass and bone demineralization.
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kbd512,
I've proposed launching the Centrifuge Accommodation Module to ISS. That module was completed, and intended to produce the data to answer that question. What are the effects of partial gravity? We have lots of data in Earth gravity. We now have lots of data in zero gravity. Data from Apollo on effects of lunar gravity is too small and "contaminated". Astronauts experienced high acceleration at launch, zero gravity in transit, moderate acceleration when landing, then Moon gravity. The moderate acceleration when lifting off from the Moon, zero gravity in transit, then high acceleration when re-entering Earth's atmosphere. So the data on effects of Moon gravity are contaminated, useless. We need that module for ISS to answer that question.
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Robert,
I would like to see them fly that experiment as well, but NASA is worried about a centrifuge module "contaminating" their zero-g lab environment. Unless someone at the top directs them to do it, it's never going to happen. Even then, I have a feeling that all of the engineers involved will drag their feet to slow the program's progress or derail it entirely by driving up the cost to something that Congress ultimately pulls the plug on. NASA's inflatable habitat development program had its funding plug pulled by Congress because it provided a practical means of sending humans back to the moon and onto Mars. Bigelow Aerospace picked up development, but he's simply not "rich enough" to dump money into development without a single contract for an operational module. BEAM was a science experiment, nothing more.
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This topic is set up to produce results.
OF1939 ... your contribution (as I see it) is to encourage the contestants to deliver variable gravity.
kbd512 ... your design lends itself to the variable gravity request of OF1939.
RobertDyck ... your design is (to the best of my understanding) fixed at Mars gravity
Both approaches are important and worth developing.
kbd512, you have NOT solved the rotation at a slip joint problem.
Please return to the "Practical" topic and show a solution. Vague promises of abundant lubricants to choose from don't cut it with me. I'm looking for exact specifications and for a plan to test your theory in space.
RobertDyck ... kbd512 keeps complaining about your tumbling problem. Please focus on that and post a solution in the "Large Ship" topic.
For both contestants ... please avoid commenting upon the work of the other.
If you think something should be done better, put it into your topic and ask for feedback from the forum.
RobertDyck .... you have a deadline and I see no evidence you are taking it seriously.
I have tried to create a framework for you to use to prepare for March 12th.
You have received substantial assistance from GW Johnson for Atmosphere and for propulsion of Large Ship.
These inputs need to be integrated into your plan and made part of the presentation.
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For the counter-rotating design, the atmosphere seal at the rotating joint is of concern. There are two possibilities to design: (1) a labyrinthine seal, using some appropriate thick lubricant, and (2) a wiper gasket seal. Or some of both. The labyrinthine approach has two problems to address: (1) leakage rates, which are larger the higher the atmospheric pressure within, and (2) friction, which has to be continuously countered with the electric drive motors.
The wiper gasket seal primarily risks friction damage to the seal, requiring replacement, which in turn very likely requires stopping the rotation. The big bugaboo there is how do you counter the massive leak while you are removing and replacing the wiper seal? Carried to an extreme, the wiper seal becomes the gland seal used on rotating shafts, such as the propeller shafts on ships and submarines. A long-life gland seal is possible, but the friction it generates is very high, and removing friction heat can become a problem without a supply of cooling water ( the ocean).
There have to be ways around these troubles, but I am not the real expert in this area.
Artificial gravity applies to both designs. I second Oldfart1939's recommendation of variable gravity, by varying spin rates. You need sufficient size to reach 1 gee without disrupting the inner ear at speeds very much over 4 rpm. Why 1 gee? For the returning passengers going back to Earth. They need to arrive healthy enough to tolerate 1 gee, and the 2-4 gees of entry deceleration and landing. The best way to do that is just supply 1 gee during at least the last part the transit. Simple as that.
One would think supplying 0.38 gee during the outbound transit to Mars would be OK, since that is what they have to tolerate when they get there. The only downside is tolerating entry deceleration and landing gees once they arrive. Tolerating 2 to 4 peak gees seems mild enough to we who are 1-gee acclimatized and evolved. That might not be as true for someone acclimatized to only 0.38 gee. We do not know that answer. Nobody yet does. Just something to think about.
I have added a worksheet to the "big ship stuff" spreadsheet that takes on tug-assisted departures and arrivals at Earth and Mars. I used an elongated ellipse orbit for the tug with a periapsis speed just under escape. That makes recovery and reuse far easier and more timely. It still lets the tug shoulder the majority of the delta-vee requirements to get the ship onto the interplanetary trajectory. What I found indicates the total propellant required of the ship plus the tugs is less than the total propellant required if the ship does all the delta-vee itself.
But, it is not enough to make a two-way journey practical with chemical propulsion. It still falls in the 3-4 tons propellant per ton of dead-head payload range, for a one-way transit. So for 5000 tons of dead head payload, we're still talking 15,000-20,000 tons of propellant to ship up to load the ship and the tugs (if any). At each end of the journey. The solution is definitely high-performing nuclear and/or electric, unless of course you opt for explosion propulsion, which offers the most promise of all the types so far.
I've got both worksheets pretty well debugged and reliable, and I have written a user's manual for it. It's available, if you want it. As is the atmosphere spreadsheet for habitat and suits.
GW
Last edited by GW Johnson (2022-01-12 10:38:40)
GW Johnson
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"There is nothing as expensive as a dead crew, especially one dead from a bad management decision"
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Re: Gravity centrifuge testing. I really don't believe that an onboard centrifuge system is what we need; it should be a smaller, free floating subsidiary satellite of the von Braun "bicycle wheel" design, completely independent of the ISS structurally. It could be entirely robotic but accessible from the ISS via a spacewalk.
When I say "smaller," I simply am referring relative to the ISS proper.
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For OF1939 .... thanks for (what I interpret as) your support of both RobertDyck and kbd512 visions.
You seem to be backing kbd512 because of the counter-rotating habitat rings, but either design would help to retire human ignorance of the effect of gravity on plants and animals in the regime between zero and 1.
There ** seems ** to be some energy floating around in the human population to study artificial gravity at scale in space.
The challenge for anyone seeking to retire the uncertainty in that area is how to enlist sufficient support to yield the funds that are needed.
Mars Society is a global enterprise. There is no need to be restricted by the failings or incapability of any one country.
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th-
Yes, there really needs to be SOME effort expended to study the physiological effects of reduced gravity, and not simply ignoring it and hope the problem will "go away."
This will become a major factor in the long term, because once we inhabit/populate Mars, the call of the unexplored Asteroid belt and outer 2 Galilean moons of Jupiter are beckoning to the explorers in mankind, as well as Ceres.
As an interjected aside here, I would find that Ceres and Callisto are particularly appealing in the next 50 years of outward expansion of mankind from Earth. Ganymede would be more appealing were it not still somewhat in the Jupiter version of the Van Allen belts. It would be possible to survive there by limiting the time spent outside of a radiation sheltered environment to just a few hours per day and per week.
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tahanson43206,
Hydraulic fluid bearing technology has been in common use for more than a century. All those propellers you see on large ocean-going ships, all those gas turbines, spinning away, day after day... Those are real life examples of fluid bearings that have very high working loads placed upon them. If they didn't work, then cruise and cargo ships / gas turbine engines / flywheel energy storage would be impossible and the electric motor or internal combustion engine in your car wouldn't last for more than a few days using ball or roller bearings, at mere 2,500rpm. That's why all modern engines use hydraulic fluid bearings.
SKF Hydraulic nuts for marine applications
Locate the product labeled "OKTC 790" on the product sheet provided in the link above. Note that the bearing / hydraulic nut is designed to withstand a maximum force of 20,100kN (approximately 14.8 million foot-pounds / 7,412.5 standard tons of force). It's outer diameter is 820mm to 840mm in diameter and the bearing nut weighs 402kg / 886lbs. The entire mass of the habitation rings, consumables, and passengers is below 1,000t, split between two habitation rings with a pair of bearings much larger and therefore considerably greater bearing surface area than the "OKTC 790" bearing unit. There's two of them per habitation ring module. It's being accelerated radially outwards at 1g, so it can generate a maximum of 500t of force. Ignoring the acceleration loads from propulsion, which will never produce an additional 1g of force, and the asymmetric thrust loads placed upon the bearing due to imbalances within the habitation rings, we're below the maximum working load of a much smaller bearing surface area than the one I intend to use, by a factor of 14.8.
Q: Will we use this hydraulic nut design?
A: No. It's illustrative of how much force can be generated, thus counter-acted.
Q: Will we operate the bearing at 70mpa / 10,152.6psi?
A: No, because we don't need to. The bearing surface area will be considerably greater, so that we don't need such high working pressures to generate the force required to counteract the radial loads or asymmetric loads created by mass imbalances within the habitation rings.
Q: Will we use the exact hydraulic bearing geometry from the product shown above?
A: No. We will use a larger bearing surface area to better absorb asymmetric thrust loads generated by mass imbalances within the habitation rings.
Q: Do we need any "new technology" to make this work?
A: As near as I can tell, no, we don't.
Q: Are there some special considerations for the fluid selected, to include fire safety, toxicity, operating temperature range, fluid service life?
A: Yes. The deep space environment presents some unique but surmountable challenges. Cold is a particular problem for hydraulic fluid, but since this is attached to a ship, we can use heat to raise the temperature of the fluid as required. I would probably use a Silicone-based fluid because corrosion will not be an issue and such fluids have the highest flashpoints, and they're very chemically inert. You can technically eat some types, but nobody should be doing that.
Simple mineral oil hydraulic fluid is good for at least 5,000psi before it starts breaking down and fails to provide adequate lubrication, so I'm reasonably sure that mineral oil hydraulic fluid will get the job done, though a higher viscosity gear oil might work better, at the expense of a higher electric motor drive power to overcome the shear characteristics of a higher viscosity fluid.
Plain old mineral oil hydraulic fluid:
MultiTherm - Food Grade Mineral Oil MultiTherm PG-1®
Don't like mineral oil? Worried about environmental contamination? There are synthetics available as well:
Chevron - CLARITY® SYNTHETIC HYDRAULIC OIL AW
What about operation at cryogenic temperatures? Someone makes a product for that, too (-110F to 300F):
Superior Industries - Cryogenic Hydraulic Oil SCH-60
Gear oil for operation at cryogenic temperatures (-87F to 265F):
Synthetic Cryogenic Gear Oil SCO-808
Since this will be used in conjunction with electric motors, how about a Silicone-based fluid for a higher flashpoint, superb dielectric strength, low toxicity, superb oxidation resistance (not that we'll encounter much O2), and very long service life, for considerably more money?:
Super Lube Silicone Hydraulic Oil
The industrial pumps that these hydraulic fluids and gear oils would typically be pressurized with, routinely achieve 2,000psi to 6,000psi, but we're going to strive for lowest practical working pressures and larger bearing surface areas, within reason.
Some of these lubricants are non-toxic / food grade products, while others are not. As I said, there are literally hundreds of different products to choose from that could reasonably work well enough to do the job, and most classes of lubricants have minor variations in the additives package, using a substantially similar base stock derived from oil or methane. The base stock used by different brands frequently comes from the same refinery, which means the manufacturer's additives package is the "secret sauce". If you've ever eaten processed food, then a small quantity of food grade hydraulic fluid from the machinery in the food processing plant was inevitably included in your meal.
I would personally use something like Super Lube, because it's toxicity is pretty low, you have to get it hotter than we would for thermal breakdown to occur, fire safety is about as good as we can do relative to the other options, it stores very well, and it can still be used at relatively low temperatures. We may have to apply heat prior to startup to ensure it's liquid / at the correct viscosity, but getting it colder is not going to hurt the fluid. NASA already uses Silicone-based lubricants in rotating machinery aboard ISS.
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GW,
I suppose you could create another engineering problem to solve, or you simply have 2 totally separate rotating torus / "bicycle wheel" (as Oldfart1939 called them) habitat modules. If you need to transfer people between the two rings, which I envisioned as separate self-contained pressure vessels, then you spin-down both habitation rings and extend a very short inflatable airlock between the two, then transfer people between the two habitation rings. This would not normally be done in-transit, except to assist with mass casualties. The level of compartmentalization and massively redundant life support systems would, at least in theory, help to limit the severity of such events.
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The demands of both projects for a large mass ship that is assembled or built on orbit really are not a competition but a fleshing out of what makes them different in not only features but on staffing principles of operation.
For the AG answer we do not need such a large piece of equipment created but it does need to be independent of the ISS which makes creation of another space station the realistic answer.
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