New Mars Forums

Official discussion forum of The Mars Society and MarsNews.com

You are not logged in.

Announcement

Announcement: As a reader of NewMars forum, we have opportunities for you to assist with technical discussions in several initiatives underway. NewMars needs volunteers with appropriate education, skills, talent, motivation and generosity of spirit as a highly valued member. Write to newmarsmember * gmail.com to tell us about your ability's to help contribute to NewMars and become a registered member.

#51 2020-08-08 17:18:02

tahanson43206
Moderator
Registered: 2018-04-27
Posts: 12,008

Re: Why we need fast flights to Mars.

For RobertDyck re #50

Thanks for finding and showing the work by

Physics Videos by Eugene Khutoryansky
687K subscribers
How the angular momentum vector is affected by torque, and why this results in gyroscopic precession and for the operation of gyroscopes used for navigation.

The animation in that piece is superb!  The structure, pacing and narration are first rate!

While I appreciate your description of thruster action to change the axis of rotation of a ship with a rotating form, I think you have anticipated the objection that might occur, by suggesting momentum wheels as an alternative, but it would appear that method would be limited in impact since saturation seems likely (to me at least) if the momentum wheels are small compared to the vehicle.

The sequence with the helicopter may provide a hint of an answer, but I don't know how well it would translate to the real universe of a 1000 passenger transport.

The three axis of rotation allowed by the gimbals in the gyroscope frame allow force to be applied to the system without disturbing the rotating object.

As I understand Dr. O'Neill's intent for the counter rotating habitat cylinders, the goal is to achieve pointing without expending any mass at all.

If you (or kbd512) can design the habitat section so that it is free to maintain its axis of rotation independent of the needs of the ship itself, then thrust can be applied for major trajectory adjustment without having to worry about the habitat module.

Thanks again for finding and showing this first rate instructional material!

(th)

Offline

#52 2020-08-08 18:05:44

RobertDyck
Moderator
From: Winnipeg, Canada
Registered: 2002-08-20
Posts: 7,343
Website

Re: Why we need fast flights to Mars.

Actually, I already see an issue. Angular momentum of the ring of a 1000 passenger ship is very large. If you work out the angular momentum vectors, it takes a great deal of force to move. With two counter rotating rings, the angular momentum vector of one ring is one direction, the other ring is the opposite. Result is they cancel out. This leaves you with simple mass of the ship. Firing thrusters will not turn the vehicle 90° to the thrust, because one ring would cause the thrust to apply 90° ahead while the other ring 90° behind. So again, firing thrusters with a two counter rotating rings would apply just like a spacecraft that isn't spinning.

So now we have fundamental design decisions. Do you use two counter rotating rings with all the potential problems: pressure leaks, friction, movement between counter rotating sections? Or do you use momentum wheels (reaction wheels) with enough force to move a ship this big? If momentum wheels can move the ship, then turning in one direction to fire the main engine would saturate the wheels, but turning back would desaturate the wheels.

Offline

#53 2020-08-08 18:29:08

tahanson43206
Moderator
Registered: 2018-04-27
Posts: 12,008

Re: Why we need fast flights to Mars.

For RobertDyck re #52 and gyroscopes in general

Thanks for giving the matter more attention ....

While you were doing that, I was visiting Thingiverse to see what they might have in ready-to-print gyroscopes.  There were a number of offerings.  I have chosen the two which seemed closest to the example given in the Physics animation.

1c0ab0c13e5087199db0f92d17627518_preview_card.jpg

The example above is interesting because of its professional appearance (a) and (b) the similarity of the rotor to what a passenger section might look like.

The version below was marked as a 'toy gyroscope".  I included it because it appears to be a bit simpler to print and assemble.

IMG_20120401_235333_display_large_preview_card.jpg

A distinct advantage of the gyroscope design is the fact the disk can be set spinning so the axis is lined up with that of the Solar System, and thus the edge of the habitat module will always be pointing toward the Sun.  When the ship outside the disk is not performing thrust maneuvers, it can be positioned so that the bulk of it lies between the Sun and the spinning habitat.

***
I note your review of the counter rotating design advantages.

The gyroscope design has ** really ** caught my attention at this point.

In ** that ** design, the habitat module can be spun up and sealed for the trip to Mars, and trips "outside" would only be needed in an emergency.

(th)

Last edited by tahanson43206 (2020-08-08 18:38:21)

Offline

#54 2020-08-08 18:33:35

SpaceNut
Administrator
From: New Hampshire
Registered: 2004-07-22
Posts: 26,753

Re: Why we need fast flights to Mars.

Reaction motors on the ISS are used quite often to save on thruster fuels.

Offline

#55 2020-08-08 18:59:48

tahanson43206
Moderator
Registered: 2018-04-27
Posts: 12,008

Re: Why we need fast flights to Mars.

For SpaceNut re #54 ...

Thanks for the reminder of momentum wheel use on the ISS ... I found a lengthy discussion on Stack Exchange ...

https://space.stackexchange.com/questio … ment-gyros

In the case of the ISS, the drag of the atmosphere is a factor that would not apply to a Mars bound passenger vessel, but apparently it is not a significant factor. What seems to be the main driver of need for station orientation changes is arriving visiting space craft, and (I gather) the docking requirements, which would require a station that holds position for an extended period, while the approaching vessel eases forward.

The discussion includes speculation on the frequency of expenditure of fuel to desaturate the wheels.  No doubt NASA has precise numbers somewhere.

One impression I came away with is that management of station momentum must be a full time job of at least one NASA employee, and perhaps more.

(th)

Offline

#56 2020-08-08 20:37:04

kbd512
Administrator
Registered: 2015-01-02
Posts: 6,228

Re: Why we need fast flights to Mars.

tahanson43206,

The mass wheels failed because they were using steel ball bearings.  During extreme space weather events, you basically had "spot welding" going on between the steel ball bearings and bearing cages.  If the bearings were ceramic, no "spot welding" occurred.  In any event, if you "spin down" the gravity wheels during thrusting or docking maneuvers, then you don't have to concern yourself with the effect of the counter-rotating masses on those maneuvers.

The design I selected, which is not "my design", strictly speaking, uses adequate structural mass to provide passive shielding against CME or SPE, as well as the ability to absorb minor MMOD impacts by not flying to / from Mars at insane speeds.  To supplement the passive shielding, it also electromagnetically inflates an electrostatic / charged particle "bubble" around the ship to deflect protons and most light ion GCR.  The fusion drive and electromagnetic / electrostatic bubble are both work products of NASA and MSNW LLC.  The Sr90 direct thermal SCO2 RTG is a work product of US DOE and various contractors.

This space-based frigate design would not precisely resemble the Star Trek "Stingray" concept artwork stand-in, though it would be substantially similar in appearance.  There's no "main deflector dish" in my design, for example, and the engineering section of the hull would be shaped with aerodynamics as one of the design criteria.  If I was purely interested in an in-space-only design, then it would consist of a pair of counter-rotating wheels with a spherical or cylindrical center section for the power / propulsion systems and cargo.  We could certainly go that way with the design and that would optimize the structural mass to put more space background radiation shielding mass where it's needed most, but then it would have to be assembled in space, rather than being fitted out in space, and a special shadow shielding arrangement devised to deal with the neutron radiation from the fusion drive.  Keeping distance and shadow shielding mass in the form of thick metal fuel tanks and hull sections between the crew and the fusion engines was another benefit of the Stingray design.  I didn't have to work out a separate shielding arrangement for the crew, as with the "counter-rotating steering wheels connected to a beach ball" design.

If the people want the in-space-only mass-optimized design vs the Star Trek starship design, then I say we give them what they want.  There's benefits to both designs.  I'm somewhat ambivalent about the final design.  I don't know what the "best" solution "looks like".  I do know that Star Trek ships catch the attention of young people.  A weird-looking counter-rotating steering wheels / beach ball designs probably won't.

Recall that I said the ship would be approximately half the size of the Stingray concept ship.  A ship of that size is just big enough to squeeze in a pair of counter-rotating gravity wheels in the saucer section with the minimum diameter required to comfortably deliver 1g at 4rpm.  By calculating the internal volume of the design, it also happened to meet NASA's standards for volume per crew member for long duration space flight for 250 crew.  Therefore, that was the design criteria that set minimum size for the ship and acceptable head count.  There's still plenty of internal volume for the rest of the ship's systems and outsized cargo in the engineering section of the hull.

Offline

#57 2020-08-09 06:14:00

tahanson43206
Moderator
Registered: 2018-04-27
Posts: 12,008

Re: Why we need fast flights to Mars.

For kbd512 re Post#56

Thank you for insight into bearing failure in space momentum wheel designs.

SearchTerm:FailureOfBearingsInSpace  http://newmars.com/forums/viewtopic.php … 09#p170909

The designs you've selected and combined into your version seem worth developing further.

***
In continued reply to RobertDyck about the gyroscope concept that was revealed by the Physics video in your recent post ...

I thought about the design overnight, and realized that only one frame is required for a deep space vehicle, instead of the three frames that are required for a gyroscope orientation reference in a vehicle. 

In fact, in Space, only one half of a circle is required.

I'll try to make a sketch that shows what this would look like.

In words, the spinning habitat would be pinned at both ends of the axle by bearing housings capable of transferring force between the external ship (propulsion, fuel, storage, navigation, communication, etc) and the spinning habitat.

In this concept, the habitat would never stop spinning throughout a voyage, regardless of the number of thrust maneuvers that might be required.

The propulsion unit would be able to crawl up or down the arch of the half ring to position itself where needed to provide thrust in the desired vector.

Furthermore, the propulsion unit would translate around the spinning habitat so it is in the plane where thrust is to be applied.

As suggested in earlier posts, when the propulsion unit is not performing thrust maneuvers, it can move itself to a position between the habitat and the Sun, to provide additional shielding for the habitat.

It is even possible to imagine swapping out the propulsion unit for a newer one, if the system is designed to allow it.

Thus, the habitat would be buttoned up for the trip to Mars, and there would be no load on the bearings except during thrust events.

kbd512 ... I realize it may not be practical for you to make a sketch of your vision, but if you run across a link to artwork that is similar, it would surely be of interest to NewMars readers.

Edit#1: After re-reading the description above, I realized that if the propulsion unit takes up a position between the Sun and the spinning habitat, the bearings at the tips of the habitat axle would have to deal with rotation, even though there is no force being applied between thrust events.  Thus, a small investment of energy would be needed to maintain the position of the propulsion unit, but it is possible to imagine an electric (magnetic) solution to this problem, which would allow precious mass to be saved for trajectory changes.

Edit#2: There is a slide show at the Thingiverse shop at the link below.  The "wishbone" shape is at the right in the display.

It is that shape I am imagining as the link between the rotating habitat and the propulsion unit.

https://www.thingiverse.com/thing:1545662

Edit#3: ThingiVerse is a share ware Open Source environment.  I downloaded the plans for the gyroscope, as shown at the link above.

Gyroscope (https://www.thingiverse.com/thing:1545662) by ArtiBoyut is licensed under the Creative Commons - Attribution license.
http://creativecommons.org/licenses/by/3.0/

I'm thinking of using the rotor and the outermost yoke, to try to make an image to illustrate what an interplanetary ship based upon the gyroscope model might look like.

Edit#4: In recognition of the hard work invested in the gyroscope design which I've downloaded, for an Interplanetary Ship model, here is a credit:

Gyroscope by ArtiBoyut
Published on May 6, 2016
www.thingiverse.com/thing:1545662

(th)

Last edited by tahanson43206 (2020-08-09 10:07:17)

Offline

#58 2020-08-09 12:33:35

tahanson43206
Moderator
Registered: 2018-04-27
Posts: 12,008

Re: Why we need fast flights to Mars.

This is a follow up to Post#57

The gyroscope sample from the ArtiBoyut group on Thingiverse turned out to be relatively amenable to the new purpose I have in mind. 

Here is an image that shows the four components from the original model that can be adapted for an Interplanetary Passenger Transport.

The idea that stimulated this study was kbd512's vision of counter rotating habitat modules in a Startrek Enterprise (like) form.  However, it was RobertDyck's investigation of gyroscopes that led to the insight that an interplanetary vessel only needs one yoke to deliver thrust to a rotating mass, in the environment of free space.

sJLYLoz.png

Please note: The original model has text on the exterior of the habitat module.  I don't know what that text is, at this point, but think it may be the identification of a university where the model was created.

Edit#1: The view of the Interplanetary Transport shown above is from the perspective of the navigator in the propulsion section.  The navigator can rotate the propulsion unit around the axis of rotation, and slide the propulsion module left or right along the yoke framework, to insure that thrust is delivered as needed. The thrust will be transferred to the rotating habitat via the roller bearings in the intersection of the yoke and the axle.

A detail that came to me as the model came together, is that entrance to or egress from the habitat module is possible during flight, via ports in the axle.

The location for ports that makes the most sense to me is at the ends of the axle.  A small "captain's gig" can exit the propulsion module and "fly" to the docking port on the end of the axle.  Thus, the crew can live in the habitat module but travel to the propulsion module as needed to make physical adjustments. Otherwise, I would expect all control activities to be managed via electronics from the habitat module.

The movie sequence RobertDyck provided from the movie "2001" shows what the docking would look like.

http://newmars.com/forums/viewtopic.php … 57#p170857

In the movie sequence, the ends of the central axle are shown with large openings for arriving ships.  The habitat module under "development" here could be fitted with similar openings, which would serve not only for crew movement to the propulsion section during flight, but for interaction with landing craft at Mars.

It is worth repeating (since not everyone reads every post) ... I am NOT interested in any design for an interplanetary transport that anticipates interaction with an atmosphere.   To my way of thinking, that idea is so dangerous that no sane person (able to make free decisions) would buy a ticket on a vessel so designed.

The concept I am working on here is for a true Interplanetary Transport, able to provide artificial gravity, radiation protection, comfortable lodgings, acceptable meals and related benefits of travel, and plenty of enrichment opportunities while the vehicle is in transit between stations, and while holding at either Mars or the Earth.

Please note that the model shown above does ** not ** include a radiation shield that would be part of the yoke, or details of the propulsion model.

Since this is a Blender model, I am open to suggestions for added features forum contributors might recommend.  While I have limited experience setting up animation, I have a rudimentary understanding of how animation might be provided to show the habitat module rotating, and the propulsion module adjusting position in order to carry out a thrust maneuver.

(th)

Last edited by tahanson43206 (2020-08-09 12:56:10)

Offline

#59 2020-08-09 14:39:15

GW Johnson
Member
From: McGregor, Texas USA
Registered: 2011-12-04
Posts: 4,952
Website

Re: Why we need fast flights to Mars.

If there is no rotating joint.  there need be no leaky seal risk.  That argues very strongly for one-piece designs.

GW


GW Johnson
McGregor,  Texas

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

Offline

#60 2020-08-09 15:42:45

kbd512
Administrator
Registered: 2015-01-02
Posts: 6,228

Re: Why we need fast flights to Mars.

GW,

If there are counter-rotating joints, then we can also put airlocks between them to minimize leakages.  There's no such thing as a "leak-free" design, even with the non-rotating joints of the ISS.  The leakage rate is so low that it's manageable and that's all that need be accomplished for this design to work.  We could have a multitude of Aluminum alloy torus segments bolted or welded together and then put a flexible membrane or liner on the inside that maintains internal pressurization by pressing against a smooth inner torus wall.

Offline

#61 2020-08-09 16:11:37

SpaceNut
Administrator
From: New Hampshire
Registered: 2004-07-22
Posts: 26,753

Re: Why we need fast flights to Mars.

So far man is only building at a 10m diameter such that it means build the assembly on orbit.
That requires hundreds of tons of materials and plenty of flights to build.
When will we start?

Offline

#62 2020-08-09 17:01:23

tahanson43206
Moderator
Registered: 2018-04-27
Posts: 12,008

Re: Why we need fast flights to Mars.

The ship design shown in mockup form in post #58 has ** NO ** seals that can leak at the points of rotation.

The design is evolving (of course) ... the most recent addition was docking ports in the ends of the axle.

Thus, leakage would occur ** only ** when the docking ports are activated.

(th)

Offline

#63 2020-08-09 17:24:09

kbd512
Administrator
Registered: 2015-01-02
Posts: 6,228

Re: Why we need fast flights to Mars.

SpaceNut,

We need SpaceX and NASA to fund and build a fully reusable super heavy lift launch vehicle first.  After that's done, then we'll use Starship to construct true interplanetary transports.  If it were up to me, Starship would be a 15m diameter "fat stack" for comparatively "short" rockets with better stability during landing.

Anyway, a pair of tori 15mm thick, with a major radius of 52.5m and a minor radius of 3m, would weigh 1,172,486kg if they were made from 2219 Aluminum alloy (the same alloy that the ISS modules are made from).  This would be for the "pair of three-spoked counter-rotating steering wheels connected to a beach ball engineering / propulsion section" hull design.  That's just for the gravity wheels, not the spokes, nor anything else inside them, nor the "beach ball" / "engineering section".  At least a dozen Starship cargo flights would be needed to deliver the materials to orbit.  Even if the gravity wheels need to be 25mm thick, which burns through the entire projected dry mass for the ship (1,954,145kg), we can still manage to deliver 1,000t of cargo per flight.

Since Elon Musk is planning on sending 3 BFS to Mars and that would require at least 18 flights, I figure we can build these ships and deliver a hell of a lot more people and cargo at each launch opportunity.  We can deliver at least 10 times as much tonnage, per ship, assuming he intends to launch 3 Starships at every opportunity.

Edit:
The pressurized volume of the pair of spinning wheels would be 18,654m^3 / 658,1744ft^3, equivalent to more than 14 AN-225 cargo holds.  According to NASA, that meets the minimum volume requirement for 746 people.  If we were to compromise and only send 500 people per vehicle, their net habitable volume falls between Salyut and Mir.  We'd have to increase the power and propulsion system mass to do this, but it still looks feasible.

Human Research Program (HRP) - Minimum Acceptable Net Habitable Volume for Long‐Duration Exploration Missions - Subject Matter Expert Consensus Session Report

If we built ten of these ships, it'd still take 200 launch opportunities to send 1,000,000 people to Mars.  However, we could ultimately send 100,000 people in about half a human lifetime.  If 6 nations built 10 ships, then we'd need 33 launch opportunities to send 1,000,000 people.

Using nuclear reactors and larger ships with larger gravity wheels, we could feasibly send 10,000 people per ship.  If Elon Musk is correct about $10/kg, then a 25,000t nuclear powered ship should only cost $250M to launch.  That's basically the cost of a wide-body airliner.  Given its simplicity, each ship might cost $1B to construct.  If we increase NASA's budget by $2B, then we should be able to construct / launch / crew a ship per year.  We could also do crewed missions to Jupiter / Saturn / Uranus / Neptune.  There's little reason not to explore and colonize all of the planets.

Last edited by kbd512 (2020-08-09 22:06:22)

Offline

#64 2020-08-10 06:14:51

Calliban
Member
From: Northern England, UK
Registered: 2019-08-18
Posts: 2,218

Re: Why we need fast flights to Mars.

A prototype non-rotating ship would make establishment of a permanent base on the moon a lot easier.

Whilst a radiothermal or nuclear power source undoubtedly increases the capability of a ship, developing, building and launching such a thing is likely to be an administrative nightmare.  This is why Musk's Mars colonisation plans have come to rely on a solar power source.  Over the past fifty years, it has become all but impossible to develop and build a new nuclear power source in a Western country.  NuScale were founded 20 years ago.  They have yet to produce a single reactor plant.  There have been at least half a dozen similar attempts to develop SMRs since the 1990s.  They have all gone nowhere for reasons that have nothing to do with engineering practicality.  No one can afford the costs and programme delays imposed by the crushing weight of regulation.

In principle, there is no practical reason why we could not build a reactor very quickly.  One of the reasons I was interested in building natural uranium reactors on Mars is that we could actually get on and build things there without the crushing mountain of regulatory BS and red tape.  If we find uranium ores on Mars, then a large ship could be fitted with a graphite moderated, natural uranium, CO2 cooled reactor.

One idea that did occur to me: the fusion drive that you have described will produce a lot of 14MeV leakage neutrons.  Some of these would be absorbed by the lithium and aluminium tamper.  But a large fraction will leak out.  These will produce fast-fission in thorium or depleted uranium without need for breeding, because they exceed the fissile energy thresholds for 238U and 232Th.  Could these be absorbed into a sub-critical assembly (a shell of thorium metal, say) to produce the heat we need to operate the drive?  What I am describing is a fusion-fission hybrid drive.  We configure the drive such that the fusion pellet explosion takes place inside of a uranium or thorium assembly, which will then generate heat when exposed to the leakage neutrons.  The advantage would appear to be that we do not need to lift radioactive material into orbit.  We would operate the drive using solar power until the thorium or DU shell has generated enough heat to start the S-CO2 powerplant.

Last edited by Calliban (2020-08-10 06:47:42)


"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."

Offline

#65 2020-08-10 07:08:57

Calliban
Member
From: Northern England, UK
Registered: 2019-08-18
Posts: 2,218

Re: Why we need fast flights to Mars.

For a hybrid design drive to work, we are essentially relying on leakage neutrons generating enough energy in a fissionable blanket to power the fusion part of the process.  The combined fusion-fission assembly needs to achieve breakeven, as we are using the fissile assembly to generate the power needed to run the fusion microexplosions.

To achieve this, we would need to remove all sources of moderation from the combined assembly, to maintain the hardest neutron spectrum possible within the fissionable assembly.  That means using aluminium in the fusion pellets instead of lithium.  The fissionable assembly should be made from uranium nitride or maybe even solid uranium metal, to provide the highest possible fissionable atom density and minimise moderation.  The entire assembly will be shielded in a tank of molten lithium, which will reflect neutrons back into the assembly and catch any neutrons generated by secondary fission that leak out of the assembly, which will breed fresh tritium for new fuel pellets.  The lithium bath will also contain the heat exchanger for the S-CO2 power generator.

The fissionable assembly would be a spherical ball of sintered uranium metal grains, with a cylindrical hole running through its middle, where the fusion assembly would fit.  The gaps between the grains would be just large enough to allow  fission products to migrate out of the assembly.  This ensures that fission gases cannot build up placing mechanical pressure within the assembly as it burns up.  Experiments on metallic fuel in the integral fast reactor experiments, suggest that metallic fuel pellets maintain structural integrity even as burnups reach 20-30% of heavy metal atoms present.  So the intention is for a single uranium assembly to produce power for the lifetime of the ship.

At end of life, the uranium ball should contain a high percentage of plutonium and heavier actinides.  This would be useful material for Martian built fast reactors.

Initially, with only 238U being present, only fast fission will occur within the assembly.  At this point, fission power will be used in addition to solar power in powering the fusion drive.  As heavier actinides like plutonium, protectionism and americium build up, the number of fission events resulting from each fusion leakage neutron will increase until fission along is capable of powering the process.  Ships that have achieved energy breakeven like this would be able to accelerate more rapidly and would be suitable for missions to destinations further from the sun, where solar power is too weak.  For ships with heavily irradiated cores, radiothermal power should be sufficient to power life support functions even with the fusion drive deactivated and all fission stopped.

Last edited by Calliban (2020-08-10 07:39:11)


"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."

Offline

#66 2020-08-10 07:29:46

RobertDyck
Moderator
From: Winnipeg, Canada
Registered: 2002-08-20
Posts: 7,343
Website

Re: Why we need fast flights to Mars.

Radiation: I suggested orienting the ring so one side always faces the Sun. That means radiation shielding is only required on one side wall of the ring. None on the outer surface (floor) of the ring. None on the inner surface (ceiling) of the ring. None on the dark side of the ring. My ship for 1,000 passenger, ring width 19 metres plus outer wall, but height 2.8 metre (8 feet) ceilings. So this minimizes radiation shield surface area.

Your idea of the half ring mad me think. The main engine can apply thrust to the hub in any direction. It doesn't need a large semicircular ring, it can be close to the hub. In fact, we could have several engines aimed in different directions, but all oriented so the vector of thrust first through centre of ship mass. Simply use differential thrust to for course correction. This doesn't require full thrust, course correction engines can be smaller.

Offline

#67 2020-08-10 07:48:35

RobertDyck
Moderator
From: Winnipeg, Canada
Registered: 2002-08-20
Posts: 7,343
Website

Re: Why we need fast flights to Mars.

Hmm. GCNTR requires a fission reactor at critical mass to operate. Very efficient, but only for one continuous sustained boost, such as TMI. Open cycle GCNTR dumps the entire reactor core at shutdown sit not appropriate for small course correction, especially not for an array of several moderate size engines. I downloaded a paper from NASA's advanced concepts group: microfusion thruster. Magnetic nozzle, and uses more regular hydrogen than fission fuel. It's designed for pulsed operation. I find it ironic than injectors are MPD thrusters. Appropriate for course correction?

Offline

#68 2020-08-10 07:58:56

Calliban
Member
From: Northern England, UK
Registered: 2019-08-18
Posts: 2,218

Re: Why we need fast flights to Mars.

RobertDyck wrote:

Hmm. GCNTR requires a fission reactor at critical mass to operate. Very efficient, but only for one continuous sustained boost, such as TMI. Open cycle GCNTR dumps the entire reactor core at shutdown sit not appropriate for small course correction, especially not for an array of several moderate size engines. I downloaded a paper from NASA's advanced concepts group: microfusion thruster. Magnetic nozzle, and uses more regular hydrogen than fission fuel. It's designed for pulsed operation. I find it ironic than injectors are MPD thrusters. Appropriate for course correction?

This is not a gas core concept.  My idea is to surround the micro-fusion reaction chamber with fissionable blanket material.  That way the neutrons created by the fusion reaction generate fission in the blanket, which can then power the fusion process.  Ultimately, in a mature blanket, each fusion event that takes place in the pellet will generate several fission events in the blanket.  More than enough to power the micro-fusion reaction.  The assembly remains subcritical when fusion stops, but will generate a lot of decay heat which could be used to generate power to support residual ship functions, such as life support, even when the drive is shut down.

The assembly need not vent fission products during operation.  Hence the obvious problems with operating a GCNTR in Earth orbit would not apply.

Last edited by Calliban (2020-08-10 08:05:05)


"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."

Offline

#69 2020-08-10 08:14:27

tahanson43206
Moderator
Registered: 2018-04-27
Posts: 12,008

Re: Why we need fast flights to Mars.

For RobertDyck re #66

Thank you for the reminder of your suggestion of keeping the edge of the habitat aligned with the Solar plane.  I have tried to give credit for ideas I am using, but the members of the forum are occasionally too productive for me to keep up.

While I am closely following developments in your Large Ship topic, and this one, occasionally I may fail to properly acknowledge ideas I am incorporating in my design, so I appreciate the reminder!

My immediate next addition to the Gyroscope Transport is a U shaped form that would extend from the propulsion unit to shield the habitat during non-thrusting flight, which is most of the time.  I'm hoping to find previously posted descriptions of the optimum material for shielding ... my recollection is that material that contains a lot of Hydrogen is favored, and that there are solid materials made from hydrocarbon that are well suited for the application.

A large structure filled with such material would serve as a radiation shield most of the time, but it also represents a stored backup of usable materials (Hydrogen, Carbon, etc) that could be consumed in an emergency.

I'll have to study your idea for propulsion ... could you make a drawing to show what you have in mind?  The word picture that generates images in my mind (or any reader of the forum) may differ from what you are "seeing" in your mind's eye. 

One change I am planning to make as soon as possible is to bring the thrust from the propulsion unit closer to the hub of the axle of the rotating habitat.

An engineering detail for the Gyroscopic Transport is the vulnerability of the bearing traces where thrust is transferred to the rotating habitat, which (I am guessing) would mass 1000 tons for the smallest possible version, and many thousands of tons for larger versions.  Thus, I am anticipating the need for a propulsion system that provides modest thrust for an extended period instead of massive thrust for a short period, which is the existing standard practice.

(th)

Offline

#70 2020-08-10 15:11:40

kbd512
Administrator
Registered: 2015-01-02
Posts: 6,228

Re: Why we need fast flights to Mars.

Calliban,

I presume that this new power / propulsion concept is intended to do away with the requirement for some of the hardware in order to initiate fusion, but also to combine parts of the power and propulsion system?

In the MSNW design, fusion was initiated by a supersonic implosion of the foil liner around the D-T pellet using a bank of super capacitors.  In this concept, if I understand correctly, we're using fission to sustain fusion.

How do we expel the vaporized Aluminum fuel to produce thrust?

Instead of dozens of individual electromagnetic compressors that initiate fusion, does this new concept permit us to design a single "main engine"?

tahanson43206,

I guess the shielding material could be consumed by another process that requires reaction mass or coolant or its own radiation shielding, but it wouldn't be suitable for human consumption if that's what you were thinking.  The radiation shielding materials, in most cases, would need to remain in place.

Offline

#71 2020-08-10 15:17:29

Calliban
Member
From: Northern England, UK
Registered: 2019-08-18
Posts: 2,218

Re: Why we need fast flights to Mars.

kbd512 wrote:

Calliban,

I presume that this new power / propulsion concept is intended to do away with the requirement for some of the hardware in order to initiate fusion, but also to combine parts of the power and propulsion system?

In the MSNW design, fusion was initiated by a supersonic implosion of the foil liner around the D-T pellet using a bank of super capacitors.  In this concept, if I understand correctly, we're using fission to sustain fusion.

How do we expel the vaporized Aluminum fuel to produce thrust?

Instead of dozens of individual electromagnetic compressors that initiate fusion, does this new concept permit us to design a single "main engine"?

tahanson43206,

I guess the shielding material could be consumed by another process that requires reaction mass or coolant or its own radiation shielding, but it wouldn't be suitable for human consumption if that's what you were thinking.  The radiation shielding materials, in most cases, would need to remain in place.

The propulsion concept is exactly the same.  The only difference I foresee is that the magnetic implosion chamber is surrounded by a blanket of 238U.  Neutrons that stream out of the imploding fuel pellet produce fast fission in the blanket.  The idea is that ultimately, neutrons streaming from the imploding fuel pellet cause enough fission events in the blanket to power the fusion drive.  This may take some time, as there would need to be buildup of 239Pu and other actinides in the blanket, in order for each fusion neutron to generate enough downstream fission events to power the drive.  But ultimately, the surrounding fissionable blanket should generate enough power from each pulse to power the next pulse.

Last edited by Calliban (2020-08-10 15:23:39)


"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."

Offline

#72 2020-08-10 18:07:00

kbd512
Administrator
Registered: 2015-01-02
Posts: 6,228

Re: Why we need fast flights to Mars.

Calliban,

Do you have any ballpark estimate on how long this would take, because the thrusting events for minimum energy trajectories would occur over a period of a day or two at most?

Offline

#73 2020-08-11 00:28:50

Calliban
Member
From: Northern England, UK
Registered: 2019-08-18
Posts: 2,218

Re: Why we need fast flights to Mars.

kbd512 wrote:

Calliban,

Do you have any ballpark estimate on how long this would take, because the thrusting events for minimum energy trajectories would occur over a period of a day or two at most?

Not sure.  Fusion is a poor source of energy, but a superb source of neutrons.  Fission is the opposite.

Each fusion reaction will release 17.6MeV, of which 14.1MeV is carried away by the fast neutron and 3.5MeV is carried away by the Helion.  Each fast fission in the blanket will release 180MeV of thermal energy and on average 3 neutrons per fission.  If each of those neutrons cause a transmutation event, then the rate of conversion could be calculated from the fusion rate, I.e 3 actinide atoms created per fusion event.

With a lot of time and effort I could work out what level of transmutation would be required to produce a certain amount of heat output and how many fusion events it would take.  But it would be a project.  Given that fast fission alone will likely yield several times as much energy as the fusion event that initiates it, generating enough power to drive the fusion engine  is unlikely to be a problem.  The neutrons yielded by fission will thermalise very slowly, as it will take a large number of collisions with uranium nuclei to thermalise them.  Most fission neutrons will therefore be absorbed in 238U resonances.  I would estimate that at least 10% of 238U atoms must transmute before power production were to double.  But it would appear that transmutation may not actually be necessary, as fast fission of 238U will generate several times more energy than the initiating fusion event.

Last edited by Calliban (2020-08-11 01:09:28)


"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."

Offline

#74 2020-08-11 07:31:05

tahanson43206
Moderator
Registered: 2018-04-27
Posts: 12,008

Re: Why we need fast flights to Mars.

For kbd512 re minimum energy trajectory ...

In trying to follow this discussion between you and Calliban, I am wondering if what is under discussion is a potential opportunity to develop sustained thrust for an extended period, far in excess of what is possible with ion drives.

In other words, can the limitations of the minimal energy trajectory be set aside, if a propulsion system becomes available to supplement it?

I see no reason why a chemical impulse could not be given to a vehicle with atomic propulsion, and (potentially) enlisted to dock with vehicle with a destination object.

(th)

Offline

#75 2020-08-11 10:08:57

tahanson43206
Moderator
Registered: 2018-04-27
Posts: 12,008

Re: Why we need fast flights to Mars.

For SpaceNut re possible new topic in Interplanetary Transportation topic ...

Here is an updated view of a Gyroscope Interplanetary Transport.

Edit@20:08: I've decided to reconsider the name in light of the similarity of this evolving design to the "Big Wheel" toy.

While the concept is evolving from the concept of a gyroscope, the appearance of the modified "ship" is much more reminiscent of a "Big Wheel" than it is of a Star Trek(tm) design.

This concept arises from ideas posted by RobertDyck and kbd512.

I'd like to invite you to consider setting up a topic for this hybrid concept.  Each of them is hard at work developing their visions.

I'd like to try to catch this moment in the flux of creativity and focus on developing this version of their ongoing work.

YdVeJOS.png

In this version of the Interplanetary Ship Model, I've added a radiation shield that is part of the Propulsion Unit.

As a reminder, and for anyone seeing the model for the first time:

1) kbd512 suggested mounting habitat modules in a form factor that looks similar to the Startrek Enterprise.
2) RobertDyck suggested rotating a habitat edge on to the Sun

This model incorporates those ideas into a system that can be spun up to give passengers artificial gravity during transit to Mars.

In addition, the design incorporates the capability of moving the propulsion unit so that when chemical (or other) thrust is needed, the force can be applied to the bearings between the Yolk Axle and the Habitat, so that the entire assembly is accelerated smoothly in the desired direction, without disturbing the rotation of the habitat.

Finally, this updated version includes a radiation shield that is part of the propulsion unit.  When the propulsion unit is not thrusting, it will be aligned so that the central axis of the propulsion unit is parallel to and aligned with the line between the center of the Sun and the center of the Habitat.

Entrance to and exit from the Habitat would be via ports in the two ends of the Yolk Axle.  There would be no opportunity for leaks at any other location.  The exit ports could be used for crew movements during flight, and for loading and unloading the Habitat at destinations.

Edit#1: Credit for the gyroscope model I am using for this illustration goes to the designers who posted it on Thingiverse.
Specific details are posted earlier in this thread.

Edit#2: My first attempt to add a propulsion module to the base of the propulsion stub was not successful.  Working in Blender, the boolean operations to try to merge a new object into the structure created by the Thingiverse team resulted in massive damage to the model.

One slicer gave a count of 1.5 million errors.  I'll try again, of course.  Extrusion of the base of the existing stub may work.

(th)

Last edited by tahanson43206 (2020-08-11 18:10:39)

Offline

Board footer

Powered by FluxBB