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#51 2019-09-09 07:59:27

GW Johnson
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From: McGregor, Texas USA
Registered: 2011-12-04
Posts: 3,562
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Re: Large scale colonization ship

I added a worksheet for a colony-type ship to Ceres,  as “typical” of the asteroid belt.  The only feasible choices were nuke explosion propulsion and nuke-powered electric propulsion.  It’s the same calculation,  just bigger delta-vees.

The same outcome choices obtain:  your nuke explosion ship is robust,  promising a long service life,  while the ion ship is rather flimsy.  For this application,  the ignition to payload ratio is substantially more favorable for the nuke explosion ship,  vs the ion ship.

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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#52 2019-09-09 08:15:36

tahanson43206
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Registered: 2018-04-27
Posts: 904

Re: Large scale colonization ship

For GW Johnson re #51 and fission propulsion in general ...

Thanks for continuing to develop this concept.  While the United States seems likely to avoid developing this technology, the Russians under Putin (and likely even without his leadership) will most probably have no such hesitation.  I'd rather see them designing and building a nuke powered space vessel than a nuclear powered cruise missile.

Yesterday, inspired by your persistence, I ran a quick Google search looking for Uranium resources in the Solar System.  It would appear that there may be substantial amounts available on the Moon and Mars.   Since the Moon is likely to "enjoy" the attention of miners looking for Helium 3 (ref SpaceNut recent post), as well as other more mundane materials such as aluminum and oxygen, it would seem reasonable to look for Uranium as well.

This may be more than you want to tackle, but I'll toss this out for your consideration:

Can you estimate the Uranium requirements to support a single flight of RobertDyck's Earth-Mars Space Liner?   The "launch" would be from Earth and the "docking" would be with Phobos at Mars.  The return trip would be the reverse.

Also, since I've not seen a purification level for the Uranium ore, can you estimate what that would be?

A good use for the stockpile of fission weapons we humans have accumulated would be powering flights around the Solar System.

(th)

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#53 2019-09-09 11:05:59

RobertDyck
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Re: Large scale colonization ship

So you haven't even considered nuclear thermal? Again, I started this because this particular ship is the same interior volume as Musk's proposal for Starship 2. His Starship uses chemical rockets, LOX/LCH4. His description for Starship 2 is simply twice the diameter, and passenger compartment twice the length. If we use the 1990 version of NERVA for propulsion, that means increasing specific impulse from 380s in vacuum to 925s. That's a significant improvement.

At Mars Society conventions I spoke with a couple people involved with developing NERVA. They used 99+ percent pure U-235, so that's highly enriched. One NERVA engineer said they start with 99.9% enriched uranium, but that goes down as uranium is consumed by an operating reactor. I could give some arguments for technical improvements, but let's just run the numbers with NERVA as is.

Assume passenger shuttle is the original Starship. Liquid hydrogen fuel is transported by the tanker version of the original Starship, with LOX/LCH4 for Starship propellant, but it will carry LH2 propellant to this ship. On Mars we will have another original Starship, again the passenger version will be used to shuttle settlers from Mars orbit down to the surface. Propellant will be carried by the tanker version of Starship from Mars surface to this ship in Mars orbit. The interplanetary colonization ship will aerobrake to rendezvous with ISS. Whether ISS has to be upgraded to support construction and maintenance of this ship is a separate discussion. In Mars orbit the ship will park in highly eliptical high Mars orbit. That means periapsis will be just barely out of Mars atmosphere, because it used aerocapture to enter Mars atmsophere. Apoapsis will be very high, barely in orbit at all. That minimizes delta-V necessary to depart Mars orbit. Starship should be able to reach that from Mars surface because Mars has 38% gravity.

Mars Global Surveyor (MGS) entered Mars orbit in 1997. It mapped thorium on Mars surface. I've argued to use a thorium reactor for Mars surface facilities, but thorium is an indicator mineral for uranium. On Earth's surface there is 3 times as much thorium as uranium, and 100% of thorium is usable as nuclear fuel while only 0.72% of uranium is the right isotope. This argues strongly to use thorium for a surface reactor, but again thorium is an indicator mineral so that's where you would prospect for uranium.

By the way, Russia is a signatory to the Outer Space Treaty. That treaty bans weapons of mass destruction in Earth orbit or anywhere else in space. Nuclear explosives for propulsion are not exempt, they're banned under that treaty.

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#54 2019-09-09 12:11:52

GW Johnson
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From: McGregor, Texas USA
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Posts: 3,562
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Re: Large scale colonization ship

Robert:

Yes,  I did look at nuclear thermal,  specifically the NERVA technology more or less as it was tested.  For Mars,  it was feasible in that I had a positive payload fraction,  but nuke explosion and ion propulsion had far more attractive ignition/payload ratios.  For Ceres as "typical" of an asteroid belt trip,  payload fraction wasn't even positive with nuke thermal (meaning infeasible).  Remember,  this is for doing the whole round trip single stage,  and jettisoning nothing.

Tahanson43206:

The 1950's nuclear explosive technology is essentially WW2-vintage "Fat Man"-style plutonium implosion devices,  updated to 1955-vintage with a shaped-charge reflector and a big slug of polyethylene "propellant" mass.  Look at the expended mass of "propellant" for the explosion drive.  Something like 80-90+% of that is the plutonium cores in those devices.  We can do better than that today.

NERVA used very highly-enriched uranium fuel for its reactor.  I don't think they considered a variant on plutonium.  Buden in his book mentions using thorium bred to U-233 in the nuclear cycles he discusses,  but I don't think they ever designed an engine around that.

Myself,  I'm with RobertDyck:  use the thorium,  even if you have to breed it to U-233 to use it.  There seems to be a whole lot more thorium than there is uranium,  and only about 0.3% of that uranium is the 235 isotope you can use.  The nonfissile 238 isotope is what you can breed to plutonium-239,  which is how the fission implosion cores are made.

The explosion drive is just too attractive,  even in this antique 1950's technology form.  We're going to have to change the treaty.  If we are careful how we update the technology,  the "scary weapons objection" should be tolerable  enough to do that. 

Remember,  you won't be building this thing next week.  We are still very far from ready to mount any colonization efforts. 

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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#55 2019-09-09 13:07:37

RobertDyck
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Re: Large scale colonization ship

I don't know what the extraction efficiency is for uranium enrichment. I saw a presentation about the Canadian reactor design, CanDU, which uses uranium with no enirchment what so ever. The presenter said only 0.7% of uranium is U-235, but if you look up a periodic table it says 0.72% of uranium in nature on Earth.

Webelements: Uranium isotopes

When I talked to the NERVA engineer, he said they had not considered U-233. It does have smaller critical mass than U-235, though larger than Pu-239. U-235 produces more energy per unit mass of nuclear fuel than U-235, though less than Pu-239. So in every way it's between U-235 and plutonium. Plutonium is so poisonous that if you get a piece the size of a grain of sand in a cut in your skin, you're dead. Uranium is toxic, but not that poisonous. Uranium is a natural element in our soil.

India designed a thorium reactor for small towns. It doesn't separate U-233 from Thorium. The reactor cycle is Th-232 absorbs a moderated neutron to become Th-233. That decays over days to become U-233. When U-233 absorbs a moderated neutron, it splits. But the India design does not separate uranium from thorium, instead reacts the uranium in place as it's produced. I saw a presentation by one woman from USA who went into the detail how to separate U-233 from thorium fuel rods to produce pure U-233 for use in a reactor. That's stupid, you just don't. As India did, you just keep the thorium fuel rock in the reactor. Neutron absorption cross-section of U-233 is greater than Th-232, which means U-233 absorbs neutrons more readily. It'll split, when it does it'll produce heat. Just don't go through the ridiculous process to separate it.

I also calculated numbers. Ion engines have low thrust, high Isp. Whether you calculate using an NSTAR engine that has 3,000s Isp in vacuum or MPD designed by the Glenn Research Centre with 8,400s Isp with extreme electric power requirement, it still takes more time to get to Mars. Chemical rockets get you there faster. I notice you keep saying Ceres. I don't care about Ceres, this is about Mars. Ion engines are very efficient but slow. Nuclear thermal gives you the high thrust of chemical rockets, and high Isp at the same time. Isp isn't as high as ion or MPD, but it's much higher than chemical. It's the best for Mars.

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#56 2019-09-09 13:59:01

tahanson43206
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Registered: 2018-04-27
Posts: 904

Re: Large scale colonization ship

For RobertDyck ...

Thanks for the reminder of the Outer Space Treaty!  It was timely for something I'm working on.

For GW Johnson ... Thanks for the support of the need to update the Outer Space Treaty to permit peaceful uses of atomic energy in space.

Any changes would (it seems to me) require strong protections against misuse of fissionable material, and we humans have managed to monitor each other for several decades now.

The bottom line (for me at least) is that if we humans have any hope of advancing beyond our current Korolev Level 0 status, we're going to have to find ways to manage nuclear forces safely.

(th)

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#57 2019-09-09 14:30:53

RobertDyck
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Re: Large scale colonization ship

Bottom line: nuclear pulse propulsion is illegal. I seriously believe it will never be legal. Give it up. This was a bad idea from the 1950s that survived into the 1960s, but died a merciful death.

Ion or MPD are efficient but slow. Useful for cargo. If it takes 2 years to transit from Earth to Mars, you can do that. Not with humans. For humans your options are chemical or nuclear thermal. If you don't want to calculate with NTR, then do so with chemical. Again the purpose was to say Starship 2 is ridiculous; you don't want to launch something that big from the surface of Earth. Instead this ship has the same interior volume as Starship 2, but it has artificial gravity.

Nuclear pulse is not going to happen. Ever. Period. Give it a break.

Jumping straight to 56 metre radius is an order of magnitude larger than this. It won't happen right away. This is the next step after Starship. Instead of Starship 2, do this. But your 56 meter radius is the next generation after this. Expanding from 14 meter wide to 19 meter wide makes it convenient. It's wide enough for 2 isles, with cabins on either side of each isle. Assuming 2.4 metre (8 foot) ceilings, that works out to 10,475 cubic metre volume, not including central zero-G hub or spokes. So this is already a little bigger than the 8,000 cubic metres of Starship 2.

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#58 2019-09-09 18:40:26

SpaceNut
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Posts: 15,806

Re: Large scale colonization ship

We do use nuclear materials in space in the form of RTG's  and soon the kilowatt reactors so its not without posibilities.

We can always use what is there when you plan for doing the work once there to create the system to refine it.

The main thing is having it in orbit around the earth as kenetic or nuclear bomb staged for war purposes.

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#59 2019-09-09 20:02:33

tahanson43206
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Registered: 2018-04-27
Posts: 904

Re: Large scale colonization ship

For SpaceNut re #58 ...

Thanks for the note of moderation in the discussion.

I'm in favor of abiding by laws, as a general proposition.  It seems to me that nations that adhere to the rule of law have better prospects of success as communities of people in an often hostile environment than those who glorify individual males as dictators for life.  However, that may just be wishful thinking, in an age when dictatorships are feeling their oats all over the planet.

However, I think it is worth pointing out that any law can be revised, as time passes and problems with the original formulation are identified.

Thanks again to RobertDyck, for bringing up the Outer Space Treaty.

I found this article contains a helpful summary of the history of the treaty, and of Space Law in general.

http://theconversation.com/the-outer-sp … -age-71381

The article allows itself to include a question as to whether the Treaty needs updating.

Edit: Since this topic is managed by RobertDyck, I would honor a request to discontinue discussion of nuclear power for spacecraft propulsion.

At the moment, I understand that for the purposes of THIS topic, further discussion of a nuclear pusher concept is not welcome, even if it is superior to all other non-fusion solutions.

(th)

Last edited by tahanson43206 (2019-09-09 20:05:53)

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#60 2019-09-09 21:47:44

GW Johnson
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From: McGregor, Texas USA
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Posts: 3,562
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Re: Large scale colonization ship

Well,  we are talking colonization ships and missions here.  Those are going to be very large payloads,  inherently.  Ships that size will require great effort and resources to build and to launch.  All I did was plug in some realistic values to a spreadsheet,  looking for guidance as to how best to propel such a ship. 

I looked at Mars,  and I looked at Ceres as "typical" of main belt asteroids.  The asteroid belt is a more demanding mission in terms of delta-vee,  but not that more demanding.  Both might be the first places we plant colonies,  once we get around to committing the effort and resources to do so.  What I looked at was baseline Mars,  with Ceres serving to pin down trends as the demands increase.

It's not possible to just post my spreadsheet file here in a form anyone could use.  All I know how to do is to write text here.  I could post text and images on my "exrocketman" site.  Those images are copyable for download.  So,  I wrote up the study and posted it tonight.  The text contains the equations and the input data.  Two of the images are of the spreadsheet itself.  So,  now you all can do this for yourselves.

The results I got favor explosion propulsion and ion propulsion as the lower risks of attempting "Battlestar Galacticas" that we cannot ever hope to afford.  They are the only feasible items for Ceres.  Of those two,  explosion propulsion has the more favorable payload fraction. 

For Mars,  nuclear thermal and LOX-LH2 are also feasible,  but the payload fractions are far less favorable than explosion propulsion and ion propulsion.  The "best" one (biggest payload fraction) is explosion propulsion.

Go take a look.  You can see what I did,  with sufficient detail to duplicate it for yourself.  I did this independently of whatever anyone might think of the propulsion options.  The idea was to look at what is fundamentally required to do the round trip orbit-to-orbit mission single stage,  jettisoning nothing.  I did this for 2000 metric tons dead-head payload,  same for all propulsion options.  The results scale easily up and down.  Take your pick.

GW

Last edited by GW Johnson (2019-09-09 21:48:20)


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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#61 2019-09-09 22:13:40

SpaceNut
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Re: Large scale colonization ship

So what does a colonial sized ship need for atributes?

Plenty of supplies for all crew and then some.
Some methods for recycling so we are not needing gross amounts of anything burdening the mass of the ship futher making the means to move it slide up the nuclear power required scale.
Ag, radiation protection and work that can be carried on in the passage of time from place to place.

Cere would be a good loop destination as its got water but you only have a short time for the crew to exit, mining and then return to the ship as it comes back by.

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#62 2019-09-10 01:40:33

RobertDyck
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Re: Large scale colonization ship

I said a 37.76 meter radius ring at 14 metre wide would equal the volume of Starship 2. Increasing width to 19 metres makes it more practical. That gives 2 corridors each 1.5 metres (59 inches) wide. On either side of each corridor is 4 metre depth for cabins. This increases volume of the ring from 8,000 cubic metres to 10,475 cubic metres, assuming 2.4 metre (8 foot) ceiling height. Is that reasonable?

I also worked out a mix of cabins (staterooms). I said 162 economy class cabins that are effectively 3rd class from ocean going passenger liners a century ago. Titanic had a washing basin in each 3rd class cabin, and only a single bathtub for all male 3rd class passengers for the entire ship. And a second bathtub for all female 3rd class passengers, again for the entire ship. I said each "economy class" cabin would have a washroom with 30"x30" shower stall, toilet and sink with about as much room as a washroom (lavatory) in an RV, passenger train, or modern commercial jet airliner. Each "economy class" cabin would have 6 "small single" bunks, one pair of bunks that could be moved together to form a single queen size bed; intended for a family with 2 parents and 4 children. In addition 90 "single" cabins the same size but with a single queen size bed. And 4 "premium cabins" with a single king size bed, and a couch/sofa that could open as a queen size hide-a-bed. And a single "luxury suite" also with a single king size bed and a single queen size hide-a-bed. Is this an appropriate mix?

Assume that a "single cabin" would sell for about the same price as an "economy cabin" since they take the same deck area. However, maximum 2-person occupancy for a "single cabin" while the "economy cabin" has 6-person, so the cost per person is triple. Assume premium cabin would cost 4 times the price of a the other cabins, since it takes 4 times the deck area. If the hide-a-bed is not used, cost per person for a premium suite would be 4 times that of a "single", or 12 times that of "economy". The single "luxury suite" would be 4 times deck area of "premium" but rather than 4 times the cost of "premium", it would most likely be higher.

Current cruise ships have dining rooms sized so only half the passengers can be seated at once. This requires two shifts for all meals. I suggested 3 shifts for all meals. I also cited a guide for restaurant dining room design which said 10-11 sq.ft. per seat for school Lunch Room, fast Food or banquet room. So the ship dining rooms would have 10 square feet per person. One room for "fine dining" with only 20 seats, 20 square feet per seat. Is that enough?

I said no common room, instead use the dining rooms. No promenade, although the ship will have a zero-G reception hub that can be used for zero-G entertainment in transit. No swimming pool, no deck, no shuffleboard, no basketball/tennis/billiard (pool tables)/ping-pong, no library, no casino or shops. No cinema or theatre, instead live entertainment in the dining rooms.

Cruise ships today have 20,000 square feet for a ship that carries 2,695 passengers. Our ship carries 1,000 passengers. Providing 4,000 square feet for gym means half the number of square feet per passenger. Enough?

Found a reference for hotel laundry here. It says 500-700 sq.ft. for 120-key hotel. Our ship has 257 cabins, but "economy" cabins have 6 "small single" beds rather than a queen, so double laundry for them? So our 581 "keys" for the purpose of laundry: 500/120*581=2,420 square feet! Ack! The reference also says "each most hotel laundry equipment requires 24” of rear clearance for servicing, and washers should be spaced a minimum of 6” to 12” apart." This is a space assumes separate washers and dryers. I said assume a design based on RV washing machines that use the same drum from washing and drying. So cut the space in half. Then mount the machines with zero rear clearance, the machine would have to be pulled out for servicing. The layout shows machines side-by-side, but a laundromat can have machines stacked 2 high. So 1/2 for single machine, 1/2 for stacked, 2/3 for zero rear clearance? 403 square feet?

Cruise ship rule of thumb is one infirmary bed per thousand passengers. This ship will have 1,000 passengers so 1 medical bed? Let's say 2. This article says for a cruise ship with 2,000 passengers the infirmary sees 20 passengers per day. So our ship 10 per day? This floor plan has 2 "consultation" rooms; not sure why, any clinic I've been to the doctor consults in the examination room. The second is a dental office with 3 chairs and a lab. So based on the first floor plan, replace one toilet with pharmacy storage, replace the second "consultation room" with a lab. The first is 13'x20' so 260 square feet?
741ad434790f367f2d8cc1ade3aeddf8.png bca5763f0429d4f5028a7b692d93177a.jpg

Ship's bridge. So what? 200 square feet?
9b1bc47e2db2429a2925278f4e6b8aca.jpg

We're left with 2,411 square feet. That has to include corridors. Cabin corridors are already accounted for, but not the rest. Do we put food storage in zero-G, or some storage in the ring? There's life support with oxygen generator, water processor, Sabatier reactor. Does this leave us with room for a lounge/bar/club?

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#63 2019-09-10 02:39:47

RobertDyck
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Re: Large scale colonization ship

Captain's cabin would be a "single cabin" but would have a Murphy bed that folds up to become a desk.
Click image for YouTube video.

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hqdefault.jpg?sqp=-oaymwEjCPYBEIoBSFryq4qpAxUIARUAAAAAGAElAADIQj0AgKJDeAE=&rs=AOn4CLBnGoV1UNMy-fSvi3-_8G_agcP4ng

hqdefault.jpg?sqp=-oaymwEjCPYBEIoBSFryq4qpAxUIARUAAAAAGAElAADIQj0AgKJDeAE=&rs=AOn4CLC3IpsuzRqI8blegcwChLVrz9wbfQ

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#64 2019-09-10 03:51:14

Calliban
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From: Scotland, UK
Registered: 2019-08-18
Posts: 36

Re: Large scale colonization ship

Some variation of the nuclear pulse option that GW refers to would allow take off from Earth surface and landing on Mars; all with a good payload fraction.  The ship can be built on the Earth's surface and can be loaded with fuel, passengers and supplies on a planetary surface at both ends.

The ion propulsion concept would presumably require multiple chemical rocket launches to allow assembly of the vehicle, fuelling, victualling and delivery of passengers.  That implies a lot more capital and operational costs.  And the vehicle would have a shorter lifetime.  I think a reasonable estimate would put the cost of a seat on an ion driven ship at least an order of magnitude greater than a nuclear pulse ship.

The implications are clear; mankind will not colonise the solar system until we get much cosier with radioactivity in the environment.  We are prepared to tolerate substantial human health consequences from fossil fuel air pollution.  We need to be comfortable with radioactive pollution is much the same way.


Interested in space science, engineering and technology.

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#65 2019-09-10 04:50:49

Terraformer
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From: Lancashire
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Re: Large scale colonization ship

If we develop beamed power and lightweight rectennas, ion propulsion becomes a lot more viable. We can run the entire infrastructure on solar power in that case.

As Hop has pointed out many times before, though, tethers and chemical rockets + gravity assists offer a lot more potential than is usually discussed. The trip time to Mars, departing from L1 and using the Oberth effect, can be brought down to three months.


"I guarantee you that at some point, everything's going to go south on you, and you're going to say, 'This is it, this is how I end.' Now you can either accept that, or you can get to work." - Mark Watney

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#66 2019-09-10 06:03:33

Calliban
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From: Scotland, UK
Registered: 2019-08-18
Posts: 36

Re: Large scale colonization ship

A tether (rotating skyhook) would presumably be used to boost a spacecraft tangential velocity such that it reaches orbital velocity.  What sort of boost to dV is likely to be achievable?  If a rocket were to fly straight up to 100km say, could a tether provide all of the tangential velocity increment?

If this is achievable, then a rocket at takeoff would only need to achieve about 3km/s dV (1500m/s altitude, 500m/s drag, 1000m/s gravity loss) to reach orbit.  That is within reach of a single stage Kerosene/methane oxygen stage, or even a large nuclear powered lower stage using water propellant, taking off and landing on the ocean.  A single stage booster could be heavy enough to have a long fatigue life and its economic model would be closer to that of an aeroplane.  An upper stage that needs to reach orbital velocity could never work like that.


Interested in space science, engineering and technology.

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#67 2019-09-10 07:36:44

Terraformer
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Re: Large scale colonization ship

Tethers =/= rotating skyhooks. If we had a large counterweight in orbit, we could build a long tether to add or subtract perhaps a couple of km/s at each end. In a high enough orbit, that would allow us to launch payloads towards Mars without expending any propellent.


"I guarantee you that at some point, everything's going to go south on you, and you're going to say, 'This is it, this is how I end.' Now you can either accept that, or you can get to work." - Mark Watney

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#68 2019-09-10 10:27:54

tahanson43206
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Registered: 2018-04-27
Posts: 904

Re: Large scale colonization ship

For Terraformer

Terraformer wrote:

Tethers =/= rotating skyhooks. If we had a large counterweight in orbit, we could build a long tether to add or subtract perhaps a couple of km/s at each end. In a high enough orbit, that would allow us to launch payloads towards Mars without expending any propellent.

RobertDyck has yet to give a position regarding the relevance of skyhooks to his topic here.

While we wait for that, I'd like to add to your observation above, that momentum transferred from the counterweight must be restored.

The "usual" way to do that is to expend propellant.  However, solar sails can collect momentum from the Solar Wind (in very small increments), so if your project has enough time between swings, you would be able to recover.

My rule of thumb in thinking about tethers is to allocate 50% of whatever mass I've launched towards the tether to be allocated to momentum recovery.

I am confident that others can show how that percentage could be reduced.

Hopefully someone on the forum who knows orbital mechanics better than I do, and who is willing to clarify the picture a bit, can help here.

Alternatively, if there is someone reading the forum who has the needed qualifications, and who is NOT yet a member, here is an opportunity to assist.

If such a person runs into difficulty with registration (happens occasionally) just use the contact option in the registration page.

(th)

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#69 2019-09-10 12:41:09

Terraformer
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From: Lancashire
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Re: Large scale colonization ship

The usual method I've seen is to use ion thrusters to continually reboost the orbit with very little expenditure of propellent. Tethers allow you to bank that momentum and release it all at once.


"I guarantee you that at some point, everything's going to go south on you, and you're going to say, 'This is it, this is how I end.' Now you can either accept that, or you can get to work." - Mark Watney

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#70 2019-09-11 05:03:58

RobertDyck
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Re: Large scale colonization ship

This website describes cruise ship standard cabins made with composite materials. It says total cabin mass is reduced 50%, and they're saving one ton per cabin. That means each cabin is 1 ton. The article mentions material thickness in millimetres, so let's assume that's metric tonnes (1,000 kg) not imperial long tons (2,240 pounds) nor imperial short tons (2,000 pounds).

International Space Station module Leonardo in it's original configuration as Multi-Purpose Logistics Module. This is basically an empty hull. Mass 4,082 kg, length 6.6 m (22 ft) (cylindrical part 4.8 m), outside diameter 4.57 m (15.0 ft), inside diameter 4.2 m. This tells us mass of a hull. This includes pressure hull, multi-layer insulation, and micrometeorite protection.

So we can start to estimate ship mass.

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#71 2019-09-12 11:58:02

Calliban
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From: Scotland, UK
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Posts: 36

Re: Large scale colonization ship

RobertDyck wrote:

Mars Global Surveyor (MGS) entered Mars orbit in 1997. It mapped thorium on Mars surface. I've argued to use a thorium reactor for Mars surface facilities, but thorium is an indicator mineral for uranium. On Earth's surface there is 3 times as much thorium as uranium, and 100% of thorium is usable as nuclear fuel while only 0.72% of uranium is the right isotope. This argues strongly to use thorium for a surface reactor, but again thorium is an indicator mineral so that's where you would prospect for uranium.

By the way, Russia is a signatory to the Outer Space Treaty. That treaty bans weapons of mass destruction in Earth orbit or anywhere else in space. Nuclear explosives for propulsion are not exempt, they're banned under that treaty.

The thorium fuel cycle is not nearly as good as it sounds.  The significant advantage that it does have over other breeder reactor cycles is that in molten salt mode, reprocessing is not needed - aside from fission product removal from the (already) molten salt.  The thorium breeder creates all the U233 it needs insitu, without need for fuel processing.  This removes a certain amount of cost; reduces the risk of diversion of fissile materials into weapons programmes and has beneficial effects in terms of reducing contamination of reprocessing equipment.

But there are significant downsides.  Firstly, you need a reactor vessel that will reliably contain a complex mixture of molten fluoride salts for the design life of the reactor - 25-100 years.  That's a tall order, even using advanced nickel alloys.  Heat exchangers need to be immersed in the salt and will typically have short design lives, necessitating a long shutdown period for replacement.

Secondly, the breeding ratio is poor because of all the parasitic losses from dissolved actinides and fission products.  That may sound like a good thing from a proliferation viewpoint, but it really isn't a good thing if you want to increase reactor capacity to meet the needs of a rapidly growing Martian economy.  The only way to improve breeding ratio is go down a full reprocessing route and adopt a fast reactor design.  But then you are essentially building a fast breeder reactor using solid thorium fuel and blankets instead of uranium fuel.  There isn't much difference between the two fuel cycles at this point.  The uranium-plutonium cycle has better breeding ratio because plutonium yields more neutrons in the fast spectrum compared to U233.  And U233 is heavily contaminated with U232, which is a powerful gamma emitter, which makes fresh fuel fabrication and handling very difficult.

Another thing to consider is that a sodium cooled reactor using metallic uranium fuel, can deploy electrorefining in reprocessing, which is far more compact, cheaper and more proliferation resistant than old fashioned oxide fuel treated with nitric acid.  You just melt the metal, remove fission products and recast; adding fresh uranium to dilute as necessary and shuffling DU rods into the blanket radially.  Unless we face a truly catastrophic shortage of uranium in the future, it is unlikely that any rational cost benefit analysis would opt for a thorium fuel cycle.

Last edited by Calliban (2019-09-12 12:02:11)


Interested in space science, engineering and technology.

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#72 2019-09-12 14:30:09

RobertDyck
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From: Winnipeg, Canada
Registered: 2002-08-20
Posts: 5,748
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Re: Large scale colonization ship

Indian-Designed Nuclear Reactor Breaks Record for Continuous Operation

India’s 220-MW Kaiga 1 nuclear power plant, an indigenously designed pressurized heavy water reactor (PHWR), on Dec. 31 became a world record holder for running 962 unbroken days. The previous record for continuous operation was held by Heysham-2 Unit 8 in the UK, which ran 940 days before it was taken offline on Dec. 10.

The state-owned Nuclear Power Corp. of India Ltd. (NPCIL) said the 1999-completed unit (Figure 1) at the four-unit plant in Uttara Kannada district of Karnataka state continuously operated from May 13, 2016, until Dec. 31, 2018, when it was taken offline for inspection and maintenance. During that period, the unit generated about 5 billion units of electricity at a plant load factor of about 99.3%.

Heavy water, not molten salt.

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#73 2019-09-12 14:41:03

elderflower
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Registered: 2016-06-19
Posts: 1,091

Re: Large scale colonization ship

Development following on from the CANDU reactors.

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#74 2019-09-12 19:23:11

kbd512
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Registered: 2015-01-02
Posts: 2,883

Re: Large scale colonization ship

Calliban,

If the Norwegians thought that Thorium wasn't an economical fuel to use, then it's highly unlikely that they would've spent the money to qualify it as a fuel for use in commercial light water reactors.  Then again, they have rich deposits of Thorium and may want to mine and breed their own fuel rather than relying on outside sources.

I agree that containment and heat exchange materials longevity in corrosive salts is an issue that needs to be addressed.

With respect to poor breeding characteristics, I assume you're talking about Thorium in fast breeders.  If that's the case, then yes, the neutron economy associated with processing what will become Plutonium is better in a fast breeder.

We're in no danger of running out of Uranium, using only what we've already mined and never mining / enriching another kilo, for at least the next thousand years or so.  Even so, I say we obtain, store, and diversify our fuels as much as possible to assure that there will be no shortages.

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#75 2019-09-13 12:19:01

GW Johnson
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From: McGregor, Texas USA
Registered: 2011-12-04
Posts: 3,562
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Re: Large scale colonization ship

I took a closer,  more nuanced look at nuclear propulsion thermal rocket propulsion,  just because RobertDyck dislikes nuclear explosion propulsion so much.  The nuance was not carrying the dead-head payload both ways,  only to Mars.  That makes a big difference to the outcome,  but it makes the calculation inherently iterative.  The spreadsheet really came in handy for this.

I looked at some 6 different implementations of nuclear thermal propulsion.  There was NERVA as tested,  what NERVA could be updated to,  particle bed concepts as embodied by Timberwind,  the gas core "nuclear light bulb",  and two closely-related open-cycle gas core concepts (one limited to regenerative cooling,  the other weighed down by a massive radiator to reject waste heat).

The results are posted over at "exrocketman".  I liked the updated NERVA as the best near-term solution,  but recommended spending effort trying to make the "light bulb" or the regeneratively-cooled gas core actually work as a longer term solution.

The nuance of not carrying dead-head payload back to Earth got 4 of these 6 down under 5:1 ignition:payload ratio.  It's a really big effect.  The open cycle gas core is under 2:1,  right up there with pulse propulsion,  except pulse propulsion does that good carrying massive payload both ways.  NERVA-as-tested and the radiator-cooled gas core are just too heavy to look attractive,  even on this nuanced mission.

For colonization,  carrying the big payload one-way to Mars and returning unladen-of-payload is appropriate.  Later on,  as a trade economy establishes,  that is inappropriate.  You will need big payloads transported both ways!  Hopefully there will be better propulsion available by then,  as that is still some time off. 

All of this begs the question of the surface-to-orbit-and-back ferry at Mars (and Earth).  What I looked at in both articles is orbit-to-orbit transport only!!

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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