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#1 2018-06-30 13:26:14

SpaceNut
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From: New Hampshire
Registered: 2004-07-22
Posts: 16,181

Kbd512's Space BFR variants

I thought it was time to put the variations of the Space x BFR and second stages into a spot for updating as we develope what they could be for with regards to the first stage being reuseable and capable of lofting to LEO 150T..

kbd512 wrote:

BFR-OC (Orbital Cargo) Concept: specifically designed to deliver cargo (spacecraft) to orbit
* small habitable section, unpressurized cargo bay
* intended primarily to deliver satellites or other spacecraft components
* first variant to be flown and tested

BFR-OT (Orbital Tanker) Concept: specifically designed to deliver propellant to an orbital propellant depot
* small habitable section, larger propellant tanks
* intended primarily for lunar exploration
* second variant to be flown and tested

BFR-MC (Mars Cargo) Concept: delivers heavy cargo (LOX/LH2 plants, PV arrays, robots, materials, etc) to Mars
* BFR-MC is just an internally reconfigured BFR-MP (has life support, but no seats or very few seats, just cargo space)
* Stays on Mars and continues to fetch heavy cargo from LMO
* third variant to be flown and tested

BFR-MP (Mars Passenger): delivers humans and light cargo (consumables) from the ITV to Mars
* Stays on Mars and continues to fetch people and consumables from LMO (has seats and personal living quarters)
* fourth variant to be flown and tested

ITV-P (Passenger): long duration deep space habitation
* beefed up for durability, redundancy, and protection
* first variant to be flown and tested

ITV-C (Cargo): long duration deep space cargo delivery
* ITV-C is just the engineering section of ITV-P and does not provide artificial gravity
* second variant to be flown and tested

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#2 2018-06-30 13:43:53

SpaceNut
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Re: Kbd512's Space BFR variants

The latest being solar oriented in BFS meant to be the power creation and distribution as well as part of the ISPP fuel plant.

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#3 2018-06-30 14:37:23

louis
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From: UK
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Posts: 4,925

Re: Kbd512's Space BFR variants

There's supposed to be an Earth-to-Earth BFS as well, isn't there?  I guess the E2E BFS would have more passengers than even the Mars people transporter.

Last edited by louis (2018-06-30 14:37:38)


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#4 2018-07-01 03:51:48

kbd512
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Posts: 2,963

Re: Kbd512's Space BFR variants

Louis and SpaceNut,

The BFS-EP (Earth Passenger) is optimized for Earth orbital / sub-orbital travel and landing on concrete or steel pads.  It needs a thicker heat shield to contend with Earth reentry velocity, but only minimal protection from SPE and GCR since it stays below the Van Allen belts.  The internal layout is optimized to carry passengers with minimal cargo.  It's structure is optimized to contend with harder and more frequent landings.  The cabin structure is reinforced and designed to permit break away from the propellant tanks for parachute landings.  An explosion during the early phases of launch would still be fatal, just as it already is on takeoff for a commercial airliner, but catastrophic events that occur at significant altitude, during reentry, or upon landing will have better outcomes as a function of the protections afforded by its design.

The BFS-MP (Mars Passenger) is optimized to provide redundancy in critical systems for deep space operations.  It contains a large water tank to contend with SPE and a thick BNNT liner to intercept and absorb as many GCR ions as is practical.  The cabin structure is not reinforced because there is not enough mass available to allocate for that purpose.  The heat shield is optimized for reentry at Mars from Mars orbital velocity (3.8km/s).  It also has wider landing gear to inhibit tipping on unprepared surfaces.

The BFS-LP (Lunar Passenger) is optimized to provide some redundancy in critical systems, but to a lesser degree than BFS-MP as a function of its short flight duration.  It contains a smaller water tank for SPE protection and a thinner BNNT liner for GCR protection.  The cabin structure is not reinforced because there is not enough mass available to allocate for that purpose.  There is no heat shield because there is not enough mass available to allocate for that purpose.  It's a short duration LEO to lunar surface transport only.  It never reenters, just like ITV.  It also has wider landing gear to inhibit tipping on unprepared surfaces.

The design requirements for Earth orbital / sub-orbital transport, lunar transport, and Mars transport are too variant.  The design will be tweaked to optimize it for a particular purpose in light of that fact.  BFS-C will deliver the elements required to construct true ITV's that are purpose built for long duration flight.  The BFS-MP will serve as the life boat for ITV-P.

The ITV-P and ITV-C carrying the BFS-MP as its cargo for Mars surface operations will depart from LEO at the same time.  If the ITV-P suffers a catastrophic failure, then the ITV-C docks with the ITV-P to transfer the crew from the stricken ITV-P to the BFS-MP strapped to the nose of the ITV-C.  ITV-P is just a rotating wheel habitat / spin gravity enabled variant of ITV-C.  ITV-C is just the engineering section (power and propulsion module) of the ITV, known as ITV-E (for engineering), plus BFS-MP as the cargo / payload strapped to the nose of the ITV-C.

The ITV stacks look like this:

ITV-P: [ITV-P]-[ITV-E]

ITV-C: [BFS-MP]-[ITV-E]

ITV-E = 1 BFS-C delivery to ISS
ITV-P = 2 BFS-C deliveries to ISS (cargo volume restriction, not mass)

ITV's use electric propulsion and have the dV capabilities required for orbit-to-orbit transport and abort-to-Earth.  There are no reentries made from interplanetary transfer velocities.  Apart from artificial gravity and radiation protection, that's the added survivability factor that ITV's provide.  There's no such thing as a precision landing in a highly variable atmosphere from an interplanetary reentry.  It's too fast.  The actual transit time to Mars for the ITV's will match that of the BFS if the ITV departs from LLO.

It's not impossible to do a Mars exploration mission without artificial gravity or the control afforded by electric propulsion, but it's far riskier than necessary, the useful service life of BFS decreases, and most of the tonnage delivered to LEO is propellant, rather than useful payload.  There are so many advantages afforded by the ITV that only someone who is willing to ignore every possible way that the BFS could be lost and the crew lost with it would propose such a mission when the technology to build the ITV is already available or required for BFS anyway.

If we face facts here, the best way to execute this mission is with purpose built interplanetary transport hardware that BFS-C delivers to ISS for construction and automated transfer to LLO.  The ITV provides generous delta-V performance margins for various abort scenarios and the overall mission hardware architecture includes redundancies and protections that BFS alone can't provide.  The basic BFS design is already extreme enough.  It's a reusable rocket stage that delivers a 150t payload.  Let's not start loading it up with stuff that's either unnecessary, necessary for specific use cases only, or only necessary for a single part of the overall mission.

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#5 2018-11-09 18:20:41

SpaceNut
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Posts: 16,181

Re: Kbd512's Space BFR variants

Another nice addition to this toipic:

kbd512 wrote:

Louis,

I still think the right way to do this is a split-mission using a small fleet of BFS variants.  The primary reasons for this are habitable volume limitations, the radiation problem, and all these new dust particle clouds we've very recently discovered around Earth near the LaGrange Points.  There's no telling where other dust clouds are located since we only discovered those clouds by chance, which means we don't have a good method for locating debris fields that could impact a spacecraft in interplanetary space.  The walls of the Bigelow Aerospace inflatables are well over a meter thick, far superior to what's reasonably achievable with BFS, for absorbing impacts from debris.

Anyway, here's what I was thinking:

ITV - Interplanetary Transfer Vehicle - The combination of a radiation protected BA-2100 inflatable habitation module that stays in orbit and contains consumables for interplanetary transits, docked to a specialist space tug variant of BFS

BFS and special equipment features denoted with asterisks

Vehicle Geometry (VG):
STD - standard, which means standard overall vehicle length and bow canards; suitable for prepared surface landings
SHT - short, which means shorter overall vehicle length and smaller bow canards; suitable for rough field landings
TUG - space tug vehicle without a heat shield or aerodynamic control structures for reentries; Combined Chemical / SEP (CC-SEP) propulsion using Raptor and Aerojet-Rocketdyne X-3 hall thrusters

Vehicle Accommodations (VA):
H - habitable
R - robotic, therefore not habitable

Heat Shield (HS):
NR - No Reentry (not capable of reentry)
SR - Single Reentry (not durable)
MR - Multiple Reentries (durable)

Avionics (A):
R - radiation hardened
N - not radiation hardened

BFS-OC - orbital cargo delivery of satellites and spacecraft components
* VG - STD; VA - R; HS - MR; A-N
* robotic arms for cargo deployment and recovery

BFS-OT - orbital cryogenic propellant delivery; to be tested for satisfactory operation with BFS-OC
* VG - SHT; VA - R; HS - MR; A - N
* propellant tanks slightly longer than standard BFS propellant tanks, since the payload is propellants, to save weight
* specialized pumping and refueling probe equipment installed to avoid docking maneuvers

BFS-ST - orbital transfer space tug that provides propulsion for crew and cargo deliveries to interplanetary destinations
* VG - TUG; VA - R; HS - NR; A - R
* LOX/LCH4 propulsion for orbital transfer
* Argon-based electric propulsion for cruise, course correction, and spiraling into orbit at the destination
* multi-megawatt class deployable thin film solar arrays for primary electrical power
* robotic arms for cargo mating
* chemical propellants replenished using BFS-OT (in LEO; no docking required) or BFS-MP (in LMO; requires docking)

BFS-MC (robotic) - contains the LOX/LCH4 propellant plant
* VG - SHT; VA - R; HS - SR; A - R
* deployable thin film solar arrays for primary power to avoid complications associated with construction of permanent surface structures
* onboard CH4 fuel cell for startup / shutdown / emergency power
* specialized propellant tank insulation for long duration propellant storage
* specialized pumping and propellant transfer equipment
* provides a source of spare engines or engine components for the BFS-MP, if required
* stays on Mars and never returns to Earth

BFS-MP (crewed) - contains the consumables and surface habitation inflatables for living on the surface of Mars
* VG - SHT; VA - H; HS - MR; A - R
* designed only for crew transfer in Mars orbit and subsequent landing on Mars, rather than long duration habitation in deep space
* crew radiation protection provided by cargo and consumables, rather than liners, to save weight
* more pressurized volume allocated to cargo than crew accommodations
* specialized cargo transfer equipment for deployment of surface habitation structures and transfer of consumables
* can also be repositioned using suborbital hops, as required
* stays on Mars and never returns to Earth

This family of vehicles will work with each other to make the Mars missions possible

Sprint 1
1. BFS-MC is delivered to orbit
2. Multiple BFS-OT flights transfer fuel to BFS-MC until the tanks have been filled
3. BFS-MC performs the TMI burn
4. BFS-MC arrives at Mars and performs EDL burns
5. The fuel cell is activated to provide startup power, the solar arrays are deployed, and propellant production tests begin
6. If sufficient propellant production rate is achieved, then the next sprint begins

Sprint 2
1. BFS-OC delivers the BFS-MP to ISS for temporary storage
2. BFS-ST delivered to orbit below ISS
3. Multiple BFS-OT flights transfer fuel to BFS-ST and BFS-MP until the tanks have been filled
4. BFS-ST performs the TMI burn
5. BFS-ST arrives at Mars and circularizes its orbit, waiting for the ITV

Sprint 3
1. BFS-OC delivers the ITV to ISS for temporary storage while inflation, checkout, consumables and crew loading takes place
2. BFS-ST delivered to orbit below ISS
3. Multiple BFS-OT flights transfer fuel to BFS-ST until the tanks have been filled
4. BFS-OC delivers the consumables to ISS, for transfer to the ITV
5. Falcon 9 delivers the crew to the ITV using Dragon 2
6. ISS disconnects the crewed ITV from ISS, whereupon the ITV is mated to BFS-ST
7. ITV’s BFS-ST performs the TMI burn
8 ITV arrives at Mars and BFS-ST circularizes its orbit

Sprint 4
1. ITV docks with BFS-MP in Mars orbit for crew transfer to the BFS-MP
2. BFS-MP performs the EDL burns to land on Mars
3. Crew unpacks, inflates, and transfer consumables from BFS-MP to the surface habitat
4. Crew performs surface mission until BFS-MC propellant production is complete
5. Crew transfers propellant from BFS-MC to BFS-MP
6. Crew boards BFS-MP for return to the ITV

Sprint 5
1. BFS-MP ascends to orbit and docks with ITV
2. Crew transfers to ITV in preparation for TEI
3. ITV performs TEI burn
4. BFS-ST previously attached to BFS-MP performs TEI burn
5. ITV returns to Earth and spirals into LEO
6. ITV and BFS-ST docks at ISS
7. ITV crew departs ISS aboard their Dragon 2
8. Dragon 2 performs reentry burn and returns to Earth

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#6 2018-11-10 13:29:15

louis
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From: UK
Registered: 2008-03-24
Posts: 4,925

Re: Kbd512's Space BFR variants

Well here's a novel one: a Falcon 9 BFR!

https://twitter.com/elonmusk/status/1060253333116473344

Seems to be testing heat shield and high speed re-entry...


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#7 2018-11-10 14:59:54

SpaceNut
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From: New Hampshire
Registered: 2004-07-22
Posts: 16,181

Re: Kbd512's Space BFR variants

That also gives him a chance for the fin landing foot testing, refueling on orbit as well and more depending on how far he wishes to go with the ship....

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#8 2018-11-10 15:16:10

kbd512
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Posts: 2,963

Re: Kbd512's Space BFR variants

Scale models that provide real world experience with all the required technologies will immeasurably improve the final BFR/BFS product.

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#9 2019-05-30 19:19:11

kbd512
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Posts: 2,963

Re: Kbd512's Space BFR variants

I'm adding my Starship Lite Interplanetary Transport Vehicle (SL-ITV) concept to my list of BFS / Starship variants.

After reading a bit about Masterbond's epoxy adhesives that were engineered to withstand repeated thermal cycling to cryogenic temperatures of as little as 4K (below the boiling point of LHe2), I think we've determined how to create CNT composites that can withstand cryogenic temperatures.

Epoxy Adhesives for Cryogenic Applications

We're going to use a layered approach to thermal protection and cryogenic liquid propellant storage.  The entire vehicle will be made from various types of CNT fabrics and composites.

The habitable module / front half of the vehicle will consist of a pair of deployable inflatable donuts that are stowed for launch and landing.  The inflatables will wrap around a smaller diameter composite center section / barrel that contains the avionics, life support equipment, and consumables.  This portion will be protected by various CNT-based fabrics consisting of elastic woven MWCNT fabrics to protect the habitable section during launch and reentry.  The inflatable donuts will be inflated and counter-rotated during deep space transits to provide artificial gravity.  The barrel section will have a water tank / shield to provide radiation protection from solar flares and coronal mass ejections.  The gas impermeable layers will be bonded to the inner CNT layer in small sections, such that a hull breach from a micrometeoroid does not depressurize the entire vehicle.  The intent behind this feature is to make small breaches repairable using adhesives and CNT fabrics.  As an additional defensive measure against hull breaches, both the inflatables and the inner barrel section that the inflatables are connected to, via inflatable spokes, will be compartmentalized like a warship.  An inflatable arm, similar to Festo's Octopus Gripper, will be available to inspect the exterior of the ship for damage and to attach to astronauts conducting spacewalks for any repair activities.

The propulsion module / rear half of the vehicle will consist of CNT composite propellant tanks made with Masterbond's epoxies.  The tanks will be filled with Aerographene foam, which retains its pliability / stretchability down to deeply cryogenic temperatures, to inhibit propellant sloshing as propellant is depleted during the various burns required.  The propellants themselves will provide autogenous tank pressurization.  The propellant tanks will also be protected from ascent and descent heating by woven MWCNT forest fabrics wrapped around the tanks to inhibit heat transfer.  The propellant tanks themselves will be fabricated from CNT composites consisting of appropriate tapes and epoxies.

Primary vehicle power will be provided by a combination of super capacitors for surge power demands and radioisotope thermoelectric generators that also use MWCNT forests to provide improved thermal power conversion efficiency.  A solar device that produces the same effect could potentially provide power without the need for radioisotopes, but it would always have to be facing the Sun in order to work.  As avionics, electronics, and life support power demands are greatly reduced using modern electronics, having a reliable "always available" power system to supply critical systems becomes more practical.  Vehicle lighting will be provided by a combination of light pipes while the vehicle is in space and LED's to provide interior lighting.  A series of deployable thin film solar arrays will provide supplemental power for inflation / deflation of the inflatable donuts, counter-rotation of the donuts to provide artificial gravity, thermal control, and high continuous power draw crew activities such as cooking or washing clothes.

Heat Trap: A New Way to Generate Electricity Using Nanotechnology?

The intent here is to reduce Starship's weight by approximately half of what a similar stainless steel ship would otherwise weigh and retain far greater strength, at the expense of some heat shield durability.  The fabric heat shields would have to be repaired or replaced after reentry.  However, the Martian atmosphere contains the base material (Carbon) required for fabrication of CNT materials in abundance.  Eventually, major engine components would be fabricated from CNT ceramic composites.  A combination of CNT and ceramic powders (various metal oxides, mostly Iron and Titanium) fused together at high temperatures in non-oxidizing / inert atmospheres.  Those ceramic oxide powders are also plentiful on Mars.

Carbon Nanotube Ceramic Composites and their Performance

From the article:

Additionally, these novel composites with excellent room/high temperature mechanical properties combined with the lubricating properties of CNTs will be ideal for the manufacture of parts for high temperature applications such as heat engines, gas turbines, etc.

Carbon Nanotube Reinforced Ceramic Matrix Composites- A Review

Synthesis of Carbon Nanotube-Metal Oxides Composites; Adsorption and Photo-degradation

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#10 2019-05-31 14:08:07

tahanson43206
Member
Registered: 2018-04-27
Posts: 1,075

Re: Kbd512's Space BFR variants

For kbd512 re #9 ...

Thank you for the link to the video on heat trap conversion of light to electricity, using carbon nanotubes.

There are probably many applications of carbon nanotubes (and you've listed some already) but this is one that really connects for me.

The presenter did not discuss efficiency, but since the process shown is operating at the quantum level, efficiency has the potential to be high.

Moreover, (if I understood the presentation correctly) there is NO heat lost in the process.  That seems (way) too good to be true, so I'll be watching for further discussion of this discovery.

***
Over in SpaceNut's "poverty" topic, I tried to introduce a concept for alleviating poverty by moving ownership of production of selected chemicals from gigantic corporations to a large number of individuals or families.  The impetus for this concept was a post by void, reporting on discovery of greatly improved performance of catalysts used for chemical reactions.  The author of the article to which void linked appeared to think that the cost of setting up chemical production facilities might be reduced from current levels, which might open up the prospect of smaller facilities.

I'm curious to hear your assessment of the potential for the discovery, and (in particular) your assessment of the potential for development of income producing capabilities at the small business level, as an alternative to the megacorporate level we see today.

I apologize for departing from the topic, but I'm doubtful you would see my message anywhere else.

(th)

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#11 2019-05-31 19:11:09

SpaceNut
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From: New Hampshire
Registered: 2004-07-22
Posts: 16,181

Re: Kbd512's Space BFR variants

The post 9 is not all that new its how we are using them which is changing and how we are pushing the limits on these materials which as we look to change cost are looking at new materials to make it happen.

The BFR is becoming the erector set of building designs for one size does not fit all...

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#12 2019-05-31 21:47:52

kbd512
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Registered: 2015-01-02
Posts: 2,963

Re: Kbd512's Space BFR variants

tahanson43206,

I'll refer you to the "cottage industry" model for making Graphene-infused batteries / super capacitors that YouTuber "Robert Murray Smith" is involved in:

First Working Generation Ltd. - Business Plan

There's no reason at all that a group of smart people can't pool their resources and know-how to start a cottage industry for some of this stuff.  However, starting any small business is a risk, most small businesses fail within 5 years, and you have to both accept and have a solid plan to overcome that statistic to receive investment capital from venture capitalists or banks.

In the future, this is how I envision both materials and parts being fabricated on Mars, especially for the transportation vehicles and habitat structures.  You only make what you need or what you can sell / share with other colonies and then use whatever you've made for all its worth until you absolutely must make a new one.  The use of better materials is all about simplicity of manufacture, use of a plentiful and readily available resource- Carbon, and the longevity of the finished products.

The Space Shuttle model of completely replacing a part after a single use with a one-off custom-made part used nowhere else is not going to work for the Mars transportation architecture.  The availability of everything, but especially metals, will be at a premium.  Metals will be used where metals have to be used.  By some stroke of pure dumb luck, we have this fantastic building material called Carbon that's readily available everywhere in our solar system that we could actually live using current technology.  Therefore, it makes a lot of sense to incorporate Carbon technology into this new Starship Lite ITV.

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#13 2019-06-01 10:23:21

SpaceNut
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From: New Hampshire
Registered: 2004-07-22
Posts: 16,181

Re: Kbd512's Space BFR variants

Cottage industry is a corporation view of tax avoidance in staying below an employee count numer for some but I see it as the small business do it yourself family run setting. This is a narrow scope business in they make just one thing that is profitable and do not try to make anything else as it takes away from the eficiency or being streamlined...
This forum is a cottage industry that we are doing full of the ideas for mars and more...We contribute as we enjoy doing so otherwise we would be asking for cash for our thoughts.

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#14 2019-06-01 14:45:08

kbd512
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Registered: 2015-01-02
Posts: 2,963

Re: Kbd512's Space BFR variants

Can we please try to keep personal political beliefs about small businesses out of this?

Thanks.

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#15 2019-06-02 10:18:47

tahanson43206
Member
Registered: 2018-04-27
Posts: 1,075

Re: Kbd512's Space BFR variants

For kbd512 ...

kbd512 wrote:

tahanson43206,

I'll refer you to the "cottage industry" model for making Graphene-infused batteries / super capacitors that YouTuber "Robert Murray Smith" is involved in:

First Working Generation Ltd. - Business Plan

SearchTerm:BusinessPlanSuperCapacitor

Thank you for posting the link to this active business plan, for growth of a competitor within the supercapacitor industry.

The business angle which (I think) you are tracking is the (apparently) unique focus upon use of Carbon as the primary material from which the newly designed supercapacitors are made.

The html document is served by a site with which I was not familiar.  Apparently there is a business built around facilitating the exposure of all kinds of documents to Internet search engines, and through them on to Internet users. 

As I read the document, I realized that it is a top tier example of what wealthy investors and venture capitalists must see frequently, and which I have never seen because, like many others, I have never had the resources to be looking for investment opportunities.

I'd like to call your attention to a short invitation buried within the financial projections and market analysis .... The founders are interested in promoting a downstream industry which sounds (as I read it) similar to franchise operations.  The founders (as I understand the text) appear to be willing to share manufacturing know-how and other business practices to individuals elsewhere on Earth who are willing to buy carbon material from them, as a feedstock for manufacture of supercapacitors in their locations.

This is similar to the concept I had in mind, when following up on void's discovery of research to improve performance of catalysts to manufacture selected chemicals.  I have not pursued void's lead far enough to know if the catalyst discovery would extend to manufacture of NH3, but am hoping that would be the case, so that the cost of a plant to make Ammonia from Nitrogen in the air and Hydrogen in sea water could become low enough for small business development. 

There is a LOT of land on the coasts of oceans, rivers and inland bodies of water where sunlight is abundant, so that solar power could be enlisted to provide power for the operations to be performed.

It seems to me possible that Louis' ambition to make methane might be achieved with reduced investment as well.

The process of capture of solar energy is fairly well explored at this point, so that it is now "traditional" to propose use of photovoltaic cells, but I would like to remind forum readers that kbd512 recently published a link to research showing that carbon nanotubes can be enlisted to generate electricity using solar energy as input, without needing any of the traditional materials.

While (at this point) I have no idea if the carbon photon capture to electricity discovery can be developed into a practical device, I certainly hope that the research will continue.  If so, we currently have an abundance of carbon available in the atmosphere for use in such devices, as kbd512 has repeatedly pointed out.

Since this IS the NewMars forum, I'll close with the observation that carbon based solar energy collecting systems would be a likely success on Mars, where there is also an abundance of available carbon and a dearth of traditional photocell materials.

(th)

Last edited by tahanson43206 (2019-06-02 10:22:38)

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#16 2019-06-02 10:23:27

GW Johnson
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From: McGregor, Texas USA
Registered: 2011-12-04
Posts: 3,653
Website

Re: Kbd512's Space BFR variants

I find Kbd512's sketch of a spaceship design using carbon nanotube technology-based composites and an anti-slosh foam fill in the tanks to be intriguing.  I'm too old and obsolete to know much about the advanced materials he describes,  so I leave the question of technological readiness of such materials to him and others to debate.  I just offer the school-of-hard-knocks observation that it is usually years and $millions between something that looks good in a lab experiment,  and something you can rely on for regular use.

I do know anti-slosh is the reason cited by Musk for the internally-nested "header tanks" in his company's "Starship" design.  There is also the problem of ullage during free-fall between main engine burns.  With liquid propellant rockets,  the liquids in the tanks form free-floating globules during zero-gee.  There is no way to guarantee liquid present at the pipe suction in the tank for the engines in free fall unless you do something specific to prevent this action.  In fact,  void at the suction opening is way-to-hell-and-gone more probable than a liquid globule.  That's been the experience,  as I understand it.

There are two ullage solutions so far: 

(1) an internal bladder containing the liquid that is compressed by gas pressure between it and the tank shell.  That way there is no excess-void space within the bladder in which surface tension can pull the propellant into globules.  That way a void space at the suction pipe never forms.  But you cannot do this with cryogenics,  because all known bladder materials have no flexibility at such temperatures. They just crack and split with the tiniest movement at all.  No known polymer has a glass transition temperature down in the cryogenic range.

(2) Provide a small thrust in the travel direction by means of "ullage motors",  so that there is some small amount of acceleration gee settling the liquid into one pool in the end of the tank where the suction pipe is located.  Because the gee level is small,  these motions take significant time.  You need several seconds of "ullage motor" burn before you can successfully light the liquid engine. The turbopump "net positive suction head" and anticipated depth of liquid set the acceleration level required.  The stage mass at ignition and that acceleration set the ullage thrust you must have.

The first approach only works with room-temperature storable propellants,  where bladder polymer materials can actually be flexible enough to move that far.  It is routinely done with them,  as the very most practical way to accomplish this.  A similar thing is used in many aircraft fuel tanks,  down to cold stratospheric temperatures,  but these are nowhere close to cryogenic.

The second approach,  "ullage motors",  is routinely done with both cryogenics and with room temperature storables.  On the old one-shot Saturns,  these were small solid-propellant rocket motor cartridges mounted on the aft end of the upper stage,  in threes.  You can see the solid rocket plumes for several seconds in the old films as the stages separate, before the upper stage motor(s) fires.  On a reusable vehicle equipped with attitude control thrusters (which the Saturns did not have),  you could use some of the attitude thrusters as your "ullage motors",  as long as your thruster propellant supply is large enough to cover that function,  too.  I believe that Spacex intends to use this approach for ullage in their "Starship",  although they have not yet indicated publicly whether this is so.

My questions here relates to the ullage problem when you have anti-slosh foam present within the tank.  In zero-gee,  globules of propellant will form and float within the void spaces (porosity) of the foam.  There will inherently be some void volume as well as globules of liquid adjacent to the suction pipe,  even if the foam abuts the pipe opening (which it cannot in real world practice).  Thus this anti-slosh foam design approach still faces the same ullage problem as a conventional open tank.

The difference is the flow resistance moving liquids through the foam (governed by its connectivity).  At slow velocities,  this is negligible,  but at faster velocities,  it is overwhelming,  with any imaginable practical levels of foam porosity and connectivity.  This greatly extends the micro-acceleration ullage burn time interval,  and perhaps a higher ullage thrust level to fight the connectivity drag,  before you have sufficient liquid volume around the suction opening to actually light the main engine.  The result is that you need much larger ullage burn propellant supply,  or a much larger ullage burn thrust level,  or likely both,  to move enough of the tank contents to the suction opening against the flow resistance of the foam,  in any reasonable interval of time. 

My questions:  (1) am I right to think this might be a serious design problem requiring solution?,  and (2) has anyone a better solution than an ullage burn to offer?

GW

Last edited by GW Johnson (2019-06-02 10:41:34)


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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#17 2019-06-02 15:54:11

kbd512
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Registered: 2015-01-02
Posts: 2,963

Re: Kbd512's Space BFR variants

GW,

The "foam" in this case is NOT a polymer of any kind.  It's Carbon.  It's a disordered forest (tangled web) of Carbon NanoTubes that is already being manufactured in multiple cubic meter quantities.  There are no plastics to be found here.  The material is spongy / stretchy, just like a foam, but has mechanical and electrical properties quite unlike any foam made from petrochemical processes.  It remains fully flexible at deeply cryogenic temperatures.  It also has one other interesting property.  When you run electricity through it, it can contract like a muscle does.  I realize that some of this stuff may seem as alien to you as a smart phone would've been when you were a kid, but it's quite real and it's also a commercial product.

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#18 2019-06-02 17:39:11

GW Johnson
Member
From: McGregor, Texas USA
Registered: 2011-12-04
Posts: 3,653
Website

Re: Kbd512's Space BFR variants

Kbd512:

That's a very intriguing material indeed.  Based on your description as a "tangled forest",  I'm guessing the fluid dynamics of liquid moving through this material would resemble "orifice flow from chamber to chamber" less,  and "flow around and past cylinders in crossflow" more. 

That would point to higher values of connectivity (lower drag) for any given level of porosity (void fraction).  The propellant should migrate more easily through it,  all else being equal.   

That eases the ullage burn requirements,  but it may not be as effective at anti-slosh characteristics.  Those depend directly on the drag of the liquid moving through the material.  I dunno,  of course. 

Does the shrink upon electrification apply to these carbon nanotube fibers when twisted into yarns and woven like fabric?  If so,  there might be a way to use them as part of an MCP space suit,  one whose compression you can literally turn on and off with a switch.  That would go a long way to solving the donn/doff problem with MCP suits. 

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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#19 2019-06-02 17:51:32

kbd512
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Registered: 2015-01-02
Posts: 2,963

Re: Kbd512's Space BFR variants

GW,

The twisted CNT yarns can contract about 30,000 times faster than human muscle tissue and generate a force of up to 50,000 times their own weight.

The link below is for Carbon Fiber artificial "muscles", but this should give an idea of the kind of force that can be generated:

Strong carbon fiber artificial muscles can lift 12,600 times their own weight

That's quite a bit weaker than CNT, yet still 18 times as powerful as natural human muscle fibers.  I presume that plain old carbon fiber tech is suitable for space suits, but CNT would take things to an entirely new level.

Edit:

Metals were great technology when that's all that was available.  In point of fact, metals are what permitted humanity to advance to the point where we're at today.  However, heavy metal is rapidly becoming a relic of a bygone era.  When compared to CNT, the strength-to-weight ratio of the strongest alloys we know of aren't even visible on the chart unless you use a logarithmic scale.

That said, the cut and abrasion resistance of CNT is what is truly stunning.  I posted a link to a video of someone at the company that makes the CNT shielding for satellite data cables hammering a CNT tape, about the same thickness as a piece of Scotch tape, into a block of wood with a razor blade.  After that ordeal, the CNT tape hadn't even lost any of its mechanical strength, let alone been cut at all.  It's just seriously tough stuff with crazy mechanical and electrical properties.

This is the kind of technology we need when we go to Mars, yet it'll be every bit as useful here on Earth to make lighter everything with vastly superior strength-to-weight / conductivity / insulation / thermal resistance.  It really is that good.  That's why we need a lot more of it.  That's why we need to capture the CO2 we emit to obtain the atomically fine Carbon powders to make the stuff by the cargo ship load.  The cost of pure Carbon is $24,000 per ton.  The cost of capturing CO2, whether from the atmosphere or by sucking it out of the tailpipe of a combustion engine, and splitting the Carbon using EUV light is VERY far below the cost of mining it from the ground.  Furthermore, some processes are already using CO2 sucked out of the atmosphere to make CNT.

Last edited by kbd512 (2019-06-02 18:07:50)

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#20 2019-06-03 10:30:14

tahanson43206
Member
Registered: 2018-04-27
Posts: 1,075

Re: Kbd512's Space BFR variants

For kbd512 ...

kbd512 wrote:

<snip>
This is the kind of technology we need when we go to Mars, yet it'll be every bit as useful here on Earth to make lighter everything with vastly superior strength-to-weight / conductivity / insulation / thermal resistance.  It really is that good.  That's why we need a lot more of it.  That's why we need to capture the CO2 we emit to obtain the atomically fine Carbon powders to make the stuff by the cargo ship load.  The cost of pure Carbon is $24,000 per ton.  The cost of capturing CO2, whether from the atmosphere or by sucking it out of the tailpipe of a combustion engine, and splitting the Carbon using EUV light is VERY far below the cost of mining it from the ground.  Furthermore, some processes are already using CO2 sucked out of the atmosphere to make CNT.

I tried to find the spot market for pure carbon, and found the carbon trading sites instead.  The trading value of CO2 appears to be a lot less.

According to this site: http://calcarbondash.org/
the price was $15.10 on March 29th.

I recognize that the carbon trading market is not a ** real ** market, but thought the difference was interesting.

Can you provide a link to a site where pure carbon is traded, or at least reported?

The spread between the value of pure Carbon suitable for direct input to the CNT manufacturing process and the cost of setting up and running a business to make it is what I am looking for.

The size of the market is also unclear (to me at this point) although the potential as you describe it seems awe inspiring.

The goal I am trying to reach is to find a business opportunity that is a good match for the limited means of NewMars forum members and feasibility for long term investment, AND which coincides in a meaningful way with the overall objectives of the forum itself.

(th)

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#21 2019-06-04 22:27:20

kbd512
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Registered: 2015-01-02
Posts: 2,963

Re: Kbd512's Space BFR variants

tahanson43206,

Price of pure Carbon: $2.4 / 100g; $24kg; $24,000/1,000kg
Source: Carbon Element Facts

Price of 99.997% pure 75 micron Carbon powder: $557/100g; $5,770kg; $5,770,000/1,000kg
Source: GoodFellow Corporation - Carbon - Powder

The stuff you see advertised on Alibaba is low-grade / high-impurity crap that's loaded with metals and oxides.  Absent a very costly and complex refining process to remove the impurities, it's not suitable for making CNT at all.  The impurities are, specifically, an impediment to making CNT's that achieve theoretical mechanical and electrical properties.  Since there's an emerging market for pure Carbon in the form of base stocks for CNT structural materials, CO2 is the obvious source.  I'm pretty sure we won't have any trouble obtaining CO2, either here or on Mars.  CO2 can be split in a single step process with an EUV source, either a laser or that oddball device created by Brilliant Light Power that spits out EUV like mad by doing whatever it does with Hydrogen.  Frankly, it doesn't even matter if their device ever makes power.

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#22 2019-06-05 07:54:40

tahanson43206
Member
Registered: 2018-04-27
Posts: 1,075

Re: Kbd512's Space BFR variants

For kbd512 re #21 ...

Are you OK with continuing discussion of carbon production in this topic?

I found a "Happy Carbon" topic if you would prefer to move this to another topic.

That said... Thank You for clarifying and expanding the potential market for pure carbon suitable for CNT manufacture.

SearchTerm:PureCarbonMarket

Six dollars for a gram is amazing, and that is for "only" 99.997% pure << grin >>

I agree with your observation that sourcing CO2 from the atmosphere would help to remove impurities by avoiding them in the first place, but (on the other hand) there is a lot of material floating in the air that needs to be filtered out.

I will follow the links you provided over the next day or two.

I'll be looking for any hints that may show up along the way to answer (or show a path to answer) these questions:

1) What is the minimum quantity of pure carbon that would be of interest to a CNT manufacturer
2) Who are the competitors already serving this market (GoodFellow is the starting point, of course)
3) With the objective in mind of finding a package of technology that can produce pure Carbon from CO2 using solar power/wind power:
   A. What equipment is needed
   B. What amount of that equipment is needed to deliver the minimum marketable quantity in a reasonable time (eg, a week)
   C. How much power is required, which leads directly to how much land (or rooftop)  is required for solar, or wind flows for wind power
   D. What training is needed for owner/operator
   E. What risks are involved and how can they be avoided or mitigated (or handled in worst case)

Thanks again!

To repeat for forum readers who may discover this discussion today or in future ...

I am looking for business opportunities that would enable a typical forum member to secure funding for a technology that could be operated by an individual or a family to produce reliable income with modest time requirements, AND which relate in some way to the mission of this forum, which supports the Mars Society, and thus supports activities related to exploration and settlement of Mars.

(th)

Last edited by tahanson43206 (2019-06-05 08:04:05)

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#23 2019-06-06 11:06:43

tahanson43206
Member
Registered: 2018-04-27
Posts: 1,075

Re: Kbd512's Space BFR variants

Following up on the link provided by kbd512 in #21 ...

Goodfellow Cambridge Ltd.
Goodfellow was established in the City of London in 1946. The Company now has associate operations in France, Germany, America and China. The Group's research laboratories, production and workshop facilities, and central administration are located in Huntingdon, England.

From Google search:
http://www.microplanet-psl.com/index.ph … -materials

Our partner Goodfellow is a British company based in Cambridge. Goodfellow started its operations 40 years ago supplying products to scientists at the University and currently has branches in the US, China and Japan offering a wide range of high quality semi-finished goods internationally for basic reaserch, prototype development and specialised production in industrial and scientific areas.

(th)

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#24 2019-06-09 09:07:16

SpaceNut
Administrator
From: New Hampshire
Registered: 2004-07-22
Posts: 16,181

Re: Kbd512's Space BFR variants

Straight out of Buck Rogers is the single stage to orbit design which is taking shape in Texas.

5ce81a8922bc8d694d58c264-1334-1001.jpg

The article posted in other topics are talking about altering the test vehicles design...

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#25 2019-06-10 11:56:32

GW Johnson
Member
From: McGregor, Texas USA
Registered: 2011-12-04
Posts: 3,653
Website

Re: Kbd512's Space BFR variants

Well,  as near as I can tell,  the Starship/BFS/second stage is a design that is still evolving,  and will continue to evolve as various prototypes get tested.  The delta-vee calculation off published mass statement figures says this stage is not an SSTO design:  if the dry tanks/no payload weight is 85 metric tons,  and the propellant load is 1100 tons,  then for Isp ~ 330 sec,  the max theoretical delta-vee at zero payload (!!!) is  8.5 km/s,  but you need to knock off about 5-10% of that for gravity and drag losses to 7.6 to 8.1 km/s.  LEO speed is just about 8 km/s.  And you have no propellant left over to de-orbit or to land.  And that's if you really believe this thing comes in at 85 tons dry/no payload.

Put payload on board,  and you see the effect of the higher dry tanks mass.  The nominal payload is said to be 100 tons.  That gives a max theoretical delta-vee of 6.2 km/s.  Far short of LEO even without correcting it down for gravity and drag losses.  And there is still no allowance for deorbit burn or for the landing burn.  That allowance is likely not too far from 1 km/s delivered delta-vee.

The image in the photo is about 2:1 cg height / fin span,  which is an improvement over earlier illustrations.  That's good.  But the landing pad area is still way to small to takeoff from a soft sand surface,  whether on the beach or desert here,  or most anywhere on Mars.  By the time some of these prototypes actually get flight-tested,  they may actually start to address that.  And once they do,  I'd bet real money the dry tanks/no-payload mass exceeds 85 tons.

That's just school-of-hard-knocks talking.

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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