ISRU propellant production - energy requirement for the BFR?

SpaceNut · 2018-01-03 17:56:33

Doing a reverse engineering on

According to the link below one of the better sites in the USA (California) gives 4.5 Kwhs per Kw installed capactiy of PV Panel per day (equates to 7 sq metres at 15% efficiency).

based on my post#16 you are recieving solar 3.9 hours out of the day at an approximate 34 degree location to achieve the numbers.

My question is how do you lower automatically and position without human hands to 167 tonnes for the solar and not brake and or misalign such that it will not work?

Thanks for the posted link 3015 from Nasa on the solar.... need to look up all parts to get full picture.

I see the images are of the ATK fan panels. and that nasa pegs the human side of the equation as bring 10 kw which sounds very reasonalbe as I am on par with the collected 3 hours a day for use at 30kwhrs.

"Season (Mars Sun distance changes by 18.5%, flux by 38%" Such a drop in power levels ouch..

Nice slide 6 as it gives the data such at the average over all the time is 200 w/m2 plus and we would be reigning back power consumption for the 150 day winter when its below that level. Just a 20 degree further south means we will not see the winter condition.

The power covertor and battery details of the PMDA are in a seperate document
....

louis · 2018-01-03 18:36:16

SpaceNut - That seems the least of our worries. We have automobiles that will park themselves, accurately time and time again without fail...as long as we have a few transponders on site I think robot rovers could lay out the solar arrays as desired.

SpaceNut wrote:

Doing a reverse engineering on
According to the link below one of the better sites in the USA (California) gives 4.5 Kwhs per Kw installed capactiy of PV Panel per day (equates to 7 sq metres at 15% efficiency).
based on my post#16 you are recieving solar 3.9 hours out of the day at an approximate 34 degree location to achieve the numbers.
Thanks for the posted link 3015 from Nasa on the solar.... need to look up all parts to get full picture.
My question is how do you lower automatically and position without human hands to 167 tonnes for the solar and not brake and or misalign such that it will not work?

kbd512 · 2018-01-03 18:44:38

That system 3015 posted weighs 4.2t (slides) or 4.4t (diagram), not 2.5t. The 4.2t figure is on multiple slides. For whatever reason, the mass associated with the regenerative fuel cell was not taken into account.

Edit:

Vanguard Space THINS (thin film roll-out solar array that's already demonstrated 362Wh/kg, with an ultimate project goal of 500Wh/kg) and Li-ion batteries (.25kWh/kg for Tesla cells) would provide substantially more power for less mass. There's no reason to even consider TJ IMM, even at future projected power output levels. They weigh too much, cost too much, and are more difficult to deploy than thin film ROSA. It's like a film canister that can protect the cells at night, can clean the cells before nightly stowage, and provide 1-DOF sun tracking. Set it up the right way and it pretty much takes care of itself.

Last edited by kbd512 (2018-01-03 18:55:29)

Oldfart1939 · 2018-01-03 18:44:57

How much more mass are we talking about w/r robot rovers? What about difficulties w/r terrain?

3015 · 2018-01-03 18:56:11

kbd512, the 4.4 t mass is for panels, PMAD, and a RFC (regenerative fuel cell) to provide astronauts power at night. The RFC is not necessary to produce propellant. So the mass for producing propellant is 1.5t for panels plus 1 t for PMAD for a total of 2.5 t.

3015 · 2018-01-03 19:34:55

louis, I think that 17 MWh/t is very conservative for producing methalox from your own hydrogen supply. However if you're doing it the SpaceX way and mining water, you have to do twice as much electrolysis and you need energy to mine the water, so there are differences that drive the power needs both ways. From this spreadsheet I linked before, the power needs would be about 9 MWh/t. I am missing some power draws from the Zubrin paper in that spreadsheet, like liquefying the produced propellants and keeping them cold, and some heating elements and pumps and stuff. So I'd say with things I've forgotten and some numbers I may have made too optimistic, the power needs are probably more like 12 MWh/t.

louis wrote:

Thanks 3015. V. interesting observation...essentially you appear to be saying the 17 MWh figure is a very conservative one i.e. we can probably get that amount of propellant for far less. Well, again, I think this would confirm that Space X's goal of a solar powered propellant production is feasible. What would be your guesstimate for a lowest possible energy input per tonne, taking full benefit of economies of scale on a Space X style mission? Would we be saving 50% overall?

kbd512 · 2018-01-03 19:36:21

Oldfart1939,

The types of rovers I wanted to use are manned tracked vehicles that hold two people in the passenger compartment. The P/W ratio is sufficient to climb a 60% gradient and it has the mobility characteristics of a miniature armored personnel carrier because that's what it's based on. A front dozer blade attachment can level regolith or push small boulders out of the way. It's purpose built for off-road travel and ultimate durability.

The cargo compartment is for holding stuff like solar arrays, CO2 tanks and air tools, food, water, batteries, spare rover parts, or extra crew members to assist with construction. It's outfitted with a polyethylene liner to stop SPE / GCR instead of nuclear blasts. The top of the cargo compartment is about 4 feet high, so climbing atop the front of the vehicle is possible, even in a space suit. It has attachment points for ROSA canisters to unfurl the array while it's connected to the top of the vehicle and a small crane to hoist the canister onto a stand assembled to hold the device. The stand has a motor that tilts the array to track the sun using cabling connected to the end stand.

Each pair of ROSA has its own battery that it charges. If a panel or battery system goes down, you can unplug everything and cobble together working systems using remaining parts. All of the batteries in the array feed into a set of PMAD systems. This setup is intended to minimize wiring, but maximize redundancy and total array and battery power. The array must be located a ways away from the vehicle to prevent array loss or damage when BFS launches. The individual canisters are light enough for a pair of humans to lift by hand (with effort), but the crane (manual, not powered) exists to assist with emplacement.

kbd512 · 2018-01-03 19:37:32

3015 wrote:

kbd512, the 4.4 t mass is for panels, PMAD, and a RFC (regenerative fuel cell) to provide astronauts power at night. The RFC is not necessary to produce propellant. So the mass for producing propellant is 1.5t for panels plus 1 t for PMAD for a total of 2.5 t.

How are you keeping the propellant cold at night? It's cold on Mars at night, but not cryogenically cold.

3015 · 2018-01-03 21:01:53

Valid point kbd512. There will definitely be some energy needed to keep the propellant cold. I expect the need is much less than in the NASA design, but I guess I shouldn't assume that without the math to back it up. The energy required to keep propellant cold depends heavily on whether produced propellant is stored in the return vehicle or in an insulated storage tank. In the former case, heat transfer into the propellant is very significant, but with the right shielding, heat transfer (and therefore energy to keep the temperature low) can be kept quite low. I am assuming the second case, which is what I expect SpaceX is pursuing.

Heat transfer on Mars is mostly through radiation, so it can be very effectively minimized using multi layer insulation. This paper tested the effectiveness of sheets of aluminized mylar each separated by 10 cm, and found thermal conductivity to be only about 10 mW/mK at -50 C. So with six layers providing 50 cm of shielding, the heat conductivity would be about 20 mW/K, so if the liquid oxygen was kept at -200 C and the air temperature was -50 C, heat transfer would be about 3 W/m^2 of tank surface area. My best guess is that the BFR spaceship has about 700 m^2 of tank surface area, but external storage tanks for it would probably more long and narrow, so maybe its better to assume 1400 m^2 of tank surface area, meaning 4.2 kW of heat would enter the propellant at night. I'm not sure of how much energy is required to reject that much heat, does anyone know how I might make an estimate of that?

The NASA design suggests nighttime power use of 75 kW, for a level of power generation that is less than 1/30th the size of the one that would be needed to refuel a BFR. So I expect that unless rejecting each watt of heat that enters that the propellant takes many tens watts to remove, the nighttime power use needed should be well below 1/10 of what it is in the NASA design. I guess I should add a bit of mass to the simple calculations I did before, that would probably bring the leverage down to more like 8.5 instead of 9.1

kbd512 · 2018-01-03 23:09:14

3015,

For various practical reasons, BFS's propellant tanks will probably be where the propellant gets stored. The tanks need to be insulated. The insulation will undoubtedly be effective, just not as effective as we'd like it to be. The math of this calculation is absolutely critical, too.

It's not possible to have 10cm between insulation layers. This is an aerospace vehicle with a cryo plant subsystem aboard, not a proper cryo plant. SpaceX is trying hard to save mass using composite tanks, so some sort of aerogel foam insulation is required. Maybe it also functions as a replaceable ablative heat shield for reentry, but that's just a random thought. Irrespective, either batteries or fuel cells have to reject waste heat. No cryo plant I know of is 100% efficient, even when mass is not an issue.

Oldfart1939 or GW,

Please tell us how we can use stored liquid CO2 and some sort of turbo expander to circulate and refrigerate the propellant and possibly provide electrical power at night.

louis · 2018-01-04 10:04:48

FWIW, the official illustrations of Space X's Mars Mission appear to show propellant tanks.

http://www.spacex.com/sites/all/themes/ … on-bfr.jpg

kbd512 wrote:

3015,
For various practical reasons, BFS's propellant tanks will probably be where the propellant gets stored. The tanks need to be insulated. The insulation will undoubtedly be effective, just not as effective as we'd like it to be. The math of this calculation is absolutely critical, too.
It's not possible to have 10cm between insulation layers. This is an aerospace vehicle with a cryo plant subsystem aboard, not a proper cryo plant. SpaceX is trying hard to save mass using composite tanks, so some sort of aerogel foam insulation is required. Maybe it also functions as a replaceable ablative heat shield for reentry, but that's just a random thought. Irrespective, either batteries or fuel cells have to reject waste heat. No cryo plant I know of is 100% efficient, even when mass is not an issue.
Oldfart1939 or GW,
Please tell us how we can use stored liquid CO2 and some sort of turbo expander to circulate and refrigerate the propellant and possibly provide electrical power at night.

3015 · 2018-01-04 12:07:23

kbd512, after thinking on your comment, I think I was wrong to assume that SpaceX will use external propellant tanks. Certainly it is plausible that they will do so, since it reduces power needs, allows for faster reuse of BFSs in the long term, and since as louis pointed out, external tanks appear in their concept art.

But external tanks have two major challenges as well. They will have to be made extremely lightweight, and they must either be simple to assemble, or must be expandable. These are huge challenges and I should probably not assume they can be overcome. I'll see if I can get an estimate of how much energy it would take to keep BFR tanks at cryogenic tempertaures. I worry it will be quite high since the tanks on the BFR spaceship appear to have essentially no insulation. Musk has stated that the heat shield plates will be mounted directly on the tank wall, and the tank wall makes up the structure of the craft, so I don't see where there's any room for insulation. A single sheet of aluminized Mylar draped over the side of the tanks would go a long way, but I'm not sure if that could be easily mounted.

SpaceNut · 2018-01-04 12:10:08

The image is of prepackage brought from Earth tanks in the lunar moon use but mars would not be that much different except for that payloads to the moon can be greater than that of mars due to fuels need to get to mars are greater....

Active cooling aught to have its own topic as its been meantioned before....
http://newmars.com/forums/viewtopic.php?id=7004
http://newmars.com/forums/viewtopic.php?id=5230&p=2
http://newmars.com/forums/viewtopic.php?id=7977&p=2

Oldfart1939 · 2018-01-04 12:43:52

What would seem to be the best solution for fuel production/storage is a dedicated one-way spacecraft with all the necessary cryogenic apparatus built-in.

Using liquid CO2 for refrigeration is something I would find fraught with problems; once pressure on the liquid is released we get--dry ice (solid CO2). Solid CO2 is capable of cooling things down to -77 deg C.

SpaceNut · 2018-01-04 15:54:19

I like the use of boiloff attached to the top of the tank to create power as a subfunction to movement of the gas as it seeks out the exspansion tank for later recooling.

https://en.wikipedia.org/wiki/Liquid_oxygen

liquifying oxygen will require nitrogen which has a lower boiling point at −196 °C (77 K) than oxygen's −183 °C (90 K)

Liquid oxygen has a density of 1.141 g/cm3 (1.141 kg/L or 1141 kg/m3) and is cryogenic with a freezing point of 54.36 K (−218.79 °C; −361.82 °F) and a boiling point of 90.19 K (−182.96 °C; −297.33 °F) at 101.325 kPa (760 mmHg). Liquid oxygen has an expansion ratio of 1:861 under 1 standard atmosphere (100 kPa) and 20 °C (68 °F)

Making Liquid Oxygen

https://www.stirlingcryogenics.com/en/m … management

Solutions can be either be the supply of stand-alone cryogenerators or special designed closed loop systems. These systems can be based on cryogenic liquid (mostly liquid Nitrogen) or cryogenic gas (typically Helium) in a temperature range of 150-15 Kelvin (-190°F to -430°F or -120°C to -260°C).

http://www.airproducts.com/~/media/File … gram-6.pdf

kbd512 · 2018-01-04 20:38:27

Oldfart1939,

I was thinking that a purpose-built vehicle may be required to store the propellants, but this seems to have its own set of challenges.

1. landing near the cryo plant vehicle
2. transfer of propellants from vehicle to vehicle
3. take-off without damaging or toppling the cryo plant vehicle

Is there any way to heat the blades of the turbo expander to prevent dry ice formation?

Heating Component to Reduce Solidification in a Cryogenic Distillation System

Oldfart1939 · 2018-01-04 21:51:49

kbd512-

There are several challenges facing the proposal of using a purpose built fuel manufacturing spacecraft. You've touched on them, but there are some deeper issues to consider.
(1) Landing near the cryo plant vehicle. Problem here is landing a flame-spewing rocket near a supply of fuel and oxidizer without blowing up the whole facility and the landing vehicle all at the same time.
(2) Transfer of the propellants from vehicle to vehicle. This will definitely require construction of major infrastructure--underground transfer lines from the fuel manufacture/storage facility to the use point.
(3) Takeoff without damaging the cryo plant vehicle. This is essentially the same issue as in (1) above re: landing vehicle.

To answer your question re: heating blades; that would require a LOT of additional and scarce energy.

SpaceNut · 2018-01-04 22:42:17

We do have solar to make use of if the dry ice is moved into a chamber to be turned back into vapor to which we then compress into the pressure tank to hold at a warmer temperature to make liquification easier.

Thats not all that hard to turn the blades into a warming surface as the element is attached to the surface of the blade with the conductors running down the shaft to a keep isolated from the shaft for each end of the element to have a contact ring. Then you make contact to that ring with the power brush much in the same manner that we use in a car alternator.

I agree that a safe area of landing and relaunch are unknown at this time for a fuel plant to which we could test out here with the grasshopper stage that Space x has.
How many uses do we get from current earth refueling hoses, trucks and or other gear used for fueling rockets now?

SpaceNut · 2018-01-06 09:24:31

louis wrote:

3015 pointed out that isn't the Space X plan. Propellant production begins with the arrival of the human transport.
elderflower wrote:
If the propellant is produced automatically it can start at once. Then you have approx. 4 years to accumulate a return ship fuel load. The personnel would just transfer to the refuelled ship after their time on the surface is up.

This means that with 2 ships landing 1 of them is a duplicate to the other which means you only have half the payload if 1 is damaged and we must wait another full cycle to send another ship to make up for the lose. So the question is can we send in the 1 ship what we need for a human mission?

Oldfart1939 · 2018-01-06 09:58:33

The actual construction of the BFR may be easier than that of all the necessary infrastructure capable of supporting it! On some other websites (Space Review Essays), there is quite a bit of skepticism about the size of the ITS or BFR, and thoughts similar to mine that the final version is still prone to substantial downsizing. Looking at the old concept rockets published 6-7 years ago, the BFR is similar in size to the Falcon XX, but a more realistic version may be the Falcon X. Maybe only on an intermediate, short term time frame during which work is continued on the BFR? Who really knows where things will lead? Falcon Heavy took 5+ years to develop and is still sitting on the pad awaiting a first launch. BFR is probably an order of magnitude more difficult! So--the time frame stated by Musk is subject to some major extension. Instead of the 2022 initial launch projected, my guesstimate is 2026. Probably after I've croaked.

Do not take my comments as negativism, but as conservatism tempered with a large dose of reality. I still am a strong supporter of Musk and SpaceX. This is not a defeatist attitude--just one based on their corporate track record. Theu will still be on Mars as the welcoming committee for NASA and everyone else.

Last edited by Oldfart1939 (2018-01-06 10:02:32)

louis · 2018-01-06 11:45:37

I don't mind you being realistic and sceptical, but I am interested in what exactly is the "order of magnitude" difficulty in your view. The engines are near the end of their development. The art of retro landing seems to have been resolved. The fuel tank prototype has been constructed. The design process itself must be much quicker these days with CAD. They have a launch pad that can handle the launch I believe. What do you think are the major choke points?

BTW, for those of us entering the "twilight zone", I'm sure hanging around waiting for humans to get to Mars will add a few years to all our lives!

Oldfart1939 wrote:

The actual construction of the BFR may be easier than that of all the necessary infrastructure capable of supporting it! On some other websites (Space Review Essays), there is quite a bit of skepticism about the size of the ITS or BFR, and thoughts similar to mine that the final version is still prone to substantial downsizing. Looking at the old concept rockets published 6-7 years ago, the BFR is similar in size to the Falcon XX, but a more realistic version may be the Falcon X. Maybe only on an intermediate, short term time frame during which work is continued on the BFR? Who really knows where things will lead? Falcon Heavy took 5+ years to develop and is still sitting on the pad awaiting a first launch. BFR is probably an order of magnitude more difficult! So--the time frame stated by Musk is subject to some major extension. Instead of the 2022 initial launch projected, my guesstimate is 2026. Probably after I've croaked.
Do not take my comments as negativism, but as conservatism tempered with a large dose of reality. I still am a strong supporter of Musk and SpaceX. This is not a defeatist attitude--just one based on their corporate track record. Theu will still be on Mars as the welcoming committee for NASA and everyone else.

Oldfart1939 · 2018-01-06 12:22:38

louis wrote:

I don't mind you being realistic and sceptical, but I am interested in what exactly is the "order of magnitude" difficulty in your view. The engines are near the end of their development. The art of retro landing seems to have been resolved. The fuel tank prototype has been constructed. The design process itself must be much quicker these days with CAD. They have a launch pad that can handle the launch I believe. What do you think are the major choke points?

Louis-
Having an engine prototype nearing the end of development is a far cry from having a production engine. Having a single large prototype fuel tank is fine, but it's really a matter of system integration and engineering. There is one helluva lot of basic engineering work to complete before any final hardware gets built. Maybe I'll be a lot more positive in my outlook once FH takes flight and sends those two billionaires around the moon. I would also feel a lot more optimistic were Musk to include an intermediate scale test vehicle between the BFR and Falcon Heavy series. We really need to develop the Mars base infrastructure for the refueling and see some orbital assembly accomplished. It isn't just about building the Big F*%$#ng Rocket itself.

Put it in this order:

(1) Complete development of the raptor engines and have production versions test-flown; my guess is the first Raptor to fly will be in an expanded/redesigned upper stage of the FH. That's how test data can be accumulated. I'm sure there will be a first stage "grasshopper" built to work out the re-landing details with sea level engines. Time required: 2 years absolute MINIMUM!
(2) Build and test fly an upper stage of the BFR; maybe as the payload on a FH? Do on a single orbit and then re-land? Time required: 5 years, based on the history and track record of SpaceX.
(3) Build and test orbital tanker vehicles. Demonstrate fuel transfer capabilities. Time required: 5-6 years.
(4) Design, build, and test Mars refueling facility. Send a scale model to mars; test. Not even started yet, so time required: 8 years.
(5) Send first unmanned BFR to Mars for landing tests. Given the Hohmann transfer orbit time requirements; time estimate: 6 very optimistic years.

There is much, much more work to accomplish--all of which takes LOTS OF $$$$$? And LOTS OF TIME. We are only talking here about the tip of the iceberg. It's one thing for we dilettantes here to make wishful thinking our imaginary realities, but the hard facts are in the engineering and financing this whole idea set.

Last edited by Oldfart1939 (2018-01-06 12:25:39)

louis · 2018-01-06 13:00:04

Thanks - interesting to see your concerns spelled out.

I think Space X have got the money. That is probably the least of their concerns. They raised $450 million just last year. I think the recent BFR presentation will make it even easier to raise funds this year, if they need additional money. They are valued at over $22 billion now, I believe - about the same as one year's funding for NASA (though of course NASA are trying to do 1001 things, whereas Space X is now very much focussed on the BFR development as an all purpose vehicle).

I don't think there needs to be testing with a flight to Mars. Capability can be shown in test flights to the Moon and back.

On the upside I would note:

- The huge Saturn V rocket was developed in under 5 years, at a time when design and prototyping was much more difficult.

- When Space X started they have very few experienced engineers on board. Musk had to do a lot of the design work himself. I think they now have the people talent and the technical know-how for fast development.

- Musk is really desperate to get to Mars. He won't be holding back.

Oldfart1939 wrote:

louis wrote:
I don't mind you being realistic and sceptical, but I am interested in what exactly is the "order of magnitude" difficulty in your view. The engines are near the end of their development. The art of retro landing seems to have been resolved. The fuel tank prototype has been constructed. The design process itself must be much quicker these days with CAD. They have a launch pad that can handle the launch I believe. What do you think are the major choke points?
Louis-
Having an engine prototype nearing the end of development is a far cry from having a production engine. Having a single large prototype fuel tank is fine, but it's really a matter of system integration and engineering. There is one helluva lot of basic engineering work to complete before any final hardware gets built. Maybe I'll be a lot more positive in my outlook once FH takes flight and sends those two billionaires around the moon. I would also feel a lot more optimistic were Musk to include an intermediate scale test vehicle between the BFR and Falcon Heavy series. We really need to develop the Mars base infrastructure for the refueling and see some orbital assembly accomplished. It isn't just about building the Big F*%$#ng Rocket itself.
Put it in this order:
(1) Complete development of the raptor engines and have production versions test-flown; my guess is the first Raptor to fly will be in an expanded/redesigned upper stage of the FH. That's how test data can be accumulated. I'm sure there will be a first stage "grasshopper" built to work out the re-landing details with sea level engines. Time required: 2 years absolute MINIMUM!
(2) Build and test fly an upper stage of the BFR; maybe as the payload on a FH? Do on a single orbit and then re-land? Time required: 5 years, based on the history and track record of SpaceX.
(3) Build and test orbital tanker vehicles. Demonstrate fuel transfer capabilities. Time required: 5-6 years.
(4) Design, build, and test Mars refueling facility. Send a scale model to mars; test. Not even started yet, so time required: 8 years.
(5) Send first unmanned BFR to Mars for landing tests. Given the Hohmann transfer orbit time requirements; time estimate: 6 very optimistic years.
There is much, much more work to accomplish--all of which takes LOTS OF $$$$$? And LOTS OF TIME. We are only talking here about the tip of the iceberg. It's one thing for we dilettantes here to make wishful thinking our imaginary realities, but the hard facts are in the engineering and financing this whole idea set.

Oldfart1939 · 2018-01-06 15:40:28

Louis-

Your comments are always interesting and filled with boundless enthusiasm. However there are several built-in fallacies in what you stated regarding SpaceX versus NASA.
(1) Money: just because SpaceX has been valued at $22+ Billion does not mean it has that available for a single project (BFR). That means the assets such as plant infrastructure, materials inventory, machinery, etc. give a rosy picture. But for capital required to undertake all the work remaining--they will have to be very careful in order to maintain the cash-cow of the Falcon rocket production.
(2) Regarding the Saturn V rocket; that took virtually the entire manpower of the space agency to get built in that 5 years. It also was a much less sophisticated engineering problem as the vehicle was basically a "brute force answer" to the then existing problem.
(3) There will have to be a full scale Earth to Mars test flight--unmanned of course. It could conceivably carry some construction supplies, food, and essential construction tools--which do NOT EXIST YET.

My overall desire is the same as yours: get a manned flight to the Red Planet, by SpaceX, and do it in a manner in which no lives are lost due to haste and associated stupidity.

Last edited by Oldfart1939 (2018-01-06 15:41:56)

louis · 2018-01-06 17:43:01

Oldfart1939 wrote:

(1) Money: just because SpaceX has been valued at $22+ Billion does not mean it has that available for a single project (BFR). That means the assets such as plant infrastructure, materials inventory, machinery, etc. give a rosy picture. But for capital required to undertake all the work remaining--they will have to be very careful in order to maintain the cash-cow of the Falcon rocket production.

I think the more relevant figure is the $450 million raised last year. I think the fact that investors can now see there is a lot of money to be made from tourism and quite possibly earth-to-earth (let's call that E2E) rocket transport. I think their global internet satellite system will be a huge success. Governments are very concerned about the vulnerability of internet cables to attack.

Oldfart1939 wrote:

(2) Regarding the Saturn V rocket; that took virtually the entire manpower of the space agency to get built in that 5 years. It also was a much less sophisticated engineering problem as the vehicle was basically a "brute force answer" to the then existing problem.

True but a lot of what they were doing was first time invention...a lot of the BFR capability will be working with known materials within known parameters.

Oldfart1939 wrote:

(3) There will have to be a full scale Earth to Mars test flight--unmanned of course. It could conceivably carry some construction supplies, food, and essential construction tools--which do NOT EXIST YET.

I don't know why the double cargo landing scheduled for 2022 can't be the effective test flight. The worst that can go wrong is you lose two BFRs. No lives lost.

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