ISRU propellant production - energy requirement for the BFR?

EldenC · 2018-01-22 17:21:48

The lander melting though the perma forst....... the Alaskan pipeline solves this with those passive radiators (https://en.wikipedia.org/wiki/Construct … member.jpg)

.... but those would look kinda ugly on BFS's pretty little feet. :-)

SpaceNut · 2018-01-22 18:24:13

Its actually the engine plume on landing that is melting the perma frost.....this also happened on the Pheonix lander as can be seen on the legs of the lander as droplets....

For the other problem fill it with aerogel and do the same under it to fill the voids that might not hug the rocket close enough....

EldenC · 2018-01-23 14:51:47

there is a bad thought, BFS comes down the plume melts a few inches of water, during the time that the fuel is being made that refreezes. BFS goes to launch and either it can lift the legs, or one or two of the feet break off and stay while the ship takes off!

I don't know how aero gel is manufactured. Could an automated system deploy the aero gel? Could it be stored in BFS unexpanded?

elderflower · 2018-01-23 15:41:23

If the descending BFS melts water as it arrives the exhaust will blow that away, probably as a shower of mud and stones, not necessarily taken evenly from the surface of the terrain so that apparently level ground may end up not at all level.
When the descent engines are cut, the residual heat in the bottom of the rocket will be radiated to the ground below and this will generate a pond. I don't know how big that might be, or how deep. Then when the people descend on some kind of hoist they will, perhaps, need wet suits.
This could be avoided by suitable reconnaissance by a pioneer mission using small equipment like the Dragon to land. Being much smaller it would melt a smaller puddle if it were to land on permafrost or ice and it would float if the puddle were large. The heat shield might have to be left behind on re-ascent of the expedition if it were to get frozen in, so you would need spare heat shields in orbit to allow use of the same vehicle for another landing, or for Earth return.

SpaceNut · 2018-01-23 17:22:46

The vertical engine exhaust can be overcome with a canted engines just like in the dragon for landing just shutoff the vertical engines prior to getting close to the ground by firing up the canted engines for the finishing of the landing..

elderflower · 2018-01-24 04:06:09

That thought had occurred to me, Spacenut, but the mass involved in having those extra engines is likely to be prohibitive. They need to have a vertical thrust component equal to the landed mass plus a small margin to account for unused fuel, maybe 4 Newtons per Kg. You need at least six total, arranged in pairs, or probably eight total, to allow for an engine fault. Each of the eight must therefore generate a vertical thrust of 4/6N/kg of landed mass. For six engines each must generate 4/3 N/kg in the vertical, ie they have to have twice the thrust to allow balance on landing
To avoid landing with hot main engines final manoeuvring can be carried out using the auxiliary engines and the main engines can be cooled by venting excess fuel through them. You can't use the main engine feed pumps as they are driven by partial combustion, so auxiliary ones will be needed, although they might be electrically powered, being considerably smaller than the main engines. Alternatively you might have a feed from tank pressure but that brings its own complications. Hypergolic fuel would also be handy, saving the complication of igniters.
Monopropellant could be used but Isp is much lower so you need more fuel and bigger auxiliary engines.

Last edited by elderflower (2018-01-24 04:09:21)

EldenC · 2018-01-24 08:56:27

Mr. Musk is adament about using the fewest number of fuel types possible, so much so liquid helium is being replaced by autogenous tank pressurization (figuring out the cooling rate/liquification of the gas is going to be a beast).

I saw a great animation of BFS landing on Mars ( https://www.youtube.com/watch?v=9SCvenRvUVs), it showed the sea level engines being used for landing.....I wonder if that is accurate since the pressure on Mars would be more like a Vaccum (100Pa) than sea level (100,000Pa). Though I don't think they plan to gimbal the Vacuum engines.

SpaceNut · 2019-09-07 07:54:37

Some more time is at hand for the developement of the equipment needed for a mars manned flight. The cargo ships for mars will be more than half duplication of each other as the redundancy is required for man's safety.

SpaceNut · 2019-10-05 10:23:29

Current discussion is linking the probable use of fuel in emergency situation as what we might bring with us for a backup generator should solar panels not be able to sustain life under a prolonged dust storm. Since its methane fuel lox we will still have boiloff to contend with if its on each type of starship that lands on the mars surface. That the mass of the backup fuel oxidizer combination cuts into the landable payload mass on each cargo starship. The good thing would be is if we do not use it before a return cycle it could be used for the finally tank top off before launch depending on how muuch we still have after a mars cycle.

Edit to add in more data

On Mars, near the equator, the duration of daylight is about 12 hours, followed by approximately 12 hours of darkness.

Mars, spring is 7 months, summer is 6 months, fall is 5.3 months and winter is a little over 4 months long..

Page 1

Louis wrote:

Zubrin's original sums gave an energy input of 17 MwHs per tonne of propellant.
If that is the case, for a returning BFR that requires 1500 tonnes of the propellant, that would imply an energy input of 25500 MwHs or, over 660 sols, an input of 38.64 MwHs [per sol] or about 1.6 Mw constant.

kbd512 · 2019-10-05 11:47:43

SpaceNut,

Any cryogenic propellants manufactured on Mars will be used as propellant in the rockets needed to return home, not powering ground vehicles and backup generators. If you're burning your "get home" fuel in a backup generator just to stay alive, that means your power provisioning solution lacks sufficient excess power to both sustain life and produce fuel. Merely finding yourself in a situation such as that is entirely predicated on an absurdly bad idea placing pointless artificial constraints on which energy sources to use to satisfy the religious beliefs of certain people who worship at that altar of "green energy".

Oldfart1939 · 2019-10-05 15:07:57

kbd512 wrote:

Any cryogenic propellants manufactured on Mars will be used as propellant in the rockets needed to return home, not powering ground vehicles and backup generators. If you're burning your "get home" fuel in a backup generator just to stay alive, that means your power provisioning solution lacks sufficient excess power to both sustain life and produce fuel. Merely finding yourself in a situation such as that is entirely predicated on an absurdly bad idea placing pointless artificial constraints on which energy sources to use to satisfy the religious beliefs of certain people who worship at that altar of "green energy".

I tried making exactly this point in several posts to the Green "true believer." I will say no more.

Last edited by Oldfart1939 (2019-10-05 15:08:37)

louis · 2019-10-06 07:48:54

This is just silly. I've been through all this.

A. You arrive with a store of meth-ox. That is simply part of the total energy system - just like the solar panels are that all you nuclear enthusiasts want to take along for convenience - they are part of a total energy system based primarily on nuclear power. I don't claim the inclusion of solar power invalidates the nuclear option.

B. PV Panels can collect power in even the worst case dust storms on Mars and the cargo ships already on the surface will have charged batteries available offering at least around 2000 KwHs of power.

C. It is extremely unlikely that you will need to use any of your emergency meth-ox store (which can keep you powered at least 100 sols) but if you do, you will replenish as part of the propellant production plant process as necessary.

D. There is no question of jeopardising the return journey propellant supply because of course you plan for that as part of your overall approach. Whatever option you choose, you plan accordingly. In the case of a nuclear reactor you plan to "earth" (or should that be "mars") a large proportion of your energy output overnight because it won't be needed.

kbd512 wrote:

SpaceNut,
Any cryogenic propellants manufactured on Mars will be used as propellant in the rockets needed to return home, not powering ground vehicles and backup generators. If you're burning your "get home" fuel in a backup generator just to stay alive, that means your power provisioning solution lacks sufficient excess power to both sustain life and produce fuel. Merely finding yourself in a situation such as that is entirely predicated on an absurdly bad idea placing pointless artificial constraints on which energy sources to use to satisfy the religious beliefs of certain people who worship at that altar of "green energy".

louis · 2019-10-06 08:29:55

Returning to the original theme of this post, this article gives an estimate of about 16 GWhes required to produce the propellant:

http://www.thespacereview.com/article/3484/1

I think this might be an overestimate for a number of reasons including failure to allow for economies of scale and it's possible this article references the larger previous BFR design.

But let's run with the figure for the moment. It equates, over 650 sols, to near enough 1 Mwe of constant power.

So, in terms of 10Kw Kilopower nuclear reactors that would be a requirement for 100 to be delivered to the surface. Unshielded and without packaging that would be 150 tons. With shielding and packaging? Probably in excess of 300 tons. It would be a huge logistical challenge if, as some suggest the things are going to be buried under regolith.

You would need something like 31,000 sq. metres of PV Panel to produce 24.6 MwHs per sol. However, that requirement might rise to something more like 70,000 sq. metres to provide a not too erratic input to the propellant plant across the sol (with the help of chemical batteries). You would likely need possibly another 30% of PV area to account for worst case dust storms, taking it up to 91,000 sq. metres - about 300 x 300 metres. You might increase the size of the propellant plant under a PV solution - but that will not have a big impact in terms of mass I would suggest. I doubt the whole propellant plant is going to mass more than 5 tons (a guess on my part) for something producing about 40 kgs of propellant per hour - 660 millilitres a minute, just over one millilitre a second. If you increase the plant by 30%, that's only 1.5 tons additional mass. Increasing the plant in size may make more sense than increasing the PV and battery mass.

The crucial issue then is how heavy the PV array is per sq. metre. Are we talking 5kgs, 1kg, 0.5 kgs or 0.1Kg? The relevant figures are then 455 tons, 91 tons, 45 tons and 9 tons. Potentially it can be seen that PV could offer a huge mass saving over Kilopower - that's even if you allow for 20 tons of batteries to provide 6 Mwhs of storage, it would still be a large saving at 1 kg per sq. metre. So I think that's where the focus should be...could a 1 kg per square metre solution be doable on Mars?

Last edited by louis (2019-10-06 08:35:16)

Oldfart1939 · 2019-10-06 09:03:14

Louis-
I think you need to carefully re-read what GW has written about the dust storm that killed Opportunity.Through my telescope, I've observed dust storms that lasted through an entire observing opportunity from Earth. Mars is nothing more than a blob with zero surface details observable during these storms. I can appreciate your enthusiasm for solar, but you need to realize that your suggestion using methane and oxygen for in situ energy, doesn't have a chance of application. ALL the Methane and Oxygen produced will be needed for a return to Earth, and especially will be a scarce commodity in view of the size of Starship with it's energy requirements. The only reason Opportunity lasted as long as it did was due to the fantastic construction at JPL, using only the best and most durable components--not because Solar was so wonderful. There was a lot of mechanical reserve built in. That's according to Jim Rice, one of the guys doing the controlling from Earth.
I know you love Solar power, and so do I. I simply want BOTH systems in place to ensure mission success and that nobody dies as a result of an energy shortfall. Only Nuclear has the ability to keep everyone alive and still manufacture methane and oxygen during dust storms.

kbd512 · 2019-10-06 09:06:32

Louis,

A. Explain how you're keeping 12t of LCH4 and the 43t of LOX to burn that 12t of LCH4 cold enough to remain liquid. The Martian surface temperatures are not sufficiently cold to keep that propellant liquid on its own, nor can insulation keep it liquid on its own, so active refrigeration is required. Active refrigeration requires power and lots of it. If you're not getting that power from batteries, then were are you getting it from? Please don't tell me you're planning on burning your LOX/LCH4 reserve to keep it cold.

I never claimed that solar panels invalidated anything, nor that nuclear power invalidated anything. I have repeatedly stated or intimated, as have others, that solar power on a planet like Mars is an opportunistic energy source- meaning you use it when you can. It's not guaranteed to be available at all times. Since photovoltaic panels are reasonably light, relative to other power production technologies, that's why I said that they could power LOX/LCH4 generation during the day. However, when the night rolls around, I don't want to lose any propellant produced earlier in the day or burn any of it to produce power to keep from losing more of it. Furthermore, if propellant production grinds to a halt during the day because there's not sufficient power to run the propellant plant from the solar panels, I still want to keep all of the propellant already produced and keep the plant operating in some minimal fashion. I can't do that by burning propellant or depleting batteries or with solar power I need to keep people alive.

B. Yes, PV will still continue to collect "some" power during a dust storm. It most definitely won't be enough to continue propellant production or even active refrigeration merely to prevent losing what was already produced, so unless the array is massively oversized, some form of backup that continues to produce power, rather than depleting a stored energy reserve, is a much more logical and practical way of ensuring that propellant isn't lost.

C. How do you guarantee that you can produce any propellant to begin with? The very first ISRU experiment has never been operated on Mars and neither you nor Musk nor anyone else has a clue about what they'll actually need to do to obtain the quantity of water required. Speaking of relying on something that's never been tested before, this has never been tested at all. There's vastly more flight heritage behind using nuclear reactors in space than there is in producing cryogenic propellants on another planet by drilling for water and splitting CO2. We don't "make" O2 or CH4 here on Earth. O2 is simply pumped out of the atmosphere and CH4 is pumped out of the ground, compressed and liquefied, at tremendous energy cost. Thereafter, cryogenic liquids are "used" or "losed" in a near-immediate fashion.

D. The way you "plan" for your power provisioning and propellant production scheme is by devoting a substantial portion of the delivered tonnage to low energy density batteries and/or cryogenic propellants that you claim will probably never be needed to supply power, yet still have to provide power to keep cold or else you lose them (the fact that you've never addressed this point means you either don't understand what's going on here or continue ignoring it for sake of argument; and that excess propellant would be gone in less than 100 days without active refrigeration). A solar / nuclear power production, rather than power storage, solution "plans" for continuous power production, which leads to continuous availability of power for whatever uses there are for that power, because here on Earth refineries and cryogen plants operate 24/7.

GW Johnson · 2019-10-06 10:03:00

Propellant production requirements on Mars are speculative at best, because the final sizing and characteristics of "Starship" are speculative at best. Those numbers will NOT be known with any relative certainty until more realistic prototypes have successfully demonstrated flight to orbit with return.

However, those numbers will likely be in the 1000-1500 metric tons of propellant class, as the bounding calculations indicate. Of that, you are looking at about 4 times the oxygen as methane tonnages. If you want to be able to return home the next orbital opportunity after the manned landing, you must generate that tonnage in about 2 Earth years. That's about 1.4 to 2.1 metric tons (TONS NOT KILOGRAMS!!!) of finished and liquified propellant EACH AND EVERY DAY. Size your propellant manufacturing plant power draw from that figure, and don't forget the continuing cooling and densification sub-cooling requirements, either!

Waiting through an orbital opportunity to the next one (four years instead of two) only reduces that requirement by a factor of 2. It's still tons per day, not kilograms. That's a BUNCH of KWe, guys! No matter what numbers we use.

And what do you do if there's a major dust storm and you don't have enough nuclear power to keep your propellant plant running? Shut it down? Now any possible return is 4, 6, 8, maybe even 10 years away. Depends upon how many months the major dust storm lasts, and just how low the insolation really goes during the event. (The worst case observed precedes all the surface observations since Viking in 1976: the Mariner 9 event observed from orbit in 1969.)

My own opinion is take enough nuke power to run the settlement and propellant production plant regardless, and count on the solar to power rovers and construction machinery. Just oversize its array to still harvest enough during an ordinary dust storm. That would be more KWe of nuke than solar. I have no actual percentage, just that notion, to offer. We know too little to size things yet.

I have said elsewhere that "somebody" needs to be working on an industrial-scale tons(!!!)/day propellant production plant rated for Mars; that "somebody" needs to be working on real deployable surface habitation modules; "somebody" needs to be working on the rechargeable battery-powered rovers, bulldozers, etc; and NASA needs to get off its butt and get Kilopower ready to go at full size. Coordinating those needs is a perfect role for NASA, but they are not doing it effectively.

Failing that, what good is sending a "Starship" to Mars, if you cannot do anything but camp out in it until you die in the cold?

GW

Last edited by GW Johnson (2019-10-06 10:15:28)

louis · 2019-10-06 12:40:13

Well if you are going to take 100 Kilopower units to power your base and propellant production you need to decide whether you unload them or operate them from one or more Starship. If you have them all in one Starship that is an eggs in basket situation. A major fire, explosion or structural defect could result in total calamity as your energy system breaks down. Unloading 100 units at 1.5 to 3 tons each, and then towing them to wherever they are supposed to be would, and possibly burying them in regolith according to some proposals, I would suggest would be an extremely challenging logistical operation.

GW Johnson wrote:

Propellant production requirements on Mars are speculative at best, because the final sizing and characteristics of "Starship" are speculative at best. Those numbers will NOT be known with any relative certainty until more realistic prototypes have successfully demonstrated flight to orbit with return.
However, those numbers will likely be in the 1000-1500 metric tons of propellant class, as the bounding calculations indicate. Of that, you are looking at about 4 times the oxygen as methane tonnages. If you want to be able to return home the next orbital opportunity after the manned landing, you must generate that tonnage in about 2 Earth years. That's about 1.4 to 2.1 metric tons (TONS NOT KILOGRAMS!!!) of finished and liquified propellant EACH AND EVERY DAY. Size your propellant manufacturing plant power draw from that figure, and don't forget the continuing cooling and densification sub-cooling requirements, either!
Waiting through an orbital opportunity to the next one (four years instead of two) only reduces that requirement by a factor of 2. It's still tons per day, not kilograms. That's a BUNCH of KWe, guys! No matter what numbers we use.
And what do you do if there's a major dust storm and you don't have enough nuclear power to keep your propellant plant running? Shut it down? Now any possible return is 4, 6, 8, maybe even 10 years away. Depends upon how many months the major dust storm lasts, and just how low the insolation really goes during the event. (The worst case observed precedes all the surface observations since Viking in 1976: the Mariner 9 event observed from orbit in 1969.)
My own opinion is take enough nuke power to run the settlement and propellant production plant regardless, and count on the solar to power rovers and construction machinery. Just oversize its array to still harvest enough during an ordinary dust storm. That would be more KWe of nuke than solar. I have no actual percentage, just that notion, to offer. We know too little to size things yet.
I have said elsewhere that "somebody" needs to be working on an industrial-scale tons(!!!)/day propellant production plant rated for Mars; that "somebody" needs to be working on real deployable surface habitation modules; "somebody" needs to be working on the rechargeable battery-powered rovers, bulldozers, etc; and NASA needs to get off its butt and get Kilopower ready to go at full size. Coordinating those needs is a perfect role for NASA, but they are not doing it effectively.
Failing that, what good is sending a "Starship" to Mars, if you cannot do anything but camp out in it until you die in the cold?
GW

louis · 2019-10-06 12:54:02

You don't seem to understand the difference between opacity and insolation levels. Dust will obscure a view. It doesn't necessarily stop light getting through. There's a lot more ambient light when you have dust.
Read my links carefully.

Your claim that "all" the meth-ox will be required for propellant production is simply an assertion. If you want, you can design your mission so that maybe 2% of the production is allocated for insitu electricity generation.

If you are looking to Kilopower Units to power your propellant production you are looking at taking maybe 100 units at anything between 1.5 and 3 tons a time. It is a huge logistical challenge. Nuclear enthusiasts haven't even begun to address how you meet this challenge.

Oldfart1939 wrote:

Louis-
I think you need to carefully re-read what GW has written about the dust storm that killed Opportunity.Through my telescope, I've observed dust storms that lasted through an entire observing opportunity from Earth. Mars is nothing more than a blob with zero surface details observable during these storms. I can appreciate your enthusiasm for solar, but you need to realize that your suggestion using methane and oxygen for in situ energy, doesn't have a chance of application. ALL the Methane and Oxygen produced will be needed for a return to Earth, and especially will be a scarce commodity in view of the size of Starship with it's energy requirements. The only reason Opportunity lasted as long as it did was due to the fantastic construction at JPL, using only the best and most durable components--not because Solar was so wonderful. There was a lot of mechanical reserve built in. That's according to Jim Rice, one of the guys doing the controlling from Earth.
I know you love Solar power, and so do I. I simply want BOTH systems in place to ensure mission success and that nobody dies as a result of an energy shortfall. Only Nuclear has the ability to keep everyone alive and still manufacture methane and oxygen during dust storms.

louis · 2019-10-06 12:55:22

kbd512 wrote:

Louis,
A. Explain how you're keeping 12t of LCH4 and the 43t of LOX to burn that 12t of LCH4 cold enough to remain liquid. The Martian surface temperatures are not sufficiently cold to keep that propellant liquid on its own, nor can insulation keep it liquid on its own, so active refrigeration is required. Active refrigeration requires power and lots of it. If you're not getting that power from batteries, then were are you getting it from? Please don't tell me you're planning on burning your LOX/LCH4 reserve to keep it cold.
I never claimed that solar panels invalidated anything, nor that nuclear power invalidated anything. I have repeatedly stated or intimated, as have others, that solar power on a planet like Mars is an opportunistic energy source- meaning you use it when you can. It's not guaranteed to be available at all times. Since photovoltaic panels are reasonably light, relative to other power production technologies, that's why I said that they could power LOX/LCH4 generation during the day. However, when the night rolls around, I don't want to lose any propellant produced earlier in the day or burn any of it to produce power to keep from losing more of it. Furthermore, if propellant production grinds to a halt during the day because there's not sufficient power to run the propellant plant from the solar panels, I still want to keep all of the propellant already produced and keep the plant operating in some minimal fashion. I can't do that by burning propellant or depleting batteries or with solar power I need to keep people alive.
B. Yes, PV will still continue to collect "some" power during a dust storm. It most definitely won't be enough to continue propellant production or even active refrigeration merely to prevent losing what was already produced, so unless the array is massively oversized, some form of backup that continues to produce power, rather than depleting a stored energy reserve, is a much more logical and practical way of ensuring that propellant isn't lost.
C. How do you guarantee that you can produce any propellant to begin with? The very first ISRU experiment has never been operated on Mars and neither you nor Musk nor anyone else has a clue about what they'll actually need to do to obtain the quantity of water required. Speaking of relying on something that's never been tested before, this has never been tested at all. There's vastly more flight heritage behind using nuclear reactors in space than there is in producing cryogenic propellants on another planet by drilling for water and splitting CO2. We don't "make" O2 or CH4 here on Earth. O2 is simply pumped out of the atmosphere and CH4 is pumped out of the ground, compressed and liquefied, at tremendous energy cost. Thereafter, cryogenic liquids are "used" or "losed" in a near-immediate fashion.
D. The way you "plan" for your power provisioning and propellant production scheme is by devoting a substantial portion of the delivered tonnage to low energy density batteries and/or cryogenic propellants that you claim will probably never be needed to supply power, yet still have to provide power to keep cold or else you lose them (the fact that you've never addressed this point means you either don't understand what's going on here or continue ignoring it for sake of argument; and that excess propellant would be gone in less than 100 days without active refrigeration). A solar / nuclear power production, rather than power storage, solution "plans" for continuous power production, which leads to continuous availability of power for whatever uses there are for that power, because here on Earth refineries and cryogen plants operate 24/7.

SpaceNut · 2019-10-06 14:00:49

The moving target has transioned throught the designs of ITV, MTV BFR and now to starship each with many changes to payload and capabilities. The landing as well has gone through landing 1 cargo to 2 cargo and following with a human crew, next up was sending all three together to now wanting to send out 6 at one time.
One must remember that each cargo ship is identical for the purpose of failure to land and of distance from the crewed vehicles landing site.

Something to remember is the seasons of mars for 12 months will yeild with the panels the energy less storm dust accumilations but for the winter 12 months the same panels will fall quite quickly to next to nothing from them. The difusing of light matters for all of the period of wanting energy as for any months that fall short can not be made up. For winter to get the same energy as you do in summer you will need 2 panels.

Now back to the tanks which are on the starship as these are cyrogenic and not high pressure to keep the methane and oxygen in a liquid form. These as other have indicated that these will need active cooling for the ability to store until used on each vehicle that returns home. We have posteed the active cooler documents in several topics before for the level of power requirement.

The power from the array supplies not just the batteries to charge but also the colonies power needs as the batteries will power the colony for night and a reduced level for the making of fuels to be able to make the schedule which is got less time in it as you will need time to setup the array and to cover for any reduced power levels during the time frame to launch. Since launch windows are a couple months depending on fuel load and timing of transit to mars the return trip will be about the same.

So the 668 day cycle means or leaves you with less time to reach the garrantee return home fuel needs of nearer to 600 days to make fuel which up's the power requirement again...

kbd512 · 2019-10-06 17:09:07

SpaceNut,

Exactly. Any sort of energy storage scheme that relies upon low energy density batteries and fuels will mandate substantially over-sized energy production and storage systems to ensure that no matter what happens, sufficient power exists to survive and come home.

For a mission such as ambitious as this, I think I would take 40 Kilopower reactors, or 8 per cargo flight, a total of 60t of cargo. That guarantees 300kWe of stable base load. The other 700kWe of the roughly 1MWe of continuous power (16GWh over 730 days) that must be provided has to be provided by an over-sized photovoltaic array. If the array provided the same level of continuous output, which it will not, that amounts to 2.1MWh of power per hour, assuming 8 hours of useful sunlight.

Mars InSight, which uses the latest generation of technology from Orbital ATK (array integration) / SolAero (photovoltaic cell provider), has a pair 2.15m diameter ATK fans that generate a maximum of 600W to 700W on a clear day, 200W to 300W on a dusty day, according to NASA. Mars InSight set the solar power record of 4.588kWh for a single day. InSight's ATK fans are 7.26m^2 in area, so that works out to 688.7Wh/m^2/day under the best conditions and using the best of the best in hand-tested, voltage-matched photovoltaic cell technology from SolAero assembled into hand-built arrays by Orbital ATK. NASA pays Orbital ATK between $250/W and $500/W of nominal BOL output.

Our requirement is 16,800,000Wh from our array to provide the rest of the power that current fission reactor design from LANL won't be able to provide. Therefore, our array must have a minimum area of 24,394m^2 for ideal atmospheric conditions. NASA says ATK's state-of-the-art arrays are 2kg/m^2, which means our minimum array mass is 48,788kg. To provide 100% of the daily power requirement to produce propellant, the array would have an area of 34,848m^2 and have a mass of 69,696kg.

All ATK fan masses provided include power conditioning / inverter mass, but do not include wiring mass nor structural support masses associated with affixing / emplacing the arrays on the surface of Mars.

Between the solar panels, nuclear reactors, and ancillary hardware such as wiring and power conversion equipment for step-down / step-up of voltage and/or amperage, we've likely consumed 150t of the total 500t of cargo for power production alone.

Even if we go with the oversized array that provides 100% of the nominal power requirement for propellant production on a string of perfectly clear days, total power output drops to less than a third on less-than-perfectly-clear days. It'd be impossible to meet production targets with that array if there was a dust storm that lasted for just 3 months out of the 2 years they'd spend on the surface. Basically, there's no guaranteed way to come home with a solar array less than double the size of the one that provides 100% of the output requirements.

A minimum of 100 Kilopower reactors would be required to produce all of the output for propellant production, for a total mass of 150t. A solar solution that could guarantee a return flight during the regular 26 month cycle would weigh about 209t. Any batteries would add to that mass of that solution. My rough guesstimate is that 25kW of continuous power is required throughout the night for habitation and keeping the propellant cold, presuming excellent insulation. That would put the power requirement at 400kWh, which gives me a little more faith in the numbers that Elon Musk is coming up with because that was also the battery capacity he said each Starship would have. That puts the mass of a 400kWh battery at about 14t, using NASA accepted engineering practices that don't result in un-contained fires and explosions from ruptured cells.

I guess there's a technically feasible way to do this using solar power and batteries alone, but based upon my own calculations that also means that about 300t would be devoted to solar panels and batteries and wiring. That doesn't leave a lot of mass left for useful payload. For initial exploration and colony setup operations, that might be acceptable. Later on, there's just no way solar power alone would provide stable power. Also note that the mass estimates were just to produce return propellant. Also, some of those ships are going to be permanent residents of the red planet. Feeding everyone would rapidly overtake energy requirements for return propellant, although at that point there's no need for anyone to return.

So... My verdict on solar power and batteries is that it's technically feasible, but more than 50% of the delivered tonnage will end up being solar panels and batteries. There's no way in hell someone will clean arrays that size, either, which means technology needs to be developed to keep the panels clean.

Now, about finding that water... We really should look into that.

SpaceNut · 2019-10-06 18:02:44

SpaceNut wrote:

MK1 prototype to get
https://www.teslarati.com/spacex-starsh … s-spotted/
https://www.nextbigfuture.com/2019/09/s … entry.html
Same batteries that burst into flame and total your car to power starship is not such a good idea...

louis · 2019-10-06 18:11:42

"Next to nothing" generation in winter from PV panels? Where did you get that "next to nothing" idea from? Because of the Mars rotational "wobble", seasonal variation in insolation in mid latitudes is far less on Mars than on Earth - and it's why the optimal latitude for PV generation is around 29-30 degrees in the Northern hemisphere, rather than closer to the equator as on Earth.

I am not accepting this idea that Starships are going to be landing all over the place. We've seen in recent years that landing technology has moved on remarkably. I think the default position is that all the Starships will land pretty much wherever we determine. They will use a range of techniques to achieve that - transponders, terrain mapping, laser tracking and probably satellite-Starship communication.

The point about the energy system I am proposing is that there are a lot of variables you can tweak to get the desired result:

1. Bigger or smaller PV array.

2. Bigger or smaller propellant plant production facility.

3. Bigger or smaller chemical battery storage

4. Bigger or smaller meth-ox energy storage.

5. Bigger or smaller mass for the energy system transferred from Earth to Mars.

The more I am reading into this and thinking about it, the more I think it makes sense to increase 2 in order to facilitate a solar power solution.

The PP facility is not going to be huge. My previous guess was maybe 5 tonnes max. Increasing it by 20% is a mass increase of 1 ton. But you could be talking about 8 tons increase in mass if you increase the PV system by 20%.

If we could get methane clathrate storage on the surface of Mars (ie without the need for pressurised or cyrogenic tanks) that could lead to even greater mass savings.

SpaceNut wrote:

The moving target has transioned throught the designs of ITV, MTV BFR and now to starship each with many changes to payload and capabilities. The landing as well has gone through landing 1 cargo to 2 cargo and following with a human crew, next up was sending all three together to now wanting to send out 6 at one time.
One must remember that each cargo ship is identical for the purpose of failure to land and of distance from the crewed vehicles landing site.
Something to remember is the seasons of mars for 12 months will yeild with the panels the energy less storm dust accumilations but for the winter 12 months the same panels will fall quite quickly to next to nothing from them. The difusing of light matters for all of the period of wanting energy as for any months that fall short can not be made up. For winter to get the same energy as you do in summer you will need 2 panels.
Now back to the tanks which are on the starship as these are cyrogenic and not high pressure to keep the methane and oxygen in a liquid form. These as other have indicated that these will need active cooling for the ability to store until used on each vehicle that returns home. We have posteed the active cooler documents in several topics before for the level of power requirement.
The power from the array supplies not just the batteries to charge but also the colonies power needs as the batteries will power the colony for night and a reduced level for the making of fuels to be able to make the schedule which is got less time in it as you will need time to setup the array and to cover for any reduced power levels during the time frame to launch. Since launch windows are a couple months depending on fuel load and timing of transit to mars the return trip will be about the same.
So the 668 day cycle means or leaves you with less time to reach the garrantee return home fuel needs of nearer to 600 days to make fuel which up's the power requirement again...

kbd512 · 2019-10-06 18:31:06

Louis,

Cite a credible source for your propellant production plant mass. Unless you can do that, then you're just speculating. You're always telling an actual rocket scientist to cite his sources after he's done it multiple times, so cite your sources on that methalox plant mass.

louis · 2019-10-06 18:49:09

I never claimed a credible source for that. I said explicitly it was a guess on an earlier post. Happy to discuss it. I did work out propellant production would be something like 11 millilitres per second. That was really what I based the 5 tons on. I find it difficult to believe it would need to be bigger than that to produce that sort of amount per second.

What's your estimate?

Even if it was ten times my estimate and amountd to 50 tons, a 2% increase is still only 1 ton. Remember - your 100 Kilopower units are clocking in at at least 150 tons and possibly 300 tons. Got to keep the scale of things in mind.

I fully respect GW's rocket expertise. As I always admit - I don't understand the rocket equation. But this isn't about the rocket equation.

You've got to admit no other nuclear enthusiast has admitted here that they might have to transfer 100 Kilopower units to Mars to deal with propellant production. I was the one who pointed that out. And, so far, no nuclear enthusiast has explained how they will deal with the logistical challenges of that: storage, deployment, cabling and safety issues. I name it the "Kilopower Challenge". Can any nuclear enthusiast here explain here the logistics of how 100 x 10 Kw Kilopower units will be deployed on Mars.

kbd512 wrote:

Louis,
Cite a credible source for your propellant production plant mass. Unless you can do that, then you're just speculating. You're always telling an actual rocket scientist to cite his sources after he's done it multiple times, so cite your sources on that methalox plant mass.

Last edited by louis (2019-10-06 18:51:31)

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