Powering a Propellant Plant Facility

louis · 2019-10-15 16:43:10

What is required in terms of mass to produce enough propellant on Mars for a return Starship?

This is an interesting analysis from Blake on Reddit:

https://www.reddit.com/r/spacex/comment … ant_plant/

He comes up with a combined figure of only 74 tons for both a 1 Mwe Propellant Production Facility and the mass of the PV facility generating the power for the process.

As I suspected, it would seem the propellant plant itself doesn't mass much. So scaling up to allow for peak power production from a PV facility (Blake uses 3 Mwe as the upper limit) is not a major penalty.

I see Blake also plans for a methalox turbine, as do I, and has given a mass figure for atmospheric compression.

I think the 25 ton figure for solar power is probably an underestimate. I just have doubts that you can go so lightweight on Mars on the PV panelling...I think I'd continue to favour a smaller PV area but with heavier panelling and greater efficiency...

When it comes to day-night battery storage Blake favours a mix of Tesla batteries and fuel cells, massing a total of 7 tons. This is a much lower figure than I started out with, but Blake's proposal allows for much greater use of peak power. Blake assumes a requirement of 100Kws overnight...This could easily be covered by the battery system on the Starships (used for fin actuation) - which Blake would not have known about when he produced his analysis, so you could probably subtract 7 tons from the 74 ton figure, making it 67 tons.

Certainly on the basis of this detailed analysis, it would seem that a PV solution is far superior to a Kilopower solution which would amount to a minimum of 160 tons plus 40 tons for the non-power elements of propellant production. That makes a total of 200 tons compared with Blake's figure of 74 tons - the nuclear solution requires 126 additional tons of mass. Even if the PV mass was upped from 25 to 50 tonnes to allow for (a) heavier, more efficient flexible PV and (b) making good the power loss during a severe dust storm (while Blake provides for base power, Blake doesn't indicate how the overall loss of power to produce propellant would be made good - it could be the equivalent of losing 100 sols or more of normal production), that differential is still over 100 tons. Even if you have to add another 12 tons for the propellant facility to accommodate higher peak production (to make good severe dust storm losses), it's still better than Kilopower by over 80 tons.

Last edited by louis (2019-10-15 16:44:27)

SpaceNut · 2019-10-15 18:09:30

mars year 687 days - journey from earth and return

The total journey time from Earth to Mars takes between 150-300 days depending on the speed of the launch, the alignment of Earth and Mars, and the length of the journey the spacecraft takes to reach its target. The typical time during Mars's closest approach to the Earth every 1.6 years is about 260 days.

In the nine months it takes to get to Mars, Mars moves a considerable distance around in its orbit, about 3/8 of the way around the Sun. You have to plan ahead to make sure that by the time you reach the distance of Mar's orbit, that Mars is where you need it to be! Practically, this means that you can only begin your trip when Earth and Mars are properly lined up. This only happens every 26 months. That is there is only one launch window every 26 months.

Just like you have to wait for Earth and Mars to be in the proper postion before you head to Mars, you also have to make sure that they are in the proper position before you head home. That means you will have to spend 3-4 months at Mars before you can begin your return trip. All in all, your trip to Mars would take about 21 months: 9 months to get there, 3 months there, and 9 months to get back.

Base numbers to make fuel is lots smaller that the article 600 as numbers can not lie. Lets say starship could get to mars in a free return trajectory of 6 months so the most time still is 21 - 12 = 9 months to 11 months at most for lauch return windows. That said you are not coming home in 1 mars cycle with the above power and masses.

Nasa is using a 400 day to make fuel as indicated in multiple documents of course the short time means more power and equipment to make the fuel...

tahanson43206 · 2019-10-15 18:43:38

As I recall Dr. Zubrin's plan, robot ships would land and make a full load of propellant BEF0RE a ship with crew leaves Earth.

The recent discussion about nuclear fission vs solar cells seemed (to me as I read it) to NOT assume the return fuel has to be present before the crewed mission leaves for Mars.

Impatience will put crew at risk, but competition between nations (or perhaps companies) may force expeditions with crew to depart for Mars before return fuel is in place.

(th)

louis · 2019-10-15 18:54:43

I don't understand the point being made in this post. All discussions here about Mars Mission suggest Mars pioneers are going to be on the planet for about 2 years. Not sure why you say "3 months there". And that doesn't tally with what you say NASA is planning to do - producing propellant over 400 days. Do NASA's plans involved as large a craft as Starship landing? I don't think so.

600 sols seems a reasonable propellant production period for planning purposes to me. With the sort of PV facility I am proposing, the likelihood is it will take much less than 600 sols, unless the Mission is unlucky enough to experience a worst case dust storm scenario.

SpaceNut wrote:

mars year 687 days - journey from earth and return
The total journey time from Earth to Mars takes between 150-300 days depending on the speed of the launch, the alignment of Earth and Mars, and the length of the journey the spacecraft takes to reach its target. The typical time during Mars's closest approach to the Earth every 1.6 years is about 260 days.
In the nine months it takes to get to Mars, Mars moves a considerable distance around in its orbit, about 3/8 of the way around the Sun. You have to plan ahead to make sure that by the time you reach the distance of Mar's orbit, that Mars is where you need it to be! Practically, this means that you can only begin your trip when Earth and Mars are properly lined up. This only happens every 26 months. That is there is only one launch window every 26 months.
Just like you have to wait for Earth and Mars to be in the proper postion before you head to Mars, you also have to make sure that they are in the proper position before you head home. That means you will have to spend 3-4 months at Mars before you can begin your return trip. All in all, your trip to Mars would take about 21 months: 9 months to get there, 3 months there, and 9 months to get back.
Base numbers to make fuel is lots smaller that the article 600 as numbers can not lie. Lets say starship could get to mars in a free return trajectory of 6 months so the most time still is 21 - 12 = 9 months to 11 months at most for lauch return windows. That said you are not coming home in 1 mars cycle with the above power and masses.
Nasa is using a 400 day to make fuel as indicated in multiple documents of course the short time means more power and equipment to make the fuel...
http://canada.marssociety.org/winnipeg/ … chart2.jpg

SpaceNut · 2019-10-15 21:02:49

The typical time during Mars's closest approach to the Earth every 1.6 years is about 260 days.
https://www.jpl.nasa.gov/edu/teach/acti … h-windows/
https://www.nasa.gov/centers/ames/engin … ature.html

Time on Mars surface has to do with launch to return resonent cycles which is 2 years and 7 weeks for when we are the closest together but thats not when we launch as we follow an arc to mars.
Short stays on mars surface are 30 to 90 days.
Long stays are 300 to 500 days on the surface to account for the cycles.

louis · 2019-10-16 03:58:40

Well we can discount the short stay for a Starship mission. Blake's analysis was clearly based on a long stay.

I thought the long stays were longer than an average of 400 days/sols.

If we were reducing from 600 sols to 400 sols we'd have to increase plant and energy input by roughly 50%. But that would also apply to the nuclear option as 1.5 Mwe would be required. So a nuclear energy approach would require roughly 300 tons of Kilopowers, propellant plant and associated equipment against 156 tons for a PV-based approach as outlined by Blake with my additional tonnage incorporated for dust storm compensation.

This article references 500 days as the planning base for Space X but whether that's a minimum, average or maximum is not stated...

https://arstechnica.com/science/2019/06 … fely-back/

SpaceNut wrote:

The typical time during Mars's closest approach to the Earth every 1.6 years is about 260 days.
https://www.jpl.nasa.gov/edu/teach/acti … h-windows/
https://www.nasa.gov/centers/ames/engin … ature.html
Time on Mars surface has to do with launch to return resonent cycles which is 2 years and 7 weeks for when we are the closest together but thats not when we launch as we follow an arc to mars.
Short stays on mars surface are 30 to 90 days.
Long stays are 300 to 500 days on the surface to account for the cycles.

Calliban · 2019-10-16 06:08:22

"Certainly on the basis of this detailed analysis, it would seem that a PV solution is far superior to a Kilopower solution which would amount to a minimum of 160 tons plus 40 tons for the non-power elements of propellant production."

Shipping dozens of small kw-level nuclear reactors to Mars makes no sense at all. It balloons the mass requirements for a system that is already one of the most reliable mission components. The original SP-100 concept from the 1980-90s had a mass budget of 4.58tonnes for a 100kWe system, using thermoelectric generators with a 2MWth heat source at an efficiency of 5%. With Sterling or Brayton cycle engines, power density would be greater still. Nuclear systems producing ten times as much power need not be ten times heavier. But very small fission systems are not very efficient because there are minimum effective sizes for critical assemblies.

https://ntrs.nasa.gov/archive/nasa/casi … 003294.pdf

Kilopower appears to have been designed as replacement for RTGs on deep space missions, where you need 100s-1000s of watts to power transmitters and heat components. Mass efficiency is not the driving concern, as the driver is to produce small amounts of power reliably for decades. The RTGs that they replace have even poorer power density, but huge energy density. Not necessarily a suitable system if power of a MWe or more is needed for 2-3 years. The fact that MW grade space reactors are not being developed, tells us that NASA probably aren't taking manned Mars missions very seriously.

A reactor system with more than one power generation loop is no less reliable than a solar power plant backed up by a methalox gas turbine. Both have moving parts. The reactor achieves redundancy by having multiple pumps and power generation loops. If everything goes wrong, you freeze to death. Then again, if the propellant pump fails on the descent stage engine you are going to die. Given that there are so many ways of dying on a mission like this, the priority is to make sure no single component dominates risk; there will never be any perfect solutions.

Consider that nuclear submarines here on Earth need propulsion to get to the surface. If reactor power fails unexpectedly, the entire submarine could be lost along with its crew. The Earth's navies do not generally mitigate this problem by bringing backup reactors along. The systems are reliable enough and have enough stored energy to mitigate the hazard.

"He comes up with a combined figure of only 74 tons for both a 1 Mwe Propellant Production Facility and the mass of the PV facility generating the power for the process."

74 tonnes is a great deal of mass budget for a Mars-direct style mission. Is that what we are discussing here? Even for Musk's much more ambitious starship concept it sounds like rather a lot.

Last edited by Calliban (2019-10-16 06:38:17)

louis · 2019-10-16 06:47:53

I don't really want to get sidetracked on to this but I guess it's important in terms of the PP facility and energy system. This is a helpful discussion.

https://space.stackexchange.com/questio … -frequency

The Case for Mars seemed to establish 550 days as a norm for the stay on Mars on a long mission.

But this analysis suggests something more like 400-450 days.

These are Earth days, so even fewer sols.

Based on this site, which was referenced in the discussion, for the 2024 window, would would arrive after nine months and spend some 15 months on the planet, so about 455 days.

http://clowder.net/hop/railroad/sched.html

However, the windows are over 2 or three months each way, are they not? So I guess you could get close to spending 600 days on the planet if you left early in a window and returned late in a window.

Maybe 500 sols would be a better reference point than 600 which would be an increase of roughly 20% in tonnages, so nuclear would become 240 tons and PV would rise to 123 tons (in relation to my figures in the OP).

louis · 2019-10-16 07:32:25

1. This is a Space X style mission being discussed here - so you need to produce about 1000 tons of propellant to get back home. 74 tons, or even 120 tons seems a reasonable mass for the energy system and PP facility - not more than 24% of a 500 ton mission. You're left with 380 tons! And that is a huge amount. Probably means you could bring habs ready to deploy for up to 50 people who follow.

2. I have raised that issue about KP units being designed for robotic deep space missions rather than human missions - which is why there are issues about deployment and location.

3. I accept you could potentially produce more efficient nuclear reactors for Mars in terms of power to mass, but (a) no one is developing them (b) it's taken about 10 years already for the KP units to get to this stage of development - not yet at the demonstration stage - how much longer for bigger nuclear reactors? (c) The bigger the individual reactors, the greater the concern about radioactive pollution in the case of a catastrophic flight failure over Earth.

4. What about protecting humans from the larger reactors? Presume you are activating them on the surface? Of course, the bigger the tonnage that needs to be unloaded from the Starship, the bigger the logistical problem. What machine is towing 4.5 tons to its location and at what speed? I would say 4.5 tons was definitely an upper limit, any maybe even that is too big. You certainly don't want to have to start assembling anything on the Mars surface - that would be hell. What about protection from dust storms? Your reactor is going to have to be sealed up. It might be best to leave it on a Starship but if so you might need to provide effective shielding...otherwise what happens with the other cargo - you don't want to lose 95 tons of potential cargo because you can't use the Starship due to radiation. Not wise to put all your eggs in one basket, so probably need two Starships which would mean if you had 5 on each of two Starships you might lose 55 tons of cargo space in both if cargo could not be offloaded prior to activation. If you offload cargo first, where is your power coming from?

Calliban wrote:

"Certainly on the basis of this detailed analysis, it would seem that a PV solution is far superior to a Kilopower solution which would amount to a minimum of 160 tons plus 40 tons for the non-power elements of propellant production."
Shipping dozens of small kw-level nuclear reactors to Mars makes no sense at all. It balloons the mass requirements for a system that is already one of the most reliable mission components. The original SP-100 concept from the 1980-90s had a mass budget of 4.58tonnes for a 100kWe system, using thermoelectric generators with a 2MWth heat source at an efficiency of 5%. With Sterling or Brayton cycle engines, power density would be greater still. Nuclear systems producing ten times as much power need not be ten times heavier. But very small fission systems are not very efficient because there are minimum effective sizes for critical assemblies.
https://ntrs.nasa.gov/archive/nasa/casi … 003294.pdf
Kilopower appears to have been designed as replacement for RTGs on deep space missions, where you need 100s-1000s of watts to power transmitters and heat components. Mass efficiency is not the driving concern, as the driver is to produce small amounts of power reliably for decades. The RTGs that they replace have even poorer power density, but huge energy density. Not necessarily a suitable system if power of a MWe or more is needed for 2-3 years. The fact that MW grade space reactors are not being developed, tells us that NASA probably aren't taking manned Mars missions very seriously.
A reactor system with more than one power generation loop is no less reliable than a solar power plant backed up by a methalox gas turbine. Both have moving parts. The reactor achieves redundancy by having multiple pumps and power generation loops. If everything goes wrong, you freeze to death. Then again, if the propellant pump fails on the descent stage engine you are going to die. Given that there are so many ways of dying on a mission like this, the priority is to make sure no single component dominates risk; there will never be any perfect solutions.
Consider that nuclear submarines here on Earth need propulsion to get to the surface. If reactor power fails unexpectedly, the entire submarine could be lost along with its crew. The Earth's navies do not generally mitigate this problem by bringing backup reactors along. The systems are reliable enough and have enough stored energy to mitigate the hazard.
"He comes up with a combined figure of only 74 tons for both a 1 Mwe Propellant Production Facility and the mass of the PV facility generating the power for the process."
74 tonnes is a great deal of mass budget for a Mars-direct style mission. Is that what we are discussing here? Even for Musk's much more ambitious starship concept it sounds like rather a lot.

SpaceNut · 2019-10-16 19:39:36

I think the equipment and water extraction numbers are to low as this picks on an untested area to do a proof of concept to see if the well ice task would work if there. Most of mars is not a glacier covered away for easy access and that means preplanning a mission just to land a robotic mission with the stuff to test the site long before sending man to it.

My home had a drilled well done over the course of nearly a week to a depth of 280 ft just to get 2 gallons of rusty water flow from it a minute. It used metal casings till it hit bedrock before no more were needed to line the hole. You will not get away with PVC pipe for the liners. It did get water at 50 ft but to have a reservoir to pump from means you need to drill deeper. It is about an 8" diameter.

http://americanartesianwell.com/drilling-a-well-faq/

Typical drilling truck in full active drilling
new+pic.jpg

this is not a drilling rig for mars which is bedrock and broken layered rock.

The nuclear thermal heat could be used to force water out of soil via a conveyer beld track with a pan of soil being moved over the radiator with a moist capture dome over it to allow for it to become steam as it moves over the heat such that we can capture the water from its processing.

SpaceNut · 2019-10-16 21:26:58

Submarine oxygen generation
https://www.energy.gov/sites/prod/files … hamdan.pdf

fuel cell
https://www.intelligent-energy.com/uplo … asheet.pdf

Oldfart1939 · 2019-10-16 22:06:21

SpaceNut-Now you have shown what I've only talked about here--a REAL drill rig! And that's a small one, by my standards.

Before I moved from Wyoming to the Euphoric State of Colorado, my neighbor was a professional oil driller; I seem to recall him saying that a big drill rig cost something like $25 Million. Could drill a natural gas well down to 36,000+ feet.

When my friend from Lawrence Livermore Lab sent me a pic of the fabulous drill rig, now stuck, on the Mars rover I laughed in his face.

louis · 2019-10-17 04:22:04

Whilst it's true most of Mars is "not a glacier covered away for easy access" some small parts are. These are the locations being looked at by NASA and Space X for possible landing sites - and we have proof that they have been looking in Accidia Planitia/Amazonis Planitia border region. I think Felix covered this in his one of his recent "What About It Videos" or maybe it was Ryan MacDonald ("Martian Colonist")...All the measurements point to there being places where water ice has pushed through crater walls and is only a metre or so below fairly loose regolith. As far as I can tell these tend to be on inclines, being crater walls.

So I think what is likely to be required is earth moving equipment - small bulldozers - and robots with powerful drills. All need to be tracked or otherwise able to deal with inclines and demanding terrain. I think breaking off chunks of ice may well be the most effective method of recovering water. Then you just need other rovers to transport the ice chunks back to the PP Facility in sealed holds. A transport rover might carry maybe half a ton. You might need maybe four of those to cope with the process.

Even if you're right about the mass allowance being too low, of course both the nuclear power and PV power approaches would need the same sort of equipment to tackle water mining, so I do think it affects the fundamentals of the nuclear v PV comparison, as outlined in Blake's analysis.

One point, I have always assumed water mining operations will be overseen close up by a humans in a human-rated rover, probably directing the robot rovers a lot of the time. That might put limits on how much you can use nuclear power at the mining location. It could be observed from afar using rover coms but I just have a feeling we need close-up supervision of what could be quite a complex task.

SpaceNut wrote:

I think the equipment and water extraction numbers are to low as this picks on an untested area to do a proof of concept to see if the well ice task would work if there. Most of mars is not a glacier covered away for easy access and that means preplanning a mission just to land a robotic mission with the stuff to test the site long before sending man to it.

elderflower · 2019-10-18 03:21:39

However you mine your water, at some point you will have to melt it. Melting of ice requires a lot of heat, but not necessarily at high temperature. The rejected heat from a thermal engine would be suitable for this, so a nuclear source coupled to a Brayton or Sterling engine could provide for both your power needs and the heat to melt your ice and warm your habs and green houses. PV does not provide rejected heat, only power, so you would need more of it to cover this demand.

tahanson43206 · 2019-10-18 04:34:42

For Elderflower re #14

Nice! Thanks!

The 100 10 Kw power plants could be fitted with conveyor belt passages between the reactor and the surface.

The excess heat that would normally radiate to space could be directed to the incoming ice/regolith mixture which could be monitored by sensors to confirm that melt has occurred before advancing the conveyor.

If Calliban's concept for a larger reactor wins the competition for funding, it too could be fitted with a moving passageway for material to be heated in this manner.

(th)

elderflower · 2019-10-18 05:36:30

You probably want to heat it in closed vessels. Conveyors are notorious for spillage and wet spills will freeze and cause trouble with moving parts and frost heave.

Calliban · 2019-10-18 06:09:38

tahanson43206 wrote:

For Elderflower re #14
Nice! Thanks!
The 100 10 Kw power plants could be fitted with conveyor belt passages between the reactor and the surface.
The excess heat that would normally radiate to space could be directed to the incoming ice/regolith mixture which could be monitored by sensors to confirm that melt has occurred before advancing the conveyor.
If Calliban's concept for a larger reactor wins the competition for funding, it too could be fitted with a moving passageway for material to be heated in this manner.
(th)

I would suggest a solution mining approach. Use reactor waste heat to heat water to 100 degrees centigrade in some sort of heat exchanger and pump it underground using a centrifugal pump. Next, inject cold liquid CO2 into the well in controlled quantities. The hot water will melt the ice and evaporate the CO2 creating a layer of melt water covered in pressurised CO2 gas. The pressure will push the melt water out of extract wells drilled along the glacier. Heating and melting the ice will take a lot of energy, about 500KJ/kg. So you need to inject about 1kg of hot water for every 2kg you extract. That's ignoring heat losses. Using steam would be far more efficient, because the latent heat of boiling/condensation of steam is about 2MJ/kg. But that implies higher temperatures.

GW Johnson · 2019-10-18 11:56:40

Is not steam extraction something I advocated some time ago?

It's a variant on something done in somewhat-depleted oil fields for decades now.

GW

Calliban · 2019-10-18 13:12:33

GW Johnson wrote:

Is not steam extraction something I advocated some time ago?
It's a variant on something done in somewhat-depleted oil fields for decades now.
GW

I'm quite new here, so have missed a lot of valuable discussion. Apologies if I have duplicated things that were discussed before.

Generating steam at temperatures of 200-300C is something that could be accomplished using native graphite moderated reactors burning natural uranium. But these will be low power density monstrosities. I wonder if a better long-term approach would be to import fast reactor cores and reactor vessels and build the pipework and secondary systems on Mars

louis · 2019-10-18 13:30:55

Why bother?

You could import 300 tons of PV equipment on Mission 2 if you wanted - enough to generate 300 MwHes per sol.

Alternatively you could import a highly automated PV manufacturing facility and begin manufacturing PV panels on Mars. More than that you can begin constructing a Mars ISRU PV manufacturing facilities using 3D printers after Mission 4, once various vital industrial machines have been imported. Some specialist materials and parts might still need to be imported but they would be low mass.

Calliban wrote:

GW Johnson wrote:
Is not steam extraction something I advocated some time ago?
It's a variant on something done in somewhat-depleted oil fields for decades now.
GW
I'm quite new here, so have missed a lot of valuable discussion. Apologies if I have duplicated things that were discussed before.
Generating steam at temperatures of 200-300C is something that could be accomplished using native graphite moderated reactors burning natural uranium. But these will be low power density monstrosities. I wonder if a better long-term approach would be to import fast reactor cores and reactor vessels and build the pipework and secondary systems on Mars

Last edited by louis (2019-10-18 13:33:47)

Calliban · 2019-10-18 14:15:25

louis wrote:

Why bother?
You could import 300 tons of PV equipment on Mission 2 if you wanted - enough to generate 300 MwHes per sol.
Alternatively you could import a highly automated PV manufacturing facility and begin manufacturing PV panels on Mars. More than that you can begin constructing a Mars ISRU PV manufacturing facilities using 3D printers after Mission 4, once various vital industrial machines have been imported. Some specialist materials and parts might still need to be imported but they would be low mass.

Any decision on power supply will be informed by cost benefit analysis. Maybe the analysis will opt in favour of solar panels. For early missions where power requirements are modest, it may indeed be cheaper to develop a space-solar solution than a nuclear reactor.

But the more energy you need, the less true that will be. An SP-100 reactor would generate 2MW of heat around the clock and the core weighs about 700kg. You would be hard pressed to match that sort of power density with solar panels on Mars. And the bigger the reactors are, the better their fuel utilisation and power density.

Living on the planet will require water in abundance. It will require large amounts of heat for surface greenhouses or large amounts of electricity for compact artificial lighting. And of course reducing metals, making concrete, making fuel, air, carrying out mining and manufacturing is power hungry. Living on Mars will require a lot more energy than living on Earth. That energy must be cheap if any serious colonisation effort is to stand a chance.

Last edited by Calliban (2019-10-18 14:19:41)

SpaceNut · 2019-10-18 17:29:28

Louis the size of missions with the vehicle count being doubled or trippled is not how to solve the problem just to get tonnage for mars is not how you make a system work.

Mission 1 if we can land 2 cargo is a first with both of them being identical for manifest. First problem if all goes well with landing is to setout a power creation system to keep the ship and contents viable with anything more than that a bonus for the future human missions. The big if is the risk factor for sending a human starship crew with the cargo units since we do not know how well they will land.
The question is how much equipment can be used to prepare the way for the human mission that follows in mission 2 and how much fuel do we think we can get with the remaining mass for the system plus energy source seperate from the ships.

Mission 2 would send 2 more cargo with different manefest than the first but these still are duplicate content with the crew since you have a good basis for reduced risk for landing. With the first human crew to leverage from where the first mission leaves off.

kbd512 · 2019-10-19 22:22:58

SpaceNut,

NASA couldn't make a permanent base on the moon work without nuclear power on any reasonable mass budget. On the moon, you have a fixed period of time that solar arrays would be in darkness. Despite an extreme energy storage requirement for a period of 29.5 days in the case of a lunar base, not even that applies on Mars. There have been multiple periods of functionally useless insolation for more than a month at a time, directly observed by multiple robotic missions sent by JPL / NASA to Mars, so we can't even get the kind of power guarantee we'd get with a solar powered lunar base.

Solar power won't work reliably on the surface of Mars, no matter how modest nor how great the power requirements happen to be. We had two solar powered rovers on Mars that only required 24 Watt-hours of electricity per day to keep their computers alive. Both were killed by dust storms. Only chance and circumstances allowed them to live as long as they did, else both rovers would've died around the same time. If both rovers had landed during a major dust storm, then they'd be dead on arrival. Their electronics, batteries, and solar panels worked so well that nothing except being completely deprived of power could kill them, yet that's exactly what the dust on Mars did. Each and every solar powered robot we've sent to the surface of Mars dies from the same cause. They all function flawlessly until the dust kills them. The planet is trying to tell us something, even if some people here don't want to hear it. If we can't send something to Mars that can live on the same power consumed by an iPad, unless the weather cooperates, then we're certainly not going to send a human mission there with vastly increased power requirements and get a different result. The definition of insanity is trying the same thing over and over again, expecting a different result. It's time to try something new that might actually work.

tahanson43206 · 2019-10-20 07:09:03

For kbd512 re #23, and your continued development of a vision for use of nuclear power on Mars in other topics ...

Recently someone (it might have been Calliban) proposed using waste heat from 10Kw nuclear power supply devices to perform useful service, instead of just radiating to space as is the default design.

My question for you here has two parts (it may have more but I haven't written it yet) ...

First ... what is the closest the 10Kw plants could be situated with respect to underground human habitats. I'm guessing the 1 kilometer distance discussed in earlier posts in this forum is a distance chosen for maximum safety.

Second, is it feasible to route water around the plants to collect waste heat and deliver it back to underground human habitats for maintaining a comfortable habitat temperature? I am thinking of the ploy used in "The Martian" to heat the rover for the long slow trip across the terrain. No one (that I recall) made much of the radiation that would inevitably have been accompanying the welcome heat, but under the circumstances, I suppose it was a risk worth taking.

In other words, if you were an architect given the appropriate budget to work with, could you (would you?) design a nuclear powered human habitat able to maintain a family in comfort on Mars (or in the Northern reaches on Earth)?

I note that designers of nuclear powered submarines and aircraft carriers are able to enlist ALL the features of nuclear power to maintain a comfortable and safe environment for human crew for long periods of time.

My expectation is that the very same high level of performance is possible for civilian habitation anywhere, given suitable access to planetary mass for heat sink.

(th)

GW Johnson · 2019-10-20 10:06:02

A part of the problem here with propellant facility size and production rates is the disparity between what Spacex proposes as a Mars vehicle and what everybody else has proposed. The others require a few dozen to a few hundred tons at most; Spacex's vehicle will require something in the 1000-1500 ton class, for each and every vehicle that returns. And return they must to be reusable, and hold the price down, so don't kid yourself about leaving the first few dozen one-way on Mars.

Another part of the problem has to do with whether the production process works adequately as an intermittent process, or whether it is better operated continuously, around the clock. If the process works better continuously, then a solar-powered plant must have huge batteries not just to get through the night, but also the early morning and late afternoon hours, when sun angles are adverse. The only way around that dilemma is the tracking collector, a much heavier, more expensive, and difficult-to-maintain item in dusty conditions.

The alternative to solar with huge batteries is currently nuclear power. It is one thing to propose a methlox electric generator set, it is quite another to propose something like that to power your plant, even for a short time. The second law of thermodynamics says the propellant you consume making electricity is way to hell and gone far larger than the quantity your plant can make, while the generator is running.

One thing I remember from thermo class is this: "first law says you cannot win, second law says you cannot come close to breaking even, third law says not only can you not get out of the game, but also that you are gonna lose really big-time". Crudely put, but accurate.

What makes chemically-fueled combustion engines in the least feasible on Earth is the presence of a substantially-oxygenated atmosphere available "for free" and at a significant pressure. The fuel is quite the minority of the total propellant feed to the engine, usually at most around 6.5%, sometimes less as with diesel and gas turbine. 95.5+% of your propellant is free, with sufficient dilution of the oxygen to limit flame temperatures to survivable values, and at sufficiently-high inlet pressure to enable a positive return from the thermodynamic operating cycle.

Mars has neither the freely-available and properly-diluted oxygen, nor an adequate inlet pressure level. Even if it had a 21% oxygen atmosphere, at 6 mbar pressure, the giant inlet turbocharger you must have to function at all, would draw far more power than the engine could ever produce. I think you can pretty well discard the notion of "airbreathing engines" on Mars, because of those two lacks.

Not much else is known besides solar and nuclear that would work on Mars. Solar has best output between about 10 AM and 2 PM solar hour angle time, reduced output between dawn and 10 AM, and between 2 PM and sunset, and no output at all at night. Hence the need for a really big set of batteries to get you through about say 14-16 hours of the 24 more-or-less hour cycle, on Earth or Mars. And we already know its output is sharply reduced during big dust storms, even at midday. It can be essentially zero in the worst ones, which can last for days, weeks, even months.

Nuclear on the other hand, is continuous and constant 24/7 regardless. All you need is redundant power units, in case something bad happens to one of them. Mars is NOT the place to be putting all your eggs in one basket, with regard to electricity, or anything else. Too hostile to our kind of life.

And that is why I say use nuclear for the base load of propellant plant operation and night-time life support, with solar adding daytime recharge for the rechargeable battery-powered vehicles and equipment we are going to need. Use it to the max when its max is available, and you don't need such massive battery installations. That's just plain old common sense talking.

GW

Last edited by GW Johnson (2019-10-20 10:11:17)

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Powering a Propellant Plant Facility

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