Will SpaceX use NASA Kilopower Nuclear Reactors?

[Jcc]

As NASA's Kilopower program undergoes it first tests, will it be a suitable technology for SpaceX Mars plans?

On the plus side, it is already under active development and is likely to be the first practical fission power system to get approval for flight to the Moon and Mars, it is compact lightweight and you can take several of them.

On the minus side, a 1 kilowatt nominal initial rating is too small for Mars colonization plans, and you would need a very large number of them, or much higher power.

This design uses an "umbrella deployed" radiator to send waste heat to the thin Mars atmosphere or a vacuum, I have heard some suggestions that you really want to send waste heat into the Martial soil as it can conduct heat more efficiently, and possibly use the waste heat for habitats or industrial purposes.

Kilopower is meant to use Stirling engines to spin a generator. Is there a better approach? 

https://www.nasa.gov/directorates/spacetech/feature/Powering_Up_NASA_Human_Reach_for_the_Red_Planet

https://www.scientificamerican.com/article/nasa-seeks-nuclear-power-for-mars/

[John Alan]

Kilopower is meant to use Stirling engines to spin a generator. Is there a better approach? 

No... not really... my opinion...
A well made, high pressure Helium, Stirling engine is a good choice for the application...

Hooked to a battery bank... it could sit there making 1000 watts all the time...
But the battery could serve a surge load of many times that for a short period
 

[deruch]

FISO presentation from February: 
"Kilopower: Small Fission Power Systems for Mars and Beyond"  http://spirit.as.utexas.edu/~fiso/telecon/Mason_2-1-17/
Lee Mason

I don't recall if Lee discusses SpaceX specifically, but it gives a very nice overview of the project and goals.  For SpaceX focus, I know Tom Mueller mentioned it during his talk with they NYU Astronomy Society that was recorded and widely discussed.  I think he even mentions SpaceX partnering or participating in the Kilopower project.  Though, I don't recall any details actually being mentioned.

[Jcc]

Noting from the linked presentation, they envision 10kW class systems going to Mars, so that is an order of magnitude better than what I mention in the OP.

Even if these systems are available for early SpaceX Mars flights, they will deploy solar also, but need nuclear when available.

[meekGee]

For what SpaceX wants, they need ~MWatt almost immediately - and much more shortly afterwards.

Just fuel and oxygen production, digging and trenching, construction...

I'm still waiting to hear the specifics of what the power plan is.

[john smith 19]

For what SpaceX wants, they need ~MWatt almost immediately - and much more shortly afterwards.

Just fuel and oxygen production, digging and trenching, construction...

I'm still waiting to hear the specifics of what the power plan is.

True, and for the foreseeable future they will be using PV arrays as the primary system.

But they don't run at night and Martian nights can get pretty cold. One or more Kilopower units makes a very useful insurance policy, given that we know  months long sand storms have happened before. You can also deep discharge cells in sequence, knowing you have the power to reliably charge them

In an ideal world SX would be able to acquire a naval reactor, which is about the right size. Unfortunately they are geared up to dump heat into an ocean of water. You could argue that a glacier is an ocean of (frozen) water, but we have no idea if it's a giant ice cube, or more like permafrosted mud.

And of course there is no navy that will let them have one.  this is one system that SX really can't do in house.

FISO presentation from February: 
"Kilopower: Small Fission Power Systems for Mars and Beyond"  http://spirit.as.utexas.edu/~fiso/telecon/Mason_2-1-17/
Lee Mason

I don't recall if Lee discusses SpaceX specifically, but it gives a very nice overview of the project and goals.  For SpaceX focus, I know Tom Mueller mentioned it during his talk with they NYU Astronomy Society that was recorded and widely discussed.  I think he even mentions SpaceX partnering or participating in the Kilopower project.  Though, I don't recall any details actually being mentioned.

One of the take aways from the Mueller presentation (I think it was sumarized on the BFS 0.2 thread) was that SpaceX is talking to NASA about KiloPower.  He was vague on details and there was no indication if SX was actively supporting it (IE part funding it or supplying staff). As a US corporation SX would have standard access rights to the results when published.

This months Kilopower full test (excluding the radiators, which will vary a lot depending on space or planet and uses for the waste heat) is 1Kw but I think there's a test series at the end (time, money, no issues permitting) that lays the ground work to go up to 10Kw.

The nice thing about KiloPower is it's granular. .
A 1Kw unit is a viable RTG replacement without the hassle of Pu241 mfg.  Attractive for mission planners to start penciling it in now.
A 10Kw unit is good enough to run an ion thruster to the outer planets with huge delta v and then run a big (by current standards) suite of instruments when it gets there.
On Mars they have already pivoted the DRM 5.0 architecture away from a single (point of failure) big reactor to multiple KiloPowers. That also means you carry 1 of 7 of them as a spare, whereas before it was carry 2 reactors, which was much bigger.

IOW There are quite a lot of stakeholder in NASA would like it to succeed.

The especially nice features are the 24/7/365 operation and the fact the can be made on a series basis, not a lovingly crafted one off.

[Ludus]

For what SpaceX wants, they need ~MWatt almost immediately - and much more shortly afterwards.

In an ideal world SX would be able to acquire a naval reactor, which is about the right size. Unfortunately they are geared up to dump heat into an ocean of water. You could argue that a glacier is an ocean of (frozen) water, but we have no idea if it's a giant ice cube, or more like permafrosted mud.

In order to make large quantities of propellant to meet the planned ISRU they need a settlement site with a lot of available water as well as a lot of power. Water to cool a reactor shouldn’t be an issue since they need it anyway prepped to feed into the ISRU plant. Whether it’s pure or like permafrost that’s what they have to design the process around, so they have some incentive to pick a site where it’s easier.

There are a lot of Small Modular Reactor designs in development that might be suitable too.

Not that the little 10k plants won’t be useful too.

I’d think with large amounts of Methane and LOX stored they’d have some use for Methane Fuel Cells. The waste heat would come in handy and the fairly pure CO2 could feed back into ISRU. Reactors would be better for cranking out LOX and Methane 24/7 than Solar.

[AncientU]

...

In an ideal world SX would be able to acquire a naval reactor, which is about the right size. Unfortunately they are geared up to dump heat into an ocean of water. You could argue that a glacier is an ocean of (frozen) water, but we have no idea if it's a giant ice cube, or more like permafrosted mud.

Yes, this is about the right size*.  Naval reactors aren't made to 'dump heat into an ocean of water' though.  The reactors are closed cycle, and dump heat into a steam generator.  That system, which remains uncontaminated with radioactive products, uses a portion of its energy to turn turbo-generators, another portion to turn the shaft/propeller, and the 'waste heat' is dumped to the ocean.  Substitute more turbo-generators for the shaft/propeller, and dump 'waste heat' into closed cycle heating loops for the colony, agriculture, whatever, and you have tens or hundreds of megawatts.

The nice thing about KiloPower is it's granular. .

So are solar panels... this is a disadvantage if the grains are too small -- massively inefficient if you need tens or hundreds of megawatts.  Grain size needs to be a megawatt if it is to be useful for a settlement that is charged with making thousands of tonnes of methlox, water for hundreds and for agriculture, heat, light, etc...

IOW There are quite a lot of stakeholder in NASA would like it to succeed.

Are they making it for anyone or any planned mission?  The concept was pushed 10-15 years ago, but not sure anyone stepped up with the killer app or claimed it as a solution to their problem.

* A Naval vessel has many similarities to a settlement on Mars... hundred to few thousand people, independent of 'shore', lots of power consumed, etc.

[tesla]

I talked with a SpaceX representative a few weeks ago about this given that I am a nuclear engineer.

They have essentially no realistic concept of how to refuel on Mars. They are not really looking into nuclear given that their god and overlord is pro solar and is actively fighting the nuclear industry in the US.

Given that their concept rocket is not even on paper yet and merely a concept, with no funding for it, I understand that they dont really care about a realistic mars plan. It is essentially just a marketing thing. As far as I have been told, essentially only low/unpaid interns are given the task to look into that.

Looking at other physically and economically impossible concepts like the hyper-loop and BRF Earth to Earth, I have no doubt that they just dont care.

Edit: I also asked them about a CO rocket engine, given that it could be extracted easily from the air without water mining, I was given the answer that this was rejected by Elon's trade studies. So yeah, the god doesnt like it, so it wont be done.

-Tesla

[QuantumG]

I talked with a SpaceX representative a few weeks ago about this given that I am a nuclear engineer.

Oh yeah? Who'd ya talk to?

They have essentially no realistic concept of how to refuel on Mars. They are not really looking into nuclear given that their god and overlord is pro solar and is actively fighting the nuclear industry in the US.

Citation needed. Last I checked Elon is pro-nuclear. Why wouldn't he be?

[tesla]

I wont tell you who I talked with. He was a propulsion engineer.

I read somewhere that Tesla, with Elon as CEO is fighting against subsidies needed for nuclear to compensate for the artificially low whole sale prices. Of course, Solar City and Tesla Powerwall wants all the subsidies in the world.

Dont get me wrong, IMO he is acting super anti nuclear. I cant find a reference sorry, I read it a while ago somewhere.

-Tesla

[QuantumG]

I wont tell you who I talked with. He was a propulsion engineer.

I read somewhere that Tesla, with Elon as CEO is fighting against subsidies needed for nuclear to compensate for the artificially low whole sale prices. Of course, Solar City and Tesla Powerwall wants all the subsidies in the world.

Dont get me wrong, IMO he is acting super anti nuclear. I cant find a reference sorry, I read it a while ago somewhere.

This is a very non-scientific way to approach the world. Do your research, validate your sources and don't propagate rumours.

[envy887]

I wont tell you who I talked with. He was a propulsion engineer.

I read somewhere that Tesla, with Elon as CEO is fighting against subsidies needed for nuclear to compensate for the artificially low whole sale prices. Of course, Solar City and Tesla Powerwall wants all the subsidies in the world.

Dont get me wrong, IMO he is acting super anti nuclear. I cant find a reference sorry, I read it a while ago somewhere.

-Tesla

Maybe you should cite some actual sources, instead of spouting stuff you maybe read about somewher sometime.


Here is what Tom Mueller, THE SpaceX propulsion engineer had to say on the topic:

To get one ship back, you need about eight football fields worth of solar cells on Mars. And you have to keep the dust off them. Um; so that’s tricky. It’s much better to use nuclear, fission reactor, it gets, you know, more compact; you actually get more; you get more power out per pound of reactor than you do out of solar cells, so it’s more mass-efficient. So if you’re taking it to Mars, it’s more efficient to ship reactors than it is to ship solar; it’s just that nobody’s really developed a space reactor yet. We’re working with NASA on that, and hopefully they’ll get funding to develop that. They’ve got a program called kilopower going that’s like, ten thousand watts, a 10 kilowatt reactor. We need a megawatt, but you know, you need to start somewhere.
Eventually, the right way to have power on Mars is fission, but initially, it’ll probably be solar. But in order to get the rockets back, we need a lot of power there to make propellant.

https://zlsadesign.com/post/tom-mueller-interview-2017-05-02-transcription/

Also Gwynne Shotwell, SpaceX COO, via notes from on reddit:

Initially, Elon was not sold on nuclear propulsion - his position may have changed somewhat. SpaceX is looking at nuclear power sources (not necessarily propulsion).

https://www.reddit.com/r/spacex/comments/6ix76m/interview_with_gwynne_shotwell_on_the_space_show/

[tesla]

I wont tell you who I talked with. He was a propulsion engineer.

I read somewhere that Tesla, with Elon as CEO is fighting against subsidies needed for nuclear to compensate for the artificially low whole sale prices. Of course, Solar City and Tesla Powerwall wants all the subsidies in the world.

Dont get me wrong, IMO he is acting super anti nuclear. I cant find a reference sorry, I read it a while ago somewhere.


-Tesla

Maybe you should cite some actual sources, instead of spouting stuff you maybe read about somewher sometime.


Here is what Tom Mueller, THE SpaceX propulsion engineer had to say on the topic:

To get one ship back, you need about eight football fields worth of solar cells on Mars. And you have to keep the dust off them. Um; so that’s tricky. It’s much better to use nuclear, fission reactor, it gets, you know, more compact; you actually get more; you get more power out per pound of reactor than you do out of solar cells, so it’s more mass-efficient. So if you’re taking it to Mars, it’s more efficient to ship reactors than it is to ship solar; it’s just that nobody’s really developed a space reactor yet. We’re working with NASA on that, and hopefully they’ll get funding to develop that. They’ve got a program called kilopower going that’s like, ten thousand watts, a 10 kilowatt reactor. We need a megawatt, but you know, you need to start somewhere.
Eventually, the right way to have power on Mars is fission, but initially, it’ll probably be solar. But in order to get the rockets back, we need a lot of power there to make propellant.

https://zlsadesign.com/post/tom-mueller-interview-2017-05-02-transcription/

Also Gwynne Shotwell, SpaceX COO, via notes from on reddit:

Initially, Elon was not sold on nuclear propulsion - his position may have changed somewhat. SpaceX is looking at nuclear power sources (not necessarily propulsion).

https://www.reddit.com/r/spacex/comments/6ix76m/interview_with_gwynne_shotwell_on_the_space_show/

I am aware of those comments. However, I have the impression that they are not seriously looking into nuclear given my sources. I just wanted to share this bit of info. I cant and wont say more. Feel free to disregard my comments.

Edit, I am sorry if I upset someone. This forum is supposed to be a joy. What I am saying is dont bet on SpaceX. NASA is our biggest hope for a manned mars mission still, IMO.

-Tesla

[QuantumG]

I cant and wont say more. Feel free to disregard my comments.

You've already said too much. You're an anonymous name on a forum, not a respected journalist for a renowned newspaper - you don't get to have anonymous sources.

[deruch]

They have essentially no realistic concept of how to refuel on Mars. They are not really looking into nuclear given that their god and overlord is pro solar and is actively fighting the nuclear industry in the US.

Firstly, I reject the premise unless I see some citations or direct quotes to support the idea Elon is "actively fighting the nuclear industry."  But more importantly, there is a clear failure of logic in your statement regardless of whether the underlying premise is actually true or not.  Even if Elon thought nuclear power was a terrible idea for terrestrial power production, that has nothing to do with power generation on Mars.  Especially when you consider that the benefits of solar on Earth are lessened on Mars due to reduced insolation.  If you know anything about SpaceX's development it should be that they invariably pivot to what works and what they think will get them to Mars faster.  IMO, there's very, very good arguments for why nuclear power will have to be the main power source for the style of Mars missions Elon and SpaceX are proposing.  That being the case, I can't at all see some hypothetical (and irrelevant) ideological position dictating how they design such missions.  Especially when virtually every argument against the wider adoption of nuclear power has almost no overlap with conditions on early to medium Mars missions.

[BrightLight]

There is an L2 thread on the Kilopowr program at:
 NASASpaceFlight.com Forum » NASASpaceflight L2 Subscription Sections » L2 Orion and Future Spacecraft »    Nuclear Power for Space Applications

There are limits to the output of the Kilopower reactor designs using HEU and are well under 1mW and NASA Glenn is funding 10kW systems. Frankly, the fundamental limitation for these reactors right now is the ability to test and validate full-up systems at the Nevada Test Site (NNTS) and not launch vehicle pedigree.
"The study concluded that both the in situ resource utilization (ISRU) and crew phases of the early Mars missions were easily achieved with several 10-kWe Kilopower reactors. The Kilopower-based system won the mass and power trades for the crewed missions by a factor or two, even at solar favorable sites, which provides additional support for nuclear systems when moving further from the equator." From:
NASA's Kilopower Reactor Development and the Path to Higher Power Missions Technical Report · November 2017
DOI: 10.13140/RG.2.2.32371.22565

[AncientU]

SpaceX doesn't have the motivation to develop nuclear power... too regulated and too unpopular among the low-tech masses -- a significant majority of the US population.  If NASA has a program that can be leveraged, then it might be a possibility using NASA's good will as a cover.  Kilo-power is only a baby step along that road and they are pursuing it even so.

As discussed above, megawatts are needed to get started. Tens to hundreds of megawatts eventually.
Refueling is a cake walk compared to getting appropriately sized systems developed and made available for space use.

From my own nuclear background, water-cooled reactors are the simplest and most proven technology. It isn't some fancy, high tech solution that is needed, just a way to smuggle a few naval reactors off planet.  With appropriate approvals, of course.

[Jcc]

Ok, so if SpaceX is "looking into nuclear power" where are they looking? they obviously are not certified to do nuclear research internally ( with actual nuclear materials), so they could be talking with commercial companies or universities, or government.

The only government would be the US Government, specifically NASA and/or DOE. I am pretty sure DOD would be excluded, as would any foreign defense related technology. Commercial companies could include foreign ones, as well as US, but what company is potentially working on space-qualified nuclear? Universities have lots of ideas, but not the resources needed to develop them unless government pays.

Bottom line is that NASA Kilopower may be the only place they can look at present. Where else?

[Nomadd]

I read somewhere that Tesla, with Elon as CEO is fighting against subsidies needed for nuclear to compensate for the artificially low whole sale prices. Of course, Solar City and Tesla Powerwall wants all the subsidies in the world.

Dont get me wrong, IMO he is acting super anti nuclear. I cant find a reference sorry, I read it a while ago somewhere.

-Tesla

Come on you guys. He cited the unimpeachable source of "I read it somewhere". Admit defeat and move on.

[Ludus]

I'm quite confident that solar power will be the single largest source of electrical energy for humanity in the future. It will be combined with other things, of course, such as hydro power, geothermal, and I actually think nuclear is not a terrible option, so long as you're not located in a place that's susceptible to natural disasters. That, also I think, defies common sense. So long as there are not huge earthquakes or weather systems that have names coming at you, then I think nuclear can be a sensible option. There are much safer and better ways of generating nuclear energy - I'm talking fission here - than existed in the past when nuclear reactors first came out. At some point in the future it would be nice to make fusion work, of course. That'd be quite good, but in the mean time I think indirect fusion, being solar power, is a good thing to do. That's what Solar City is doing, it's really trying to improve the economics of solar power, and they're doing a great job. I don't run the company, so the credit really goes to the two key guys who run that company. They're doing a great job of really accelerating the good option of solar power in the United States, and hopefully they'll come to the UK as well.

From: http://shitelonsays.com/transcript/elon-musk-the-future-of-energy-and-transport-2012-11-14

[lamontagne]

There is that quote of Shotwell about ''trying to lay hands on nuclear material''
And there was some L2 information about nuclear reactors for SpaceX.
And there is a quote of Mueller saying that eventually nuclear will be superior to chemical.
And the excellent quote above :-)

But one think is certain, nuclear will not be quick.  Not today, not in this age.  We might regret this, we might think it makes no sense, but if you want to build soon, you will go solar.  BFR is fuel rich architecture, mass efficiency is not the most important thing.

I expect Mars will be one of the best possible clients for small nuclear.  Eventually.

You can't cool a 'real' reactor without circulating a fluid through it.  And then cool the fluid in a heat exchanger. Heat exchangers with soil are large, as soil is not very conductive.  You need to experiment.  You don't need to experiment (as much) with solar.  I think the choice is simple.

Tesla may not know this, but most important designs, at the conceptual level, are made by small teams, with little money to spend.  The big design machine, the detailed engineering, comes latter.  After the dream is set, and the money is found.

[Ludus]

Mars settlement may help change popular attitudes toward nuclear. It would be a case of people who very much want a nuclear reactor in their backyard, who have no other interest than their own survival. It would be politically different if it’s demand pull from heroic people already on Mars. I know I’d be a lot more comfortable living on Mars with reactors (preferably both Megawatt and Kilowatt) than without.

[CuddlyRocket]

A well made, high pressure Helium, Stirling engine is a good choice for the application...

I get the impression that SpaceX has a bit of a downer on high pressure Helium!

[Eric Hedman]

A well made, high pressure Helium, Stirling engine is a good choice for the application...

I get the impression that SpaceX has a bit of a downer on high pressure Helium!

That's probably only when it's inside another cryogenic tank.

[john smith 19]

In order to make large quantities of propellant to meet the planned ISRU they need a settlement site with a lot of available water as well as a lot of power. Water to cool a reactor shouldn’t be an issue since they need it anyway prepped to feed into the ISRU plant. Whether it’s pure or like permafrost that’s what they have to design the process around, so they have some incentive to pick a site where it’s easier.

Depends on how much data SX have to decide a site.

There are a lot of Small Modular Reactor designs in development that might be suitable too.

No, there are a lot of Powerpoints for Small Modular Reactor designs.

The number that have got actual hardware built is much smaller.

The number that have actual hardware built in the US smaller still.

Not that the little 10k plants won’t be useful too.

I think people underestimate how useful a steady supply of heat 24/7/365 can be on Mars. Such a unit can be melting through a glacier at night while continuing to charge batteries for high rate processing during the day. In fact it would allow more batteries to be carried.

I’d think with large amounts of Methane and LOX stored they’d have some use for Methane Fuel Cells. The waste heat would come in handy and the fairly pure CO2 could feed back into ISRU. Reactors would be better for cranking out LOX and Methane 24/7 than Solar.

Methane FC's do sound like a good backup plan. But we know Musk is not a fan of "Fool cells" and I'm not sure how developed MFC's are.

[AncientU]

If you want to use methlox as your back-up/emergency power source, just install gas turbines.  They are compact for power delivered, low maintenance in long idle condition, and can quickly start and pick up load.

Discussion of nuclear is base load related... this is the long pole for expanding beyond the outpost stage on Mars or the Moon.  Wonder if the Moon could be a 'proving ground' for 10KW Kilopower or space versions of naval nuclear reactors.  A research-sized reactor modeled after that on the Navy's NR-1 deep submersible (MW scale) could be developed quickly by the USG...

[john smith 19]

Are they making it for anyone or any planned mission?  The concept was pushed 10-15 years ago, but not sure anyone stepped up with the killer app or claimed it as a solution to their problem.

That's why I said it's granular. At the bottom end (the actual hardware that's being tested right now) is AFAIK at the 1Kw level. So it's in drop in replacement territory for an RTG (but able to be throttled up or down depending on flight phase, or even inert until it reaches its target).

As I said it's already moved the Mars DRM 5.0 baseline to these units from the single, custom built reactor they were planning to use.

Lastly there is IIRC a road map up to 1MW IOW a 1:1000 range in power outputs with the same basic design.

And let me repeat. It's not a Powerpoint. It's actual hardware being tested now.

I'd be very interested in any other system that's got to that stage so far.

[john smith 19]

I talked with a SpaceX representative a few weeks ago about this given that I am a nuclear engineer.

They have essentially no realistic concept of how to refuel on Mars.

WRT to the thread title do you mean "refueling" as in refueling the BFS to get home or refueling nuclear reactors?

Looking at other physically and economically impossible concepts like the hyper-loop and BRF Earth to Earth, I have no doubt that they just dont care.

Checking Wikipedia's entry on Musk

https://en.wikipedia.org/wiki/Elon_Musk
we find

Musk transferred to the University of Pennsylvania, where in May 1997 he received a Bachelor of Science degree in physics from its College of Arts and Sciences, and a Bachelor of Science degree in economics from its Wharton School of Business

But you reckon his ideas are both physically impossible and uneconomic, making him incompetent to practice the both the subjects he graduated in?

Edit: I also asked them about a CO rocket engine, given that it could be extracted easily from the air without water mining, I was given the answer that this was rejected by Elon's trade studies. So yeah, the god doesnt like it, so it wont be done.

Possibly because O2/CO gives substantially lower Isp but (more importantly) there is no long term settlement without a large supple of water.

if you can't find a reasonably accessible large water supply there's no point in going to begin with. 

[EDIT BTW for maximum Isp using Mars atmospheric the Reaction Engines "Project Troy" team looked at the little known "Cyanogen" combination. Very potent, but burns hotter than H2 and very toxic. OTOH needs no water, so could be made anywhere on the surface with a suitable power source.  ]

[KelvinZero]

I did a google of Elon Musk's quote about "Nuking Mars" and found some cool details I hadn't met before.
http://mashable.com/2015/10/02/elon-musk-nuke-mars-two-suns/#_Q_aY4aeEPq0

I expect this is just a brainstorm he had, but he certainly is not anti nuclear when it comes to Mars. In the short term I don't expect him to do much more than verify that success is still an option with solar though. Anything that distracts too much from BFR commercial success around earth would be a mistake IMO.

[lamontagne]

If you want to use methlox as your back-up/emergency power source, just install gas turbines.  They are compact for power delivered, low maintenance in long idle condition, and can quickly start and pick up load.

Discussion of nuclear is base load related... this is the long pole for expanding beyond the outpost stage on Mars or the Moon.  Wonder if the Moon could be a 'proving ground' for 10KW Kilopower or space versions of naval nuclear reactors.  A research-sized reactor modeled after that on the Navy's NR-1 deep submersible (MW scale) could be developed quickly by the USG...

Is nuclear really needed if you have a hydrogen/oxygen back up system?  The big fusion reactor in the sky is so reliable...
What is the overall efficiency of a reversible hydrogen/oxygen electrolysis/fuel cell cycle? Taking into account that heat losses for a Martian colony are part of the system and that since heating will be maximum at night, when there is no sun,  but when electrical demand should be low, there is excellent correlation with the heat loss from the fuel cell system?

[lamontagne]

I think nuclear is just one thing too many for Spacex at this time.

They need to develop so much stuff, in so many fields, that anything they can do without is a gain.

The question should really be: What can Spacex do without and still achieve its goal?

[meekGee]

The question is - can you have a realistic MWatt solar solution that is compatible with the task at hand.

Those tunnel machines, the ground vehicles, the fuel for return trips - it's a lot of Watts.

By "reallistic" I mean that it is a fraction of the total upmass plan, and can be installed by a fraction of the crew, using power production that already exists.

[RoboGoofers]

The question should really be: What can Spacex do without and still achieve its goal?

What about beamed solar? Sure there are a lot of issues with it and it's never been done before but at least it doesn't require getting hands on a reliable Mars-rated reactor.

Oh and I'm a nuclear engineer too and also talked to SpaceX recently. /s
(Come on, Tesla, if you want to be believed you could at least give some personal details to back up your credentials. I also question why they would reach out to you professionally when you are so ill-informed and opinionated, unless by "SX representative" you mean "tour guide". In addition, I doubt that anyone at SpaceX would discuss their Mars plans with just a random nuclear engineer, but if what you say is really true it at least confirms that SpaceX is interested in nuclear on Mars.)

[john smith 19]

Is nuclear really needed if you have a hydrogen/oxygen back up system?  The big fusion reactor in the sky is so reliable...

Not when it's blanketed by a dust storm that cuts off 75% of your daytime sunlight and lasts for months, which can, and does happen, on Mars. IOW to handle such an event you'd need 4x to maybe 5x the baseline load to maintain power levels. That ignores how you're going to grow food in months long twilight as well, as artificial light multiples power needs about 6x IIRC.

What is the overall efficiency of a reversible hydrogen/oxygen electrolysis/fuel cell cycle? Taking into account that heat losses for a Martian colony are part of the system and that since heating will be maximum at night, when there is no sun,  but when electrical demand should be low, there is excellent correlation with the heat loss from the fuel cell system?

Poor, if you have to liquefy or pressurize the H2, which you do if you want to store reasonable amounts. Basically LH2 or GH2 uses 3-4x the energy used to make it, and by extension 3-4x the energy you can recover from it. 

When you factor that energy into the process it makes a fairly poor way to move energy, let alone store and release it cyclically.

[M.E.T.]

Is nuclear really needed if you have a hydrogen/oxygen back up system?  The big fusion reactor in the sky is so reliable...

Not when it's blanketed by a dust storm that cuts off 75% of your daytime sunlight and lasts for months, which can, and does happen, on Mars. IOW to handle such an event you'd need 4x to maybe 5x the baseline load to maintain power levels. That ignores how you're going to grow food in months long twilight as well, as artificial light multiples power needs about 6x IIRC.

What is the overall efficiency of a reversible hydrogen/oxygen electrolysis/fuel cell cycle? Taking into account that heat losses for a Martian colony are part of the system and that since heating will be maximum at night, when there is no sun,  but when electrical demand should be low, there is excellent correlation with the heat loss from the fuel cell system?

Poor, if you have to liquefy or pressurize the H2, which you do if you want to store reasonable amounts. Basically LH2 or GH2 uses 3-4x the energy used to make it, and by extension 3-4x the energy you can recover from it. 

When you factor that energy into the process it makes a fairly poor way to move energy, let alone store and release it cyclically.

How about space based solar power to counter the threat of Martian dust storms - which seems very alarming based on your description. If they don't have nuclear power for the first decade or so, it seems a months long dust storm could wipe out the entire colony by cutting off its power source.

So would SpaceX feasibly be able to build orbital solar farms in geostationary orbit above a colony, and beam the power down through a dust storm?

[Jcc]

Is nuclear really needed if you have a hydrogen/oxygen back up system?  The big fusion reactor in the sky is so reliable...

Not when it's blanketed by a dust storm that cuts off 75% of your daytime sunlight and lasts for months, which can, and does happen, on Mars. IOW to handle such an event you'd need 4x to maybe 5x the baseline load to maintain power levels. That ignores how you're going to grow food in months long twilight as well, as artificial light multiples power needs about 6x IIRC.

What is the overall efficiency of a reversible hydrogen/oxygen electrolysis/fuel cell cycle? Taking into account that heat losses for a Martian colony are part of the system and that since heating will be maximum at night, when there is no sun,  but when electrical demand should be low, there is excellent correlation with the heat loss from the fuel cell system?

Poor, if you have to liquefy or pressurize the H2, which you do if you want to store reasonable amounts. Basically LH2 or GH2 uses 3-4x the energy used to make it, and by extension 3-4x the energy you can recover from it. 

When you factor that energy into the process it makes a fairly poor way to move energy, let alone store and release it cyclically.

The best way to store energy on Mars is to make methane and oxygen, since they will need large quantities of that for rocket fuel and oxygen to breath. Eventually other industrial processes that use a lot of energy, make more of those products when excess energy is available. So if you have a continuous nuclear source plus variable solar, increase fuel production when the sun shines. Batteries will help, building up a stock of energy intensive essential commodities is better from an efficiency standpoint.

[RoboGoofers]

So Elon is not a fan of space based solar, apparently, though his comments on it relate to Earth.

NSF topic on spaced based solar on Mars:
http://forum.nasaspaceflight.com/index.php?topic=39583.0

[john smith 19]

The best way to store energy on Mars is to make methane and oxygen, since they will need large quantities of that for rocket fuel and oxygen to breath. Eventually other industrial processes that use a lot of energy, make more of those products when excess energy is available. So if you have a continuous nuclear source plus variable solar, increase fuel production when the sun shines. Batteries will help, building up a stock of energy intensive essential commodities is better from an efficiency standpoint.

And best of all you have some very large tanks available to store it in from the day you land. 

[WindnWar]

Basically need a much smaller version of these SMR designs that Nuscale is working on, with a higher enriched fuel to be able to last longer between refuelling. The weight they list seems wrong though as you can't transport a 700 ton item by truck. 70 tons seems more realistic. 50 megawatts of electric power and 160 megawatts of thermal power would be quite useful.

http://www.nuscalepower.com/our-technology/technology-overview

[JamesH65]

I think nuclear is just one thing too many for Spacex at this time.

They need to develop so much stuff, in so many fields, that anything they can do without is a gain.

The question should really be: What can Spacex do without and still achieve its goal?

It's really a question of cost. They can always spin off an independent lab to do the work, but it all costs money. It's not like Musk himself needs to run everything. Better to get others to do the leg work.

[john smith 19]

Basically need a much smaller version of these SMR designs that Nuscale is working on, with a higher enriched fuel to be able to last longer between refuelling. The weight they list seems wrong though as you can't transport a 700 ton item by truck. 70 tons seems more realistic. 50 megawatts of electric power and 160 megawatts of thermal power would be quite useful.

http://www.nuscalepower.com/our-technology/technology-overview

According to this presentation

https://www.iaea.org/NuclearPower/Downloadable/Meetings/2013/2013-09-02-09-04-TM-NPTD/20_usa_colbert_nuscale.pdf

The standard reactor core will weigh 264 tonnes.

When one is actually built.

Kilopower has been built and is in test right now.  That makes quite a difference.

[lamontagne]

I think nuclear is just one thing too many for Spacex at this time.

They need to develop so much stuff, in so many fields, that anything they can do without is a gain.

The question should really be: What can Spacex do without and still achieve its goal?

It's really a question of cost. They can always spin off an independent lab to do the work, but it all costs money. It's not like Musk himself needs to run everything. Better to get others to do the leg work.

Financing is the key.  Not cost but getting people to invest.  The best market for small nuclear reactors may be Mars, but this market needs to exist before the product is developed!

For the moment, SpaceX needs to limit areas requiring investment.  As Spacex succeeds (one hopes) other will start putting money into the field.
History shows that in fact once something gets going there is over investment, as everyone tries to jump onto the bandwagon.  A typival example being rail in the nineteenth century.  What SpaceX is trying to do in survive the initial phase.  So they need to focus on the bare minimum requirements, in the expectation that once they succeed, others will follow.

A typical example, the Cseries frosm Bombardier.  Once it was shown to be viable, then Airbus snapped it up (anf Boeing tried to destroy it).   But they didn't risk anything before.  SpaceX wants to succeed with enough funds left over to continue existing.  A tough proposition.

[nacnud]

Could you make solar panels on Mars? Built a factory inside a BFR and land it as one piece. You'd need to refine the raw materials into semi conductors and conductors and then make into panels.

You would bring the harder to refine elements from Earth but if you could make silicon and aluminium that might be enough to be worth the bother.

[Patchouli]

Could you make solar panels on Mars? Built a factory inside a BFR and land it as one piece. You'd need to refine the raw materials into semi conductors and conductors and then make into panels.

You would bring the harder to refine elements from Earth but if you could make silicon and aluminium that might be enough to be worth the bother.

You'll have to send several hundred maybe even thousands of tons of hardware before you can manufacture silicon solar cells from Martian materials.
Building a solar concentrator and using a turbine based system would be a better option.
Even building nuclear power plant may be easier than setting up a semi conductor plant as most of the heaviest stuff is just steel and concrete which is pretty low tech stuff that could be manufactured using fairly simple hardware without an extensive chemical industrial infrastructure.

[AncientU]

Basically need a much smaller version of these SMR designs that Nuscale is working on, with a higher enriched fuel to be able to last longer between refuelling. The weight they list seems wrong though as you can't transport a 700 ton item by truck. 70 tons seems more realistic. 50 megawatts of electric power and 160 megawatts of thermal power would be quite useful.

http://www.nuscalepower.com/our-technology/technology-overview

Interesting.  Proposed same concept (except for 100MW electric per unit) in 1985-6 to GE Nuclear.  The economies-of-scale legion had a fit.  10 units to produce the GigaWatt electric, one being refueled, one in standby.  Leveled the utility workforce and made pre-constructed, modular units available to start producing power in 18-24 months instead of five years.  Full automated operation -- no TMI-Peach Bottom-like operators.

Half or quarter scale is just right for Mars.

[KelvinZero]

One interesting thing about nuclear power: It could make initial ISRU pretty trivial. You could land right on or near the exposed ice at Louth crater. Just trundle a nuclear heated probe onto the ice. Something a lot easier than the proposed europa landers could melt down 30 meters and begin creating a lake of water. It could be tiny compared to BFS cargo. A couple of tons. At that depth you get radiation shielding and robust earth pressure for free.

Would it just get too cold there? Maybe. However the crater is at a latitude of about 70°, so I don't think you would face permanent night, and one ridge of the crater should be well placed to catch the sun every day.

Another option could be to initially just land the BFS in the long summer and bring it home before the long winter. Permanent infrastructure could be buried in the ice, which is a good heat insulator.

I think we will find much better locations right near the equator, but if anyone is too worried about the unknowns, here is a known. You can see the ice right there in photos.

Maybe this could just be an initial location. You land your heavy prospecting equipment there in the summer and bring the BFS home, but then this equipment all moves in a caravan toward the equator, prospecting as it goes. This could all be done robotically because the ISRU is so simple.

[john smith 19]

You'll have to send several hundred maybe even thousands of tons of hardware before you can manufacture silicon solar cells from Martian materials.

IIRC Silicon is one of the 10 most common elements in the Universe. The question is how much capacity do you want to build out and how fast do  you want to do it.

Building a solar concentrator and using a turbine based system would be a better option.

Certainly more scalable, although prone to dust storms. Also much simpler supply chain that can (in principle) be built on Mars.

Even building nuclear power plant may be easier than setting up a semi conductor plant as most of the heaviest stuff is just steel and concrete which is pretty low tech stuff that could be manufactured using fairly simple hardware without an extensive chemical industrial infrastructure.

If you have a large supply of fossil fuel to use as fuel.

Which Mars does not.

It's only when you'd don't have it that you realize just how big an enabler of large engineering projects a large, ready source of energy is to making them happen. For example heating Silicon to its melting point (about 1450c) is every energy intensive but its heat of fusion is huge so getting it that 1 degree over the line to liquid Silicon doubles the energy bill at least. That's why you need a very big solar array already to make more of them on orbit for SPS, or anywhere else for that matter.

[john smith 19]

Interesting.  Proposed same concept (except for 100MW electric per unit) in 1985-6 to GE Nuclear.  The economies-of-scale legion had a fit.  10 units to produce the GigaWatt electric, one being refueled, one in standby.  Leveled the utility workforce and made pre-constructed, modular units available to start producing power in 18-24 months instead of five years.  Full automated operation -- no TMI-Peach Bottom-like operators.

Half or quarter scale is just right for Mars.

Do you know anyone who's constructing units of such size anywhere in the world?

Right now AFAIK the closest fit to a  Mars power plant would be the naval ship reactors, or the few designs developed for nuclear civilian vessels in the 1950's and 1960's by (IIRC) the US, Germany and Japan.

AFAIK most Western naval reactors are PWR's but they are (were?) sealed for life with suitable fuel loads and fissionable poisons to level the power output. They also have tended to run with HEU but I think that's changing.

On that basis if any navy is operating a refuellable LEU PWR for its fleet then that would be the best (near term) design you could get if SX could get it.

Otherwise AFAIK Kilopower is at the Nevada test site right now and going through tests. 

People seem to obsess about how it's only 10Kw, but you don't have to send just one, do you?
Incidentally Kilopwer is (in principle) moveable by a team of astronauts on a trolley (provided it's been shut down for about a week), no crane required. It has also been designed to be started by remote control. The biggest variable is the deployment of the cooling radiator, which will vary with the environment, but could be a fixed design, no moving parts needed.

I think we will find much better locations right near the equator, but if anyone is too worried about the unknowns, here is a known. You can see the ice right there in photos.

At this point there are enough unknowns that eliminating even one of them is pretty attractive. You'd have proved out ISR recovery and ISRU so their TRL's would have gone to 9.

In principle ISRU is a simple idea but it's the implementation (especially how to handle faults and keep working) that makes designing it such a PITA. Life gets very tough when you can't just send a guy out to fix it (because "the guy" is about 140 million miles from the hardware    ).

Maybe this could just be an initial location. You land your heavy prospecting equipment there in the summer and bring the BFS home, but then this equipment all moves in a caravan toward the equator, prospecting as it goes. This could all be done robotically because the ISRU is so simple.

Well simpler than having to drill through a surface layer to get to the ice that's true. Do we really know if that's just a liquid, or could it be more like permafrost, with lots of solids to filter out first?

I don't think there's any doubt that the first pair of BFS's to Mars will not be crewed.

[JamesH65]

You'll have to send several hundred maybe even thousands of tons of hardware before you can manufacture silicon solar cells from Martian materials.

IIRC Silicon is one of the 10 most common elements in the Universe. The question is how much capacity do you want to build out and how fast do  you want to do it.

I think availability of silicon* is fairly irrelevant to the cost of making solar panels. It's the process that costs, not the raw materials. http://www.madehow.com/Volume-1/Solar-Cell.html

* Although silicon of the required grade for chip manufacture is fairly thin on the ground on Earth.

[speedevil]

It's only when you'd don't have it that you realize just how big an enabler of large engineering projects a large, ready source of energy is to making them happen. For example heating Silicon to its melting point (about 1450c) is every energy intensive but its heat of fusion is huge so getting it that 1 degree over the line to liquid Silicon doubles the energy bill at least. That's why you need a very big solar array already to make more of them on orbit for SPS, or anywhere else for that matter.

I note that launch to Mars surface costs $130/kg or so. (BFR, 2016)

Picking the first more-or-less suitable cell off alibaba gives me this 3.5W cell for $1.7.

It produces 3.5W, and weighs 5g.

For $130 or so, you can transport the $360 worth of cells to Mars, where they will produce about 350W peak, and perhaps 100W average in a good location.

If you are claiming that it's worth it making cells on Mars, you are also implicitly assuming that it is considerably cheaper to make cells on Mars than on earth.

Which seems a rather extravagant claim.

The cells picked were on the first page of the listings for Solar Cell, the first bare cell. Somewhat thinner cells are coming onto the market, and thin film cells may be considerably lighter.

[jpo234]

* Although silicon of the required grade for chip manufacture is fairly thin on the ground on Earth.

I'm not sure what you mean here. Silicon with the "nine nines" purity required for chip making always requires multiple refinement steps...

[KelvinZero]

For $130 or so, you can transport the $360 worth of cells to Mars, where they will produce about 350W peak, and perhaps 100W average in a good location.

If you are claiming that it's worth it making cells on Mars, you are also implicitly assuming that it is considerably cheaper to make cells on Mars than on earth.

Which seems a rather extravagant claim.

You can't just do a mars dollar to earth dollar conversion though. For example, consider the extreme case where mars is 100% self sufficient and yet has $0 products to sell to earth. Mars would then be entirely capable of building it's own solar cells but entirely incapable of buying anything from earth.

[speedevil]

You can't just do a mars dollar to earth dollar conversion though. For example, consider the extreme case where mars is 100% self sufficient and yet has $0 products to sell to earth. Mars would then be entirely capable of building it's own solar cells but entirely incapable of buying anything from earth.

No, you can't.
However, even widening out the question a lot from 'Will SpaceX use NASA Kilopower Nuclear Reactors' to include possible alternatives from earth (note that the Kilopower reactor is from earth)  doesn't get you to questions of a local economy till a very, very long time in the future.

[WindnWar]

Interesting.  Proposed same concept (except for 100MW electric per unit) in 1985-6 to GE Nuclear.  The economies-of-scale legion had a fit.  10 units to produce the GigaWatt electric, one being refueled, one in standby.  Leveled the utility workforce and made pre-constructed, modular units available to start producing power in 18-24 months instead of five years.  Full automated operation -- no TMI-Peach Bottom-like operators.

Half or quarter scale is just right for Mars.

Do you know anyone who's constructing units of such size anywhere in the world?

Right now AFAIK the closest fit to a  Mars power plant would be the naval ship reactors, or the few designs developed for nuclear civilian vessels in the 1950's and 1960's by (IIRC) the US, Germany and Japan.

AFAIK most Western naval reactors are PWR's but they are (were?) sealed for life with suitable fuel loads and fissionable poisons to level the power output. They also have tended to run with HEU but I think that's changing.

On that basis if any navy is operating a refuellable LEU PWR for its fleet then that would be the best (near term) design you could get if SX could get it.

Otherwise AFAIK Kilopower is at the Nevada test site right now and going through tests. 

People seem to obsess about how it's only 10Kw, but you don't have to send just one, do you?
Incidentally Kilopwer is (in principle) moveable by a team of astronauts on a trolley (provided it's been shut down for about a week), no crane required. It has also been designed to be started by remote control. The biggest variable is the deployment of the cooling radiator, which will vary with the environment, but could be a fixed design, no moving parts needed.

I think we will find much better locations right near the equator, but if anyone is too worried about the unknowns, here is a known. You can see the ice right there in photos.

At this point there are enough unknowns that eliminating even one of them is pretty attractive. You'd have proved out ISR recovery and ISRU so their TRL's would have gone to 9.

In principle ISRU is a simple idea but it's the implementation (especially how to handle faults and keep working) that makes designing it such a PITA. Life gets very tough when you can't just send a guy out to fix it (because "the guy" is about 140 million miles from the hardware    ).

Maybe this could just be an initial location. You land your heavy prospecting equipment there in the summer and bring the BFS home, but then this equipment all moves in a caravan toward the equator, prospecting as it goes. This could all be done robotically because the ISRU is so simple.

Well simpler than having to drill through a surface layer to get to the ice that's true. Do we really know if that's just a liquid, or could it be more like permafrost, with lots of solids to filter out first?

I don't think there's any doubt that the first pair of BFS's to Mars will not be crewed.

US Naval reactors are all HEU reactors in order to have the power density and time between refuelling required for service, some of the older Los Angeles class subs had core lifespans of 10-15 years but refuelled cores used a newer design and both them and the newer Virginia class are all 30 plus year lifespans. They can be refuelled but it's a pretty massive operation. I grew up not far from Mare Island and knew a lot of folks that worked at the base doing refueling ops back in the day. Nuclear non proliferation agreements require commercial reactors to be 14% or less enrichment. Current US Naval reactors are 90% or more enrichment. Not sure what the lifespan would be using lower enriched fuel though it is possible to use it in them.

I would think it would require a pretty major waiver to be able to use and launch such a reactor, but that's not my specialty...

[Kenp51d]

First let admit to a relatively low knowledge level here, so this may not be the brightest question.
The constraints and risk can be fairly easy to emagine with luanching a fueled reactor.
How feasable would it be to luanch an unfueled reactor, and then fuel it in orbit (roboticly perhaps, yeah I know that even on Earth fuel is remotely handled).
Fuel sent up on another launch with extra safe guards, maybe?

Ken


Sent from my XT1565 using Tapatalk

[JamesH65]

* Although silicon of the required grade for chip manufacture is fairly thin on the ground on Earth.

I'm not sure what you mean here. Silicon with the "nine nines" purity required for chip making always requires multiple refinement steps...

You need very high silicon content sand, with very few impurities, which is not beach sand. Locations on Earth where the raw materials are a high enough quality are not common. I'm sure if you wanted to, you could make a process that removed the impurities and could therefor use 'beach' sand, but we don't do that on Earth. Of course, if you find a pure quartzite deposit on Mars, you could use that.

[john smith 19]

First let admit to a relatively low knowledge level here, so this may not be the brightest question.
The constraints and risk can be fairly easy to emagine with luanching a fueled reactor.
How feasable would it be to luanch an unfueled reactor, and then fuel it in orbit (roboticly perhaps, yeah I know that even on Earth fuel is remotely handled).
Fuel sent up on another launch with extra safe guards, maybe?

Key issues with reactors are crashes are a) Dispersion of nuclear material b)Reactor going critical.
 
Your idea means you now have to have two perfect launches and a rendezvous and a docking in space.

a) Conventional reactors use powered Uranium Oxide as the fuel. It's pretty safe but it's a ceramic, so if it gets crushed it'll generate powder, and there's a lot of it. Kilopower uses quite big lumps of solid metal. They can burn but the big lumps mean they can absorb a lot of heat before doing so.

b) Sea water (or water logged sand, which is the other test condition) is an effective moderator and a lot of conventional designs have "voids" where the conventional coolant could be forced out of and replaced by this better moderator, forcing the reactor critical.  Kilopower does not have a single coolant flow it uses multiple sealed heat pipes. Individual sealed fluid loops. To push moderator into the reactor one (or more) of these would have to rupture, along with the removal of the control rods that help prevent criticality to begin with.

Until startup reactors are fairly safe. The fuel is an Alpha emitter which requires minimal shielding. Essentially it's like the engine block of a truck. It'll kill you if it falls on you. Once it starts up (and the truck it's attached to starts moving) things change a lot.

That's when they become neutron emitters and dangerous to get close to.

Which is why AFAIK no space reactor has ever  launched while operating. They are always started up in space.  Kilopower (by design) is also meant to be approachable within 1 week of shut down, which is AFAIK a first for space nuclear reactors and may not be possible for nuclear thermal rocket IE direct thrust generation rather than electrical power applications.

[TrevorMonty]

What are mass estimates for operational 1KW and 10KW versions?

Would they stay mounted to lander that delivers them to surface? Lander may need  wheels to move to final location.

[Kenp51d]

Thanks John.
Good info. I have a much better understanding now.

Ken

Sent from my V10 using Tapatalk

[BrightLight]

What are mass estimates for operational 1KW and 10KW versions?

Would they stay mounted to lander that delivers them to surface? Lander may need  wheels to move to final location.

This table came from:
NASA's Kilopower Reactor Development and the Path to Higher Power Missions, Technical Report · November 2017
DOI: 10.13140/RG.2.2.32371.22565
https://www.researchgate.net/publication/320834023

Five 10kWe reactors - 40kWe plus a spare on a single lander gives a roughly a 2:1 advantage over solar at Mars surface for ISRU.  Additional advantages include the rate at which fuel can be created.

[Kaputnik]

It must be difficult to directly compare the power/kg of solar and fission systems: you need to consider battery storage for solar (if necessary- it may be more mass efficient to only run your ISPP during daylight hours), and also any potential uses for the heat waste from fission.

Any ideas how the above numbers were derived?

[BrightLight]

It must be difficult to directly compare the power/kg of solar and fission systems: you need to consider battery storage for solar (if necessary- it may be more mass efficient to only run your ISPP during daylight hours), and also any potential uses for the heat waste from fission.

Any ideas how the above numbers were derived?

Most of what your asking is in the paper:
"The study took three different approaches to the solar architecture design including—1A, daylight-only operation at 1/5 production; 1B, around-the-clock operation at 1/5 production; and 1C, daylight-only operation at 2/5 production. All three designs used the ATK Ultraflex™ arrays that were designed to operate at 120 Vdc, with a conversion efficiency of 33 percent. The arrays were mounted on a gimbal that would track the Sun and perform dust mitigation by sloping to 45°. Array and battery sizing changed with architecture options with contingencies for a 120-d global dust storm and an average of 10 h/sol of daylight. Lithium ion batteries were used for energy storage at 165 Wh/kg.
The fission option used a slightly oversized 10-kWe Kilopower unit with a permanent radiator attached to the top of the lander. The reactor operated 24 h a day at 6.5 kWe (65 percent capacity) with no interruptions or power loss from dust storms or landing locations. Power conversion was performed by eight 1,250-We Stirling engines in the dual opposed configuration."

[john smith 19]

Most of what your asking is in the paper:
"The study took three different approaches to the solar architecture design including—1A, daylight-only operation at 1/5 production; 1B, around-the-clock operation at 1/5 production; and 1C, daylight-only operation at 2/5 production. All three designs used the ATK Ultraflex™ arrays that were designed to operate at 120 Vdc, with a conversion efficiency of 33 percent. The arrays were mounted on a gimbal that would track the Sun and perform dust mitigation by sloping to 45°. Array and battery sizing changed with architecture options with contingencies for a 120-d global dust storm and an average of 10 h/sol of daylight. Lithium ion batteries were used for energy storage at 165 Wh/kg.
The fission option used a slightly oversized 10-kWe Kilopower unit with a permanent radiator attached to the top of the lander. The reactor operated 24 h a day at 6.5 kWe (65 percent capacity) with no interruptions or power loss from dust storms or landing locations. Power conversion was performed by eight 1,250-We Stirling engines in the dual opposed configuration."

Note that means the radiators don't need any complex (and potentially unreliable) unfolding mechanism, and can presumably be shaped to allow dust to drop off them, or carry some kind of sliding "wiper" mechanism to keep them clean.

It also means they had a lot of reserve power in case the schedule had to be accelerated.

AFAIK Kilopower is under test in Nevada right now. I wonder if anyone has an update on how the testing is going?

[BrightLight]

Most of what your asking is in the paper:
"The study took three different approaches to the solar architecture design including—1A, daylight-only operation at 1/5 production; 1B, around-the-clock operation at 1/5 production; and 1C, daylight-only operation at 2/5 production. All three designs used the ATK Ultraflex™ arrays that were designed to operate at 120 Vdc, with a conversion efficiency of 33 percent. The arrays were mounted on a gimbal that would track the Sun and perform dust mitigation by sloping to 45°. Array and battery sizing changed with architecture options with contingencies for a 120-d global dust storm and an average of 10 h/sol of daylight. Lithium ion batteries were used for energy storage at 165 Wh/kg.
The fission option used a slightly oversized 10-kWe Kilopower unit with a permanent radiator attached to the top of the lander. The reactor operated 24 h a day at 6.5 kWe (65 percent capacity) with no interruptions or power loss from dust storms or landing locations. Power conversion was performed by eight 1,250-We Stirling engines in the dual opposed configuration."

Note that means the radiators don't need any complex (and potentially unreliable) unfolding mechanism, and can presumably be shaped to allow dust to drop off them, or carry some kind of sliding "wiper" mechanism to keep them clean.

It also means they had a lot of reserve power in case the schedule had to be accelerated.

AFAIK Kilopower is under test in Nevada right now. I wonder if anyone has an update on how the testing is going?

From the paper - the Kilopower reactor thermal radiators don't require complex folding to fit into the LV fairing.
I will talk to the Kilopower folks and find out if I can release the info on the NNTS results.

[john smith 19]

From the paper - the Kilopower reactor thermal radiators don't require complex folding to fit into the LV fairing.

Eliminating the tricky failure modes of bespoke folding mechanisms. that's very attractive from both a cost and a reliability standpoint

I will talk to the Kilopower folks and find out if I can release the info on the NNTS results.

That would be very exciting. The first space rated power fission reactor designed in the US since the early 60's.

I think most people here would consider that a pretty big deal.

[BrightLight]

Kilopower briefing on Thursday, Jan 18
https://www.nasa.gov/press-release/nasa-partners-discuss-power-for-future-space-exploration

NASA and its partners will host a news conference at noon EST (9 a.m. PST) Thursday, Jan. 18, at the National Atomic Testing Museum in Las Vegas, to discuss a recent experiment involving a new power source that could provide the safe, efficient and plentiful energy needed for future robotic and human space exploration missions.
Audio of the news conference and presentation slides will stream live on NASA’s website.

[john smith 19]

Kilopower briefing on Thursday
https://www.nasa.gov/press-release/nasa-partners-discuss-power-for-future-space-exploration

NASA and its partners will host a news conference at noon EST (9 a.m. PST) Thursday, Jan. 18, at the National Atomic Testing Museum in Las Vegas, to discuss a recent experiment involving a new power source that could provide the safe, efficient and plentiful energy needed for future robotic and human space exploration missions.
Audio of the news conference and presentation slides will stream live on NASA’s website.

Terrific news. It would be great if someone from the site can be there, but I don't know if that's going to be possible. 

TBH after 54 years since SNAP 20a even a bad result would still be pretty amazing, given the competing pressures of very limited time and budget and highly expanded H&S oversight.  I'm guessing the fact they are going to a formal press conference indicates the the results have been quite positive.

Watching those videos of SNAP 20a being assembled, and the somewhat relaxed attitude to radiation safety (by modern standards) was eye opening.

[docmordrid]

>
Watching those videos of SNAP 20a being assembled, and the somewhat relaxed attitude to radiation safety (by modern standards) was eye opening.

It was a different time with many radiologists direct viewing non- intensified fluoroscopic imaging screens, their head and much of their neck entirely within the exit beam. 20+ patients a day, 5-6 days a week.

The good old days.... /s

[Dave G]

It must be difficult to directly compare the power/kg of solar and fission systems: you need to consider battery storage for solar...

Exactly.  Many people seem to miss this.

However, reliability increases when you have multiple power sources of different types, so I suspect they'll use a combination of solar, batteries, and nuclear.

And that's not a bad combination for Earth either.

[ppb]

Kilopower briefing on Thursday, Jan 18
https://www.nasa.gov/press-release/nasa-partners-discuss-power-for-future-space-exploration

NASA and its partners will host a news conference at noon EST (9 a.m. PST) Thursday, Jan. 18, at the National Atomic Testing Museum in Las Vegas, to discuss a recent experiment involving a new power source that could provide the safe, efficient and plentiful energy needed for future robotic and human space exploration missions.
Audio of the news conference and presentation slides will stream live on NASA’s website.

This is a HUGE deal. I would argue that our lack of progress in spaceflight over the last 50 years is highly correlated to little advancement in propulsion/energy technology development. Consider our chances of landing men on the moon had we not developed LH2 engines. Or anything beyond Mars without RTEG.

[john smith 19]

Kilopower briefing on Thursday, Jan 18
https://www.nasa.gov/press-release/nasa-partners-discuss-power-for-future-space-exploration

NASA and its partners will host a news conference at noon EST (9 a.m. PST) Thursday, Jan. 18, at the National Atomic Testing Museum in Las Vegas, to discuss a recent experiment involving a new power source that could provide the safe, efficient and plentiful energy needed for future robotic and human space exploration missions.
Audio of the news conference and presentation slides will stream live on NASA’s website.

This is a HUGE deal. I would argue that our lack of progress in spaceflight over the last 50 years is highly correlated to little advancement in propulsion/energy technology development. Consider our chances of landing men on the moon had we not developed LH2 engines. Or anything beyond Mars without RTEG.

True.

Kilopower opens up the possibility of extending the ability to power probes beyond Mars to propelling them (by ion thruster) potentially out to Pluto with constant thrust, something just about impossible with RTG's.  It also opens up the range of sensors that can be carried, either in number or in type, for example active radar

[speedevil]

Kilopower opens up the possibility of extending the ability to power probes beyond Mars to propelling them (by ion thruster) potentially out to Pluto with constant thrust, something just about impossible with RTG's.  It also opens up the range of sensors that can be carried, either in number or in type, for example active radar

I somewhat disagree with the latter, if the argument is for pulsed power over a few minute encounter - batteries can do a kilowatt for half an hour in five kilos or so. They do require to be kept warmer than -30C or so over cruise and warmed up to 20C.
But this is some orders of magnitude lighter than a kilowatt reactor.
If you choose to use radio, using high output power for post encounter data return in principle is one option, but this can also be addressed by LASER.

[john smith 19]

Kilopower opens up the possibility of extending the ability to power probes beyond Mars to propelling them (by ion thruster) potentially out to Pluto with constant thrust, something just about impossible with RTG's.  It also opens up the range of sensors that can be carried, either in number or in type, for example active radar

I somewhat disagree with the latter, if the argument is for pulsed power over a few minute encounter - batteries can do a kilowatt for half an hour in five kilos or so. They do require to be kept warmer than -30C or so over cruise and warmed up to 20C.
But this is some orders of magnitude lighter than a kilowatt reactor.
If you choose to use radio, using high output power for post encounter data return in principle is one option, but this can also be addressed by LASER.

I chose radar as an example of a system that would be much simpler to implement with more power.  The big thing is that you can run electric thrusters going to the outer planets, then switch over to running sensors when you get there. That's not really possible with RTG's and solar arrays at this size is quite large and heavy.

[speedevil]

I chose radar as an example of a system that would be much simpler to implement with more power.  The big thing is that you can run electric thrusters going to the outer planets, then switch over to running sensors when you get there. That's not really possible with RTG's and solar arrays at this size is quite large and heavy.

Outer planet electric thrusters are a great example of game-changing stuff enabled by reactors.
Encounter power rather less so, given the very short encounter times.
I haven't looked at kilopower properly, and suspect it's not useful for higher thrust gravity manoevers using hydrogen heated by 'waste' heat. (~700s@300C).

I do wonder if the political environment is sensitive enough to the fact reactors are safe to launch to not consider them as a PR issue compared to RTG.

[john smith 19]

Outer planet electric thrusters are a great example of game-changing stuff enabled by reactors.
Encounter power rather less so, given the very short encounter times.
I haven't looked at kilopower properly, and suspect it's not useful for higher thrust gravity manoevers using hydrogen heated by 'waste' heat. (~700s@300C).

I don't think anyone's talked about this. 10Kw can drive an ion thruster with an Isp of 3000secs. H2 is a real PITA to managed. I'd guess it would we simpler (at 300c) to vaporize water (that would hit 200bar).

I do wonder if the political environment is sensitive enough to the fact reactors are safe to launch to not consider them as a PR issue compared to RTG.

That's a good question.  RTG's are very hot and much more radioactive after mfg, but before they start generating power, than reactors.

Will future programmes announce they run on Kilopower, or simply not bother to mention how they are powered?

[Robotbeat]

10kW is like 40kW thermal. At an Isp of 700s, that's about 7km/s exhaust velocity... That's about 12 Newtons at 100% thermal efficiency (real engine will be somewhat less than that, maybe 50%, so 6 Newtons?). So you're stuck doing fairly low-thrust maneuvers.

...but much the weight of kilopower is in the radiators and dynamo. Don't need much of that stuff if you're building a rocket engine.

[john smith 19]

10kW is like 40kW thermal. At an Isp of 700s, that's about 7km/s exhaust velocity... That's about 12 Newtons at 100% thermal efficiency (real engine will be somewhat less than that, maybe 50%, so 6 Newtons?). So you're stuck doing fairly low-thrust maneuvers.

...but much the weight of kilopower is in the radiators and dynamo. Don't need much of that stuff if you're building a rocket engine.

Again it's 700s Vs 3000 secs of Isp. It's also the mass of that LH2 tank  you're carrying and of course what will do for cooling when it runs out?

That said 6N sounds like quite a high thrust level (by ion thruster standards), so could as an upper stage during Earth departure. However that's another development project. The question would be does the faster acceleration offset the complexity (LH2 tank, valving, injectors, nozzle) of this new stage (which is basically what it is) versus just making the Xenon tank bigger?

In terms of developmental "leverage" improving radiator efficiency sounds like it could be more broadly applicable. My instinct is better "tuned" high emissivity coatings, or carbon "hair" can make smaller, higher efficiency radiators which can operate in any environment better than existing designs.

In truth I doubt that on Mars any heat will be "waste" heat. A use can (and will) be found for all of it

[Robotbeat]

6N is only high thrust because it's low Isp. You can do a similar thing with a solar panel and resistojet/arcjet. Probably would be lighter weight in the inner solar system.

Nah, I think using kilopower for a nuclear thermal rocket doesn't make sense. Too low power. A REAL NTR is like Gigawatts.

[jpo234]

A REAL NTR is like Gigawatts.

1GW is a full sized power plant. Do you mean MW?

See for instance https://en.m.wikipedia.org/wiki/AP1000

[kfsorensen]

No, gigawatts.  The nuclear thermal rocket cores they tested back in the 1960s had thermal powers of several gigawatts apiece, making them the largest nuclear reactors (by thermal power) ever built in the United States.

[john smith 19]

6N is only high thrust because it's low Isp. You can do a similar thing with a solar panel and resistojet/arcjet. Probably would be lighter weight in the inner solar system.

Nah, I think using kilopower for a nuclear thermal rocket doesn't make sense. Too low power. A REAL NTR is like Gigawatts.

Technically what you were proposing is more like those Solar Thermal Rocket concepts in the 80's, with a lump of porus carbon at the focus of a mirror array with GH2 streamed through it.

Actually I think the thrust was about that level as well.

An actual full on NTR is indeed in the GW range and AFAIK there is no serious funding on the table to build one of those. I think they're trying to recover the mfg technology of both NTR designs (the graphite thermal spectrum and the tungsten cermet fast spectrum) but that's a long way from being able to design (or even recreate) an NTR, not to mention the serious ground level test facilities needed.

[Robotbeat]

Yeah, there has been some fuel element work on NTR.

kfsorensen convinced me NTR really isn't that great, but I think that it is a useful long-term technology, so I'm not opposed to work on it.

I guess if I had multiple gigawatts of thermal fission power, I'd probably want it as a surface power reactor rather than as a rocket engine. The designs are obviously very different typically, but perhaps you could somehow dump heat to the CO2 atmosphere (compressed somewhat) instead of hydrogen. Someone had proposed such a modification for a Mars nuclear aircraft, but it should work on the ground, too.

Apparently some of the low TRL work NASA is doing on NTR is about using low enriched uranium (~30%, right at the cut-off for some definition of "low") in order to reduce the cost and regulatory burden of NTR.

[john smith 19]

Yeah, there has been some fuel element work on NTR.

kfsorensen convinced me NTR really isn't that great, but I think that it is a useful long-term technology, so I'm not opposed to work on it.

I think Mueller while at SX said they saw NTR as a key long term enabler of settlement. While 90-1000secs Isp doesn't sound great next to Ion thrusters or fission fragment designs it's still 100% than the best available LO2/LH2 engines and it's the only high thrust  technology available with a TRL above 0 (highly energetic materials like monoHydrogen , or Nitrogen rings might deliver but their storage and mfg is close to SF.

I guess if I had multiple gigawatts of thermal fission power, I'd probably want it as a surface power reactor rather than as a rocket engine. The designs are obviously very different typically, but perhaps you could somehow dump heat to the CO2 atmosphere (compressed somewhat) instead of hydrogen. Someone had proposed such a modification for a Mars nuclear aircraft, but it should work on the ground, too.

The fundamental problem is the design lives of NTRs are measured in hours and a surface thermal system is in years. The power densities are much higher. IMHO a surface power reactor would be a completely different design. I think the best  you could do is reuse the fuel rod design, with greater spacing and different stacking, lower gas speeds but higher gas flows etc.

Apparently some of the low TRL work NASA is doing on NTR is about using low enriched uranium (~30%, right at the cut-off for some definition of "low") in order to reduce the cost and regulatory burden of NTR.

LEU is a legal definition. Kilopower is HEU, but the volumes are quite small. An NTR is HEU and is big and its Uranium is relatively accessible (not one single big block). That makes people very nervous.

Kilopower is a relatively low profile effort, but formal NTR testing will be much more public and public concerns will need to be dealt with. It will also be much more expensive (IIRC the line item for NTR was $13Bn, compare that with Kilopower to date. $100m? $200m? From lots of disparate sources)

What's been achieved by the Kilopower to get even this far (given we don't know the results of the press conference) on the funding they've secured, is amazing.

[speedevil]

I think Mueller while at SX said they saw NTR as a key long term enabler of settlement. While 90-1000secs Isp doesn't sound great next to Ion thrusters or fission fragment designs it's still 100% than the best available LO2/LH2 engines and it's the only high thrust  technology available with a TRL above 0

I would say Orion has a TRL above 0 too.
But that has issues with other sorts of readiness levels.

[john smith 19]

I think Mueller while at SX said they saw NTR as a key long term enabler of settlement. While 90-1000secs Isp doesn't sound great next to Ion thrusters or fission fragment designs it's still 100% than the best available LO2/LH2 engines and it's the only high thrust  technology available with a TRL above 0

I would say Orion has a TRL above 0 too.
But that has issues with other sorts of readiness levels.

I'd forgotten about Orion. That would be another candidate in the high thrust area, but it's engineering (despite massive improvements in CAD/CAM CFD and FEA) remains very tough.

[Space Junkie]

Here are the the slides from the Kilopower briefing today:

https://www.nasa.gov/sites/default/files/atoms/files/kilopower-media-event-charts-final-011618.pdf

[Robotbeat]

I think Mueller while at SX said they saw NTR as a key long term enabler of settlement. While 90-1000secs Isp doesn't sound great next to Ion thrusters or fission fragment designs it's still 100% than the best available LO2/LH2 engines and it's the only high thrust  technology available with a TRL above 0

I would say Orion has a TRL above 0 too.
But that has issues with other sorts of readiness levels.

I'd forgotten about Orion. That would be another candidate in the high thrust area, but it's engineering (despite massive improvements in CAD/CAM CFD and FEA) remains very tough.

Additionally, the most realistic implementations of Orion didn't have an Isp really much better than NTR.

[john smith 19]

Here are the the slides from the Kilopower briefing today:

https://www.nasa.gov/sites/default/files/atoms/files/kilopower-media-event-charts-final-011618.pdf

Thanks for that.

Do we  have any idea what the contents of the presentation were? We know the goals of the tests, but do we have any idea of how well they've been achieved?

[john smith 19]

Additionally, the most realistic implementations of Orion didn't have an Isp really much better than NTR.

I'd thought Orion was meant to be orders of magnitude over the best chemical systems.

[Robotbeat]

Tests aren't finished, yet.

They did the live-fission proof of concept test in FY12, I believe, where they used heat pipes to extract heat from the small HEU core and generate a small amount of power with a Sterling engine. But the actual fission tests for this round of Kilopower won't be done finished until March of this year, so in a couple months.

[RotoSequence]

Additionally, the most realistic implementations of Orion didn't have an Isp really much better than NTR.

I'd thought Orion was meant to be orders of magnitude over the best chemical systems.

Specific impulse doesn't matter as much when each impulse releases more energy than an entire rocket.

[Robotbeat]

Additionally, the most realistic implementations of Orion didn't have an Isp really much better than NTR.

I'd thought Orion was meant to be orders of magnitude over the best chemical systems.

Yup, but the nearer term implementations aren't. You can, for instance, increase the thrust a lot if you add ballast (inert mass). That also reduces the thermal load on the pusher plates, making them easier to engineer.

[Space Junkie]

Do we  have any idea what the contents of the presentation were? We know the goals of the tests, but do we have any idea of how well they've been achieved?

The audio doesn't seem to have been posted yet. Here are a few tweets:

https://twitter.com/SciGuySpace/status/954041916353630208

Listening to the Kilopower news conference. Not much "news" yet, but NASA says it wants the power system for ISRU activities on the lunar and Martian surfaces.

https://twitter.com/SpcPlcyOnline/status/954046295227949061

NASA's Lee Mason is explaning the Kilopower Project.  Compact reactor for human missions on planetary surfaces.  Compact means core is size of paper towel roll and height is about the same as a man or woman.
Scalable from 1-10 kWe.

https://twitter.com/SpcPlcyOnline/status/954055664078336002

Q - any other space agencies working on space fission reactors?
A - Russians have always had program, launched 33, but their financial situation has slowed it.  China has published papers on it, but don't know what they may be doing beyond that.

@SpcPlcyOnline has some more tweets about the briefing, but it's nothing we didn't already know. The audio was apparently pretty bad.

BTW, this recent op-ed by John Casani in support of space fission power was pretty good. Basic, but there were a few nuggets I hadn't seen before.
http://spacenews.com/op-ed-an-argument-for-space-fission-reactors/

This blogger also goes into Kilopower in some detail.
https://beyondnerva.wordpress.com/2017/11/19/krusty-first-of-a-new-breed-of-reactors-kilopower-part-ii/

[docmordrid]

An important slide wrt the thread title,

[john smith 19]

Specific impulse doesn't matter as much when each impulse releases more energy than an entire rocket.

For the kind of money such a programme would cost it has to offer a serious increase in Isp. NTR is estimated to cost 10s of $Bn for a 2x increase over chemical Isp.  Orion would be much more expensive give the safety precautions needed throughout the whole design, build and operating of the system.

Yup, but the nearer term implementations aren't. You can, for instance, increase the thrust a lot if you add ballast (inert mass). That also reduces the thermal load on the pusher plates, making them easier to engineer.

I didn't think lack of thrust was ever an issue with Orion. 

My first thought would be put a bag of water between the pusher plate and the (what's the correct term these days?) "fission package."

Tests aren't finished, yet.

They did the live-fission proof of concept test in FY12, I believe, where they used heat pipes to extract heat from the small HEU core and generate a small amount of power with a Sterling engine. But the actual fission tests for this round of Kilopower won't be done finished until March of this year, so in a couple months.

I hadn't realized that. I knew they were expected to start Nov/Dec '17 but I'd thought they were only run a couple of months.

If I'd realized they were running to March I wouldn't have expected anything substantial till then beyond "We put all the bits together. It's gone critical. Nothing has blown up,"  which is encouraging but obviously they've still got a long way to go.

[john smith 19]

This blogger also goes into Kilopower in some detail.
https://beyondnerva.wordpress.com/2017/11/19/krusty-first-of-a-new-breed-of-reactors-kilopower-part-ii/

The blog is very interesting. Especially the ways they've managed to leverage existing resources to get the tests done. Especially the issues with thermal vacuum testing, which is absolutely vital for this sort of thing.  Making the system realistic as necessary (to collect data that will accurately model the full system) without unnecessary duplication.
Putting the reflector on a lift is kind of like the Toshiba 3S design, and obviously makes very easy to shut the reactor down by bleeding the hydraulic fluid off the drive cylinders.

One odd thing about the blog was it talked about the "DU Core" mfg for testing to have 15% U235. That makes no sense. A DU core should have U235 levels substantially below the 0.7% of natural Uranium.
[EDIT
Small note. Large Stirling engines have been used IRL. They are one option for the power plants of Diesel electric submarines mfg (IIRC) by German and Dutch companies. So there is operational experience with the technology, it's just not with nuclear reactor heat sources or in the US ]

[john smith 19]

An important slide wrt the thread title,

Indeed.

Realistically there is no chance that SX could ever have done this on their own. However if they can get it supplied as a service IE a complete package, that radically changes the playing field, just as a nuclear thermal "tug" would (although I think the chances of such a thing happening anytime soon are very remote).

[Robotbeat]

An important slide wrt the thread title,

What's important for commercial missions is price of Kilopower units. If they cost $100m, no way in heck it will be affordable. Even $10 million is a lot for just 10kW of power.

[AncientU]

An important slide wrt the thread title,

What's important for commercial missions is price of Kilopower units. If they cost $100m, no way in heck it will be affordable. Even $10 million is a lot for just 10kW of power.

Especially since many apps will require tens of mega-Watts... $10billion is laughable from commercial perspective.

[RotoSequence]

Specific impulse doesn't matter as much when each impulse releases more energy than an entire rocket.

For the kind of money such a programme would cost it has to offer a serious increase in Isp. NTR is estimated to cost 10s of $Bn for a 2x increase over chemical Isp.  Orion would be much more expensive give the safety precautions needed throughout the whole design, build and operating of the system.

That was an aside reference to Orion type nuclear pulse propulsion, with each pulse supplied by an atom bomb, rather than nuclear thermal rockets.

[Robotbeat]

Specific impulse still matters tremendously.

[john smith 19]

Specific impulse still matters tremendously.

WRT to this thread the relevant measure is additional sec of Isp (compared to Raptor)/$ invested by SpaceX.

On that basis a NTR tug would be a good deal (even at only double the Isp) if the whole package cost less than whole conventional fuel + consumables for a BFS flight with Raptors provided it either cut the transit time at the same payload (less consumables, more payload, depending on how closed loop the ECLSS is) or it allowed BFS to carry a lot more payload for the same journey time

The same would apply to high thrust ion drives/VASIMIR/Fission fragment/magic fairy dust systems.

An important slide wrt the thread title,

What's important for commercial missions is price of Kilopower units. If they cost $100m, no way in heck it will be affordable. Even $10 million is a lot for just 10kW of power.

Let's not get too far ahead of the game here. Kilopower is in testing right now. So
1) A full Mars design does not exist yet, although NASA and its contractors are pretty familiar with Martian surface conditions
2) NASA has already shifted it's baseline DRM 5.0 architecture to use multiple Kilopowers rather than a single 40Kw unit. This suggests they really want Kilopower to succeed. Kilopower is good for NASA. A nice convenient size for a lot of missions, with (claimed) design stretch  into the MW range.
3) IIRC on Earth nuclear capacity is roughly $1000/Kw, so by "Big Nuclear" standards that's a $10K build cost (fuel on Earth is an ongoing expense).
4) But this is Mars, so what's a fair multiplier is negotiable. 10x Earth build cost? 100x? 1000x? that negotiation has not even started.
5) Nuclear can operate anywhere, and under any conditions, without power reduction. 24/7/365/. These are attractive qualities for a power system.
6) The availability of Methane deposits in large quantities is (potentially) another major game changer for the balance of judging where to put a first settlement down. With it and a big enough PV array to bootstrap LOX production, large scale mfg becomes much more possible.

So people should not fall into any negative thinking yet.  The ability to add capacity in man portable (the 40Kw design needed it's only specialist transporter, which was the lasted single item of downmass for the DRM 5.0 architecture) units, and the consistent output, are valuable benefits.

An important slide wrt the thread title,

What's important for commercial missions is price of Kilopower units. If they cost $100m, no way in heck it will be affordable. Even $10 million is a lot for just 10kW of power.

Especially since many apps will require tens of mega-Watts... $10billion is laughable from commercial perspective.

We are a long way from NASA even giving SX a possible price for this.

[AncientU]

SpaceX or any other commercial company will not be able to afford a buy from NASA.  Anything.  Ever.

[TrevorMonty]

For Lunar polar ISRU operations, even single 1KW reactor plus batteries maybe all that is needed to keep equipment warm and alive few days a month without sunlight.

Production would be suspended during these dark periods.

[Jcc]

SpaceX or any other commercial company will not be able to afford a buy from NASA.  Anything.  Ever.

Then it's a good thing NASA doesn't really sell technology, but more likely license it or give it away freely.

The R&D that is going into Kilopower is something no commercial company could justify doing (maybe Lockheed Martin once they finish their "mini" fusion reactor .

[RotoSequence]

Specific impulse still matters tremendously.

~6000 newton seconds for a bomb powered pusher plate design; up to 100,000 for a Medusa type bomb-sail design.

[BeyondNERVA]

Hi! I'm new here! Kinda weird doing this as my first post, but I found this thread from my blog being linked above, so it feels a BIT less strange... I'm an astronuclear geek, and write the Beyond NERVA blog. I've dug into this system quite a bit, but not SpaceX so much.

I haven't heard anything about Elon looking at nuclear power in space, either fission power systems or nuclear propulsion, but it would make a lot of sense to. If you want NASA's take on the question of whether to do solar or fission, you can find it here: https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20160011275.pdf

(The other odd omission is a complete lack of any interest in Aldrin cyclers... which absolutely baffles me)

Space reactors are weird things... they kinda belong to everyone and no one at the same time, because they haven't had to be a thing. IIRC the fissile component is the responsibility of the DOE until integration into the full fission power system, when it gets handed over to NASA, but I'm not 100% sure on that. The design side tends to be a mish-mash of ideas and program requirements.

If you're interested in the origins of the program, I highly recommend Dave Poston's personal blog from before this program got started, during the Fission Surface Power program in 2010-2012: http://spacenuke.blogspot.com/

Someone posted my blog above about KRUSTY, if what you're looking for is not written up in there, check the in-line references: https://beyondnerva.wordpress.com/2017/11/19/krusty-first-of-a-new-breed-of-reactors-kilopower-part-ii/
if you're interested in the precursor fission test, DUFF, I did a writeup on that as well: https://beyondnerva.wordpress.com/2017/10/07/duff-father-of-krusty-kilopower-part-1/

There's talk of converting the core to low enriched uranium, with no insurmountable problems seen, there's just a lot that's different about this reactor, and the design particulars of nuclear spacecraft in general and this reactor in specific meant that the high security costs associated with HEU could be minimized. Basically, you take a 55%-74% mass hit on the full system if you do that, although there are areas that could possibly be optimized on the system. A recent paper by Dave Poston and Patrick McClure looks at it: https://fas.org/nuke/space/leu-reactor.pdf

If this design were to be commercialized (and it may be, BWXT could certainly handle it as a commercial provider - and they've got good connections at every point in the US nuclear supply chain), then it would probably be the LEU variant... but that will require a re-test of the core. Depending on how regulations are changed over the next few years (largely driven by advanced terrestrial designs, but space reactors will benefit as well), that could be either a very inexpensive test or virtually impossible to squeak through. Hopefully it's the former, and this team has done wonders on a shoestring and pocket change budget.

There are much larger variants of this reactor, which I look at briefly at the end of my KRUSTY rundown, called MegaPower. This is a Defense Nuclear Security Agency program, so you don't hear much about it, but it's rated up to 40 MWe, with a Brayton (?) PCS. My bet, though, is on a reworked version of the Fission Surface Power reactor, which is the next size class up from Kilopower, at 10 kWe - 1 MWe. It was the first fission system in this design series that proposed the Stirling PCS that I've seen developed to any degree, but it also had a very complex heat rejection system that ate the project's incredibly skimpy budget.

The design is basically solid, though, and could be reworked to overcome the problems that were seen during the development: https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20110007114.pdf

[jpo234]

I haven't heard anything about Elon looking at nuclear power in space, either fission power systems or nuclear propulsion, but it would make a lot of sense to. If you want NASA's take on the question of whether to do solar or fission, you can find it here: https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20160011275.pdf

We have a quote from Gwynne Shotwell during her talk at MIT from last September:

https://twitter.com/charlottelowey/status/913145922976190464?s=17

Shotwell on @SpaceX work on nuclear propulsion: "We're actually trying to get hold of some nuclear material - it's hard, by the way"

[jpo234]

I haven't heard anything about Elon looking at nuclear power in space, either fission power systems or nuclear propulsion, but it would make a lot of sense to. If you want NASA's take on the question of whether to do solar or fission, you can find it here: https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20160011275.pdf

We have a quote from Gwynne Shotwell during her talk at MIT from last September:

https://twitter.com/charlottelowey/status/913145922976190464?s=17

Shotwell on @SpaceX work on nuclear propulsion: "We're actually trying to get hold of some nuclear material - it's hard, by the way"

And we have a few quotes from the Tom Mueller Skype interview (https://zlsadesign.com/post/tom-mueller-interview-2017-05-02-transcription)

So we’re looking, actually, at like electric propulsion for the satellites, and we’re talking to people about nuclear-thermal, you know, the NASA centers are working on nuclear; it’s just prohibitively expensive to test because you can’t; it’s not like the 60s, like when you can just let fission products fly out of your rocket into the desert. You’ve now got to scrub it and clean it and capture it, which is super-expensive. I don’t think SpaceX could really afford to develop that rocket ourselves. If NASA ever gets turned on to develop those test stands, we’d probably want to jump in on that. You can just about double the performance of a rocket to Mars compared to a really-good, like a Raptor system, a chemical system, with fission; nuclear fission. Theoretically, fusion may be ten times better, and antimatter maybe a thousand times better, but I think those are certainly not going to happen in my lifetime. Maybe in your lifetimes.

It’s much better to use nuclear, fission reactor, it gets, you know, more compact; you actually get more; you get more power out per pound of reactor than you do out of solar cells, so it’s more mass-efficient. So if you’re taking it to Mars, it’s more efficient to ship reactors than it is to ship solar; it’s just that nobody’s really developed a space reactor yet. We’re working with NASA on that, and hopefully they’ll get funding to develop that. They’ve got a program called kilopower going that’s like, ten thousand watts, a 10 kilowatt reactor. We need a megawatt, but you know, you need to start somewhere.

[butters]

I'm confident that nuclear fission will be used for off-world surface power before it is used for orbital propulsion. Chemical propulsion is more "good-enough" than solar farms for Mars, and nuclear propulsion is barely superior at all for the Moon. We'll need reliable electrical power on Mars before the surface presence can grow to the point where nuclear propulsion really begins to pay off for supporting the supply chain.

[Robotbeat]

For Lunar polar ISRU operations, even single 1KW reactor plus batteries maybe all that is needed to keep equipment warm and alive few days a month without sunlight.

Production would be suspended during these dark periods.

That sort of thing is the best use of Kilopower, IMHO. Leaning on its strengths.

[TrevorMonty]

Low cost lunar and asteriod source fuel could eliminate need for nuclear propulsion. Especially for earth Mars trips.

The development cost of nuclear would pay for lot ISRU operations.
While ISRU fuel can compete against SEPs,  ISRU needs large scale solar power systems that are part of SEP development. 

[john smith 19]

Low cost lunar and asteriod source fuel could eliminate need for nuclear propulsion. Especially for earth Mars trips.

Provided you have a means to collect enough energy in the first place to process that raw material into propellant.

The development cost of nuclear would pay for lot ISRU operations.

Assuming they all were part of one unified budget.

But they are not.

And the point of Kilopower is that in fact it's budget has been very modest relative to previous plans to do this, which may explain why it's got this far, which is much further than earlier efforts ever have.

While ISRU fuel can compete against SEPs,  ISRU needs large scale solar power systems that are part of SEP development.

It's a balance.

[john smith 19]

There's talk of converting the core to low enriched uranium, with no insurmountable problems seen, there's just a lot that's different about this reactor, and the design particulars of nuclear spacecraft in general and this reactor in specific meant that the high security costs associated with HEU could be minimized. Basically, you take a 55%-74% mass hit on the full system if you do that, although there are areas that could possibly be optimized on the system. A recent paper by Dave Poston and Patrick McClure looks at it: https://fas.org/nuke/space/leu-reactor.pdf

That looks like a version of the Kilopwer architecture with LEU

If this design were to be commercialized (and it may be, BWXT could certainly handle it as a commercial provider - and they've got good connections at every point in the US nuclear supply chain), then it would probably be the LEU variant... but that will require a re-test of the core. Depending on how regulations are changed over the next few years (largely driven by advanced terrestrial designs, but space reactors will benefit as well), that could be either a very inexpensive test or virtually impossible to squeak through. Hopefully it's the former, and this team has done wonders on a shoestring and pocket change budget.

AFAIK BWXT is nothing to do with Kilopower, however it is much closer to the idea of "beyond NERVA," being an LEU NTR project, rather than an NEP (where I'm using the "P" for power, rather than propulsion).

There are much larger variants of this reactor, which I look at briefly at the end of my KRUSTY rundown, called MegaPower. This is a Defense Nuclear Security Agency program, so you don't hear much about it, but it's rated up to 40 MWe, with a Brayton (?) PCS. My bet, though, is on a reworked version of the Fission Surface Power reactor, which is the next size class up from Kilopower, at 10 kWe - 1 MWe. It was the first fission system in this design series that proposed the Stirling PCS that I've seen developed to any degree, but it also had a very complex heat rejection system that ate the project's incredibly skimpy budget.

The design is basically solid, though, and could be reworked to overcome the problems that were seen during the development: https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20110007114.pdf

Nuclear, even more so than space launch, seems obsessed with pedigree, the (traceable) history of a development.
So if Kilopwer can scale up with roughly the same materials and structure that's going to be viewed as the "less risky" option.  IIRC the increasing power output from the larger versions is mostly due to insertion of heat pipes inside the block, as opposed to just on the periphery.

WRT the Kilopower ground tests and the initial presentation I noted a 200c temperature drop due to poor conduction between two parts of the design.

Historically space thermal tactics have used carefully machined flat surfaces or equally carefully machined interlocking "hedgehogs" (like the cooling for the EMU's on the SSME's) to transfer heat.

However a small project  for the ECLSS on the ISS mentioned use of (essentially) carbon fibre knitted "socks" which when compressed between too surfaces could radically increase heat transfer (like thermally conductive grease, but with no danger of evaporation)

Aside from being more compact I thought HEU was easier for the DoE to procure, as it had quite a lot in stockpile from decommissioned nuclear weapons? It was (essentially) free.

[BeyondNERVA]

I haven't heard anything about Elon looking at nuclear power in space, either fission power systems or nuclear propulsion, but it would make a lot of sense to. If you want NASA's take on the question of whether to do solar or fission, you can find it here: https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20160011275.pdf

We have a quote from Gwynne Shotwell during her talk at MIT from last September:

https://twitter.com/charlottelowey/status/913145922976190464?s=17

Shotwell on @SpaceX work on nuclear propulsion: "We're actually trying to get hold of some nuclear material - it's hard, by the way"

And we have a few quotes from the Tom Mueller Skype interview (https://zlsadesign.com/post/tom-mueller-interview-2017-05-02-transcription)

So we’re looking, actually, at like electric propulsion for the satellites, and we’re talking to people about nuclear-thermal, you know, the NASA centers are working on nuclear; it’s just prohibitively expensive to test because you can’t; it’s not like the 60s, like when you can just let fission products fly out of your rocket into the desert. You’ve now got to scrub it and clean it and capture it, which is super-expensive. I don’t think SpaceX could really afford to develop that rocket ourselves. If NASA ever gets turned on to develop those test stands, we’d probably want to jump in on that. You can just about double the performance of a rocket to Mars compared to a really-good, like a Raptor system, a chemical system, with fission; nuclear fission. Theoretically, fusion may be ten times better, and antimatter maybe a thousand times better, but I think those are certainly not going to happen in my lifetime. Maybe in your lifetimes.

It’s much better to use nuclear, fission reactor, it gets, you know, more compact; you actually get more; you get more power out per pound of reactor than you do out of solar cells, so it’s more mass-efficient. So if you’re taking it to Mars, it’s more efficient to ship reactors than it is to ship solar; it’s just that nobody’s really developed a space reactor yet. We’re working with NASA on that, and hopefully they’ll get funding to develop that. They’ve got a program called kilopower going that’s like, ten thousand watts, a 10 kilowatt reactor. We need a megawatt, but you know, you need to start somewhere.

This is good news! (Minor nitpick, there have been 34 reactors flown, of three different designs, plus KRUSTY... and XE-PRIME was flight-qualified, so there have been reactors developed - and flown!)

The vast majority of the testing can be done with non-nuclear components, fortunately. A lot of the questions aren't that different from many chemical engines, especially LH2/LO2 engines. Most of the problems that Rover and NERVA faced were actually solved by the development of cryo hydrogen stages. The questions that remain tend to be on issues of thermal expansion, chemical reactions (2500+K hydrogen will ruin ANYONE's day if not handled properly), erosion and flow issues in the fuel elements... none of this study requires a nuclear reactor, just a rocket engine development facility with some specialized facilities.

These are still in the development phase right now, but I've got a page started for the types of test stands that have been built, and are currently operating. I hope to add more to it in the future, but... there's a ton of stuff out there that no one has had the time to make available outside conference papers, and test stands aren't sexy, neither are the engineering nitty-gritty details... for most people! Unfortunately, this is supposed to be a YouTube channel, the blog was just to point people to as kind of an in-depth FAQ that's taken on a life of its own fairly quickly.

https://beyondnerva.wordpress.com/nuclear-test-stands-and-equipment/

The reactor physics side has never really stopped, on a theoretical level. The problem is that no-one ever hears about it, because it's a small, specialized part of an attention-shy industry. When a lot of this work that I'm researching was done, maybe 1k people knew about it in any detail. That's changing now, but other than Winchell Chung at Atomic Rockets, there's no-one to repackage the information to make it more accessible, and there's WAY too much for just a couple people, or a hundred, to get the interested public caught up on 50+ years of materials science and technological development as it applies to in-space nuclear power.

Low cost lunar and asteriod source fuel could eliminate need for nuclear propulsion. Especially for earth Mars trips.

The development cost of nuclear would pay for lot ISRU operations.
While ISRU fuel can compete against SEPs,  ISRU needs large scale solar power systems that are part of SEP development.

I hear this a lot, and while it technically is true, it's not as efficient, or as powerful, as many designs that are possible with NTRs. Remember, we're playing in the kiddie end of the pool with what's possible here... a CERMET-fueled NTR will give you the same level of thrust for about 3x the isp of a hydralox stage, which is a very nice boost in capabilities. An open-cycle gas-core NTR, on the other hand, makes Hohmann transfers look like exactly what they are: pretty much the bare minimum effort to get anywhere.

The other advantage that an NTR has is it lends itself perfectly to having an afterburner. The LOX-augmented NTR uses a cascade injector ring to dump LOX into the hot H2 as it leaves the reactor and enters a combustion chamber. Your isp takes a tank, but your thrust gets a nice big boost.If you're trying to hit a particular launch window, that is a nifty little trick for a GNC to have up their sleeve.

This paper is now 20 years old, so the engine isn't exactly what we would try to build today, but the general concept is still just as valid.

https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19950005290.pdf

There's talk of converting the core to low enriched uranium, with no insurmountable problems seen, there's just a lot that's different about this reactor, and the design particulars of nuclear spacecraft in general and this reactor in specific meant that the high security costs associated with HEU could be minimized. Basically, you take a 55%-74% mass hit on the full system if you do that, although there are areas that could possibly be optimized on the system. A recent paper by Dave Poston and Patrick McClure looks at it: https://fas.org/nuke/space/leu-reactor.pdf

That looks like a version of the Kilopwer architecture with LEU

That's because it is. If you want to do the design commercially, this is the best way to do it in the short term - piggyback off difficult and expensive work someone else has already done!

AFAIK BWXT is nothing to do with Kilopower, however it is much closer to the idea of "beyond NERVA," being an LEU NTR project, rather than an NEP (where I'm using the "P" for power, rather than propulsion).

You're correct, but they also offer U-Mo fuel, of various types, and are able to do the same tooling and machining as Y12, who made this fuel element. Y12 is not a commercial enterprise, and the government can't sell anything, they need a commercial partner. BWXT is the logical choice. They already make all of the DOE's experimental fuel elements, most of the FEs for research reactors in the US, and fabricate, supply, and dispose of most (all?) of the US Navy's nuclear fuel as well. I can't think of anyone else even remotely as qualified...

Aside from being more compact I thought HEU was easier for the DoE to procure, as it had quite a lot in stockpile from decommissioned nuclear weapons? It was (essentially) free.

Absolutely. Y12 has unique procedures in regards to accountability of material (for good reason), which make HEU basically free in the overall operating budget (absolutely absurd...). This isn't an option for a commercial company, like SpaceX in the OP, who are stuck with LEU as long as they want to be an American company (or federal policy on that changes).

Nuclear, even more so than space launch, seems obsessed with pedigree, the (traceable) history of a development.
So if Kilopwer can scale up with roughly the same materials and structure that's going to be viewed as the "less risky" option.  IIRC the increasing power output from the larger versions is mostly due to insertion of heat pipes inside the block, as opposed to just on the periphery.

Not quite, the core also increases in size, which has a much bigger effect than you would think. a 200 MWt core and a 2000 MWt core of the same basic geometry are only marginally different in size. Nuclear scales UP very fast, but you tend to have a hard limit on DOWN fairly quickly... basically Flattop, which was the reactor used for DUFF.

WRT the Kilopower ground tests and the initial presentation I noted a 200c temperature drop due to poor conduction between two parts of the design.

Yeah, this was expected. Basically, it wasn't worth the money to re-tool, they'd just do conceptual work for the next iteration (which may or may not be a flight article). It's not a nuclear component, so GRC can do what they need to in order to fix the problem.

[john smith 19]

This paper is now 20 years old, so the engine isn't exactly what we would try to build today, but the general concept is still just as valid.

https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19950005290.pdf

Getting closer to 25 YO. And a belated welcome to the forum.

You're correct, but they also offer U-Mo fuel, of various types, and are able to do the same tooling and machining as Y12, who made this fuel element. Y12 is not a commercial enterprise, and the government can't sell anything, they need a commercial partner. BWXT is the logical choice. They already make all of the DOE's experimental fuel elements, most of the FEs for research reactors in the US, and fabricate, supply, and dispose of most (all?) of the US Navy's nuclear fuel as well. I can't think of anyone else even remotely as qualified...

Now that I did not know. They do sound like one of those outfits that's quietly been building their skills, and their relationship with the DoE.

Absolutely. Y12 has unique procedures in regards to accountability of material (for good reason), which make HEU basically free in the overall operating budget (absolutely absurd...). This isn't an option for a commercial company, like SpaceX in the OP, who are stuck with LEU as long as they want to be an American company (or federal policy on that changes).

I don't see either changing any time soon.

Not quite, the core also increases in size, which has a much bigger effect than you would think. a 200 MWt core and a 2000 MWt core of the same basic geometry are only marginally different in size. Nuclear scales UP very fast, but you tend to have a hard limit on DOWN fairly quickly... basically Flattop, which was the reactor used for DUFF.

For people used to conventional (LEU) reactor design these units are very small, but given you've not near minimum surface area and near maximum enrichment the only options left would be going fully enriched (100% U235), moving to a sphere (which looks a PITA to make and extract heat from) or a better reflector material(s). But I don't what is a better reflector, given this is a fast spectrum, rather than a thermal spectrum reactor.

WRT the Kilopower ground tests and the initial presentation I noted a 200c temperature drop due to poor conduction between two parts of the design.

Yeah, this was expected. Basically, it wasn't worth the money to re-tool, they'd just do conceptual work for the next iteration (which may or may not be a flight article). It's not a nuclear component, so GRC can do what they need to in order to fix the problem.

The Kilopower team have been very pragmatic regarding their of funds to test what really needs to be tested to demonstrate the viability of the concept, starting from DUFF, demonstrating the first use ever of a nuclear reactor to drive a Stirling engine.

BTW as I noted earlier large Stirlings are in commercial use for Diesel electric submarine propulsion. It's not done in the US, and it's not something you can get hold of easily, but it's certainly in the known SoA.

[BeyondNERVA]

And a belated welcome to the forum.

Thank you.

They do sound like one of those outfits that's quietly been building their skills, and their relationship with the DoE.

They helped build, and decommission, the USS Nautilus. IIRC they're one of the first commercial nuclear companies. They're also one of the more discrete, which has been appreciated during the anti-nuclear hullaboo of the last 40 years.

For people used to conventional (LEU) reactor design these units are very small, but given you've not near minimum surface area and near maximum enrichment the only options left would be going fully enriched (100% U235), moving to a sphere (which looks a PITA to make and extract heat from) or a better reflector material(s). But I don't what is a better reflector, given this is a fast spectrum, rather than a thermal spectrum reactor.

You're never going to want 100% enriched 235, it's an expensive and finicky pain in the butt that makes pretty much everyone nervous, and gives most people the heebie jeebies, for a reason. Having it be at 85+% is largely a holdover of working with fuel element geometries and critical assembly geometries that were originally designed for HEU, and are belatedly having LEU shoehorned into them.

I'm currently digging my way through documentation on the NCPS (Nuclear Cryogenic Propulsion Stage), which is one example of what I'm talking about. It started as a 95% enriched 235U, and is now currently being reduced to <20%, using CERMET fuels (https://beyondnerva.wordpress.com/2018/01/19/leu-ntp-part-two-cermet-fuel-nasas-path-to-nuclear-thermal-propulsion/). However, due to thermal constraints, propellant flow considerations, and the need to maintain a similar fuel element architecture in order to ensure the balance of the various elements and neutronic behaviors was correct in the reactor, the same ANL-2000 fuel element has been used throughout the program. Made out of different materials, with different enrichment, but the same fuel element nonetheless. This fundamentally limits the flexibility of the system, but at the same time this element has been tested in-reactor, and has data available that is unavailable on any other fuel element besides the graphite composite legacy NERVA fuel elements.

It should be relatively easy to work in a positive breeding ratio for the reactor, which would allow for the "useless" 238U can be bred into 239Pu, and then fissioned, without taking a significant mass hit... as long as you're willing to redesign your reactor from the ground up, including your fuel elements. Until 5-10 years ago, that idea was a non-starter. Combining discrete enough modeling for a full-flow expander cycle rocket engine, coupled with the same for a very high temperature gas cooled reactor, is still enough to give me the willies, but it's possible now, which is new. It doesn't replace testing, but hopefully KRUSTY will be that camel's nose in the tent that doesn't get the riding crop taken to it...

I expect we'll see lots of nifty things come down the pipeline in the next few years.

BeO is a good reflector in pretty much any spectrum. There are other options, and some quite interesting metamaterial options that have started peeking over the horizon, but those are still years away from an in-core test on the benchtop level.

BTW as I noted earlier large Stirlings are in commercial use for Diesel electric submarine propulsion. It's not done in the US, and it's not something you can get hold of easily, but it's certainly in the known SoA.

Very true. I guess I forgot to include the word "nuclear" in there...

[john smith 19]

They helped build, and decommission, the USS Nautilus. IIRC they're one of the first commercial nuclear companies. They're also one of the more discrete, which has been appreciated during the anti-nuclear hullaboo of the last 40 years. 

Would that have included any work on non-naval nuclear ships. Long term that would seem to be the way to go for Mars, unless bulk Methane mining work out.

You're never going to want 100% enriched 235, it's an expensive and finicky pain in the butt that makes pretty much everyone nervous, and gives most people the heebie jeebies, for a reason. Having it be at 85+% is largely a holdover of working with fuel element geometries and critical assembly geometries that were originally designed for HEU, and are belatedly having LEU shoehorned into them.

TBH none of them sounded that attractive, just possible options. Running with HEU was Kilopowers least attractive quality when looked at through the optics of public opinion about "The N word." 

I'm currently digging my way through documentation on the NCPS (Nuclear Cryogenic Propulsion Stage), which is one example of what I'm talking about. It started as a 95% enriched 235U, and is now currently being reduced to <20%, using CERMET fuels (https://beyondnerva.wordpress.com/2018/01/19/leu-ntp-part-two-cermet-fuel-nasas-path-to-nuclear-thermal-propulsion/). However, due to thermal constraints, propellant flow considerations, and the need to maintain a similar fuel element architecture in order to ensure the balance of the various elements and neutronic behaviors was correct in the reactor, the same ANL-2000 fuel element has been used throughout the program. Made out of different materials, with different enrichment, but the same fuel element nonetheless. This fundamentally limits the flexibility of the system, but at the same time this element has been tested in-reactor, and has data available that is unavailable on any other fuel element besides the graphite composite legacy NERVA fuel elements.

Don't underestimate that data, given the (historically) eyewatering cost of qualifying an element.
That's why I thought (if possible) a shared element between NTR and NEP would be a very good investment. Not optimal in performance, but cheaper than  2 separate qualifications and good enough to get the job done.

It should be relatively easy to work in a positive breeding ratio for the reactor, which would allow for the "useless" 238U can be bred into 239Pu, and then fissioned, without taking a significant mass hit... as long as you're willing to redesign your reactor from the ground up, including your fuel elements. Until 5-10 years ago, that idea was a non-starter. Combining discrete enough modeling for a full-flow expander cycle rocket engine, coupled with the same for a very high temperature gas cooled reactor, is still enough to give me the willies, but it's possible now, which is new. It doesn't replace testing, but hopefully KRUSTY will be that camel's nose in the tent that doesn't get the riding crop taken to it...

People make a big deal of how tough breeding is but most PWR have been breeding for decades in order to extend in core FE life.

I expect we'll see lots of nifty things come down the pipeline in the next few years.

At 10Kw you could power 2 QuitiQ T6 thrusters at 145mN at 4.5Kw each, and still have a Kw to run any science tasks en route to your destination.

BeO is a good reflector in pretty much any spectrum. There are other options, and some quite interesting metamaterial options that have started peeking over the horizon, but those are still years away from an in-core test on the benchtop level.

"Metamaterials?" That sounds very exotic for a reflector, or a moderator.  TBH for commercial projects I've always thought the best way to go would be natural Uranium. But that's tough.

Very true. I guess I forgot to include the word "nuclear" in there...

DUFF answered the question "Could you power a Stirling with a nuclear reactor" once and for all. that completely changed the debate from "We'd like to do this but no one's ever done it before" to "We don't have a Stirling linked reactor system available."

Hopefully KRUSTY will answer that second question in the next few months.

[BeyondNERVA]

Don't underestimate that data, given the (historically) eyewatering cost of qualifying an element.

Oh, I absolutely agree. The problem, though, is that in order to make modern NTRs, which meet the requirements of testability (and therefore the ability to reach flight qualification status) and LEU, we need to be able to test both new critical core geometries and in-core fuel element effects (mainly radiation and thermal, but erosive tendencies are the ultimate doom of a lot of FEs in tests). Back in the days of Rover, there were test stands to do this: Honeycomb for critical geometry experiments, and a modified Kiwi-A reactor for in-core cold flow testing were both at Los Alamos, and there were three reactors designed for repeated use with different fuel elements for hot fire testing (the A6-derived PAX, Pewee, and the Nuclear Furnace). That's the infrastructure that we need to rebuild, but I don't see that happening at Stennis. One design, maybe two, but not enough to develop a whole new fleet of FE designs.

That being said, I'm not a nuclear engineer, just a nerd with a bent for research, and a passion for the subject. I haven't heard much about a concerted push to a new fuel form, although there are some other designs floating around (that I'll also cover at some point this spring) that may be better options than NCPS. Those are also far, far less well researched, though, so once again the old FE geometry tends to win out on sheer cost.

That's why I thought (if possible) a shared element between NTR and NEP would be a very good investment. Not optimal in performance, but cheaper than  2 separate qualifications and good enough to get the job done.

I think that bimodal is the way to go. Depending on how power distribution in the core is done, it may be possible to do something like a KRUSTY PCS inserted into the propellant tubes, but that seems... iffy, I guess, especially at changeover. With bimodal, you've already got a secondary cooling system (primary is thermal propellant), PCS, and PCS cooling system in place. This is what the Russians are doing with the RD-0411, and it makes sense for so many reasons (I love that design, but I'm also an OTRAG fan - and they built a nuclear OTRAG!), not the least of which is being able to maintain hotel load for the spacecraft at minimum, while providing power for electric propulsion. You get the big dV kicks from the thermal side, then kick on the electric thrusters until orbital insertion.

The NTR is a specialized form of very high temperature gas cooled reactor. The GE 0710 fuel element (one of the two biggies in the CERMET world) was designed both for NTR and high temp gas cooled power plant use. Basically, you have a parallel to your system for delivering hydrogen to the propellant tubes, with a matching system to attach to the other side, for (usually) helium. If you want thermal, the hydrogen switches off, the hot-end He collector moves into place, and the hot He is run through a PCS (usually a Brayton). This is usually done at lower power, so radioactive flux is minimized (ALARA...), and often the limitation here is "how much mission mass do I want to waste on radiators?"

"Metamaterials?" That sounds very exotic for a reflector, or a moderator.  TBH for commercial projects I've always thought the best way to go would be natural Uranium. But that's tough.

77% mass hit, IIRC, for NU in Kilopower. It definitely can be done, though.

There are some things that are being played around with on the theoretical reactor materials side that kinda make my eyes pop. Biologically based gamma radiation shields are apparently an are of research in Russia (based on these: https://en.wikipedia.org/wiki/Radiotrophic_fungus), for instance, so the foil-and-cloth lined suits of 20 years from now may be enough to keep you completely safe, for quite high radiation fluxes, and ships (even inflatable ones) can be effectively shielded for reasonably low mass penalty. Unfortunately, I'm definitely NOT a materials guy (the CERMET post was about the limit for me), so I can nibble at the edges of some of these concepts but can't really explain it to myself, much less someone else!

[Robotbeat]

77% mass hit? To the whole power unit, which is already heavy? Or just the core?

[Space Junkie]

This is all very exciting. I'm actually just as interested in the technology for unmanned outer Solar System missions as for manned Mars missions.

I have one big question, though. Even if all the tests go well, what chance does this technology has of being funded through to a flight model? I hate to be the pessimist in the room, but this strikes me as one of those programs that gets cut as soon as there's a budget squeeze - particularly since there's no immediate need for this system.

Am I off base on this? Does NASA seem committed enough to this technology to see it all the way through?

(Maybe I'm just bitter about the ASRG program being defunded.)

[john smith 19]

77% mass hit? To the whole power unit, which is already heavy? Or just the core?

Assuming the LEU core duplicates the energy O/P of the HEU that would be the core only, including it's associated shielding. The Balance of Plant would remain the same, since it's producing the same output at the same temperature.

[BeyondNERVA]

I have one big question, though. Even if all the tests go well, what chance does this technology has of being funded through to a flight model? I hate to be the pessimist in the room, but this strikes me as one of those programs that gets cut as soon as there's a budget squeeze - particularly since there's no immediate need for this system.

Am I off base on this? Does NASA seem committed enough to this technology to see it all the way through?

NASA has always been interested in nuclear power, since they have always understood the inherent advantages. However, due to the way the government is structured, it's not just NASA's show, but the DOE's as well - and the DOE make NASA seem like daredevil risktakers. The DOE has also always been interested in in-space nuclear use, but hasn't had much funding for it. The director of Oak Ridge puts it like this: "We don't get a check that says Oak Ridge National Labs, $1.8 billion (probably the wrong number), go do good things." Everything's allocated by program, except for a small slush fund.

That small slush fund was just enough to get DUFF to happen, and now KRUSTY as well (less than $100 million, IIRC, it's in the post). These are the expensive bits. Now that the fuel fabrication has been proven out to Y12's satisfaction, and the reactor fueling and spacecraft integration have already been dress-rehearsed by NASA, the DOE, and the NNSA, we know how much it'll cost, to a much higher degree than many other new systems. That means that it's far more likely to fly, especially since it truly is a game changing development.

If we have a new flagship probe like Cassini, then this will probably fly. If we're doing Martian or lunar ISRU, this will quite probably fly. If we have Mariner III, or Cassini II, or whatever you want to call it, this will probably fly. Just like any other space component, this provides a capability with a set of engineering and financial tradeoffs. For the right mission, it's perfect, and a steal. For others, it's a cool piece of metal hanging out on the end of your spacecraft that you don't really need.

(Maybe I'm just bitter about the ASRG program being defunded.)

Yeah, I like the ASRG as well, but if you look at the recent GAO report (https://www.gao.gov/products/GAO-18-161T) about 238Pu production, you can see the problems that NASA's running into for RTG/ASRG fuel. The other advantage is that a reactor is radiochemically inert during launch, so assuming you can prevent accidental criticality during a launch failure (which they've done) you have no radiological concerns. This isn't necessarily the case with an RTG.

The ASRG's Stirling is actually running on KRUSTY. It still lives, even if as something like one of Terry Pratchett's Igors...

[Robotbeat]

77% mass hit? To the whole power unit, which is already heavy? Or just the core?

Assuming the LEU core duplicates the energy O/P of the HEU that would be the core only, including it's associated shielding. The Balance of Plant would remain the same, since it's producing the same output at the same temperature.

Right, but the 77% could already be (and quite likely is) taking that into account. That's why I want BeyondNERVA to respond.

[BeyondNERVA]

77% mass hit? To the whole power unit, which is already heavy? Or just the core?

That's the whole power unit. Because of the different distribution of energy within the reactor, and the different reactor geometry, there are different shielding requirements. The PCS, neutron shield, and heat rejection system stay the same, but everything else will need a little bit of a tweak. Unsurprisingly, fuel mass accounts for a lot of it, but gamma radiation shielding also accounts for quite a bit of it as well. There's a breakdown in the paper (https://fas.org/nuke/space/leu-reactor.pdf).

A 10 kWe unit for Mars ISRU, using the same fuel form, but LEU instead of HEU, weighs in at 2187 kg, instead of 1519. The equivalent space system would be 1945 kg vs 1120 kg. The 1 kWe units face a bigger hit.

All of the options (except advanced UZrH fuel-moderator composite) examined are metal fuel, which isn't ideal for LEU. It's just what's available for cheapest at the moment from NASA's suppliers. CERMET fuel may be a good option in the future, but a different fuel type means requalifying the fuel element... which is a pain in the butt. Nevertheless, you do have other options (at the higher power levels, oxides become the preferred fuel type, see toward the end of my post) for LEU fuel that may be easier on the mass budget!

This is very much still a first step, although an awesome one, even when it flies.

[speedevil]

I idly wonder if the licensing cost of launching a reactor is more expensive than stealing one of the many deactivated ones in orbit.
(above article goes into history, and is recommended.)

_{I suspect this is probably a silly idea.}

[BeyondNERVA]

I idly wonder if the licensing cost of launching a reactor is more expensive than stealing one of the many deactivated ones in orbit.

_{I suspect this is probably a silly idea.}

There were three types of reactors launched, SNAP 10A (which had an electrical bus failure), TOPAZ (used on the Soviet US-A RORSATs until 1990), and the BES-5 (launched twice in the late 90's-00's, and certified by NASA and the DOE). The American one is probably cold-welded to oblivion. The TOPAZ and BES-5 were both sodium-cooled, and were designed to eject the core, which all but three did (http://www.svengrahn.pp.se/trackind/RORSAT/RORSAT.html), so there's no way to start them up again.

There are two Soviet-built BES-5's at Los Alamos, IIRC. Originally, one of NASA's DRM's for a lunar base specified using one or both of those reactors for power. If we really wanted to, we could probably refurbish them and launch them... but I'm betting it would cost as much or more to do than just going ahead with Kilopower.

Here's some background on the TOPAZ International program: https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20140016877.pdf

[Patchouli]

This is all very exciting. I'm actually just as interested in the technology for unmanned outer Solar System missions as for manned Mars missions.

I have one big question, though. Even if all the tests go well, what chance does this technology has of being funded through to a flight model? I hate to be the pessimist in the room, but this strikes me as one of those programs that gets cut as soon as there's a budget squeeze - particularly since there's no immediate need for this system.

Am I off base on this? Does NASA seem committed enough to this technology to see it all the way through?

(Maybe I'm just bitter about the ASRG program being defunded.)

Even 10KW would  be a game changer for larger missions as you'd be going from half a hair dryer's worth of power to something comparable to entire house.

Data rates can be many times higher, a probe can have more powerful scientific instruments and much more powerful computers for autonomous operation etc.

[A_M_Swallow]

I talked with a SpaceX representative a few weeks ago about this given that I am a nuclear engineer.

They have essentially no realistic concept of how to refuel on Mars. {snip}

IMO with Kilopower on Mars you do not bother to refuel just shut it down and buy a new reactor.

With a submarine the old reactor core needs removing from the submarine to make room for the new reactor and core. With surface Kilopower just leave the assembly where it is. Install a replacement cable to get the power into the base.

10 year old Sterling convertors may be nearing the end of their life so replacing the whole assembly is the easiest way of replacing them.

[Robotbeat]

I wont tell you who I talked with. He was a propulsion engineer.

I read somewhere that Tesla, with Elon as CEO is fighting against subsidies needed for nuclear to compensate for the artificially low whole sale prices. Of course, Solar City and Tesla Powerwall wants all the subsidies in the world.

Dont get me wrong, IMO he is acting super anti nuclear. I cant find a reference sorry, I read it a while ago somewhere.

This is a very non-scientific way to approach the world. Do your research, validate your sources and don't propagate rumours.

Tesla apparently supported the shutdown of Diablo Canyon in California. I haven't independently confirmed it, but it made me mad (it's possible, but not very likely IMHO, that this was done without Musk). Musk at other times has been somewhat pro-nuclear. So saying he's "super anti-nuclear" is not accurate, but supporting the shutdown of Diablo is not very encouraging.

[Robotbeat]

Tesla (new user, not the company): You don't refuel space reactors. You just fill them up with all the fuel they'll need in their lifetime.

[Robotbeat]

I want to point out that sometimes the pro-nuclear community considers anything that could replace nuclear (such as storage-backed solar, if you oversize it a lot) as being anti-nuclear, which is dumb. Just because Tesla is enabling an alternative to nuclear doesn't mean Musk is anti-nuclear. I support both nuclear and renewables, and I realize that it is usually possible to do without nuclear (although northern nations benefit from nuclear a LOT, since seasonal solar output is anti-correlated with energy requirements for heat...).

...a mix is best.

[BeyondNERVA]

You don't refuel space reactors. You just fill them up with all the fuel they'll need in their lifetime.

That's certainly the way we do it now, but how is that different from every other piece of space hardware we've launched other that Hubble and the ISS? One benefit to the Kilopower design that doesn't get talked about (because of its' mission, no doubt) is that having a single fuel element, that's roughly cylindrical, could make refueling a snap. Isolating the used fuel element is a different problem, although due to the low power level, long mission life, and small amount of fissile material it shouldn't be TOO hot (but spent nuclear fuel is the most complex mess of isotopes known to humanity, and what comes out depends on a TON of factors that I don't even pretend to begin to understand).

Satellite refurbishment is already getting more attention. The problem is that we don't have a space tug to do the mission. Obviously, I'm a fan of a nuclear thermal-based infrastructure, but assuming lunar ISRU then ULA's ACES becomes very attractive. The other concept that I've always loved (which would probably give mission controllers headaches) is an old Rockwell design, the Solar Moth. Not super powerful, but you don't REALLY need that for refurbishing/refueling missions. http://www.projectrho.com/public_html/rocket/enginelist.php#solarmoth

Once it becomes possible, I'm pretty certain that swapping out fuel in space reactors WILL be a thing. They'll be very different designs, but as an example: current NTR designs aren't really set up for in-flight repairs, much less cracking open the core. This is something that would undoubtedly change once cislunar space becomes developed and manned interplanetary missions become infrequent news rather than the stuff of speculation.

The information I was looking for on the infrastructure needed for refueling reactors is buried in here (somewhere), I just can't seem to find it at the moment: http://www.projectrho.com/public_html/rocket/infrastructure.php

[Nomadd]

 Considering the logistics of refueling a core in space, and the fact that the core will be optimized size and mass wise, I'm not sure it wouldn't be much easier in every way to simply swap out the entire core every 30 years.

[BeyondNERVA]

Considering the logistics of refueling a core in space, and the fact that the core will be optimized size and mass wise, I'm not sure it wouldn't be much easier in every way to simply swap out the entire core every 30 years.

Depends on the reactor! If it's something like Kilopower, definitely, but Westinghouse Astronuclear had a design for what they called a PAX reactor, based on the NERVA A6 (about 2000 MWt, IIRC), that was designed to swap the core out fairly easily. There were other issues that would have made servicing a bit more challenging (graphite wool everywhere, for one), but nothing fundamentally unfixable. That doesn't seem to be the case with nuclear electric systems to nearly the same degree that I've seen, though - there's just never REALLY been a point. An in-core thermionic setup with a "flashlight" configuration should be fairly easy to refuel, though...

[acsawdey]

Considering the logistics of refueling a core in space, and the fact that the core will be optimized size and mass wise, I'm not sure it wouldn't be much easier in every way to simply swap out the entire core every 30 years.

Depends on the reactor! If it's something like Kilopower, definitely, but Westinghouse Astronuclear had a design for what they called a PAX reactor, based on the NERVA A6 (about 2000 MWt, IIRC), that was designed to swap the core out fairly easily. There were other issues that would have made servicing a bit more challenging (graphite wool everywhere, for one), but nothing fundamentally unfixable. That doesn't seem to be the case with nuclear electric systems to nearly the same degree that I've seen, though - there's just never REALLY been a point. An in-core thermionic setup with a "flashlight" configuration should be fairly easy to refuel, though...

Wasn't one of the design goals of Kilopower that it be easy and quick to fuel it (i.e. insert the fuel element) right before launch? Doesn't that imply that it might also be easy to open it up later and swap the fuel element for a new one?

[BeyondNERVA]

Wasn't one of the design goals of Kilopower that it be easy and quick to fuel it (i.e. insert the fuel element) right before launch? Doesn't that imply that it might also be easy to open it up later and swap the fuel element for a new one?

Possibly, although with the combination of the thermal load from the core and the thermal environment of space, I could see issues developing that would prevent removal.

You're correct about the fast fueling, however. It sounds like it needs less than a week from the reactor showing up on site (probably the VAB) to the shroud being able to be installed. At that point, it's really up to KSC how long they want it to sit around with all those guards...

[biosehnsucht]

The future documentary "The Fifth Element" covered refueling of nuclear-powered spacecraft :

Joking aside, it seems like not a hard problem to solve, if it was a problem worth solving. But I don't think it will be in the short term - and likely by the time it makes sense to solve it, other solutions will have occurred (at least for power on Mars or similar - build bigger reactors, or replace with some magical fusion, or whatever)

Though I don't think you'd leave a Kilopower module laying in place once done with it, you'd truck it out to be retired someplace out of the way - not because of radiation concerns from the old reactor, but because it's taking up valuable real estate and you could either install another one right there or expand the base / settlement a bit into where it was.

[BeyondNERVA]

Though I don't think you'd leave a Kilopower module laying in place once done with it, you'd truck it out to be retired someplace out of the way - not because of radiation concerns from the old reactor, but because it's taking up valuable real estate and you could either install another one right there or expand the base / settlement a bit into where it was.

It's quite possible that the real estate would be important, but the unit isn't that big, even with the surface radiators (which are approx. the same size as the space-based ones), and it seems like a lot of the designs call for a separation from the base greater than what NASA shows in its' animations. This is due to the dreaded ALARA, or "as low as reasonably acceptable," principle, which is fishy enough to pin down on Earth, but in space (esp. with NASA's current crew career dose limits) becomes a whole new slippery swimming pool full of hagfish.

If you're interested, much of the shielding and emplacement planning for Kilopower is based on an earlier design, the Affordable Fission Surface Power System (AFSPS, also sometimes called FSP), which Poston and McClure (the two nuclear engineers with the DOE spearheading this effort) both worked on. Some of the information is in here. I'm currently trying to track down their paper from NETS 2009 about this, but it doesn't seem to be published on either NASA or the DOE's websites...

http://www.neofuel.com/Poston-2009-NASs%20Lunar%20Fission%20Surface%20Power%20System-LA-UR09-02470.pdf

http://aip.scitation.org/doi/abs/10.1063/1.3115554

https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20110007114.pdf