[HN Gopher] The US government is taking a step toward space-base...
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The US government is taking a step toward space-based nuclear
propulsion
Author : vinnyglennon
Score : 93 points
Date : 2023-08-12 17:56 UTC (5 hours ago)
(HTM) web link (arstechnica.com)
(TXT) w3m dump (arstechnica.com)
| dtagames wrote:
| This might be a good time to review the number of failed rocket
| launches we've seen in the last few years.
|
| Now, imagine them with nuclear materials aboard.
| valine wrote:
| Reusability helps with long term reliability. You would
| probably want to avoid launching nuclear material on a new
| rocket, but a human rated rocket like Falcon 9 would be totally
| fine.
| ben_w wrote:
| Depending on the design, failure during launch can be anywhere
| from "meh" to "basically high-altitude Chernobyl" -- random
| actinide decay products (and plutonium fuel) are bad, unreacted
| uranium fuel is mostly a heavy metal hazard rather than a
| radiation hazard.
|
| (Could be worse, but the Orion drive is currently illegal by
| treaty and hopefully nobody is dumb enough to use that in
| Earth's ionosphere anyway).
| aio2 wrote:
| I remember learning that when they started testing atomic
| bombs (I think?) the nuclear debris in the air spread
| basically throughout the whole united states and the
| government tried to keep quiet about it. Something similar
| will probably happen here if they mess up with the launch.
|
| Btw, the video I saw was on Veritasium.
| PartiallyTyped wrote:
| I remember that video; the long story short was that a
| manufacturer of films for photography noticed that their
| films had spots on them, they initially thought it was
| defects, but because they had samples prior to testing,
| they saw an uptick.
|
| But maybe I remember wrong.
|
| Edit: the video in question is [1] and the conpany was
| Kodak.
|
| [1] https://youtu.be/7pSqk-XV2QM
| 23B1 wrote:
| Not sure about camera film, but there's certainly a need
| for 'low-background steel' for several applications:
| https://en.wikipedia.org/wiki/Low-background_steel
| PartiallyTyped wrote:
| Speaking of, one way we verify old wine is through
| background radiation!
| db48x wrote:
| The thing to remember about that is that we can measure
| tiny amounts of radiation very cheaply, and tiny amounts
| are harmless. In fact we are bathed in a constant, but
| tiny, background level of radiation all the time. Thousands
| of nuclear weapons were tested all across the world, in the
| United States, in the Soviet Union, on Pacific Islands,
| etc, etc. The radiation from that certainly caused a small
| uptick in the background level of radiation, but it hasn't
| actually harmed people.
|
| The main reason that the US was secretive about it was that
| nuclear weapons were a secret, not because there was a
| shameful health problem to hide.
|
| Incidentally, the best way to reduce your exposure to
| radiation is to move away from the mountains and go live at
| the beach. Mountains are mostly made of granite, and
| granite always contains small amounts of uranium and
| thorium which decay to radon gas. Also, live as far away
| from coal power plants as possible, those things are
| horrifying.
| Loquebantur wrote:
| Background radiation is categorically different than
| ingesting/inhaling radioactive substances with the latter
| many orders of magnitude more dangerous.
|
| The claim, nuclear testing related increases in radiation
| exposure not being relevant for public health is probably
| false. There are only very few studies with dubious
| reliability. The lifetime increase due to that nuclear
| testing is estimated to be 4.4 Millisieverts. It would
| have risen continuously with more surface tests, which
| got abolished accordingly.
|
| The idea, beaches were a sanctum against radiation is
| wrong again. Sand is ground down mountains in case you
| wondered. Some are highly radioactive. But of course, UV
| light is harmful radiation as well.
| 7952 wrote:
| Background radiation may be unlikely to give an
| individual cancer whilst still causing cancer across a
| population. It just isn't possible to attribute the
| cause. Surely the same is true of fallout from testing
| and estimates would back that up. It may not be something
| we worry about as individuals. But it is something that
| nasa should worry about.
| gibolt wrote:
| The nuclear payload could be treated similar to humans, with
| eject systems and soft landing built in.
|
| The fuel will only be needed for a lighter craft in deep
| space. Getting it up with a high reliability rocket (like
| Falcon 9) significantly decreases risk.
| asu_thomas wrote:
| What does "meh" mean? Is that english?
| sircastor wrote:
| "Meh" is a casual response that means "this does not matter
| much". I don't know that it's proper English by any means,
| but it is certainly a common colloquialism. A cursory
| search suggests that it's imported from yiddish.
|
| [1] https://en.wikipedia.org/wiki/Meh
| asu_thomas wrote:
| I have never seen it used outside of Hacker News.
| arrosenberg wrote:
| Its Yiddish, but came into popular use because of an
| episode of the Simpsons.
| fastneutron wrote:
| > Once it reaches a safe orbit, the reactor will be turned on.
|
| Fission reactors aren't appreciably more radioactive than rocks
| you can dig out of the ground until you turn them on. This is
| something that wouldn't be brought online until the riskiest
| part of the launch has past.
| 23B1 wrote:
| I'm no engineer, but it sure seems to me like you could either
| split things up into multiple launches, or potentially
| manufacture the fuel in orbit, no?
| dzhiurgis wrote:
| Falcon9 hadn't had a failure for nearly a decade
| gibolt wrote:
| Falcon 9 has had more than 200 consecutive successful flights
| in a row. That is more than double the next most successful,
| Delta II with 100 in a row.
|
| It also has well over 100 successful landings in a row, while
| the next closest rocket has 0. (Rocket, not capsule or
| shuttle, which are all still far lower)
| moffkalast wrote:
| Well look at the number of missions with RTGs on board and you
| don't have to imagine, nuclear powered probes and satelites are
| not unheard of. The soviets also had an entire series of
| fission powered spy sats way back.
| dotnet00 wrote:
| Well that's the most obvious way to put FUD out there.
|
| It might be a good time to review the number of failed launches
| on crew rated rockets (the safety requirements on which are
| roughly equivalent to the requirements for carrying nuclear
| material). Particularly ones which led to a loss of crew, as
| those would correspond most closely to a possible nuclear
| material release.
|
| It's far less scary, but alas not as convenient for FUD.
| whycome wrote:
| > Wernher von Braun, the German engineer who defected to the
| United States after World War II, recognized the potential of
| nuclear thermal propulsion even before his Saturn V rocket landed
| humans on the Moon with chemical propulsion
|
| > German engineer
|
| Why does von Braun get such a pass from his Nazi past? Because he
| was useful?
| schiffern wrote:
| >Why does von Braun get such a pass from his Nazi past?
|
| Partly it's because his Operation Paperclip dossier was
| _conveniently misplaced_ before it could be declassified.
|
| Who knows what was in there? Not historians, that's who...
|
| Source: https://www.archives.gov/iwg/declassified-
| records/rg-330-def...
| themodelplumber wrote:
| Yeah, I think a lot of people would say that one's actions
| post-war are worth some weight in the equation, and culturally
| this person was positioned so as to not only make a big
| positive contribution in that quite separate context as far as
| values go, but a contribution which was also part of "our side"
| of a pitched cultural battle which is still raging. So like,
| how Nazi could you still be, in that actions-speaking sense.
|
| Plus, people-controversy is a topic that's actively avoided in
| writing for a lot of audiences, especially if it invites fault-
| spreading, like if it's going to end up as a big whataboutism-
| fest.
|
| Difficult topic in its way. Including of course the WW2-and-
| prior way involving terrible aspects like forced labor working
| under him, etc. So, less of a defense of a person here and more
| of a guess about rationale in authorship.
| Arkhaine_kupo wrote:
| "If Hannibal Lecter ran a 4.3, the NFL would call it an eating
| disorder".
|
| People who are extremely succesful in certain fields get an
| impressive amount of leeway to break every conventional rule,
| law or protocol.
|
| Allowing nazis to clean up their past and work for NASA is not
| the only horrible things the US did during the war or
| immidietly after either...
| zgluck wrote:
| The reason communications with the Voyager 1/2 twin probes have
| lasted for like 45 years:
|
| _Voyager 2 is equipped with three Multihundred-Watt radioisotope
| thermoelectric generators (MHW RTG). Each RTG includes 24 pressed
| plutonium oxide spheres, and provided enough heat to generate
| approximately 157 W of electrical power at launch._
| wmf wrote:
| Note that RTGs don't provide propulsion.
| zgluck wrote:
| Clarified this. Thanks.
| version_five wrote:
| The basic idea is straightforward: A nuclear reactor rapidly
| heats up a propellant, probably liquid hydrogen, and then this
| gas expands and is passed out a nozzle, creating thrust. But
| engineering all of this for in-space propulsion is challenging,
| and then there is the regulatory difficulty of building a nuclear
| reactor and safely launching it into space.
|
| Can anyone give a eli5 explanation of what makes this better than
| a conventional rocket? There still needs to b some mass ejected
| obviously. Is it that nuclear heat is able to make it go faster
| and provide more reactive force than burning it? What does the
| analysis look like?
| rich_sasha wrote:
| The propellant is important for its bulk (some mass to shoot
| out the back) and it's energy.
|
| In a chemical rocket, the propellant provides both the bulk and
| the energy. As it happens, there isn't that much energy in
| chemical propellants per kg, but the rest of the engine is
| light enough that these things can fly to orbit.
|
| In a nuclear rocket, the energy comes from a nuclear reaction
| and the gaseous fuel only provides the bulk. This is way more
| efficient. But such rockets likely cannot achieve orbit on
| their own because the whole set up is too heavy.
| morcheeba wrote:
| Good explanation! For completeness:
|
| In an Ion jet, the energy comes from (usually) solar power
| and the gaseous fuel provides the bulk. These are even weaker
| because of the limited instantaneous power that can be
| generated to feed it, but they are very efficient in how much
| thrust they can provide per propellent weight. Some versions
| (like arcjet) are a combination chemical rocket/Ion jet.
| morkalork wrote:
| Would it be possible to skim the upper atmosphere while in
| orbit around a planet and top-up the gas reserves?
| MPSimmons wrote:
| Almost definitely not. If there's enough material to
| collect in a realistically short timeframe, there's enough
| drag to bring the craft back into the atmosphere.
| dgoldstein0 wrote:
| Also you'd be fighting conservation of momentum - if the
| material you gather isn't going your speed and direction,
| you lose some of your speed and direction to pick it up.
| Given how fast anything has to go to reach orbit (about
| 17000mph for low Earth orbit) and escape velocity is
| about 41% higher, that speed difference would be a major
| problem.
|
| For atmospheric flight the closest thing is a jet engine
| which is "air breathing", i.e. requires air to run and
| works in part by sucking air in, using some of the Oxygen
| in it for combustion, and shoving the extra air out the
| back. This gives them much higher efficiency than
| chemical rocket engines, as they don't have to carry
| their own oxidizer or the mass to eject for propulsion -
| but only works because the air is dense enough where they
| operate. Which is not true for space flight. Commercial
| jets typically fly a bit under the speed of sound in air
| which is 767mph. Of course supersonic air craft exist - I
| think mach 5 is achievable by some military jets - but
| that's still a fraction of orbital velocity. Anyhow
| running in the atmosphere means jets don't "scoop up air"
| in any sense but rather just use it immediately - so any
| lost momentum can be immediately countered by the engine.
|
| Another direction to think about it - a simple model for
| air resistance says that air resistance increases with
| the square of your velocity (and with the density of air,
| which exponentially decays with height though also
| depends on temperature. I think the height wins out
| though. Not sure if the equation works at extremely high
| altitude. But certainly this favors using air at lower
| altitudes and probably also lower speeds
|
| https://en.wikipedia.org/wiki/Drag_(physics)
| https://en.wikipedia.org/wiki/Density_of_air
| hutzlibu wrote:
| "Is it that nuclear heat is able to make it go faster and
| provide more reactive force than burning it?"
|
| Yes, that is mostly it. Just compare the explosion from some
| hydrogen with a nuclear bomb. It is all about energy for mass
| in space, because all the fuel you have, you have to bring up
| into space, which needs more fuel, so need more fuel to bring
| that fuel up ... nuclear could help with that mass ratio a lot.
| And I like the concept in theory - as long as none of them
| explodes halfway up to space.
| p1mrx wrote:
| The temperature of a gas is proportional to the average kinetic
| energy of its particles. So if you compare (e.g.) water vapor
| to hydrogen at the same temperature, the hydrogen molecules are
| moving faster.
|
| A hydrogen+oxygen chemical rocket propels H2O, while a nuclear
| thermal rocket can use the lightest propellant (H2) because the
| heat comes from elsewhere.
|
| Smaller molecule, faster exhaust, better rocket.
| dgoldstein0 wrote:
| Wouldn't we care more about the momentum of the exhaust
| rather than the mass? I'm not quite following why lighter
| particles are better
| ridgeguy wrote:
| It's the high temperature and the lower exhaust molecular
| weight.
|
| Specific impulse (Isp) is how much force you get from each mass
| unit of propellant you exhaust. So an engine with Isp = 300
| gives 300lbs force for every pound of exhaust gas mass.
|
| IIRC, Isp scales as the inverse square root of exhaust
| molecular weight. So a pure (molecular) hydrogen exhaust would
| have a molecular weight of 2. A pure H2/O2 engine would have an
| exhaust of H2O (assume it's running at stochiometric H2/O2
| ratio to simplify things), or an average molecular weight of
| 18.
|
| For everything else being equal (temperature, pressure, etc.),
| the H2 Isp would be sqrt(18/2), about 3x the H2/O2 Isp. That's
| mainly why rocketeers would like nuclear engines, more oomf
| from a given mass of propellant. It's also (conceptually)
| simpler because you only need to handle one propellant vs. two
| or more for conventional liquid fuel combustion.
|
| It's more complex, of course. If the reactor is really hot, it
| can partially dissociate H2 into atomic hydrogen, lowering the
| exhaust molecular weight still more. But dissociation is an
| energetically expensive process, so there's bound to be a
| tradeoff between energy consumed by dissociation vs. increased
| Isp. I've no clue how that would work out.
| lazide wrote:
| The real limiting issue tends to be materials in the reactor
| - at some point, every known material is a liquid or a gas
| and the reactor stops being an ongoing concern.
|
| Usually reactors run cooler by several orders of magnitude,
| as this is referred to as a 'meltdown' and people get snippy
| about the releases of radiation and expensive cleanup crews,
| etc.
|
| Space is more forgiving and has fewer HOA types, so they can
| go closer to the limits - but it's still the same underlying
| issue.
| pseingatl wrote:
| But, can we get to .99c?
| yieldcrv wrote:
| If we can build them in space I would be interested
| foreverobama wrote:
| [dead]
| mdorazio wrote:
| Finally! This is one of the few fission uses I'm genuinely
| excited about. Nuclear-thermal just makes so much sense for in-
| space propulsion of large vessels compared to chemical rockets.
| somenameforme wrote:
| I think the obvious concern would be failure scenarios. There
| will always be failures in space technology. As space expands
| exponentially (as it is likely to do so in the future),
| failures will become relatively regular. So the obvious
| question would be what would happen if a nuclear rocket, with
| reaction in process, crashed to Earth. Or even if it broke up
| in the atmosphere.
| semi-extrinsic wrote:
| I assume here you mean to denote by "space" the number of
| human spacecraft, and not the negative pressure contribution
| in the cosmological stress-energy tensor. In that case, why
| should it be likely to expand exponentially in the future?
| ethbr1 wrote:
| The idea is also to use this for solar system propulsion,
| rather than Earth to orbit.
|
| Consequently, reactor payloads would be carried on a very
| small fraction of launches, then used in space for an
| extended amount of time.
| sebzim4500 wrote:
| >As space expands exponentially (as it is likely to do so in
| the future), failures will become relatively regular.
|
| It's possible that reliability/safety will improve as fast as
| the launch cadence does, in which case we could see the
| accident rate staying flat or decreasing.
| avar wrote:
| > Or even if it broke up > in the atmosphere.
|
| The atmosphere we've already detonated over 500 nuclear
| weapons in?
| pdntspa wrote:
| Isn't there a way you can shoot the whole apparatus into the
| sky while it is inert and then activate in space?
| nukeman wrote:
| Yes, you can have the reactor offline, with control rods
| inserted for launch. Then when you reach the requisite
| altitude, withdraw the control rods and start up the
| reactor. In the event of a launch accident and potential
| destruction of the reactor, the enriched uranium fuel would
| be a chemical hazard (uranium is a heavy metal like lead),
| but only a mild radiation hazard (since there are no high-
| gamma fission products, and the uranium has undergone heavy
| purification prior to fuel fabrication).
| aziaziazi wrote:
| It already happened with Kosmos 954 and will probably happen
| again soon: ~20 other satellites had been sent in space with
| the same tech. Kosmos crashed away from (human) life centers
| but that was a huge stroke of luck. Research area was 100k+
| km2.
|
| Launches are less to be feared because they are oriented
| toward sea and the most critical moment are the first
| minutes. The device discussed is intended to travel away from
| earth so as you noted it won't be dangerous after it quit
| orbit.
|
| Disclaimer: not skilled in any related field, just a consumer
| of space science popularization videos for newbies.
| SkyMarshal wrote:
| _> As space expands exponentially (as it is likely to do so
| in the future), failures will become relatively regular._
|
| Or it could go the way of the airline industry where failures
| become less regular as the industry develops ways of
| systematically reducing them.
|
| Also, nuclear rockets should probably be launched to earth
| orbit in pieces, separately, so that if any one launch fails
| it won't create a nuclear accident in the biosphere. Then
| assemble and power up the nuclear rocket as far away from
| earth as possible.
| jamesaurichs wrote:
| US seems to be in a hardware/science renaissance, now that
| there is a new Cold War enemy, and manufacturing and research
| are being brought back to US.
| echelon wrote:
| Peace time = smart phone incrementalism, social media, ad
| tech, Bitcoin, NFTs, WeWork, low interest rate malinvestment,
| Twitter/Tumblr pessimism
|
| Cold war = rocket science, new fuels, materials science,
| major computing advancements, supply chain changes,
| innovation, science hype, broad optimism
|
| I know most of this is happenstance and that peace time
| doesn't itself cause lackluster development, but it is
| interesting and palpable.
|
| I was so down on 2000 - 2020, but the decade ahead is
| exciting, and I'm filled with motivation.
| rbanffy wrote:
| > Cold war = rocket science, new fuels, materials science,
| major computing advancements, supply chain changes,
| innovation, science hype, broad optimism
|
| Next time the cold war cools down, we need to invent
| something to replace it.
| gpderetta wrote:
| They tried with the war on terror, but it just wasn't the
| same thing.
| vkou wrote:
| Broad optimism? Science hype? Are we living in the same
| country?
| rbanffy wrote:
| One thing I learned from the outside, the US - like any
| large country, BTW - is wildly diverse in pretty much
| _every_ aspect.
| goodbyesf wrote:
| Are all your comments propaganda talking points? Every single
| one of your comments is anti-china propaganda talking points
| we hear everywhere.
| 0xDEF wrote:
| From across the pond it feels like American millennials and
| Gen-Z have already declared their country to be a failed
| state.
|
| How much can a nation progress if its youth is pessimistic
| about everything? It doesn't matter whether the pessimism is
| based on actual problems (healthcare, housing prices etc.) or
| learned through terminally online reddit/twitter consumption.
| bogota wrote:
| Don't confuse what you read online or in the news with what
| is actually happening.
| jamesaurichs wrote:
| If we're talking about the contents on TikTok, there's
| probably a very good reason why the ultimate owner of
| TikTok, the Chinese government, wants that kind of content
| to be the majority sentiment on the platform.
| SonicScrub wrote:
| As the folk-wisdom goes "Twitter isn't real life". The ones
| who have that opinion are the terminally online.
| godzillabrennus wrote:
| It's amazing reading this knowing a billionaire
| squandered that brand name after pouring billions into
| acquiring it. I hope when the smoldering ruins are
| auctioned at the bankruptcy proceedings jack gets to buy
| it back and uses it for his decentralized network.
| asu_thomas wrote:
| Personally, I'd rather prioritize our fellow citizens having a
| dry place to sleep at night.
| version_five wrote:
| It's funny because it's this, turning inward and waging war
| on ourselves after there wasn't an obvious enemy anymore
| that's responsible for the decline the upstream comment was
| talking about. Post WWII through the 90s saw massive
| increases in global standard of living, 2020's the west has
| gone back to religious squabbles over absurd ideological
| things. _Watchmen_ had a similar idea.
| zaptrem wrote:
| Investment in space has historically led to a
| disproportionate return in economic growth.
| honeybadger1 wrote:
| The more adoption of nuclear technologies with practical
| application, the better.
| bigfudge wrote:
| That's an odd thing to say. Almost as if you're in favour of
| nuclear for nuclear's sake? Plenty of people have reasonable
| reservations about use of nuclear, not least the social
| /political ones of where to store waste that are still mostly
| unsolved. Blasting fission cores into space on rockets with
| fairly high failure rates in absolute terms seems like a fairly
| fine balance to strike?
| 23B1 wrote:
| Probably depends on your risk profile. Do we find new ways to
| safely generate energy using nuclear, or slowly cook
| ourselves alive on the planet's surface?
|
| Or to put it another way, at what point should we throw a
| Hail Mary in the energy demand game?
| randallsquared wrote:
| You don't need to store nuclear waste, since you can burn it
| up in some fuel cycles. Essentially all the problems of
| nuclear power on the ground are political issues --
| entrenched interests, weapons proliferation, and so forth --
| not technological ones like safer reactors and nuclear waste.
| [deleted]
| mvdwoord wrote:
| So they are strapping a nuclear power plant to a huge vessel of
| explosive liquids..
|
| Will the first launch be on PPV?
| JumpCrisscross wrote:
| RTGs have been going to space since the 60s [1].
|
| [1]
| https://en.m.wikipedia.org/wiki/Radioisotope_thermoelectric_...
| flangola7 wrote:
| RTGs do not use fission and do not create fission products.
| Nuclear fuels are harmless in comparison to Strontium-90 and
| Cesium-137.
| philipkglass wrote:
| There won't be any fission products in the fuel if the
| chemical launcher fails to take the nuclear payload to
| orbit. The reactor activates for the first time after the
| initial orbital launch. The virgin fission fuel is less
| radiotoxic than RTG fuel.
| 65a wrote:
| Then you are going to love SNAP-10A
| https://en.wikipedia.org/wiki/SNAP-10A
| moffkalast wrote:
| And the 31 RORSAT reactors
| https://en.wikipedia.org/wiki/BES-5
| devanatha wrote:
| https://en.wikipedia.org/wiki/TEM_(nuclear_propulsion)
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(page generated 2023-08-12 23:00 UTC)