Feasibility of nuclear detonation for deep planetary science on Mars

[ElfredaCyania]

Mars has a lower surface gravity, so one would have to bore deeper - more than double, and perhaps triple.

I've just found a paper for this, the crater diameter for the same explosive charge D is proportional to g^-1/6, which means a Martian crater is likely to be 1.176 times as big as an Earth one. According to the paper, its conclusion holds for buried and zero-depth charges, as well as the cohesionless soil of Mars. The soil used in the paper has a similar density to Martian soil. On page 3839 in 4.3 it mentioned the condition for a charge to crater. The optimal depth to crater is the critical depth d_c, calculated using d_c=C₀/ρg, where C₀is the cohesion (100-1000 Pa for Martian regolith, Chang et al.), ρ is density (1.37 as mentioned earlier), and g is Martian g, 3.71. The critical depth would vary between 20 m and 200 m. It is achievable with the current ground penetrators on the soft Martian sand but this doesn't say anything about the choice of yield.

Crater efficiency is discussed on page 3835 but I haven't found numbers for nuclear bombs yet. But if we assume a nuclear bomb is somewhere between the explosives shown in Fig.1 and the sand is Ottawa sand (the most similar to the regolith) we may say the crater efficiency for 1e7 to 1e9 J bomb is around 10^1.5 or 30. And it can go as low as 15 at 1e11 J. This is a bad sign for nuclear detonation but only in terms of efficiency.

Before employing a nuclear device, one should determine the energy and explore a non-nuclear method for achieving such energy, e.g., from an impact of say 1 or 10 tonne accelerated into the Martian surface.

I agree that we lack the data for designing a nuclear detonation, for now. We need data for the underground structure of Mars (considering the depth we are targeting, a Borebot-like mission is required), the effect of explosives on Martian regolith (installing a bomb would be better but artificial impactors or observing existing crater will also do the job).

Er, what could go wrong?

As for this, it highly depends on the mission design, like installed by the rover, penetrator bomb or delayed penetrator bomb. But for penetrators, after penetrating to a depth of around or more than 15 m, the soil would move back and rebound, burying the warhead (See page B-2 of the Mars Penetrator concept).

For risk control, it would be similar to any controlled nuclear detonation or ground penetrator and it needs to be solved by engineering.

What yield is a 'very large fully-couple bomb'.

I said that because even a small bomb like the current active B61-12 in the US assets is 100 times more energetic than the 2021 63GJ event at its 1.5 kt configuration (50 times, considering the inferior efficiency of explosion compared to an earthquake, explained before). And for such a 1.5 kT bomb to be fully coupled, you only need a depth of 3.45m on Earth. (Maybe ~2.6 times on Mars, but I currently didn't find direct data to support this, the critical depth is 2.6 times for sure)

I would like to add that a nuclear detonation is a "very sharp, very brief, very powerful" seismic source according to Vidale from this report. Also, I would like to quote from the preface of Explosion Source Phenomenology: "Data from nuclear tests provide the most directly useful observations and constitute the most effective benchmarks for a quantitative evaluation of our forward-modelling capabilities.", particularly on a planet like Mars where significant geological activity is minimal. We are not able to rule out nuclear methods in deep seismology in the foreseeable future.

 

[Astronuc]

I would like to add that a nuclear detonation is a "very sharp, very brief, very powerful" seismic source according to Vidale from this report. Also, I would like to quote from the preface of Explosion Source Phenomenology: "Data from nuclear tests provide the most directly useful observations and constitute the most effective benchmarks for a quantitative evaluation of our forward-modelling capabilities.", particularly on a planet like Mars where significant geological activity is minimal. We are not able to rule out nuclear methods in deep seismology in the foreseeable future.

An explosive like C-4 (or RDX+TNT, or HMX+TNT) is also fairly sharp.

A tungsten penetrator from orbit might work. Where possible, it's best to use an inert (non-radioactive) material/system.

One would want a network of seismic detectors placed around the Martian surface, from which one could apply both reflection and transmission seismology.

Nuclear explosives produce a neutron flux, which activates (by neutron absorption) all matter surrounding the device, in addition to fission products and transuranic elements, all of which are vaporized, and they either permeate the surrounding matter or a dispersed in the environment (aka fallout).

 

[ElfredaCyania]

they either permeate the surrounding matter or a dispersed in the environment (aka fallout)

Contamination is the most tricky part of this whole idea and it's hard to find concrete data for this. From what I have known, we can take the SEDAN test, it's one of the two most radioactive nuclear tests in the US, and it's shallowly buried--analogous to the one on Mars. Unlike power plants, the fallout of nuclear explosions has a much shorter half-life, but 249Pu is still a major concern (only considering pure fission here). Anyway, the radiation in the Sedan crater dropped from 500 Rr/h to 500mR/hr in 27 days, and to 35mR in half a year. Its 1990 reading at the most radioactive place is 0.053 mrem/hr or 0.00053 mSv/hr, which is considered safe for tourist visits.

https://en.m.wikipedia.org/wiki/File:Nevada_Test_Site_-_Sedan_Crater_-_1.JPG

Meanwhile, Mars has an all-time radiation dose of 240-300 mSv/yr (0.027-0.034 mSv/hr) due to its thin atmosphere. The Sedan crater was the result of a 100kt bomb plus the background radiation from all the other tests in Nevada. This suggests that, purely from a health risk perspective and over time, such a site would be no more hazardous than the general Martian environment by the time humans can stand in that crater.

But the complexity comes from the Earth's weather, rain, while rare in Nevada is an example of a radiation wash-out mechanism on Earth, wind can also move the radiation around. Mars has no rain and its wind is fast but weak. Also, Martian regolith may affect the induced radioactivity since it is mainly basalt. Besides, Martian fallout tends to be concentrated due to a lack of weather (similar to the Moon in project A119). Other influencers like the effect of gravity are not well-documented as far as I searched.

Ethically speaking it's always bad to bring radiation there but considering the cost-effectiveness of creating the largest events, there might be a trade-off.

 

[ElfredaCyania]

Many are worried about a launch failure so I did some math on this, all assuming the plausible worst-case scenario.

In a famous broken arrow (in which you lost a nuclear warhead) 1966 Palomares B-52 crash, and two B28 1.45MT H-bombs (this is bigger than any nuke you would want on Mars) were released and crashed into the ground, releasing some Pu-239. ofc the design of B28 is classified but we assume it's the worst thermonuclear weapon possible, only 20% of its yield is from fusion, 80% from fission, and its fission efficiency is also 20%, pretty much a Fatter Man. Then we are looking at 711 kg of 239Pu in total (this is 71 times its critical mass, enough to make a 14.4MT bomb on its own, there's no way the B28 is that bad). With its specific activity of 2.3 GBq/g, we have 1.64e15 becquerels. Then we assume the fail-safe failed (see safety data for the New Horizon, if we use its setup, the chance is 4/62 in catastrophic fail). That's not enough, we want maximum contamination, so it can't break up in the air, can't go into the ocean (no one could bother if it ends up in the ocean with all the fissionable we've dumped in the ocean). So it landed on the land (which is impossible unless your rocket experiences severe control problems & self-destruction failure and delivers the thing to the land while in one piece). The Pu-239 magically dispersed into the land evenly and instantly, akin to the distribution of the Hanford Site, one of the most costly sites to clean up. It would cost 17,500 per Curie, so our becquerels would cost 775.7 million dollars.

Even deliberating such a contamination would be challenging, that's pretty much a coordinated dirty bomb attack.

Now let's see what if a regular mission goes wrong a bit, you will lose,150 million for Hayabusa2, 250 million for each GPS 3F, 316 million for NROL-87, 1.7 billion for the Challenger, 2.2 billion for the Perseverance, and 9 billion if you crash the JWST. Yet these missions used launch systems with a safety record inferior to Falcon 9's current track record.

You get the idea.

 

[Astronuc]

I was listening to a program on the 'Polygon' tests in Kazakhstan (1949-1989), where the USSR did atmospheric testing and underground testing. Some tests produced significant craters, and even some underground tests produced fractured formations such that radionuclides found their way out of the underground caverns in the Degelen Mountains. The USSR did test some large yield devices. The area remains heavily contaminated with fission products, U, Pu and TU residues.

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

Later tests were moved to the Balapan complex by the Chagan River in the southeast of the Semipalatinsk Polygon, including the site of the Chagan test, which formed Chagan Lake. Once atmospheric tests were banned, testing was transferred to underground locations at Saryozen, Murzhik in the west, and at the Degelen mountain complex in the south, which is riddled with boreholes and drifts for both subcritical and supercritical tests. After the closure of the Semipalatinsk labour camp, construction duties were performed by the 217th Separate Engineering and Mining Battalion, who later built the Baikonur Cosmodrome.

Between 1949 and the cessation of atomic testing in 1989, 456 explosions were conducted at the STS, including 340 underground borehole and tunnel shots and 116 atmospheric, either air-drop or tower shots. The lab complex, still the administrative and scientific centre of the STS, was renamed Kurchatov City after Igor Kurchatov, leader of the initial Soviet nuclear programme. The location of Kurchatov city has been typically shown on various maps as "Konechnaya", the name of the train station, now Degelen, or "Moldary", the name of the village that was later incorporated into the city.

Sometimes a crater forms when the ground collapses into the cavity that is produced. The ground above sometimes ruptures, even if it is not pulverized.
https://en.wikipedia.org/wiki/Semip...-_Flickr_-_The_Official_CTBTO_Photostream.jpg

One would probably need a deep bore hole (km or more), which would require a drilling rig, not something one puts on a small 'rover'.

 

[sophiecentaur]

I know that I can't nuke it and no one can nuke it at least not soon. I'm not calling for nuking it. Rather, my interest lies in understanding whether the hesitation around this idea stems from its scientific merit and feasibility or primarily from regulatory and ethical concerns (or both).

The title of the thread seems to have been deliberately chosen (click bait?) to draw attention. A title, something like "What size of detonation would be optimal for seismology on Mars" would have soon elicited the same amount of useful views without the image of great big 20th century Earthling boots clomping all over an unexplored planet. More like normal PF style.

 

[ElfredaCyania]

The title of the thread seems to have been deliberately chosen (click bait?) to draw attention.

It was indeed about the feasibility of the whole idea at the beginning, I thought there might be some technological challenge so we have a project like A119 to bomb the moon for a similar purpose but there's no Mars counterpart in history (not even a preprint). But the direction went to seismology after the conclusion that sending one isn't technically implausible. Also, seismology is the most promising and justifiable among all the potential areas. For now, the conclusion is that we lack sufficient data, mainly on the radiation to push the idea further. Even if we are going to choose the yield, it will be more about geology and seismology rather than aerospace engineering.

Too bad I can't edit the title now.

 

[sophiecentaur]

Too bad I can't edit the title now

Not to worry.
Imo, it's always better to say "I want to find out xyz; what's the best way?" rather than "I want to use this tool to find out XYZ"
This is especially true when nukes are involved, with all that baggage and worry.

 

[sandy stone]

I think the day we set off a nuke on Mars would be the day Klaatu and Gort show up.