*(Coincidentally, the first serious project was cancelled about 20 years before the present day [1]. That would have been an interesting alternate history...)

[0] https://www.howeindustries.net/ppr

[1] https://en.wikipedia.org/wiki/Jupiter_Icy_Moons_Orbiter

edit: To explain my reasoning a little: 10 gigawatts is gigantic amount of violently destructive energy—thermal energy, radiation energy, mechanical and vibrational [2] energy—you're trying to squeeze into a lightweight, complex, mass-optimized aerospace device that needs to run unattended and without maintenance for many years, without failing. That's probably very hard to get right. There have been many nuclear electric reactors in space already, but remarkably none of them, in operation, had any moving parts! They were all solid-state thermoelectric converters. I believe the bulk of that design choice boils down to "it's simple and conservative". Thermoelectrics aren't impressive by any other metric—just simplicity.

Even the first, smallest nuclear electric turbine in space will be a majorly impressive achievement, for whoever succeeds at it.

[2] Let's not forget: https://en.wikipedia.org/wiki/Galileo_project#High_gain_ante...

Fittingly, the project is part of NIAC (NASA Innovative Advanced Concepts) which is specifically for borderline outlandish, far-future ideas like magnetic sails, space elevators, nuclear propulsion, a "Lunar Crater Radio Telescope" and many other somewhat crazy ideas.

From NASA:

> The NASA Innovative Advanced Concepts (NIAC) Program nurtures visionary ideas that could transform future NASA missions with the creation of breakthroughs — radically better or entirely new aerospace concepts

https://www.nasa.gov/stmd-the-nasa-innovative-advanced-conce...

The reason for pulsing the engine, and the advantage over a normal nuclear thermal rocket is that the heat generated by operating at full power continuously would be unmanageable.

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

https://www.euronuclear.org/glossary/pulsed-reactor/

[1] https://www.youtube.com/watch?v=myYs4DCCZts

Of course once astronauts are on mars they will still be exposed to radiation, until some sort of shielding can be built.

Which would be an obscene undertaking, and involves moving lots of raw and refined materials to mars.

Which means hopefully the price of this rocket to get stuff off of earth is dirt cheap, because moving squishy humans to Mars, no matter the speed, is not the limiting factor! (Getting humans to Mars and keeping them alive there is!)

Further, Mars itself shields you from half the radiation (at night), the Martian atmosphere shields you from a little more, and Mars is further away from the Sun on average than an Earth-Mars spaceship.

Radiation during transit really does seem like a bigger issue.

An experiment measured that kind of radiation about 20 years ago https://en.wikipedia.org/wiki/Mars_Radiation_Environment_Exp...

Here is a recent (2022) paper[1] on the concept, but you can easily find scholarly work on this going back many decades...

[1] https://www.sciencedirect.com/science/article/abs/pii/S00320...

https://en.wikipedia.org/wiki/Caves_of_Mars_Project#/media/F... "HiRISE image of Mars hole 'Jeanne', about 150 meters (492 feet) across and at least 178 meters (584 feet) deep."

solar power / RTGs could power such effort. Digging shelters could be done by unmanned missions before the manned missions would arrive.

No, a RTG-powered bulldozer isn't going to be clearing caves and trenches on Mars, ever.

Excavating earth and rock in the volume being proposed (to build underground dwelling spaces) is not trivial...

Your other concerns are power source agnostic.

It's just a non-starter of an idea...

[1] https://www.smh.com.au/business/companies/no-one-behind-the-...

This line of thinking also dramatically underestimates the energy requirement to excavate dirt and rock...

Then, figure it's on another planet with dust storms that have already killed solar-powered rovers, etc.

I never mentioned hydrocarbon energy. You keep bringing it up for some reason.

> Solar, electric, batteries, etc do not even remotely come close.

I don't need them to come close. I need them to do the job, and they do it

> This line of thinking also dramatically underestimates the energy requirement to excavate dirt and rock...

here are some electric, battery powered excavators:

- https://www.volvoce.com/europe/en/products/electric-machines...

- https://www.wackerneuson.cz/en/zero-emission/electric-excava...

- https://www.komatsu.jp/en/newsroom/2023/20230721

- https://www.jcb.com/en-us/products/compact-excavators/19c-1e

- https://www.bobcat.com/na/en/equipment/excavators/compact-ex...

- https://www.volvoce.com/europe/en/products/electric-machines...

- https://www.hitachicm.com/eu/en/onsite/article/Introduction_...

- https://www.casece.com/en/europe/products/excavators/d-serie...

- https://www.kubota.com/news/2023/20231218.html

There are excavators both small and big so yes you can definetely excavate using electricity alone.

> dust storms that have already killed solar-powered rovers

Looking at list here https://en.wikipedia.org/wiki/Mars_rover I guess you talk about Zhurong and Opportunity? Both of these seems like success story given that they survived way longer than they were expected to..

https://www.cat.com/en_US/products/new/equipment/dozers/medi...

Not to mention this bulldozer still burns hydrocarbons. It uses electric drive for it's tracks - and the electricity is generated by hydrocarbons!

> The submarine reactor compartments that have been taken to Hanford are about 33 feet high and 40 feet in length. They weigh between 1,130 and 1,680 tons. Eventually, the Navy may deactivate its Ohio class submarines in the same manner. Those compartments would be much larger and heavier.

Submarines don't have to get them into orbit.

[1] https://www.nasa.gov/directorates/stmd/tech-demo-missions-pr...

[2] https://www.nasa.gov/tdm/fission-surface-power/

RTGs aren't gonna power a good-sized base; they're a few hundred watts at best.

edit: I very much hope Kilopower pans out.

Water is heavy and difficult to replace if lost for whatever reason.

It's expensive. Every gram takes tremendous resources and energy to extract. It would be like using antimatter for a small-town fireworks show.

A reactor should be among the first things we put down, ahead of the arrival of humans. And even if we’re processing lots of water, it would be a long time before it’s so abundant that sequestering (and irradiating) such a large amount of it is cheaper than other methods.

Yup. Mars is radioactive to the degree empty space is.

After all the pedantry is out of the way, the point is that humans on Mars already have to deal with radioactivity, which makes using nuclear power a no-brainer.

I know, I wouldn't want that in my back yard either, but Mars is exactly nobody's back yard at present. Bootstrapping a (necessarily!) technological civilisation on another planet is not an un-risky business.

Sure, but you're not going to need major shielding for the first few hundred reactors on the planet. Putting the stuff that requires maintenance away from the reactor will be enough for a few decades. (Put simply, the aspiring interplanetary powers who insist on heavily shielding their reactors aren't going to be releavant on the ground. You can launch a second reactor for the cost of one's shielding.)

There is no such thing on Mars, and that significantly increases the mass and size of your radiators, making it uncompetitive with solar for example, unless the waste heat is needed for something else.

The ones the boring company uses are battery powered (using containers full of batteries). The batteries are swapped out periodically and charged overnight.

Or they can dig a hole and/or pile mars dirt on top of their living structures. Some materials are better than others at absorbing radiation but, as a general rule, mass/depth of the protection counts more than composition.

realistically, the assembly could be done remotely, and you would want at least two habitable shielded pods with a very large excess of food/oxygen/supplies stored by the time humans arrived.

This might seem impossible, but i don't think it's particularly difficult, the only major hurdle would be the budget. The rocket vessel will make a good living pod, the small nuclear reactor was studied by the US Gov in the 50s, so that shouldn't be a problem, except maybe cooling, but again that should be a solvable problem.

The real problem is finding enough time and money to waste on such a fruitless endeavor. If that can't be managed it nullifies the entire problem of digging a hole on Mars since a Mars base is nothing but a waste of time and money. Wasting time and money is table stakes.

Before you get angry with me: I'm not saying this is the way it ought to be, but it's the way it is.

What would a realistic answer even look like? I imagine that since nothing like jump-starting an economy ex nihilo on a cold, desert planet has been done before, any proposal at all would sound wildly unrealistic.

When steam engines decreased that time to 16 days, 200-passenger ships crossing Atlantic purely for tourism were very popular.

So, yes, some billionaire paying for their kid to spend 12-18 months on a Mars trip is a possibility. Or maybe even for themselves if they retire, or as a sabbatical.

However, I think the much greater time and expense is going to make Martian tourism a much smaller market than lunar tourism.

I think in the medium term, the Moon is a much more feasible destination for humans than Mars is. It is much easier for an ultra-wealthy person to take a few weeks out of their schedule for a trip to the Moon, than months or years for a trip to Mars. Since it is only a bit over a light-second away, they could even quite feasibly work remotely from there – the delay is small enough that real-time audio and video calls are possible. Mars is 3–22 light minutes, which forces all communication to be asynchronous.

The enterprise of starting a colony on Mars is so unprecedented that any economic solution sounds nuts.

I think the only realistic answer at this point is "We need more information".

Let's assume the colony itself is built by some idealist willing a trillion dollars to the project or something. Now that you have a base on Mars, how do the inhabitants pay to keep it going? Self sufficiency is too far fetched at this stage so they need regular supply shipments from Earth, so they need income of Earth currency.

Emotional blackmail: “If Congress doesn’t pass the Martian colony funding bill, Americans on Mars will die”

National competition: “China’s Mars colony is bigger than ours”

Religion: “God wants us to send money to Mars” (that may sound bizarre, but religion motivates humans to spend fortunes on all sorts of strange things, maybe at some point one or more religions will latch on to Mars)

Let's say for instance that some answer were "handicrafts built from local, Martian materials" along with "YouTube channel revenue". Sounds unrealistic to me, but maybe people would be willing to pay $1M for a little puppet made on Mars, and they could ship them out by the ton. The economics on this are unusual.

I don't know. I honestly think Martian colonization just will not happen until we have a global, peaceful, prosperous civilization. Then it would just be funded by the global government in a similar way and for similar reasons as the antarctic stations.

Send tunnel boring machines. There a company making electric ones.

This is not a launch technology.

But it's only a few days with a million ISP from fusion.. let's raise the bar ;)

So, do they mean 2 months at the minimum distance, or the maximum?

This is a high delta-v vehicle, so anything on the outside of the porkchop [1].

[1] https://en.wikipedia.org/wiki/Porkchop_plot

The diagram the parent linked is the conventional presentation for how to relate orbital transfer times with orbital phases—conventions that do not apply to high-Isp transfers, such as this concept. Orbital phases are not important here.

https://trajbrowser.arc.nasa.gov/traj_browser.php?maxMag=25&...

The "View" and play on any of those is neat. Well, Earth - Mars isn't as neat as some other routes. I can't recall the exact settings, but I've dabbled with it in the past and had some EVEJ routes (Earth to Venus to Earth to Jupiter)

https://trajbrowser.arc.nasa.gov/traj_browser.php?maxMag=25&...

You can get routes like EVM-ME - where it does a Venus flyby on the way to Mars.

The minimum distance to Mars is 33.9 million miles. The maximum distance to Mars is 225 million miles. You're telling me this engine is so powerful it doesn't matter when you launch you'll always get there in 2 months?

Isn't Mars occasionally on the other side of the Sun from us? I'm still failing to grasp this.

Two identical spacecraft could travel the same distance between Earth and Mars and arrive at wildly different times. You’re never taking a linear path; it’s like talking about the diameter of the Earth when comparing two steamboats.

Okay, but this is one spacecraft with a single stated time.

So, does that mean it takes the same time regardless of when it was launched in the cycle? Or, does the two month figure only apply to launches at or near the minimum distance?

The path we're talking about is not this straight-line distance; it's a much longer trajectory that looks closer to this [0] (probably longer than the one in this particular diagram). Part of the reason is vector velocity addition with Earth's orbital velocity; part of it is that the electric acceleration phase is not instantaneous—rather it's very, very slow.

[0] https://www.researchgate.net/figure/Mars-transfer-trajectory...

According to that show, we should have been on Mars for the last twenty years.

Both numbers are pulled out of thin air. The Hohmann transfer time between 2 planets is about half a year. Which year, you ask? The year of the inner planet, or of the outer planet. Well, it's the average of the 2 years. A Martian year is about 2 of our years, so the average is 1.5 years, divided by 2 it's 9 months.

But if you are willing to burn more fuel, you can cut down the travel time. The delta-v between Earth orbit and Mars is surprisingly low. From the Moon transfer orbit to the low Mars orbit it is 2.5 km/s. The rule of thumb is that a rocket can achieve twice the delta-v of its exhaust velocity. In the case of the SpaceX Starship, the exhaust velocity is 3.7 km/s, twice that is 7.4 km/s, about 3 times the delta-v needed for the Hohmann transfer. SpaceX states they will be able to get to Mars in 6 months [1]. Musk went further and claimed that the Starship could get to Mars in as little as 80 days, and this fantastic Stack Exchange post [2] explains that maybe 80 days is slightly too optimistic, but 90 days is doable.

Now this design here claims that the rocket can achieve an ISP of 5000 seconds, which means an exhaust velocity of 50 km/s. With such an exhaust velocity, basically they can pick any random number and claim they can get to Mars that fast. The shortest path between the two orbits, the radial one, is about 75 million km long. At 50 km/s, it takes 1.5 million seconds, or 17 days. Of course, this is for a one-way trip, but presumably in the far future we could preposition fuel in Mars orbit for the return trip.

Maybe they thought half a month will sound too wild, so they went for the 2 month number to make it sound more realistic. The problem is that compared to the 3 months doable by SpaceX, it's not all that impressive.

[1] https://www.spacex.com/humanspaceflight/mars/

[2] https://space.stackexchange.com/questions/57568/elon-musks-i...