Can Nuclear Power Take Us to Mars? - Nuclear Engineer Reacts to Real Engineering

[tfolsenuclear]

Thanks so much for watching! If you want to hear more about bizarre nuclear units, please check out:

[ncdavelife]

18:40 You're right about the ineffectiveness of solar power, but at least in space the solar panels don't shut down at night.

22:04 No, hydrogen is not explosive in space (or on Mars). It's only explosive on Earth because we have a (very unusual) 21% oxygen atmosphere. But hydrogen is still highly reactive, and hot hydrogen can, indeed, react with ("attack") things that you'd rather it not.

22:50 If you put the reactor/engine in the back, and put the crew capsule atop a tall tower, then (#1) distance reduces your need for shielding, and (#2) you only need to shield a small part of the reactor, to protect the crew. You probably put most of your cooling system there (mounted on & in the tower), and the coolant, radiators & tower structure become part of your radiation shield.

[idris]

The reason the exhaust velocity is important at 14:35 is that its directly preportionally to specific impulse. The higher exhaust velocity the more bang for your fuel bucks

[michaelbobic]

That's why the Voyager satellites got pictures of these planets and moons! What you could do with calculators and sliderules! That makes me a little happy when i get my sliderule out in class

[emmata]

11:40 in intergalactic space it will increase, since the electromagnetic field of the sun, shields us from it more, than it expells at such distances

[soulwynd]

Reminder that the last thing you want to is try to block gamma rays. The resulting hadronization is way worse for astronauts than the chance of gamma rays interacting with them. You want to block relatively low energy ones, but not high energy ones. So there is a balance for shielding.

[rasimbot]

There is a third type of nuclear engine. A thermal nuclear reactor, but where the same media serves as both the fissile material and the working fluid. The Zubrin engine is an example

[johnbennett]

Reactor shielding in space is a long rod separating the reactor from everything else. You might need a small disk shield near the reactor to keep the rod down to a practical length. Still the mass of this is trivial compared to the shielding needed on Earth. Remember space is already radioactive, there is no reason to protect it from the reactor.

[andrewreynolds]

28:45 What we could do is use a hybrid of both nuclear thermal and nuclear electric . What we could likely do is something nasa, and the technology researchers have suggested is the most efficient for the best speed

[philiptetherow]

"there is no disk brakes in space" well, I guess ablative shields are non- Disk Shape. These are more of a Hyperboloid or Elliptic Parabaloid. With center at highest heat

[robertheinrich]

the most efficient nuclear engine is a nuclear reactor in the focal point of a parabolic mirror. but since that thing needs to reflect infrared and some gamma rays (alpha and beta are welcome too), the mirror needs to be a bit different. maximum reflectivity in infrared.
power up the reactor, it radiates infrared light. the light gets radiated to the mirror and reflected back out. this gives you the best specific impulse, but acceleration that is comparable to solar sails.

[rolypoly]

Alternative: Go crazy and use a nuclear salt water rocket. It uses a continuous nuclear explosion instead of transferring reactor heat to a propellant. Although that would be overkill unless you really needed to get to Mars in a couple weeks. It has a specific impulse of up to 20, 000 sec.

[mattw]

Shielding isn't a concern for a (sufficiently large) nuclear powered space-only craft. A small shield close to the reactor shields a cone reducing the dose over a small solid angle, then put the crew a long way away from the reactor where the small angle is a large area (you only need 0.01g acceleration or less).

What does ruin the concept is there are few niches where they could potentially compete with solar inside jupiter. Current PV modules (compact and self unfurling) are 200W/kg (or 500W/kg simply by making them larger), current tech under testing is >2kW/kg. You will struggle to come close to that with either your reactor+heat engine or the waste heat rejection system (most proposals for either are under 100W/kg). So pure nuclear electric drives are obsolete.

Chemical rockets substantially outperform the NERVA concept for lofting (do the math with real tank mass and possible volume envelopes rather than just assuming isp is all). So they are only useful in space where the thrust advantage over ion drives is useless.

Low thrust solar thermal outperforms low thrust nuclear thermal as a 10gsm mylar mirror exceeds nuclear specific power out to saturn. You can't even carry fuel for a >15yr mission and beat an inflatable <7gsm mirror (with a few spare membranes and patches for repairs) in terms of specific energy.

NTERs are an interesting concept though. Using propellant for heat rejection is a huge advantage, and not carrying radiators or collectors makes landing a possibility.

[uberdang]

When he says hydrogen attacks the fuel rods he means hydrogen causes materials to become extremely brittle. It first crept up in steel materials and later in welding.

[Melechtna]

"Maybe not meant to take it too seriously"
Said after taking it MOUNTAINS too seriously.

[moozoowizard]

No, or little shielding. The ship is long and thin so there is a lot of distance between the reactor and the crew. The fuel tanks also shield the reactor. I'd imagine maintenance only being done at Earth and Mars in orbital assembly and maintenance structure. In flight work would need to be robots of some kind.

[TCustodian]

I love the idea that another species that is watching us has collected the voyagers when they are completely out of contact 😂

[Tommy-hedx]

I remember seeing a documentary from the BBC Horizon series called "Nuclear Nightmares" and it was about debunking the myths and fears of nuclear energy and some of the flaws in conclusions, like using atomic explosion data in worse case meltdown situations.
But one of the thing they talked about was a place on Earth, I think Iran but could be wrong, that is basically sat on a huge Granite deposit, the amount of natural background Radiation it produced gave an average of over 125 millisieverts per year. The effect was counter to what people expected, the overall cancer rates were way lower than most places on Earth.
This doc was over 15 years ago now, but there were 2 theories one was just these people evolved to be more resistant, or that constant dosing helped the body to be more prepared to fight off cancer before it gets a foothold.

[Hamstray]

in space, i'd be more worried about kinetic impacts.

[robertheinrich]

if you want a funny nuclear engine, search for the nuclear salt water rocket. it is quite efficient and has a lot of thrust.
but don't launch from earth, it's maybe worse than orion.
essentially, you have uraniumnitrate or plutoniumnitrate dissolved in water. push that water through a neutron source or reflector, and it goes over critical. or in other words: you are riding a constantly igniting nuclear bomb.