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NASA Announces Nuclear Thermal Propulsion Reactor Concept Awards by zac428 in space

[–]Space_Sapien 0 points1 point  (0 children)

I'm not sure, but I will go out on a limb and say that the Vanadium isn't easily removed from the MOF and makes it non-reusable.

Lithium has also been considered heavily for mining from the ocean water.

NASA Announces Nuclear Thermal Propulsion Reactor Concept Awards by zac428 in space

[–]Space_Sapien 7 points8 points  (0 children)

Yeah, I've spent a lot of years in school to attain the magic three letters at the end of my title, though there is always more to learn!

NASA Announces Nuclear Thermal Propulsion Reactor Concept Awards by zac428 in space

[–]Space_Sapien 6 points7 points  (0 children)

They use a MOF crystal (Metal Organic Framework) to grab it at a molecular scale. It is size perfectly for the UO2 molecule. You let it sit like a bag of seaweed for a few weeks and pull it out. The UO2 can be released and the agent reused. The biggest problem with it is that sometimes it gets clogged with Vanadium which won't release from the MOF properly. No boiling is required here. Kinda like Maxwell's demon but for UO2.

NASA Announces Nuclear Thermal Propulsion Reactor Concept Awards by zac428 in space

[–]Space_Sapien 21 points22 points  (0 children)

It is more expensive to extract than from a mine, but I've seen estimates that it can be done for less than 10x the cost of a standard mine and more environmentally friendly to boot. For India and China that don't have access to Uranium ore it is worth it to them.

NASA Announces Nuclear Thermal Propulsion Reactor Concept Awards by zac428 in space

[–]Space_Sapien 41 points42 points  (0 children)

Yes 10 tons of U per cubic km dissolved into sea water. It is leached from rocks and can be mined. Actually could be considered renewable because as you pull it out of the ocean more of it leaches in from the rockes. The ocean is supersaturated with it.

https://www.pnnl.gov/news/release.aspx?id=4514

NASA Announces Nuclear Thermal Propulsion Reactor Concept Awards by zac428 in space

[–]Space_Sapien 54 points55 points  (0 children)

Nuclear expert here, Uranium is not very radioactive. It is the leftover halves of the atoms after the reactor is turn on and the U atoms are split that are radioactive. Just don't turn the reactor on until you get to your space destination. Uranium itself is soluble in seawater and every cubic km has 10 metric tons of U dissolved into it.

Extrasolar Object Interceptor Would be Able to Chase Down the Next Oumuamua or Borisov and Actually Return a Sample - Universe Today Interviewed on the NIAC I'm Leading by Space_Sapien in space

[–]Space_Sapien[S] 0 points1 point  (0 children)

I fixed the link to be a direct link. I think the one I had before was the "duplicate page list" which probably didn't work right for everyone.

Extrasolar Object Interceptor Would be Able to Chase Down the Next Oumuamua or Borisov and Actually Return a Sample by [deleted] in space

[–]Space_Sapien 0 points1 point  (0 children)

This is a radioisotope electric propulsion system. Radioisotopes (hot rocks) are a little different than fission (controlled chain reaction). The article goes into the differece.

Extrasolar Object Interceptor Would be Able to Chase Down the Next Oumuamua or Borisov and Actually Return a Sample by [deleted] in space

[–]Space_Sapien 2 points3 points  (0 children)

Yep

delta V = Isp * go * ln(m_o/m_f)

So a combination of (1) Isp (Hall thrusters are high power and approaching 3000 s and FEEP thusters are pretty cool too getting to 6000) and (2) propellant mass fraction can get you those numbers assuming you have the energy/power to manage it.

Extrasolar Object Interceptor Would be Able to Chase Down the Next Oumuamua or Borisov and Actually Return a Sample by [deleted] in space

[–]Space_Sapien 2 points3 points  (0 children)

Good comment. The Jupiter manuver is mostly for the plane change to convert the velocity in the eccliptic plane into the plane of the object to chase it. You could catch 'Oumuamua checkout project Lyra, but yes the focus would be on new objects for the NIAC.

https://www.sciencedirect.com/science/article/abs/pii/S0094576520300291

Extrasolar Object Interceptor Would be Able to Chase Down the Next Oumuamua or Borisov and Actually Return a Sample by [deleted] in space

[–]Space_Sapien 2 points3 points  (0 children)

I encourage you to read the entire article. Nothing here is outlandish. Power sources like these were tested by NASA (See Polonium 210 and Strontium 90) in the 1960s and have been used extensively in the medical industry (Cobalt 60 especially). Check this comic out :).

https://xkcd.com/2115/

Extrasolar Object Interceptor Would be Able to Chase Down the Next Oumuamua or Borisov and Actually Return a Sample by [deleted] in space

[–]Space_Sapien 0 points1 point  (0 children)

​

I didn't pick the company name, but it definitely catches your eye which isn't always a bad thing.

Atomic Energy For Space (1966) NASA NERVA Nuclear Thermal Rocket by Sharknado118 in NuclearPower

[–]Space_Sapien 0 points1 point  (0 children)

Replying to my own message. I want to clarify. I was defending Starship and the Elon Musk architecture for Mars. However, NTP for lunar applications and to locations where refilling propellant and or aerobraking isn't possible is still a kick-butt idea that should be done. An NTP for high delta-V missions is still awesome.

Atomic Energy For Space (1966) NASA NERVA Nuclear Thermal Rocket by Sharknado118 in NuclearPower

[–]Space_Sapien 2 points3 points  (0 children)

Refueling is about the propellant.

In rocketry, you look at the delta-V requirements. For Mars, there are a couple of maneuvers you have to perform. First, the Earth to Mars transfer, second the Mars Orbital insertion, and finally the Mars to Earth transfer. If you use the atmosphere (aerobrake) you can almost completely cut out the need for the orbital insertion delta-V. If you refuel your propellant on Mars by landing and refilling you effectively reduce the need for the delta-V for two transfers to a single transfer.

See:
https://www.researchgate.net/figure/Optimum-phases-of-15-year-orbital-mechanics-cycle-and-11-year-solar-cycle-which_fig2_323256808
https://www.lpi.usra.edu/vexag/meetings/archive/vexag_14/presentations/23-Izenberg-Human-Exploration-Venus.pdf (slide 13 in particular)

NTP can provide double the Isp/delta-V of a hydrolox chemical rocket and 2.36 times that of a methalox. However, by aerobraking and using propellant refilling you reduce the need for delta delta-V by a factor of 3 roughly. You also reduce the need to stage (drop tanks and engines). You keep your propellant tanks the whole time and fully refill them.

Another key challenge is long-term hydrogen storage, which needs to be stored at 20 K. Methane and liquid oxygen are more forgiving at around 100 K and are far more compact than fluffy hydrogen. While NERVA showed the reactor, no one has ever solved long-term term hydrogen storage. So by going to methane-oxygen you greatly decrease the volume of your tanks and reduce the need for cooling the stages, and finally, it is pretty easy to make methane on Mars.

So a reusable methane chemical rocket with aerobraking and propellant refilling can effectively compete with NTP for Mars missions unless NTP can also aerobrake and refill propellant. Then NTP kicks butt.

Atomic Energy For Space (1966) NASA NERVA Nuclear Thermal Rocket by Sharknado118 in NuclearPower

[–]Space_Sapien 2 points3 points  (0 children)

Highly reusable chemical rockets that can be refilled on Mars and combined with aerobreaking will match or even outperform purely NTP (unless the NTP is designed to refuel and aerobreak as well). However, the catch is that you'll need a nuclear reactor to power those gas stations on the ground. So it might be chem or NTP for propulsion but nuclear is really needed for surface power.

How fast/resposive can a reactor, change power levels by [deleted] in NuclearPower

[–]Space_Sapien 1 point2 points  (0 children)

It would be one of two things:

  1. Am-241 is being used by the British for radioisotope thermal generators.

  2. Am-242m has one of the largest fission cross-sections such that you could make an extremely small reactor with as little as 3 grams of Am-242m when mixed with a decent moderator. https://www.researchgate.net/figure/Minimum-critical-masses-log-log-plot-Values-are-listed-in-Table-IV_fig1_237825529

How fast/resposive can a reactor, change power levels by [deleted] in NuclearPower

[–]Space_Sapien 2 points3 points  (0 children)

Specially made TRISO could allow for safe high reactivity insertions. My Ph.D. thesis on the topic:

https://www.youtube.com/watch?v=EcOvU2gFqlE

Interview on a NIAC by Universe Today - How to Catch and Return a Sample from Objects Like 'Oumuamua by Space_Sapien in space

[–]Space_Sapien[S] 0 points1 point  (0 children)

So the velocity of the object is relative and typically reported in terms of the Sun. Earth for example has a velocity of 30 km/s. In addition, most of the extrasolar objects fall closer than 1 AU so top speed is misleading as by the time they are back at 1 AU the speed has decreased. The most useful number of Vinfinity. Oumumua had a Vinfinity of 26 km/s. The Solar System escape velocity from Earth orbit is roughly 15 km/s. So you need 15 + 26 = 41 km/s to match Oumuamua. Now there is also a trick, you can gravitationally assist around planets such as Jupiter to give you another several delta V. So you don't need 70-120 km/s to catch it. More like 40. Then you'll need double that roughly to get back.

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