NASA and DARPA will build a nuclear rocket by 2027

Nov 19, 2021
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Yes, nuclear thermal is essential to reduced travel time to Mars. Cosmic radiation damage to humans is a huge issue. Problem is, there will be a public outcry like we've never seen when people find out they plan to launch a nuclear reactor overhead. I doubt they'll get away with it.
 
Oct 21, 2019
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Yes, nuclear thermal is essential to reduced travel time to Mars. Cosmic radiation damage to humans is a huge issue. Problem is, there will be a public outcry like we've never seen when people find out they plan to launch a nuclear reactor overhead. I doubt they'll get away with it.
Any outcry will be due to ignorance. As the reactor is only started for the first time once it's safely in orbit having been launched on a conventional chemical rocket the amount of radioactivity in the uranium fuel at launch is much less than that of the radio-isotope thermal generators (RTGs) already safely launched into Space on many occasions.
 
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Nov 19, 2021
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Nuclear reactor core creates vast amounts of heat, liquid hydrogen is introduced as a coolant, gassifies, disassociates and is ejected at high velocity out through a nozzle. It only has one tenth the thrust to mass ratio as a chemical rocket thus cannot be used to lift off from Earth, but in outer space its mass doesn't matter. The efficiency is about twice that of chemical rockets. It would halve the time needed to get to Mars.
 
Mar 30, 2020
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Great news! If NASA is serious about a crewed mission to Mars then a nuclear thermal rocket has obvious advantages, principally reduced journey times.
Big, Big Question for this.

Where will we get the Pu238 that will be the probable fuel?
Russia or China?

All our plants at Hanford and Savanah River closed DECADES ago.
 
Oct 21, 2019
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Big, Big Question for this.

Where will we get the Pu238 that will be the probable fuel?
Russia or China?

All our plants at Hanford and Savanah Riverocket reactors use r closed DECADES ago.

Pu238 will definitely not be used, it's a very powerful alpha emitter and the intense heat it produces (in its pure form it glows dull red hot) makes it ideal for use in radio-isotope thermal generators (RTGs) as used on deep space probes and the Curiosity and Perseverance Mars rovers. It is not a reactor fuel, the proposed new nuclear thermal rocket reactor designs use relatively low enriched Uranium fuel i.e much less than 20% U235, typically about 5%, the rest being U238. The designs successfully tested in the 1960s e.g NERVA used highly enriched uranium, but highly enriched Uranium has to be closely guarded as it is a proliferation risk (if diverted into the wrong hands you can use it to make an atomic bomb). So low enrichment Uranium fuel is now preferred as it doesn't pose that problem. https://www.energy.gov/ne/articles/6-things-you-should-know-about-nuclear-thermal-propulsion
 
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Jan 14, 2020
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Thank you billslugg. So they accelerate half way and decelerate the other half? Some were saying 45 days? To Mars?
Let's not get carried away. No way such a device has the power to accelerate on the whole Martian journey. As a estimate it might be sufficient to accelerate for an hour perhaps, then decelerate for another hour.

When you consider that a chemical rocket accelerates no more than about 12 minutes to get up to a speed sufficient to get to Mars from earth orbit, an hour of added nuclear assisted acceleration is a significant add-on. This kind of nuclear rocket is certainly not warp drive. Nuclear heating of hydrogen to accelerate its mass as rocket exhaust is still limited by how much hydrogen can be carried. Heat, as from nuclear fuel is not the only requirement, you have to have mass to throw out to get thrust. Energy or heat alone does not equal thrust. Put another way, unlimited acceleration duration requires unlimited thrust mass.
 
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The length of time over which the rocket can accelerate is dependent on how much fuel it has, how much reactive mass, the exit velocity and how much acceleration is achieved.
Nuclear thermal has plenty of fuel, the exit velocity would be limited by how hot they could keep the core temperature.
It would be in their interest to ration the reaction gas such that it lasted the entire journey then keep the core temperature at its highest allowable level.
 
Oct 21, 2019
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It would be in their interest to ration the reaction gas such that it lasted the entire journey then keep the core temperature at its highest allowable level.
I don't quite follow what you are saying there. Obviously they have to have sufficient reaction gas on board to cover the acceleration towards Mars, deceleration as they approach Mars and then have sufficient for the return trip to Earth. As regards the first acceleration from Earth orbit towards Mars the journey time will be quicker if the allowable amount of reaction gas for that phase of the journey is used all at once over the course of say an hour to get the vehicle up to the fastest possible speed at the start rather than to have a minimal thrust lasting for days or weeks. The total impulse imparted to the vehicle is the product of thrust times duration of the burn time which would be the same in the two situations (the maximum allowable core temperature will be determined by core material constraints, not the flow rate of the propellant through it. If you have greater propellant flow which takes away heat from the core you just increase the power level of the reactor to maintain core temperatures at the optimum safe maximum) but the first situation of doing a short but high thrust burn at the start of the mission gets the vehicle up to high speed at the start of the journey thus minimising journey time.
 
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Nov 19, 2021
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I was responding to post #12 in which Edward Coulter made the statement:
"No way such a device has the power to accelerate on the whole Martian journey."

Of course, the quickest journey is when the acceleration is compressed into the shortest periods at start and end of journey.

And yes, the maximum allowable core temperature is determined by material of construction. Gas flow rate and power output setting will establish an equilibrium core temperature. This must be kept below maximum allowable core temperature or it will melt.
 
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Jan 27, 2023
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This is excellent news! I always wondered why NASA never dusted off the NERVA program and updated it with today's technology and infrastructure. I wish there was a way to keep this project from being canceled a few years from now when Congress cries about it being too expensive. Onward to the Moon and Mars!
 
Jan 28, 2023
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In order to shorten the trip to Mars, nuclear thermal is unavoidable. Damage from cosmic radiation to humans is a serious problem. The issue is that when people learn that they intend to launch a nuclear reactor overhead, there would be an uproar like we have never seen. They won't probably get away with it.
 

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