General Electric HTRE-3 Nuclear Jet Engine | Hacker News Reader

General Electric HTRE-3 Nuclear Jet Engine

planehistoria.com

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Here's another fun one:

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

An unmanned nuclear-powered ramjet designed to spew warheads, with a predicted range of 116,000 kilometers.

And for scale that’s circling the earth three times.

Well, that's the best setup for the roadrunner ACME missile launcher joke I've ever heard.

...at ground level.

The correction for cruising height would be insignificant.

A ram-jet is an air-breathing engine and would be confined to the atmosphere. Even a 60km cruising height (which is much higher than what would be used) would only correspond to a 1% increase in flight path circumference compared to the surface value of 40.000km.

I think the GP might have meant that Mach 3 at ground level is even more technically astonishing - a lot of the historial benchmarks for airspeed (mach 2 fighters and interceptors, the SR71's mach 3) were only valid at very high altitudes were the atmosphere is sufficiently thin to make the achivement teneable from a drag and heat-flux perspective. To cruise along at Mach 3 at sea level is a quite astonishing display of brute force.

I'm skeptical of such a capability. Even granting the engines the power and durability to do that, what about the rest of the airframe and avionics? How do they prevent those from being baked if not outright melted? The SR-71 required a substantial engineering effort to withstand the shock heating at that speed but the SR-71 flew very high in thinned air.

It’s not about physical distance, it’s about drag. Masssively more drag at sea level than in a thin atmosphere, way up in the sky.

Over enemy territory, ground-level flight was considered a feature, as the passing missile would shred the ground with sonic shockwaves, and bake it with radiation from its unshielded reactor.

One of the most evil military designs ever conceived.

> as the passing missile would shred the ground with sonic shockwaves

Reminds me of this “oopsie”:

> Three-quarters of the windows in an eight-block area of downtown were shattered by a sonic boom accidentally created by the Blue Angels, the U.S. Navy's flying aerobatic team

https://www.kelownadailycourier.ca/news/article_5e48d6a2-f6c...

To be fair, in the wikipedia article they talk about the radiation hazard being minimal and not part of the design - at mach 3 any exposure to the reactor is so brief it doesn't really do damage.

Of course, it going mach 3 at 1000 feet or lower, is going to knock your toupee right off.

This reminds me of the Bob & Ray satellite. Their plan was to put a satellite into an orbit 50 feet up, and then sell advertising space on the sides of it.

Cruise altitude for a ramjet would be between 5 and 20 miles up. The earth has a 4,000 mile radius. There would be no meaningful difference because of the change in circumference because of altitude.

We were lucky, and got ICBMs instead.

The problem with it was that they realized they didn't even need the warheads, they could just switch the plane to an open cycle reactor over enemy territory, spewing endless radioactivity and making the entire Soviet Union a nuclear death zone for thousands of years.

That's also why it was classified I believe. No one wanted the Soviets to get the same idea.

As someone else already said - there wasn't really any risk of that, the reactor wasn't "shedding" enough radioactive material or even emitting enough radioactivity to be a danger to anyone standing on the ground. Maybe if you made it fly in a loop around one place it would start to add up, but it wouldn't be anywhere on the scale of "making the entire soviet union a nuclear death zone" - you'd need thousands and thousands of these flying across their entire landmass 24/7 for weeks if not months, which

1) is just a stupid idea

2) if you have the capability to do this, you also have the capability to detonate actual nukes which can be tuned to produce maximum amount of fallout if that's your goal.

Such a wild concept from a wild time in history.

I have wanted upon occasion to put together a YouTube channel where I drop in on nerdy road trip destinations to try and get others to roll out and check these places out as well. I think in fact it was my stumbling upon the Experimental Breeder Reactor 1 [1] where I first hatched the idea.

Such an amazing place and with those crazy nuclear jet engines just sitting outside.... So sublime: a picnic lunch with the wife and kids at a table by the experimental nuclear engines....

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

They have also tried to use nuclear power for space propulsion. Here is a fun one: https://en.wikipedia.org/wiki/Project_Orion_(nuclear_propuls...

Neal Stephenson put this to good work in his novel Anathem.

And, much earlier, Larry Niven and Jerry Pournelle in Footfall.

This is not just a curiosity though. Nuclear pulse propulsion like Orion is actually the most advanced form of space propulsion that is within technical reach and doesn't use science fiction ingredients like large amounts of antimatter. When you read the article, you see that Orion was considered quite doable even decades ago. There actually is one system that would be even more efficient than Orion, the Medusa:

https://en.wikipedia.org/wiki/Nuclear_pulse_propulsion#Medus...

Though the Medusa design is less fleshed out than Orion.

I wonder if a RTG could produce enough to run an electric quad or optocopter?

For certain applications if unmanned you wouldn’t really need to worry about shielding. I wonder how long those motors can run continuously?

The RTGs on the Voyager spacecraft weigh 38kg. They initially produced 160 Watts. That sounds like a no-go to me.

It might not have great power density but boy does that thing keep going for decades

Full power for ~10,000 years, give or take.

No. You're thinking of nuclear waste. Voyager's RTG lasted "only" a few decades.

Design choice, not an inherent constraint. Plutonium has a half life in excess of 25000 years

> Design choice

Presumably this is why Pu-238 is used for RTGs where power density matters; a half life of 87.7 years means a reasonably long working life using with only 1/3% of the mass compared to Pu-239.

Oh yeah you're probably right, I didn't think about it being a different isotope. I figured they just kept it near-critical to keep it toasty instead of a shorter half life.

Long half life also means low energy output.

I think you need 1 hp per 10-15 lbs of weight to fly. I think that's around 130 W/kg. I checked a piper cub is something like 100.

Other hand Pu-238 produces 570 W/kg. A piper cub with it's 48kw engine would need 87kg of Pu-238 to produce the same energy.

I looked up the cost, $1968/g. So 48kw would cost $171 million.

Interesting idea but doubt.

Forgot the efficiency of an RTG is at most 10%. So you'd need 870kg of Pu-238. Which is twice what a Piper Cub weighs.

I wish Toshiba would have actually sold that RTG laptop battery. Imagine never having to charge!

On the other hand, imagine carrying in your bag a heater you can never turn off.

Depends on where you live I guess! Maybe you could plug it in the feed the grid.

Not just Voyager but the mars robots as well.

Dragonfly is NASA's RTG-powered octocopter. It launches for Titan in 2028

https://dragonfly.jhuapl.edu/

https://en.wikipedia.org/wiki/Dragonfly_(Titan_space_probe)

I got nerd sniped by this and asked GPT some questions.

Given a 45kg RTG plus the weight of the drone itself, you’d need to be able to lift, say, 60kg.

Energy required to hover 60kg using a 4-rotor drone at 70% efficiency is about 10kW - according to GPT. I don’t know enough to say if this is true or not.

Assuming it’s correct, and that a 45kg RTG generates about 300 watts, give or take, the answer is:

no.

There is no technical minimum; the only thing to keep in mind is that lift/drag ratio relates potential energy (moving mass up against gravity) to travel distance. This applies independent of speed and vehicle type (even running counts!).

Nuclear Stirling engines can run for a decade or more, but are still too heavy for a helicopter.

I see your GE HTRE-3 and raise you a https://en.wikipedia.org/wiki/Ford_Nucleon

This was never serious. Technical writing e.g. in textbooks in the 1950s explain that a nuclear-power car is 'not within the bounds of reality'.

https://babel.hathitrust.org/cgi/pt?id=mdp.39015003994194&vi...

Today, we have nuclear powered cars on Mars.

And with their amazingly powerful (checks notes) 0.13hp engine, you'll have plenty of time to admire the view.

Hey, don't knock it, the West was won on 1hp.

Today?, Curiosity landed 2012 in the Gale Crater on Mars: https://en.wikipedia.org/wiki/Multi-mission_radioisotope_the...

With no humans close to them.

Hmm, I don't know, it's a concept car, not a sci-fi car. Show me a big shot realist and I'll show you an even bigger dreamer.

I guess the author gets paid by word count. The piece could have been written in one third of the length.

I see you’re getting downvoted, but that was my first, second and third thought when reading the article. It’s suspiciously hand-wavy about the technical details, things are repeated several times and it really does feel like the writer was trying to stretch the article with the help of a LLM.

The piece was definitely written by an AI.

And a bad one at that. It is a redundancy nightmare.

To save your time:

"In 1951, the United States military initiated a program aimed at developing a nuclear-powered aircraft capable of unlimited range (ANP program).

The program’s goal was to create a nuclear reactor small enough to fit into an aircraft yet powerful enough to provide the necessary thrust while ensuring the safety of the crew from radiation.

General Electric (GE) initiated the HTRE (Heat Transfer Reactor Experiment) series to create and refine the technology necessary for integrating a nuclear reactor with a jet engine.

The reactor in the HTRE-1 was essentially a modified version of existing nuclear technology adapted for aviation use.

The HTRE-2 tested different configurations and setups to optimize the efficiency of the nuclear jet engine concept.

The HTRE-3 featured a more compact and efficient reactor design that was closer to what would be needed for actual aircraft implementation. The HTRE-3 incorporated a modified General Electric J47 turbojet engine, which was a well-known engine in military aircraft at that time. The HTRE-3’s design was sophisticated, involving a direct cycle in which the air passed directly through the reactor core, getting heated in the process and then expelled to generate thrust. Moreover, the HTRE-3 featured improved radiation shielding techniques

While the HTRE series ultimately did not result in operational nuclear-powered aircraft due to various strategic, technical, and ethical considerations, it significantly advanced the understanding of nuclear propulsion."

We've come a long way in material construction in the last 50 years, I wonder if this could now be built.

Would be interesting in a drone, no need for the weight of shielding

You’d need a lead catcher’s mitt after it lands. Might make maintenance a bit tricky.

I think it’s basically a non-starter to fly an open cycle nuclear reactor around spewing radiation out in its exhaust to rain down on the people below it. Even if it is a relatively small amount, and is fairly dilute at ground level.

Summarize using AI?

Prompting an AI service, like ChatGPT, to write an essay of a certain length about a given topic, then adding imaging and publishing the output on a website.

And this is, what ChatGPT replied to the prompt:

"Sure, here is a detailed and extensive essay on the Aircraft Nuclear Propulsion (ANP) program, including the role of General Electric and the Heat Transfer Reactor Experiment. While aiming for comprehensiveness, this essay might contain some redundancy to fulfill the length requirement.

The Aircraft Nuclear Propulsion (ANP) program was an ambitious initiative undertaken by the United States during the Cold War era. Its primary goal was to develop aircraft capable of prolonged flight durations without the need for refueling, thus providing significant strategic advantages in terms of endurance and range. The program was marked by extensive research and development efforts, significant investment, and a considerable degree of technical challenge. The program is particularly notable for the involvement of major corporations such as General Electric and the development of significant technological experiments like the Heat Transfer Reactor Experiment (HTRE).

The concept of nuclear-powered flight emerged during the early stages of the Cold War, a period characterized by intense rivalry between the United States and the Soviet Union. The strategic advantages of nuclear-powered aircraft were clear: they could remain airborne for extended periods, potentially for days or weeks, without the need to land for refueling. This capability would be invaluable for strategic bombers and reconnaissance aircraft, providing a persistent presence over critical areas and enhancing deterrence capabilities.

General Electric played a crucial role in the ANP program. As one of the leading corporations in the United States with significant expertise in both aviation and nuclear technology, General Electric was well-positioned to contribute to the development of nuclear-powered aircraft. The company's involvement included designing and testing nuclear reactors that could be integrated into aircraft systems. This was no small feat, as it required overcoming substantial technical hurdles related to reactor design, thermal management, radiation shielding, and integration with aircraft systems.

One of the most significant technical challenges in the ANP program was the development of a suitable nuclear reactor that could be used in an aircraft. Traditional nuclear reactors used in power plants were far too heavy and bulky for aviation purposes. Therefore, the ANP program focused on developing compact, lightweight reactors that could provide sufficient power for sustained flight without compromising the structural integrity or performance of the aircraft. This led to the development of several experimental reactor designs, including those tested under the Heat Transfer Reactor Experiment (HTRE).

The Heat Transfer Reactor Experiment was a series of tests designed to evaluate the performance and feasibility of nuclear reactors for aircraft propulsion. These tests were conducted at the Idaho National Laboratory and were critical to understanding how nuclear reactors could be effectively integrated into aircraft systems. The HTRE program involved several iterations of reactor designs, each incorporating lessons learned from previous tests. These reactors were designed to test various aspects of nuclear propulsion, including heat transfer efficiency, radiation shielding effectiveness, and overall reactor performance.

The first reactor in the HTRE series, HTRE-1, was primarily focused on demonstrating the basic principles of nuclear-powered flight. It was a significant milestone, as it successfully demonstrated that a nuclear reactor could be used to generate the necessary power for aircraft propulsion. HTRE-1 was followed by HTRE-2 and HTRE-3, each of which incorporated improvements and refinements based on the findings from earlier tests. These reactors were tested under various conditions to simulate the operational environment of an aircraft, including high-altitude and high-speed flight conditions.

One of the critical aspects of the HTRE program was the focus on heat transfer efficiency. In a nuclear-powered aircraft, managing the heat generated by the reactor is of paramount importance. Efficient heat transfer systems are essential to ensure that the reactor operates within safe temperature limits while providing sufficient power for propulsion. The HTRE reactors were designed with advanced heat exchanger systems that could effectively transfer heat from the reactor core to the aircraft's propulsion system, enabling sustained flight without overheating.

Radiation shielding was another major challenge addressed by the HTRE program. Nuclear reactors emit significant levels of radiation, which can be harmful to both the aircraft's crew and sensitive electronic systems. Effective shielding is necessary to protect against this radiation while minimizing the additional weight that the shielding adds to the aircraft. The HTRE reactors were designed with innovative shielding materials and configurations to minimize radiation exposure while maintaining the overall weight and performance of the aircraft.

General Electric's contributions to the ANP program were not limited to reactor design and testing. The company also played a key role in developing other critical components of the nuclear propulsion system, including control systems, fuel handling systems, and safety protocols. These components were essential to ensure the safe and reliable operation of the nuclear-powered aircraft. The integration of these components into a cohesive system required meticulous engineering and testing, with a focus on reliability and safety.

Despite the significant progress made under the ANP program, the initiative faced numerous challenges and criticisms. One of the primary concerns was the safety of nuclear-powered aircraft. The potential consequences of a nuclear reactor failure or crash were catastrophic, raising concerns about the feasibility and wisdom of deploying such aircraft. Additionally, the technical challenges of developing a practical nuclear propulsion system proved to be more formidable than initially anticipated. The weight and complexity of the required shielding, combined with the challenges of heat management and reactor control, posed significant hurdles.

The ANP program also faced competition from other technological advancements. During the same period, significant progress was being made in the development of intercontinental ballistic missiles (ICBMs) and other advanced conventional aircraft. These technologies offered alternative means of achieving strategic objectives without the inherent risks and challenges associated with nuclear-powered flight. As a result, the perceived strategic value of nuclear-powered aircraft diminished over time.

In light of these challenges and shifting strategic priorities, the ANP program was eventually canceled in the early 1960s. The decision to terminate the program was influenced by a combination of technical difficulties, safety concerns, and the emergence of more viable alternatives. Despite its cancellation, the ANP program left a lasting legacy in the field of aerospace engineering and nuclear technology. The research and development efforts undertaken during the program contributed to advancements in reactor design, heat transfer systems, and radiation shielding, which had broader applications beyond aviation.

General Electric's involvement in the ANP program also had a lasting impact on the company. The expertise and experience gained through the program contributed to GE's broader capabilities in nuclear technology and aerospace engineering. While the dream of nuclear-powered flight was never fully realized, the lessons learned from the ANP program informed future projects and initiatives in related fields.

In conclusion, the Aircraft Nuclear Propulsion (ANP) program was an ambitious and technically challenging initiative that sought to develop nuclear-powered aircraft capable of prolonged flight without refueling. General Electric played a crucial role in the program, contributing to the design and testing of nuclear reactors and other critical components. The Heat Transfer Reactor Experiment (HTRE) was a key element of the program, providing valuable insights into reactor performance, heat transfer efficiency, and radiation shielding. Despite its eventual cancellation, the ANP program left a lasting legacy in the fields of aerospace engineering and nuclear technology, highlighting both the potential and challenges of nuclear propulsion."

For example, try this prompt on ChatGPT:

"Please write a lengthy essay about the Aircraft Nuclear Propulsion program, including details about the role of General Electric and the Heat Transfer Reactor Experiment. I need about 100 paragraphs. I know, this is a lot, but it is ok if there is a lot of reduncancy in the essay."

This one didn't get cancelled https://en.m.wikipedia.org/wiki/9M730_Burevestnik

Did they just expect these aircraft to never crash?

No, that was one of the practical problems with the concept.

As far as I can tell, aircraft and space nuclear propulsion still hasn't actually be used in flight, right?

Correct depending on if you count spacecraft with electric propulsion powered by radioisotope generators.

Reactors have been flown and made critical in flight, but never used to provide power for aircraft propulsion. The Soviets got the closest, but they abandoned it as well.

Recently Putin has revived a nuclear powered cruise missile design. Status is unknown publicly, but it is believed to have been set back by a major test failure and contamination event.

Today, one can imagine solving the crew shielding problem of these large, nuclear powered bomber concepts by simply eliminating the crew and foregoing most of the requisite shielding. Had that been possible at the time these concepts might have been deployed.

Correct. Snap-10A was a nuclear fission powered satellite. It was not propulsion.

Not in flight, but Nerva had multiple prototypes built and tested - the longest run being over an hour long. It was cancelled due to politics, not technical viability.

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

Sounds like a keeper. I don't see what could possibly go wrong with deploying these at scale everywhere.

We could see nuclear aircraft engines deployed on Titan. They would work great there.

Does someone know how long an unmanned unclear powered aircraft could fly?

Sitting here with my morning coffee and reading about a nuclear jet engine I've never heard of makes me realize how special HN is. Please, never change!

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