USA Put A Nuclear Reactor In Space And Abandoned It - How Did It Work?

Hi, I'm Scott Manley, here in April 1965, an Atlas Agena took off from Vandenbberg Air Force Base with a payload that was unique to the US Space Program. It would be called a snapshot, meaning it was a

space

takeover of the Snap program systems. for

nuclear

auxiliary power yes, this rocket carried a

nuclear

payload, specifically a nuclear

reactor

. In the 1950s, the US anticipated that there would be a need for nuclear power sources in

space

and there are many missions still operating today, the oldest of which is the Voyager spacecraft. They headed into deep space, but we also have on Mars the perseverance and curiosity of the Rover.

These

work

with radioisotope thermoelectric generators that use decaying radioactive materials to function as a heat source to drive thermocouples and generate electrical power, but they cover the entire spectrum of nuclear energy at once. technology and, in fact, they developed multiple

reactor

designs and one of them flew into space. This design was specifically called Snap 10A. They had started building small reactors very early in the program, things like Snap 2, and there was a lot of ground testing of devices before they were confident enough to be able to fly one in space and get it

work

ing safely, so this reactor It was extraordinarily small for space flight.

In fact, they are supposed to assemble the reactor and place the fuel rods by hand, one by one. Of course, it was designed in such a way that it would not be critical in these circumstances. To make it critical, they would have these rotating glow neutron reflectors that would reflect the neutrons back to the core and thus push it above the critical geometry by a large extent. When we talk about nuclear reactions, we talk about critical mass when, in fact, mass depends on geometry. In fact, there have been cases where accidents have involved unfavorable geometries, unfavorable in the sense that they killed someone, but as far as I know, there were no criticality accidents with this reactor to get the compact size, they use highly uranium. enriched, something like 93% enrichment, which is more than what they used for atomic weapons, this uranium would be converted into fuel elements by becoming an alloy of uranium, zirconium, hydra.

You may remember my video about the Trier reactor, a reactor that is so safe that high school students were allowed to operate and that is because the uranium-zirconium hidde has a highly negative temperature coefficient: the hotter it gets The less it wants to react, so this will allow it to passively control its energy output, so there were 37 of these fuel rods in the core and each of them contained about 150g of uranium which of course was mixed with about 1.2kg of zirconium and some hydrogen and then it was wrapped with a hasteloy which I think is haum TI and tungsten which was the hard protective coating of the fuel.

It was supposed to protect the fuel from physical damage because the fuel was a little more fragile, so in total there is only about 5 and a half kg of uranium in this reactor. and yes, that is significantly below the bare critical mass for uranium 235. It is because of the geometry and things surrounding the reactor that can make it work as a CR iCal. The reactor was designed to operate at a thermal power of about 30 KW, which was much more energy than any spacecraft of the time needed, but that, of course, is misleading. Because the actual electrical power was only about 500 watts, the conversion step to go from heat to electricity was actually inefficient.

A series of thermocouples were used that were connected to those. radiators the conical structure at the bottom that held the entire radiating surface for the small rear part at the top notice how large the radiators must be in relation to the size of the reactor. This is a common feature of spacecraft. Energy systems where you can get the best. The thermal efficiency must have the greatest gradient between the hot spot and the cold spot and that means the largest radiators possible, so now the way the power generation would work is that the reactor would cool down and the coolant would flow through the pipes towards the rear. of these radiators and then they would connect through these thermal couples that used silicon and germanium thermocouples to basically convert the heat, the thermal gradient into electrical energy and the coolant for this reactor is well, it's a cool thing, it's called Knack, which is a na for sodium and K for potassium is a mixture of the two and while these are metals that are solid at room temperature, if you make the perfect alloy with them, you get what is called a tic mixture whose melting point is about below the freezing point, it's like about... 9 C and it's also an excellent coolant because its boiling point is close to 800 C and there's another big advantage of using liquid metal to cool your reactors, which is that you can actually pump it using Magneto hydrodynamics with no moving parts and It would be really cool to say they did that here, except they didn't, they actually just pumped it using more conventional pumps, all of them sealed and driven using magnetic force to drive the rotors internally and if the idea of a nuclear reactor and highly reactive alkali metals like potassium and sodium, make it sound pretty scary, the scientists weren't even done yet because they had plans for a more efficient energy conversion system, those solid state converters weren't particularly good and They wanted to use a more powerful and efficient Rankin cycle, in which you take a liquid, heat it until it boils, and as the vapor expands, it is used to drive turbines.

Now normally we do this on Earth with water, but they thought you could do it with Mercury, that's right, you would boil the Mercury, use it to drive the turbines and then recover it now. Despite developing and testing it, it obviously never flew, but did you know that in the US there were actually a handful? From electric power plants, you know, the traditional coal-fired power plants that used a mercury vapor system as the first stage of their energy production for more efficiency. This was clearly back in the days when you know the environmental rules weren't exactly the same and I know the scientists who developed this project thought very clearly about the environmental problems of launching a nuclear reactor into space, as we saw before, before it started. , it was something that could be handled by a human, but once the reactor was turned on, it would fill up. with, you know, fishing products and it would become incredibly radioactive and you wouldn't want to come back to Earth and land somewhere for people to find it, so yeah, part of the mission requirements was that the reactor not activate until it was at a high level. stable orbit and in that high, stable orbit it would remain for thousands of years allowing the fish products to decompose, but they also wanted to verify that the spacecraft would disintegrate and burn, uh, when it returned to Earth, you know, millennia later, so they started obviously. with designs that were expected to disintegrate during re-entry forces, they conducted plasma wind tunnel tests to verify that the results were at least somewhat consistent with what they thought and then built a dummy reactor that used depleted uranium instead of El Uranium 235 could not go critical in this state, and since it did not go critical, they did not need any of the radiators, pumps, or other pieces of hardware that would add mass m to the launch that would allow them to shrink.

The mass of the object was reduced a lot and that allowed them to use a smaller rocket, so we got a suborbital flight of the Scout taking this on a trajectory that would take it above the atmosphere, take it sideways down and then they could observe . It disintegrates using cameras, I guess from the ground, and after all those tests, they showed that the reactor would burn up in the upper atmosphere, basically leaving behind radioactive dust, and the altitude would introduce less radioactivity than an atmospheric nuclear test, which sounds pretty bad. . except they did them all the time back then, so they said, well, at least we're better than those guys over there and you know what happens if that's no longer acceptable, as I suspect it may well be, it still stands.

It'll be up there for at least another thousand years, giving us plenty of time to figure out what to do with this thing that's orbiting in space. Meanwhile, there are plenty of other Soviet nuclear weapons. reactors in orbit which we would also like to discuss, since it turns out that the United States almost didn't even launch this reactor in mid-1964. It looked like this reactor test in space was going to be canceled and it took some time, you know. political campaign, I guess some lobbying to get it advanced to launch, so the reactor would be paired with an atlas and placed on top of the aena spacecraft bus to provide most of the propulsion to take it into its target orbit and, uh, the fairing would sit neatly over the conical reactor at the front.

The launch was from Vandenbberg, which I suppose had the advantage of being closer to where the reactor was actually being developed, so it didn't. They didn't have to travel that far, but I think the trajectory also allowed them to stay above the water for most of the initial launch. If something went wrong on the first orbit, they could make sure it ended up landing in the ocean. safely or at least less dangerously than if it had landed on the ground, but all those contingencies were not necessary, the booster worked as expected, it dropped its thruster engines, used the sustainer, separated the aena, entered the initial orbit and then they lifted it into high orbit and they were preparing for the test now this was not the only payload on this vehicle the aena spacecraft bus they were going to carry some other things one of which was the first ion engine in the space a networked ion based on cesium ions Thruster that actually had to run on batteries because the reactor only produced 500 watts and they needed something like, you know, 7 times that it would only be 3 and a half hours of flight before they gave the signal. order to turn on the reactor so that like this I said they turn it on by turning these neutron reflectors into position, there were four of them, two of them just turned 100% into position and then there were the two fine control ones that were turned slowly little shortly by ground command and 6 hours later the reactor reached criticality and began reacting in orbit for the next 7 days, they would manually adjust these reflectors, monitor how the reactor was performing and ramp it up to full power, but after know the first week they just left. them in their final position and the reactor was stable, they demonstrated the ability of the reactor to operate and sustain the reaction without any ground input due to its natural stability and as for that other great experiment, the lattice ion thruster was a disaster .

So apparently they had all kinds of arc flash problems and that produced a voltage, you know, electromagnetic interference that affected the sensors on the Horizon sensor and the spacecraft lost control, so they finally had to shut the thing down, isolate it and, well, You know, forget about it. At the moment the reactor had been designed to operate for a year but unfortunately it was never proven that because there was some type of failure with the uh aena spacecraft it was an error related to the high voltage power system that you know triggered an emergency and as part of the emergency procedures the reactor uh went into safe mode which it did was essentially released as a band that burst open and that meant that the neutron reflectors were jettisoned around the core now they weren't thrown into the space, they were still connected by cables, but once they were ejected, the reactor was shut down and operations ceased.

At this time, Agena was running on battery power and continued for a few more days before finally shutting down, so while the reactor was proving whether it was working in orbit or not. It did not prove that it would work for an entire year in space due to a failure of the support spacecraft. It was not believed to have anything to do with the relatively harsh radiation environment coming from the reactor at the top. It was believed to be something inherent to electronics more than anything else, while the snap program had developed other reactors, none of which had flown into space, it would actually develop a series of radioisotope thermoelectric generators that would reach spacecraft. , but the specific niche, you know, for which a 500-watt nuclear reactor would make sense never really materialized.

The Soviet Union would fly a lot of reactors. These would power radar satellites that had to operate atlow altitudes and therefore they did not want to have large solar panels for endurance reasons and with the return to the Moon perhaps to continue to be part of a space policy that you already know, we are seeing conversations, discussions and development of new reactor designs and Maybe if everything works, I will be able to talk about one of these things that are happening in Spain. I'm Scott Manley. fly safe