Nuclear rockets rely on atomic energy to heat propellant up to extreme temperatures. When that superheated propellant shoots out, it creates a powerful thrust.
This tech gives you specific impulse values that are two or three times better than what chemical rockets manage. At the same time, you still get the kind of thrust that electric propulsion just can’t offer.
Nuclear thermal propulsion systems use a nuclear reactor as their main heat source. Engineers pump liquid hydrogen through the reactor, where it heats up past 2,500 Kelvin.
The hydrogen then expands fast as it exits the rocket nozzle. That expansion pushes the spacecraft forward.
Specific impulse for these rockets lands between 800 and 1,000 seconds. Chemical rockets, by comparison, usually max out around 450 seconds.
Nuclear electric propulsion works differently. Here, the reactor generates electricity, which then powers ion thrusters or plasma engines.
Key Nuclear Propulsion Components:
Neutron flux in the reactor heats the fuel elements. Heat jumps from the fuel to the propellant, either by direct contact or through heat exchangers.
Chemical rockets burn fuel and oxidizer, making hot gases for thrust. They offer high thrust, but their efficiency isn’t great.
Nuclear propulsion gets you about twice the efficiency of chemical rockets. For example, a Mars mission with chemical propulsion might take 6 to 9 months.
Nuclear thermal rockets could cut that trip down to 3 or 4 months. That’s a huge deal for reducing crew radiation exposure.
Electric propulsion is super efficient with fuel, but the thrust is tiny. Ion drives hit specific impulse numbers over 3,000 seconds.
Electric systems just can’t lift heavy payloads from planets. They really shine on deep space missions with lighter cargo.
Propulsion System Comparison:
| System Type | Specific Impulse (seconds) | Thrust Level | Best Applications |
|---|---|---|---|
| Chemical | 300-450 | Very High | Launch, landing |
| Nuclear Thermal | 800-1,000 | High | Interplanetary transfer |
| Nuclear Electric | 3,000+ | Very Low | Deep space missions |
Nuclear propulsion sits between chemical and electric systems. It offers a pretty good mix of thrust and efficiency.
Project Rover kicked off America’s nuclear rocket program back in 1955. Over nearly two decades, the team built and tested nuclear thermal rocket engines.
NASA and the Atomic Energy Commission developed several test reactors. The NERVA program even put together flight-ready nuclear engines.
Engineers ran these engines for hours at full power during ground tests. The tech worked reliably without major failures.
Budget cuts eventually shut down the program before any actual flights. Political worries about nuclear tech also played a big role.
Lately, nuclear propulsion is back in the spotlight. NASA restarted nuclear thermal propulsion research in 2017.
They picked three companies to design new nuclear rockets, mainly for Mars missions.
Major Program Milestones:
Russia and China are also pushing nuclear propulsion forward. Both countries are working on thermal and electric systems for space.
Nuclear thermal propulsion marks a big leap in space travel. Instead of burning chemicals, it heats propellant using nuclear fission.
These systems double the specific impulse of chemical rockets. At the same time, they keep the high thrust needed for deep space missions.
Nuclear thermal propulsion works by sending liquid hydrogen through a reactor core. The reactor heats the hydrogen above 2,500 degrees Celsius, then the propellant blasts out the nozzle.
Inside the core, uranium fuel elements sit in a hexagonal pattern. Designers use low-enriched uranium to make handling safer than highly enriched fuel.
Key NTP components include:
Fuel elements use ceramic-metallic materials that can handle intense heat and radiation. These modern materials replace older graphite designs that tended to crack and erode.
NTP engines reach specific impulse values of 800–900 seconds. Chemical rockets usually stop at 450 seconds.
That extra performance means you need less propellant and can get to Mars faster. Spacecraft can carry bigger payloads without ballooning the launch mass.
With NTP, mission planners can launch during less ideal planetary alignments. The flexibility here is something chemical rockets just can’t match.
The high thrust-to-weight ratio lets astronauts leave Earth orbit quickly. That helps limit how long crews spend in the Van Allen radiation belts.
Handling the heat from nuclear fission is the biggest challenge for NTP. The reactor needs to transfer energy to the hydrogen propellant efficiently, while keeping parts from melting.
Modern NTP engines use advanced cooling channels built right into the fuel elements. Hydrogen flows through these channels, soaking up heat as it passes.
Control rods made from neutron-absorbing materials help regulate the reactor. Operators move these rods in or out to keep the temperature stable at different mission stages.
Critical thermal management features:
Ground test facilities have to trap radioactive hydrogen safely. NASA’s planning to run subscale tests at Stennis Space Center to prove out these safety systems before moving to full-scale engines.
Nuclear electric propulsion turns reactor heat into electricity, then uses that power to run electric thrusters. You end up with a super-efficient propulsion system.
The main parts? You’ve got the nuclear reactor for power, electric thrusters to push the propellant, and conversion systems to connect the two.
Nuclear electric propulsion starts by turning fission heat into electricity, using thermoelectric converters or sometimes dynamic power systems. The reactor burns uranium fuel for heat, and the converters make that into electric current.
Electric thrusters then use the electricity to accelerate ionized propellant at very high speeds. This gives you specific impulse between 3,000 and 10,000 seconds. By comparison, chemical rockets manage only 450 seconds, tops.
The high efficiency comes from how electric thrusters accelerate particles. Ion and plasma engines can fling particles at 30 to 90 kilometers per second. Chemical rockets can’t get anywhere near that—they’re limited to about 4.5 kilometers per second.
Nuclear electric propulsion is a game-changer for deep space. Solar panels just can’t cut it past Mars, since sunlight drops off fast out there.
Ion thrusters are the most established tech for nuclear electric systems. They use electric fields to accelerate xenon ions, giving you thrust between 20 and 250 millinewtons, and specific impulse over 3,000 seconds.
Hall effect thrusters deliver higher thrust density than ion engines but keep efficiency high. They trap electrons with magnets and use electrostatic forces to accelerate ions. Thrust can range from 50 up to 5,000 millinewtons.
Magnetoplasmadynamic thrusters handle the biggest power levels from nuclear reactors. These use magnetic fields to push plasma, generating up to several newtons of thrust. They work best when you’ve got over 100 kilowatts of nuclear power.
Variable specific impulse magnetoplasma rockets can switch between high-thrust and high-efficiency modes. That makes them handy for missions that need both quick maneuvers and long-distance travel.
The nuclear reactor makes thermal energy, but the electric thrusters need electricity. Thermoelectric converters turn heat directly into electricity, but they aren’t super efficient—maybe around 6 to 8 percent.
Dynamic conversion systems get better efficiency by using mechanical generators. Brayton cycles use turbines, and Stirling engines use external combustion. These can hit 20 to 35 percent efficiency.
Power conditioning units make sure the voltage and current are just right for each thruster. Ion engines need high-voltage DC, while other thrusters have their own requirements.
Thermal management is a big deal here. Nuclear electric systems create a lot of waste heat, so radiators have to dump that energy into space and keep everything at safe temperatures.
Nuclear thermal propulsion (NTP) gives you higher thrust with decent efficiency. Nuclear electric propulsion (NEP) offers outstanding fuel efficiency, but the thrust is much lower.
Each one fits a different kind of mission in commercial space.
Nuclear Thermal Propulsion can reach a specific impulse of about 800 to 900 seconds. That’s roughly double what chemical rockets can do. NTP systems generate solid thrust by heating the propellant with a reactor.
The thrust-to-weight ratio is good for quick acceleration. Instead of burning chemicals, you heat the propellant with nuclear energy for faster exhaust.
Nuclear Electric Propulsion gives you a specific impulse from 3,000 up to 10,000 seconds. That’s three to ten times better than NTP. NEP turns reactor power into electricity for ion or plasma thrusters.
The catch? You get a lot less thrust. Electric thrusters shoot out charged particles at crazy high speeds, but the force is tiny.
NEP burns way less fuel than NTP for the same change in speed—up to 90% less propellant. NTP uses more propellant but gets the job done faster.
NTP is great for missions where time matters. Crewed flights get there faster, so astronauts spend less time exposed to space radiation and life support risks. A Mars trip could drop from nine months to three months with NTP.
Heavy cargo missions benefit from NTP’s strong thrust. If you’re building a lunar base or supplying a space station, NTP fits the bill.
NEP works best for long, unmanned missions where saving fuel is more important than speed. Deep space probes can run for decades on NEP.
Commercial satellite deployment and space debris cleanup match NEP’s steady, precise thrust. If you don’t care how long it takes, NEP’s efficiency is unbeatable.
Researchers are always looking past the usual nuclear thermal and electric systems. They’re exploring some wild nuclear propulsion ideas that could totally change deep space travel.
Some of these concepts really stretch what’s possible in physics and engineering. If they ever work, the performance could be out of this world.
Project Orion stands out as one of the boldest nuclear propulsion ideas ever imagined. The system works by detonating small nuclear charges behind a spacecraft, with a huge pusher plate up front to catch the blast and turn it into forward motion.
Engineers designed Orion to drop nuclear pulse units through a hole in the pusher plate. Each charge would explode at a set distance behind the ship. Giant shock absorbers would help smooth out those violent jolts.
Key Performance Metrics:
They figured Orion could hit 3-5% of light speed—fast enough to make interstellar trips possible within a human lifetime. No chemical rocket comes close to that kind of thrust-to-weight ratio.
Modern pulsed nuclear propulsion takes cues from Orion. Researchers now look at fusion pulse systems and smaller-scale nuclear detonations. The goal is to keep Orion’s performance but finally solve the safety and control headaches.
Radioisotope thermal propulsion uses the heat from radioactive decay to warm up propellant gases. Unlike nuclear reactors, these systems don’t need a chain reaction or critical mass.
Plutonium-238 is the usual choice. It puts out steady heat for decades. That heat warms hydrogen or other light gases, which then shoot out for thrust. The system runs continuously and doesn’t need complicated reactor controls.
Advantages over reactor systems:
But the power output is pretty low compared to fission reactors. Most radioisotope systems only produce kilowatts, not megawatts. So, they’re best for small spacecraft and missions that last a long time.
NASA has studied radioisotope thermal propulsion for exploring the outer planets. These systems are great for missions needing steady, low thrust over many years. They keep working long after solar panels stop being useful in deep space.
Nuclear propulsion opens doors for missions that chemical rockets just can’t handle. These systems make longer human Mars trips and deep space robotic exploration possible. They’re also changing the game for satellite operations and lunar missions.
Nuclear thermal propulsion (NTP) can cut travel time to Mars from nine months down to about four. That means astronauts spend half as much time exposed to cosmic radiation. Shorter trips also help with stress and lower the risks.
Nuclear electric propulsion keeps pushing for months or years. This tech lets ships haul more cargo with less fuel than chemical rockets. That’s a big deal for Mars missions—more supplies, more science gear.
NASA’s current programs are all about building nuclear propulsion for Mars trips. These engines heat up propellant with nuclear reactors. The result? About twice the efficiency of normal rocket engines.
These systems let crews bring return fuel and more supplies. Compact reactors can power surface operations on Mars, giving steady electricity even when dust storms or seasons knock out solar panels.
Nuclear electric propulsion is the go-to for outer planet missions. Spacecraft with these engines can reach Jupiter, Saturn, and their moons carrying a lot more science instruments than chemical rockets could ever manage. The engines just keep pushing, building up speed over time.
Robotic missions to asteroids and comets really depend on nuclear systems for their long lifespans. Solar power just isn’t enough out there. Nuclear propulsion lets these spacecraft fine-tune their paths and orbit around distant objects.
Deep space missions need power that doesn’t quit. Nuclear reactors supply steady electricity for comms, science gear, and sending data back to Earth. This stretches mission lifespans from just a few years to decades.
NTP engines help ships escape Earth’s gravity fast. That means less time in the Van Allen radiation belts. They also let missions take direct routes to the outer planets, skipping the complicated gravity assists.
Nuclear electric propulsion is changing how satellites work. Satellites with these engines hold their positions with hardly any fuel. That could mean lifespans of 20-25 years, not just 15.
Lunar missions get a boost from nuclear power too. The 14-day lunar night makes solar panels useless, but nuclear reactors keep the lights on. This is a must for permanent lunar bases and long surface missions.
Nuclear propulsion lets you deploy satellite constellations fast. One launch can drop satellites into different orbits, cutting down on launch costs and the number of rockets you need.
Nuclear-powered space tugs move big payloads between Earth and lunar orbit. They haul construction gear and supplies for moon bases. The high efficiency of nuclear electric propulsion makes regular cargo trips much more affordable.
Nuclear thermal propulsion (NTP) systems need serious safety measures to protect crews from radiation and keep ground operations secure. Agencies enforce strict regulatory oversight for launches, and ground tests have to handle radioactive materials carefully.
Spacecraft designers keep nuclear reactors as far from the crew as possible. Usually, the reactor sits at the back, with propellant tanks in between as extra shielding.
Main shielding approaches include shadow shields that block direct radiation and structural shielding built right into the spacecraft. Shadow shields use dense stuff like tungsten or lead-lithium to create a safe zone behind the reactor.
NTP systems put out both neutron and gamma radiation. Hydrogen-rich materials work best for neutrons, while dense metals handle gamma rays.
Crew exposure limits stick to established space radiation standards. Mission planners have to figure out the total dose astronauts will get—from space itself and from the reactor.
Where you put the reactor compared to the crew matters for shielding mass. More distance means less shielding needed, but it can mess with the ship’s structure and balance.
Nuclear propulsion systems don’t get to launch without a mountain of paperwork. The Department of Energy, NASA, and other agencies go over every safety analysis and risk assessment.
Launch safety rules require that reactors stay subcritical on the ground and during launch. NTP reactors only go critical once they’re safely in orbit, so a launch failure won’t contaminate the ground.
Safety teams look at every possible accident—explosions, bad trajectories, broken parts. They have to prove radioactive material stays contained or that any risk is acceptable.
Environmental impact reviews check for possible contamination at launch sites. Ground teams have to handle radioactive parts safely before launch.
Regulatory reviews can drag on for years. Mission planners have to build these long approval times into their schedules.
Testing NTP systems on the ground makes radioactive exhaust and contaminated gear. Test sites have to capture and process all that waste so it doesn’t get out.
Exhaust capture systems grab hot hydrogen gas and fission byproducts. Special filters and tanks trap radioactive bits before anything escapes to the air.
Test facilities need loads of radiation sensors to monitor contamination. Strict access controls keep people safe during and after tests.
Waste processing deals with contaminated hardware, filters, and other gear. All radioactive waste goes into secure storage or gets disposed of by the book.
Test sites need to be remote, with stable geology and good weather. That keeps the public safe and makes it easier to secure nuclear materials.
Ground tests give engineers vital data on reactor performance and let them prove their safety systems actually work.
Nuclear thermal propulsion relies on advanced materials that can take extreme heat and radiation without falling apart. The fuel forms and ceramic composites you pick decide how well these engines work and how long they last.
NTP systems mostly use uranium-based fuels. Highly enriched uranium (HEU), over 90% enrichment, gives you the most power and performance.
Low enriched uranium (LEU) is safer from a proliferation standpoint. LEU runs between 5-20% enrichment. You need bigger reactor cores, but it’s safer overall.
Uranium nitride (UN) is a top candidate. It has better thermal conductivity than uranium dioxide and can run hotter without breaking down.
Uranium carbide (UC) is another strong option. It handles high temps and thermal shock really well. UC also packs more uranium per unit than oxides.
Composite fuels mix uranium with tough metals. Uranium-molybdenum-tungsten (UN-Mo-W) combos have performed well in tests. These blends help with heat management and last longer.
Ceramic fuel elements are the backbone of NTP reactor cores. They have to survive rapid heating and neutron hits.
CERMET fuels blend ceramic uranium with metal. These hybrids spread heat better and stay stable at high temps. The metal helps move heat around inside the fuel.
Spherical fuel elements are a newer idea. Their shape spreads heat evenly and reduces stress. They also use neutrons more efficiently than rods.
Graphite-based composites do double duty as fuel holders and neutron moderators. They can take temperatures over 2500°C and don’t warp much. Graphite also shrugs off thermal shock.
Beryllium moderators work great for neutrons, making reactors more compact. But beryllium is toxic, so you have to handle it with care.
Nuclear thermal propulsion systems need a lot of testing before anyone trusts them with people on board. Most current research focuses on ground-based reactors and in-space demos planned for the late 2020s.
NASA and DARPA are teaming up on the DRACO program, which is the biggest nuclear propulsion effort right now. They want to fly a nuclear thermal rocket in space by 2027.
The DRACO engine uses a fission reactor to heat liquid propellant, which then expands through a nozzle for thrust. Engineers think this setup is about three times more efficient than chemical rockets.
NASA’s Space Technology Mission Directorate works on the engine. DARPA takes care of spacecraft integration and the overall timeline. It’s a partnership that mixes NASA’s nuclear chops with DARPA’s fast-paced style.
Nuclear electric propulsion research is happening alongside thermal systems. Here, reactors make electricity for ion thrusters. This tech is super efficient for long missions.
New aerospace materials are making a difference. They can take higher temperatures and more radiation, which makes nuclear space systems more realistic than they were back in the 1970s.
Testing facilities have to handle radioactive materials with care. Engineers use ground tests to check reactor performance before anything ever leaves Earth.
By 2028, teams plan to run comprehensive tests on power systems. Right now, most of the focus lands on fuel element performance.
Researchers dig into how uranium fuel acts when pushed to extremes. They test fuel with temperature cycling and radiation exposure to make sure it holds up during missions.
NTP systems need pretty specialized facilities. These places require serious radiation shielding and remote handling gear.
NASA teams up with the Department of Energy to work on building out these test sites. It’s a big job, and not a quick one.
Computer simulations play a big part, too. Advanced modeling helps predict how reactors might behave once they’re in space.
These simulations can cut down on how much physical testing is needed, but still keep safety front and center.
Testing takes years before anyone thinks about flying. First, engineers run component tests, then move to full system checks.
It’s a slow, methodical approach, but it’s all about keeping future passengers safe.
Nuclear propulsion brings tough engineering challenges in reactor design and fuel management. Political pushback and environmental safety worries add more obstacles.
Designing nuclear thermal propulsion (NTP) systems that can survive space isn’t easy. Reactors have to handle wild temperature swings, radiation, and the vacuum, all while keeping control systems working smoothly.
Heat Management Issues
Nuclear reactors crank out intense heat that can fry spacecraft parts. Engineers need to invent cooling systems and materials that can take temperatures over 2,500 degrees Celsius.
Fuel and Reactor Complexity
Modern NTP systems use special low-enriched uranium fuel, which costs way more than chemical propellants. Reactor cores have to be tiny but still powerful enough to heat the propellant.
Weight and Size Constraints
Reactors and their shielding add a lot of weight. That extra mass cuts into payload space and makes mission planning trickier—especially if you want to keep a crew safe.
Limited Testing Infrastructure
Testing nuclear propulsion on the ground needs rare and expensive facilities. Not having enough sites slows everything down and drives up costs for both space agencies and private companies.
A lot of people still fear nuclear tech, which makes political support tough to get. Many folks link nuclear power with disasters or weapons, so government funding is a hard sell.
Regulatory Complexity
Launching nuclear materials means jumping through hoops with multiple agencies and international groups. Reviews and approvals can drag on for years.
Launch Site Restrictions
Nuclear-powered launches call for special facilities with extra safety systems. That limits where launches can happen and squeezes mission flexibility for both governments and private companies.
Radioactive Waste Management
Nuclear propulsion creates radioactive waste that needs safe handling in space. Scientists still haven’t cracked what to do with this waste on other planets or in deep space.
International Treaty Concerns
Space nuclear tech raises flags about possible military uses. International agreements have to balance these concerns while still letting peaceful exploration move forward.
Nuclear propulsion is inching toward big milestones, with ground tests set for 2028 and space demos by 2030. Aerospace giants and government agencies are teaming up, aiming to use these systems for Mars missions and deep space exploration.
Nuclear propulsion tech is moving fast, with DARPA and NASA’s DRACO project planning demonstrations as soon as 2027. Lockheed Martin is building test systems to show off nuclear thermal propulsion in space.
The current timeline targets ground testing by 2028 and space demonstrations by 2030. These steps are crucial for getting operational nuclear propulsion systems ready for deep space.
Engineers still have some tough problems to solve before this tech goes commercial. They need materials that can survive harsh nuclear, chemical, and thermal conditions.
The industry also wants better modeling and more test data. That’s not easy, but it’s doable.
Key development priorities include:
Nuclear thermal propulsion could be two to five times more efficient than chemical rockets. That’s a game-changer for Mars or deep space.
Space agencies are looking at nuclear propulsion for three main uses: spacecraft propulsion, surface power generation, and onboard energy. NASA’s roadmap calls nuclear systems essential for lunar and Mars surface missions.
Right now, radioisotope power systems give reliable, low power for robotic explorers. Future nuclear systems will need to scale up for human missions needing much more juice.
Mission integration focuses on:
The International Space Exploration Coordination Group points out nuclear tech gaps to fix by 2040. Both radioisotope decay and nuclear fission will power future missions.
International cooperation will be key. Agencies are working together on safety protocols to protect space and still push exploration forward.
Nuclear space propulsion brings up a lot of tough questions—reactor designs, thrust generation, and all sorts of practical hurdles. People want to know how these nuclear systems actually work in space, what progress exists, and what engineering headaches still remain.
Nuclear thermal propulsion heats propellant—usually liquid hydrogen—directly with a nuclear reactor. The hot propellant blasts out a nozzle and creates thrust.
Nuclear electric propulsion works differently. Here, the reactor makes electricity, which then powers electric thrusters like ion or plasma engines.
The thrust characteristics really differ. Nuclear thermal propulsion produces high thrust, similar to chemical rockets, but it’s way more fuel-efficient.
Nuclear electric propulsion gives very low thrust but can run for months or years straight. Each system fits different missions: nuclear thermal is great for fast crewed trips, while nuclear electric works best for cargo or science missions that aren’t in a rush.
A nuclear thermal rocket has a reactor, propellant tank, heat exchanger, nozzle, and controls. The reactor uses uranium rods to start controlled fission, which creates a ton of heat.
Liquid hydrogen flows through the reactor core and soaks up that heat. The propellant gets super hot—over 2,500 degrees Celsius—and expands fast.
That superheated hydrogen shoots out the nozzle at speeds over 9,000 meters per second. The high-speed exhaust pushes the rocket forward, thanks to Newton’s third law.
Special materials like tungsten and ceramics keep the reactor together at those crazy temperatures. Control rods let engineers adjust the nuclear reaction and dial in the thrust.
Managing extreme heat is the main headache for nuclear rocket engineers. Reactor parts have to survive temperatures that would melt most metals.
Radiation shielding adds a lot of bulk and complexity. Crews need heavy barriers to stay safe from radiation while the engine’s running.
Handling nuclear fuel creates logistical complications for launch operations. Ground teams need special training and gear to stay safe around radioactive stuff.
Getting regulatory approval can take ages. Multiple agencies have to sign off on safety and environmental plans before any nuclear launch.
Public worries about nuclear launches can stall funding and support. Even with all the safety measures, a lot of folks just aren’t comfortable with it.
NASA and DARPA are working together on Project DRACO to test nuclear thermal propulsion in cislunar space. The project aims to show the reactor and safety systems can actually perform in space.
Back in the 1960s and 1970s, NASA ran the NERVA program and did a ton of ground testing. Those tests proved nuclear thermal propulsion could work and set the foundation for today’s designs.
Modern computer modeling lets engineers simulate how a reactor will behave in all sorts of conditions. These tools help optimize designs and test safety systems before anyone builds hardware.
NASA researchers now focus on making reactors smaller and lighter. New manufacturing techniques help with better heat transfer and fuel use.
The agency sees nuclear propulsion as essential for future crewed Mars missions. Nuclear systems could cut travel time from nine months to just three or four.
SpaceX’s manufacturing style could really slash costs for nuclear propulsion. Their focus on reusable parts and fast production might work for building reactors, too.
With Starship’s heavy-lift muscle, SpaceX could launch bigger, better-shielded nuclear spacecraft. More payload means more options.
Their quick development cycles could speed up nuclear testing. SpaceX isn’t afraid to try, fail, and try again—unlike some traditional aerospace players.
Private companies jumping in could bring more investment and fresh ideas. Competition tends to light a fire under innovation, doesn’t it?
SpaceX’s Mars dreams line up perfectly with nuclear propulsion. Nuclear systems are just what’s needed to make regular trips to Mars a reality.
Submarine nuclear reactors work underwater, where water naturally cools the system and shields against radiation.
In space, reactors have to run in a vacuum, so they miss out on those perks.
Naval reactors just keep going for months, sometimes years, holding steady at the same power level.
Space nuclear systems, on the other hand, need to start up, shut down, and adjust power a lot during missions.
Submarines rely on pressurized water to pull away heat and manage neutrons.
Space systems usually switch to gas cooling and handle neutrons differently.
Maintenance is a whole different story. Submarines can just sail back to port for repairs.
But space reactors? They need to keep running without any hands-on maintenance the entire time.
Safety brings its own challenges. Submarine accidents mostly affect the local area.
If a space reactor fails, it could add to orbital debris or cause trouble during reentry.
