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Engine RoomWhat's in the engine room? Remember, outside the engine room hatch will be a decontamination booth. And I'm sure over the hatch will be mounted an alarm with a red rotating light, so you don't have to put your ear on the bulkhead to hear Astro say "oops!". Past the hatch will be a short corridor, with a dog-leg bend in it, so you can get in but radiation cannot get out (radiation has to travel in straight lines, but crewmen can zig-zag). Be sure you are wearing your dosimeter. |
 Waldo by Robert A. Heinlein, 1940
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 The various controls, tongs, and remote control "waldoes" will reach around or penetrate the anti-radiation shadow shield, and there may be auxiliary lead baffles. Peeking around the baffles is how Rhysling lost his sight in Heinlein's "The Green Hills of Earth". |
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Remember that the shadow shield will be in the floor, with the engine below that. Closed-circuit TV monitor will help Astro see what he is doing, but if they are damaged, he'll have to make do with mirrors and/or doing it by touch. What he really needs is one of Tom Swift Jr.'s Giant Robots, which were designed to do maintenance inside nuclear power plants. There is more about robots here. |
 Galaxy magazine, July 1952
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 Canadarm 2 socket. Each socket provides the arm with power and a
computer/video link to astronaut controllers inside.
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For external repairs, the chief engineer might use something similar to the amazing Canadarm 2, which is currently on active duty on the International Space Station. Unlike the first Canadarm, this one is not attached at either end. Instead, either end can plug into special sockets ("power data grapple fixtures") built at strategic spots on the surface of the station. Canadarm 2 can literally walk on the surface of the station to where it is needed, moving end-over-end like a giant metal inch worm. The main limitation is that each "step" must end at a socket, but this is due to power and control signal issues. A more advanced version might be self contained enough to not require sockets, just hand-holds or other protrusions that it could grab. Canadarm 2 is quite large, 17.6 meters (57.7 feet) long when fully extended. On your atomic rocket, one would use arm(s) long enough to reach any spot on the radioactive engine. |
The main engine controls will be the dampers. In a NERVA engine, these are rods of cadmium or other neutron poison inserted or removed from the reactor to control the chain reaction. Make sure they are not warped. A non-automated set-up will have the dampers positioned by hand using a "multiplying vernier" and a danger gauge. The gauge tells you how hot the reaction is. Verniers tell how far a given damper has been inserted into the reactor. Pull the dampers out slowly until the danger gauge tells you the reaction is at the desired level. A vernier is what they used to use back in the ancient days before digital read-outs. Standard gauges have a pointer that runs along a scale. A vernier is a clever way to increase the accuracy of the scale.
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In some NERVA designs, instead of rods of cadmium inserted into the body of the reactor, they instead have drums imbedded in the neutron reflector around the body of the reactor. One side of the drums are composed of neutron reflector, the other side is composed of neutron absorbers (AKA "neutron poison"). If the reflector side of the drums are facing the reactor, enough neutrons are reflected to sustain the chain reaction. If the absorber side is facing, it sucks up the neutrons and there are not enough neutrons to sustain the reaction. The control drums are rotated to partial positions in order to throttle the reaction to desired levels. |
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In both cases you want a damper fail safe, so if anything happens the failure modes will tend to make the dampers slam in to the full "quench reaction" position. There will be damper safeties. When no acceleration is expected for some time, these lock the dampers in the full-quench position. |
 Core is gold, drums are blue, with a green neutron-poison segment.
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From "Transit of Earth" by Arthur C. Clarke (1971)
The countdown was still at ten seconds when we were startled by a blast of light. For a moment, we wondered if Olympus had also met with catastrophe. Then we realized that someone was filming the take-off, and the external floodlights had been switched on.
During those last few seconds, I think we all forgot our own predicament; we were up there aboard Olympus, willing the thrust to build up smoothly and lift the ship out of the tiny gravitational field of Phobos, and then away from Mars for the long fall sunward. We heard Commander Richmond say "Ignition," there was a brief burst of interference, and the patch of light began to move in the field of the telescope.
That was all. There was no blazing column of fire, because, of course, there's really no ignition when a nuclear rocket lights up. "Lights up" indeed! That's another hangover from the old chemical technology.
But a hot hydrogen blast is completely invisible; it seems a pity that we'll never again see anything so spectacular as a Saturn or a Korolov blast-off.
 Control drums and actuators in green, gimbals in blue
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In a 1969 US Atomic Energy Commission pamphlet on NERVA, it had this to say: A critical structural problem arises at the junction between the engine and rocket body, however. Across this junction must be transmitted the entire engine thrust that is conveyed upwards from the nozzle through the engine exoskeleton. Ordinarily, such a joint would present no engineering difficulties. But in this case, the joint must be flexible. All big rockets have their engines mounted on gimbals that permit the "driver" to steer them. Gimballing chemical engines is relatively easy because they are lightweight. But, in a nuclear rocket, the heavy reactor replace the empty combustion chamber of the chemical rocket. Despite the added weight, suitable flexible joints now have been designed. |
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In the images here, the gimbals are the network of blue rods emerging from the bottom of a hydraulic piston. The wasp-waist in the center is the pivot. The green "mushroom caps" are the control-drum actuators, perched on top of the control drums protruding from the reactor. Note that the gimbals are a nasty trouble spot. If one jams, that engine cannot be steered. The proximity to the dangerously radioactive engine makes repair difficult. This is a good place for a waldo. |
 Control drums and actuators in green, gimbals in blue
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There will also be controls for the flow rate of propellant, and pyrometer (temperature) gauges with red bands marked "DANGER - MELTDOWN IMMANENT!". There will be a large red "discoverer" button which activates the "there's been a nuclear oopsie" alarms, right next to the even bigger button marked "SCRAM", which is the emergency reactor shutdown.
But there will be one even bigger red button, marked "PANIC!". This one activates the explosive bolts and JATO units that jettison the reactor out the stern of the spacecraft, hopefully removing the spacecraft from the lethal radius. The reactor isn't going to explode like a nuclear weapon, it will just act like a midget neutron bomb, utterly destroying all life on the ship except for the cockroaches.
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Around the engine deck will be auxiliary propellant tanks. The main tanks provide propellant, which is also used to cool the reactor and keep it from melting. In case something happens to the main tanks, the auxiliary tanks give Astro a few precious seconds of coolant time so he can scram the reactor. The engine deck will also have some kind of Geiger counter to warn the crew of a radiation leak. There will also be controls for the ship's power plant, whether the power is tapped from the propulsion system or from a separate unit. Outside but adjacent to the engine deck will be the maintenance shop and storage for replacement parts. On larger ships this might be the place for damage control central. |
 from Spaceways (1953)
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From Jovian Confederation: Ships of the Fleet, Vol 2 by Dream Pod 9.
Rather than carry many extra tons of spare parts, which might or might not be used, the ship is equipped with extensive workshops to repair or manufacture the required parts as they become needed by the maintenance crews. Each workshop features a large number of automated machine tools and precision autofacs that hold the specifications of all parts in memory. Only the most sensitive and specialized parts, such as the microscopic computer nodes and chips, are held in storage.
The microgravity stations are sealed transparent bays with built-in gloves. Items to be repaired are slipped inside through a zippered opening, and can then be disassembled without fear of small parts flying off. Tools can also be left floating free inside the enclosure rather than having to be tethered. Machine tools are housed within similar enclosed bays for safety and tidiness reasons; articulated arms hold the part while it is being machined.
(ed note: I will observe that enclosures make sense from the standpoint of eye safety. You do NOT want to have a free-floating metal shaving getting into your eye. However, it is not a good idea to have one's tools untethered if unexpected spacecraft accelerations can occur.)
The machinery, decks, and walls will have lots of access panels to allow the engineers to make repairs. If the machinery is large, there will be ladders and catwalks. The lighting will also be bright and harsh. The walls will have tool bays, spare parts lockers, fire control gear, and similar items.
The engineers will also have lots of interesting things in their tool boxes.
The engineering deck is likely to be a noisy place, with all the heavy machinery. Engineers might need ear-plugs, and good lip-reading skills. If the situation is more high-tech, they will wear combination radio/hearing protection headsets.
The engineer has a logbook as well.