Decks: Astrogation Deck

Astrogation Room

What's in the astrogation room? Everything needed for interplanetary navigation. Instrument to determine the ship's current trajectory and calculating devices to plot new trajectories. There will be an incredibly precise chronometer. A periscope sextant to take navigational readings, with its azimuth ring. (In THE REVOLT ON VENUS, this is what Roger Manning was looking through when he noticed the atomic bomb attached to the Polaris' tail) In addition to the sextant, there also might be a goniometer, which is used to measure angles. A good-sized telescope, either in a dome or with a coleostat. (The periscope, the telescope, or both will be equipped with a filar micrometer.) The big radar scope.

Maybe an "astrodome", which is a blister dome of some strong but transparent material used with a manual sextant as a back-up to the periscope. (Note that astrodomes cause optical distortion that need a mathematical correction.) Star trackers, star scanners, solar trackers, sun sensors, and planetary limb sensors and trackers. Inertial tracking repeaters (note that the inertial tracker platform will have to be manually realigned every twelve hours because it tends to drift. The star tracker is used for reference.). An indicator of the spacecraft's current mass ratio. Doppler radar and radar altimeter. An integral audio recorder and a log book for radio messages and navigational fixes.

Communication gear, perhaps even with something like a Morse code key for use when radio interference becomes a problem (If this was a Metalunan ship, this is where you'd find the interociter).

There might be a separate communications room, which is generally called a "radio shack." If this is a military spacecraft this might be the place for the safe containing the code book. Hit the red "incinerate" button to keep the one-time pad and Captain Midnight secret decoder ring from falling into enemy hands. On some ships this safe might be in the captain's cabin.

If there is an astrodome, the room will have alternative lighting that is all red, like a darkroom. This is to preserve night vision. It should also have a retractable shield. This is to preserve day vision in case the rotation of the ship moves the eye-destroying fury of the Sun into view. The shield is not only useful to keep sunlight out, but to keep the atmosphere in, in case the astrodome is breached or shattered.

If the ship spins on its axis for artificial gravity, it might be a good idea to locate the astrodome in the nose of the ship, i.e., at the center of the axis of rotation. A tiny room with the astrodome in it could be counter-spun. So while the ship was spinning, the room would be stationary, freeing the astrogator from the difficulty of making observations of a sky that is madly spinning about. It is possible to rig in a coleostat a shutter that is synchronized with the spin of the ship. This will provide a stroboscopic but steady image if you cannot counter-spin the astrodome.

If the ship is advanced enough to have an actual centrifuge, instead of spinning the entire ship, things will be easier. Just make sure the astrodome is on the stationary part of the ship.

If this is a pre-transistor ship, there will be a ballistics integrator, a current ephemeris, a book of nine-place logarithms, a large circular slide rule, special purpose navigation slide rules, books of nomograms, rulers, dividers, protractors, pads of light green Keuffel & Esser graph paper, realms of scratch paper and lots of pencils. And a pencil sharpener designed to capture every last shaving. You don't want electrically conductive bits of graphite floating into the circuitry. The ballistics integrator is an analog computer. It uses using tiny electric motors to drive mechanical shafts and gears - to position shafts to represent some mathematical value, and drive cams shaped to represent mathematical functions or statements. It is used to solve navigational equations.

If it is a post-transistor ship, there will be a computer with navigational software. Period. Actually there will still probably be manual equipment, in case the computer gets fried by a solar storm or the EMP from a near miss by a nuclear weapon. A slide rule will be in a box on the hull, with a sign that says "In case of EMP, break glass."

Remember that early computers are going to give their results by spitting out Hollerith punch cards, punched tape/ticker tape, or printed fanfold sheets. Standard CRT monitors displaying text come later, and monitors with cute graphic user interfaces come later still.

Computers, whether analog or digital, should be of the 'I-tell-you-three-times' variety. It is actually three computers, each of which does the calculation. If operating perfectly, all three answers will be the same. If a malfunction occurs, two answers will agree and one won't. Use the answer the two agree on, which will allow you to get though the burn. Then fix the bad computer, pronto! If all three disagree, it's time to break out the slide rule.

These will be used to calculate the course change burns: level, start and stop times, and vector in the form of the guide star settings. If this is a pre-transistor ship, all the books, slide rules and whatnot should be magnetized to stick to the desk, be on tethers, under elastic straps, or otherwise restrained so they don't float around the room. (Or turn into deadly missiles if the spacecraft has to abruptly accelerate. Spacers have a fastidious horror of unsecured objects.) For Tom Corbett fans, the ephemeris is the functional equivalent of Roger's space charts.

Other critical instruments might be in triplicate as well. If you have one clock, you know the time. If you have two clocks, you are never quite sure, since they probably won't agree with each other. But if you have three clocks, you take a reading from the two clocks with values closest to each other, and assume that the actual time is somewhere in between.

Say Roger want's to fix the position of the Polaris. From the ephemeris he knows where Terra is, and thus the Sol-Terra line. The ephemeris also tells him where Venus is, and thus the Sol-Venus line. Roger uses the periscopic sextant to measure angle A and angle B. With simple geometry the Polaris' current position is fixed. Of course this is an approximation based on assuming that everything is in the plane of the ecliptic. If the course gets more three dimensional a third angle will be required.

The spacecraft's velocity isn't quite so simple. If you are close to a planet, you can use Doppler radar. Otherwise you will have to wait a while, make a second position fix, and calculate what the velocity had to be.

In a dense asteroid drift a variable-baseline stereoscopic radar could come in handy. Look through the double eyepiece and you'll see the surrounding asteroids in 3-D. Use the sweep control to pan the view fore, aft, port, or starboard. The pilot might have one of these as well.

If you are close to a planet, the distance to it can be determined by radar. Further away, the filar micrometer in the periscope can be used to determine the angular size of the planet. Since the planet's diameter is known, simple trigonometry will yield the distance. A filar micrometer is an instrument mounted in a telescope. It displays two cross hairs that can be positioned with dials (one dial rotates the micrometer, the other adjusts the distance between the two cross hairs). Once set, the angular separation between the two cross hairs can be read from the scale.

The author's father, Major Winchell D. Chung, (ret.) used to be the navigator/bombardier officer on a SAC B-52 aircraft. He wrote the following notes about using a periscope sextant:

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