There is more than one way to see the truth...
The alternate reality around us.
Doing some plotting in my head for a background scene in one of my alternate world novels ( yes I do that a lot, with the intention of reaching deeper into my scenario rather than using the scene in a novel ) I came across a huge reality gap in most science fiction scenes of planetary arrival.
My scenes first. My modern people have been stranded on an alternate earth, with a culture very like our timeline in the early 1700s. On the first ocean voyage in a sailing ship that has been recaptured from the nasties Zak Ascher, a naval reserve officer from back home, is showing the locals the way to navigate with a sextant and chronometer. (Well, the sextant could come from stores, but his time signals come by radio from the starship – now low on fuel and supplies and relegated to be a space station in a stationary orbit.)
At first I saw no difficulty, the sights are taken at local noon, latitude comes from the date and the sun's altitude, longitude comes from the time the sun crosses the noon meridian. Wait a minute . . . the time difference between local and the zero meridian has to be multiplied by 15 (the number of degrees the earth rotates in an hour) to get the longitude . . .. But when did my people ever fix a zero longitude here, the prime meridian?
How could one fix a prime meridian and determine the time of noon on it from space? Some astronomer or surveyor needs to be down there to take those observations. For that matter, latitude is also a problem, how can newcomers determine a table of the declinations of the sun (the amount it swings from one hemisphere to the other during the year) without having set up an observatory to measure it? No big problem for the author, just mention somewhere in a scene when they start establishing such standards, and Zak can astound everyone with the precision of his plotting.
Now we come to every other SF novel that has Dan Dare, the hero, blasting in from space to land on a planet. Is he going to blast straight in? Rotate the spaceship and let himself down to the surface on his rocket thrust? Not if rocket fuel is $3 a gallon, and he needs to save some to go back home. If he pays his own bills he'll do what our astronauts do and use an atmospheric re-entry to kill off all that kinetic energy by friction in the atmosphere.
Means he must know the rate of rotation of the planet, the axis of its rotation, and its circumference – he needs to begin his re-entry from some location in an orbit that will bring him to the surface within spitting distance of his objective. If the planet is inhabited and has a spaceport, he should be able to learn all this from the local traffic control. They'll direct him into an appropriate orbit – stacked in a holding pattern above the starship from the horsehead nebula filled with retirees on their anniversary cruises, and underneath the big freighter loaded with deuterium from the watery satellite of a nearby gas giant – and give him the planet-centered coordinate values, and Keplerian elements he needs to set his autopilot for landing.
On a world no one has ever visited it would be somewhat more difficult. He has to do all that himself. He would need to do enough orbits to measure the mass of the planet (for its g value – very necessary for calculating decelerations); to locate the axis of rotation; to determine the coordinates of his intended landing spot and figure some way to fix the coordinates of the point he must begin his re-entry next orbit; check for gravitational anomalies (humps and bumps in the geoid, as our earth has); and a whole batch more things I won't try to mention as well. But Dan Dare never has that problem – he just switches on his Windows 5400 notebook and selects his planet analyzer while he's still parsecs away. Then he blasts right in as if Exxon has a service station down there, right where he needs to land. Science Fiction? And they call wizards and magic fantasy!
Chris.
My scenes first. My modern people have been stranded on an alternate earth, with a culture very like our timeline in the early 1700s. On the first ocean voyage in a sailing ship that has been recaptured from the nasties Zak Ascher, a naval reserve officer from back home, is showing the locals the way to navigate with a sextant and chronometer. (Well, the sextant could come from stores, but his time signals come by radio from the starship – now low on fuel and supplies and relegated to be a space station in a stationary orbit.)
At first I saw no difficulty, the sights are taken at local noon, latitude comes from the date and the sun's altitude, longitude comes from the time the sun crosses the noon meridian. Wait a minute . . . the time difference between local and the zero meridian has to be multiplied by 15 (the number of degrees the earth rotates in an hour) to get the longitude . . .. But when did my people ever fix a zero longitude here, the prime meridian?
How could one fix a prime meridian and determine the time of noon on it from space? Some astronomer or surveyor needs to be down there to take those observations. For that matter, latitude is also a problem, how can newcomers determine a table of the declinations of the sun (the amount it swings from one hemisphere to the other during the year) without having set up an observatory to measure it? No big problem for the author, just mention somewhere in a scene when they start establishing such standards, and Zak can astound everyone with the precision of his plotting.
Now we come to every other SF novel that has Dan Dare, the hero, blasting in from space to land on a planet. Is he going to blast straight in? Rotate the spaceship and let himself down to the surface on his rocket thrust? Not if rocket fuel is $3 a gallon, and he needs to save some to go back home. If he pays his own bills he'll do what our astronauts do and use an atmospheric re-entry to kill off all that kinetic energy by friction in the atmosphere.
Means he must know the rate of rotation of the planet, the axis of its rotation, and its circumference – he needs to begin his re-entry from some location in an orbit that will bring him to the surface within spitting distance of his objective. If the planet is inhabited and has a spaceport, he should be able to learn all this from the local traffic control. They'll direct him into an appropriate orbit – stacked in a holding pattern above the starship from the horsehead nebula filled with retirees on their anniversary cruises, and underneath the big freighter loaded with deuterium from the watery satellite of a nearby gas giant – and give him the planet-centered coordinate values, and Keplerian elements he needs to set his autopilot for landing.
On a world no one has ever visited it would be somewhat more difficult. He has to do all that himself. He would need to do enough orbits to measure the mass of the planet (for its g value – very necessary for calculating decelerations); to locate the axis of rotation; to determine the coordinates of his intended landing spot and figure some way to fix the coordinates of the point he must begin his re-entry next orbit; check for gravitational anomalies (humps and bumps in the geoid, as our earth has); and a whole batch more things I won't try to mention as well. But Dan Dare never has that problem – he just switches on his Windows 5400 notebook and selects his planet analyzer while he's still parsecs away. Then he blasts right in as if Exxon has a service station down there, right where he needs to land. Science Fiction? And they call wizards and magic fantasy!
Chris.
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