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In a world where there are strict controls on "computational and instruction following machines" (all calculation machinery are basically none reprogrammable and limited to specific narrow tasks - frequently mechanical or nomograms/slide rules ) how would such laws effect regular travel to Earth/Sun L4/L5 (specifically not Luna/Earth L4/L5)

Assuming a technological level that doesn't have warp drives or hyperspace (or other magic), but must use a reaction drive (some kind of rocket expelling mass) what would be a reasonable travel time to Earth/Sun L4 or L5 from Luna orbit (assuming you need low velocity on arrival)

Is there any useful abort path at roughly the halfway point or somewhere between say approx 1/3 and 2/3 the journey) ? relying on what if any sling shot effect or other orbital mechanics effect. (remembering this worlds IT controls and rocketry)

what would be a reasonable return strategy and time taken (could a departure be done at any time or would it be safer to wait for specific conjunctions - again because of IT restrictions or fuel/mass concerns )

what are the main differences between L4 and L5 journey and are these roughly cancelled by a return leg?

While I've experimented with scaled up mods for kerbal space project to get a feel for time scales vs delta v / fuel tonnages etc, I'm fairly sure ksp's gravity model doesn't include Lagrange points as you are only ever in one "sphere of influence"

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    $\begingroup$ I'm not seeing why travel time would change for a non-reprogrammable computer. Clearly it can branch, otherwise you wouldn't have an abort path, which is all most programs will do. Can you explain why you think it makes a difference? Do you reckon that space probes often reprogram themselves? $\endgroup$
    – Samuel
    Jul 15, 2015 at 22:55
  • $\begingroup$ You miss read my question in an impressive number of ways! Abort path is vehicle path, computers are usually mechanical for production of tables, electronics never on ships only in very closely regulated environments, time taken longer possibly because need to rely on specific conjunctions for ease of calculation and anyway how long would it take? $\endgroup$
    – Chris Camacho
    Jul 16, 2015 at 0:51
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    $\begingroup$ No, I don't believe I misread your question. Though you may have misread my comment. If all you're asking for is the launch windows to the Earth Sun Lagrange points, they occur daily. This, interestingly, is independent of the capability of the on board control system. My previous question remains. $\endgroup$
    – Samuel
    Jul 16, 2015 at 1:48
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    $\begingroup$ When in an orbit, you are only ever in a single sphere of influence. Wikipedia sums it up nicely in the introductory section: A sphere of influence (SOI) in astrodynamics and astronomy is the oblate-spheroid-shaped region around a celestial body where the primary gravitational influence on an orbiting object is that body. (My boldface.) There can only ever be a single primary source of gravitational influence. Lagrange points are, basically, what you get at the boundary between two SOIs. $\endgroup$
    – user
    Jul 16, 2015 at 15:33

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I think your question is too broad so I will focus on your request on travel durations.

Do you only have access to mechanical computers?

  • Yes: it is not likely your society would ever space travel.
  • No: it would take the same travel durations as we know.

Explanation

Your non-reprogrammable computer is very much like the chips we human beings can produce: it's programmed when it is fabricated. Since we know we can build mechanical computers which are Turing-complete, I can confirm your people would have no theoretical problems to safe travel to Moon-Earth or Earth-Sun Lagrange points with very similar programs we find in actual rockets.

Realistically and if they have nothing but mechanical computers they would certainly have to optimise them an awful lot but I'm not persuaded they could obtain anything capable of controlling a space rocket attitude fast enough.

If they have semiconductors (or something similar) but nothing reprogrammable then I think it would much depends on your people propelling mechanisms than their computational power.

Furthermore I'm practically sure that rockets don't need reprogrammable chips to work properly. PLDs are generally used for safety, tests, debugging or optimisation but I don't think that it is an essential feature in space-travelling.

We went to the moon with computers you can find in your car today.

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    $\begingroup$ If you believe the question is too broad, then please don't answer it. Instead, comment to have it narrowed down, and flag (or once you have the necessary reputation, vote to close) as too broad. $\endgroup$
    – user
    Jul 16, 2015 at 15:39
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The question actually has two answers, and they are both "it depends".

For how long it takes to get to the Earth Sun trojan points, that depends on both orbital mechanics (for example, are you going there directly, or are you planning to use some sort of orbital manoeuvre like "slingshotting" around Venus?), and the nature of your drive system. A solar sail may take a long time just to spiral out of the Earth's gravity well, while a nuclear thermal rocket will be able to blast away fairly quickly. Since we don't know "how" you intend to get to the Trojan point, I suggest you look up the Atomic Rockets website to get some background on the sorts of engines available. the site is also full of links, there may be tables or links to online calculators which will provide a rough approximation of the trip time.

Using a calculator or computer is great because they are very fast and very convenient. You can navigate throughout space without a computer, though, much like the navigators of old did, by using sightings of the stars. This presupposes someone on Earth may have access to a Babbage Machine to do the initial calculations and create a star table for the pilots to use with their sextants (or astrolabes). The Apollo 13 astronauts famously improvised a similar system by sighting on a limb of the Earth as they approached, so there are possibilities.

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Rockets that we use today have a need for precise guidance systems due to the fact that they just barely have enough fuel to get where they need to go. Due to the rocket equation, there is a huge penalty to be paid for taking along extra fuel. If you can have a rocket ship that has lots more fuel than it needs to have in order to get its destination, then you can compensate for your lack of precise navigation. To do this might require a rocket on the order of 10 to 20 times larger than the rocket that would be required using precise guidance. Of course in reality, rockets use computers for all sorts of other thing besides just navigation.

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Sure, it's possible. They'll just have to fly their rockets like the scifi stories from the 20s and 30s imagined the men of the future flying their rockets: with gauges on their equipment to tell them things like the thrust of the rocket and the amount of fuel remaining, telescopes with measurement devices to calculate the position of the orbital bodies, along with paper, pencils, books full of printed tables, and slide rules to work out the mathematics of the orbital transfers.

As for things like travel times, it depends on the sort of rocket your rockets are using. It could vary from months to days, depending on how your rockets work and how much fuel your rockets have. Similarly, whether or not you're able to turn back or divert to an alternate destination also depends on how your rockets work. There's a lot of math involved, and the numbers in question can vary quite widely depending on a number of factors (amount of fuel/propellant, velocity of propellant, thrust-to-weight ratio, etc).

Here's the engine list page of a rather good website that talks about these sorts of things in detail, with tables of all the numbers laid out for you if you want to go become as realistic as possible:

http://www.projectrho.com/public_html/rocket/enginelist.php

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