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Background:

In the early 22nd century, a laser station has been established on Uranus' moon, Cordelia to shoot chunks of frozen deuterium into the inner solar system for fusion fuel. However, the single laser also needs a relay in case Earth is behind the Sun or otherwise inaccessible. This relay station needs to generate a laser beam to redirect and decelerate the small chunks of deuterium payload either to arrive at the station or to be redirected towards Earth. For maximum angular separation from the Sun and Earth as seen from Uranus, this will be positioned somewhere in the Saturn system.

Now, to get to the meat of the question. Where exactly should I put it? The surface and in-orbit options on the airless moons of Saturn both have their advantages and disadvantages, but I wonder which one is actually superior in terms of designing as efficient and light station as possible.

TL;DR: Factors to consider are 1) mass of station with cooling equipment, any thrusters, etc. and 2) optimum position for relay of energy.

Thank you for your input!

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    $\begingroup$ Deuterium's not prohibitively expensive, and can be produced pretty much anywhere you have hydrogen compounds.70% of the Earth's surface is covered by one such compound, water. $\endgroup$ – notovny Aug 19 '20 at 18:59
  • $\begingroup$ Why use deuterium to power fusion when there's a ginormous fusion engine that already powers the entire planet? At the point you can build this sort of infrastructure, you should be able to use beamed microwave power from orbital satellites. Although apparently just a ground-based solar array would do better.... $\endgroup$ – Clockwork-Muse Aug 19 '20 at 23:28
  • $\begingroup$ @Clockwork-Muse I am already doing this for civilian power in the story, but in this case I am focused on providing fusion fuel for starships. $\endgroup$ – Lelu Aug 20 '20 at 17:02
  • $\begingroup$ @Clockwork-Muse the required microwave energy for flight of an aircraft over the surface area of said aircraft is typically enough to melt said aircraft. $\endgroup$ – BMF Aug 20 '20 at 21:21
  • $\begingroup$ @BMF - yeah, and? That's why you don't put it on an aircraft in the first place, you give them batteries charged by a ground station instead. $\endgroup$ – Clockwork-Muse Aug 20 '20 at 21:56
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Put English on it.

One laser is enough. It can be precisely aimed. Of course this is Chekov's Laser and later in the story it will be aimed to produce mayhem...

But pods of deuterium for now. Yes. You shoot the pods at Earth. You must calculate the trajectory of the pod considering your motion relative to the earth, as well as the gravitational pull of other objects in or near the path. These could include inner planets. Gravity from the sun will of course be important.

When you do not have a direct shot at the Earth you can use a gravity well to bank your shot, sending it on a curved path to avoid the sun and still intercept Earth. Ultimately this is like a gravity assist but rather than acceleration or deceleration, to make the projectile follow a curved path. Various planets are handy for this. Jupiter is weighty and an obvious choice but you could use Mars or Saturn itself.

Using a gravity assist like this for your regular shots might also save energy.

https://space.stackexchange.com/questions/10021/how-are-gravity-assists-conceived gravity assist


Oh, the question. Put it on the surface as close as possible to your refining operation. Bracing it on the surface will help with aim and allow you to dampen vibrations. There is no atmosphere to get in the way.

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Assuming the Deuterium is being mined and processed on the moon itself, the laser launcher shoudl also be on the moon. This provides several advantages:

  1. The Laser can use dueterium fusion powerplants on the moon itself, fueled from the same deuterium ice being mined for export
  2. The waste heat of the laser launcher is more easily disposed of by using the moon as a heat sink. Some of the heat can actually be used in the processing faciity, but dumping heat by convection or conduction into the ice is far better than trying to radiate it away in a vacuum.
  3. By modulating the launch laser, you can essentially send your packages of frozen Deuterium to any point in the Solar System. All that is needed is to calculate the appropriate minimum energy trajectory, attach a suitable block of ordinary ice to the pod and heat it with the laser to generate thrust. The customers are responsible for catching it at the other end, either with thier own laser or using another means like a mass driver.
  4. With the laser mounted on the moon, it is much easier to service, upgrade and so on. You don't have to design the laser for zero g operations, docking fuel tankers or other complications.

Mining and transportation of bulk cargo always works towards minimizing costs. A single laser on the moon is far less espensive than one in orbit, and much less expensive than multiple lasers or mirrors across the Solar System. Using the already available fusion fuel on the moon, and recycling the waste heat from the laser back into the processing facility makes the overall efficiency of the facility higher, and results in lower overall costs. The issue of transportation is already resolved by simply plotting the minimum energy trajectory to whatever target you have a customer at - obviously the very least amount of energy is needed during the synodic periods between planets, but there is always a minimum energy path thoughout the orbital period.

Given the lenght of time for Uranus to orbit the Sun, synodic periods are few and far between, so simply sending a constant stream of pods on minimum energy orbits creates a sort of "pipeline" to the customer - if you have done your caclulations correctly an individual pod will arrive on target years or even decades later, but it will arrive on a predetermined date and time. The real issue is how you manipulate the "futures" market to ensure your costs plus the time value of money over the transport period is covered - hopefully at a profit!

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First: the most efficient way would be to use gravity, and not a laser. Earth will need deuterium for the next 100s of years. So nobody cares if you ship the deuterium along an orbit. Basically shoot it into an Earth orbit or straight into the ocean.

But in your scenario, they decide to go the fast way. Which TBH is not unrealistic. We like it when stuff is fast. So lasers FTW.

For the most amount of control, you need, at the very minimum, 3 lasers that are on opposite sides of the solar system. Since the solar system is, more or less, a 2 dimensional plane, 3 lasers at 120 degrees offset each would give you unlimited control.

To where those need to be, I would guess around the orbit of Uranus or maybe Saturn itself. You don't want a Gigawatt laser shooting through the solar system for weeks. So they should be as close together as possible.

I would also assume having them in orbit is the best. Why ? Because it is probably cheaper. But this sort of depends what sort of laser you have. And how much energy they need.

Existing stations and so on may also be a factor.

To the orbit itself, well, you want those stations to always point at the Sun. So they would be very far away from Saturn or which ever body is close. I mean, you could probably consider them Deep Space Stations.

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  • $\begingroup$ Thanks for your answer. Why is it cheaper to put the stations in orbit rather than on the ground? $\endgroup$ – Lelu Aug 19 '20 at 21:09

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