# What is the cheapest way to move large amounts of trade goods to orbit?

Given a world with similar size and atmospheric composition to Earth that has a commodity export, be it grain or oil etc, that has trade with other planets, what would be best way to orbit massive amounts of goods at the lowest per-unit cost.

My goal is the separate the technology that drives ships between planets vs the ground to orbit technology, similarly to how modern Earth shipping ports work (with trucks or trains bringing containers to large ocean going vessels), as opposed to the Star Wars/Star Trek method of handwaving everything as part of the ships' functionality.

Any science based sci-fi method is allowed as long as it keeps the goods in their regular form—i.e., no teleportation.

• Within currently known physics the best solution is very obviously a space elevator. With fantastic physics anything is possible. – AlexP May 2 '19 at 23:03
• Hey, I've edited the tags as I thought appropriate, you can roll-back or re-edit if you wish. AlexP got there before I finished composing the comment. All I have to say is - why not space elevators? Then you'd need to think about the energy cost of space elevator maintenance V's rockets from the surface. – Tantalus' touch. May 2 '19 at 23:08
• – Alexander May 2 '19 at 23:16
• I'm going to need some of those explained to me @Alexander. – knowads May 2 '19 at 23:17
• @AlexP Space elevators are stronly overrated. No scalability, transport only up to geostationary orbit, long transport times, horrible transport rates, asteroid, satellite and space debris collisions,... – TheDyingOfLight May 3 '19 at 10:38

## Orbital Ring [1]

In summary an orbital ring is a space elevator for grown-ups and allows the kind of logistical endeavours a true solar system spanning civilisation would face daily.

Crucial to an orbital ring is the concept of active support. Whenever you build a structure you want it to stay stable. Buildings do this by relying on passive support, i.e. their own structure can carry their weight. This approach is limited by the ability of the building materials to resist the force the rest of the structure exerts on them. This is Newtons third law, actio = reactio. Actio is the force the structures weight delivers and reactio is usually the force the material must be able to muster. Yet nowhere it is said that reactio must be provided passively. Imagine a friend of yours is walking over a thin plank, which would break under his weight. The passive support of the plank isn't sufficient to counteract the force your friend exerts. Now you go under the plank and push it up, so that it can hold your friends weight. You are providing active support. The great thing about active support is that you aren't limited by puny compressive or tensile strength, you are dumping energy into the system to keep it stable. And you can dump infinite ammounts of energy into a system.

Secondly some basic orbital mechanics are important for the ring. An object moves through space on an elliptical trajectory corresponding to it's speed. The faster the object moves (i.e. the more energy it carries) the higher it will move. If the object is restrained from moving into a higher orbit appropriate for it's speed it will exert a upward force on the restraint.

Now imagine bringing a stream of orbiting, magnetic slugs in a circular orbit arround earth, lets say 200 km high. They will move at orbital velocity. Arround each slug we have a a metal ring containing electromagnets. The rings are loosely connected and under power. They too move at the same orbital speed as the slugs. Then we activate the magnets, forcing the slugs to move though the center of each ring.

Finally we start decelerating the rings with their magnets. This will transfer their momentum to the slugs speeding them up. The now faster slugs want to move to a orbit higher than their current 200 km. The now slower rings want to move to a lower orbit. But the magnets force both to interact. To be precise the rings want to fall down with the same force the slugs want to go up. Like on the plank with your friend, the situation is stable and the structure stays in place. We continue this until the outer structure sits statically over the earth. The rings, also called stator, sit fixed 200 km over the earth and levitate magnetically over the slugs, also called rotator, which keep the structure in the sky.

At this point you can drop tethers down from the ring to ancor it and to install elevators. One of the rings many advantages is that normal nylon ropes will work for this and that no fancy carbon nanotubes are required. You can send tethers down to everywhere within a ca 500 km distance from the ring.

On top of the ring you install several maglev rails. Since the ring spans arround the planet and the velocity an object can achieve on a mass driver is given by this formula.

$$v = d/\sqrt[2](d/(0,5*a))$$

$$v$$ = velocity

$$d$$ = distance (track length)

$$a$$ = acceleration

As the track is circular, $$d$$ can be considered to be infinite, thus setting the theoretical limit of $$v$$ to $$c$$.

The best thing is, that this subverts the Tyranny of the Rocket Equation [5] and allows for practically free transfer of goods between two planets with orbital rings. Just strap some ion drives on the cargo pods to allow the to adjust their Brachistochrone trajectories [2] to correct for the orbital inclination differences. Regenerative breaking will make this more efficient than any rocket.

This video [3] will give you some more insights and this paper [4] deals with the construction of the ring base. As soon as such a base has been established the ring can be expanded at an extremly low cost. While the ring can be constructed with current day technology, high or even room temperature superconductors would be nice to have.

• While all the answers are really good. I like this one the best. I used to live close to the ports in Oakland, CA and I've been thinking that the real advantage was not the massive ships we produce today, but the system of containerization, cranes, and infrastructure that allow such throughput. This one, in addition to being in-depth, feels the closest to what an interplanetary civilization would consider equivalent to what the United States considers the port of Oakland – knowads May 7 '19 at 0:09

I would say a space elevator would be one of the better technologies to use compared to current day space craft. It would more reliable, cost effective, and could be easily build around cargo. There's also less resources wasted potentially per trip.

Ships could definitely be better though if there were improvements in engines, fuel efficiency and power compared to today. Then they would work more like the trucking industry. Taking cargo only to lower orbits and coming back down.

It just depends on what style you'd like to go with and the technology level of the planet.

• Let's say they have access to Fusion rockets - like Expanse S1 level. – knowads May 2 '19 at 23:14
• Fusion rockets can mean a lot of things. For example, a fusion powered Ion thruster would be great for covering distance in space, but not be able to overcome Earth's gravity. However, a rocket that can convert hydrogen-fusion power to trust at the same rate as a traditional rocket, could render fuel costs trivial compared to the cost of building a space elevator. – Nosajimiki May 3 '19 at 4:23
• Fusion rockets are not the solution. Most proposals are generally good at highly efficient drives, and not good as launch drives. Unless you have torchships, but then all bets are off. The expanse is full of torch drives, and their fusion rockets are not realistic. – Whitecold May 3 '19 at 8:25
• @Whitecold Torchdrives can be done realistically. I recommend the "Torchship" section of the Atomic Rockets website. One's gonna need lots of radiators and magnetic rocket nozzles though. – TheDyingOfLight May 3 '19 at 10:43
• @TheDyingOfLight I am well aware of torchship proposals, but if you do have those kinds of fusion drives, you don't really need separate launch vehicle technology, just dump enough remass into your torch and take off from the surface directly – Whitecold May 3 '19 at 10:47

Wikipedia has a nice article on non-rocket space launch, offering multiple possibilities.

If the goods you need to move to space can resist large g forces, I would suggest a railgun, where magnetic force accelerates containers to escape velocity (11 km/s) over several hundred meters, perhaps a few kilometers. For a 1 km launch tube, the acceleration would be roughly 6,000 gees.

For more fragile goods, a space elevator or space tether is probably a better idea.

• +1, Giving a link to a Wikipedia article listing possibilities is not usually a good answer but in this case it is the best one available I think. Actual costs of any of the alternatives are just guesstimates at this point and many of the cheaper ones are still at the stage where we do not even know whether they really can be made to work. The best solution here is to pick the solution you find most appelaing, then state that in your setting they have technology to make it work and make it work CHEAP. – Ville Niemi May 3 '19 at 9:32

Two people have sent you to Wikipedia, but in a comment, you said that you needed more explanation.

A space elevator is a system where a giant cable is extended from the ground out past the geostationary orbit level such that the centripetal force of the counterweight at the top exactly balances the pull of gravity on the portion below geostationary orbit. For our purposes, we can simply think of it as a really long cable that specially designed elevator cars can climb. It allows a slow, low-g launch. At the top, you can launch with a space gun or rocket. We do not currently have materials strong enough to make the cable but think they are possible.

A non-rotating skyhook is essentially a space elevator that doesn't reach the ground. You fly up to the bottom in a shuttle.

A rotating or hypersonic skyhook, a rotovator, or a HASTOL are essentially the same thing. In order to reduce the velocity needed to match the bottom of the hook, they rotate the hook backwards relative to the orbit. Note that this means that most of the time, there is no bottom to reach. You have to time things so that you get to where the bottom should be at a time when it is there. The rest of the time, it will be at a different point in its rotation.

An orbital ring is a superstructure with multiple tethers (space elevators) connecting it to the ground.

A space gun is a launch system where a projectile or vehicle is accelerated to maximum speed while in the gun. If shot from the ground, this would not be able to handle the stress from air resistance. Also, to get the necessary speed, the acceleration is too high for humans if shot from the ground. Some think that a space gun could launch to a rotating skyhook, as its velocity is lower.

A slingatron is a space gun with a curved barrel.

A launch loop is a superstructure where a belt loops around in continuous motion. The motion of the belt would cause the middle of the loop to rise. Vehicles would exit the loop in the middle, above the atmosphere.

A space fountain is another superstructure. It's basically a space gun that reaches outside the atmosphere using pellets to hold up the end of the barrel. So it launches a continual stream of pellets that are redirected back to ground at the end of the barrel, imparting the force of pellets to the end of the barrel to hold it up. The pellets are then allowed to return to the ground where they are launched again. So it works like a fountain of pellets. The pellets are reused the same way a fountain continually moves the same water around.

A ram accelerator is a variant on the space gun where the vehicle contains the engine but the barrel of the gun contains the fuel. The Ramjet engine is designed to pull in fuel from outside and use it for forward propulsion.

### Frame challenge

I just want to point out that it is extremely unlikely that there is anything that it is cheaper to launch into space than to grow in space. Space travel is most likely to be about passengers rather than freight. Because the contents of the human brain are irreplaceable while any kind of freight could be created in space. In particular, note that there are many places in space where solar panels can be scaled to an arbitrarily large size for efficient collection of solar energy.

That's one of the problems with space travel now. We haven't created the orbital infrastructure to grow food, mine minerals, and in general get what we need from outside Earth's gravity well. So we have to use a ridiculously large amount of fuel just to move things like water and food to support the astronauts on the space station. In the long run, it will be cheaper to get materials from the asteroid belt than from Earth. Because it is cheaper in energy terms to move from the asteroid belt than to launch from the surface of the Earth.

You have several options for surface-to orbit transport:

SpaceX on steroids

A truly fully reusable system with turnaround times like an airport is a significant engineering challenge, but it should bring down launch costs a lot already. If you accept service lives of 100s of launches, you are paying mostly for the fuel. Of course this is the least exotic solution. If you are brave enough, you can include nuclear thermal engines in your launch vehicles to bring fuel costs down.

Laser Launch

Essentially you focus a massive ground based laser onto the back of your spacecraft where you have either a mirror or some ablative target, superheating either air, or your target respectively to generating thrust. This frees you from carrying your powerplant with you, and you can use large mirror arrays on your launch site. A craft with mirrors will need some additional engines to actually circularize and reach orbit, but that can be achieved with conventional engines.

Space elevator

Very hard to build, but once it is up there, you only need electricity to carry stuff to orbit. Once built, it will be the cheapest launch form per kg of payload. The upfront costs are likely the highest though.

Orion Drive

The orion drive was developed to lift massive payloads to orbit. It will also make for a wonderful main propulsion system. Only use this if you don't care about nuclear fallout along your entire launch path.