# What would be the “cheapest” non-rocket solution to getting cargo to and from Earth's surface?

Prometheus, your friendly neighborhood mega corp, has done it: dragged that pesky asteroid near Earth's orbit. Now with a rich source of ore right in Earth's orbit Prometheus is looking to improve its surface to orbital infrastructure.

Prometheus for the past decades have been out phasing the old "rocket ships" of the frontier with newer cargo vessels (nuclear powered space craft). Surface to Orbital transportation is the final sector still dominated by the rocket.

What infrastructure would allow Prometheus to mainly (you'd still have cases of rockets where it makes more sense) out phase rockets? The only requirements are two things: not a fancy rocket and near future preferably.

Note: SSTO (single staged to orbit) are allowed as long as they, well don't look like a plane with a rocket strapped under it

I'm not too worried about a not rocket solution being "inefficient" or requiring construction on a grand scale, that's Prometheus' strong suit after all.

• I could swear I've seen this question before, but during my search (I couldn't find one... deja vu!), I uncovered a couple of questions that you should look at: this, this and this. – JBH Jun 15 '19 at 22:36
• Lots of possibilities in the non-rocket space launch wikipedia article and more details on some of them (with nice diagrams) starting in this section of the projectrho.com "surface to orbit" page. If anyone wants to write up one of the ones that hasn't been mentioned you can use the references in these articles. – Hypnosifl Jun 15 '19 at 23:46
• What are they trying to do? Ferry ore from their asteroid down to earth? I can think of a really cheap way to do that, no rockets needed... – Willk Jun 16 '19 at 1:24
• @Willk they're just using the ore to build the infrastructure – Celestial Dragon Emperor Jun 16 '19 at 1:35
• Infrastructure of what? A city on the asteroid? – Willk Jun 16 '19 at 2:26

## Orbital Ring

Why an orbital ring?

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 better than any other launch asssist concept. Space elevators have a terrible throughput of only about 15 t/week according to recent papers and only bring one up to geostationary orbit with a litte push allowing one to bring out stuff to the asteroid belt on a slow transfer orbit. If you want to launch a 150 t space craft it would take 10 weeks to do so. Most other launch assist concepts face similar issues and are inferior to the orbital ring in most points but construction cost and energy demand (this will become irrelevant quickly as the energy cost is mostly upfront and the ring is a great base for off-world solar, Helium-3 or fissile material import). In terms of scalability, throughput, interplanetary launch assist and general utility no other launch assist method can rival the ring. With that out of the way...

Active Support

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.

Orbital Mechanics

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.

Constitution of the Ring

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 $$c$$.

Miscellaneous

The best thing is, that this subverts the Tyranny of the Rocket Equation 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 to correct for the orbital inclination differences. Regenerative breaking will make this more efficient than any rocket.

This video will give you some more insights and this paper 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.

• Any estimates of how many slugs and rings you'd need to put into orbit before turning it on, how much mass they'd have in total? This could be very expensive to get started (compared to other concepts like the space elevator or laser-assisted takeoff) even if it provided nice savings on putting further stuff in orbit once it was in place. – Hypnosifl Jun 16 '19 at 16:59
• @Hypnosifl The paper I referenced deals with this in detail. It has been a while since I read it but it will provide you with all the technical information you need on the subject. If I remember correctly the author concluded that even with one SpaceX Starship launch the material for a functional ring skeleton could be brought into orbit. Everything depends on your specific design, but the author suggests that 9 billion USD might be the skeletons pricetag and as soon as it is up there cost plummets. – TheDyingOfLight Jun 16 '19 at 17:13
• this idea is new to me, thanks! i doubt the feasability of the aiming, though: with even 100 stations in orbit, you'd still have to be accurate to within 100 mas in a shot. every time, all the time. miss by a few mas and you slug one of your platforms. but as you are not 'just' trying to aim to hit into the other platform' s receiver, but are actually finetuning your own and your neighbor's trajectories with each shot, this sounds a bit too optimistic. every tiniest bit of misalignment will cause the receiver's force vector to not go through it's center of mass, imposing a rotational momentum. – bukwyrm Jun 17 '19 at 15:28
• @bukwyrm While I agree that accurately iis crucial for the rings survival, it becomes less relevant the mor complete the ring is. On a ring where the planet spanning mass driver has been installed the acceleration station might only be a few kilometers or hundreds of meters away form each other and the projectiles will only move within the enclosed superstructure. During the construction phase factors like radiatin pressure, moment transfer from construction equipment and spacecrafts and later chaotic influences from the atmosphere due tp the tethers must be considered. – TheDyingOfLight Jun 18 '19 at 12:32
• @bukwyrm While these things are certainly a challenge, they are an organisation, coordination, engineering, coding and surveillance challenge. As long as the space phase of the construction can be kept short, gravitational influences should remain insignificant. At the point when tethers let cargopods and the atmospere influence the ring, the distances between acceleration stations should be short enough. – TheDyingOfLight Jun 18 '19 at 12:36

Balloon-mounted railgun

Getting stuff in orbit means getting it high off the ground and also getting it moving sideways fast enough that when it tries to fall back down to the earth, it misses.

1. It is nice having atmosphere on the ground. But if you want to get going fast, all that gas gets grabby. The balloon hoists the railgun and payload up above most of that.

2. Railgun accelerates payload into orbital trajectory.

3. To descend, internal compressors pump lift gas into holding tanks for later use. Or if it is cheaper, vent the hydrogen and get more on the ground.

4. Back down for another load. Clip a fresh capacitor onto the railgun.

Benefits

1: No moving parts.

1. Hydrogen is cheap.

2. Balloons work well.

3. If you have one of these, people will be very nice to you.

• This sounds like somthing straight out of Kerbol Space Programm. It doesn't seem very practical, but the idea has a rag-tag feel to it which makes it amazing. I love it. – TheDyingOfLight Jun 16 '19 at 14:49
• @Willk this pretty sick! Definitely gonna use it for some space western now – Celestial Dragon Emperor Jun 16 '19 at 16:35
• The balloon would need to be ENORMOUS but, to be fair, it would still be smaller than a space elevator. – Robyn Jun 17 '19 at 5:27

# LASER-Powered Ablative Propulsion

A ship carries a supply of plastic or other material, probably hard and external, that is vaporised by a groundside LASER turret in a controlled manner, producing thrust. While this requires significant power, all the power generation can be situated groundside, and thus doesn't need to be expensively pushed to orbit with the rest of the ship.

Bonus points: the turret can be repurposed for a combat role by a government or terrorists if your plot calls for it.

• Probably the best near-future solution. And if you design your engine carefully, you can even use air as a propellant while in atmosphere, and save the internal propellant for higher altitude. – Eth Jun 17 '19 at 9:38

## Space elevator

It's unclear how far in the future it is. On Earth, it's a considerable challenge. On other places, like the Moon or Mars its much more feasible. Experience from building it there, could boost an Earth Elevator.

A mega corp would definitely invest considerable resources into researching and building it. Though its questionable if a single mega corp would have the capacity to build it.

## Laser assisted take off

Sadly, I'm not knowledgeable enough about this option, but I heard/read off a concept about massive lasers pushing payload up into space. It probably wouldn't worth as it would require astronomical energy investment. Especially the further it is from the ground.

## Space Hooks?

Even less sure, if this is possible. Basing it on an idea from a sci-fi book. A massive asteroid in stabil orbit, with a long hook lowered into the atmosphere. Not good enough for the elevator, but good enough to catch a payload which only has thrust to reach that height. I'm not sure if it would be useful, as the most energy are used for takeoff.

• would be cool if multiple companies pitched into the space elevator – Celestial Dragon Emperor Jun 16 '19 at 0:58
• @Celestial Depending on the way you want it to play out, it has a limitless potential and options. Eligible nations would fight over its earth side location to be near them, which would become the most used transportation nexus overnight. It would skyrocket space commerce. Raw resources down, finished product up. Provide clean energy (solar farms in space). Could eventually lead to a ring habitat around Earth. It would be a risky investment too as its security could be easily compromised. However all corporations would fight over its shares as it would generate immense profit. – Lupus Jun 16 '19 at 1:41
• @Lupus I don't really see space elevators kicking the space economy into high gear as they have a very limited throughput of only about 15 t/week. If energy prices are the only thing that is considered, space elevators seem very promising, but the market forces of its very limited supply and the high demand for its service will set the price of a climb slightly below the cost of a rocket launch. Economics make space elevators unfeasible. – TheDyingOfLight Jun 16 '19 at 14:42
• @TheDyingOfLight The challenge currently is building the FIRST. Scaling up from that with additional elevators or with extra tethers (lanes) next to the first, shouldn't be an issue. One, the transportation cost would still be very low compared to rockets. That would mean immense profits to those how control it, which will most likely be invested again. Second, to save money on the "costly" elevator, space manufacturing would boom. While lift something up, when you can make it in space. It would lessen the burden on the elevator and be an incentive for expanding space economy. – Lupus Jun 16 '19 at 15:17
• @Lupus The economics of a space elevator are dubious, to say the least. While space elevators do not scale as bad as some other launch assist structures do they look still terrible compared to an orbital ring, which is the crux of the matter. Even if there were a material which could be used to build a space elevator (there isn´t as even carbon nanotubes will have too many material errors to deliver their theoretical tensile strength) it would simply be knocked out of the market by orbital rings. I think space elevators are a cool SIFI concept, but like FTL unobtainable. – TheDyingOfLight Jun 16 '19 at 17:22

Getting cargo to the surface is easy, drop it. Works really good for metals mined from the asteroid. Box it up in steel, add transponders and guidance and maneuvering thrusters and toss it down the gravity well. Admittedly, not a great way for eggs or people travel if you want them resembling eggs and people later.

Up is a matter of Work and Delta-V, boils down to the same thing. Magnetic accelerators on high mountains could conceptually throw heavy masses into orbit. And the longer the accelerator the lower the acceleration and the more comfortable for transporting eggs and people into space and having them still whole when they disembark at the asteroid.

Another way is similar but its a giant cannon. It fires big hollow bullets straight out of the atmosphere. Using multiple propellant stages to keep acceleration constant, it has same kind of behavior as magnetic acceleration.

# Airship to orbit.

JP Aerospace has been testing scale models for a while now.

Their plan is to use a large airship to carry cargo to a "dark sky station" that floats in the upper bounds of the atmosphere. From there, the cargo is transferred to the ATO which is an aerodynamic airship that spins out of the atmosphere. The faster it goes, the more lift it gets so the higher it can go. the higher it goes, the faster it can get.

The founder of the company believes that he can get enough delta-v to reach Mars. Conveniently, Mars' ground level atnosphereic pressure is the same pressure that the dark sky station will be in over Earth (I don't think he's worked out what to do with surface winds yet).

The trip won't be fast but it will be cheap and will be able to take fragile things like people up.

# BFG6000

Just a really big gun with a long barrel. You wouldn't want to send up anything delicate. But bulk items can be sent into LEO (Low Earth Orbit) fast and cheaply.