Let's Make Space Travel Cheaper Than a Bus
Can we make it affodable to commute to and from space daily?
Before we can do things in or around space, it does need to get cheaper. Not many people would move around if it is millions of dollars.
And we are making progress, fast progress. In 1980, the cost per kg was almost $100,000 per kg. When SpaceX first launched the Falcon 1, the cost was about $10,000 per kg. The 2021 Falcon 9/Falcon Heavy costs per kg is about $1,000. SpaceX’s Starship has a target cost of $10 per kg.
As we increase our presence in space and make travel regular, we will reduce the cost. Musk’s $10 per kg target involves regular travel. The average human is about 80kg, so that is basically $800 per trip. That is about the cost of international air travel in many cases. But it would be nice if we could get that price another order of magnitude lower, something like $80 per trip. Then, its basically affordable for everyone for a trip. At $8 per trip, you can commute daily to and from space for things.
How might we get 10-100x cheaper than even Starship? Probably not with rockets. To do that, we need to build large structures.
There are many designs for structures, with some good ones being called:
In each of these cases, the upfront investment is very high, so you need to be putting a lot of things to and from space to make it worth it.
The main one I will focus on is the Orbital Ring. It’s a personal favorite of mine, and it has the advantage of being almost certainly possible using known physics and material science. In theory, it should hit the $1 per kg or $0.10 per kg range possible to allow daily commuting to/from space.
I won’t go into lots of detail, but here is how they work.
Building an Orbital Loop
The principle behind an orbital loop is the following:
Put objects into orbit. We do this all the time.
Connect the objects in orbit.
Do this all around the planet, and you create a ring around the planet. The objects are in orbit, which means they are moving really fast. At this phase, you haven’t solved anything because someone leaving earth would need to get to orbital speed to land on the ring. So we need to keep going.
Put magnets on this fast-moving ring.
Use the magnets to suspend a tunnel around the fast-moving ring, similar to the way maglev trains are over the track.
Now you have a stationary tunnel-like platform around the earth, with a fast-moving ring in the middle holding it up with centripetal force.
4.1.2. Getting to the loop
Putting the ring about 100km up makes sense. It is above the atmosphere, which is what really matters. It has basically the same gravity as the Earth’s surface, just higher up. But it’s only 100km up, which would take about 10 minutes to travel with current high-speed trains.
100km is a bit long for a cable though, you can’t just use steel for this. You need something a bit more exotic.
Here are some materials we could use:
Kevlar is the most obvious material that can work. It has ton of extra strength, and we already produce it in large quantities. Once you have the Kevlar support structure up, you can attach plumbing, power, and other things to the line as well, that part is easy. We have oil pipelines and such much longer than that.
So now you have a platform in space, and you have cables going down to earth. What can you do on it?
Well, you can do just about anything on it like space hotels. However, the main purpose of this orbital loop is transportation, which in space really means acceleration and deceleration.
Launching from the Orbital Ring
To get places in space, you need speed. A lot of speed. Almost all the energy of a rocket is used to get up to speed, not altitude. The orbital ring gives you 2 huge advantages:
No atmosphere. Travelling on it is outside the atmosphere. Cutting through the atmosphere consumes a ton of energy for rockets.
No need to carry fuel. Normal rockets require you to carry fuel to get it into space, but then you need more fuel to carry the fuel, etc. This makes most rockest mostly fuel. Orbital rings solve this, you just launch from a maglev track. You don’t necessarily need any fuel at all.
If you flip the ship upside down, and are not moving, it will feel like 1G “up”. So if you accelerate to 2Gs on the track, while upside down you will feel 2G “up” and 1G “down”, leaving you with 1G “up”, or normal gravity.
You can easily surpass Earth’s escape velocity of 11.2 km/s with this method, and get to Mars or nearby space stations.
You can make more rings at different angles to allow you to point yourself at various locations. You can connect these other rings together. You can build larger rings, which allow you to go even faster.
When you get to another location, you can slow down in other ways: rockets, lasers, maglev tracks, or another orbital ring. The most important thing right now is making getting off Earth easy. Its much easier to leave Mars, and trivial to leave a space station.
Orbital rings, or something like it, is a really good step to making humans move seamlessly between space and Earth.
How Expensive Is It?
How much would it cost to build an orbital ring? If Starship works, it becomes in the range of building now. Here is roughly how it might work:
First you build a small loop around the earth, something as small as a wire. It has to go around the 40 million km circumference of the earth, which is ballpark 10 million kg for the wire. The stationary ring might be 20 million kg, for a total of 30 million kg.
If Starship hits their target of $100/kg, this is $3B in launch costs.
The materials cost would be about $500M.
The labor would cost…a lot. We won’t have astronauts doing this work. Oil crews can lay about 1 mile per day, so this would take about 29,000 days to complete. But if you have 100 robots working in parallel, you can complete the thing in under 1 year. I’m not sure anyone has priced this out completely, but having 100 robots seems pretty good. Its not bespoke, nor large scale, so I wouldn’t be surprised if each robot cost like $50M, so like $5B in robot costs.
This doesn’t feel like the hardest R&D task ever done in space, so maybe $10B in other costs? In some ways, this feels easier than building a tunnel through Boston. But in other ways, its space?
This puts an estimated total of $18.5B. You probably want to just double it because its crazy, so maybe its $40B.
Once the first ring is up, it can then be used to shuttle up mass to bulk up the rings and get it ready for launch. You can probably re-use the robots and techniques you learned, so probably the transportation and materials cost are the main blockers. Now launch costs are much cheaper now, so 10x the size of the ring is probably now more like $5B. If you wanted to 1000x the size of the ring, you probably will keep seeing more scale benefits, and can probably do that for $200B. At that point, its probably strong enough to carry and launch things without issue.
So you are maybe looking at $250B to get a usable orbital ring, able to launch things into orbit. On the one hand, this isn’t something you cavalierly construct. On the other hand, the SLS rocket will cost something like $25B to develop, and that just gets us an old-fashioned rocket. And we spend way more than $250B on projects all the time (e.g. COVID relief, wars, etc).
This is also something that someone can just start doing? I mean, for about $200M you can probably build a robot load up a starship with some material, and send that thing to space, and just start building.
Can we do this tomorrow? It seems like “yes”, but we probably shouldn’t. I mean waiting on Starship is a no brainer. Then we probably want to do
An orbital ring is something we should seriously consider and plan for as a follow-up to Starship. It’s my favorite approach right now to make traveling to space as easy as a daily commute.