How can you get to space and orbit the earth cheaply? Today, it costs $1,500-$3,000 to get 1 kg into low earth orbit (LEO), and more to go further. Is it possible to bring these prices down? The answer is, maybe. Let's have a look at some of the possible technologies and what they might cost; but first, let's talk about where space begins.
Space and Altitudes
There's no clear boundary between earth and space; the atmosphere and gravity don't just end suddenly. The space starting point is usually taken as the so-called Kármán line at 100 km above the earth's surface. Low earth orbit goes from 160 km to about 2,000 km, with the ISS orbiting in the range 400–430 km. For comparison, the distance between London and Paris is 454 km.
Getting to these heights is relatively easy; staying there is much harder. To stay in orbit you need a substantial orbital velocity; for example, at 200 km above the earth, you need to reach 7.7 km/s to stay in orbit. Because of the high cost of entering orbit, the earliest space launches were suborbital, the first being a V-2 on 20 June 1944, which reached 176 km. Achieving orbit takes more fuel, meaning a bigger rocket, so it took longer; the first orbital flight was Sputnik 1 on 4 October 1957, with an orbit of 223–950 km.
Rockets
Although rocketry is proven technology, it has its limitations. Because a rocket has to carry its own fuel, it burns fuel to carry fuel; during the Apollo 11 mission, the Saturn V rocket was 85% fuel by weight.
The fuel fraction needed to get to orbit is expressed by the rocket equation:
Where:
- \(\Delta v\) is the change in velocity
- \(v_e\) is the exhaust velocity, given by:
- \(I_{sp}\) — the specific impulse
- \(g_0\) — gravitational acceleration
- \(m_0\) is the mass of the entire rocket, including propellant
- \(m_f\) is the mass of the rocket without propellant
This equation is a simplification that applies in this form to single-stage-to-orbit (SSTO) rockets, but it's enough to show the problem. Wikipedia's example calculation shows that an SSTO rocket must be 88.8% fuel. This percentage drops for a two-stage rocket, but the cost is added complexity.
The rocket equation tells you how much fuel you need to carry a payload to orbit. The bigger the mass, the more fuel, and hence the bigger the engineering challenge which is the so-called tyranny of the rocket equation.
(Copilot's retro rocket.)
To put rocket costs into perspective, let's look at something simple. A cup of coffee weighs about 240 g, or 82 g just for the coffee. The cost to orbit for this mass is $360–$720 for the cup, or $123–$246 for the coffee itself. These costs are coming down, but they're still high enough that rocket space travel is restricted to governments and billionaires.
Fuel costs aren't the only costs. There's obviously R&D which is extremely high. By using mass-production techniques and riding the experience curve, we can cut costs to orbit, but the rocket equation puts a floor on costs; rockets are always going to be expensive.
Planes
Normal jet engines require oxygen to burn fuel and sufficient atmosphere for their wings to provide lift. Both fall off with altitude, preventing jets from reaching space. However, a high-flying jet can reach the Kármán line by carrying momentum built up from acceleration at lower altitudes.
In the 1960s, the US X-15 experimental plane was flown above the Kármán line twice, and in 2004 SpaceShipOne did it three times. These are suborbital flights; the craft only briefly touched the highest altitudes. Reaching orbit by plane would require a rocket at some point, and might require three types of propulsion: a jet, a scramjet, and a rocket.
Commercial planes typically fly at about 9–12 km; much, much lower than the Kármán line.
Guns
The idea is simple: build a large gun and fire a payload into space. It's an old concept, famously appearing in Jules Verne's 1865 novel From the Earth to the Moon. In practice, it's much harder than it seems.
The acceleration in a space gun is enormous, over 1,000 g, which would kill a person almost instantly. This limits space guns to launching satellites, though a cheap satellite launch is still hugely valuable.
The most notable real-world space gun attempt was the HARP project in the 1960s, which managed to send a projectile to 179 km, comfortably above the Kármán line, at a cost of only $300–$500 a firing. The project ended in 1967, apparently from funding pressure and politics.
Chemical space guns run into pressure problems that limit acceleration and the height the projectile can reach, so electromagnetic rail guns have been suggested as alternatives. The StarTram concept uses this idea with some additional twists, but remains only theoretical.
The HARP project was the high-water mark of the space gun approach. Its architect, Dr. Gerard Bull, subsequently tried to get more space guns built but struggled for funding. Eventually he persuaded Saddam Hussein to fund "Project Babylon," a supergun capable of firing projectiles 750 km. The project ended when Bull was assassinated, most likely by Mossad, in a Brussels hotel in 1990. No one has seriously attempted a space gun since.
Centrifugal Launches
Taking inspiration from a bolas, what if you accelerate an object in a circle and, once it reaches a high enough velocity, release it? If you accelerated a payload in a vacuum, you could hit 10,000 g and reach a tremendous exit velocity, enough to fling your payload high into the atmosphere. Even if you couldn't reach orbit, by sending a rocket far into the upper atmosphere, you would dramatically reduce its fuel needs (and hence cost). Of course, a person would be squished by this acceleration, but once again, a satellite or cargo launch would be good enough.
A company called SpinLaunch built a prototype in New Mexico to investigate the idea. Unfortunately the engineering challenges proved too much and they've since pivoted to more traditional rockets.
The Space Elevator
Space elevators are beloved by science fiction authors. The idea was popularized by Arthur C. Clarke's novel The Fountains of Paradise and it's appeared in several other novels since.
Here's the concept: move an asteroid into geostationary orbit as a counterweight, deploy a cable down to earth, anchor it to the ground, and ride an elevator up the cable into space. Simple in principle, but the forces on the cable would be extraordinary, requiring entirely new super-strong materials. Clarke suggested threads of buckyball-type nanoparticles, which didn't exist when he wrote the book.
The engineering challenges are immense: capturing an asteroid, developing the cable material, surviving lightning strikes and weather, and so on It's not likely to happen any time soon.
A baby step towards a space elevator was attempted in 1996 ,when the space shuttle crew tried to deploy a satellite on a 20 km tether; unfortunately it snapped before being fully deployed, illustrating the difficulties.
Skyhooks
Imagine a satellite with two huge rotating arms long enough to reach into the upper atmosphere. As the satellite rotates, one arm dips into the atmosphere. A plane flies up, the arm catches it and flings the plane into orbit. Conversely, you could de-orbit spacecraft without dangerous re-entry.
(Claude's view of the skyhook)
To use this system, a plane only needs to reach Mach 10+ at high altitude, far cheaper than reaching orbit unaided. Although it sounds outlandish, it appears more feasible than the space elevator. Still, it's likely decades away from development.
Space Fountain
Imagine a water fountain pushing a ball aloft, now scale that up to lifting a platform to space. Instead of water, a space fountain would use a stream of metal pellets fired electromagnetically upwards to lift a platform high into space. Like the space elevator, the platform transports people and cargo into space and back again.
The key idea is that the pellets never physically contact the platform. Instead, a magnetic deflector captures each pellet and an electromagnetic accelerator fires it back down; the ground station catches and re-fires them upward. The pellets are continuously recycled.
It's an elegant concept, but the engineering challenges are immense, and the electricity bill to run the electromagnets would be enormous.
Balloons and Rockets (Rockoons)
A balloon can carry a rocket high into the atmosphere, the combination is called a rockoon. One of the early pioneers was James A. Van Allen, whose rockoon experiments provided the first evidence of the radiation belts now named after him.
The idea is cheap and effective for experiments, but suffers from a fundamental problem: balloons are nearly impossible to steer. Payload capacity is also limited by the balloon's lifting power. Rockoons may work for small scientific payloads, but won't get large amounts of material into orbit.
There have been a lot of pictures in the press showing the curvature of the earth taken from balloons, giving the impression a balloon can get you to space, but that's not so. Balloons typically reach about 30 km where 99% of the atmosphere is below them and the sky above is dark black. It looks like space, but it isn't. The highest a balloon has ever reached is 53.7 km.
Atomic Bombs
There's an urban myth that the first object into space was a manhole cover launched by the first atomic bomb test. In reality, it was during the 1957 Plumbob test, not the original Trinity test; and it was a steel bore cap, not a manhole cover. In any case, the "manhole cover" was almost certainly vaporized in the explosion and never made it to space.
In the 1950s–60s, Project Orion envisaged using miniature nuclear bombs to push a vehicle into orbit, requiring around 800 detonations per launch for a crewed mission. Thankfully, the project never progressed beyond simple chemical explosive tests.
Nazi Super-Science
While researching this post I came across a demented conspiracy theory claiming the Nazis developed an anti-gravity device called Die Glocke (the Bell), supposedly capable of time travel, anti-gravity, and spatial distortion. It's plainly nonsense, but it does have believers.
So It's Rockets for the Foreseeable Future?
Unless there's some extraordinary breakthrough, it really is just rockets for now.
AI statement
This is all my own writing. I used AI to generate images and to help with some research, but not for any piece of the writing itself.