Surface to Orbit

There is a simple yet implacable rule in space travel: the fanciest faster-than-light device doesn't mean anything if you cannot leave your dear homeworld in the first place. Even in the age of the geometry drive, the most complex and expensive part of space travel is usually the one that involves sending people and material from the ground to low orbit. No matter how advanced a planetary civilisation is, nor how many orbital shipyards have been built, there is no way to go around it. At one point, any space-faring society will have to fight its uphill battle against the escape velocity of whatever planet it calls home. 

There are many ways to handle this surface-to-orbit part of space travel and virtually every one of them is in use somewhere in human space. Some of them pay their tribute to the tyranny of the rocket equation. Others aim higher and try to industrialize low orbit.

As usual, this guide does not aim at describing every single one of these methods, which would be a pointless task but to provide a simple and handy guide for the interstellar traveller. Methods are organized from least to most complex.

1 - Rockoons

Rockets are practical but have one problem: they're mostly made of highly explosive fuel. The less rocket one needs, the better. As such the single cheapest way of achieving space flight without any specific facility is to attach the final stage of a rocket to a high atmosphere balloon, let it ascend towards the edge of space, and then fire up the engines. This is called a rockoon, or rocket-balloon. The payload being carried by such crafts is minimal - in the range of fifty to one hundred kilograms - but the price is unrivalled. Rockoons are incredibly cheap and can be launched from virtually anywhere with very minimal ground facilities, which makes them a perfect tool to deploy nanosatellite constellations, orbital beacons or single microsatellites. As an additional advantage, rockoon launches are virtually impossible to detect until rocket ignition: they are the perfect stealth launch vehicle...for better or worse.

2 - Mass drivers

Much like their military counterparts, civilian mass drivers use the Lorentz force to provide a payload with enough velocity to escape a gravity well. They are only usable on airless or thin atmosphere worlds, require fixed facilities and are not always well considered by the powers that be due to how easy it is to turn a mass driver into an artillery railgun. Despite these shortcomings, however, mass drivers are very widely used to transfer payloads between moons in gas giant systems thanks to a simple fact: propellant is always going to be more expensive than electricity. Mass drivers can even be human-rated, provided their acceleration is progressive enough to avoid g-force induced injuries.

3 - Rocket launchers

Rocket launchers have endured the Low Age as a "Lost Invention" - a technology whose theoretical principles were still known but that could not be built anymore due to the technical and organisational limitations of the slow apocalypse. Modern launchers run on highly efficient organic fuel, are often made of one to two stages, are reusable and can carry up to five hundred tons in low orbit yet in spirit and design they have more in common with industrial era contraptions than the elegant FTL ships of the interstellar age. Rudimentary. Rugged. Powerful. Rocket launchers have a certain elegance in their brutal simplicity.

4 - Spaceplanes

The first spaceplane to ever fly was the American space shuttle in the 1970s though it is now but a memory, a wreck buried somewhere in the Remembrance Plains of North America. Yet what it once represented - a glimmer of hope and elegance - has not been forgotten. Reusable launchers capable of aerodynamic re-entry are not used because they are efficient, they are used because they are elegant. Spaceships are tubes and rings attached to engines but spaceplanes aim at being more than that. Streamlined, beautiful crafts capable of taking off from a dusty runway in the middle of a desert, power up to low orbit, deploy a payload, glide back home, land on a commercial airport, all the while looking awesome. In a capitalistic world, they would be a luxury item. In a world of communes, they're art installations.

5 - Rotating Skyhooks

Rotating skyhooks are the lightest and cheapest example of industrial surface-to-orbit facilities, far more efficient than individual vehicles when it comes to lifting large amounts of materials and personnel to low orbit. A rotating skyhook, or orbital sling, consists of a tidally stabilized, low orbit space station equipped with a semi-rigid tether that periodically reaches into the high atmosphere, where a suborbital vehicle can reach the end of the tether which then captures the payload and slingshots it to low orbit. After orbital insertion, the tether needs to be reeled before being reused. The counterweight must be 1,000 to 2,000 times as heavy as the payload and the tether around 600 kilometres in length. Altitude control of the skyhook station is ensured either by onboard thrusters or by deorbiting a payload with a similar mass in which case the skyhook can double as an orbital waste disposal system.

Skyhooks are a tried and tested technology in the interstellar age that is widely deployed on inhabited planets inside and outside of Communal Space. Their main advantage doesn't reside in the maximal payload they can send in orbit, which is limited by the counterweight mass and generally not higher than a few hundred tons, but in their low cost in the long run: with cheap suborbital vehicles, the building cost of a skyhook is recouped within less than five years on high traffic planets.

6 - Space elevators

The space elevator is in many ways the ultimate end goal of surface-to-orbit transportation: a vast tether connecting a point on the equator of a planetary surface and a counterweight located beyond geostationary orbit, creating an imbalance between gravity and centrifugal forces that keeps the hundred thousand kilometre-long cable uptight and stationary over its surface origin point. Cargo and passenger modules climb up and down the fixed tether, exiting at different points on the cable to reach low orbit, the geostationary orbit, or stellar system transfer trajectories. Space elevators are extremely expensive and complex to set up, however, the payload capacities are measured in thousands of tonnes per day, far surpassing any other kind of surface to orbit method. A space elevator also enables an orbital economy to abandon the use of surface-to-orbit vehicles entirely.

Two kinds of space elevators must be distinguished.

The first kind is the one that is attached to low-gravity celestial bodies, such as the Moon. These space elevators tend to be on the shorter end of the scale in terms of size and the gravitational forces involved do not require the use of advanced materials, hence cutting down the cost by several orders of magnitude and making space elevators rather cost-competitive even compared to skyhooks. In this case, the main obstacles to the deployment of a space elevator on a planetary body are matters of political stability, and the need for a developed space economy to pre-exist in order to justify the building costs. This explains why worlds like Trappist 1-e or Smyrnia do not have space elevators despite ideal conditions.

The second kind is the space elevator that is attached to a higher gravity body with a dense atmosphere, such as Earth or Elora. In this case, the length and strength to density requirements of the cable literally skyrocket, with the denser, more dynamic atmosphere offering an additional challenge. Even in the interstellar age, building such a space elevator is a daunting endeavour that requires hundreds of communes to coalesce for several decades in a shared planetary project. Only three major space elevators exist in human space: two on Earth (In Kenya and the Philippines) and one on Elora, with potentially a planned structure on Okean. 

Space elevator picture: Liftport.

Rockoon: Zero 2 Infinity concept art.

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