The Utility of Space Stations

There have been space stations on orbit almost continuously since the 1970s. But what are they actually for? Is there a case for building new and bigger ones?

In 1955, before even an unmanned Satellite had flown, Werner von Braun was planning for human spaceflight. In a film made for Disney, he describes an architecture for orbiting the Moon, using a spacecraft assembled in space at a space station

He shows a model of this 50-man space station, shaped like a wheel which rotates to provide artificial gravity. This crew would have several jobs:

1. Weather observation

2. Military reconnaissance

3. Astronomical observations, which also included tracking of other spacecraft

4. Assembly of spacecraft bound for the Moon

5. Operating a "biological and zoological laboratory"

6. Various functions for keeping the station operating

Its interesting to compare this proposal to what the International Space Station does. Functions 1-3 are all performed by unmanned satellites these days. 4 is not done at all. There is a small amount of biological research performed on the station, but most of the time and money invested into it is spent on its mere operation.

Von Braun's original intention was that the station be operated to permit its crew to perform certain functions; as those functions became automated by technology, the function of a space station was reduced to operating for its own sake.

This perhaps shouldn't even have been surprising at the time; in von Braun's architecture, the observation functions are actually performed by free flying platforms which relay their information to the crew of the station. In the 50s and 60s, this would be done by physically sending a film capsule. But this raises the question of why not return film capsules to analysts on Earth? That is indeed what spy satellites of that era did (and, in the case of the Soviet Zenit satellite returned the camera, the optics and the electronics as well). The advent of satellites that used CCDs to gather images electronically and transmit them made the station even more redundant in this regard.

There is a slight advantage of humans being able to reach and repair the observation platforms; close proximity to a permanent station could offer missions comparable to the Hubble servicing missions for lower cost and risk. Free flying observatory platforms were proposed for Space Station Freedom - the predecessor to the US segment of the ISS - for this reason, but were cancelled early on due to cost. The upcoming Chinese space station will have a space telescope flying in formation with it, for this purpose.

Earth Orbit Rendezvous

As for assembling spacecraft, von Braun does not make it very clear here, or in the Colliers articles he penned around the same time, exactly how the station facilitates the construction of spacecraft. Presumably he envisions it as being a home for the astronauts who will manually assemble it, and possible a storage space for components awaiting assembly. Its difficult to assess how practical this is using a real world example to go on; the only one is the Gemini-Agena spacecraft.

In July 1966, Gemini 10 docked with a separately launched Agena booster, and the combined spacecraft fired its engines to reach a then record breaking altitude of almost 800km. This was the first successful flight of a spacecraft assembled on orbit; an earlier attempt in May that year with Gemini 8 had led to a dangerous failure of attitude control, as dramatised in the film First Man. In September, Gemini 11 combined with an Agena booster to reach an altitude of almost 1,400km. Aside from comparatively small reboost maneuvers performed by space stations to restore altitude lost due to drag, these two flights are the only two real world examples of a spacecraft assembled on orbit travelling anywhere. They both occurred around 4 years before the first space station, Salyut 1, was flown. Neither required an EVA to mate the capsule to the booster.

An on-orbit assembled spacecraft underway; Gemini 10 attached to its Agena booster

Such docking is now commonplace in spaceflight, and does not involve human operators manually bringing components together as depicted in the 1955 film. It is also incorrect to use the analogy of a shipyard to justify the involvement of a space station as well; a shipyard provides physical support against gravity for the ship under construction, and heavy equipment such as cranes needed to move large components around, neither of which are really necessary when docking things in space. There are also dry docks, which keep the ship under construction out of its intended environment until its ready to handle it, but it seems hard to envision any advantage to doing the analogous thing in space and docking components together in a large pressurised chamber before releasing them into space.

The construction of the ISS, the largest on orbit assembly so far attempted, did require the use of robot arms and some EVAs; but these were all provided by the station itself or a visiting Space Shuttle. There was no large external shipyard facility required. There isn't any reason to suspect it would have been cheaper, quicker or easier to assemble the ISS if there had been such a thing.

Stations Everywhere

Despite all of the above, space architectures around the world have included space stations ever since von Braun made his presentation. In 1969 the NASA Space Task Group was asked to provide a vision for post-Apollo spaceflight, and offered up an overpriced plan that included space stations in Earth and Lunar orbit. When in 1989 President George H. W. Bush launched the Space Exploration Initiative (SEI) NASA came back with another proposal for building a large 'shipyard' station in Earth orbit, which was for some reason required to construct their even larger interplanetary spacecraft. The current Artemis plan, and the unnamed plan that preceded it, call for a new space station to be constructed in a lunar orbit. The Chinese human spaceflight program has since its first manned flight in 2003 been focused on space stations, and the Russians have also proposed a lunar orbit station. It seems whenever political leaders actually pay attention to human spaceflight, and offer serious funding, agencies always begin their response "First, we must build a space station..."

Its as if the von Braun plan is the only possible game in town. To paraphrase John Maynard Keynes; practical men who believe themselves to be quite exempt from any intellectual influence, are usually the slaves of some defunct rocket scientist.

The concept of the space station has far outlasted its original justifications; but are stations a complete waste of time? Should they be bypassed entirely in favour of sending humans straight where they want to go, be it the Moon, Mars or an asteroid?

Salvaging the Station

Given all this, is there actually a role for space stations? Possibly. Stations must have a purpose they serve which cannot be met in other, easier, ways. The should not be constructed for their own sake. Here are some possible functions that I can think of: