A couple of stories caught my attention this week about the possibility of building a space station outside the confines of Earth's orbit, in what's sometimes called deep space. Before considering whether such an idea makes sense, let's take a look at how we could do it.
There are two basic ways to build a space station. Either you construct a bunch of structures from scratch or you repurpose an existing object. The International Space Station (ISS) was built through the first approach, as was the now-defunct Russian space station Mir. These types of stations allow for complex, highly specialized environments to be constructed. The ISS has laboratories, sleeping quarters, an observation module with a panoramic view of the Earth, and much more. Different countries could send different modules to fill their purposes until the retirement of the space shuttles ended that capability. But all this specialization comes with a big upfront cost: the consortium of nations operating the ISS will spend more than $150 billion during its lifetime. Fully a third of that cost was just for the 36 shuttle flights needed to construct and service the station.
A cheaper way to go is to modify an existing space-ready piece of hardware into a workable station. This was the approach used during the Skylab missions. Skylab repurposed the upper stage of the giant Saturn V rockets left over from the Apollo missions. Hollowed out, the upper stage was basically a giant airtight can within which a living area was constructed. Solar panels were attached to the exterior to provide power, and a sunshade was positioned to keep the station cool. The advantaged of piggy-backing off of existing technology is easy to see: the Skylab program cost just $10 billion (adjusted to 2010). Although the upfront costs were cheaper, inefficiencies in a repurposed design meant that the station was never as flexible or capable as the Mir station that followed it or the ISS today. A single person-day aboard Skylab cost more than twice as much as an equivalent stay aboard the ISS. When you consider that Skylab was occupied in total for less than half a year (compared to 12.5 years and counting on the ISS), the cost differential starts to make more sense.
So which model - Skylab or ISS - would a future deep space station follow? Arguments could be made both ways, but current speculation seems to be leaning the Skylab route. Instead of using repurposed Saturn V components, the so-called Skylab 2 would use the upper stage of the as-yet un-tested Space Launch System (SLS). The SLS is the next generation rocket being developed by NASA for use in future trips to the Moon and Mars. With private rockets like the SpaceX Falcon Heavy seemingly progressing more quickly, NASA is under considerable pressure to produce actual results with SLS. The engineering work already done for that program could be applied to give Skylab 2 a head start. Another advantage of this approach is the relative ease of deployment. Unlike the ISS, Skylab 2 can't be assembled in the relative comfort of Earth orbit. Being able to launch it in one or two pieces with SLS is much preferable to the bevy of space shuttle flights it took to build the ISS.
Where would this station be? It could be just about anywhere, but the most logical destination is a place in space called L2. Technically known as the second Lagrange point, L2 is a place in space where the gravitational forces of the Earth and the Sun exactly balance the centrifugal force of orbit. In theory, if you placed an object here, it would staty stationary (excluding its orbital motion around the Sun). In reality, small uses of thrusters would be needed to keep station. Skylab 2 would not be the first man-made object at L2 - several space telescopes already orbit in this area.
So I think that there's little doubt that we can build a station in deep space, but should we? We already have one space station, what would a second allow us to do that we can't accomplish right now? Proponents would argue that working in deep space is an important step towards a future mission to Mars. In addition to the experience gained in living at such distances from Earth, a base at L2 could eventually serve as a way-station on the route to the outer solar system. Opponents of such a base maintain that little science is generated per dollar spent on a space station in comparison to orbiters, rovers, etc. Undoubtably the value proposition for a second space station would be even lower.
On which side of this debate do I fall? I'm pretty torn - on one hand, I'm definitely a supporter of the manned space program as an avenue towards future advances in science. On the other, I wonder if we should just go ahead and send astronauts to the places we really want to go: the Moon, asteroids, Mars. Is the experience gained from a deep space station enough to offset the money spent and the time expended in such an effort? Or, should we just leverage our experiences on the ISS and make the jump directly to Mars? I'm tempted to say yes - if we can go safely now (or soon), let's be bold.