The Obama Administration has approved an extension of the International Space Station (ISS) program from 2020 until at least 2024. This is an unfunded statement of intent, which must be both approved and funded by the US Congress. Neither NASA nor the White House have revealed from where the additional US$4 billion per year of funding for this extended operation will come. At present none of the ISS international partners have plans to support such an extension. Is this the best decision for the future of manned space exploration?
The deorbiting of the US Orbital Segment (USOS) of the ISS was originally scheduled for 2016. Deorbiting was extended in 2010 to 2020, but Russia has at least nominal plans to use their most recent ISS segments as the core of a new space station designed as an assembly shop to support future deep-space missions. The US extension to 2024 may or may not affect Russia's plans.
Unfortunately, as the USOS was not designed for disassembly, the US legal responsibility [PDF] for removing the USOS from orbit will eventually result in throwing away roughly a million pounds of refined materials that are already in orbit – placed there at a cost of about $30K/lb ($66K/kg). Even at future launch costs of $1000/lb ($2200/kg), the USOS is worth around a billion dollars in reusable materials. Throwing this lot away is not necessarily the best use of space resources. It might be better to push it into a higher orbit and treat it as a mine in space, or a scrap yard.
It is interesting to look at the reasons put forward (not necessarily in order) for maintaining the US ISS activities by the official communiqué from John Holdren (Director of the White House Office of Science and Technology Policy) and Charles Bolden (NASA Administrator.).
One contentious claim is that extending the ISS will "help cement continuing US leadership in human spaceflight." Leadership is earned, not claimed. I believe that the US ceded this position some years ago by voluntarily demolishing its ability to launch people into space, leaving only the Russian and Chinese space programs with that ability. The US is playing catch-up, not leading the pack.
Another claim is that the ISS is needed for "an increasingly important role in the study of the Earth and its changing climate." The statement lists a number of instruments that will be sent to the ISS over the next few years, but in fact none of these gain any real benefit by being mounted on the ISS. Their missions would be carried out less expensively and more flexibly by systems of satellites.
There is only one experiment on ISS for which it has been claimed that positioning on the ISS was required, the Alpha Magnetic Spectrometer 2. This task was considered sufficiently important that one additional Shuttle flight was authorized to put it in place. The problem? AMS2 required about 2-2.5 kW of power, and that was supposed to make it impractical to put on a satellite. The thing is, a modern communications satellite provides in the range of 6-8 kW of continuous power for its operations. A satellite dedicated to the AMS2 would have cost a fraction of the $1.5B Shuttle flight.
We'll go quickly by the claim that research done on the ISS has been worth the cost. Similar to claims made about the entire space effort, it hasn't.
Holdren and Bolden also advance the notion that further research on spaceflight-associated human-health issues must be carried out aboard the ISS "in support of planned long-duration human missions beyond low-Earth orbit—including our planned human mission to an asteroid by 2025 and to Mars in the 2030s." There already exist medical records on people who have spent years in orbit, which one would think would provide answers to many of the open questions. Many others, such as physiological response to cosmic radiation exposure while weightless, cannot be examined in the ISS. In either case, even without the extension, there remain six years without the extension to fill in the holes.
It's also worth noting that the planned "human mission to an asteroid" has transmogrified into robotic capture of a (tiny) asteroid or rock from one, orbiting it around the Moon, and sending what is essentially a manned lunar orbit mission to work with it. Not really a deep space manned mission with unknown conditions.
The fact is that the hardest medical problems with interplanetary space travel are extremely prolonged exposure to weightlessness (we have nearly 150 man-years total experience in zero-g; Sergey Krikalev alone has spent 2.2 years in orbit), radiation exposure, which can't be endured on a trip to Mars, so it has to be cured (shielded), and keeping 2-3 people in a closet-sized capsule for several years while keeping them from driving each other around the bend. This latter is often considered the most difficult part of surviving interplanetary travel at our level of technology.
It is also argued that the ISS extension will provide more opportunities for the commercial space industry to get off the ground. The problem is that the extension will keep the commercial space industry highly focused on a type of commercial activity that will suddenly disappear when NASA sticks an Orion with the ESA rocket propelled Service Module on top of an SLS booster rocket sitting atop a cluster of two or three SLS boosters (this combination will get an Orion capsule to any LEO orbit).
I believe it is easier to argue that, compared to enabling three Orion/SLS manned flights during the 2020s at an overall cost estimated at $41B (add-on flights are estimated by NASA at nearly $2B a throw), it is probably worth evaluating the use of slightly stretched Dragon/SpaceX Falcon Heavy craft, currently aimed at the capability of lifting 57 metric tons to LEO with an estimated per launch cost of under $200M. Even given that both costs are probably conservative, it would be difficult for the cost of the Falcon Heavy to catch up with that of the SLS. Of course, if the $4 billion a year from 2021 through 2024 comes out of the SLS development budget, there won't be an SLS in the 2020s.
The ISS has already served its main real-world goal of helping us learn to live and work in space. Should the ISS be deorbited in 2024, 2020, or 2016, boosted to serve as a source of materials, or meet some other fate? In the long run, it probably doesn't matter. Ultimately, we as a species will have to find a reason for living, working, and establishing property rights in space so compelling that its pursuit can't be upset by economic fluctuations or the decisions of a single government.
(Full disclosure: your correspondent is a US citizen who has been involved in various parts of his career with NASA projects.)