There have been stories in the news recently that NASA intend to deorbit the International Space Station (ISS) in 2031. They are largely based upon a recent NASA report outlining the future of the ISS.
This report makes interesting reading and describes how NASA will transition away from the ISS towards commercial space stations (which it calls CLDs). It also contains the statement
‘The latest budget estimate for ISS life extension through 2030 … assumes deorbit in January 2031’
The ISS cannot keep operating for ever and has already well exceeded its original lifetime which was only 15 years. In 2018 it looked as though the ISS might need to be temporarily abandoned following the failure of a Soyuz capsule, bringing fresh crew and supplies, to reach orbit. Fortunately, this did not happen, and the Soyuz flights resumed. At the time I wrote an article about the future of the ISS which I’ve reposted here
—- Revised post below
After the Soyuz spacecraft bringing crew and supplies failed to get into orbit on 11 October 2018, it looked like Soyuz flights to the ISS might be on hold for a period of time, while the causes of the failure were investigated. It was possible ISS would even need to be temporarily abandoned. Luckily this didn’t! happen and the next Soyuz launched in December.
Although this was good news, the future of the ISS is still uncertain. In February 2018, the Trump administration indicated that NASA would cease to receive government funding for the ISS by 2025. If this were ever enforced, billions of dollars will need to come from private companies, and other countries benefiting from the ISS will need to make a much greater contribution to the costs.
Although the ISS is labelled as an international project, in reality most of the costs of building and operating it have been born by the American taxpayer. Each year it remains in orbit, NASA allocates roughly half of its total human space flight budget to ISS operations – an expenditure that limits its ability to fully fund development of manned spacecraft to visit the Moon and other destinations beyond low Earth orbit.
Is privatising the ISS realistic?
In reality it is difficult to see how private companies would pick up America’s contribution towards running the space station, which is currently running at about $4 billion per annum.
Although in recent years NASA has taken steps to commercialise the ISS, a 2018 NASA audit report was highly sceptical about NASA being able to run the ISS without government support.
‘NASA’s current plan to privatize the ISS remains a controversial and highly debatable proposition, …. it is questionable whether a sufficient business case exists under which private companies can create a self-sustaining and profit-making business independent of significant Government funding.
In particular, it is unlikely that a private entity or entities would assume the Station’s annual operating costs, …. Such a business case requires robust demand for commercial market activities such as space tourism, satellite servicing, manufacturing of goods, and research and development, all of which have yet to materialize. Candidly, the scant commercial interest shown in the Station over its nearly 20 years of operation gives us pause for thought about the Agency’s current plan.’
According to this report America pays 77% of the ISS operating costs. It is unlikely that other nations would want to significantly increase their contribution if the US pulled out. The European Space Agency (ESA) has been working with the Chinese Space Agency and we may well see European astronauts aboard the Chinese space station (Tiangong) in the near future.
So what happens next to the ISS?
Assuming that private companies do not take over the running of the ISS over the next 5-10 years I can see four options.
Option 1: Continue with US government funding beyond 2024.
At the time of writing this is the preferred option BUT one thing to bear in mind is that the ISS has already exceeded its original lifetime. At the start of the programme in 1998, it was expected to be decommissioned in 2015. In 2011, as construction was nearly complete, this was extended to 2020. In 2014, it was further extended to 2024.
By 2024 some of the components in the ISS will be almost 30 years old and nearing the end of their operational lifetimes. Although this does not mean that there will be a major failure in the ISS, it is inevitable that as the ISS gets older there will be increased risks to the crew due to ageing hardware and equipment. However the NASA report stated
‘While the ISS will not last forever, NASA expects to be able to operate it safely through 2030.
It is in the interests of the United States that a seamless transition be made from ISS to one or more future CLDs such that no gap in the Government’s ability to use low Earth orbit space platforms is experienced. A gap could jeopardize the strong network of international partnerships that have matured over the last two decades. Operating ISS through 2030 gives NASA and our U.S. industry partners the time necessary to bring one or more CLDs online in the late 2020s, concurrent with ISS operations, to ensure these newcapabilities can meet the needs of the Agency, its partners, and the Nation.‘
Option 2 Perform a controlled re-entry.
Even if option 1 is chosen, which seems to be the most likely, the ISS will not remain in orbit forever. When the decision is taken that the ISS has reached the end of its lifetime, a rocket would dock with it. The rocket’s thrusters would fire to lower the ISS’s orbit, from its current altitude of 400 km to around 100 km. At this altitude there is sufficient atmosphere for air resistance to rapidly slow it down. The ISS would break up into many pieces each moving so fast that friction would generate enough heat for most of them to burn up in the atmosphere. However, a few larger parts might survive to hit the Earth’s surface.
A controlled re-entry would ensure that the ISS’s final disintegration would take place over an unpopulated area. The Russian space station MIR, which had a mass of 132 tonnes, was destroyed in a controlled re-entry over the South Pacific in 2001.
Path following by MIR during its re-entry – image from Wikimedia commons
The cost of this option would be hundreds of millions of dollars. It could not be done by America alone, it would also need agreement from Russia, the European nations and Japan who legally own some of the ISS modules.
Option 3 When the ISS reaches the end of its lifetime it is abandoned and left to its fate (the cheap option)
At the ISS’s altitude (400 km), there are sufficient traces of the Earth’s atmosphere to cause it to lose energy as it moves against air resistance. This causes the ISS to very gradually spiral down to Earth. The distance a satellite drops in altitude is known as its orbital decay and for the ISS is 2 km per month. This is the reason why the ISS needs to be periodically pushed upwards by firing its boosters or those from attached spacecraft.
If the decision were taken to abandon the ISS and stop boosting it upwards periodically, it would return to Earth within a few years and as it hit the thicker atmosphere it would disintegrate. However, there would be little or no control over where the disintegration happened. There would a small risk that debris could land over a populated area and cause damage to people or property. This is what happened to the American space station Skylab which was abandoned in 1974 and re-entered the Earth’s atmosphere in July 1979.
Skylab weighed 77 tonnes (compared to the 420 tonnes for the ISS) and is to date the largest ever satellite to return to Earth in an uncontrolled re-entry. The inclination of Skylab’s orbit was 50 degrees to the Earth’s equator, which meant that anyone between latitudes 50 degrees North and 50 degrees South was in danger from being hit by debris, although the actual risk of anyone coming to harm was exceedingly low. On July 11 1979 it re-entered and disintegrated over a sparely populated region of Australia.
No one was hit by debris, but some large pieces of Skylab hit the Earth’s surface including part of an oxygen tank (shown below) which was found 15 miles southwest of the town of Rawlina, Western Australia.
President Jimmy Carter issued the following message of apology, when it was clear that Skylab hadn’t fully broken up in the Earth’s atmosphere.
‘ I was concerned to learn that fragments of Skylab may have landed in Australia. I am relieved to hear your Government’s preliminary assessment that no injuries have resulted. Nevertheless, I have instructed the Department of State to be in touch with your Government immediately and to offer any assistance that you may need.’
From the New York Times
Although this option is the cheapest, given the size of the ISS and risk of large pieces hitting a populated area, I cannot see this happening when the ISS reaches the end of its lifetime
Option 4 boost the ISS into a higher orbit.
At the end of its lifetime, a booster is attached to the ISS to place it into a higher orbit where the atmospheric drag is very low. If the ISS could be boosted to an altitude of 900 km if would remain in space for about 1000 years This option is likely to have similar cost to option 2 but gives the fascinating possibility that future generations would be able to visit the ISS. Eventually, it might become an historical site where extremely wealthy space tourists would travel to !
An opportunity for international cooperation?
The ISS provides a platform in which humans can spend a long period of time in near zero gravity. This research is important because, in the next few decades, when astronauts travel to Mars they will have to spend at least six months in zero gravity when travelling to the red planet and a further six months on the return journey. An extension of the ISS’s lifetime to 2028 or beyond would enable NASA to continue in-orbit research to prepare for future long duration space missions, .
As mentioned in a previous post, China has already successfully launched two small space stations, Tiangong 1 and 2, which have been visited by Chinese astronauts. It is completing a larger space station this year (2022) which will be open to foreign astronauts. ESA already has an agreement with China to send astronauts to the new Chinese Space Station once it is operational. However, there is no cooperation between America and China in manned spaceflight. In 2011 Congress passed a law prohibiting any official American contact with the Chinese space program, citing national security concerns. This policy has hardened over recent years and NASA currently prohibits any of its engineers or scientists from working with China.
To me what should happen, although it might be politically very difficult, is for America and China to sit down together and to come to an agreement making America a big partner in the new Chinese Space Station. Perhaps there should be an International Space Station Mark Two?
This space station would be truly international with all the major nations of the world contributing, rather than being America-led and [largely] American taxpayer funded.