How have space stations evolved?

Outposts off planet are a sure sign of humanity’s deepening engagement with space. To date, the most significant one has been the International Space Station (ISS). Its presence is historic, and many people – whether or not they are avid space buffs – are aware of its existence. But few individuals beyond specialists know about previous space stations. To learn more about the history of space stations and how they are likely to continue evolving, we spoke to Eric Dahlstrom. Besides being an active member of New Zealand’s space community as a co-founder of the social enterprise SpaceBase, he previously worked at NASA Langley on ISS design. 

What role do space stations place in space exploration?

In essence a space station is just a building in space. Just as there are many reasons for having buildings on Earth, there are many reasons for having buildings in space. Space stations have been used as laboratories, habitats, observatories, transportation nodes, manufacturing and assembly centers, and even hotels. The main function of most space stations has been to serve as a laboratory to study the effects of microgravity. Each day on the International Space Station there are a couple hundred microgravity experiments operating.

Next year will be the 50thanniversary of Salyut 1, the first space station. (Unfortunately, the first crew to that station died as they returned to Earth.) Before the International Space Station (ISS), the Soviet Union launched six stations and the United States launched one. China has launched two so far. So, in total, there have been ten space stations. Today, on the ground, there are somewhere between four and ten space stations being assembled and prepared for launch (the number is uncertain due to the secrecy of some private companies).

The early space visionaries studied how people might live in space on space stations. When Werner von Braun proposed missions to the Moon, he thought we would build a space station along the way. The urgency of the race to the Moon meant the space stations were delayed until after Apollo. But the Space Shuttle was planned (and named) with the intention of shuttling crews to a space station.

The current NASA plan to return to the Moon involves building the Lunar Gateway – a space station in a high orbit around the Moon. NASA hopes to use this lunar space station as a staging location to coordinate international missions to the Moon, somewhat like the Everest base camp. There are also several commercial companies planning to build privately-owned space stations in low orbit around Earth, to be used as labs and hotels. The recent flight of astronauts on the commercial SpaceX Dragon-2 vehicle shows that these companies can now purchase crew flights to their space stations. We are seeing new opportunities for space station concepts.

What lessons can we learn from previous space stations to improve future space stations?

The Russians pioneered the concept of modular space stations, where you could launch different modules and plug them together – like adding rooms to your house. The Russians made the modules almost independent. They kept this philosophy on their side of the ISS. They are still building new modules to add to the five they have currently on orbit. The next Chinese space station, planned for 2021, borrows heavily on the Russian design. The US portion of the ISS (including modules from Japan, Europe, and the Canadian robot arm) was designed to function as more of an integrated whole. It still was assembled in parts, but the station was not fully powered until the large solar arrays were completed. 

All space stations’ modules and elements have been limited by the size of the launch vehicle – the Space Shuttle, the Proton, the Long March 5, or (in the case of Skylab) the Saturn V. The ISS was designed to be assembled by connecting component parts. But even the ISS required more than 200 EVAs (spacewalks) to assemble (1,400 hours). In the future, space stations will be assembled and constructed on orbit to an even greater extent, perhaps robotically. Companies like “Made in Space” are studying how to 3D-print space stations and space habitats, perhaps using asteroid resources. There has also been one experimental module testing the ability of a module to inflate to provide a larger space than when it was launched, while still protecting astronauts by layers of Kevlar.

All space stations so far have been designed for research on the effects of microgravity. I expect the next generation of space stations to be designed for long-term habitation. Some will likely have artificial gravity through rotation. We may see the construction of large wheel-shaped space stations, or simpler designs of modules tethered together to flip end over end. Many of the health concerns of long duration spaceflight could be avoided with some artificial gravity. 

The ability of parts from different nations to plug equipment together was demonstrated with the ISS (this was an area I worked on, connecting the Russian and US parts together). It was a significant victory when NASA adopted the Russian docking system – even to connect the US Shuttle to the US space station node. NASA plans to continue to use this system on the future Moon missions. Maintaining these international standards is a constant effort, but also represents a vision of a future of cooperating in space. I’m not positive, but I think the recent videos from China show they have also adopted these international standards for docking systems and robotic grapple features. This is a clue that China hopes for a future of everyone working together in space.

What are some of the most formidable engineering challenges that stand in the way of creating better space stations?

Space stations need more autonomy in how they operate. Each space station typically has hundreds of people on staff monitoring all the systems and keeping in touch with the astronauts and cosmonauts. In the early days, the US Mission Control used to schedule all astronaut activities in 15-minute increments, 24 hours a day, which drove the astronauts crazy. They finally accepted the advice of the Russians and backed off, giving the astronauts more flexibility and more free time. But all astronauts still operate according to detailed instructions from the ground. In the future, space stations far from Earth should operate more like ships on the ocean, without the detailed directions from the “standing army” at Mission Control.

The challenges of logistics and resupply of space stations remain a limiting factor in their use. The Russians developed the “Progress” robotic spacecraft. Its first automated flight was in 1978 to the Salyut 6 space station. Newer versions of Progress are still used to supply the ISS, along with robotic spacecraft from Europe, Japan, and the United States. NASA’s plans for a lunar space station include resupply from US commercial companies, allowing them to develop commercial capabilities throughout cislunar space. Advocates for commercial space development often note this has an exciting historical analogy here on Earth. In 1849, the US government purchased supplies for only two years for the Texas military outpost Fort Worth; this led directly to the creation of the modern cities of Dallas and Fort Worth.

The ISS has gradually made progress toward closed life support systems, with the addition of water recycling in 2009. It is 85% effective as it processes roughly six tons of water per year. Ideally, space station systems would more effectively recycle all consumables and eventually produce food onboard. But experiments at growing food in space have only progressed slowly.

The ISS and all previous space stations have orbited close to the Earth and under the protection of the Earth’s magnetic field. The NASA Lunar Gateway station planned for high lunar orbit will be outside the protection of the Earth’s magnetic field and exposed to stronger radiation from the Sun and galaxy. Radiation protection will remain a challenge for space stations in deep space. Some designs plan for a “storm shelter” where the crew could remain for some hours during solar radiation events. In the long-range future, larger space stations with more shielding mass will be desired.

The next major step in the development of space will be the use of local resources in space, including mass from the Moon and asteroids. Current hardware development is proceeding in preparation for small-scale experiments, but conceptual designs are being developed for large-scale space habitats constructed from lunar and asteroidal resources. It is an exciting time to design future space stations.