Rockets of Today


It’s the most expensive moving vessel ever made. It’s also the most expensive building ever built, and quite probably the most expensive artificial object of any kind in history, unless you count something like an entire national highway system as a single construction. It has been occupied continually now for twenty years. And it’s becoming increasingly commercialized. It’s the only one of its kind, but it won’t be for much longer... building another one can now be done far cheaper.

Overall, one end of the station is Russian and the other is American. They were originally going to be two rival stations, Mir 2 and Space Station Freedom, but after the fall of the Soviet Union they decided to stick the two together so they could cooperate. Even now, it may be possible for the two to separate and be independent, and with recent political tensions, the idea has been brought up. (One thing that would make this problematic is that though the Zarya module is Russian built, it’s legally owned by the United States, which paid most of its construction costs.) To spread the cost around, additional help was recruited from Europe and Japan. (Some nominally American parts were built in Italy.) The Chinese were pointedly not invited. Fresh memories of the Tiananmen Square massacre may have been a factor in the decision. Since then, concerns about sharing our space technology have kept the Chinese excluded even as visitors.

When looking at the station as it is today, it's easy to just see a tangled jumble. But the layout can be understood by starting with the core — the backbone of the structure. This consists (currently) of a stack of five pressurized modules. Each module is sized to make a full load for a shuttle or a Proton or whatever other craft might bring it up, weighing up to twenty tons. It took about two dozen launches to build the station up to its present size.

To navigate the station, it helps if we have a clear sense of direction when moving about. Fortunately, the station mostly keeps a quite consistent orientation relative to the Earth, with one end pointed in the direction of orbital motion and one side faced toward the ground (except sometimes when docking or maneuvering, when it may angle itself differently, as in the image above). This allows the people on it to designate certain directions as fore and aft, port and starboard, above and below, like on a traditional ship. (But for the latter, they prefer the terms zenith and nadir.) Or, given its shape, one might be more tempted to compare it to an airplane instead of a ship, with the solar panels and so on taking the role of wings. The five main modules are fairly comparable in size and shape to an airliner’s fuselage... but this analogy breaks down once you start looking at the side modules.

Generally speaking, these modules have a round cross section on the outside and a square one on the inside. Each wall is tall enough for someone to “stand” in front of while working with equipment mounted there, and having it flat instead of concave makes this easier. Cubbies such as sleeping nooks and bathrooms have a flat door and a concave back wall. Installed equipment is designed to fit into standardized slots with round backs and flat fronts, each about the size of a fridge.

Let’s list off the five main modules, going forward from the aft end:

That’s a total of six sleeping spaces in the core modules. When seven or eight people are up there, someone — often the commander — uses a docked spacecraft as a bedroom, which offers more room than the scant 2.1 cubic meters of a normal cabin, but less privacy. Space is tightest during a crew change, when for as long as a week there might be up to eleven people. At crowded times, schedules for the exercise machines need to be tightly managed. This gear stays busy because in zero gee, it takes like two hours a day of workouts to stay healthy.

So if you think of the station as a small town, these five modules constitute its main street. It’s a continuous tube that allows you to float from one end of the station to the other in a nearly straight line — the main traffic artery. Now let’s look at some of the side streets.

The longest cross street is at the front, branching off of Harmony. Up here you find:

Back in the middle, branching off of Unity, we have the most complicated part:

The Russian modules each have some attachments, most of which are much smaller than the main modules, but still sizable compared to small fry like BEAM or Bishop. And unlike the international section, where the side modules protrude to port and starboard, the Russian ones are vertical, sticking out above and below.

The Russians had been planning to expand their end further in the near future, but then decided that the ISS was too old to keep investing in, and maybe that American astronauts have cooties. But they did build another module which could have been ready to attach soon. It is called NEM-1 or the Science Power Module, and does not yet have a friendly name. It would provide additional large solar panels and plenty of other external equipment, along with a good amount of multipurpose habitable space. This would have stuck out from the starboard side of Nauka’s bottom junction. They originally were going to have an NEM-2 as well, presumably on the port side, but the budget got cut.

Zvezda, which is critical for life support, is showing its age, and they’re starting to feel a bit nervous about trusting cosmontauts’ lives to it. It recently sprang a leak, and while that was being fixed, some oxygen equipment broke. (They make oxygen by electrolysing recovered water vapor.) They recently had to repair the toilet as well, and its rear rocket motors may now be unusable due to equipment added next to them. Then they found that the leak they’d patched was just one of two leaks. (Also, Zvezda is an unpleasantly noisy place to live... some cosmonauts bring earplugs.) The new Nauka module has problems too: its main engine wouldn’t fire, and while it was docking a thruster fired for no reason, briefly turning the whole station upside down. And it had a leak of its own. After that mishap, they found cracks in Zarya. Because of issues like these, the whole ISS might be retired within a decade, in favor of new stations... or if those cracks spread, maybe a lot sooner.

So the Russians are now saying they will build a whole new independent station instead of expanding the old one, though to budget such a thing sounds like it might be very difficult. After a round of American diplomatic sanctions in 2021, they said they were going to pull out of the ISS at the earliest possible date, after the current term of agreement ends in 2024. After all, they say, “the station’s modules... have mostly worn out their service life.” But a couple weeks later they backed down from this attitude, which probably means they gained some concession. They now say they plan to stay until 2028... or they did before the Ukraine invasion. After the very negative response from the west, they started hinting that ISS cooperation may be ending. Eventually things smoothed down and cooperation seemingly went back to normal. Then Putin fired Dmitri Rogozin from Roscosmos, and the new guy Yuri Borisov (who we had hoped would be less of a fascist blowhard) started the noise right up again. They again announced they’d leave in 2024, but then once again backpedaled, saying they’d leave only once their new station is ready.

When they do leave, it looks like they will have to write off Nauka despite getting only brief service from it. It is arguably obsolete, as it is, like Zarya, based on a Salyut design that dates back to the nineteen seventies. They’re going to keep NEM-1 on the ground for now, saving it for the new station. We shall see if they hold to this plan once they get into the process of actually budgeting and constructing the new station, which even before the economy-crushing sanctions of 2022 would have been a huge stretch for what was left of Roscosmos.

The name would be Russian Orbital Service Station (Российская орбитальная служебная станция), which handily abbreviates as ROSS (РОСС), the root name of the motherland. They want to put it into a sun-synchronous polar orbit so all of Russia would be visible from it. (This would make relocating existing modules such as Nauka rather impossible, as the orbital plane change would require something like six km/s of delta-V). It sounds like NEM-1 will be the first module, after some refitting to give it Zvezda-like core functionality. This would be followed by a second similar module which would apparently take over as core, then a node section and a gateway piece. Eventually they plan to have four large modules arranged into a plus-sign shape around a cluster of minor pieces at the center, if they still have the budget to expand that far (spoiler: they won’t).

On the American side, there was talk for a while of adding a big centrifugal wheel up front, so people could sleep in simulated gravity for better health, but it has not been funded. NASA plans to keep the ISS going until 2031, and then transition to one or more commercially built stations. At that point they will be faced with the problem of safely disposing of the empty station before it falls on someone. They plan to have it plunge to a fiery death over the South Pacific, but controlling such a massive object to reenter correctly will not be easy. It might take twenty tons of fuel to make sure it doesn’t come down in an inhabited area.

Meanwhile, to keep the ISS running until then, they might have to replace stuff that’s currently being handled by Russian equipment... and they just might end up having to do it on short notice, and if not they may need to be ready by 2024. They might need new life support gear to recover water and oxygen, new thrusters to stabilize their orientation, and new propulsion (hopefully ion engines, like China is using) to maintain the orbit. None of these things are costly or difficult... unless they are needed in a hurry.

Where, you may ask, does the big “Canadarm” attach? The answer is, anywhere it wants to. It can swing its free end around, attach it, and detach the former base, switching end for end, and by this means it can inchworm its way all over the station, using any of several attachment points, one of which is a sort of railroad car that allows it to slide to any position along the width of the big external truss. This truss car may be its most used anchorage. Recently an attachment point was added to Zarya. There are two control stations for it, one in the Cupola and one in Destiny. The arm is 17.6 meters long and weighs about 1.6 tons, without the optional “dexterous manipulator” that it can add to the end, which is called Dextre for short, or the Canada Hand. Another add-on that can go on the end is a boom which can add fifteen more meters of reach.  The arm is capable of wrassling objects as big as a space shuttle, as long as it moves them slowly enough. (Moving anything around the outside of the station is always slow... docking and undocking can take a couple of hours, for instance, and the top speed of the truss rail car is one inch per second.)

The ESA is planning to add a smaller arm to Columbus. That would make four arms overall, with those of Kibō and Nauka.

All in all the station is 75 meters long, and the truss has a width of 109 meters. The outer parts of the truss have eight solar panel wings, each with two panels 35 meters long and about 4 wide, which together can produce up to 240 kilowatts peak power... or could when they were new. Some are now being replaced, with new better cells being rolled out on top of the old ones. The whole station masses somewhere toward 500 tons — triple the size of Mir, the next largest object ever put into orbit. There are 1032 cubic meters of pressurized volume in it, if I’ve added it up correctly — enough to hold about one ton of air, as they use full sea-level pressure — but less than 500 cubic meters in the passageways open to people, which is still the size of a house, though much longer and thinner.

It may yet get a lot bigger — several private companies have plans to attach more modules, and perhaps eventually set them free to become independent stations. The company most serious about this right now is Axiom Space, which already sells ISS tourism flights to multimillionaires. They want to build about eight new modules — a whole second ISS, essentially — onto the front of Harmony, then eventually separate it to become a successor station. Their modules are being built by Thales Alenia, so there is direct continuity from the technology and construction techniques already in use. Bigelow also had plans, but these are probably kaput. Nanoracks has been making some noises... they suggested an approach with some modules added to the ISS while others share the same orbit without being attached. Then they teamed up with Lockheed to propose a new station to be called Starlab, with the habitable space being a single large inflatable module. It would be quite roomy yet could be put up with a single big launch.

Sierra Nevada is also working on a large inflatable module, similar to Bigelow’s proposal, but using somewhat different materials. (Sierra likes to note that they actually helped Bigelow build BEAM, specifically the berthing ring and hatch.) Like Starlab, it would be roomier than anything rigid that can be packed into a rocket fairing. They call it LIFE, for Large Inflatable Fabric Environment. And they ain’t kidding when they say large: just one would have more habitable space inside than either half of the ISS. (What an inflatable module usually lacks is windows — if you want a view, go to one of the small hard portions of the station.) They say it could be used at the Lunar Gateway, or even on a Mars expedition. But they have not said how much it will weigh... some estimates say over 50 tons, which would make getting it to such locations quite costly. Then Blue Origin announced they would partner with Sierra to put up a big station which will now be called Orbital Reef. Even in its smallest starting configuration it will house ten, and they plan for it to grow a whole lot larger from there, with many LIFE and other modules attached to a common backbone. The backbone would be made of cylinders that dwarf existing ISS modules, and could be lengthened indefinitely, with each segment hosting a couple of large attachments such as LIFE balloons. Bezos wants it to be a starting point for expanded space industry — a “business park”.

But though Sierra Nevada is trying to make it sound like it’s a race for who will have the first commercial station, it’s Axiom that has gotten a green light from NASA to send up a module. They will be paid a fixed price up front for the first five years use of it. Bigelow thought the NASA offer was too low, and the consensus is that a purely commercial station isn’t viable without a lot of governmental support. Ideally, this should not be a problem to get as long as it’s significantly less expensive than the ISS.

This first Axiom module is mainly living space — it would add four sleeping quarters, each with a window. The next module, in current plans, would add four more, plus a large cupola. Only after that will they add a lab, though even the first module has some working facilities. Then they’ll add a big solar array on a vertical tower, and some methane-burning thrusters, making it ready to function independently of the ISS. After that, they can keep adding however many more modules there’s demand for. The modules themselves will be built for Axiom by Thales Alenia Space. In 2022, some Axiom people rode a Dragon up to the ISS to do groundwork for starting the construction, along with some tourism for wealthy backers while they’re there. They’ve got three more tourist Dragon flights booked for later. They plan to launch their first module in 2024.

The trend is toward separate stations rather than joint ones. The Russians want to put up their separate one by 2030, though it would be tough for them to budget such a thing. India also wants to start its own station by 2030. The Chinese should have their own station fully built out by that time... and the Russians might just see if they can go halfsies on that, or that may be just talk. And there’s increasing speculation that Jeff Bezos’s end goal for the New Glenn is to put up many orbital habitats with it. None of these have articles here yet except China’s, as none of the plans are definite enough.