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For quite some time I wonder why spacefaring countries find it necessary to go to space stations instead of doing scientific research on the spacecraft they launched on. Of course, modular space stations have the advantage of having all the necessary scientific equipment in certain modules, are more spacey than capsules, and can host more people.

But what about the bigger spacecraft such as the U.S. Space Shuttle? Does the ISS have something the Spacelab and Spacehab didn't? And why can people stay on the ISS for more than a year, but obviously couldn't so long on the Space Shuttle? Couldn't something dock to the shuttle to provide it with further energy supplies? Staying in the spacecraft would have the advantage of being able to go to any orbit with any altitudes, eccentricity and inclination. E.g. the ISS can't go into a polar orbit nor have a more elliptical orbit extending to the Van Allen belt(s).

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    $\begingroup$ It seems like you're just dismissing the 'more space & more people' part, and I don't really get why. The space shuttle's pressurized space isn't that big, and even with Spacelab attached it's basically the size of the ISS Unity module all by itself. Having a lot more space IS the big advantage of a space station... $\endgroup$
    – Darth Pseudonym
    Commented Aug 13 at 15:13
  • $\begingroup$ "Couldn't something dock to the shuttle to provide it with further energy supplies?" I assume you are including consumables also (food, oxygen etc). Yes that capability could be developed but it would require resupply missions every few weeks. This could be reduced somewhat by increasing storage space, but that would reduce the usable volume for experiments, crew movement etc. Part of the size increase mentioned in other answers is in fact to add more storage space so that the station can go for months if needed between resupply missions, while still having plenty of space for other activities $\endgroup$
    – Steve Pemberton
    Commented Aug 13 at 15:50
  • $\begingroup$ @DarthPseudonym I didn't know the volume in the shuttle with spacelab is merely the volume of Unity module. It seemed much larger. $\endgroup$
    – Star Captain
    Commented Aug 13 at 16:00
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    $\begingroup$ I'm probably being unfair to the Shuttle's native interior volume. Unity and Spacelab were basically the same size, give or take 10 cubic meters, which makes sense because they were both hollow tubes made to be transported in the Shuttle's bay. The shuttle's cabin has about the same interior volume as either (though some of it isn't really usable because it's where the flight controls are). It would be more fair to say that ISS Nodes 1 and 2 together (Unity and Harmony) are the same size as the Shuttle + Spacelab, and the ISS has a dozen more modules besides, some of which are much larger. $\endgroup$
    – Darth Pseudonym
    Commented Aug 13 at 18:50
  • $\begingroup$ Shuttle volume numbers are given here space.stackexchange.com/a/25524/6944 Those numbers are the volume of the cabin atmosphere, i.e. space not occupied by equipment. $\endgroup$
    – Organic Marble
    Commented Aug 13 at 23:54

4 Answers 4

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Space stations are huge, especially by comparison with the capsules that service them.

As a point of comparison, the internal, pressurized volume of a Crew Dragon capsule, where the crew is seated for the whole flight, is about 10 cubic meters. The Space Shuttle was much larger and designed for the crew to move about; its pressurized volume was about 75 cubic meters. The pressurized volume of the ISS is a thousand cubic meters. It masses more than 50 times as much as a capsule and is over a hundred meters long. This size translates directly into mission capabilities like solar panels (the ISS's solar array alone masses as much as four fully loaded Crew Dragons), life support, crew areas, science equipment, and other items needed to carry out experiments in space.

Launching a craft this size in a single flight would be very difficult if not impossible with anything approaching current technology. Even superheavy lift vehicles like the Saturn V (which launched Skylab) and Starship could only carry a payload that was a fraction of the ISS's size and mass. To get around these limitations, the ISS was built in modules - currently 18 crewed modules and a number of other unpressurized components, including the main truss and solar panels - and assembled in orbit. This allowed it (along with Mir) to reach great sizes but it means that there's no practical way to recover the station and return it to Earth. It must stay in orbit until the end of its operational life.

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    $\begingroup$ A fraction the mass, but a large fraction. Starship and the Saturn V could each put about a third of the mass of the ISS into orbit in one go. $\endgroup$
    – Mark
    Commented Aug 14 at 2:09
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    $\begingroup$ @Mark Sure, but if you had the ability to use Starship to routinely launch 100-ton science payloads, you'd also have the ability to routinely launch 100-ton modules to build an even bigger station. $\endgroup$
    – Cadence
    Commented Aug 14 at 18:55
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    $\begingroup$ @Mark yes. Skylab also had roughly a third of the pressurized volume of the ISS! $\endgroup$
    – leftaroundabout
    Commented Aug 15 at 15:36
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Couldn't something dock to the shuttle to provide it with further energy supplies?

There was an Extended Duration Orbiter project for shuttle that included pallets in the payload bay carrying extra power reactants, extra breathing nitrogen tanks under the payload bay liner, a more efficient toilet, and a regenerative CO2 removal system. The original shuttle design also featured a payload bay kit for propellant - Columbia had switches for this - but it was never completed. (factual statement) Since this project threatened to compete with the ISS, it was shut down. (opinion statement)

Even this would not have allowed the shuttle to stay in orbit for as long as a month. Various sources give 16 to 18 days for the requirement, with possible future growth to 30 days.

Does the ISS have something the Spacelab and Spacehab didn't?

For one thing, it has a lot more electrical power. 105 kW. Shuttle was no more than 30 kW. The ISS has immensely more pressurized volume to install and operate experiments than the Shuttle did.

And why can people stay on the ISS for more than a year, but obviously couldn't so long on the Space Shuttle?

Shuttle was not designed or certified for so long a duration. From the beginning it was intended to tend low Earth orbit space stations.

enter image description here

Source: Space Flight Evolution (aka Integrated Program Plan, 1970)

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  • $\begingroup$ Concerning the first point: I meant you can launch a crewed spacecraft into any orbit, not change the orbit once you're in e.g. LEO. If you go to a space station, you need to go to the orbit the space station is at. The upcoming Polaris Dawn mission for instance wants to investigate the effects of Van Allen radiation on humans. It doesn't go to the ISS, but to a higher orbit. $\endgroup$
    – Star Captain
    Commented Aug 13 at 15:58
  • $\begingroup$ @StarCaptain thanks for the clarification. When you said "staying in the spacecraft" in the same sentence as "being able to go to any orbit", I thought you meant on the same mission. I'll remove that part of the answer. $\endgroup$
    – Organic Marble
    Commented Aug 13 at 17:21
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    $\begingroup$ Thank you. I better leave that comment there so that other users or readers get it correctly too. $\endgroup$
    – Star Captain
    Commented Aug 13 at 17:54
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    $\begingroup$ @Woody I know, I worked on a simulation of it for the Shuttle Mission Simulator. The ISS CDRA is a similar device. They use amine beds to absorb the CO2 and then exhaust it into vacuum, using two beds in a cyclic fashion. The shuttle one failed spectacularly on a mission and was recovered by a very cool IFM. $\endgroup$
    – Organic Marble
    Commented Aug 14 at 4:04
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    $\begingroup$ @Woody In-Flight Maintenance. See the RCRS section archive.org/download/flight-maps-and-charts/IFM-d10.pdf $\endgroup$
    – Organic Marble
    Commented Aug 14 at 13:55
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Space stations and Space Shuttles are purpose built

Yes, there are size concerns that others have pointed out, but the bigger concern at the end of the day is that re-entry vehicles are designed from the ground up to take off and land whereas space stations are designed from the ground up for long term exposure to space; so, design choices are made for both vehicles based on what is optimal for each purpose.

A lot of what makes up a reusable reentry vehicle are the features that allow it to re-enter the atmosphere without burning up. When you look at a space shuttle for example, you have Wings, landing gears, heat shields, parachutes, crash seats, etc. which collectively make up about 25% of the vehicle's total mass. None of these features add any value to a space station.

However, because space stations do not have to accomodate all the hatches and surface geometries of theses things, they have fewer points of failure, more efficient use of space, and they can instead use those surfaces for things more relevant to space station design like whipple shields and radiation shielding which improve the station's long term survivability in the hostile environment of space. Space stations also have no "preferred up" meaning that every surface is essentially useful wall space. You don't have areas reserved for walking or that are ignored because they are on the ceiling whereas a space shuttle's interior has to be considered in terms of how ground crews will service it between missions as well as how it will function in space.

Can a space shuttle spend a few days in space within a reasonable margin of safety? Sure, but trying to design a shuttle that could survive in spaces as long as ISS would not be as good at being a space shuttle as a space shuttle, and it would not be as good at being a space station as a space station because of all the compromises that would have to happen to accomodate all of your roles.

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Other advantages of a permanent space station:

  • The ability to have long-running experiments that require continual micro-gravity and also need human interaction.
  • Experiments which measure human long-duration space time (and although this could be somewhat mitigated by sending up new spacecraft on a regular basis and transferring the humans to the new spacecraft each time a new spacecraft arrives and de-orbiting the previous one, this is non-optimal)
  • It looks cool to watch the large space station fly over at night time.
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  • $\begingroup$ I agree with the last point! It is something that is sad to think about when ISS is eventually deorbited to no longer be able to watch it pass overhead. It's so recognizable that there have been at least a dozen occasions when I spotted it by happenstance and knew exactly what it was, although I always check the app to verify. I don't think we will see another object of that size again in LEO for a long time. Although I don't know what future expansions might be planned for Tiangong. $\endgroup$
    – Steve Pemberton
    Commented Aug 16 at 14:36

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