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Rockets are expensive. And for the most part, one-time-use-only.

SSTO promises to change that.

However, SSTOs will have limited payload capacity (as will every launch vehicle), and eventually missions we will require more Delta-V and more payload mass than a single trip can handle.

If we're going to put people on Mars, it's going to require a lot of equipment, and a lot of Delta-V to get it there.

  • What are the specific difficulties of assembling (anything) in space?
  • Has anything been "built" in space before?
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  • $\begingroup$ If we agree that SSTO stands for single stage to orbit, can you clarify how SSTO rockets promise to change "single usage?" I reckon you meant to talk about reusable first, and eventually second, stages without major refurbishment. $\endgroup$
    – ChrisR
    Nov 4, 2014 at 23:39
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    $\begingroup$ There is a 3D printer on the ISS as we speak! This may be the first example of "manufacturing" in space. $\endgroup$
    – Stu
    Nov 5, 2014 at 16:26
  • $\begingroup$ @ChrisR Yes, I meant to mean a reusable craft capable of achieving LEO (and delivering a payload), re-entering and landing safely, essentially reducing the cost of a trip to orbit to one tank of fuel. I assume this craft will use air-breathing engines, taking advantage of oxygen available in the atmosphere and hugely reducing the oxidizer mass usually required to bring along. I see what you mean though, an "SSTO rocket" could certainly be a single stage rocket capable of achieving orbit, though such a system would be difficult to make retrievable and reusable. $\endgroup$
    – IT Bear
    Nov 5, 2014 at 20:09

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Has anything been "built" in space before?

Absolutely. Perhaps not "built" in the sense you're talking about, but certainly assembled. A sterling example is the International Space Station. There are about a dozen distinct modules in the ISS that are pressurized and fit for occupation. The first was Zarya, and the latest is Leonardo. They've been constructed by many different countries, and have been added on individually. There are also many unpressurized components. Here's a handy-dandy map - a guide to the ISS (from Wikipedia) The ULF6 configuration of the International Space Station following the addition of the Alpha Magnetic Spectrometer and ExPrESS Logistics Carrier 3, launched by the Space Shuttle Endeavour on STS-134.

Some details regarding the assembly process can be found here, but I feel that this section better explains things. Many components were brought up on launches of the Russian Proton rockets, as well as numerous Space Shuttle launches. Each new module connected smoothly with the others. They were pre-built, but were put together in orbit.

The other thing a project like this is going to take is money. And a lot of it. The ISS may have cost 150 billion dollars. That's a staggering amount of money. That does appear to take into account the cost of Space Shuttle flights. Now, this site says that a mission to Mars would be cheaper:

To put that number in perspective, just over 10 years ago NASA estimated the cost to send astronauts to Mars. Their rough estimates put the price of a human Mars mission in the ballpark of $40 billion US dollars.

Small change, clearly.

A mission to Mars would require a decently-sized rocket. The ISS is about 357 feet long. That's roughly the size of a Saturn V rocket. Now, if you built the rocket in orbit, it might not need to be so large, because it would already be in orbit.

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Another huge disadvantage to 'building' something vs. assembling something, is working in a spacesuit. Tool use and everything else is much, much, much harder than in a shirtsleeve environment (just the amount of effort you need to do to close your hands while working through 5 pairs of gloves that're pressurized, while hauling around the weight of micro-heaters on each finger). Just suiting up and unsuiting eats a fair amount into each work day. Once you start working longer hours to try and make up for that, you start making errors.

Diagram of spacesuit glove with layers:

Using spacesuit gloves can cause your fingernails to fall off

Working on the Hubble

Which talks about the problems of merely unscrewing(!!) a connector (makes micro metal debris which can short out / impair your electronics). On Earth; gravity, wind and vacuum can all be used to get rid of that debris and make it into dust which just 'magically' goes 'away'.

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  • $\begingroup$ Excellent links, I was hoping for an answer like this! Reminds me of a story about designing the Apollo suits, apparently the first designs by NASA engineers were so restrictive they made it nearly impossible for astronauts to move and do what they needed to, so they contracted the work out to other companies one of which was bra-manufacturer Playtex. The women who designed and sewed bras seemed to understand how the human body flexes and moves better. If I'm not mistaken Playtex eventually won the contract and sent their suits to the Moon! $\endgroup$
    – IT Bear
    Dec 15, 2014 at 19:25
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Has anything been "built" in space before?

Depends on your definition of built (see HDE's answer for a detailed explaination of the ISS' assembly), but for the purposes of this answer I will presume you mean where a team in space would receive an IKEA-esque flat pack of parts and then assembles it into a working vessel in space.

Can it be done?

Yes, in fact the ISS shows us a working example of a similar process, the crew frequently receive repair kits or scientific modules that have to be attached to the outside of the station on EVA. This involves alot the regular engineering works my might expect a construction team to do:

  • Bolting things into other things
  • Welding joints
  • Soldering circuitry
  • eta eta

Has it been done?

Not to my knowledge. This might seem strange, but the reasoning is actually quite simple if we examine the potential advantages and disadvantages.

Current Advantages

  1. Designers no longer have to be concerned about the vessel fitting inside the aerodynamic fairing of the rocket.
  2. Can split the final vessel into smaller, more efficient rockets
  3. Low gravity environment makes moving components "easier"

Current Disadvantages

  1. Still have to transport the same mass to space, so fuel savings are limited to what you can save by using smaller rockets.

  2. Smaller limit on the size of the construction crew

  3. Every specialist you need for the construction also needs to be a trained astronaut

  4. Extra Launches to assemble and maintain shipyard/construction team

  5. Loss of components due to drifting off into space

  6. No heavy construction equipment

Until we have a way of gathering fuel or the raw materials in space there isn't much to gain from building in space.

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    $\begingroup$ Your pros and cons lists are great, but I disagree with your conclusion that there isn't much to gain from building in space. Your first two advantages are actually compelling, and the ISS is the proof of concept. Other advantages include distribution of risk on launch (one failed launch doesn't lose the whole project) and ability to incrementally upgrade (though that's more relevant to stations than to ships). $\endgroup$
    – Russell Borogove
    Nov 5, 2014 at 19:34
  • $\begingroup$ I don't doubt that they are compelling reasons, I doubt that they are compelling enough to out way the practicalities of the task at this moment. $\endgroup$
    – CyanAngel
    Nov 5, 2014 at 19:57
  • $\begingroup$ @CyanAngel If building out ISS is a task of the moment, then yes, they are compelling. No rocket could lift the whole ISS (nearly 420 tons nasa.gov/mission_pages/station/main/onthestation/…). And just imagine the size of fairing that would be required. The ISS gives us a blueprint for a simple first step to in-space shipbuilding: start with toolless assembly. With that, your disadvantages 2-6 simply disappear. Granted, instead you get added complexity and a lot of dead weight in module docks, but you can assemble what otherwise would be impossible. $\endgroup$
    – Lesser Hedgehog
    Feb 2, 2016 at 3:55
  • $\begingroup$ Your basically saying "lets use the ISS construction techniques to build other stuff". My disadvantages are not aimed at addressing that construction method, see the accepted answer for that point. for the purposes of this answer I will presume you mean where a team in space would receive an IKEA-esque flat pack of parts and then assembles it into a working vessel in space My opening statement deliberately eliminated the ISS construction method because a better answer already exists $\endgroup$
    – CyanAngel
    Feb 2, 2016 at 9:56

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