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For e.g. if we want a telescope in space, can't we assemble it in space? Send the constituent assembly parts up there (unmanned). Have the individual units, assemble (unmanned) to constitute the actual thing.

The assemblies themselves constitutes a small payload so it won't be very cost prohibitive to get it into space. The building of assembly parts themselves can be distributed across nations in some way.

There could be small shuttle space ships that carry small payloads, put, those payloads, into orbit, and re-enter back into earth once their missions are over. They can be subsequently re-used for more such missions.

And there could be one global body to coordinate all of those activities. Why are there not any projects in this direction?

marked-down
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deostroll
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    What you propose here is exactly how the ISS was assembled, and to a lesser extent how the Hubble Space Telescope was fixed/upgraded over time. So it has been used in the past. – NeutronStar Jan 31 '18 at 16:01
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    "Sending small drones instead of huge rockets" sounds like you're exaggerating how much smaller the rockets could be made. – JiK Jan 31 '18 at 16:07
  • I agree with JiK--there are penalties for smaller rockets, such that we're already apparently exploring the smallest possible orbital launchers for our current technology base. https://space.stackexchange.com/questions/18789/how-small-could-an-orbital-rocket-be – Erin Anne Jan 31 '18 at 17:13
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    Won't there be an inefficiency for multiple small rockets? That is, there's overhead weight that is not part of the payload, like a computer system, guidance system, and others. With one big rocket, I have fuel to lift one guidance system. With five rockets, I need fuel to lift five guidance systems. – Don Branson Jan 31 '18 at 20:44
  • @JanDoggen Yeah, realized that "drones" can't make it up there...but the main inspiration was to send something small...and why not... – deostroll Feb 01 '18 at 09:09

3 Answers3

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Let's say you have a 6500kg piece of equipment you want to launch into space, but your rocket design can only lift 2500kg to the desired orbit. You can:

  • Build five of these
  • Strap them together
  • Put said piece of equipment on the nose of the middle one.
  • Launch

That's already worse than designing a new rocket, but at least it cuts down on R&D time. The vital part is to realize that five rockets glued together are almost as powerful as five rockets launched separately (you need some extra mass to hold the rockets together and the aerodynamics are affected as well).

If you can figure out a way to transfer fuel from one rocket to another, the combined rocket has even more delta-V than the original.

Your suggestion is to:

  • Build five of these
  • Chop up the payload to five equally sized parts in a way that it can be assembled back together in space.
  • Add an assembly machine with one of the launches, or add a sixth one
  • Arrange the launches so that they meet at the same orbit. This will likely require maneuvers after reaching orbit (costs fuel).

You saved: the cost and R&D time for strapping the rockets together; the cost for a launchpad that can carry the bigger rocket (both insignificant); mass of the struts holding five rockets together (possibly less mass than the assembly drone); you lose only 1/5 of the payload, not all of it, if a rocket fails.

You introduced: the assembler cost; orbital maneuvering fuel and logistical challenge; R&D how to chop up the payload and assemble it. I'm not sure if automated docking is already a thing, but at the very least someone has to program the drone - or send a human (bad for PR if the rocket fails, and they can't handle as much acceleration).

Not a win.

Perhaps you could decide to build one rocket and reuse it five times. Unfortunately, recycling a used rocket takes time, and it still does cost money (though less than a brand new rocket). Also, it's kind of a new thing and not very thoroughly tested, meaning you might not want to rely on this. You also don't save the cost of the fuel. Overall, you might save money (or not), but I'm afraid the extra time it takes makes the idea not worth it.

John Dvorak
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    Five rockets glued together are not as powerful as five rockets launched separately, the glue weight (additional structure for bundling) reduces the payload weight. The aerodynamics of a single rocket may be better than that of the bundle.The reliability of the bundles is much worse, every single failure of one of the bundled rockets will cause a failure of the bundle. – Uwe Jan 31 '18 at 14:11
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    A purpose built rocket five times the size of your baseline rocket is more efficient and can be more reliable than five rockets launched separately. One copy of the avionics instead of five, better drag characteristics, engine-out capability, potential redundancies. – Russell Borogove Jan 31 '18 at 16:10
  • @RussellBorogove a stray "not" has wandered into that sentence. Sorry about it. – John Dvorak Jan 31 '18 at 16:45
  • @Uwe Good point about points of failure. Addressed all of your concerns. Thanks for the feedback. – John Dvorak Jan 31 '18 at 16:46
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    Worth emphasizing: You saved R&D resources on strapping together rockets that could have been used for multiple different payloads. You introduced R&D resources on how to chop up and assemble each individual payload, and that is a significant cost that must be incurred anew on each subsequent mission. – E.P. Jan 31 '18 at 20:06
  • "the combined rocket has even more delta-V than the original." What logic did you use to arrive at that conclusion? – Acccumulation Jan 31 '18 at 21:28
  • Just an FYI, but strapping more rockets together is also much riskier (see the ill-fated Soviet N1 rocket – Machavity Jan 31 '18 at 22:34
  • @Acccumulation You can drain the outer fuel tanks first while using all five thrusters. So far, things look similar. Now, when they empty, discard them. The result is an assembly of three rockets, all with full tanks, that is an appreciable distance from the launch pad. Repeat again to get the original rocket at its full Delta-V, except it's at a higher altitude and moving fast. It's an engineering nightmare, but it really saves fuel. The extreme version of this is called asparagus staging – John Dvorak Feb 01 '18 at 03:05
  • @JohnDvorak I asked you what logic you used, and you responded with simply argument by assertion. And providing a citation to a space simulator rather than actual physics doesn't help much. – Acccumulation Feb 01 '18 at 15:21
  • What do you mean, argument by assertion? – John Dvorak Feb 01 '18 at 16:43
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The building of things is already split across nations - but it's much easer to assemble them here on Earth than remotely in space.

Due to various factors, but mostly due to surfaces increasing as the square of size, and volumes increasing as the cube, it is more expensive to have two launches of one tonne than one launch of two tonnes.

There are a lot of things where having a single global body to coordinate activities would be beneficial, but human nature wont allow it. Space is one of the areas that has better coordination than most.

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I will not discuss the use of smaller or bigger space crafts, that is already done here by others. I will discuss the use of drones.

Drones will never make it into space. At least not a drone with propeller blades or wings. The blades need air to generate some lift. And the higher you get, the thinner the air is. So there will always be a 'ceiling' where a drone can get, ignoring the amount of energy it needs to get that high (bigger batteries = bigger drones = bigger batteries, etc.). The lack of air is why airplanes cannot make it to space either.

AFAIK there are only two ways of escaping from earth: with a deflating balloon (propulsion) or a canon ball (no propulsion). A canon ball needs to get the "escape velocity" which is for earth a little more than 11 km/s. This is not practical, since you will have to release all the energy at once to the space craft. So it has to withstand a huge acceleration (and forces). Although you do not need to reach the escape velocity when you go into orbit (but you will get close), the principles are the same.

That leaves only a rocket as being usable for escaping the earth. A rocket can release the energy it needs to escape the earth in a controlled manner. It doesn't need air to get lift, but it exhausts gases to propel itself.

ffonz
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    I read "drone" as "smaller, unmanned craft" rather than "quadcopter". If someone thought quadcopters could do it, I suspect they'd have started with a question along the lines of "why don't we just fly planes to space?" – Tin Wizard Jan 31 '18 at 23:30
  • "At least not a 'classic' drone with propeller blades." -- you mean the kind we started building a decade or so ago? ("Classic" is an extremely ill-fitting term for this.) – Nathan Tuggy Feb 01 '18 at 03:40
  • I agree with the blades part...so it has to be something that has propulsion...thats new... – deostroll Feb 01 '18 at 09:06
  • @Walt: If I think of a drone, I think of something that can hover or float. Not a rocket. – ffonz Feb 01 '18 at 12:27
  • @ffonz my point is that you're using a relatively new meaning of the word - as Nathan points out, from the last decade or so - that doesn't line up with how the word was used before that. By descriptivist logic, both meanings are valid, but I try to give people the benefit of the doubt and assume they intend the meaning that's not moronic in context. – Tin Wizard Feb 01 '18 at 15:28
  • @Walt and Nathan Tuggy: Ah, I get it. Since English is not my mother tongue, I didn't use the word ten years ago. I thought of a drone as a quadcopter or an unmanned aircraft like the MQ-1 Predator. Even though English is used as a lingua franca, it still can give confusion. My appologies, I will remove the word 'classic'. – ffonz Feb 02 '18 at 08:29