Orbital construction

[nestor_d]

So I admit I'm thinking a bit like KSP here, but hear me out. So, a very large chunk of the delta-V budget of a mission is spent escaping earth's gravity and getting into LEO, hence that Robert Heinlein quote "if you can get your ship to orbit, you're half-way to anywhere". Of course it's not mathematically accurate, but it's meaningful in some sense. We spent a lot of launches and delta-v building the ISS, and that thing is huge, but imagine if instead of a station it was a spacecraft with propulsion, probably much less massive than the ISS, imagine the Delta-V that thing would have. It would have full tanks in space! I do think with something of that size and power, we could have put humans on mars and back by now, couldn't we?

[Mazon Del]

When the ISS was originally budgeted and such, the plan was for the ISS to be two stations right next to each other. The one that we got, plus a giant empty space that was to be a drydock for large craft assembly. It was to be separate from the other one to keep the science-ISS isolated from the vibrations in the other to keep the science data good. Alas, it was pretty much the first thing on the chopping block as time went on. But yes, there has been some discussion on the idea of re-configuring the ISS and slapping an engine on it. If I remember right, the big problem is that the ISS lacks the radiation shielding to adequately protect the crew and electronics through the VA belts and into space beyond. It was designed to get most of that protection from the VA belts, which means staying within them.

Correcting that deficiency is one of the harder parts to fix about the plan to snag the US modules and send them into the lagrange point behind the moon to act as an observatory.

[nestor_d]

When the ISS was originally budgeted and such, the plan was for the ISS to be two stations right next to each other. The one that we got, plus a giant empty space that was to be a drydock for large craft assembly.

I didn't know that, that woul've been awesome!

[Mazon Del]

I know. T-T

[Pipcard]

When the ISS was originally budgeted and such, the plan was for the ISS to be two stations right next to each other. The one that we got, plus a giant empty space that was to be a drydock for large craft assembly.

Drydocks would be too complex and expensive. It's more practical to assemble things via direct docking of prefabricated modules, or at the most, berthing with a robotic arm (with two ends that can "inchworm" between grappling points).

Edited August 25, 2015 by Pipcard

[Nibb31]

A drydock makes no sense. This isn't Star Trek.

Orbital assembly would be done with prefabricated modules docked together. It's much cheaper and safer than sending astronauts to do construction work.

[xenomorph555]

A drydock makes no sense. This isn't Star Trek.

Orbital assembly would be done with prefabricated modules docked together. It's much cheaper and safer than sending astronauts to do construction work.

Yeah, the Soviets had the right idea with MKBS, MIR, etc.

[Halo_003]

A drydock makes no sense. This isn't Star Trek.

Orbital assembly would be done with prefabricated modules docked together. It's much cheaper and safer than sending astronauts to do construction work.

I agree, but it (I think) would also depend on the scale we're talking about. If it's a relatively small-medium drydock to build things like probes or smaller ships I think it makes sense. It's when you talk about BIG (Thinking HERMES from The Martian trailers) ships and construction projects that it becomes many times easier to build in space rather than a dry dock. Just my $.02.

[More Boosters]

A drydock makes no sense. This isn't Star Trek.

Orbital assembly would be done with prefabricated modules docked together. It's much cheaper and safer than sending astronauts to do construction work.

How are you so sure? It's only 2015 yet.

[passinglurker]

I agree, but it (I think) would also depend on the scale we're talking about. If it's a relatively small-medium drydock to build things like probes or smaller ships I think it makes sense. It's when you talk about BIG (Thinking HERMES from The Martian trailers) ships and construction projects that it becomes many times easier to build in space rather than a dry dock. Just my $.02.

you mean like what made in space and nano racks are trying to do?

manufacturing in space can make sense you don't need near as much careful engineering and design work to transport raw materials and packaged electronic components. if you have a supply of that stowed in orbit you could have a new satellite deployed about as fast as you can transmit your designs to the station in some ways construction can be easier because the satalite doesn't have to be built to survive launch so less structural material is used.

[Gaarst]

So I admit I'm thinking a bit like KSP here, but hear me out. So, a very large chunk of the delta-V budget of a mission is spent escaping earth's gravity and getting into LEO, hence that Robert Heinlein quote "if you can get your ship to orbit, you're half-way to anywhere". Of course it's not mathematically accurate, but it's meaningful in some sense. We spent a lot of launches and delta-v building the ISS, and that thing is huge, but imagine if instead of a station it was a spacecraft with propulsion, probably much less massive than the ISS, imagine the Delta-V that thing would have. It would have full tanks in space! I do think with something of that size and power, we could have put humans on mars and back by now, couldn't we?

Putting 100t of raw materials in several launches or 100t of spacecraft in one launch to orbit is not that different: payload fraction is about the same for any launcher mass (something <5% for LEO) so launching many rockets instead of one is not really better.

Also, as said above, it is way easier and cheaper to orbit a craft assembled on the ground than to assemble a craft in orbit.

[Nibb31]

I agree, but it (I think) would also depend on the scale we're talking about. If it's a relatively small-medium drydock to build things like probes or smaller ships I think it makes sense. It's when you talk about BIG (Thinking HERMES from The Martian trailers) ships and construction projects that it becomes many times easier to build in space rather than a dry dock. Just my $.02.

How so? How is it many times easier to send hundreds of trained astronauts with supplies, life support, hab modules, tools, manufacturing and testing equipment, jigs, cranes, materials, etc... to spend months working in space? Employing hundreds of factory workers in a conventional manufacturing facility will always be cheaper, faster, and simplify the logistics chain.

It will always be easier to build, test, and integrate modules on the ground and only do limited assembly in space.

[RainDreamer]

I am thinking making 3d printed cube sat in orbit might be easier than launching them. but launching prefab modules to dock to each others sounds better for big stuff.

Once we reach better automation technologies (like, way better), I think we can even do bigger stuff using robots and such, not much different than a car factory, but in space!

Edited August 26, 2015 by RainDreamer

[kerbiloid]

If you have a ~1000 t orbital shipyard, you can build there a ~1000 t space cruiser.

If you have a ~1000 t cruiser on orbit, you must supply it with ~10000 t of fuel (maybe per flight, maybe per year, maybe per several years - doesn't matter).

To put on orbit ~10000 t of fuel you must launch ~200 000 t of rockets which means 100 SaturnV per ship just to deliver the fuel.

Simple nukes do not solve the problem as their ISP is just 2..3 times more than chemicals have.

So, you need an Earth-orbit tanker with ISP ~10000...100000 s to stay in healthy boundaries.

And if you have ISP 100000, why do you need all that orbital stuff at all?

You just sit into your "Thunderbird 2"-style ship on the backyard and fly to Pluto.

So, no orbital shipyards, would never appear at all.

[K^2]

Or you can, you know, mine just about any icy asteroid/planetoid for fuel and get it to your orbital ship for practically nothing. You can also mine rocky asteroids for everything you need to build ships at your orbital shipyard.

[kerbiloid]

Or you can, you know, mine just about any icy asteroid/planetoid for fuel and get it to your orbital ship for practically nothing. You can also mine rocky asteroids for everything you need to build ships at your orbital shipyard.

Yes, can. And now calculate delta-Energy to deliver the ice from an asteroid (icy ones are of course far from Sun, not next to Earth) - or compare an energy to deliver, say, 1 t of methane from Titane with heat energy which this 1 t of methane gives when being burnt. And you get a sad result: it's energetically simpler to deliver the fuel from Earth and to make methane from CO2 and H2O on Earth than to deliver it from Titan.

Edited August 26, 2015 by kerbiloid

[K^2]

Yes, can. And now calculate delta-Energy to deliver the ice from an asteroid (icy ones are of course far from Sun, not next to Earth) - or compare an energy to deliver, say, 1 t of methane from Titane with heat energy which this 1 t of methane gives when being burnt. And you get a sad result: it's energetically simpler to deliver the fuel from Earth and to make methane from CO2 and H2O on Earth than to deliver it from Titan.

Your orbital-fu is weak, grasshopper. The further out the asteroid, the better. You need almost no dV to get from edge of the Solar system to the inner system. Then you can aero-capture to rendezvous with a ship in LEO. Or Mars orbit. Or a cycler traveling between the two.

Best part, even what little dV you need to launch cargo into a transfer orbit - doesn't have to come from fuel. You can mag-rail stuff directly off a large asteroid. Then you just need a few puffs along the way for adjustments. These can be performed with ion thrusters if you're really worried about wasting fuel along the way.

So outer Sol System mining can make a difference between needing 9k dV or a few hundred m/s. And later can come from ion thrusters in this scheme. So again, effectively free.

By far, the hardest part about space travel is leaving a planet with atmosphere. Once you are in interplanetary space, you can go anywhere you want, combining fly-bys and aero-braking maneuvers. Provided you have time for all of that, of course. But presumably, we don't care if our fuel has to spend a decade in transit, so long as we have a steady stream.

[cryogen]

Yes, can. And now calculate delta-Energy to deliver the ice from an asteroid (icy ones are of course far from Sun, not next to Earth) - or compare an energy to deliver, say, 1 t of methane from Titane with heat energy which this 1 t of methane gives when being burnt. And you get a sad result: it's energetically simpler to deliver the fuel from Earth and to make methane from CO2 and H2O on Earth than to deliver it from Titan.

You don't need an ice-covered asteroid; you can extract water from ordinary rocks. You can find them in similar heliocentric orbits as the earth.

A key example of this is that water or other material extracted from a returned, volatile-rich NEA could be used to provide affordable shielding against galactic cosmic rays. The extracted water could also be used for propellant to transport the shielded habitat. [...] A 500-t, carbonaceous C-type asteroid may contain up to 200 t of volatiles (~100 t water and ~100 t carbon-rich compounds), 90 t of metals (approximately 83 t of iron, 6 t of nickel, and 1 t of cobalt), and 200 t of silicate residue (similar to the average lunar surface material).

http://www.kiss.caltech.edu/study/asteroid/asteroid_final_report.pdf

The delta-v distances involved can be extremely low. EML-1 is only ~150 m/s from heliocentric orbits, and some near-earth asteroids are only slightly further away.

[kerbiloid]

You need almost no dV to get from edge of the Solar system to the inner system.

And then catch it: 30..50 km/s speed.

Then you can aero-capture to rendezvous with a ship in LEO. Or Mars orbit. Or a cycler traveling between the two.

Somewhere near Yucatan we have a nice sample of such ... err... aerobreaking.

Also do not forget: nothing is 100% perfect. So, waste heat make a nice cloud of comppressed steam from the icy rock.

You can mag-rail stuff directly off a large asteroid.

Which means that you have an asteroid power plant producing interplanetary amounts of energy. Energetic balance is poor again.

An unexpected joy: such power plant would be the first extraterrestrial seaship because it will melt tonnes of ice around it with waste heat.

And later can come from ion thrusters in this scheme. So again, effectively free.

Delta of energy does not depend ion/chemical/nuke/magic.

Anyway you need (V2^2-GM/R2)-(V1^2-GM/R1).

By far, the hardest part about space travel is leaving a planet with atmosphere.

If you mean "very slow travel". Are you ready to have a 9-year trip with Rosette?

If you want a fast journey, you need tens-hundreds km/s.

And all near-Earth atmo- and gravi- loss is just abou 2 km/s - nothing to look at.

[magnemoe]

How so? How is it many times easier to send hundreds of trained astronauts with supplies, life support, hab modules, tools, manufacturing and testing equipment, jigs, cranes, materials, etc... to spend months working in space? Employing hundreds of factory workers in a conventional manufacturing facility will always be cheaper, faster, and simplify the logistics chain.

It will always be easier to build, test, and integrate modules on the ground and only do limited assembly in space.

Only reason for an orbital drydock would be repairs or rebuilds you could not do efficiently in an spacesuit.

- - - Updated - - -

Your orbital-fu is weak, grasshopper. The further out the asteroid, the better. You need almost no dV to get from edge of the Solar system to the inner system. Then you can aero-capture to rendezvous with a ship in LEO. Or Mars orbit. Or a cycler traveling between the two.

Best part, even what little dV you need to launch cargo into a transfer orbit - doesn't have to come from fuel. You can mag-rail stuff directly off a large asteroid. Then you just need a few puffs along the way for adjustments. These can be performed with ion thrusters if you're really worried about wasting fuel along the way.

So outer Sol System mining can make a difference between needing 9k dV or a few hundred m/s. And later can come from ion thrusters in this scheme. So again, effectively free.

By far, the hardest part about space travel is leaving a planet with atmosphere. Once you are in interplanetary space, you can go anywhere you want, combining fly-bys and aero-braking maneuvers. Provided you have time for all of that, of course. But presumably, we don't care if our fuel has to spend a decade in transit, so long as we have a steady stream.

Anybody who have done ISRU in KSP should know this.

Downside is that ISRU increase the weight of the mission a lot, if you are sending probes or even an simple manned mission to Mun or Minmus it does not make sense neither for an station in LKO.

This is the status of our space program.

For an base on Mun with systematic exploration of it it starts making sense. Note that ISRU in KPS is easier than in real world.

[Mazon Del]

Actually the big reason for an orbital drydock is that your workers end up being FAR more efficient if they can work in basically a tshirt/shorts environment than a space suit. Wearing a space suit and operating in one is immensely tiring. That thing is STIFF. Plus your manual dexterity pretty much goes out the window. Yes you can do all the things they did to build the ISS in a suit, but it is just so. much. harder! In the end, your work per unit time goes up because of this, and also the time you save not having to go through all the crazy effort of getting ready for an EVA and such. Incidentally, the way they'd get people back and forth between the two stations was basically a soyuz-like pod.

[Nibb31]

Do you really think that you would use actual human workers?

If work in space ever becomes a reality, it will be done by robots. There will be no space miners or space factory workers. That makes nice science fiction, but in reality it would be silly.

[Mazon Del]

Of course, robots have yet to prove themselves in orbital construction tasks. While I agree that largely in the end state robots will take up the majority of the task, humans are going to be involved if for no other reason than people don't trust robots to solo any task costing billions of dollars if they don't have to. It only costs a couple extra million to put a person or two up there to watch over things, even if they never are needed the funders will feel better.

[RainDreamer]

If we use robots, what differences would it makes if we have a few engineers down on earth and just watch live feed of them working comparing to having astronauts up there? They also don't have to pay for life support systems and maintenance of those systems.

Unless we developed sophisticated enough AI that we can fear a rebellion, of course...

[Mazon Del]

If all of your support staff are on the ground, what happens when an incident occurs that the robots cannot handle even with teleoperation? And if you say "just build robots that can do everything a human will be able to do" then you have added enough cost to the project that you probably just want to go with humans anyway. And if you say "Well only have one of THOSE robots and just have everything else be its 'cheapish' specialized cost', then you again reach the problem that people are nervous without humans in the loop. In the near term people WILL be involved, there just isn't too much point trying to get around it.