LogFAQs > #979246745

darkknight109 posted...

Debatable - you still need to ferry all the supplies up to orbit, but now you also need to ferry up the tools and equipment needed to construct the thing as well.

Yeah, but fuel consumption is exponential. Which means it's far more efficient to shuttle everything up into orbit in multiple smaller trips than it would be to load everything into a single ship that has to both reach orbit and then begin a longer trip outbound. The vast majority of its fuel would be consumed on launch. You'd use less fuel with smaller shuttles or rockets launching supplies into orbit.

It's the same reason why the shuttles used to have booster rockets and external fuel tanks. It takes a major effort to get up there. Once you're up there, though, it takes much less effort to head outward.

It's why most proposed scenarios for long-term space programs usually involve some sort of space-based drydock or other shipyard to build and maintain ships in space without having to constantly bring them through atmosphere. It's horrifically inefficient both in terms of resources and design.

Doing it that way also means you don't have to build a ship that can withstand the forces of launch and escape velocity through atmosphere - you just need a ship designed for the unique rigors of interplanetary flight. That way you can use much simpler rocket boosters to launch gear and supplies into orbit using less fuel (or even some form of rail launcher system if we can perfect it), then work from there.

As for tools and waste, that's why you'd want to set up a system/platform to do the work, where you can centralize materials and work on more than just a single ship. It would become the hub for multiple trips, and it could help streamline the entire process.

In theory, a moonbase would potentially be ideal for this sort of thing - you'd have a fixed location on a stable base that could store materials and tools but which lacks significant gravity and atmosphere to pose a problem for transport. But failing that a more significant space station/space platform could be used for the same purpose. This is also the sort of scenario where AI-controlled robot construction assembly line machines (preferably with at least some human oversight) would be ideal for the bulk of the work, because a computer-controlled EVA pod with a welding arm attached is going to have a much easier time putting stuff together than a human in a bulky suit who can only spacewalk for so long each day and who is constantly at risk of potential death.

ALL of this would involve a ridiculous investment of resources, though - and no matter how excited people on Earth pretend to be about space flight and space exploration, we always tend to balk once we realize just what the bill is going to look like. One of the many reasons why we're probably going to be more or less stuck on this mudball until we die - space is hard.



darkknight109 posted...

I don't think that's a pertinent issue. We've built plenty of (unmanned) ships that have not only made it to Mars, but have left our solar system still functional.

It very much is. Scaling up complexity increases the likelihood of failures. Larger structures will have more significant stress points and material fatigue risk. Far more complex systems lead to far more potential faults.

It's like the difference between flying (and crashing) a radio-controlled plane compared to an actual 747. The basic principles are the same for both, but one costs a LOT more than the other, is going to require a lot more maintenance, and will be far more catastrophic if something major goes wrong at the wrong time.

Most of our long-distance explorer satellites are like kit-bashed home computers attached to a lot of relatively simple mechanical tech (you don't want anything too complicated because that dramatically increases the odds of failure), and we kind of just fling them into space (after doing a lot of really complicated trajectory calculations). An actual manned ship capable of (at least) a year-long flight would be qualitatively more complex and advanced (and thus at a greater risk of failure).

We'd probably try to include multiple redundant systems, but even that's not a sure-fire precaution, and every redundant system is going to add to the weight (and thus the fuel issues), and take up more space (which in turn might make the ship bigger, hence more weight, hence more fuel...).

We barely managed to get people to the moon without killing them on the way. Getting to Mars would require a LOT more effort in terms of design and construction of any vessel.



darkknight109 posted...

Putting humans onboard does introduce additional demands on the ship, but it also introduces someone who can conduct repairs

Not necessarily.

Imagine driving your car down the freeway. Now imagine your check engine light comes on. Even with the most robust built-in diagnostic system to tell you exactly what the fault is, it would be somewhat difficult for you to crawl out of the sunroof, crawl down to the hood, then open the hood and change your alternator while the car is still driving.

Once a ship is in flight, it'll be pretty much impossible to ever stop the ship (or even slow down) without essentially committing suicide. You need to maintain the momentum and trajectory to get where you're going without completely missing the target or stopping dead in the middle of nowhere with no way to accelerate yourself again. So every repair would need to be done on the fly, and that makes any external repair a huge risk, and even internal repairs a danger if they involve critical systems (see also Apollo 13).

You could try to put every vital system inside the ship with easy accessibility for potential repair, but you'd never be able to do it for every system, and that level of access is a very inefficient use of space (so we're back to the size/mass/fuel problem).

It's possible the ship can make the entire trip without a single major problem. It's also incredibly likely that something major could go wrong that redundant systems can't compensate for and which cannot be repaired on the fly by the occupants of the ship. It would depend entirely on what the fault was.

And that's not even getting into external damage - a few micrometeors start punching holes through vital parts and you're screwed. You can potentially try to patch things, but you're only going to be able to take along so much scrap metal to repair with (and structural integrity would never be 100% after), and then we're right back to the "just how much weight are you taking with you?" problem.