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I'm writing a story in which a civilization previously capable of (firmly technobabble-based) FTL travel has become stranded, orbiting an isolated star with no rocky planets. (There was a planet, but it was destroyed by their crash-landing in the star system.) The civilization is comfortably capable of forging an existence in artificial habitats orbiting their new star, but for the plot to function, it must be prohibitively difficult for them to leave the star system (to return home, or colonize elsewhere).

Their best chance would be to get their hands on an already-constructed FTL travel device, but I'm having trouble constructing a convincing (within-universe) reason why they couldn't simply build a new one from stuff they have at hand.

Olle
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    Hint: read why we can't land on our Moon anymore. – Mołot Jan 03 '19 at 11:35
  • Welcome to worldbuilding. Please take the [tour] and visit the [help] to make yourself familiar with our community and its standard. – L.Dutch Jan 03 '19 at 11:39
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    @Mołot You piqued my interest. Do you have a link to a good resource on the subject? – Jasper Jan 03 '19 at 15:15
  • @Jasper not at hand, I'll try to find it later. Edit: basic googling gave me https://www.space.com/7015-40-years-moon-landing-hard.html – Mołot Jan 03 '19 at 15:21
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    If you really want to strive for realism but also have a completely destroyed planet, please read about the ludicrous amount of energy needed to actually destroy a planet. The Earth is a is a 4,550,000,000-year-old, 5,973,600,000,000,000,000,000-tonne ball of iron – vsz Jan 03 '19 at 18:31
  • the entire civilization? – ths Jan 03 '19 at 19:36
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    How can they crash-land into a planet with enough energy to destroy the planet and still have survivors on the ship? – NomadMaker Jan 03 '19 at 23:56
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    @Molot That article doesn't say we couldn't figure out how to land on the moon if we really wanted to; it says we're figuring out how to do more than just land on it next time, and also don't have the same kind of budget we did last time. – Ray Jan 06 '19 at 23:14
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    @Ray Duh, of course we could if we really wanted to. It's not like it's no longer possible to land on the Moon because the cosmic forces changed or whatever. The problem is it's not as simple as "just build another Saturn V" - we'd need to do most of the R'n'D again, build up all the facilities etc. We no longer have the infrastructure and even designs (the plans are no longer available due to the software not being available due to the hardware no longer being available...) to do it. As a total guess, I'd expect a blank slate project to get us to the Moon would be easier than redoing Apollo. – Luaan Jan 07 '19 at 08:26
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    FYI, in real life we just recently found a way to replicate the extremely durable concrete Ancient Romans used back in the day: http://time.com/4846153/ancient-rome-concrete-cement-seawater/ Which was simply forgotten. Maybe your civilization also just forgets how to build them? – Juha Untinen Jan 07 '19 at 14:13

32 Answers32

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The simplest way is probably to leave them with a shortage of unobtainium. A substance named for obvious reasons, that happens to be required for the production of FTL drives.

Perhaps the limited quantity they had in their existing drive was destroyed (causing the accident) or dispersed in the accident. Either way, they're now limited to space habitats and STL drive until such time as they can come into possession of more unobtainium.

Separatrix
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    Following this idea the unobtanium could be anything. It could be fuel for example. The FTL has run out of fuel, and the fuel it needs to operate requires heavy metals etc that there just aren't enough of in the current solar system. – Tyler S. Loeper Jan 03 '19 at 14:48
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    Doubly ironic if the unobtainium is on another planet. You accidentally destroy your space fleet, you can't get to the planet, you can't build another space fleet. – DJClayworth Jan 03 '19 at 15:37
  • @DJClayworth Even better, if it comes from another planet, separatists launch a concerted effort to sabotage all spacefaring vehicles and the unobtanium is out of reach. – Anoplexian Jan 03 '19 at 15:55
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    This is definitely the suggestion that's the most compatible with the story as it stands. What elements are there that e.g. are readily available in our solar system, but not necessarily in other places? Alternatively, what ones are there that are so scarce that a single FTL-drive project could all but exhaust a planet's supply, requiring a new rocky planet or set of planets to fuel construction of a new drive? – Olle Jan 03 '19 at 16:12
  • Or steal a page from Dune, and the entire supply of Spice was destroyed along with the ship. Sure they could build another FTL easily but chances are the voyage using it would be fatal w/out Spice. Maybe some folks want to chance the voyage anyway, despite the risk. – aslum Jan 03 '19 at 16:58
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    @Olle I like this Quora answer's idea of using an isotope of hydrogen. There are ways to artificially prolong the half-life of isotopes, so perhaps your people did this. Following the crash, all the remnants immediately decayed. The equipment needed to recreate the isotope could be too excessive to build in their current condition. – called2voyage Jan 03 '19 at 18:29
  • another idea is that it is not the unobtainium that is lacking, just the machine that turns regular carbon and silicon into n-dimensional meta-crystal. Think of a nuclear sub that has neither a physiscist nor a manual to build a reactor onboard. You can give them a chunk of uranium but they won't know how to turn that into power. – Borgh Jan 04 '19 at 09:50
  • @Olle, it doesn't have to be an element, it can be something manufactured that requires the production capabilities of a fully industrialised planet (or solar system) to make. The simplest of things, like a ball point pen, can be remarkably hard to make outside an industrialised society. – Separatrix Jan 04 '19 at 10:15
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    Think of how the colonists to both Greenland and Easter Island became trapped because they could not obtain large enough trees to build the ships that had brought them to their island. Even with knowledge of how to build the spaceship the materials many not be on hand to do so. – Michael Shopsin Jan 04 '19 at 15:07
  • This was essentially my easy go-to. The author can use it in conjunction with needing to locate a lost/stolen mcGuffin, or the plans for one, against a tide of road blocks (natural or otherwise) to act as a foil for intrigue and/or action sub-plots without overly focusing on the unobtainium and better allowing multiple lead characters to have interesting sub plots. Sort of like in "Quicksilver". – Ben Personick Jan 05 '19 at 09:50
  • Unobtanium is exceedingly volatile. The crash wasn't into the planet itself, it was into one of its moons. The drive section broke loose, and tumbled into moon one. The resulting unobtanium blowout plus billiard ball style reaction sent moon one hurtling into the planet, effectively making it unapproachable for the next X thousand years. Meanwhile the ship was shielded by moon two. So they are without their unobtanium and their space drive, with no hope of harvesting any raw materials from the hot mess formerly known as the planet. – Mary C Jan 09 '19 at 00:42
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Their ship and her payload were designed as a colony expedition. They had not just asteroid mining craft, and seeds for hydroponics, and modular habitat sections, they also had the blueprints and machine tools to replicate them. And they had the engineers to read the blueprints and use the tools.

For the stardrive, they had just the operators' maintenance handbook, and pilots and engineers trained to operate it.

Consider: You are obviously able to use a computer, like billions of people worldwide. And there are many millions who can program a simple website. But how many can design a microchip, or manufacture one? A programmer would know about silicon wafers, and doping it with other elements, but how many can explain the physics behind that?

So the colony would have to replicate a R&D project. They get a head start because they know it is possible, and also the principles how it works. This is balanced by the need to build the colony as planned. They know that they have a fleet of sublight ships, and that these sublight ships will wear out, and that they should start assembling the shipyard to build new sublight ships.

o.m.
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The ship consists of stages, and only the final stage arrived.

This is a very realistic explanation. That's how we build rockets, because it's efficient and much cheaper. Might not fit your plot, though. Given that they are only left with the smallest of the stages they could only guess how to build the most complex stages.

The ship carried just enough energy to arrive there, a return would have been very expensive and was not planned.

Again, this refers to the cost of interstellar travels. This should also apply to single stage vehicles. Refueling this ship would be extremely expensive, or might even be impossible due to a lack of technology or industry, see also next point.

The crew is smaller than the population of a planet.

Seriously, why would those few people be able to build a spacecraft? Imagine what an extremely complex project this would be. Remember how the soviet union struggled to put a man on moon (admittedly in a short time), because they lacked the industrial power for this huge project. They might be able to repair their ship, but build a new one? How long would it take to build up the industry? How many people can actually work on this, while there are plenty of other problems to work on?

Community
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M. Stern
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    The final point is nicely explored in Marrow - the people who are stranded on the titular object have all the knowledge to escape (they're essentially immortal humans with virtually unlimited memory and intellect vastly superior to ours); but to build up the industry required, they have to continuously increase their population and build up the infrastructure over thousands of years (and that's only because the planet's size cycles over time, and there will be a maximum that makes it easier - otherwise it would need even more preparation). – Luaan Jan 07 '19 at 08:32
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This is similar in effect to Separatrix's unobtainium answer, but a slightly different spin.

AI created all of the FTLs in existence. No flesh and blood brain can fully comprehend the details of their inner workings enough to recreate one. This doesn't mean they don't understand the broad strokes of how it works, just that they can't replicate it.

Then the AI went to war with its creator civilization, and ultimately lost. With the AI wiped out, a ban was put in place to ensure no more AI.

This means that every FTL is a priceless, irreplaceable artifact. No more can ever be constructed (by this civilization, at least).

Jeffrey Nichols
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Because they are astronauts(pilots) and not engineers.

Our society is able to do many things that I alone cannot.

James Sheils
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  • A lot of astronauts are engineers too... – Xen2050 Jan 04 '19 at 09:33
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    The Apollo software was as tall as a person. Granted, that was 50 years ago, but you can see how without highly skilled personnel, it would be difficult to reconstruct/rewrite lost software without people with expertise in multiple areas of programming and engineering. Of course, they very well could have people on board who do (it may even be more plausible), but the potential plot element is definitely sound. – Dan Jan 04 '19 at 18:43
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    @Xen2050 Even if they had all the guys who originally designed and built the original FTL drive, they wouldn't have all the infrastructure and domain knowledge required. It's easy to forget that even making a simple pencil is an industrial challenge that involves materials from all over the world and a lot of industry. Can you do it with less than that? Sure, for a greater expense. But it certainly isn't trivial. Just because you know how to do something doesn't mean you can actually do it - you need a lot of other people, tools, specialized materials, and for everything lacking even more RnD. – Luaan Jan 07 '19 at 08:45
  • @Luaan that's all true, but it's not in this answer (without seriously stretching the "our society" line, which if included would make it a better answer). And a lot of astronauts really are engineers, so this answer looks 50% wrong at best – Xen2050 Jan 08 '19 at 02:09
  • @Xen2050 You could say I'm stretching the "our society" part and that it isn't how people are going to read the answer, but that's really the main part - even if you had all the knowledge of our society at your immediate disposal, you'd still need the other people (and their tools, and roads, and mines, and...) to do anything high-tech. I've been playing around with the idea of a single immortal all-knowing human building something interesting on a "desert planet" for ages, and I'm still undecided on realistic timescales for something like building a car, much less ICs or FTL drives :D – Luaan Jan 08 '19 at 11:42
  • @Xen2050 In the early stages of technology adoption, the users tend to be restricted to specialists and engineers. It was so with the first airplanes, automobiles and computers. In a society where intergalactic space travel is a thing, one could reasonably assume that the spacecraft pilots are not possessed of the knowledge necessary to build a spacecraft anymore than an aircraft carrier captain today can build a nuclear powered warship. – James Sheils Jan 08 '19 at 21:50
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Some of the technology requires licensing from organizations that are not here. You may have gotten unlimited licenses for OperatingSystem2525, and all of the computers visible to crew and passengers run on that version. The software to run the engines requires OperatingSystem2530, which needs a long trip in the opposite direction to get an unlock key. And now that you've disassembled your engines to find that out, your current engines also want a new unlock key.

Tangurena
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Many fictional FTL drives (as if there were any others..) can only be used far away from pesky gravity fields.

Your drive is the opposite: it actually needs to be spun up at the center of a sufficiently large planet to break through to the fifth dimension or whatever.

Since you incautiously blew up the only planet in reach, now you're stuck there.

ths
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  • Presumably this system has a host star, which is orders of magnitude larger than the host planet. – Scuba Steve Jan 04 '19 at 00:15
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    yeah, but getting at the center of a star is sufficiently more difficult to warrant a whole novel :). – ths Jan 04 '19 at 07:19
  • Well you don't need to go to the center of a star, same as you wouldn't need to be in the center of a planet, presumably.

    You would need to be sufficiently deep into the gravity well. Considering the gravity of a star is orders of magnitude greater than a planet, you needn't even be that close to have the same effect.

    Don't make me break out the maths here ;)

     – Scuba Steve Jan 04 '19 at 23:48
  • I missed the part where you said at the center of the planet actually. But the gravity at the center of a planet is an uneven zero, with all the parts of the planet pulling you away from the center.

    I think this one needs more thought.

     – Scuba Steve Jan 04 '19 at 23:51
  • yes, maybe that is exactly what is needed? if you imagine the usual streched rubber mat, it's the flat point at the bottom of the well, the steep gradient won't do. – ths Jan 05 '19 at 00:20
  • So, to accomplish FTL, you need to build some kind of tunnel to the center of the sufficiently large planet, with which to launch the ship?

    It's an interesting idea, but you would need to build a new launching point at each destination. But maybe it solves the OP's issue :p

     – Scuba Steve Jan 05 '19 at 00:26
  • If they can built trillion person habitats they can amass the planet's materials into a new one to act as the ship's new way to get home. If anything, the resources from the exploded planet would be easier to harvest having had it explode. – Ben Personick Jan 05 '19 at 09:55
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It costs a lot of money and they lack the political will to use all those resources for that scope.

See what happened with the Apollo program. As long as USSR was leading the space race the US Congress was scared by the enemy supremacy and had no troubles providing funding to the program.

Once the Moon was reached more than once and public attention lowered, together with the manifest incapacity of the Soviet space program to replicate the result, suddenly the budget was limited and even scheduled launches were canceled.

L.Dutch
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    [...]manifest incapacity of the Soviet space program to replicate the result I don't think that was ever the case. The race to the Moon was a race, and there were no medals for second place. The soviets could have insisted on their N1 rocket, or build another one. They simply didn't try anymore. Instead, they focused on winning the USA in other fields, such as space habitats. – Rekesoft Jan 03 '19 at 11:56
  • @Rekesoft, exactly. USA have been on the Moon multiple times and USSR never did it (N1 failures were secret to general public), so why keep fighting a non existing enemy? – L.Dutch Jan 03 '19 at 11:58
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    @LDutch I don't know, but the whole Cold War point was keep on fighting a non-existing enemy, so why stop there if they hadn't stopped anywhere else? – Rekesoft Jan 03 '19 at 12:00
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    To expand on that answer: Original plans are incomplete, in a way that they omit things that was "obvious" to the people back then. People from that era are retired or dead so that information is lost. Technology went forward so many of the materials and tools used are no longer produced. Nor the tools and materials to manufacture them... Basically we would have to re-develop `60 tech and industry base to use them. – Mołot Jan 03 '19 at 12:58
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    @L.Dutch Soviets reached the Moon but they did it with remote controled probes and vehicles as they (correct) estimated the mission was to cost too much and be very risk. They even got a few onces of rocks but Nasa was kindly enough to donate a few more pounds of lunar rocks so, why to go all the trouble to land a cosmonaut here? – jean Jan 03 '19 at 16:35
  • @jean Prestige, of course - that's most of the reason why we went to the Moon in the first place. But as Rekesoft noted, there was little to gain by being second, and the Soviets were still very far from being able to put a cosmonaut on the Moon - the whole project was plagued with difficulties, personal clashes etc., and there was no telling if they could do it at all in any reasonable time/cost frame. Getting a crew to the Moon and back would still be a massive challenge today, half a century later. – Luaan Jan 07 '19 at 08:41
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That's going to depend on exactly what your FTL drive needs.

How about processing power equivalent to an Intel I7 processor? Oh, that's going to cost you.

Even if you know how to make transistors, the actual physical plant required for a current microprocessor includes things like soft x-ray etching mask units with nanometer precision and ultra-fine air filtration units. Plus chemical industries to supply single-crystal silicon wafers. Plus the support industries needed (Sophisticated alloys from raw ores. The chemicals required for the photoresists. Process control sensors and electronics to control fabrication. Etc) None of these things are easy, and they are the end results of decades of incremental development. All of this from a colony which is just getting started and has no basic industrial infrastructure - and may well be investing a lot of effort to adapting agriculture to the existing ecologies/biochemistry just so they can avoid starving.

Depending on your FTL, it can get MUCH worse. I suggest you read Vernor Vinge's "Marooned in Real Time". He imagines space vehicles which are essentially made of assemblies (clouds) of nanoprocessors which modulate fields cooperatively to function. Presumably such processors are built by other, slightly less complex nanomachines. And they are built... Well, the regress in not infinite, but it's certainly inconvenient.

WhatRoughBeast
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  • This is one of the reasons why 3D printing is so promising for future space exploration - anything we could make with 3D printing would vastly reduce the recursion depth of technologies needed. Even the 3D printer could be used to produce most of the parts for another 3D printer. Of course, we're still quite far from being able to 3D print what you'd need for e.g. a Mars colony, but it's something that can be further developed over a long time. – Luaan Jan 07 '19 at 08:50
  • 3D printing is one of those grossly misunderstood technologies which gets people starry-eyed when they should not. There are any number of critical technologies for which 3D printing shows no signs of promise at all. Take, for instance, processors. On the one hand, they would require feedstock of extraordinary purity, and in many cases it's not clear that you could build up the required structures. Assuming you can, the required scale is so fine that job times would be long. Very, very, long. Other apps, like high-strength alloys suffer different, not-obviously-soluble problems. – WhatRoughBeast Jan 07 '19 at 15:45
  • Hence "anything we could make with 3D printing", not "anything". Though I think you rather underestimate how many things can in fact be made with 3D printing - just look at Formula 1 for example. We're not talking about being able to make things efficiently, not by a long shot - we're talking about having the variety to replace thousands of different parts with very limited machinery and materials. Needless to say, you'd carry spare chips with you - it's exactly the kind of thing where it makes sense. But those other 100 parts of the life support system? – Luaan Jan 07 '19 at 16:41
  • Though I certainly understand the allergic reaction :) I'm not fond of the Star Trek style "nanotechnology will be used to manufacture and mine everything with perfect accuracy and it will be the only manufacturing method in the future" either. – Luaan Jan 07 '19 at 16:42
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Totaly running with ths' answer here. FTL drives arn't so much as a engine, so much as a trans dimensional artillery piece(T-DAP)... and Earth had to hollow out most of Pluto to build their outbound gun. Accuracy at colonization distances can reliably hit a solar system, but hitting a planet was supposed to be statistically impossible. Turns out, it wasn't impossible... and even worse, inflating a 200 KM bubble of space-time inside a planet's core tends to do really bad things it its structural integrity. Now 80% of the plant's mass is flying around the sun in wildly eliptical orbits and its going to take generations to collect enough mass to build a new T-DAP.....

Corbin Matheson
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When they crash-landed in the new star system, the scientists and technicians who were knowledgeable and part of producing FTL died, the computers and backups containing information on how to build/rebuild the equipment were also destroyed.

The remaining scientists and technicians have little knowledge of physics involved to produce FTL engine, and they were not property trained.

It was unfortunate for the scientists and technicians to die. There was a malfunction in the ship they were in when exiting FTL, sending the ship crashing down to the planet.

Reddy Lutonadio
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Other answers cover how you can explain why they can't leave under their own power, but your question doesn't specify why no one else from home would send more supplies or a rescue vessel to eventually rescue them.

A very simple explanation is good old incompetence. This premise reminded me of the planet Wayland from the Star Wars Legends stories. The description of the planet from the game Star Wars: Empire at War sums it up nicely.

A simple clerical error in the Old Republic planetary registry removed Wayland from all known charts and doomed the expeditionary vessel seeking to settle a colony there. Without support from the Republic, the human colonists regressed technologically, discarding their blasters for bows and arrows, their modern fabrics for furs and hides. The colonists continue to clash with the two native intelligent species on Wayland, despite being forgotten by the galaxy at large.

So basically, someone at home accidentally hit delete somewhere they shouldn't have. Maybe they deleted all records of your system, maybe only the coordinates of the destination. Then they realized that backups hadn't been running for a couple months and it was lost. Or maybe it was simpler, someone had to manually transcribe the coordinates into their navigation computer and typed a "1" instead of a "2". A small change in a trajectory spanning light years will be many light years off at the destination, so all attempts to send supplies to the colonists ended up in the wrong place. The possibilities are endless depending on the specifics. Combine it with another explanation about being out of fuel or having a damaged part and you have your setup for how they were stranded and why no one is coming to help them. Many other answers here already cover that well.

Cody
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When the ship crashed, and the FTL drive exploded it created a anti-FTL radiation field in the system. The anti-FTL radiation prevents ships traveling at FTL speeds, by destroying the craft if it tries. After the first ship they built exploded trying to go to FTL they haven't tried again. Maybe by now the radiation has dispersed but no one wants to risk the crew/resources needed to try again.

Rob
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  • The negative space wedgie might have caused their crash in the first place (and inadvertently provide the energy required to destroy a planet without also utterly destroying the whole ship and all its crew). The challenge might be building a ship big enough to get out of range of the wedgie before they can engage the FTL drive - if it needs a few year's trip at STL, that would be quite a lot of resources, especially if the civilization depends on FTL a lot and their STL isn't all that great. – Luaan Jan 07 '19 at 08:58
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Maybe they could construct a new FTL ship, but there's a reason their old ship destroyed the planet. It's an intrinsic problem of the drive principle, and they really do not want to destroy yet another nice planet...

ths
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The best answers are story based, and your story gives the best reason: "holy crap we crashed and destroyed a PLANET, next time it might be the ship!". Would you trust that ship? Would you get enough crazy people together for another jump to colonize something else? They could just not have the expertise or facilities to see why they crashed or repair it. They could be waiting for rescue, or trying to build enough of a population and facilities to research and build a new FTL drive even if it takes a few millenia to redo that research.

The other more standard answers are already given. Lack of resources for the FTL drive (either building or fueling), lack of reasons to build them (you reached a starsystem right?), lack of economical insentive to build/use the ship (cost of FTL is so high only a colonist expedition is worth it, but why waste resources on something that wont earn your local system something?)

Demigan
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They were never able to construct FTL drives - they got them from a forerunner factory that was still intact, which they had discovered during their own early steps into space.

(Or they purchased the FTL drive from extant aliens, or FTL tech is a particular company's closely guarded secret, etc...)

Jedediah
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Perhaps they have tried to create a new FTL drive from remains of their old one, and it backfired so much - risked so many lives, nearly tore through the ship, messed up with their resources, etc - and leaves barely anything of the attempt that the rest simply say 'it's not worth it' and stop any further pooling of resources into making one.

bigchickcannibalistic
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Structural Damage

During the crash some important parts of the FTL engine have been damaged or destroyed. Repairing them is not (easily) possible. Maybe they just don't have the plans required for a certain part. Maybe they lack a certain ressource that is absolutely needed to form a certain part of the engine. Maybe certain parts need a giant machinery to be produced that can't simply be reproduced from existing ressources.

Side effects

They were a test drive of a new FTL engine that had an unwelcome sideeffect of killing or heavily hurting the people on board. To extend their lives, they rather don't restart the engine. This might also not have been an initial issue, but caused by the crash that destroyed some protectors that can't be reinstalled with available ressources

Escape

Your ship is controlled by rebels that are on their escape from an evil empire. They found a reasonably well suited habitat. They might be able to restart their FTL in an emergency but would rather stay at their current place and try to establish their rebel empire. A couple of generations and propaganda later nobody remembers the fact that they were even capable of FTL travel.

Sebastian Proske
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  • I like the escape from evil empire idea. One possible addition: Firing up an FTL engine would be detectable from their home system. They do NOT want to be detected. – Stig Hemmer Jan 04 '19 at 08:28
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Interstellar Distances are just too large and they can't use high atomic number elements

I'm going to assume you want them to be able to venture into space at least to their other habitats but not much further than that.

Right now they may have access to asteroid mining where water is abundant. That gives them access to create hydrogen and oxygen propellant, which is what's used in modern chemical rockets. Hydrogen and Oxygen have smaller atomic numbers, so they're much easier to find out in space. Anything with a higher atomic number than iron needs to be created from a supernova. If they live in a region of space that has a lot of small stars, there aren't going to be many supernovae, so there's going to be very little of any high-density elements. Any high atomic number element like Gold could be used as the fuel, which is rare in space.

If they live around an average star, the nearest star to them is going to be 3-10 light years away. If we take the fastest speed any spacecraft built by people and assume that their spacecraft can exit their system with this much speed (which probably isn't true), it would take them 4060 years to reach a star the distance to Proxima Centauri, the nearest star to Earth. It's just not viable to send a rocket to another system because of the wait calculation. The wait calculation is question of whether we should send a craft to space now or wait later. If we send the spacecraft too soon, a new technology will reach before that spacecraft gets there. If we send it too late, we lose time to be at our destination planet.

It seems like your civilization has endured some losses in many respects including their home planet, why not technology? They may have some experienced people but not enough to create an interstellar drive. Consider what O.M said,

"You are obviously able to use a computer, like billions of people worldwide. And there are many millions who can program a simple website. But how many can design a microchip, or manufacture one?"

Gaining the technology to achieve interstellar travel from local travel is like technology jump from going to a bronze sword to an AK-47 or from an AK-47 to a guided missile. What makes this even harder is that advanced technology almost always requires access to new and unique materials. Why should an interstellar drive be any different? Just make stringent technology requirements on high atomic element materials, and your civilization will have a hard time acquiring it.

None of these obstacles make interstellar travel impossible, but it should take your civilization a couple hundred years (very rough estimate) to develop interstellar travel at the soonest.

Byte11
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Laws of Physics prohibit multiple FTL jumps.

There are many answers that explain why complex technology may not be reproduced by colonists. However, there could be an even stronger reason why it is impossible to make multiple jumps.

According to the laws of physics we know, FTL is impossible. The law of relativity tells us that velocity is relative so any non-accelerating object can be considered stationary relative to its own frame of reference. The law of causality tells us that us the cause precedes effect. If you had reliable FTL and relativity, you could make two FTL trips using different frames reference to arrive back where you were before you started.

There is two ways of dealing with this. Perhaps Einstein was wrong and there is some objective frame of reference that we haven't found yet. Alternatively, we could say that causality is wrong, and time travel is possible. But time travel is weird... what happens if you kill your parents before you were born?

Say FTL requires folding space, space can't be folded more than once (and definitely can't be unfolded), and technically was always folded and due to some weird quantum reason just happened to create the wormhole the exact time FTL drive was powered on.

If we limit ourselves to one FTL jump, we can mostly keep relativity and causality. Yes, according to relativity in some frames of reference you arrived before you left, but since you can't do more than one FTL jump you shouldn't be able do anything really paradoxical like killing younger versions of yourself.

gmatht
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The local solar system is located very near to the center of its galaxy. The black hole in its center requires a huge amount of energy to reach the escape velocity needed to leave the local space. The only possible solution for now is to use the gravitational pull of the black hole and use it to swing close enough and use it as a catapult to leave the near center. ( similar plot is used in the Interstellar movie ) As this is only a theory building another spaceship does not make sense until this is experimentally checked. Additionally the time shifts involved would move the spaceship forward (or backward ) in time making the whole escapade even more complicated. How would the travelers even provide feedback information back to the home planet ? While the home world is spiraling closer and closer to the hungry black hole and one day will be consumed this journey might be the only chance of preserving the civilization.

Bartus
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The simplest non-knee jerk reasoning, would be that they had a navigation problem due to ::hand wave space phenomina:: encountered along the way ( This also explains why they warped into a planet.)

And so they ended uphalf way across the galaxy, or across the universe outside of what they had previously charted and due to time dilation of observing distant stars/galaxies they are going to have a lot of work, centuries or millenia perhaps to get themselves reconnoitered to be able to message and return home.

They can;t even visit nearby stars for quite some time because it requires quite a bit of astronomical data in order for the FTL drive to properly take into account how to traverse the distances directly.

To be clear, they could still use any non Super Luminal method to go else-where, but they would also then need to build out old-school generation/cryo ship that they haven't actively used in a few millennia, and take trips to other stars on time-lines which make it more attractive to just wait until they have gathered enough data to begin using FTL again.

Lost in space is solid.

Ben Personick
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For some reason FTL engines are attracted to what ever elements are used to fuel them, this is why the space ship crashed on the planet. The crash ruptured the containment field of the FTL engine thus causing all of the fuel element in the planet to be used up instantaneously destroying the planet, or possibly accelerating the planet to FTL speeds and sending it backwards in time allowing the inhabitants the time to discover the knowledge required to stop the ship from crashing on the planet. Aren't paradoxes fun. :-)

Separatrix
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JGNI
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Idea: The civilization is comprised of hundreds of small autonomous vessels (transportation, reparation supply) and a very HUGE one who can provide FTL capabilities for all the others (can create a wormhole?). The big one was totally anhiliated on arrival, and there are not enough material available / shipyard capabilites to recreate something similar.

The vessels are more or less self-autonomous and can be used to travel within the star system, but are unable to leave it.

Onoper
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There's nowhere to go

This is the simplest. They got stranded by a factor they cannot avoid and don't know previously. That factor can still keep they from reaching any planned destination. They are like a boat without a compass and with limited food.

Another good point is: They just cannot find another more suitable place to live. If you got a starship you do want a destination to arrive at, without destination there's no reason to get aboard that starship (or any ship).

jean
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  • Kind of takes the wind out of the Enterprise's 5-year exploration missions if there's no destination & no reason to go – Xen2050 Jan 04 '19 at 09:43
  • @Xen2050 I stronlgy disagree. They have lots of destinations and a purpose and most important they can go home at any time. Also 5 years exploring don't mean 5 years wandering – jean Jan 04 '19 at 09:49
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While they might possess (or are able to recreate) the whatchamacallits and doohickeys that comprise the FTL drive they may have lost some

unique knowledge

of how they work together.

For example I'm writing a story where I needed to take the engines offline in such a way that they could be brought back online only after an extended period of time. In my scenario the engine field controllers were destroyed. The system AI can emulate the controllers but to do so it has to reformulate the resonance equations that were embedded in the lost controllers. Essentially an entire field of physics has to be rediscovered.

In your scenario you could make this knowledge prohibitively unattainable (until they discover it elsewhere).

Skek Tek
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The story is that the residents of Easter Island cut down their forest and couldn't build new ships (rafts or canoes). So they were stuck fighting each other for a fixed capacity of food production as population increased.

shleppenwulf
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Their FTL technology warps them through space in a manner that was safe until a virus broke out that makes it fatal for anyone to pass through warped space. Later in the story the the virus is revealed to have been genetically engineered by [SPOILER].

intuited
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FTL technology was possible but extremely expensive and complicated. It required all the infrastructure and knowledge available in the homeworld to make FTL ships happen. That is, FTL existed but was neither trivial nor accessible for trivial things.

Homeworld came to an end. Whatever remain stranded in their new world, even if with advanced spacefaring capabilities, it is a shell of the former self, depleted of its original population, infrastructure and engineering base, without the wherewithal to re-engage in FTL in any matter that is safe.

It still have tremendous spacefaring capabilities within their new home solar system. But much, much more has been lost. They need to re-invent and re-engineer their way back to FTL tech... and probably that took them thousands, if not eons, to achieve back in their original homeworld.

Think about how we have lost the technique to make/reproduce damascus steel (a related, but different problem since we have much better steel-making products today.)

There could also be a social impediment as religious sectors of society might blame FTL for the Homeworld's demise.

Another angle: it could be that FTL leaves traces, foot prints and the remaining survivors want to stay incognito.

luis.espinal
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My first thought when reading the title was to have a Planetary Debris Field - around our own planet, rocket launches are gradually getting riskier due to the amount of space junk in orbit around the planet. At the speeds that rockets travel, hitting even a small piece of something that broke off of a previous mission could be Very Bad for the current mission.

But in your question, you totally upped the ante, stating:

There was a planet, but it was destroyed by their crash-landing in the star system.

Bam. You have a literal planetary debris field right there. That is, the debris of an entire planet, all smashed up and still in orbit around the cloud's common centre of gravity. And since your ship's crash-landing into the planet is what kicked up all this dust, the mothership also happens to be right at the centre of this debris field.

Smaller scouting ships can navigate through the debris field in relative safety, mining the rocky bits or moving past the cloud to explore other planets in this solar system or whatever, but the mothership is stuck in the cloud for the foreseeable future. All spare power on the mothership is being pumped into keeping the shields up and hull intact, so there's:

  • No room to accelerate (and/or warping space to make your technobabble-FTL-tunnel will also warp a continent-sized asteroid into your window),
  • More pressing need for raw materials elsewhere,
  • Not enough power to fire up the engines even if they were working

And obviously, FTL drives in this universe are necessarily big. You can't exactly kit out an existing one-, five- or twenty-person craft with a warp core, drive, and engines. Even the computer programs needed to turn all that on properly are way more advanced than what the smaller vessels can run. Couldn't that program run on the mothership to remote-control your puddle-jumper? Theoretically, maybe, sure - but that would involve opening a FTL corridor since FTL is necessarily faster-than-radio, and opening an FTL connection just takes us right back to the first problem. That's also why they can't send a distress signal back home to confirm their current location.

So even if they could turn on the FTL engines, doing so would be a suicidal move. Your big colony ship is stuck and not able to move anywhere or communicate with anyone outside this solar system anytime soon. Better get those engineers working overtime so they can complete their Von Neumann mining probes. Hopefully they can get 'em going in time to dig us out of this mess sometime within our colonists' lifetimes!

The colonists getting their hands on a new FTL engine would be an FTL engine (ideally, one accessorized with a compatible ship) that's not mired in middle of the disassembled planet. Such a find would allow them to escape this solar system years sooner than they ever could have without it.

Dave B
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There are basically two possible answers :

  1. They do not actually know the technology.

  2. They lack necessary resources.

Possible reasons for not knowing the technology are :

Security

As something that can destroy habitable planets by accident the technology was highly classified and even its basic theory was only available on need to know basis to people with high security clearance in secure facilities. Basically in the facilities used develop and manufacture the drives. Only time it would be on spaceships would be in encrypted data vaults rigged to self-destruct if anything unusual happens.

This sounds as a bit of a cop out but remember that they did in fact destroy a planet. Any mumbo-jumbo FTL system is wide open to highly destructive and dangerous abuse almost by definition. There is a reason why so many authors source their FTL from advanced aliens who refuse to share the details of how it works with a species as irrational and violent as humans.

It would be entirely reasonable that nobody surviving the accident had access to FTL technology or the encryption keys needed to read the information stored in the surviving data storage. The data might as mentioned even have been only in a separate highly secure data bank that was destroyed or simply inaccessible due to nobody having anywhere near the necessary clearance. Or the authority to grant such clearance.

It does not work

FTL really is quite tricky. In theory an FTL drive accident might see you travelling backwards or forwards in time, thrown so far that nothing you recognize is within your observable universe, or maroon you in another universe with subtly different physics.

The last is one option for losing FTL technology. If you succeed in going FTL but fail to return normal in controlled fashion you should be stuck in FTL until something yanks you out. Alternate universe where your type of FTL is not sustainable would qualify as such a something.

So they would still have the technology. They could build the drives. They could turn them on. And then they'd get yanked back to normal space roughly five meters away from where they started. Probably as a rapidly expanding ball of plasma.

Obviously this works for more localized "no fly zones" as well. But alternate universe is harder to detect and you cannot circumvent it with STL travel. And it would not prevent other people from visiting with functional FTL drives compatible with the current universe and puzzling your people greatly as it has been well established that those drives could not possibly work. Every study done before the accident (in another universe) confirmed that!

So you just need to prevent the people from doing expensive theoretical physics research to confirm things that are already well proven and accidentally noticing that rules have changed. Basically that amounts to supplying an alternative theory to why drives keep exploding. Terrorist? Manufacturing quality issues? Maybe the drives required insanely precise fine tuning to work properly and that information really was highly classified (a trade secret of the manufacturer) and lost.

Possible resources they might lack :

Unobtainium

Already covered in the top answer but included for completeness. This is another common solution authors use to limit FTL abuse. Note that precursor artefacts, rare psionic talents, arcane magical runes and divine blessings amount to the same. They are all excuses why FTL cannot be used freely and they all work as excuses to prevent it entirely.

Infrastructure

You need the machines to build the machines. Realistically FTL engines might be very high in that hierarchy and making them would require an industrial base well beyond what your survivors can manage in the next thousand years or so.

Astrogation data

In many universes a successful FTL trip requires having a very good idea where you are now. This is a serious issue if you have an FTL accident that throws you to some random unknown location in time and space. Especially if you are absolutely certain that you are somewhere else. Simplest reason is an alternate universe that looks exactly like something familiar but actually has different hyperspace coordinates.

For extra entertainment have people realize they are in another universe and need to remap their coordinates but not realize that their form of FTL simply does not work in the current universe. The difference between the two might be hard to notice and it would be very simple for somebody to get it entirely wrong early on and nobody to ever question it again. Especially if the one doing that initial check is the same person responsible for the initial "accident".

Ville Niemi
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To directly answer the question, building a starship will take more resources in terms of manufacturing support than can be carried on a starship. This means it will take the development of an advanced economy at the destination, which could take decades if not centuries. So, they have the knowledge to build a new ship, just not the ability to build a new ship.

The notion, though, that the crash of a starship into a planet can destroy the planet is very weak. The gravitational binding energy of a planetary mass is proportional to the square of the planet's mass divided by the radius of the planet. For the Earth, this energy is roughly equivalent to 12 days of the total output of the sun compressed into a ten second delivery. That is over 4 trillion tons of mass converted to energy in 10 seconds or less, all of the resulting energy delivered to the Earth.

k l keegan
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