In this Answer I came up a scenareo under which Eriek’s concept makes sense.

I rather like this idea: an expedition or colony on another world has to, for some reason, pull up stakes and move. They can’t build large-scale high-tech machines from scratch, so they go all steam punk. They make simple wheels for all the hab modules, and on the building housing the nuclear reactor they fashon a pair of simple steam pistons to turn wheels, with no gear box or transmission. They have a 19th century train powered by a nuclear reactor, and likewise all the solutions they come up with have a steam-punk flair, combining modern engineering knowledge with more primitive materials handling and fabrication techniques.

So, that begs the question of: why would they have to move?

My original note suggested Mars, as it would be easy to come up with new iron parts. But what could possibly necessitate a move on Mars? So I open it up to any solar system “world” that can support humans living in sealed boxes. Some moons are problematic due to the radiation belts around their primary. Besides survivability with this level of life support, they need local resources for making new large machine parts (given they have power to smelt ores, liberate alumium, or whatever), and the environment must supply a reason why they must relocate.

Edit: The reason should be “realistic” , so ghosts are not an acceptable reason. The situation should consider real knowledge about the geology and other properties of the settled body. Use real resources, not McGuffinite.

  • $\begingroup$ Comments are not for extended discussion; this conversation has been moved to chat. $\endgroup$ – Serban Tanasa Feb 3 '17 at 16:25

18 Answers 18


This isn't our land anymore, kiddo.

There was a time in the past your old grampa here would oversee all of those mining operations, from the Red Hills all the way to the Prima City. It was such a sight - all those white, shiny domes, resting on the red blessed lands of Mars. Heh, Red. Red meant money, back then, kid. Nowadays it means just death and a idiotic flag. Nothing more.

Your gramps was all fine and good, riding under the sun on my trusty Palomino-II rover, keeping an eye on those robotic builders while they put down the tracks for the Red Planet Express, to the notes of "I'm working on a Railroad", a nice, old song from my youth. I don't know, it seemed somehow appropriate.

But them, those dammed reddies showed up. We always thought that it would be aliens, or some sort of magic gate that would wipe us out from this planet. But no, it was the reddies. Those reddies, back from earth. They weren't happy with our claim on this rock, oh, they weren't, I'll tell you that, and they went all North Korean on us. Sent some interplanetary missiles, right down on us. They would take some time to hit Prima City, but that didn't meant we could stay, oh no. We had to leave. Weren't going to be nuked by those reds that easily, oh, no.

So we had to pack up and leave. We had to scramble every single bit of tech we had to transform the Red Planet Express into this damn beast she is today. We put her on tracks, but a different type of track. Tank tracks. We buffed up her engine, we gave her a huge array of weaps and drilling tools to make sure she would be able to clear the way. We made her into this dammed beast, oh, yeah, and your grampa was there to make sure she worked just fine. I handled those nukengines as I would handle my wife, with passion and desire for my work. 'Cause, kiddo, if we weren't fast enough, we would be just bones on the red sand by now.

That's how she came to be, and just a little bit of her huge, long history. She's chugging down nukefuel for sixty years now, and it's nowhere near stopping. And you'll be the one that will make sure she keeps that way, to make sure those cogs don't stop spinning and she doesn't stop cruising the red sand.

We can't stop for long. We need to keep moving, to keep watch of the skies above us. 'Cause you never know when another nuke is coming, and you won't want to be sitting down when it arrives.

So now she is yours to drive, kiddo. Make sure to take good care of it.

I know you'll make Grampa proud.

With those words, the Machinist took out his overseer pin from his jumpsuit. He held it on his hand for a moment, looking at it with eyes that almost gave out sadness. For him, it was the end of a life of dedication to the engines that kept his people and his family alive. But he wasn't able to hold back the smile that slowly crept on his lips. Well, yeah, it may be the end of his story as the Overseer for the Red Planet Express, but it wouldn't be the end of her story. She would keep rolling on the red, dusty surface of that wild planet, running away from an invisible threat that may not even exist anymore.

She would rage on, keeping everyone inside her safe. Keeping his story safe. And, more than everything, giving those people inside her a reason to hope for a future when shouldn't be none.

Sorry for the broken english.

This works?

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    $\begingroup$ Human conflict is indeed an all-to-real reason. $\endgroup$ – JDługosz Jan 30 '17 at 19:58
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    $\begingroup$ /me stands and begins Slow Clap. (If that's broken English, how well do you write in your native language? Damn.) $\endgroup$ – Monty Harder Jan 31 '17 at 16:17
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    $\begingroup$ I wish there was a message or private message option here. TSar, I think this was a lovely bit of writing, and upvoting Monty Harder's comment isn't enough. $\endgroup$ – WRX Feb 1 '17 at 18:49
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    $\begingroup$ @MontyHarder & all the others - I'm really glad you guys liked it! Thanks for all the kind words, really. You guys made my day! $\endgroup$ – T. Sar Feb 1 '17 at 18:55

Keeping it on mars, one easy reason is flooding. If they are there teraforming, things start to warm up, a lot of permafrost will melt. That water has to go somewhere, and the most likely place is the Borealis Basin which is very low ground and covers 40% of the planet.

Water could be brought in with comets, or it could be natural ground water, since there is evidence that there may be more water on mars than we know about, but either way, if they set up their town in that area, and the water started to rise, they might suddenly realize that they miscalculated where the coastline was going to end up and now their town is going to be underwater unless they move a bit up slope.

An alternative would be setting up their town down in a canyon or up on a rim. The ground softens and it looks like the canyon wall might destabilize. The real question is how far you want them to have to travel. If they are on top of the canyon then they only need to move a few miles away. If they are down in the bottom for some reason (mineral deposits?), they could be worried that the whole canyon is unsafe, and so need to travel a very long way to get out of it.

Valles Marineris There are places in the Valles Marineris where you could stand in the center of it and the canyon walls would be over the horizon, but there are other areas where the canyon is much narrower.
A good candidate area would be the Noctis Labyrinthus, which is the twisty area on the left of the image.

Another idea, they might just decide to go nomad.
"We're here, in the middle of this dusty plain/crater/wherever and people go out and tell stories about the majestic views they see. How hard would it be, really, to just pack everything up and move the town around. We've already scouted this whole area, it's about time to move somewhere fresh anyway..."

Edit 2:
So it's not a colony, but a spaceship carrying pieces of a colony modular style. They crash on a planet that is really close to the star. Thankfully it was on the night side, but dawn is coming. It's a very slow rotation, but eventually the sun will rise and everything will burn. So they start setting up the modules to make vehicles to run away, but that's only buying time since they'd never make anything big enough to really survive, and rescue isn't coming very fast, so why not make the whole thing mobile...

  • $\begingroup$ "If they are there teraforming" , "They can’t build large-scale high-tech machines from scratch" common man $\endgroup$ – MolbOrg Jan 31 '17 at 13:38
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    $\begingroup$ @MolbOrg A lot of teraforming is going to happen through events off planet. Ice from Saturn's rings to be used for water and oxygen, ferrying nitrogen from Neptune, etc. Or ways to bring in more light. Or it's going to happen with very small things, like algae and bacteria in the soil and on the ice, fixing salts, maybe breaking the bonds to release oxygen from the soil, actually making the soil into dirt that will support plants, etc. $\endgroup$ – AndyD273 Jan 31 '17 at 14:20
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    $\begingroup$ @MolbOrg It also doesn't have to be a race against time. If they are an early colony, and suddenly a huge aquifer is found, and the simulation of where the shore of the ocean is going to be changes... OP didn't really give many details on why anything is happening, and is even willing to switch planets if need be, so I threw out a couple scenarios. I do welcome the feedback, and even from OP if they have any further information on what might be happening elsewhere in the story. $\endgroup$ – AndyD273 Jan 31 '17 at 15:18
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    $\begingroup$ XKCD have flood maps of Mars :) $\endgroup$ – PTwr Jan 31 '17 at 15:56
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    $\begingroup$ Huh, wonder why the downvote? $\endgroup$ – AndyD273 Feb 1 '17 at 14:34

One way is to look at cities that have been moved in our past. A current example is Kiruna, Sweden. Kiruna is moving because a mine caused the ground to be unstable. However, Kiruna gets to do it all high tech and such, Hibbing, Minnesota did it in 1919 with just horses, logs, farm tractors, a steam crawler, steel cables, and human power. Tallangatta, Australia, moved because of a dam's construction. For a more sci-fi bent, something similar to Winnipeg Junction's reason might be used. We can imagine that the town of Landing, Mars was important because they had the only space port. That worked until a space elevator was built. So they all pack up and move to where the space elevator is going to be built.


An extra solar colony would be heavily dependent on shipments of supplies from its parent. If these shipments are disrupted, the viability of the colony would be immediately jeopardized. The colony's growth vector would have to be adjusted, making the current location less suitable for the changed circumstance.

The shipments were disrupted by political turmoil on earth. Shipments are not expected for some time, if ever. The shipments contained heavy machinery and survey probes utilized for expanding the colony and stabilizing the subterranean supports necessary for permanent habitat domes. Current supplies were intended for short term establishment and were never intended for the creation of a permanent and self sustaining residency. The first shipment was supposed to arrive within a month of touchdown but is now 6 months late. With geological activity increasing in frequency, we must quickly find a more stable location, even if it is less geographically advantageous.

Below are why cities are founded and why they move.

Cities are built in their locations because the location is advantageous geographically. This could be due a variety of reasons.

  1. There are natural resources nearby whose extraction require a local resting area.
  2. The presence of a transportation resource: a large body of water, railroad, or spaceport makes travel and trade easy. A city naturally forms there to capitalize on this.
  3. It was the first habitable location the settlers came across, and the cost of relocating is enough to prevent them from moving once they are rested.
  4. The location is defensible in an unknown or hostile area.

Reasons why the city may be moved.

  1. The natural resources ran out, became inaccessible, or became useless.
    • Example: Whale oil was utilized heavily, but became less important as time went on. The towns that solely existed due to whale oil disappeared.
    • We mined all the iron. Why stick around?
    • Billy was playing with dynamite and accidentally blew up the uranium mines. Oops. Unfortunately, we don't have enough kids to work the now radioactive mines.
  2. The transportation nexus disappeared or became useless.
    • Example: Earth is gone, why do we need a spaceport?
    • Example: Seriously, who stole the ocean?
  3. A better location is found, or the reasons for staying here changed.
    • Example: We found Unobtanium deposits further west. Better to move there.
    • Example: We finally got the wagons fixed, no need to stay here. Pack up boys!
  4. The need for defense or the defensive situation changed.
    • Example: After further scouting there are no zerg on mars. We no longer need to turtle up by the cheese wheel.
    • Example: Turns out we built our city on top of a giant turtle, who now wants us gone. Woops. On the plus side I know I can outrun my wife, and divorces are expensive.
    • Example: We found an abandoned city with big ass walls that make our own look like Lincoln logs.
    • Example: The Romans will fear our newly discovered Indian Nukes!

Here's a rare, but plausible scenario that nobody seems to have thought of yet:

Meteor Strike

We're already tracking all known comets and meteors in case any of them have even the slightest chance of striking Earth. We're also tracking the millions and millions of bits of space debris in orbit, to try and make sure none of them hit the International Space Station. We would presumably be doing the same for any colonies we happen to establish on other worlds (be it the Moon, Mars, Europa, whatever).

Of course, that doesn't mean we can do anything about these impacts. For example, most of the space junk that might hit the ISS is very tiny, but the relative impact speed would be so great (the ISS orbits Earth at 7km/s) that the station would still take significant damage. The only real option the station has is to get the hell out of dodge, by undertaking emergency maneuvers to shift its orbital altitude (it has in fact done this repeatedly in the past).

Now, space scientists are (generally, with a few infamous exceptions) a very cautious bunch. And need I remind you, your colony is powered by a nuclear reactor. All it takes is a single impact in just the wrong place and you'll end up with another Chernobyl, or worse. An entire section of planet/moon will be rendered even less inhabitable than it was before you got there, you'll lose trillions of dollars' worth of equipment, and potentially the lives of your colonists.

So if there's even the slightest chance of something hitting your colony, and you have no way of preventing the impact, you'll want to up sticks and move. Of course, there's a few variables to consider:

  • The size and speed of the impactor (i.e. how far away do you have to get to be safe?)
  • How early you detect the potential collision
  • How fast you can set up your nuclear steampunk train
  • How fast said train moves across the rough terrain of [insert celestial body here]

But this could also add an extra element of drama into your story: can your characters pack up and get out of range in time before that big ol' asteroid hits? Does everyone agree that they need to? And where will they move to afterwards?

  • $\begingroup$ +1 This was my first thought upon reading the question title. Maybe I've played too much Space Engineers. $\endgroup$ – Pharap Feb 1 '17 at 2:30

Ground under original site not as firm as expected Subterranean lava tube in danger of collapsing Porous rock can't handle supports for planned expansions

Increased Solar storm activity predicted which will increase radiation exposure past safe levels.

Dust fines eating rubber seals Relocating to newly discovered caves to reduce wind exposure and minimize exposed surfaces.

Much better location found (large lava tube for radiation protection and structural support for inflatable habitation, better access to water and mineral deposits)

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    $\begingroup$ Some idiot convinced them that fracking was the way to go and they all bought into it. NOW they are getting smacked by earthquakes of increasing frequency. $\endgroup$ – boatcoder Feb 1 '17 at 14:22
  • $\begingroup$ @boatcoder no fossil fuels on other worlds in the solar system. $\endgroup$ – JDługosz Feb 1 '17 at 19:47

Moving the scenario to the moon, and we have an interesting situation.

If you are traveling on the moon at the moon equator, you can travel at about 15.4kph (9.6mph) and stay in the sunshine all the time. (circumference of the moon 10921km and synod lunar day of 29 days, 12.75 hours)

Suppose the nuclear reactor isn't producing enough for the inhabitants to survive through the night anymore... or the batteries that the solar panel charge up are failing... or the insulation that keeps them from being exposed to horrible low temperatures for the 354 hour "moon night" have been through too many freeze/thaw cycles and they are failing...or apply the freeze/thaw cycle problem to the entire structure.

They have devised a solution by moving the entire habitat around the moon every 29.5 earth days so that it stays in the sunlight.

I like this low speed because it allows for continued interaction with the planet itself; the inhabitants are not isolated on the train. If they travel faster at some times, they could even stop occasionally while still staying in sunshine.

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    $\begingroup$ But the nuke is good enough to drive the locomotive, but solar generates more? $\endgroup$ – JDługosz Jan 31 '17 at 19:50
  • $\begingroup$ I was posing several potential problems that may cause the need to be on the move. Considering a thorium reactor, they really would want to have other sources of power for an "on-demand" situation. Having solar panels is not even required for this scenario. If you choose "failing insulation from heat/thaw cycle" as the root cause for mobilization, the need for constant motion is still valid after throwing out everything else. $\endgroup$ – Keeta - reinstate Monica Jan 31 '17 at 20:34


A small group had illegally landed and set up a small settlement in the early stages of terraforming the planet. The terraforming equipment was owned by a large corporation that had bought the rights to terraform for Human habitation and to set up the first settlement. This group had moved in before the planet was cleared for habitation.

They had worked hard to create a subsistence living, but now that the planet was determined to be largely habitable the corporation was moving in. The squatters hadn't had any need to build any offensive weapons because they had been alone. The news they receive indicates that their colony has been labeled a failed attempt at colonization before the planet was habitable with no expected survivors by the corporation and earth governments aren't going to investigate. When the squatters realize that they aren't going to get any protection from a corporate settlement party that has no interest in sharing land or mineral rights they decide to move.

They can't get off the planet because they don't have the tech necessary to leave, and due to the logistics of governing a remote planet the only governing body with any control will be the corporation for at least some time. Their only hope is to move far enough away from the corporate settlement that they are not threatened or a threat, until a non corporate government can develop.

Instead of an moving because the land has become inhospitable, they have to move because the land has become hospitable.


Nuclear war on Earth.

This has some superposition to TSar's excellent answer, but being a one-off instead of a constant thing would make for a different story.

The Mars colony is either American or Russian. The other of the two announces that they will destroy the Mars colony in the event of a nuclear war. That's for deterrance, see Mutual Assured Destruction.

Some time later, said war breaks out. Both superpowers completely obliterate each other.

The Martian colony cannot detect any missiles, but has to assume they're coming. So they have to move. They don't know how long they have, but they know a range of plausible time values, based on assumptions of how much the enemy would be willing to spend on them.

  • $\begingroup$ This is actually quite clever. $\endgroup$ – jorfus Feb 1 '17 at 17:44

Purposeful Seeding of Water via Kuiper Belt Objects

To heat up Mars and to help seed it with water, we bombard Mars with smallish, icy Kuiper Belt Objects.

This is done by sending probes to the Kuiper belt where (with the combination of gravity-assist and gravity-tow) they send the KBOs hurtling towards Mars.

Of course, this is not undertaken until a sizable colony has already formed on Mars.

After much discussion and arguments, a proper location is determined to recieve the bombardment. This location is aimed directly at a colony. The colonist must leave.

  • $\begingroup$ Comets are hard to aim anyway, since they have their own jets that are unpredidtable, and pieces can break off. $\endgroup$ – JDługosz Feb 1 '17 at 1:10

Priced out

Well, that was embarrassing. We were selling our wares in the trade district, and one of our younglings said "we're from New Hammersmith. In Londinium." The older gent replied "I've heard of a New Hammersmith, but it's nowhere near Londinium."

Bless him, but the youngling is right. We thought we had located far enough away to avoid Mundanes (they love our products, just don't want to be near the loud and ugly machines which make them, nor our strange ways.) But in recent years, the city has sprawled in all directions. They endlessly complain as they commute to the city center on the railway we built, when they're not offering us insane sums for our housing!

Development to our west would encircle us. We delayed that, but only by letting the City annex New Hammersmith next year. With City rules, City taxes, and allowing Mundanes to live in OUR town! Unthinkable!

So we must move now. We will extend our railway west, while we still can, and use it to move our factories and our town. This time: far enough away.

What are we leaving behind? The Mundanes would build Mundane luxury housing when we're gone, so we're building it. Get your deposit in!

Doesn't really matter the reason why this colony is different and not compatible with the hardly-colonial Mundanes, the ones who hung back on Earth until Mars had city water, garbage collection, and nine Tim Horton's. There is that, plus a thousand other reasons in the history books.

The colony ends up building a dual railway (as in the VLA, shipyards, or the N1 area at Baikonur), allowing them to move their very large modules. This dual railway, being nothing less/more than a standard double-track railway with unusually wide and precise spacing, becomes an extension of their original tramway to downtown Londinium.



In Dragonriders of Pern, in the 8th year of the colony, the planet is beset by something known as "Threadfall". Dangerous silver organisms called, "Thread" fall from the sky. The Thread devour anything organic; initial losses are staggering. This is similar to other "alien life" answers, because thread is an organism, with the exception that Thread is never demonstrated in the books to have any real awareness, and Thread by itself isn't the whole story.

The colony, which by this time has begun to spread out on the Southern continent of the planet, is not immediately uprooted. However, the colonists do eventually make the decision to abandon Landing in favor of moving, en masse, to an extensive cave system on the Northern continent, later called Fort Hold.

What really sets things moving, though, is Landing is located on a plain below a volcano that was believed to be inactive. Less than a year after First Fall it becomes apparent that this is no longer the case. Instead of an orderly evacuation, the colonists must quickly pack anything they can onto a hastily assembled flotilla of just about any boat or ship that still floats, in order to get clear before the volcano erupts.

These events result in the colony losing all contact with Earth; the planet is even interdicted. Additionally, technological level is reduced over relatively few generations from an advanced and computer literate society back to a near-feudal middle ages state, thanks both to the loss of equipment and ability to adequately educate the young for a time.

This story is told in the books Dragonsdawn and Chronicles of Pern: First Fall, but most of the books — the original and "main" storylines — take place millennia later. It's as those books became popular that the author was able to write the origin story, which I admit that while well-written, has an extremely cheesy premise.

I highly recommend the Pern books. It's great early sci-fi (first book in '68), with a strong female lead that's not there just to make the male hero look good.

Failed Terraform

As a more general answer, you might also consider a failed terraform process. This could take a number of forms... a colony initially has to live in domes, but expects the terraform to allow them to expand after a suitable period of time. Failure for expected results might force a colony to withdraw. Alternatively, the initial condition of the plant might limit them to a relatively small area, with terraforming efforts aimed at extending this area backfiring to result in an unstable environment... frequent earthquakes, unexpected volcanic activity or tornadoes, excessive tides, and the like. Even atmospheric change might be possible.

There's lots of potential here to make your own world. I can already imagine a story around a remnant who stayed behind when most of a colony abandoned the world, still trying to make a go of it. 2nd or 3rd generation of this could be pretty cool, where you'd have a lawless wasteland story with the added dangers of an especially hostile alien world. Throw an alien species into the mix, and this could be something pretty nice.


Discovery of alien life

Science fiction has a number of stories where colonists set down and then discover there's an existing alien species with a claim on the land. Whether they move voluntarily or by force or by treaty, the result is packing up and moving so as to not interfere with the existing life that they didn't recognize when first choosing a colony site.

Two Star Trek episodes come to mind:

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    $\begingroup$ The bloodsucking Cicadas are discovered in the happy forest or the dormant Triffid seeds start to sprout in the lowlands. $\endgroup$ – KalleMP Feb 1 '17 at 7:18

Why would they have to move? (to another place on same planet)

Because steam generated by their machineries is basically evaporated heavy-water, so after some time they live in one place, the ground start to become radioactive. They calculated that every 100 years or so, a previously left place can get below the warning level of radiations. But depending on their production of the heavy steam they have to move every 1 or 2 years.

Why would they have to move? (to another planet / heavenly body)

They are building slowly a wormhole network, they assemble pieces sended from Earth, the assembly is basically creating a modified version of a particle accelerator, it takes years to assemble everything correctly and to changes settings for it.

Then why sending 2 expeditions training twice the people while you can send to multiple places the same supertrained crew?

To allow one or several whormholes to appear and point outside solar system are needed several devices placed on different planets, the more the devices, the more stable the wormhole becomes.

If your plot does not allow wormholes, there could still be need for particle accelerators on several different places to study rare physical phenoma and quantum mechanics.



It could be their original settlement's engineering became obsolete. Since it can sometime be easier to start fresh than build onto an old design they move to the nearest site with suitable resources.


Each country divides up the planet but the one the colony was on is putting too much pressure on them. The inhabitants must stay together to survive and so the agree to emigrate en mass.


Because the night is too long

Not applicable to Mars, but on a slower rotating world, perhaps the colony moves to maintain a reasonable day/night cycle. For example, if the world completes a rotation (i.e. a day/night cycle) every 30 earth days that would like kill plant life and lead to considerable disruption in the health of colonists. The colony moves every day to maintain a constant 12 hour day/night cycle by waiting until it is plunged into darkness and then moving back into the light (or vice-versa).

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    $\begingroup$ I'm pretty sure that if they managed to travel years through space to get to another planet, 30 days without light would be no problem for this people. They would have some way to keep everything warm and shiny. $\endgroup$ – T. Sar Feb 1 '17 at 10:46
  • $\begingroup$ Permanently mobile, steam punk, space gypsies... $\endgroup$ – jorfus Feb 1 '17 at 17:46

So you land on an ice burg or similar because it is super easy to get water from. Heat, filter, and drink.

After a number of years you consume the part of the ice burg your on, and now have to move to the next nearest one.


Discovery of unacceptably high levels of radon gas in the vicinity.

  • $\begingroup$ I think that would be too trivial of a reason: it’s easier to mitigate the situation than to come up with a crazy scheme to relocate everything. $\endgroup$ – JDługosz Mar 7 '17 at 7:03

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