Let's imagine that people, if they'd want could freely leave Earth to pursue their own destiny on other planets etc. How far could we get assuming following:

Assumption No. 1: It's trivial to get any item up to 260 metric tons ( fully loaded Boeing 777F weight ) into space ( 800 km from Earth's surface ). Anyone could save up money to buy the Space Elevator ride and get whatever they'd want into space.

Assumption No. 2: Every person has a life-span is ~500 years thanks to curing cancer and discovering how cells can replicate almost indefinitely. Then, however, the brain-structure starts to fail rapidly and no cure is found.

Assumption No. 3: People can be put into stasis up to 100 years and can reenter stasis after a year.

Assumption No. 4: No significant progress has been made in any field from today's standard. Can't use dark-matter as fuel, no opposite pole of gravity is discovered etc.

Assumption No. 5: Our hero is an engineer, has good technical education, young - only 30 years old and totally sick of Earth and how things are. He's not rich, but is definitely high-end of middle class.

So our hero wishes to take to space and establish a utopia in his understanding (doesn't matter what it is). How realistic is it for him to reach an Earth-like planet in his lifetime?

There's no pre-defined blueprint of a spaceship, whatever he puts together he'd fly, but for the sake of simplicity let's say that base components are available and wouldn't cost too much just like getting a cell-phone was a luxury some 25 years ago and now everyone has a smartphone!

Things that our hero decides to take with him:

  • Worlds library - the largest collection of books in digital format on every subject in most of the languages. Not complete collection of every book ever, but the largest that we have at this point.

  • A super computer - a PC that would seem like a super computer to us, some x10 000 times more powerful than average computer today.

  • A telescope - powerful enough to see a persons face on The Moon from Earth if the sky is clear.

  • Large solar panels that would be enough to power a large apartment if there's light.

  • A 3-d printer that can print both circuits, plastic, metal and compose diamond. It can actually refill its matter storage from rough material (eg. CO2 → diamond)

So, knowing that space is full of radiation, small razor-sharp particles, magnetic waves etc. How possible is it to construct a space-craft that would be sustainable enough for at least 120 years in-between repairs? And how safe would it be?

And finally - how far could the hero get in his lifetime if the speed he could travel is roughly twice the speed of sound (relative to Earth's atmosphere) while in vacuum of space and around 900 Km/h in atmosphere similar to that of Earth's density?

EDIT: if some of you are unimpressed by the stats that the said spaceship would have — please note it's built by finances of a single individual. It's very very possible that once landing on a planet the spaceship would not be able to leave the orbit again. So when answering the question — think in terms oh what could go wrong on his way to Planet Paradise. Also feel free to specify what our hero should prepare for/bring with him to even attempt a journey like that.

EDIT2: Made some calculations and found out that even with speed like 40 000 km/h it would take thousands of years to reach a different solar system ( and no promise that it could have Earth-like planets ). So unless there's a way to travel at least 1/4 speed of light it would seem impossible to get very far and be able to see different planets.

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    $\begingroup$ What are the dangers of long space travel? Death. $\endgroup$
    – Ranger
    Commented Aug 25, 2016 at 4:17
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    $\begingroup$ "roughly twice the speed of sound in vacuum of space", speed of sound in vacuum is zero. Do you mean speed of light ? $\endgroup$
    – Chinu
    Commented Aug 25, 2016 at 5:00
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    $\begingroup$ @CreativeMagic Escape Velocity alone is around 10 times more than what your ship is capable of > so you couldn't get off the planet once you make landfall $\endgroup$
    – dot_Sp0T
    Commented Aug 25, 2016 at 5:31
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    $\begingroup$ I see so much that could possibly go wrong, but the biggest issue, is that there are no currently known planets that could sustain life as we know it -- and the planets that are currently known aren't exactly down the street... Even then, unless you plan on printing trees, algae, and a whole lot of other needful things... well, I'm afraid CandiedOrange is the right idea. $\endgroup$
    – Fayth85
    Commented Aug 25, 2016 at 7:19
  • 2
    $\begingroup$ You ask many different questions at once. You should really focus on a single one to get started. You could ask separate follow-up questions later. $\endgroup$ Commented Aug 25, 2016 at 9:30

4 Answers 4


Getting feet confused with meters and screwing up your reentry plans. Resulting in a fiery death.

Close encounters with space clutter. Resulting in violent death.

Overestimating how long equipment will remain functional while you're in stasis. Resulting in eternal sleep, AKA death.

Technological advancements while you're in stasis. Resulting in being salvaged for scrap by faster ships that put you on display in a museum, after 'accidentally' causing your death.

Actually making it where you're trying to go and finding no one else survived and nothing interesting to do. Resulting in being bored to death.


I think you have your metrics off by several orders of magnitude.

Twice the speed of sound may seem fast here on Earth, but it's snail pace in space (it would take 13 days to get to the Moon and more than 14 years to get to Mars).

To get anywhere in the (extended) lifespan of your (misguided) hero you need speed which is a sizable fraction of the speed of light.

Said that your biggest problem is the size of the task. Unless your hero's Utopia is hermit life he will need a certain amount of people with him. That means to have a generation ship, which is something probably bigger than an aircraft carrier, 747-size is surely inadequate.

Dangers of long space trips are:

  • Lack of possible repairs/refueling for long period. This means recycling is a must and it's not allowed to fail; double/triple systems are needed and spares should be available (or possible to build with your "3D printer").
  • Some system failure is the main concern.
  • Impact with debris is a (rather remote) concern while still in our Solar System; outside the Void is... unsurprisingly empty. Chances of an impact are very low.
  • You say no major breakthrough is available, so energy production is a concern (solar panels will be unusable as your hero gets farther from the Sun); probably You need a nuclear generator with enough fuel to last (probably more than one, for above reasons).
  • Concern surely needing addressing is lack of gravity which, on the long run, has adverse influence on human health. This can be easily simulated by spinning your ship; if ship is small then deploying a counterweight (e.g.: the nuclear reactor) with a long cable and spinning "bolas like".
  • Boredom. Even with help of stasis our hero is going to be more isolated then any man ever existed. Suicide is likely.

If your hero survives all this and reaches a star system with a suitable planet then a whole new bunch of perils await him:

  • To start a community, with enough biodiversity a sizable gene pool is needed (>>1000).
  • To have a reasonable competence in all fields needed to keep a "modern" society running a large number of brains is needed (>10000).
  • To terraform a planet you need a large amount (>>1000000) of different plant/animals (it's highly unlikely local flora/fauna, if present, would be any help... regardless whatever Star Trek said).
  • $\begingroup$ A generation ship might be unnecessary because "Every person has a life-span is ~500 years" and "People can be put into stasis up to 100 years and can reenter stasis after a year". When you exploit this to a maximum, you get a chronological lifespan of 50,000 years. That puts quite a lot of interesting star systems within reach. $\endgroup$
    – Philipp
    Commented Feb 5, 2018 at 12:04
  • $\begingroup$ @Philipp: a generation ship is necessary because I have no knowledge of anyone able to survive one year completely alone in a plane sized junk mostly filled by equipment needed for survival. Notice the "second year", even if 100y have passed, will appear as if after a night sleep. Not something to look forward to. This, obviously, letting alone difficulties of building an (utopian or otherwise) society single-handed. $\endgroup$
    – ZioByte
    Commented Feb 5, 2018 at 12:33

Let's establish our reach:

he's 30. He has to be awake 1 year every 100 years and can reach 500, assuming he needs no medical attention. So he will die at a calendaric age of 30+470*101=4777 years, afer 4747 years of space travel. Let's assume he travels without acceleration after some initial lob to somewhere...

V=340 m/s

Speed of sound. Let's see where he gets... he has a whooping 149,800,728,101.76 seconds of absolute max travel before he begins to die... so his reach is $50.9 * 10^{12}$m, plus the headstart of 1AU or $149.6^{12}$m. That's roundabout 1.3 AE... he hasn't even reached mars.

V=11.3 km/s

Let's assume he is Pioneer 11. He takes 43 years to get out to 95.3AU, then travels constantly at 2.4 AU/y. After the following 4704 years he will have managed a total of 11,384.9 AU - or 0.18 LY. He is out 4% on the way to Alpha Centauri as he dies.

V=17 km/s

Ok, update that to be Voyager 1 instead. Now he travels at 3.6 AU/y and only needed 40 years to get to speed with slingshots and such... his headstart is 180 AU as we take that speed. So he ends up at 17,125.3 AU... or 0.27 LY. 6% out to Alpha Centauri.

V=6506 km/s

Let's do the math the other way round. To reach Alpha Centauri, we need to get to about 268,770 AU or something in the margain of $4*10^{16}$m. To be traveled in 4700 years, so he needs to get up to around 6506 km/s. That is 0.02c. Not really relativistic... but you should verify your calculations relativistically. Yet I have no clue how he should get about 40 times more speed than the fastest manmade object from the solar system with the current tech. It hasn't advanced much in these regards to this from 1977 when Voyager was launched, and both Voyagers had a pretty damned good row of slingshots.

So at the moment, that's it. I postulate the following to be happening when the poor young man enters the ship he bought third hand after it's latest refit for the first time:

Welcome Aboard, Captain!

I am Lysander, your dutyful ship AI. Please take your time to familiarize yourself with the controls and make your bunks as comfy as you can. We have uploaded the ship computer with videogames, TV shows, Books and music for at least 5000 years. Yet we advise you to just make a quick tour to Mars instead of targeting the unexplored depth of space, where you will just find just lonelyness.

Be advised that refit did not remove any harmful objects from your ship, including the current TP-82 successor in your portable emergency survival kit or the highly toxic and caustic hydrazine in your RCS fuel tanks. Both these could become handy if you should want to commit gruesome suicide because you can't stand the lonelyness of being confined to your spaceship any longer and knowing you can't reach any spot out of the solar system.

Our current service time before you need to dock at a maintenance base is 120 years. This is well enough time to have a grande tour with all the planets, making a stop at the docks of Neptune, and then make a trip to Pluto and back. Yet be adviced that due to the loss of efficiency of the solar panels, any non-essential system for the function of the ship will be shut down past the astroid belt1. If you didn't bought the BES-5 RTG Upgrade to heat your ship and power your life support, any travel beyond this point is unadvised. If you bought it, please don't hang your wet towels over its radiators, as you might set them ablaze and make the core melt.

If you need conseling, please schedule ahead because of the huge communication delay. While you still will be able to receive incoming messages and television programs, the lag will delay communication with earth and thus can create a huge bill for you, as the doctor can't work on other cases during this time.

Should you need serious medical assistance due to human stupidity (including knocking your head in the spacesuit while shooting at the junk you dropped for target practice), please freeze yourself as soon as possible after setting auto return to a medical facility. Should you remain active in 0-E environments for a considerable ammount of time, please be advised Space Adaption Syndrome is common and can be helped with. If you are concearned about long term effects, please read the NASA’S EFFORTS TO MANAGE HEALTH AND HUMAN PERFORMANCE RISKS FOR SPACE EXPLORATION.

Be advised that the tether of your space suit is not made to withstand cutting or sawing motions along the edges of solar panels and that the ship can't turn around to pick you up in time. Also please don't try to mess with the piping or wiring or I might need to activate the Self-Defense-Protocols.

Would you like to play a game?

1 - "Jupiter is five times farther from the sun than Earth, and the sunlight that reaches that far out packs 25 times less punch [...] our massive solar arrays will be generating only 500 watts when we are at Jupiter." Rick Nybakken, Project Manager "Juno" @ JPL Passadena, Calif.

  • $\begingroup$ "the ship can't turn around to pick you up in time" - are you sure it can't? When the tether breaks and the astronaut loses contact to the ship, he would still be moving through space with almost the same speed as the ship. The relative speed difference would just be a few m/s at most. Picking him up would just take a little course correction with the RCS thrusters. $\endgroup$
    – Philipp
    Commented Feb 5, 2018 at 12:29
  • $\begingroup$ @Philipp "a few m/s" sounds not much, but it is motion not in line with the travel path. Turning around like a sailing ship or motor ship simply is not possible (and even those have REAL problems to pick up lost crew) that easy: you'd have to break to be slower than it, then try to steer the ship in front of the person, NOT hit him with exhaust gas from RCS and then somehow give him a chance to grab onto something - all within the timeframe before he freezes. And if it was an umbillical cord... he is dead. $\endgroup$
    – Trish
    Commented Feb 5, 2018 at 12:33
  • $\begingroup$ Space isn't an ocean. Space crafts today already have RCS thrusters to maneuver freely with 6 degrees of freedom. So you don't need to turn around to use the main engine. When the astronaut is drifting away, you just need to use the RCS thrusters on the opposite side to match their speed. $\endgroup$
    – Philipp
    Commented Feb 5, 2018 at 13:01
  • $\begingroup$ @Philipp you overestimate maneuverability: a spaceship is a HUGE mass. A space shp able to leave LEO into deep space will be at least 20 tons, more likely 200 tons. the lost pilot are maybe 200 kg in suit. Factor 100 to 1000 on the mass. RCS to apply a lateral shift or breaking is minuscle: the largest is about 400N each. Calculate yourself how long you have to fire 4 400 N Thrusters to get back in front of the lost pilot... YOU said "no new tech". $\endgroup$
    – Trish
    Commented Feb 5, 2018 at 14:31
  • $\begingroup$ Wait, shouldn't that be 47500 years? And some 26km/s to get to Aplha Centauri in that time? $\endgroup$
    – t.ry
    Commented Mar 24, 2018 at 20:43

I hate to be that guy, but... not safe at all.

Unfortunately, that 'minor' issue of radiation is still under study, but we already know that it can change gene expression. In the recent case of astronaut Scott Kelly, up to 7% of his genetic expression has not returned to normal in the two years he's been back on Earth.

Take into account that Scott spent only 340 days in space, compared to the 120 years you're proposing. If scientific advances aren't made before your plot takes place, there's no telling what your character might look like by the end.

That's not even mentioning a myriad of currently inexplicable and untreatable health issues such as vision problems caused by prolonged space flight.

Ship integrity may pose a bit of a problem as well. Even the space debris the ISS encounters while simply orbiting the Earth can tear holes in the station's protective kevlar. At the speed of sound, you'd most likely run into more debris than that. The ISS has cost around 150 Billion USD to date, so parts better be a lot cheaper in the future, or little timmy there's going to be hurtling through space in swiss cheese.


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