So. A looong time ago, I asked how to remove most technology in a hundred years. However, I just realized that for my plot to work, I still need my characters to move from one planet to another. I have decided to leave a few (4-5/planet) space-elevators in place, but I got stuck there.

The question:

How do I move my characters from Mars' orbit to Mercury safely, without using anything space-age other than the elevator already mentioned?

Life support is not a problem.


  • Since I have an ex-mining colony on Mercury, I will have some sort of shielding system in place to keep my colonists safe. Hopefully, that is still there. I might add a subplot about something threatening this shield.
  • Mercury and Mars are just examples. I am not necessarily talking about those particular planets, just a pair that are a comparable distance away from each other.
  • there are probably a bunch of old spaceships around without engines, so life support should not be a problem. Also, see the next point.
  • In my universe, somehow I have some people who have energy-manipulating (as in: moving and/or absorbing heat, cold, kinetic energy, etc.) powers, so they could theoretically provide life support.


  • the space elevators are in perfect working order, with nanotech repair crews and power beamed from a Dyson cloud.
  • One idea (not mine) is to use maybe a large pot of water and boil that away. Basically a steam-powered spaceship. Would that work? Just an Idea.

Edit 3:

For those who want to know about the magic system:

Your "other" strength starts at the level of your normal strength, and drops off linearly(~1 n/m ), but can be boosted by absorbed energy. When absorbing, you can absorb 10 J before you have to dump it somewhere (say, [lifting] a nice, big, rock [for kinetic powers]). Some people can make forcefields, but need to have anchor points. Basically a thin, flat, unbreakable, [inflexible,] air-proof, waterproof, transparent cloth of arbitrary size.

Something I just thought of: when absorbing energy the drop-off is same as when projecting. Forcefields basically absorb the kinetic energy of something colliding with it, and almost instantly projects it back into the same object.

Something else: the loss of power is turned into heat.

Edit 4: in reply to a comment by @sphennings

The transfer speed of the energy is the speed of light. In theory you could move yourself, but only as far as you could lift something as heavy as you are. Teleportation is impossible for this class of Gifted, though I might add more classes that don't need these spacecraft so are irrelevant to the question. Long distance communication isn't really relevant, but I guess that you could make a pair if tiny plasma-spheres and use them to make semaphore-signals. When projecting into something, you can't chose what to project into more selectively than "that rock" or in the case of fluids "this area of fluid", so you can't filter air by molecule-type. For movement I guess I am basing my system on the system from Mistborn, more specifically the steel and iron powered allomatic powers. You push against something, it pushes back. You pull, and get pulled. Basically, Newton's laws still hold.

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    $\begingroup$ I strongly suspect you'll be hard pressed to. The vicinity of Mercury is a hostile place... Also, what research have you done in trying to answer this question on your own? $\endgroup$
    – user
    Nov 20 '17 at 12:55
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    $\begingroup$ Asimov still uses spaceships but has them run/maintained by a priesthood in order to match the medieval mindset of most planets in his foundation universe $\endgroup$
    – dot_Sp0T
    Nov 20 '17 at 13:05
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    $\begingroup$ MAGIC!!!!!!!!!! $\endgroup$
    – anon
    Nov 20 '17 at 13:14
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    $\begingroup$ I'm not going answer I am going to suggest that you read the flight time sections of Wil McCarthy's Lost in Transmission in which Conrad Mursk travels a very short distance through space in a brass sphere, and understand that even with the level of complexity, risk and hassle he presents he's taking the piss, it would be so very much worse in reality. $\endgroup$
    – Ash
    Nov 20 '17 at 13:24
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    $\begingroup$ Can you reedit your question so that all the edits are incorporated into it. If anyone wants to know how the question has changed they can read the edit history. Each subsequent edit is making the question harder to read. $\endgroup$
    – sphennings
    Nov 20 '17 at 19:35

I do not know if this fits in with your plot, but it does reflect events in human history, and is therefore realistic.

When humans left Europe and came to North America, they left the ability to build and manufacture technology behind. Everything had to be imported, so basically the new colonists reverted back to earlier more primitive technology. However, they had access to some 'modern' technology if they bought something that was imported. But given the cost, it would be prohibitively expensive, and thus rare.

So I would suggest that MOST civilizations in your world lost their technology, but one very removed civilization was able to retain it. Perhaps one on a far-removed space station orbiting a moon of Saturn. Removed enough to avoid whatever caused everyone else to loose their technology. They still had space flight, however they did not make it available to any other civilization. It was obvious to them what happens when the other 'barbarians' in the system got hold of advanced technology - they destroyed each other. So, they religiously protected their knowledge and technology. However, they provided inter-planetary travel at a price. Because they are completely removed from the other civilizations, and except for providing inter-planetary transportation they have no influence, they would not interact with your plot in any other way.

They would be like the traveling merchants who went from settlement to settlement in the old West, selling pots and pans and other 'advanced' goods imported from Europe, and then left the farmers and ranchers to live in their more primitive style. Or the traders who interacted with the native Americans, trading furs for blankets and such.

It could provide other interesting plot twists as well. You get to decide what manufactured goods they sold to the 'colonists'.


We even have similar today. People in third-world countries might not even have electricity in their homes, bu they have solar-powered smart phones. They have no idea about the technology, and could never build one themselves. They just use it.

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    $\begingroup$ Good idea! I like it! Not sure if it will work, but I might try it... In fact, I might already have this group. $\endgroup$ Nov 20 '17 at 15:19
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    $\begingroup$ They would also keep their home location completely secret and unknown to everyone else, for security reasons. Obviously, no one would be allowed to come to it. $\endgroup$ Nov 20 '17 at 15:26

You can't

Trying to travel in space without space-faring technology is kind of like trying to cross an ocean without sea-faring technology. Unless the water kills you in a matter of minutes would you try to swin on it, spans across tens of millions of kilometers, and the lands you aim at are constantly moving at several kilometers per second. But hey, you got a pontoon from the last civilization !

EDIT : Since we allow magic, I may edit my answer when given more details about the magic abilities of the energy-manipulating people.

OK, so let's use this answer to develop a bit on the magic ways of applying thrust :

Your "other" strength starts at the level of your normal strength, and drops off linearly(~1 n/m ), but can be boosted by absorbed energy. When absorbing, you can absorb 10 J before you have to dump it somewhere (say, a nice, big, rock). Some people can make forcefields, but need to have anchor points. Basically a thin, flat, unbreakable, air-proof, waterproof, transparent cloth of arbitrary size.

First of all, being able to absorb and reject 10J of exterior energy (whatever that is) won't make much difference. Especially if you have to, say, burn some fuel to gather and release that energy, this fuel will weight more that regular food for your human thrusters (the energy density of food we process is much higher that wood or fuel burning).

So let's assume that your average human thruster will be able (given that little help and a bit of mental training) to lift around two times its own weight (in the range of 150-200kg), and not use up it's own energy to do so (he won't be tired like he actually lifted that weight). That's fine, but you'll need a lot to actually lift a spaceship and, more importantly, quickly move it sideway to reach orbital speed. Once in orbit, the rest can be done with a much lower thrust on a longer period now that you don't risk falling back on Earth.

One can imagine packing a lot of human thrusters in the ship, and with a huge amount of land-based helpers. However, since 200kg of "lift" (at 1g) is rougly equivalent to 2kN, your helpers won't be able to help passed an altitude of 2km... So even if the take-off impulse is enough to get your ship to space, you'll then have to rely to your human-thrusters crew to go sideways (mandatory xkcd reference) quick enough to stay in orbit. And that will be near impossible with such a limit of force each people can apply.

But wait ! You got space elevators ! While getting them to work is another question, let's assume you have somehow put the crew and the ship up there in geosynchronous orbit. Now you can apply any kind of force given enough time to reach any orbit ! But...

Where to aim ?

That's right : with all the space faring technologies gone, I believe your characters will have a hard time knowing where to accelerate. Pointing at Mars and saying "We'll go there !" won't really be effective, given how that's not how space travel works. Your characters will need to precisely know how to make orbital maneuvers with little to no technological help. And even if they succeed in going near their destination...

Things may well go splat

Actually, it all depends on the targeted planet and the ship. If your ship is designed to use aerobraking and rely mostly on chutes to lower its speed before landing, you can pull-off a Mars landing. Otherwise, your human-thrusters crew will have to shrug off quite rapidly all that speed they build up to rendez-vous with the planet, while fighting that gravity that loves to make thing go splat. Again, it could be done given a good orbital mechanics understanding from the crew, a low gravity celestial body and a ship packed with your kinetic-energy-bending people... But that's a lot of assumptions and this need to be backed by solid numbers to give you a more precise idea of the requirements.

  • $\begingroup$ I also have the shell of an old ocean-liner, that might not survive another 100 years, but it is in usable shape. I just need to move it. $\endgroup$ Nov 20 '17 at 13:24
  • $\begingroup$ Then how exactly are the powers of your energy-manipulating peolple (the kinetic types) working ? Any restriction ? (can't move oneself, limited in force, where does the energy comes form ?) $\endgroup$
    – Keelhaul
    Nov 20 '17 at 13:29
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    $\begingroup$ Your "other" strength starts at the level of your normal strength, and drops off linearly(~1 n/m ), but can be boosted by absorbed energy. When absorbing, you can absorb 10 J before you have to dump it somewhere (say, a nice, big, rock). Some people can make forcefields, but need to have anchor points. Basically a thin, flat, unbreakable, air-proof, waterproof, transparent cloth of arbitrary size. $\endgroup$ Nov 20 '17 at 13:36
  • $\begingroup$ @Mark Gardner I expanded my answer given these information $\endgroup$
    – Keelhaul
    Nov 20 '17 at 14:39
  • $\begingroup$ Note that you have "a few (4-5/planet)" functioning space elevators at the origin and destination, so you can possibly neglect the effort of reaching orbit and safely landing from orbit. Also, you can probably just "park" your space row-boat next to the elevator, no need to take that to the ground... $\endgroup$
    – G0BLiN
    Nov 20 '17 at 15:32

Something air-tight, with thrust...and the ability to calculate where you're going

So, air tight is fairly obvious, some plants on board might do for recycling the air. I'm not sure how many medieval creations were reliably air-tight but perhaps tarring the ship and around the door when everyone is inside.

Thrust. All you need to do is throw something out to transfer momentum - this is difficult to operate from inside without breaking your air-tight seal but if you can think of a way around that you can just use some sort of ballista - obviously needs a system to reload it without going outside.

Calculations are the difficult part. It isn't easy to get your orbits right, maybe you can do the math - I don't suppose that is beyond your means - but how precise can you be with your numbers? If the mass of those projectiles is off, the error on the mass of the ship, the tension in your ballista in a vacuum, the momentum transfer won't be easy (or perhaps even impossible) to calculate precisely. Getting to your destination requires meeting up with the right orbits, knowing where the planets will be and how much momentum you will transfer. Small imprecisions over large distances become huge discrepancies.

So traveling through space may be possible but getting where you want to be won't necessarily work so well.

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    $\begingroup$ "Something air-right, with thrust ..." - You forgot radiation shielding, air scrubbers, waste reclamation, fire control, etc. $\endgroup$
    – AndreiROM
    Nov 20 '17 at 15:02
  • $\begingroup$ Good luck using a ballista to launch at many km/sec, and also not splattering your medieval astronauts in the attempt. $\endgroup$
    – imallett
    Nov 20 '17 at 15:53

You already allow a little bit of modern technology, why not stretch that a bit more?

Your world already contains functioning space elevators - meticulously maintained by infallible applied hand-wavium, and, (for the same reason) they can't be used to circumvent the tech regression crucial to your world and story.

So, unless a functioning medieval spaceship is crucial to your story (or you just find the notion too cool to skip), why not expand the space elevators concept a bit to allow your characters to travel?

Maybe the space elevator have "emergency escape pods" or, better yet, "pilot tow-ships" which can be used for longer travel. Or maybe there are completely automated crafts making runs between planets (as part of the maintenance routine of the elevators, perhaps) which a group of resourceful energy manipulators (or even clever or lucky regular humans) can stow-away inside to catch a ride. Maybe there are functioning matter transporters built into the auto-maintenance system and your characters can figure out how to use them - there are many variants to this line of thought, but the bottom line is this:

Space travel is hazardous, takes very long time, and requires advanced training, knowledge and technology across multiple disciplines (you'll need navigation, thrust, sealed and controlled environment, replenish-able supplies, waste handling, radiation shielding etc. etc. - and that's before taking into account the medical repercussions of spending months in low G...). So, unless your narrative absolutely demands doing this without the proper tech - why not throw in something usable, but limited as much as you need to stop it from toppling your medieval premise?


I have some people who have energy-manipulating (as in: moving and/or absorbing heat, cold, kinetic energy, etc.) powers

The best chance would be to invest in research and development with these individuals capabilities. The following paths could be taken in order to allow:

  • shielding: creating big enough air sockets that would endure space vacuum and prevent object collisions;
  • gravitational research: move containers with people or the persons themselves throughout space (lower friction = higher speeds);
  • energy signalling and energy source mapping: identifying planets and other travellers by energy signatures;
  • brain research: transmission of thoughts and ideas or movements manipulation by adjusting the electrical impulses of people's brains in far away places or other planets (this would likely avoid the need to travel in many cases).
  • $\begingroup$ This does not provide an answer to the question. To critique or request clarification from an author, leave a comment below their post. - From Review $\endgroup$
    – L.Dutch
    Nov 20 '17 at 17:38
  • $\begingroup$ @L.Dutch the question is "How to travel through space without modern technology?" my answer was: use the individuals with special powers who may help or perform these travels themselves... In what way do you think my answer failed to address the question? $\endgroup$
    – Armfoot
    Nov 21 '17 at 10:47
  • $\begingroup$ special powers and science based do not mix well... $\endgroup$
    – L.Dutch
    Nov 21 '17 at 15:12
  • $\begingroup$ @L.Dutch the OP edited his question and specifically added the paragraph I quoted pertaining special powers. From your last comment, you did not answer my question and it seems you are voting to close an answer based solely on a tag placed on the question. I ask you then, if science can be defined by "observation, identification, description and experimental investigation" and with "R&D" I suggested this exact set of procedures with those individuals, how does this not answer the question? What do you mean by "not mix well"? $\endgroup$
    – Armfoot
    Nov 21 '17 at 21:20

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