It is the year 2055. Only 20 years after the devastating Third World War, humanity has united together to start a golden age. Overseen by a peaceful, ambitious, and global superpower called United Earth Republic, war has finally been eradicated. Technological advancement and exploration has skyrocketed to say the least. And most importantly, colonies have begun to spread like wildfire across Luna, Mars, and Titan.

However, in the wake of this exodus to across the solar system, we are in need of a new form of transport. The older, titanic colonial ships have become too slow, too crowded, too expensive and just too impractical to remain as the only link between planets. With thousands of people crossing the solar system each day, we need a transit system that could link the planets as easily as linking two cities.

As one the UER’s top architects, you have been put in charge of developing a mass transit network across the solar system dubbed “Project Voyager”. At your disposal, the UER Senate has provided you with an unlimited budget for resource mining, fuel, construction ships, and drones (alongside a huge human workforce ready for hire). However, there is a certain set of guidelines you have to follow:

• It has to move very fast, capable of traveling from the Earth to Mars at their closest points in only 2 days or less. Also even though we did crack FTL travel, it is way too expensive to scale up past individual star ships.

• It has to have a quick turn-around time, making it possible to unload its passengers and payloads, undergo a quick systems check, restock, reload, and depart in a matter of minutes.

• It has to be small, carrying only groups of 100 people each alongside a payload weight of only 5 metric tons each. For cargo only pods, it could go up to 10 metric tons.

• The UER is almost a type 1 civilization, so dyson sphere satellites and laser driven photonic propulsion are on the table (it’s not necessary, but recommended for cutting out fuel weight)

• Although the bulk of the colonies’ populations are planetside, there are O’Neil cylinder space colonies and space elevators around each of these colony worlds. So, the surface to ground and orbital infrastructures are already in place.

So, with everything ready to go, how do you plan to build this?

  • $\begingroup$ Earth to Mars at their closest = 2 days; but Earth-Saturn is 2 orders of magnitude greater distance. Is an Earth-Saturn trip of 100 days acceptable? Can we assume that part of those 2 days is like air travel today - low-velocity travel to get out of the crowded air-traffice environment near the airport until we reach cruising altitude? $\endgroup$ – John Feltz Aug 25 '16 at 17:10
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    $\begingroup$ I hate to be a naysayer, as this all sounds intriguing, save one part - the timeframe. If WWIII is what we all fear, we will still be sorting out survival techniques, not building space stations in 2055... add a century for plausibility's sake. Just my opinion... $\endgroup$ – Joe Aug 25 '16 at 17:53
  • $\begingroup$ @Joe In the lore of the story, WWIII was started in 2027 between the US, a fully united EU, and an aggro superpower called the Russo Chinese Federation. Although nuclear weapons were used, the war pretty much was locked in a stalemate until the United Army (the precursor to the UER) pretty much sprung up out of nowhere from the ashes of the UN and NATO. Using technology reverse engineered from artifacts they discovered, they defeated all three superpowers and ended the war by 2033. The UA then settled down as the UER, and used the artifacts to advance mankind forward (hence the tech boom). $\endgroup$ – Mattias Aug 25 '16 at 20:55
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    $\begingroup$ You're still asserting that the tech is so wonderful that you build space elevators within twenty years... on distant planets. The Big Dig, the largest infrastructure project to date, took 25 years. I think you're overestimating how fast humans are willing to move. Also, the initial colony ships would themselves take years just to reach their destination - and presumably scouts are sent first? The time line is wicked short, even without a world war. $\endgroup$ – Nathaniel Ford Aug 25 '16 at 21:27
  • $\begingroup$ tool from that answer is capable to do what you wish. Also recommend that youtube channel Isaac Arthur for details of technologies, specially megastructures playlist $\endgroup$ – MolbOrg Aug 26 '16 at 12:32

There are actually several ways to do this, but one consequence the people will have to accept is that they are essentially firing cannonballs across the solar system with the impact energy of nuclear weapons. This is going to make control over the system of utmost importance, and any malfunction or accident is going to have severe consequences.

In order to send cargo rapidly across the solar system, a series of orbital mass drivers will have to be established in orbit around every transit point (planet, moon or space colony). One mass driver is energized at the launch point and shoots the cargo at some massive acceleration to the destination (at an acceleration of 100g, a cargo pod could go from the Earth to Mars in about 24hr when the two planets are at their closest approach). The receiving mass driver decelerates the pod and stores the energy to help send an outgoing pod, make orbital adjustments and so on. Since no process is 100% efficient, there will also be a large set of radiators to deal with the waste heat.

Human beings don't take very well to this sort of treatment (and a mass driver which can accelerate human cargo to these sorts of speed at 3g or less will be improbably long), so if transporting people is the goal, they will need to be pumped full of oxygenated fluid to fill all the air spaces, and then stuck in a fluid filled tube to cushion the shock of acceleration and deceleration.

These mass drivers themselves will be huge structures, possibly resembling the 1970 era visions of Solar Power Satellites the size of Manhattan island (and given the energy consumption, ones in Earth orbit might well be that size to collect enough solar energy. Deep space mass drivers might have radiator panels that big to deal with the waste heat of their fusion reactors and accelerating/decelerating payloads).

But as I said, the key issue is the potential damage a pod could cause. A 3 ton asteroid interceptor described in NextBigFuture accelerated at 100g by ORION nuclear pulse charges would impact the asteroid with a gigaton of energy, so larger pods, and ones going faster to reach destinations to and from deep space would have the sorts of energies associated with dinosaur killer asteroids.

So the ability to track and (if needed) destroy off course pods would be absolutely part of the package. Mass drivers will probably have huge telescopes to assist in aiming the pods, which can be used to track them, and if necessary be used as beam expanders for powerful laser weapons. The power plants that energize the mass drivers will also be sufficient to power the killer laser, and Ravening Beams of Death (RBoD's) are conceptually powerful enough to rapidly vaporize materials in microseconds from as far away as one light second. Since pods will be on ballistic trajectories, they could be engaged from much farther away.

Maybe your peaceful republic will suddenly discover they are sitting in the sights of interplanetary cannon if the space colonies become disgruntled by whatever political, economic or social systems the Republic is trying to implement....

  • $\begingroup$ Is there any other way to protect the passengers from the high G acceleration without getting into too much technobabble. The whole point of the Voyager network is to make interplanetary travel fast and efficient. Although filling and suspending the passengers with fluid sounds cool, it just doesn't seem to be worth it for such a relatively short flight. Maybe there could be some sort of high-G injection, or a special gas pumped into the cabin's atmosphere. $\endgroup$ – Mattias Aug 30 '16 at 2:32
  • $\begingroup$ Unless you handwave the problem away with Applied Phlebotinum, there are no ways known with current understanding of physics to protect humans from extremely high g accelerations besides full immersion and displacing all airspaces with incompressible. liquid. $\endgroup$ – Thucydides Aug 30 '16 at 2:54
  • $\begingroup$ By the way, when you said "The impact energy of nuclear weapons", just how big of an explosion would a pod create after a trip from Earth to Titan without slowing down. I just had an awesome idea for using it in a story I'm writing. $\endgroup$ – Mattias Nov 27 '16 at 21:52
  • $\begingroup$ Short answer is Ke=1/2m*v^2. You need to specify the mass of the container and the speed it tis going at. The Chelyabinsk meteor was @ 20m in diameter, weighed @ 12,000 metric tons and was moving at @ 19.5km/sec (@ 60,000 KPH) and exploded with a force of @ 500 Kt. A typical modern nuclear weapon is thought to have a yield of 300 Kt to provide comparison. projectrho.com/public_html/rocket/index.php is a good source of more detailed information as well. $\endgroup$ – Thucydides Nov 28 '16 at 3:11
  • $\begingroup$ I just crunched the numbers in for a fully loaded passenger/cargo pod. If the pod itself weighed 2 tons, then it would have the impact force of... and Jesus Christ its a lot of TNT... 454 Mt. That's almost 8 times the force of the Tsar Bomba!! $\endgroup$ – Mattias Nov 29 '16 at 6:29

In this setting people made many impossible things so lets make one more.

Lets made orbital tube transfer system around the sun. This system takes orbit between Earth and Mars and consist of rings. These rings forms space gas flow. The biggest speed of gas in the middle of ring and the lowest on the boundary.

Each space ship need a few fuel:

  1. On the way from Earth to the Sun Ring.
  2. Some fuel to smoothly reach the quickest space gas flow.
  3. Smoothly goes out from Sun Ring.
  4. Travel the rest of the way to Mars.

Lets see check list:

• It has to move very fast, capable of traveling from the Earth to Mars at their closest points in only 2 days or less. Also even though we did crack FTL travel, it is way too expensive to scale up past individual star ships.

Actually no. This system speed up all Earth-Mars distances excluding the shortest one. So this system doesn't solve the problem but it reduces the problem just to make Earth-Mars travel by shortest way in two days.

• It has to have a quick turn-around time, making it possible to unload its passengers and payloads, undergo a quick systems check, restock, reload, and depart in a matter of minutes.

Lets imagine letter container which can drop current letter on the fly and catch the new one. It seems possible.

• It has to be small, carrying only groups of 100 people each alongside a payload weight of only 5 metric tons each. For cargo only pods, it could go up to 10 metric tons.

Supported, this system can't work with big freighters.

• The UER is almost a type 1 civilization, so dyson sphere satellites and laser driven photonic propulsion are on the table (it’s not necessary, but recommended for cutting out fuel weight)

Fuel is not excluded but you don't need fuel on the ship to travel. Just for manoeuvres.

• Although the bulk of the colonies’ populations are planetside, there are O’Neil cylinder space colonies and space elevators around each of these colony worlds. So, the surface to ground and orbital infrastructures are already in place.

It is possible to use it.

UPD 1. More details. Primitive system scheme

We have a set of tube transfer stations. They collects solar energy and speed up space gas flow in tunnel. There are container ships in gas flow which catches/drops usual space ships on transfer stations. I added Earth-Mars space ship trajectory to show how it works.

UPD 2. Shortest path. My previous picture doesn't use the shortest path. Lets make it shortest. Scheme 2 Actually the ship orbit smoothness depends on speed changing possibilities. In theory we can improve the system if made satellite bus. The satellite bus is a big asteroid. This bus has elliptical orbit around the earth and can transfer smaller ships to transport ring. There is no such asteroid on picture now.

  • $\begingroup$ I really don’t see an answer here. Is the second paragraph the proposal and the rest showing that it fits the need? Hen it needs substantially more detail, since at first reading it sound like the secind para is an introduction to what you will be describing but the rest of it doesn’t go on to describe it. You only named it. So what is it? $\endgroup$ – JDługosz Aug 26 '16 at 2:28
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    $\begingroup$ You are right. The second para is an idea. And the next text is description why it is solve the original problem. I will add more details. $\endgroup$ – NtsDK Aug 26 '16 at 2:33
  • $\begingroup$ Your picture doesn’t match the description where the shortestbroute should be taken to the ring and exit the ring at its closest point to mars. $\endgroup$ – JDługosz Aug 26 '16 at 9:52

Sounds like a system of space planes that operate in the style of the railway system in the early 20th century. Since you said you already had space elevators in place, then you would need a series of space stations that act as rail stations near the elevators. The plane would dock at the station, which gives you quick turnaround time since they never enter an atmosphere. Since everything is in space the space station could be multilevel allowing several planes to dock at once.

As far as propulsion, I don't have an exact method, yet, but I know how to meet the "2 days to Mars at closest approach" requirement. An engine that is capable of sustaining 1g (Earth normal gravity) of constant acceleration will get a plane from Earth to Mars, assumed 65 million km separation, in 1d 21h 13m 1s. I would love to take credit for figuring that out, but alas, I can't. Check out How fast will 1g get you there? for a really great set of charts, graphs, and travel times. Somebody figured out all the travels times from Earth to each major body in the solar system. That time is for constant acceleration for half the trip, then the ship flips a 180 and does a constant burn for deceleration.

Another benefit of constant acceleration is that it provides Earth normal gravity to the passengers and cargo. For more about this see Space Travel Using Constant Acceleration.

As I mentioned in the beginning, I would model the entire system around the railway of the early 20th century. Through a series of transfers, a person could travel across the US with little fuss.

Constant acceleration even works for interstellar travel as well. It would take 1 year + the number of light years to reach any given star. So Alpha Centauri would take 5.2 years since it's 4.2 light years away.

While I'm writing this I thought of a possible propulsion system, an EM Drive or an RF resonant cavity thruster. I know next to nothing about the science of the drive, but my understanding is that it's a "fuel-less" drive system. An engine produces an EM field, which it needs to run the lights and whatnot anyway, it diverts a portion of the EM to the propulsion system and it produces thrust. Anyway, it's a thought.

  • $\begingroup$ That is actually a really good idea, but wouldn't it defeat the idea of making it a space "plane" if it never entered an atmosphere? $\endgroup$ – Mattias Aug 30 '16 at 2:39
  • $\begingroup$ Typically spacecraft are patterned after boats or planes. In my head I envisioned space shuttle like craft, and I've always considered them to be planes rather boats so I went with it. $\endgroup$ – FiveHead Aug 30 '16 at 3:21

In one possible scenario you'll need three elements. 1) A launcher of some type on a orbital platform 2) the Clarke elevator/skyhook to get to the orbital platform and 3) a wormhole network

Take the Clarke elevator to the orbital platform, board a launch pod, launch pod is loaded into a launcher and sent through a wormhole to its destination.

Of course if the launcher can get the pod up to FTL speed, you might not need the wormholes.

  • $\begingroup$ Cowboy Bebop, is what you're saying. $\endgroup$ – Nathaniel Ford Aug 25 '16 at 21:19
  • $\begingroup$ Hi Nathaniel, was unfamiliar with the term but wiki'd it up and yes, something like that for part 3. Thanks for turning me onto C.B. - I'll enjoy the reading. /T $\endgroup$ – Tenacity Aug 25 '16 at 22:33
  • $\begingroup$ FTL speed? What? There is no such thing. Even lightspeed is impossible to reach because it would require infinite energy. $\endgroup$ – TheDyingOfLight Sep 3 '19 at 10:59

Lets look at the velocity we need for the voyage. Look at our neighbor, Mars. Their farthest distance apart is 377Mkm. The two-day limit means we have 172,800 seconds to do it in--we need to be traveling 2182 km/sec.

To boost to this speed at 1g needs 223,000 seconds--more time than we have for the whole trip. Lets go up to 5g--now we are using 44,500 seconds to boost and a like time to stop--almost half the trip. Oops, our top speed needs to be even higher. Skipping to the answer, the continuous acceleration equation is A = 4D/T^2 (units are meters and seconds.) That gives 50.5 m/s all the way--probably not survivable.

Note, also, that this is merely to Mars, not the more distant worlds.

Thus we can conclude that we can't solve this by force, we have to resort to handwavium. Dream up what you want for your story because there's no real-science answer.

Some more snooping turns up a table of minimum transit times at 1g (look at the rightmost column):


Note that these are for the planets at their closest. Note that no planet is within the 2 day timespan even at it's closest.


Interplanetary Virtual Transport Tubes

Tubular Regions Of Space Reserved for Transports

Divided by Velocity, Direction, Acceleration Requirements

Earth is ~500 cSecs (Distance Light travels per second) from Sun.

For Other Objects

Mercury Venus Mars Main Asteroid belt

200 360 750 1000 - 2000

Jupiter Saturn Uranus Neptune

2500 ~5200 ~10,000 14,000

Note that these, like most orbital distances can vary by at least 1 part in 16.

Tube types - divided primarily by cSec per hour speed. Restricted to licensed transports as collision energy per 1200 tonnes at 1 cSec/hour (~83 Km/sec) is 1 KiloTon equivalent.

Type FP1 FP3 FP9 10mC , 33mC 99mC

Velocity is in cSecs Per Hour - 1, 3, 9, 36 (~c/100), 108 (~c/33), 324 (~c/10)

Note Relative energy multiples 9, 81, 729 , 6561 , 58 869

Acceleration in 1-3g (people), 5g-15g Emergency Response Manned, 100g-10,000g -mass only

So to get to Mars at 1 cSec/hour (FP1) ranges from 250 closest to about 1500 hours when in opposition (including sun bypass). The time is about 11 to 66 days.

FP3 would reduce times to 4 - 22 days. That is probably the safe limit for the inner system. FP3 at 1g deceleration it takes 10 cSecs (3 million kilometers) to slow to a safe approach velocity.

FP9 and FP27 - are suitable for Asteroid, Jupiter, Saturn.

10mC 33mC outer exploration speeds, and 100mC for Generation class or Hibernation equipped interstellar.


Any solution requires availability of cheap and readily available energy to be used for propulsion. It works best when the energy supply is external, so you don't have to drag the fuel or reactors or solar panels with.

Let's first build gigantic solar array as close to Sun as feasible, perhaps under Mercury's orbit. The energy will be then beamed in very tight microwave beams across the solar system to anyone who requests it. If the beam divergence could not be solved better, then also build retransmission stations. This requires very precise aiming of the beams, as everything is in motion, and precise tracking of all debris in the solar system (which should be done anyway to ensure safety of ships).

With this in place, the passenger shuttles have very simple and lightweight construction: an electric thruster powered by microwave antenna. It would request energy from the system, then blast off in desired direction after receiving the beam, carefully coordinating its path with the power system so that energy supply beam is always on spot.

Delivering power this way from sun all the way to outer solar system to Jupiter and beyond is possibly impractical due to distances and communication latencies involved. However, in the orbit of Jupiter and Saturn there could be nuclear-powered power supplies that would provide the same beaming service. So the shuttle will be accelerated from inner solar system as far as practical in Jupiter/Saturn's direction, then it will coast. Near the destination it will be intercepted and decelerated using beam energy provided from Jupiter or Saturn stations.


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