# A feasible and efficient method of fast global travel?

What would be an efficient method of global travel that can take you from, let's say, London to Hong Kong in about an hour? It would preferably be made quickly, but money is no object. I don't want something that would take 100 years to build.

• Comments are not for extended discussion; this conversation has been moved to chat. – Monty Wild Nov 28 '19 at 12:34

Your only real option here is an Evacuated Tube transport system.

Atmospheric drag is the biggest hurdle to traveling the distance you want (9,617 km) in an hour.

So simply connect the two cities with a large diameter tube and pump all the atmosphere out of it. Then magnetically levitate and accelerate cars inside the tube. With no friction and no drag your options for accelerating the cars are only limited by your power supply and materials.

This is probably achievable with today's tech, but it would be stupendously expensive and a project of major international cooperation.

Edit:

Rockets can accomplish this, but scaling it for commercial transport will be a nightmare. Factoring in fuel costs, maintenance for material fatigue from constant atmospheric re-entry, and the insurance premiums for launching passengers strapped into millions of pounds of fuel will be astronomical.

A quick calculation for a constant acceleration Evacuated Tube transit system shows that a comfortable ~3m/s^2 acceleration is required to accomplish this requirement. The cart would accelerate for half an hour, then decelerate for the last half at that rate. Energy can actually be recovered during the "slowing down" phase.

You could play with the timing by adjusting the passenger's acceleration tolerance, say spend X minutes at 1g of acceleration to get up to speed.

• Note that 1G, perpendicular to Earth's gravity, is fairly tame, amounting to a net of only √2 ≈ 1.4G. Just don't forget to rotate your seats when you reverse acceleration. – Matthew Nov 12 '19 at 19:32
• I wonder how much of an issue continental drift would pose on such a project... – Trotski94 Nov 13 '19 at 13:46
• @Trotski94 Less of an issue than thermal expansion and contraction do for traditional infrastructure. Having a structure that expands slightly over time is a well-studied problem. It would be slightly novel in that it doesn't contract, but it's still only expanding a finite amount over the lifetime of the building. – Cadence Nov 13 '19 at 14:14
• @Cadence There are existing bridges that cross fault lines and sea floor expansion lines that handle this -- one in Charleston, SC and one in Japan, that I know of. The Japanese one stretches several inches a year. – Zeiss Ikon Nov 13 '19 at 14:48
• Concerns over drift are real, same with major concerns over the impact of earthquakes or really any geological disturbance. The tube would have to be built on supports capable of dampening any vibrations. You'd also need emergency shutdown systems that can safely decelerate the cars in the event of a tube breach / pressure increase and also safeguard against attacks / sabotage. Those are all logistical issues that can be overcome though. – abestrange Nov 13 '19 at 17:57

Simulacrum.

In London, you enter a virtual reality booth. When you open your eyes you are looking out of the eyes and hearing through the ears of a comely android with approximately your build and facial features, dressed for the season. Wearing your android body, you step out into Hong Kong.

People can know who you are as an android. Your identifiers come with when you register. You can conduct business. You can see the sights and sounds, though so far not the smells and tastes. If you do crimes as your android self (and are caught), the android will be deactivated and the London police will be waiting for you outside the booth.

• Depending on the purposes OP has in mind, might wonder whether these androids are "fully functional". – R.. GitHub STOP HELPING ICE Nov 13 '19 at 12:36
• The laaag may make things quite awkward, though. Hong Kong is not Sydney, but it will still be felt. This site mentions 218ms in average; don't try anything where reflexes matter. – Matthieu M. Nov 13 '19 at 14:46
• @matthieuM. ~200ms? That's my good raiding ping. – Mindwin Nov 13 '19 at 18:52
• @MatthieuM. The 200ms is from our current internet. The distance is about 10.000km, at light speed that takes only 33ms. Can't really get better than that but 200ms can be improved quite a bit, then add some basic AI in the android and you should be fine. – quarague Nov 14 '19 at 15:25
• @zeissikon I bet the telepresence drone has an A.I. assistant to handle those delays. It would be stupid not to. And it can ride a bike on auto. – Mindwin Nov 14 '19 at 15:30

To cover that distance, you need an average speed of about 2.67km/s. That's pretty brisk... even higher than the sorts of speeds anticipated of a mature vacuum maglev train technology, even if it were possible to build the required infrastructure in the given timescale (which, given the colourful politics of the countries inbetween the endpoints, may be somewhat challenging).

You could do it today, of course... modern commercial rocketry can put you into orbit in ten minutes (albeit with a certain amount of lead time to get everything ready) and from LEO you can circle the globe in 90 minutes. That'll put you half way around the world in 45 minutes, but you'll need to sustain at least a couple of gravities average deceleration on the way down which might not be much fun.

Modern suborbital spaceflight might be capable of the task... an ICBM can strike most places on earth in 30 minutes or so, though the terminal speed would indeed be terminal. Virgin's gradiosely named Galactic only reaches a mere 1.78km/s to speed and so couldn't make it, but possibly the difference could be split. Some form of hypersonic glide vehicle is probably the correct solution, with a rocket booster to get it high enough up.

The problem with all these things is that they're indistinguishable from something like Prompt Global Strike (or as previously mentioned, an ICBM). No-one wants a multi-kilometre-per-second projectile aimed at their city. There's too much scope for terrible collateral damage in the event of an accident, and with deliberate sabotage or repurposing as a missile could cause the deaths of millions. Your need for faster global travel doesn't quite tip the balance, given those downsides.

• Not to mention, the question asks for "efficient" travel, which rockets...aren't, really. – Skyler Nov 13 '19 at 14:53
• @Skyler efficiency is relative. Given the apparent total of zero alternatives which don't require massive global infrastructure projects and political co-operation and goodwill between groups who aren't known for such, the efficiency of rockets starts to look pretty good. – Starfish Prime Nov 13 '19 at 14:55
• All the reasons mentioned against using rockets for city-to-city travel on Earth didn't stop Elon Musk from proposing it though (see theverge.com/2017/9/29/16383048/…) – rob74 Nov 15 '19 at 9:15
• @rob74 proposing is easy. Commercialising prompt global strike is a different thing altogether. – Starfish Prime Nov 15 '19 at 10:33
• On the subject of the final paragraph, there's an even bigger problem than collateral damage if something goes wrong: The fact that it's difficult to distinguish from an ICBM means that it could be mistaken for an ICBM. This mistaken identity could literally result in the launch of actual ICBMs with nuclear warheads. It wouldn't be the first time that this has almost happened. – reirab Nov 15 '19 at 20:28

You want a hole through earth. That would allow you to go to any destination in 42 minutes, without even spending energy on the traveling itself.

Boring a hole through the earth is difficult, but if you want to go between London and Hong Kong in an hour, that is the only viable solution. It is not currently within the realm of the possible, but by some definition, it is feasible, and if money is not an object, it could be done in less than 100 years. It would, without compare, be the largest infrastructural project ever taken on by mankind.

Travel between destinations not directly opposed on the globe would take hypocycloid paths, and the tunnels should probably be evacuated, in order to eliminate drag.

Read more on wikipedia's article about Gravity trains or on HowStuffWorks, about holes through earth.

• This is exactly what came to mind for me too! I wonder why this doesn't have more upvotes? I suppose it's because it's relatively short and relies on the external link. – Patrick L Nov 14 '19 at 8:19
• The scientific name of this technique is called Gravity Train. Also, this is dangerously close to a "link only answer". – Aron Nov 14 '19 at 9:40
• This was my first thought too, but might fail the feasibility aspect. The deepest hole ever dug is only 7.5 miles deep, and that took 20 years to complete. We have no means of digging deep enough, or fast enough. Current tunnel boring machines can only do ~50 feet per day, so you wouldn't even have a tunnel 700 miles long after digging from both ends for 100 years, which barely gets you from New York to Chicago. – Nuclear Wang Nov 14 '19 at 15:16
• Unfortunately this will remain outside the realm of physical possibility, probably forever. I highly doubt any material could be developed to resist the temperature and pressures anywhere near Earth's core. Fun thought though – abestrange Nov 14 '19 at 17:49
• I agree abestrange that no gravity train tunnel will ever be able to resist the temperatures and pressures of the insides of the planet Earth. However, that in no way rules out gravity trains being built somewhere. The moon is non-volcanic for example and pressures are less painful on low-mass bodies. – Dast Nov 15 '19 at 13:21

In a word, Skylon.

Skylon is a reusable space plane design propelled by a SABRE air-breathing rocket engine. Test flights are expected within the next decade. Given the pace of development, British and Australian governments have started to plan a 'space bridge' between their countries. Current estimates claim a flight from London to Sydney is possible in four hours with Skylon, and London to New York in just one hour.

The main technical challenge behind the project is the need for an engine which can reduce air temperature from 1000 to -140 degrees in a fraction of a second. This allows oxygen to be captured from the atmosphere, so it does not need to be stored as liquid fuel.

Here is a technical QA with the project's staff.

• "The main technical challenge behind the project is the need for an engine which can reduce air temperature from 1000 to -140 degrees in a fraction of a second." LOL. These kinds of "plans" always require a then a miracle occurs technology. – RonJohn Nov 13 '19 at 20:22
• Yeah, that main problem is a HUGE one. Even if we do find a way to do that the odds are that it will require immense amounts of energy and/or produce stupid amounts of wate heat. Picture me not holding my breath :) – Corey Nov 15 '19 at 2:08
• @Corey The solution is already half made, I'm assuming you read none of the links? – inappropriateCode Nov 15 '19 at 9:36
• It's not a miracle @RonJon it's decades of hard engineering and materials science on a shoe string budget that's finally started to pay off. The SABRE pre-cooler has already demonstrated the required performance for Mach 5, and is currently our most likely technology for developing a fully reusable single-state-to-orbit space plane. Wikipedia has a pretty good summary of the history stretching back to the 60's: en.wikipedia.org/wiki/SABRE_(rocket_engine) with the exception of the news on the most recent tests: reactionengines.co.uk/news – Mark Booth Nov 18 '19 at 18:27

Sedated, stasis transport via ICBM. Sedated to avoid the pain of high accelereation and deacceleration, in addition to the em-effects of the plasma around the capsule. Stasis, as in prepared against damage due to high g forces. May include filling the lungs with breathable fluids to prevent collaps and other protection mechanisms like metabolic cooling. https://en.wikipedia.org/wiki/High-G_training The longest part of the journey will be waking up from sedation.

• Being asleep won't save you from dangerous g-forces. Given the magnitude of some of the forces involved in an ICBM's trajectory, normal humans are likely to become unconscious whether they wanted to or not. – Starfish Prime Nov 13 '19 at 11:02
• "Sedated, stasis transport via ICBM" is the kind of answer that makes the site enjoyable to me :) – Renan Nov 13 '19 at 15:00
• @Renan LOL. +1 . – onnoweb Nov 13 '19 at 18:29

There have been proposals for suborbital transports going back so long that the early ones were based on the Saturn booster (the kerosene-fueled first stage of NASA's Moon rocket). Flying at just under orbital speed, anywhere on Earth is less than an hour flight time from anywhere -- five to seven minutes of boost, at most about 45 minutes at zero gee above the atmosphere, and another five to ten minutes of the steep part of reentry and landing (this is based on vertical takeoff and landing, as with the proposed point to point service for SpaceX Starship). Passengers would remain strapped in their seats for the entire flight, and the seats would move to ensure G loads are taken in a reclined position.

With throttlable engines (like the Starship's Raptors), G load on passengers is easily limited to 3 G, perhaps even 2.5 -- this is including the Earth's gravity, not on top of it -- which is a level any passenger in good enough condition to travel ought to be able to handle in a reclined position, and far gentler than the common handling of packages by courier services.

Fuel costs wouldn't be impossible, compared to past and proposed supersonic airliners -- Raptor engines run on what amounts to natural gas and liquid oxygen, distilled from air. The premium on cost is to be anywhere, same day -- or even last night, if you're flying from the Americas to eastern Asia.

• Described as the 'semi-ballistic' in R.A. Heinlein's Friday. amazon.com/dp/B077H1HVK9 – K7AAY Nov 14 '19 at 19:46
• This is actual ballistic. The "semi-ballistic", as I read it, was a horizontal takeoff and landing spaceplane that went suborbital for a significant fraction of the journey. It was "ballistic" while above the atmosphere, but landed and took off from a runway like an airliner of the 20th or 21st century. – Zeiss Ikon Nov 14 '19 at 19:57
• Big differences are true ballistic are faster, cheaper to build, and cheaper to operate, but perhaps less comfortable for passengers used to airliners to look at. – Zeiss Ikon Nov 14 '19 at 19:59
• The passage from Friday describing the trip made it clear the ship was HTOL (Horizontal Takeoff and Landing). – K7AAY Nov 14 '19 at 20:03
• I thought I recalled it that way, but I read Friday when it first came out, and that's been 30-some years. – Zeiss Ikon Nov 14 '19 at 20:24

SpaceX is talking about London to Hong Kong in 34 minutes via their Starship rocket, for less than the price of first-class airfare today. But you have to add the time of the boat rides out to the launch ports. (Taking a rocket directly from Downtown London to Downtown Hong Kong is likely to run into regulatory problems.)

• I love it when ICBM travel and regulatory problems come up in the same thread... – Bex Nov 15 '19 at 16:42

Nasa developed the X-43A, which can go around Mach 9.6(7,000 mph). You could build a fleet of those, but that is not cost effective. You could also equip jets with RAMJETS or SCRAMJETS to get your goal.

In my universes, there is a type of special crystal(not the point) that we use for almost everything. We achieve speeds of nearly M18 with special crystal reactor cores. The crystals are incredibly reactive, and we just compress them to get the speeds we desire.

• The X-43A was unmanned, had nowhere near the range to get from London to Hong Kong, and ended all its flights by crashing into the ocean because it had no other means of slowing to a stop. So it's not even close to being a feasible option. I'm not sure handwavium crystals are what OP is looking for either. – F1Krazy Nov 12 '19 at 19:19
• @F1Krazy Then again, OP did say he didn't want it to take 100 years to build. You don't think they might be able to get one functioning in 20 or 30 years if money was no object? – DKNguyen Nov 12 '19 at 21:51

With current technology, suborbital flight is feasible, while a hole through earth isn't.

Asking for efficiency, I would bet on some sort of Hohmann transfer (horizontal launch), plus using a cannon with external propulsion rather than the previously mentioned ICBM.

For approx. 5km/s, at 10g (100m/s2), that would require 50sec of acceleration on a cannon (rail?) length of 125km. For the 10g acceleration, you'd probably want to pack the passengers in some sort of water tank. The 125km cannon will probably be static, hence only shooting passengers from London to HongKong, and you will need some sort of reentry vehicle like the Space Shuttle, to burn away all that kinetic energy again.

Conclusion: Scuba divers in a water tank inside a Space Shuttle that's shot out of a 125km long cannon. Feasible? I don't know. The fins for the scuba divers are optional.

• Hohmann transfer is entirely the wrong trajectory -- it's used for changing from one orbit to another, not for launching from the surface (that's a gravity turn). – Mark Nov 15 '19 at 3:13
• You are correct. The Hohmann ellipse would have its perigee at the launch point, so that wouldn't work... It would probably require the use aerodynamic "lift" to get the craft down at Hong Kong – Carl Berger Nov 16 '19 at 10:15