Tag Archives: EM propulsion

Using Inverse Rail Guns for assisted space launch

Following on from the last article on skyline hypersonic travel, Carbon Devices will shortly announce a future space launch system with variants covering a wide range of capabilities. These will range from ultra-cheap launch of lightweight satellites into sub-orbital trajectories up to full orbital launch of large satellites or spacecraft with human crews. The system relies on novel carbon materials only in development today, but that will be routinely available in a decade or two. Once they are, this new system will offer space launches orders of magnitude cheaper and safer than current space launch systems and avoid the environmentally damaging emissions or water vapour in the high atmosphere associated with primitive rocket technology. With far lower launch costs and improved safety, the space industry will flourish.

In the next few posts, several inventions will be disclosed that may be used in our launch systems and weapons. In this article, we explain the first of those, a new technique for driving a tape through a motor at high speed using only electricity. It is related to the rail gun, currently the highest powered artillery system in action, with today’s guns able to launch 10kg metal slugs at over 2km/s, with energy of around 32MJ. By comparison, the Carbon Devices inverse rail gun will be able to launch 60kg slugs at over 50km/s and that is just the scaled down land-based variant. If you believe as we do that the route to peace is to talk softly but carry a big stick, then this is one of our big sticks. We need to learn to talk more softly to each other, because future battlefields will use weapons hundreds or thousands of times more powerful than today’s. The gulf between conventional and nuclear weapons will fully close by mid-century. This pic is a crude example of a fairly modest space weapon with a short tape. Even this would have 3TJ energy, about 100,000 times more than today’s rail gun and 0.75 kilotons of TNT equivalent. This version would only work in space but that’s where some battles in future wars will be fought. Anyway, enough about weapons, the best use of this tech is to launch spacecraft, both from space and into space.

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The Carbon Devices inverse rail gun uses exactly the same linear motor principle of the conventional rail gun, with current passing along and between the rails via the ‘slug’, but effectively inverts the idea of a slug by using a continuous tape of engineered graphene, through which high current is passed to generate the pulling magnetic field. As each short segment of the tape is pulled forwards, the rest follows behind, and although the short segment being driven suffers high heating levels due to the high currents involved, new segments of tape are continuously pulled into play as heated segments exit. The tape as a whole will survive because only a small segment at any time is being subjected to high current, but of course the entire length of tape following is accelerated, along with the attached payload. The length of the tape and thus the exit speed achievable is only limited by practicality. The tape drive has a wide range of applications from ultra-high powered rail guns with exit energy hundreds of times that of current weapons, right up to a super-fast multi-motor space system that will one day deliver crew members or supplies such as water or materials to Mars bases in just 5 days, with a launch speed of 800km/s. Even that speed is limited mainly by the slow acceleration forces that humans can cope with. Another variant that fires inert payloads is an asteroid defense system and the achievable speeds for that could be far higher. This pic gives a crude idea of the concept, using many low powered ‘rail gun’ motors.

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This powerful propulsion system is scalable  (the system shown uses multiple motors and a very long string), and exit speed is only limited by the practical size and cost of the system. 800km/s is a sensible compromise size for routine space missions, since the size of the system scales with the square of the exit speed needed. Because of that, it can not be any practical use for interstellar missions, where technology such as light sails offer much greater suitability. Even if used in conjunction with a light sail, it could only knock a few weeks off a 100 year flight time. (For those of you with weapons interests, the Mars commute system carries about 360TJ, or 85 kilotons of TNT energy equivalent, well into nuclear territory. I haven’t bothered to calculate how powerful it would be if militarized instead of running at just 5g acceleration. ‘Very’ is a good enough guess.

In space, the tape will naturally start very cold which will be an advantage, and of course the tape can also be laid out in a long line to avoid assorted mechanical issues. All of that makes high speeds reasonably feasible. On the Earth however, it is very hard to arrange for a tape to be laid out in a long line, and spooling and indeed unspooling speeds present a huge mechanical engineering problem, not least of which is that a spool spinning at high rpm is dangerous in itself. Aerodynamic heating is also a huge issue for ultra-high speeds. Therefore, land-based variants need to be greatly scaled down. A number of people over the years have suggested using rail guns to launch things into space, and heating is always a severely limiting problem. The novel system we will announce isn’t a rail gun launch and neatly circumvents this problem.

Having said that, rail gun space launch is not impossible and we have devised two novel launch variants using the rail gun linear motor principle. Carbon Devices’ graphene foam invention in 2013 outlined a solid foam that could be made lighter than helium, that would be ideal for supporting loads in the high atmosphere. MIT have more recently produced a lightweight 3d-printed matrix that could be used to print larger shells containing only vacuum (and they could even be printed at high altitude to avoid collapse in the high pressure lower atmosphere).

Slide7If circuits for a linear motor are made from graphene and on a graphene substrate, all supported by such floating platforms, then a long, vertical, linear motor could be made and supported in the air that could accelerate a sled with a disposable heat shield front end, holding a rocket. Depending on acceleration tolerable, fairly high speeds can be obtained, and although not fast enough for orbit, would greatly reduce the size of rocket needed to achieve orbit.

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The first variant is entirely vertical. The rocket and crew or satellite payload would be attached to a sled, and the reusable sled would accelerate up the linear motor. With a few system engineering tweaks, it is feasible to make the path at least 35km high, with an exit speed of around 4000mph (1750m/s) for the 5g acceleration launch that is acceptable for astronauts. Although 4000mph is fast, it is no more than a useful starter push for a rocket that needs to reach the 17,500mph of the space station. Additionally, vertical speed is a useful boost, but no use in itself for orbit – a rocket travelling vertically would simply fall back to Earth eventually unless it gets high horizontal speed.

However, our second variant curves the track into a horizontal path at high altitude, again supported along its entire length by floating platforms made from carbon foam.

Slide39Assuming a 150km track, most of which is 35km high, we would have an expensive but reusable launch system that could accelerate humans up to 8600mph (3800m/s), about half way to orbital speed, and that would all be horizontal speed. It is easily possible to engineer the final sections of track to be higher in the atmosphere, and a slight incline would get our rocket out of atmosphere quickly to minimise heating issues, but the main benefit is that most of the high speed happens in the cold and thin high atmosphere. Such as system is feasible and would greatly reduce launch costs for human spacecraft. For a non-human payload, a 150km track can give full orbital speed for payloads that can tolerate in excess of 20g acceleration. Very many fall in that category, so this system could one day be used to achieve a fuel-free orbital launch.

As mentioned, these are only early system designs and forthcoming articles will outline more advanced Carbon Devices systems with greater potential to accelerate space development.

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