Monthly Archives: June 2019

Cable-based space launch system

A rail gun is a simple electromagnetic motor that very rapidly accelerates a metal slug by using it as part of an electrical circuit. A strong magnetic field arises as the current passes through the slug, propelling it forwards.

EM launch system

An ‘inverse rail gun’ uses the same principle, but rather than a short slug, the force acts on a small section of a long cable, which continues to pass through the system. As that section passes through, another takes its place, passing on the force and acceleration to the remainder of the cable. That also means that each small section only has a short and tolerable time of extreme heating resulting from high current.

This can be used either to accelerate a cable, optionally with a payload on the end, or via Newtonian reaction, to drag a motor along a cable, the motor acting as a sled, accelerating all along the cable. If the cable is very long, high speeds could result in the vacuum of space. Since the motor is little more than a pair of conductive plates, it can easily be built into a simple spacecraft.

A suitable spacecraft could thus use a long length of this cable to accelerate to high speed for a long distance trip. Graphene being an excellent conductor as well as super-strong, it should be able to carry the high electric currents needed in the motor, and solar panels/capacitors along the way could provide it.

With such a simple structure, made from advanced materials, and with only linear electromagnetic forces involved, extreme speeds could be achieved.

A system could be made for trips to Mars for example. 10,000 tons of sufficiently strong graphene cable to accelerate a 2 ton craft at 5g could stretch 6.7M km through space, and at 5g acceleration (just about tolerable for trained astronauts), would get them to 800km/s at launch, in 4.6 hours. That’s fast enough to get to Mars in 5-12 days, depending where it is, plus a day each end to accelerate and decelerate, 7-14 days total.

10,000 tons is a lot of graphene by today’s standards, but we routinely use 10,000 tons of steel in shipbuilding, and future technology may well be capable of producing bulk carbon materials at acceptable cost (and there would be a healthy budget for a reusable Mars launch system). It’s less than a space elevator.

6.7M km is a huge distance, but space is pretty empty, and even with gravitation forces distorting the cable, the launch phase can be designed to straighten it. A shorter length of cable on the opposite side of an anchor (attached to a Moon tower, or a large mass at a Lagrange point) would be used to accelerate the spacecraft towards the launch end of the cable, at relatively low speed, say 100km/s, a 20 hour journey, and the deceleration phase of that trip applies significant force to the cable, helping to straighten and tension it for the launch immediately following. The craft would then accelerate along the cable, travel to Mars at high speed, and there would need to be an intercept system there to slow it. That could be a mirror of the launch system, or use alternative intercept equipment such as a folded graphene catcher (another blog).

Power requirements would peak at the very last moments, at a very high 80GW. Then again, this is not something we could build next year, so it should be considered in the context of a mature and still fast-developing space industry, and 800km/s is pretty fast, 0.27% of light speed, and that would make it perfect for asteroid defense systems too, so it has other ways to help cost in. Slower systems would have lower power requirements or longer cable could be used.

Some tricky maths is involved at every stage of the logistics, but no more than any other complex space trip. Overall, this would be a system that would be very long but relatively low in mass and well within scales of other human engineering.

So, I think it would be hard, but not too hard, and a system that could get people to Mars in literally a week or two would presumably be much favored over one that takes several months, albeit it comes with some serious physical stress at each end. So of course it needs work and I’ve only hinted superficially at solutions to some of the issues, but I think it offers potential.

On the down-side, the spaceship would have kinetic energy of 640TJ, comparable to a small nuke, and that was mainly limited by the 5g acceleration astronauts can cope with. Scaling up acceleration to 1000s of gs military levels could make weapons comparable to our largest nukes.

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After Brexit: EU RIP

My wife is Swiss so I tend to notice Swiss news. The EU and Switzerland have been fighting lately, with this update today, the Swiss banning EU stock exchanges in retaliation for the EU locking Switzerland out of its exchanges: https://www.telegraph.co.uk/business/2019/06/24/swiss-ban-eu-stock-exchanges-row-brussels-escalates/

The Swiss are a small nation compared to the UK, France or Germany, but they seem to do a hell of a lot with few people: banks, CERN, hosting the Global Economic Forum and acting as a neutral base for very many international negotiations, as well as being famous for chocolate, coffee, coffee machines, cheese, fondues, steel, numerous high tech industries, as well as their winter sports prowess, scenery….. And now they’re falling out with the EU, for the severalth time. So I wonder, when we leave the EU, and are making strategic alliances with other nations of compatible cultural values (strong work ethic, freedom, tolerance of others, democracy) with whom we can do great things, Switzerland ought to be pretty high on our natural allies list. Norway also has a not-quite-perfect arrangement with the EU, so they too would make a good nation to invite to a new economic alliance. So, the UK, Norway and Switzerland potentially forming a new Common Market, you know, just like that thing that formed ages ago that everyone wanted to be in, before the idiots-in-residence decided to force us all into a United States of Europe and eradicate democracy.

Holland, Denmark, Sweden, Ireland, probably Finland but I don’t know Finland well (Belgium, who cares?) would also be very tempted to say goodbye to the EU and join us. That would leave Germany to pay for everyone else, and various surveys have suggested most Germans would be happy to leave the EU even before that, which is why they don’t get asked. The French are the same, their leaders boasting about how clever they are not offering a referendum because they’d get the wrong answer, being even more exity than the Brits. But the pressures would increase too far if these other countries were leaving and joining a better club. So given a few years of the EU heading down hill and the grass on the other side getting greener and greener, the EU might not be able to keep any of its Northern countries.

The new Eastern countries have mixed approaches to life. Some have a very strong work ethic, encouraging hard work and risk-taking to get a better life, and they might well form their own block, or join the new one. The others are more similar to Spain, Portugal, Italy and Greece, and would likely join with them and possibly Turkey too, to make a less prosperous Southern Union. In fact, France might find it hard to decide which of the two to join, the Northern or Southern Unions.

Every time I see another news headline about internal EU problems, relative economic decline, shutting of borders and a more aggressive attitude by un-elected bureaucrats toward forcing a United States of Europe, this end game looks more and more likely. It’s what I predicted before the referendum, and I have even more reason to think that way now.

The EU will die, maybe over 10, 15, 20 years tops. By 2050 we will have some sort of Northern Union and Southern Union, perhaps an Eastern Union too, or they might just divide between the other two. Brexit is just the first domino in the line.

Last one out, turn off the lights.

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