Thursday, September 17, 2009
military electric rail gun - orbit would need 412 m
"Probably the most successful system was built by the UK's Defence Research Agency at Dundrennan Range in Kirkcudbright, Scotland. This system has now been operational for over
10 years at an associated flight range". The innovation is using a fly wheel to store the energy, so that a large amount can be released very quickly.
Some excerpts on the device (from page 6 on since earlier stuff explains developments to date):
The engine accelerates the flywheel to maximum safe rotation speed. At launch time, the fly wheel ...produces a high-amperage current. The gas gun takes a shot and accelerates the space apparatus up to the speed of 1500 – 2000 m/s. The apparatus leaves the gun and gains further motion on the rails where its body turns on the heavy electric current from the electric generator. The magnetic force of the electric rails accelerates the space apparatus up to speeds of 8 km/s. (or more) (Low Earth orbit requires 6.5 to 8.2 km/s)
Cost of launch one kg of payload [all calculations given in the original but omitted here] Conventional turbo engine is used for moving the fly-wheel ...frequency of launches is t = 30 min.... Let us assume the cost of magnetic launcher is 50 millions of dollars, lifetime of installation is 10 years and maintenance is $2 millions of dollars per year. The launcher works the 350 days and launches 100 kg payload every 30 min (This means about 5000kg/day and 1750 tons/year).
total cost is $6/kg.
The research shows the magnetic launcher can be built by the current technology. This
significantly (by a thousand times) decreases the cost of space launches. Unfortunately, if we want to use the short rail way (412 m), any launcher request a big acceleration about 7,500 gravities and may be used only for unmanned, hardened payload. If we want design the manned launcher the rail way must be 1100 km for acceleration a = 3g (untrained passengers) and about 500 km (a = 6g) for
Our design is not optimal. For example, the computation shows, if we increase our rail track only by 15 m, we do not need gas gun initial acceleration. That significantly decreases the cost of installation and simplifies its construction.
Personally I would be quite happy to extend it to 427 metres or indeed if we quadruple the length (& construction cost)to 2000 m we halve the acceleration to 3,750 g. Not something any of us will use but that would increase the range of, remarkably carefully packaged, items we could put in orbit. That means we are looking for a mountain at least 2000 m (6,500 ft). Though the speed advantage from launching near the equator may be less important there will still be a benefit to keeping launched objects in similar, equatorial, orbits so that they can easily be collected by the crew, or robot, in orbit.
Incidentally it also solves the longstanding & rather silly debate about manned spaceflight versus robotics. If we can put up 5 tons a day of equipment we are very quickly going to have enough to build an awful lot of structure, including a lot of robotic stuff, up there but it will take a number of real human beings to open the boxes, take out the packaging & assemble the contents. With all the equipment sent from Earth they will be able to do dozens, possibly hundreds, of times more useful work than is currently possible with a couple of shuttles a year.
What we are seeing is that there are a large number of ways to get to Earth orbit at costs far lower than we have now. Since they all have slightly different capabilities (mainly that conventional shuttles/rockets can put people there & this & Orion, while not manrateable, can ship large amounts of structure cheap - $6/kg would mean about $1.20 for a paperback book).