16 March 2012

Outer Space to Earth: Hit Me With Your Best Shot!

Dr George Maise invented the Startram orbital launch system along with Dr James Powell, who is one of the inventors of superconducting maglev - for which he won the 2002 Franklin Medal in engineering. Startram is in essence a superconducting maglev launch system. _Gizmag
When we think about space elevators and other high altitute electromagnetic space launch methods, we are typically concerned about creating materials that are strong enough to support the weight of the massive launch apparatus. The Startram approach to cheap, high frequency space launch turns this thinking on its head, by utilising a form of electromagnetic levitation which requires the launch apparatus to be tethered to prevent it from whipping out into space.
All Images Courtesy of Gizmag

It's easy to levitate objects electromagnetically. If you push enough current through two conductors in opposite directions, the conductors will be subject to a force pushing them apart. The more current the greater the force. With the advent of superconducting cables being developed for superconducting power grids, it is now possible to construct cables which can carry hundreds of megamps of current. These amperages are sufficient to supply a levitating force of 4 tons per meter of startram guideway, even when the conductors are separated by 20km.

...One of the challenges of the Space Elevator concept is to engineer tethers that have breaking lengths (i.e. the length of tether can attain before it breaks under its own weight) of thousands of kilometers. Startram tethers, in contrast, needs tethers with breaking lengths of only tens of kilometers, which is well within the specifications of modern fibers. _Startram Technology
The Startram launch tubes are evacuated in order to reduce friction losses from air resistance during high velocity launch. According to the developers, the system can be built using existing materials and technologies.
The scope of the project is challenging. A launch system design for routine passenger flight into LEO should have rather low acceleration - perhaps about 3 g's maximum, which then requires 5 minutes of acceleration to reach LEO transfer velocities. In that period, the spacecraft will have traveled 1,000 miles (1,609 km). The maglev track must be 1,000 miles in length - similar in size to maglev train tracks being considered for cross-country transportation.

Like a train, the Startram track can follow the surface of the Earth for most of this length. Side forces associated with the curvature of the surface can be accommodated by the design, but not the drag and sonic shock waves of a craft traveling at hypersonic velocity at sea level - the spacecraft and launching track would be torn to shreds.

To avoid this, the Startram track must be contained inside a vacuum tube with vents to allow air compressed in front of the spacecraft to escape the tube. A vacuum equivalent to atmospheric conditions at an altitude of 75 km (about 0.01 Torr) should suffice for the efficient operation of the Startram launch system. Rapid pumping to achieve this pressure will be provided by a magnetohydrodynamic vacuum pump.

If the entire Startram tube is at sea level, on exiting the tube the spacecraft will suddenly be subjected to several hundred g's due to atmospheric drag - rather like hitting a brick wall. To reduce this effect to a tolerable acceleration, the end of the Startram vacuum tube must be elevated to an altitude of about 20 km (12 miles). At this height, the initial deceleration from atmospheric drag will be less than 3 g's, and will rapidly decrease as the spacecraft reaches higher altitudes.... how do we hold up the exit end of the Startram vacuum tube? Well, the tube already contains superconducting cable and rings. Powell and Maise realized that the tube could be magnetically levitated to this altitude. If we arrange that there is a superconducting cable on the ground carrying 200 million amperes, and a superconducting cable in the launch tube carrying 20 million amperes, at an altitude of 20 km there will be a levitating force of about 4 tons per meter of cable length - more than enough to levitate the launch tube. _Gizmag
Sandia National Laboratories has carried out a '"murder-squad" investigation of the Startram concept, whose purpose is to find any flaw in a proposed project. They gave Startram a clean bill of health. Estimates suggest that building a passenger-capable Startram would require 20 years and a construction budget (ignoring inflation and overoptimism) of about $60 billion.

Why take on such an enormous project? Simple - $50 per kilogram amortized launch costs. The total worldwide cost of developing and using rocket-based space travel is more than $500 billion. The Space Shuttle program cost about $170 billion. The International Space Station has cost about $150 billion to date. _Gizmag
If access to space can be made safe and routine, humans will suddenly find ways to make space travel and habitation safe, sustainable, and profitable. The challenge of surviving and prospering in space is the type of challenge which malaise-laden modern humans need, to revive a much needed sense of transcendence and open-ended overcoming.

Startram website

Why it is so important for people of the western world to find their way into space

More: Brian Wang is also beginning to look at this exciting space launch technology

First published on Al Fin Potpourri

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