March 09, 2012

StarTram More Technical Details

This is a follow up on the interview by Sander Olson for Nextbigfuture of the Startram space launch concept

Startram is a mass driver, which means it requires neither rockets nor propellant to launch payload into space. Mass drivers are not a new concept. Early mass drivers were envisioned in fiction in the late nineteenth century, and have been a staple of speculative fiction ever since. Various engineering concepts of the mass driver have been described over the years, but no significant progress towards building a mass driver has been made due to large technical hurdles.

We believe that Startram is the first mass driver design that combines available technology with intelligent implementation of basic physical principles to yield a design that is actually commercially feasible.

There are two proposed configurations of Startram, Generation-1 and Generation-2. Gen-1 Startram is a cargo-only version which does not require levitated tubes (but instead is built up the flank of a tall mountain) and could be built within ten years at a cost of $20 Billion. Gen-2 Startram is a people-capable version which does require levitated tubes and could be built within twenty years at a cost of $60 Billion.

The key technologies enabling Startram are as follows.

1. Maglev for Acceleration of Launch Vehicles

* If maglev is placed in evacuated tubes with very low air pressures, it is possible to run maglev at 1000s of km/h.

2. Magnetically Suspended Superconducting Cables

* 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

3. Magneto Hydrodynamic (MHD) Pumps

* MHD applications such as pumps, generators and thrusters have been used for decades. The Startram system uses a "MHD Window" which allows one end of the launch tube to be open the atmosphere, thus permitting launch of the vehicle. Normally, atmospheric gases would immediately fill up the tube and the launch vehicle would be subject to extreme heating and stresses associated with traveling 8km/sec in air. However, the MHD window allows ionized gasses to be continually expelled from the tube, thus maintaining a near-vacuum in the tube at all times.

4. High-strength Structural Tethers

Startram tethers, in contrast, needs tethers with breaking lengths of only tens of kilometers, which is well within the specifications of modern fibers.

Startram FAQ

The Gen-1 StarTram cargo launch system does not use a levitated launch
tube. Instead, the acceleration tunnel exits directly to the atmosphere from a
high altitude surface point, e.g., on the order of 15,000 to 20,000 feet, on a
mountain or mountainous terrain.

The Gen-2 StarTram passenger/cargo launch system uses a magnetically
levitated launch tube, to keep deceleration forces on the spacecraft when it
enters the atmosphere low enough (e.g., ~2 g) so that passengers can
tolerate them. With the Gen-1 cargo system, atmospheric deceleration is in
the range of 10 to 20 g, too high for passengers.

It is possible to magnetically levitate the launch tube to an altitude of
70,000 feet, with enough superconducting current. The magnetic interaction
between a cable current of 100 Megamps (1 Megamp = 1 million Amps) on
the ground and a cable current of 40 Megamps at 70,000 feet will produce a
levitation force of 4 tons per meter of cable length. Superconducting cables
can already carry a million amps in a square inch of cross section with zero
power loss. The real trick is not levitating the launch tube, but getting the cost
of the superconducting cables down to an acceptable level. This appears
achievable with the large scale production of superconductors for StarTram.

What is the main challenge to building StarTram?

A: For the Gen-1 StarTram system, the most difficult challenge is the storage
and rapid delivery of large amounts of electrical energy used to accelerate the
StarTram cargo craft to orbital speed. Peak power delivery rates reach a
maximum of ~100 gigawatts. While the delivery time is only a few seconds,
handling such power levels in a cost effective way is challenging, requiring
sophisticated, high current/high voltage electronic switching.

For the Gen-2 StarTram system, the most difficult challenge is the erection
of the levitated launch tube. There are two options: The first is to construct
the launch tube on the surface, together with its superconducting cables and
restraining tethers, and then slowly energize the cable, levitating it over a
period of days. The second option is to erect the cable and tether system,
and then lift the launch tube into place using additional lifting tethers. At this
point, it is not clear which is the best approach.

How much would a trip into orbit cost for a passenger? How risky would it be?

A: Present passengers to the ISS (International Space Station) have to pay 20
million dollars for the trip. The cost for a Gen-2 StarTram passenger trip will
be on the order of $5,000. Present crash rates for commercial airlines are on
the order of 1 per several million takeoffs and landings. StarTram accident
rates should be comparably low.

There is a 16 page paper - Maglev Launch: Ultra Low Cost Ultra/High Volume Access to Space for Cargo and Humans

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