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May 29, 2011

Startram launch system


StarTram is a proposal for a maglev space launch system. The initial Generation 1 facility would be cargo only, launching from a mountain peak at 3 km to 7 km altitude with an evacuated tube staying at local surface level, raising about 150,000 tons to orbit annually. More advanced technology would be required for the Generation 2 system for passengers, with a longer track instead gradually curving up at its end to the thinner air at 22 km altitude, supported by magnetic levitation, reducing g-forces when each capsule transitions from the vacuum tube to the atmosphere. A SPESIF 2010 presentation stated that Gen-1 could be completed by the year 2020+ if funding began presently, Gen-2 by 2030+.





Generation 1 System

T
he Gen-1 system proposes to accelerate unmanned craft at 30 g through a 130 km length tunnel of 3 meters diameter, excavated of air with a MHD pump and plasma window preventing vacuum loss when the exit's mechanical shutter is briefly open. In the reference design, the exit is on the surface of a mountain peak of 6000 meters altitude, where 8.78 km/s launch velocity at a 10 degree angle takes cargo capsules to low earth orbit when combined with a small rocket burn providing 0.63 km/s for orbit circularization. With a bonus from Earth's rotation if firing east, the extra speed, well beyond nominal orbital velocity, compensates for losses during ascent including 0.8 km/s from atmospheric drag.

A 40-ton cargo craft, 2 meters diameter and 13 meters length, would experience briefly the effects of atmospheric passage. With an effective drag coefficient of 0.09, peak deceleration for the mountain-launched elongated projectile is momentarily 12g but halves within the first 4 seconds and continues to decrease as it quickly passes above the bulk of the remaining atmosphere.

In the first moments after exiting the launch tube, the heating rate with an optimal nose shape is around 30 kW/cm2 at the stagnation point, though much less over most of the nose, but drops below 10 kW/cm2 within a few seconds. Peak intensity is very high, yet comparable magnitude to some prior experience, such as the Galileo atmospheric entry probe to Jupiter where 34.5 kW/cm2 was reached at the stagnation point and was extreme for longer duration or another type of thermal protection system rated for up to 30 kW/cm2. Transpiration water cooling is planned, briefly consuming up to ≈ 100 liters/m2 of water per second. Several percent of the projectile's mass in water is calculated to suffice.

The tunnel tube itself for Gen-1 has no superconductors, no cryogenic cooling requirements, and none of it is at higher elevation than the local ground surface. Except for probable usage of SMES as the electrical power storage method, superconducting magnets are only on the moving spacecraft, inducing current into relatively inexpensive aluminum loops on the acceleration tunnel walls, levitating the craft with 10 centimeters clearance, while meanwhile a second set of aluminum loops on the walls carries an AC current accelerating the craft: a linear synchronous motor.


P
owell predicts a total expense, primarily hardware costs, of $43 per kilogram of payload if with 35 ton payloads being launched 10+ times a day, such an intended goal as opposed to present rocket launch prices of $10,000 to $25,000 per kilogram to LEO. The estimated cost of electrical energy to reach the velocity of low earth orbit is under $1 per kilogram of payload: 6 cents per kilowatt-hour contemporary industrial electricity cost, 8.78 km/s launch kinetic energy of 38.5 MJ per kilogram, and 87.5% of mass payload, accelerated at high efficiency by this linear electric motor.The Gen-2 variant of the StarTram would be for reusable manned capsules in contrast, intended to be low g-force, 2 to 3 g acceleration in the launch tube and an elevated exit at such high altitude (22 km) that peak aerodynamic deceleration becomes about 1g. Though NASA test pilots have handled multiple times those g-forces, the low acceleration is intended to allow eligibility to the broadest spectrum of the general public.

With such relatively slow acceleration, the Gen-2 system requires 1000 km to 1500 km length, two or three times the stretch of the Tokyo-Osaka terrestrial maglev track under construction by Japan Railways. The cost for the non-elevated majority of the tube's length is estimated to be several tens of millions of dollars per kilometer, proportionately a semi-similar expense per unit length to the tunneling portion of the former Superconducting Super Collider project (originally planned to have 72 km of 5-meter-diameter vacuum tunnel excavated for $2 billion) or to some existing maglev train lines where Powell's Maglev 2000 system is claiming major cost-reducing further innovations. An area of Antarctica 3 km above sea level is one siting option, especially as the ice sheet is viewed as relatively easy to tunnel through.

For the elevated end portion, the design considers magnetic levitation to be relatively less expensive than alternatives for elevating a launch tube of a mass driver (tethered balloons, compressive or inflated aerospace-material megastructures).[A 280 megaamp current in ground cables creates a magnetic field of 30 Gauss strength at 22 km above sea level (somewhat less above local terrain depending on site choice), while cables on the elevated final portion of the tube carry 14 megaamps in the opposite direction, generating a repulsive force of 4 tons per meter, keeping the 2 ton/meter structure strongly pressing up on its angled tethers, a tensile structure on grand scale. In the example of niobium-titanium superconductor carrying 2 x 10^5 amps per cm2, the levitated platform has 7 cables, each 23 cm2 of conductor cross-section when including copper stabilizer.

Up to 4 million people could be sent to orbit per decade per Gen-2 facility of $67 billion cost if as estimated.
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