StarTram
Encyclopedia
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 ≈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+.
invented the superconducting maglev concept in the 1960s with a colleague, Gordon Danby
, also at Brookhaven National Laboratory
, which was subsequently developed into modern maglev trains. Later, Powell co-founded StarTram, Inc. with Dr. George Maise, an aerospace engineer who previously was at Brookhaven National Laboratory
from 1974 to 1997 with particular expertise including reentry
heating and hypersonic
vehicle design.
A StarTram design was first published in a 2001 paper and patent, making reference to a 1994 paper on MagLifter. Developed by John C. Mankins, who was manager of Advanced Concept Studies at NASA, the MagLifter concept involved maglev launch assist for a few hundred m/s with a short track, 90% projected efficiency. Noting StarTram is essentially MagLifter taken to a much greater extreme, both MagLifter and StarTram were discussed the following year in a concept study performed by ZHA for NASA's Kennedy Space Center
, also considered together by Maglev 2000 with Powell
and Danby
.
Subsequent design modifies StarTram into a generation 1 version, a generation 2 version, and an alternative generation 1.5 variant.
John Rather, who served as Assistant Director for Space Technology (Program Development) at NASA
, said:
through a 130 km length tunnel, with a plasma window
preventing vacuum loss when the exit's mechanical shutter is briefly open, evacuated of air with a MHD
pump. (The plasma window
is larger than prior constructions, 2.5 MW estimated power consumption itself for 3 meters diameter). 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
.
Powell
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.
, 2 to 3 g
acceleration in the launch tube and an elevated exit at such high altitude (22 km) that peak aerodynamic deceleration becomes ≈ 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 megastructure
s).
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 105 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.
. Required tunnel length would be ≈ 270 km if at ≈ 3 g
. While the ≈ 10-15 g
maximum in optimal transverse orientation tolerated for relevant durations by fit pilots in historical centrifuge tests would make minimum length be ≈ 50 km to 80 km, slower acceleration with a longer tunnel eases passenger requirements and reduces peak power (power conditioning expense).
Though with reduced construction costs, Gen-1.5 would differ from other StarTram variants by requiring 4+ km/s to be provided by other means, like rocket propulsion. However, the non-linear nature of the rocket equation makes the payload fraction be a number of times more than a conventional rocket unassisted by electromagnetic launch, and a vehicle with high available weight margins and safety factors could be far easier to mass-produce cheaply or make reusable with rapid turnaround than current 8 km/s rockets. Dr. Powell remarks that present launch vehicles "have many complex systems that operate near their failure point, with very limited redundancy," with extreme hardware performance relative to weight being a top driver of expense (fuel itself on the order of 1% of current costs to orbit).
Alternatively, Gen-1.5 could be combined with another non-rocket spacelaunch
system, like a Momentum Exchange Tether
similar to the HASTOL concept which was intended to take a 4 km/s vehicle to orbit. Synergy
compared to highly exponential scaling for tethers applies (under limited contemporary material strengths available on the aggregate macroscopic scale), where such a tether may be much more readily doable than one providing full orbital velocity by itself.
For needed electrical energy storage (discharged over 30 seconds with about 50 gigawatt average and about 100 gigawatts peak), SMES cost performance on such unusual scale is anticipated of around a dollar per kilojoule and $20 per kW-peak. Such would be novel in scale but not greatly different planned cost performance than obtained in other smaller pulse power energy storage systems (such as quick-discharge modern supercapacitors dropping from $151/kJ to $2.85/kJ cost between 1998 and 2006 while being predicted to later reach a dollar per kJ, lead acid batteries which can be $10 per kW-peak for a few seconds, or experimental railgun compulsator
power supplies). The study notes pulsed MHD generators may be an alternative.
For MagLifter, General Electric
estimated in 1997-2000 that a set of hydroelectric flywheel pulse power generators could be manufactured for a cost equating to $5.40 per kJ and $27 per kW-peak. For StarTram, the SMES design choice is a better (less expensive) approach than pulse generators according to Powell.
The single largest predicted capital cost
for Gen-1 is the power conditioning, from an initially DC discharge to the AC current wave,
dealing for a few seconds with very high power, up to 100 gigawatts, at a cost estimated to be $100 per kW-peak. Yet, compared to some other potential implementations of a coilgun
launcher with relatively higher requirements for pulse power switching devices (an example being an escape velocity design of 7.8 km length after a 1977 NASA Ames study determined how to survive atmospheric passage from ground launch), which are not always semiconductor-based, the 130-km acceleration tube length of Gen-1 spreads out energy input requirements over a longer acceleration duration. Such makes peak input power handling requirements be not more than about 2 GW per ton of the vehicle. The tradeoff of greater expense for the tunnel itself is incurred, but the tunnel is estimated to be about $4.4 billion including $1500 per cubic meter excavation, a minority of total system cost.
The force between two conducting lines is given by
. Here F is the force, 
the permeability
,
the electric currents, 
the length of the lines and 
their distance. To exert 4000 kg/meter over a distance of 20 km in air (
≈ 1) ground 
≈ 280 x 106A is needed if levitated 
≈ 14 x 106A
. For comparison, in lightning
the maximal current is about 105A, c.f. properties of lightning, though resistive power dissipation involved in a current flowing through a conductor is proportional to the voltage drop, high for a lightning discharge of millions of volts in air but ideally zero for a zero-resistance superconductor.
While the performance of niobium-titanium
superconductor is technically sufficient (a critical current density of 5 x 105 A/cm2 under the relevant magnetic field conditions for the levitated platform, 40% of that in practice after a safety factor), uncertainties on economics include a far more optimistic assumption for Gen-2 of $0.2 per kA-meter of superconductor compared to the $2 per kA-meter assumed for Gen-1 (where Gen-1 doesn't have any of its launch tube levitated but uses superconducting cable for a large SMES
and within the maglev craft launched). NbTi was the design choice under the available economies of scale for cooling, since it presently costs $1 per kA-meter, while high temperature superconductors so far still cost much more for the conductor itself per kA-meter.
If considering a design with an acceleration up to 10 g
(which is higher than the re-entry acceleration of Apollo 16
) then the whole track must be at least 326 km long for a passenger version of the Gen-2 system. Such length allows use of the approximation for an infinite line to calculate the force. The preceding neglects how only the final portion of the track is levitated, but a more complex calculation only changes the result for force per unit length of it by 10-20% (fgl = 0.8 to 0.9 instead of 1).
The researchers themselves do not consider there to be any doubt whether the levitation would work in terms of force exerted (a consequence of Ampère's force law
) but see the primary challenge as the practical engineering complexities of erection of the tube, while a substantial portion of engineering analysis focused on handling bending caused by wind. The active structure
is calculated to bend by a fraction of a meter per kilometer under wind in the very thin air at its high altitude, a slight curvature theoretically handled by guidance loops, with net levitation force beyond structure weight exceeding wind force by a factor of 200+ to keep tethers taut, and with the help of computer-controlled control tethers.
hypersonic test applications, with too short a length of track installed yet for high speed but 3.1-3.4 km/s as a later goal). The Gen-1.5 version of the StarTram for launch of passenger RLVs
at 4 km/s velocity from the surface of a mountain would be significantly higher speed with a far more massive vehicle. However, differences intended to make such doable include accelerating in a lengthy vacuum tunnel (no air or gas drag), no hypervelocity
physical rail contact as rather a form of maglev vactrain
levitating a few centimeters above the track, and 3 orders of magnitude
higher anticipated funding requirements for development and construction.
costs of the Space Shuttle
. If StarTram's projected capital costs (an estimated $19 billion for Gen-1) are accurate, payback would depend on much higher than current launch volumes to efficiently amortize its construction expense.
The current world launch market is about 200 tons of satellites launched per year. Each 100 tons sent to orbit could have lift expense approach $4 million to the degree that the $43 per kilogram cost goal for Gen-1 full operation was approached, if not counting other expenses like payload fairing
integration and interorbital transfer requirements when different inclinations were involved. If launching more than 10,000 tons a month, the anticipated amortized ground-facility component of total Gen-1 cost is stated by Powell's
team to be as low as $15 per kilogram sent up, though the same assumptions for capital cost would make such $4500 per kilogram if launching a 35 ton payload once a month.
Anticipated civilian applications for launch capacities above a million tons per decade from a StarTram facility include space manufacturing
, satellite communications, observation satellites
, asteroid defense
, space-based astronomy
, and space exploration
. While with separate manufacturing costs, solar power satellites producing electricity worth $500 billion a decade could be sent up for each $10 billion of maglev launch expense according to Powell's estimate. Gen-1 could not launch humans (though technology for telepresence robot workers continues to improve), but passenger-capable Gen-1.5 and Gen-2 would be relevant to space tourism
, the latter to aim for $13,000 per person.
Dr. Rather envisions such permitting long-term development of massive space infrastructure to utilize material from near-Earth asteroids for space habitats. Many NEOs
such as inactive comet cores have been discovered in the past 2 decades, some taking not much more delta v
than the Moon
to reach, including billions of tons of kerogen
hydrocarbons and water ice underneath drier outer crusts. With a mass budget to help solve problems including the mass requirements for space radiation shielding and artificial gravity, a goal could be to indirectly "open space for large scale human development" and outright space colonization
.
Magnetic levitation
Magnetic levitation, maglev, or magnetic suspension is a method by which an object is suspended with no support other than magnetic fields...
, reducing g-forces
G-force
The g-force associated with an object is its acceleration relative to free-fall. This acceleration experienced by an object is due to the vector sum of non-gravitational forces acting on an object free to move. The accelerations that are not produced by gravity are termed proper accelerations, and...
when each capsule transitions from the vacuum tube to the atmosphere
Atmosphere
An atmosphere is a layer of gases that may surround a material body of sufficient mass, and that is held in place by the gravity of the body. An atmosphere may be retained for a longer duration, if the gravity is high and the atmosphere's temperature is low...
. A SPESIF 2010 presentation stated that Gen-1 could be completed by the year 2020+ if funding began presently, Gen-2 by 2030+.
History
James R. PowellJames R. Powell
James R. Powell is an American physicist notable — together with Dr. Gordon Danby — for his work on superconducting Maglev, for which he shared the Franklin Institute "Medal 2000 for Engineering"....
invented the superconducting maglev concept in the 1960s with a colleague, Gordon Danby
Gordon Danby
Gordon T. Danby is an American physicist notable for his work on superconducting Maglev, for which he shared the Franklin Institute 'Medal 2000 for Engineering'.-References:...
, also at Brookhaven National Laboratory
Brookhaven National Laboratory
Brookhaven National Laboratory , is a United States national laboratory located in Upton, New York on Long Island, and was formally established in 1947 at the site of Camp Upton, a former U.S. Army base...
, which was subsequently developed into modern maglev trains. Later, Powell co-founded StarTram, Inc. with Dr. George Maise, an aerospace engineer who previously was at Brookhaven National Laboratory
Brookhaven National Laboratory
Brookhaven National Laboratory , is a United States national laboratory located in Upton, New York on Long Island, and was formally established in 1947 at the site of Camp Upton, a former U.S. Army base...
from 1974 to 1997 with particular expertise including reentry
Reentry
Reentry can have several meanings:* Atmospheric reentry, the movement of human-made or natural objects as they enter the atmosphere of a planet from outer space** Ballistic reentry** Skip reentry...
heating and hypersonic
Hypersonic
In aerodynamics, a hypersonic speed is one that is highly supersonic. Since the 1970s, the term has generally been assumed to refer to speeds of Mach 5 and above...
vehicle design.
A StarTram design was first published in a 2001 paper and patent, making reference to a 1994 paper on MagLifter. Developed by John C. Mankins, who was manager of Advanced Concept Studies at NASA, the MagLifter concept involved maglev launch assist for a few hundred m/s with a short track, 90% projected efficiency. Noting StarTram is essentially MagLifter taken to a much greater extreme, both MagLifter and StarTram were discussed the following year in a concept study performed by ZHA for NASA's Kennedy Space Center
Kennedy Space Center
The John F. Kennedy Space Center is the NASA installation that has been the launch site for every United States human space flight since 1968. Although such flights are currently on hiatus, KSC continues to manage and operate unmanned rocket launch facilities for America's civilian space program...
, also considered together by Maglev 2000 with Powell
James R. Powell
James R. Powell is an American physicist notable — together with Dr. Gordon Danby — for his work on superconducting Maglev, for which he shared the Franklin Institute "Medal 2000 for Engineering"....
and Danby
Gordon Danby
Gordon T. Danby is an American physicist notable for his work on superconducting Maglev, for which he shared the Franklin Institute 'Medal 2000 for Engineering'.-References:...
.
Subsequent design modifies StarTram into a generation 1 version, a generation 2 version, and an alternative generation 1.5 variant.
John Rather, who served as Assistant Director for Space Technology (Program Development) at NASA
NASA
The National Aeronautics and Space Administration is the agency of the United States government that is responsible for the nation's civilian space program and for aeronautics and aerospace research...
, said:
Generation 1 System
The Gen-1 system proposes to accelerate unmanned craft at 30 gG-force
The g-force associated with an object is its acceleration relative to free-fall. This acceleration experienced by an object is due to the vector sum of non-gravitational forces acting on an object free to move. The accelerations that are not produced by gravity are termed proper accelerations, and...
through a 130 km length tunnel, with a plasma window
Plasma window
The plasma window is a technology that fills a volume of space with plasma confined by a magnetic field...
preventing vacuum loss when the exit's mechanical shutter is briefly open, evacuated of air with a MHD
Magnetohydrodynamics
Magnetohydrodynamics is an academic discipline which studies the dynamics of electrically conducting fluids. Examples of such fluids include plasmas, liquid metals, and salt water or electrolytes...
pump. (The plasma window
Plasma window
The plasma window is a technology that fills a volume of space with plasma confined by a magnetic field...
is larger than prior constructions, 2.5 MW estimated power consumption itself for 3 meters diameter). 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
Low Earth orbit
A low Earth orbit is generally defined as an orbit within the locus extending from the Earth’s surface up to an altitude of 2,000 km...
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
Orbital velocity
Orbital velocity can refer to the following:* The orbital speed of a body in a gravitational field.* The velocity of particles due to wave motion, in particular in wind waves....
, 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
Drag coefficient
In fluid dynamics, the drag coefficient is a dimensionless quantity that is used to quantify the drag or resistance of an object in a fluid environment such as air or water. It is used in the drag equation, where a lower drag coefficient indicates the object will have less aerodynamic or...
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
Linear motor
A linear motor is an electric motor that has had its stator and rotor "unrolled" so that instead of producing a torque it produces a linear force along its length...
.
Powell
James R. Powell
James R. Powell is an American physicist notable — together with Dr. Gordon Danby — for his work on superconducting Maglev, for which he shared the Franklin Institute "Medal 2000 for Engineering"....
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
Low Earth orbit
A low Earth orbit is generally defined as an orbit within the locus extending from the Earth’s surface up to an altitude of 2,000 km...
. The estimated cost of electrical energy to reach the velocity of low earth orbit
Low Earth orbit
A low Earth orbit is generally defined as an orbit within the locus extending from the Earth’s surface up to an altitude of 2,000 km...
is under $1 per kilogram of payload: 6 cents per kilowatt-hour contemporary industrial electricity cost, 8.78 km/s launch kinetic energy
Kinetic energy
The kinetic energy of an object is the energy which it possesses due to its motion.It is defined as the work needed to accelerate a body of a given mass from rest to its stated velocity. Having gained this energy during its acceleration, the body maintains this kinetic energy unless its speed changes...
of 38.5 MJ per kilogram, and 87.5% of mass payload, accelerated at high efficiency by this linear electric motor.
Generation 2 System
The Gen-2 variant of the StarTram would be for reusable manned capsules in contrast, intended to be low g-forceG-force
The g-force associated with an object is its acceleration relative to free-fall. This acceleration experienced by an object is due to the vector sum of non-gravitational forces acting on an object free to move. The accelerations that are not produced by gravity are termed proper accelerations, and...
, 2 to 3 g
G-force
The g-force associated with an object is its acceleration relative to free-fall. This acceleration experienced by an object is due to the vector sum of non-gravitational forces acting on an object free to move. The accelerations that are not produced by gravity are termed proper accelerations, and...
acceleration in the launch tube and an elevated exit at such high altitude (22 km) that peak aerodynamic deceleration becomes ≈ 1g. Though NASA test pilots have handled multiple times those g-forces
G-force
The g-force associated with an object is its acceleration relative to free-fall. This acceleration experienced by an object is due to the vector sum of non-gravitational forces acting on an object free to move. The accelerations that are not produced by gravity are termed proper accelerations, and...
, 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
Chuo Shinkansen
The is a planned maglev line connecting Tokyo, Nagoya, and Osaka, Japan. The only part of the line that exists is the Yamanashi test track, which is currently being extended from 18.4 km to 42.8 km. The line is proposed to connect Tokyo and Nagoya in the first stage in 40 minutes, and eventually...
under construction by Japan Railways
Japan Railways
The Japan Railways Group, more commonly known as , consists of seven for-profit companies that took over most of the assets and operations of the government-owned Japanese National Railways on April 1, 1987...
. 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
Superconducting Super Collider
The Superconducting Super Collider was a particle accelerator complex under construction in the vicinity of Waxahachie, Texas that was set to be world's largest and most energetic, surpassing the current record held by the Large Hadron Collider. Its planned ring circumference was with an energy...
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
James R. Powell
James R. Powell is an American physicist notable — together with Dr. Gordon Danby — for his work on superconducting Maglev, for which he shared the Franklin Institute "Medal 2000 for Engineering"....
'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
Mass driver
A mass driver or electromagnetic catapult is a proposed method of non-rocket spacelaunch which would use a linear motor to accelerate and catapult payloads up to high speeds. All existing and contemplated mass drivers use coils of wire energized by electricity to make electromagnets. Sequential...
(tethered balloons, compressive or inflated aerospace-material megastructure
Megastructure
A megastructure is a very large manmade object, though the limits of precisely how large this is vary considerably. Some apply the term to any especially large or tall building....
s).
A 280 megaamp current in ground cables creates a magnetic field of 30 Gauss
Gauss (unit)
The gauss, abbreviated as G, is the cgs unit of measurement of a magnetic field B , named after the German mathematician and physicist Carl Friedrich Gauss. One gauss is defined as one maxwell per square centimeter; it equals 1 tesla...
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
Tensile structure
A tensile structure is a construction of elements carrying only tension and no compression or bending. The term tensile should not be confused with tensegrity, which is a structural form with both tension and compression elements....
on grand scale. In the example of niobium-titanium
Niobium-titanium
Niobium-titanium is an alloy of niobium and titanium, used industrially as a type II superconductor wire for superconducting magnets...
superconductor carrying 2 x 105 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.
Generation 1.5 System (lower velocity option)
An alternative, Gen-1.5, would launch passenger spacecraft at 4 km/s instead, without a levitated launch tube as rather from a mountain at around 6000 meters above sea level. Acceleration distance scales with velocity squared while being linearly inversely proportional to g-forceG-force
The g-force associated with an object is its acceleration relative to free-fall. This acceleration experienced by an object is due to the vector sum of non-gravitational forces acting on an object free to move. The accelerations that are not produced by gravity are termed proper accelerations, and...
. Required tunnel length would be ≈ 270 km if at ≈ 3 g
G-force
The g-force associated with an object is its acceleration relative to free-fall. This acceleration experienced by an object is due to the vector sum of non-gravitational forces acting on an object free to move. The accelerations that are not produced by gravity are termed proper accelerations, and...
. While the ≈ 10-15 g
G-force
The g-force associated with an object is its acceleration relative to free-fall. This acceleration experienced by an object is due to the vector sum of non-gravitational forces acting on an object free to move. The accelerations that are not produced by gravity are termed proper accelerations, and...
maximum in optimal transverse orientation tolerated for relevant durations by fit pilots in historical centrifuge tests would make minimum length be ≈ 50 km to 80 km, slower acceleration with a longer tunnel eases passenger requirements and reduces peak power (power conditioning expense).
Though with reduced construction costs, Gen-1.5 would differ from other StarTram variants by requiring 4+ km/s to be provided by other means, like rocket propulsion. However, the non-linear nature of the rocket equation makes the payload fraction be a number of times more than a conventional rocket unassisted by electromagnetic launch, and a vehicle with high available weight margins and safety factors could be far easier to mass-produce cheaply or make reusable with rapid turnaround than current 8 km/s rockets. Dr. Powell remarks that present launch vehicles "have many complex systems that operate near their failure point, with very limited redundancy," with extreme hardware performance relative to weight being a top driver of expense (fuel itself on the order of 1% of current costs to orbit).
Alternatively, Gen-1.5 could be combined with another non-rocket spacelaunch
Non-rocket spacelaunch
Non-rocket space launch is a launch into space where some or all needed speed and altitude is provided by non-rocket means, rather than simply using conventional chemical rockets from the ground. A number of alternatives to rockets have been proposed...
system, like a Momentum Exchange Tether
Momentum exchange tether
Momentum Exchange Tethers is one of many applications for space tethers. This sub-set represents an entire area of research using a spinning conductive and/or non-conductive tether to throw spacecraft up or down in orbit , thereby transferring its momentum.Due to the centrifugal acceleration, the...
similar to the HASTOL concept which was intended to take a 4 km/s vehicle to orbit. Synergy
Synergy
Synergy may be defined as two or more things functioning together to produce a result not independently obtainable.The term synergy comes from the Greek word from , , meaning "working together".-Definitions and usages:...
compared to highly exponential scaling for tethers applies (under limited contemporary material strengths available on the aggregate macroscopic scale), where such a tether may be much more readily doable than one providing full orbital velocity by itself.
Gen-1
The largest challenge for Gen-1 is considered by the researchers to be sufficiently affordable storage, rapid delivery, and handling of the power requirements.For needed electrical energy storage (discharged over 30 seconds with about 50 gigawatt average and about 100 gigawatts peak), SMES cost performance on such unusual scale is anticipated of around a dollar per kilojoule and $20 per kW-peak. Such would be novel in scale but not greatly different planned cost performance than obtained in other smaller pulse power energy storage systems (such as quick-discharge modern supercapacitors dropping from $151/kJ to $2.85/kJ cost between 1998 and 2006 while being predicted to later reach a dollar per kJ, lead acid batteries which can be $10 per kW-peak for a few seconds, or experimental railgun compulsator
Compulsator
A compensated pulsed alternator, also known by the portmanteau compulsator, is a form of power supply.As the name suggests, it is an alternator that is "compensated" to make it better at delivering pulses of electrical energy than a normal alternator.- Description and operation:The principle is...
power supplies). The study notes pulsed MHD generators may be an alternative.
For MagLifter, General Electric
General Electric
General Electric Company , or GE, is an American multinational conglomerate corporation incorporated in Schenectady, New York and headquartered in Fairfield, Connecticut, United States...
estimated in 1997-2000 that a set of hydroelectric flywheel pulse power generators could be manufactured for a cost equating to $5.40 per kJ and $27 per kW-peak. For StarTram, the SMES design choice is a better (less expensive) approach than pulse generators according to Powell.
The single largest predicted capital cost
Capital cost
Capital costs are costs incurred on the purchase of land, buildings, construction and equipment to be used in the production of goods or the rendering of services, in other words, the total cost needed to bring a project to a commercially operable status. However, capital costs are not limited to...
for Gen-1 is the power conditioning, from an initially DC discharge to the AC current wave,
dealing for a few seconds with very high power, up to 100 gigawatts, at a cost estimated to be $100 per kW-peak. Yet, compared to some other potential implementations of a coilgun
Coilgun
A coilgun is a type of projectile accelerator that consists of one or more coils used as electromagnets in the configuration of a synchronous linear motor which accelerate a magnetic projectile to high velocity...
launcher with relatively higher requirements for pulse power switching devices (an example being an escape velocity design of 7.8 km length after a 1977 NASA Ames study determined how to survive atmospheric passage from ground launch), which are not always semiconductor-based, the 130-km acceleration tube length of Gen-1 spreads out energy input requirements over a longer acceleration duration. Such makes peak input power handling requirements be not more than about 2 GW per ton of the vehicle. The tradeoff of greater expense for the tunnel itself is incurred, but the tunnel is estimated to be about $4.4 billion including $1500 per cubic meter excavation, a minority of total system cost.
Gen-2
Gen-2 introduces particular extra challenge with its elevated launch tube. As of 2010 operating maglev systems levitate the train by approximately 15 millimetre (0.590551181102362 in). For the Gen-2 version of the StarTram, it is necessary to levitate the track over up to 22 km, a distance greater by a factor of 1.5 million.The force between two conducting lines is given by
. Here F is the force, the permeabilityPermeability (electromagnetism)
In electromagnetism, permeability is the measure of the ability of a material to support the formation of a magnetic field within itself. In other words, it is the degree of magnetization that a material obtains in response to an applied magnetic field. Magnetic permeability is typically...
,
the electric currents, the length of the lines and their distance. To exert 4000 kg/meter over a distance of 20 km in air ( ≈ 1) ground ≈ 280 x 106A is needed if levitated ≈ 14 x 106AAmpere
The ampere , often shortened to amp, is the SI unit of electric current and is one of the seven SI base units. It is named after André-Marie Ampère , French mathematician and physicist, considered the father of electrodynamics...
. For comparison, in lightning
Lightning
Lightning is an atmospheric electrostatic discharge accompanied by thunder, which typically occurs during thunderstorms, and sometimes during volcanic eruptions or dust storms...
the maximal current is about 105A, c.f. properties of lightning, though resistive power dissipation involved in a current flowing through a conductor is proportional to the voltage drop, high for a lightning discharge of millions of volts in air but ideally zero for a zero-resistance superconductor.
While the performance of niobium-titanium
Niobium-titanium
Niobium-titanium is an alloy of niobium and titanium, used industrially as a type II superconductor wire for superconducting magnets...
superconductor is technically sufficient (a critical current density of 5 x 105 A/cm2 under the relevant magnetic field conditions for the levitated platform, 40% of that in practice after a safety factor), uncertainties on economics include a far more optimistic assumption for Gen-2 of $0.2 per kA-meter of superconductor compared to the $2 per kA-meter assumed for Gen-1 (where Gen-1 doesn't have any of its launch tube levitated but uses superconducting cable for a large SMES
Superconducting magnetic energy storage
Superconducting Magnetic Energy Storage systems store energy in the magnetic field created by the flow of direct current in a superconducting coil which has been cryogenically cooled to a temperature below its superconducting critical temperature....
and within the maglev craft launched). NbTi was the design choice under the available economies of scale for cooling, since it presently costs $1 per kA-meter, while high temperature superconductors so far still cost much more for the conductor itself per kA-meter.
If considering a design with an acceleration up to 10 g
G-force
The g-force associated with an object is its acceleration relative to free-fall. This acceleration experienced by an object is due to the vector sum of non-gravitational forces acting on an object free to move. The accelerations that are not produced by gravity are termed proper accelerations, and...
(which is higher than the re-entry acceleration of Apollo 16
Apollo 16
Young and Duke served as the backup crew for Apollo 13; Mattingly was slated to be the Apollo 13 command module pilot until being pulled from the mission due to his exposure to rubella through Duke.-Backup crew:...
) then the whole track must be at least 326 km long for a passenger version of the Gen-2 system. Such length allows use of the approximation for an infinite line to calculate the force. The preceding neglects how only the final portion of the track is levitated, but a more complex calculation only changes the result for force per unit length of it by 10-20% (fgl = 0.8 to 0.9 instead of 1).
The researchers themselves do not consider there to be any doubt whether the levitation would work in terms of force exerted (a consequence of Ampère's force law
Ampère's force law
In magnetostatics, the force of attraction or repulsion between two current-carrying wires is often called Ampère's force law...
) but see the primary challenge as the practical engineering complexities of erection of the tube, while a substantial portion of engineering analysis focused on handling bending caused by wind. The active structure
Active structure
An active structure is a mechanical structure with the ability to alter its configuration, form or properties in response to changes in the environment....
is calculated to bend by a fraction of a meter per kilometer under wind in the very thin air at its high altitude, a slight curvature theoretically handled by guidance loops, with net levitation force beyond structure weight exceeding wind force by a factor of 200+ to keep tethers taut, and with the help of computer-controlled control tethers.
Gen-1.5
The current land speed record of 2.9 km/s was obtained by a sled on 5 kilometers of rail track mostly in a helium-filled tunnel, in April 2003, in a US$20 million project at Holloman Air Force Base (which has also been running a maglev high speed track development program for general DoDUnited States Department of Defense
The United States Department of Defense is the U.S...
hypersonic test applications, with too short a length of track installed yet for high speed but 3.1-3.4 km/s as a later goal). The Gen-1.5 version of the StarTram for launch of passenger RLVs
Reusable launch system
A reusable launch system is a launch system which is capable of launching a launch vehicle into space more than once. This contrasts with expendable launch systems, where each launch vehicle is launched once and then discarded.No true orbital reusable launch system is currently in use. The...
at 4 km/s velocity from the surface of a mountain would be significantly higher speed with a far more massive vehicle. However, differences intended to make such doable include accelerating in a lengthy vacuum tunnel (no air or gas drag), no hypervelocity
Hypervelocity
The term hypervelocity usually refers to a very high velocity, approximately over 3,000 meters per second . In particular, it refers to velocities so high that the strength of materials upon impact is very small compared to inertial stresses. Thus, even metals behave like fluids under hypervelocity...
physical rail contact as rather a form of maglev vactrain
Vactrain
A vactrain is a proposed, as-yet-unbuilt design for future high-speed railroad transportation. This would entail building maglev lines through evacuated or partly evacuated tubes or tunnels...
levitating a few centimeters above the track, and 3 orders of magnitude
Order of magnitude
An order of magnitude is the class of scale or magnitude of any amount, where each class contains values of a fixed ratio to the class preceding it. In its most common usage, the amount being scaled is 10 and the scale is the exponent being applied to this amount...
higher anticipated funding requirements for development and construction.
Economics and Potential
StarTram is expected to have reusability without extensive maintenance after each launch for a facility that is fundamentally a large linear synchronous electric motor, shifting most of the "requirement for achieving orbit to a robust ground infrastructure," intended to not have very high performance relative to weight requirements or such as the $25,000 per kilogram of flyable dry weightDry weight
Dry weight is the weight of a vehicle without any consumables, passengers, or cargo.It is one of the two common weight measurements included in road vehicle specifications, the other one being curb weight....
costs of the Space Shuttle
Space Shuttle
The Space Shuttle was a manned orbital rocket and spacecraft system operated by NASA on 135 missions from 1981 to 2011. The system combined rocket launch, orbital spacecraft, and re-entry spaceplane with modular add-ons...
. If StarTram's projected capital costs (an estimated $19 billion for Gen-1) are accurate, payback would depend on much higher than current launch volumes to efficiently amortize its construction expense.
The current world launch market is about 200 tons of satellites launched per year. Each 100 tons sent to orbit could have lift expense approach $4 million to the degree that the $43 per kilogram cost goal for Gen-1 full operation was approached, if not counting other expenses like payload fairing
Payload fairing
Payload fairing is one of the main components of a launch vehicle. The fairing protects the payload during the ascent against the impact of the atmosphere . More recently, an additional function is to maintain the cleanroom environment for precision instruments.Outside the atmosphere the fairing is...
integration and interorbital transfer requirements when different inclinations were involved. If launching more than 10,000 tons a month, the anticipated amortized ground-facility component of total Gen-1 cost is stated by Powell's
James R. Powell
James R. Powell is an American physicist notable — together with Dr. Gordon Danby — for his work on superconducting Maglev, for which he shared the Franklin Institute "Medal 2000 for Engineering"....
team to be as low as $15 per kilogram sent up, though the same assumptions for capital cost would make such $4500 per kilogram if launching a 35 ton payload once a month.
Anticipated civilian applications for launch capacities above a million tons per decade from a StarTram facility include space manufacturing
Space manufacturing
Space manufacturing is the production of manufactured goods in an environment outside a planetary atmosphere. Typically this includes conditions of microgravity and hard vacuum.Manufacturing in space has several potential advantages over Earth-based industry....
, satellite communications, observation satellites
Earth observation satellite
Earth observation satellites are satellites specifically designed to observe Earth from orbit, similar to reconnaissance satellites but intended for non-military uses such as environmental monitoring, meteorology, map making etc....
, asteroid defense
Asteroid impact avoidance
Asteroid mitigation strategies are "planetary defense" methods by which near-Earth objects could be diverted, preventing potentially catastrophic impact events. A sufficiently large impact would cause massive tsunamis or an impact winter, or both...
, space-based astronomy
Astronomy
Astronomy is a natural science that deals with the study of celestial objects and phenomena that originate outside the atmosphere of Earth...
, and space exploration
Space exploration
Space exploration is the use of space technology to explore outer space. Physical exploration of space is conducted both by human spaceflights and by robotic spacecraft....
. While with separate manufacturing costs, solar power satellites producing electricity worth $500 billion a decade could be sent up for each $10 billion of maglev launch expense according to Powell's estimate. Gen-1 could not launch humans (though technology for telepresence robot workers continues to improve), but passenger-capable Gen-1.5 and Gen-2 would be relevant to space tourism
Space tourism
Space Tourism is space travel for recreational, leisure or business purposes. A number of startup companies have sprung up in recent years, hoping to create a space tourism industry...
, the latter to aim for $13,000 per person.
Dr. Rather envisions such permitting long-term development of massive space infrastructure to utilize material from near-Earth asteroids for space habitats. Many NEOs
Near-Earth object
A near-Earth object is a Solar System object whose orbit brings it into close proximity with the Earth. All NEOs have a perihelion distance less than 1.3 AU. They include a few thousand near-Earth asteroids , near-Earth comets, a number of solar-orbiting spacecraft, and meteoroids large enough to...
such as inactive comet cores have been discovered in the past 2 decades, some taking not much more delta v
Delta-v
In astrodynamics a Δv or delta-v is a scalar which takes units of speed. It is a measure of the amount of "effort" that is needed to change from one trajectory to another by making an orbital maneuver....
than the Moon
Moon
The Moon is Earth's only known natural satellite,There are a number of near-Earth asteroids including 3753 Cruithne that are co-orbital with Earth: their orbits bring them close to Earth for periods of time but then alter in the long term . These are quasi-satellites and not true moons. For more...
to reach, including billions of tons of kerogen
Kerogen
Kerogen is a mixture of organic chemical compounds that make up a portion of the organic matter in sedimentary rocks. It is insoluble in normal organic solvents because of the huge molecular weight of its component compounds. The soluble portion is known as bitumen. When heated to the right...
hydrocarbons and water ice underneath drier outer crusts. With a mass budget to help solve problems including the mass requirements for space radiation shielding and artificial gravity, a goal could be to indirectly "open space for large scale human development" and outright space colonization
Space colonization
Space colonization is the concept of permanent human habitation outside of Earth. Although hypothetical at the present time, there are many proposals and speculations about the first space colony...
.
See also
- Non-rocket spacelaunchNon-rocket spacelaunchNon-rocket space launch is a launch into space where some or all needed speed and altitude is provided by non-rocket means, rather than simply using conventional chemical rockets from the ground. A number of alternatives to rockets have been proposed...
- Rocket sled launchRocket sled launchA rocket sled launch is a method of launching space vehicles. A rail or maglev track and a rocket or jet booster is used to accelerate a sled holding a vehicle up an eastward facing mountain slope...
- VactrainVactrainA vactrain is a proposed, as-yet-unbuilt design for future high-speed railroad transportation. This would entail building maglev lines through evacuated or partly evacuated tubes or tunnels...
- Magnetically Inflated Cable