Proposed spacelaunch method
Artist's conception of a mass driver on the
Moon
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. Existing and proposed mass drivers use coils of wire energized by electricity to make
electromagnets
, though a rotary mass driver has also been proposed.
[1]
Sequential firing of a row of electromagnets accelerates the payload along a path. After leaving the path, the payload continues to move due to
momentum
.
Although any device used to propel a
ballistic
payload is technically a mass driver, in this context a mass driver is essentially a
coilgun
that magnetically accelerates a package consisting of a magnetizable holder containing a payload. Once the payload has been accelerated, the two separate, and the holder is slowed and recycled for another payload.
Mass drivers can be used to propel spacecraft in three different ways: A large, ground-based mass driver could launch spacecraft away from Earth, the
Moon
, or another body. A small mass driver could act as a rocket engine on board a spacecraft, flinging pieces of material into space to propel itself. Another variation would have a massive facility on a moon or asteroid send projectiles to assist a distant craft.
Miniaturized mass drivers can also be
used as weapons
in a similar manner as classic firearms or cannon using chemical combustion. Hybrids between coilguns and
railguns
such as
helical railguns
are also possible.
[2]
Fixed mass drivers
[
edit
]
Mass drivers need no physical contact between moving parts because they guide their projectiles by dynamic magnetic levitation, allowing extreme reusability in the case of solid-state power switching, and a functional life of ? theoretically ? up to millions of launches. While marginal costs tend to be accordingly low, initial development and construction costs are highly dependent on performance, especially the intended mass, acceleration, and velocity of projectiles. For instance, while
Gerard O'Neill
built his first mass driver in 1976?1977 with a $2000 budget, a short
test model
firing a projectile at 40 m/s and 33
g
,
[3]
his next model had an order-of-magnitude greater acceleration
[4]
after a comparable increase in funding, and, a few years later, researchers at the University of Texas estimated that a mass driver firing a 10 kilogram projectile at 6000 m/s would cost $47 million.
[5]
[
need quotation to verify
]
[6]
[
failed verification
]
For a given amount of energy involved, heavier objects go proportionally slower. Lightweight objects may be projected at 20 km/s or more. The limits are generally the expense of energy storage able to be discharged quickly enough and the cost of power switching, which may be by semiconductors or by gas-phase switches (which still often have a niche in extreme pulse power applications).
[7]
[8]
[9]
However, energy can be stored inductively in superconducting coils. A 1 km long mass driver made of superconducting coils can accelerate a 20 kg vehicle to 10.5 km/s at a conversion efficiency of 80%, and average acceleration of 5,600 g.
[10]
Earth-based mass drivers for propelling vehicles to orbit, such as the
StarTram
concept, would require considerable capital investment.
[11]
The Earth's relatively strong gravity and relatively thick atmosphere make the implementation of a practical solution difficult. Also, most if not all plausible launch sites would propel spacecraft through heavily-traversed air routes. Due to the massive
turbulence
such launches would cause, significant
air traffic control
measures would be needed to ensure the safety of other aircraft operating in the area.
With the proliferation of reusable rockets to launch from Earth (especially first stages) whatever potential might have once existed for any economic advantage in using mass drivers as an alternative to chemical rockets to launch from Earth is becoming increasingly doubtful. For these reasons many proposals feature installing mass drivers on the
Moon
where the lower
gravity
and
lack of atmosphere
greatly reduce the required velocity to reach lunar orbit; also, lunar launches from a fixed position are much less likely to generate issues with respect to matters such as traffic control.
Most serious mass-driver designs use superconducting coils to achieve reasonable energetic efficiency (often 50% to 90+%, depending on design).
[12]
Equipment may include a superconducting bucket or aluminum coil as the payload. The coils of a mass driver can induce
eddy currents
in a payload's aluminum coil, and then act on the resulting
magnetic field
. There are two sections of a mass driver. The maximum
acceleration
part spaces the coils at constant distances, and synchronizes the coil currents to the bucket. In this section, the acceleration increases as the velocity increases, up to the maximum that the bucket can take. After that, the constant acceleration region begins. This region spaces the coils at increasing distances to give a fixed amount of velocity increase per unit of time.
Based on this mode, a major proposal for the use of mass drivers involved transporting lunar-surface material to space habitats for processing using
solar energy
.
[13]
The Space Studies Institute showed that this application was reasonably practical.
In some designs, the payload would be held in a bucket and then released, so that the bucket can be decelerated and reused. A disposable bucket, on the other hand, would avail acceleration along the whole track. Alternatively, if a track were constructed along the entire circumference of the Moon (or any other celestial body without a significant atmosphere) then a reusable bucket's acceleration would not be limited by the length of the track – however, such a system would need to be engineered to withstand substantial
centrifugal forces
if it were intended to accelerate passengers and/or cargo to very high velocities.
On Earth
[
edit
]
In contrast to cargo-only chemical
space-gun
concepts, a mass driver could be any length, affordable, and with relatively smooth acceleration throughout, optionally even lengthy enough to reach target velocity without excessive
g forces
for passengers. It can be constructed as a very long and mainly horizontally aligned
launch track
for spacelaunch, targeted upwards at the end, partly by bending of the track upwards and partly by
Earth's curvature
in the other direction.
Natural elevations, such as mountains, may facilitate the construction of the distant, upwardly targeted part. The higher up the track terminates, the less resistance from the atmosphere the launched object will encounter.
[14]
The 40
megajoules
per kilogram or less
kinetic energy
of projectiles launched at up to 9000 m/s velocity (if including extra for drag losses) towards
low Earth orbit
is a few
kilowatt-hours
per kilogram if efficiencies are relatively high, which accordingly has been hypothesized to be under $1 of electrical energy cost per kilogram shipped to
LEO
, though total costs would be far more than electricity alone.
[11]
By being mainly located slightly above, on or beneath the ground, a mass driver may be easier to maintain compared with many other structures of
non-rocket spacelaunch
. Whether or not underground, it needs to be housed in a pipe that is
vacuum pumped
in order to prevent internal air
drag
, such as with a mechanical shutter kept closed most of the time but a
plasma window
used during the moments of firing to prevent loss of vacuum.
[15]
A mass driver on Earth would usually be a compromise system. A mass driver would accelerate a payload up to some high speed which would not be enough for orbit. It would then release the payload, which would complete the launch with rockets. This would drastically reduce the amount of velocity needed to be provided by rockets to reach orbit. Well under a tenth of orbital velocity from a small rocket thruster is enough to raise
perigee
if a design prioritizes minimizing such, but hybrid proposals optionally reduce requirements for the mass driver itself by having a greater portion of
delta-v
by a rocket burn (or orbital
momentum exchange tether
).
[11]
On Earth, a mass-driver design could possibly use well-tested
maglev
components.
To launch a space vehicle with humans on board, a mass driver's track would need to be almost 1000 kilometres long if providing almost all the velocity to
Low Earth Orbit
, though a lesser length could provide major launch assist. Required length, if accelerating mainly at near a constant maximum acceptable
g-force
for passengers, is proportional to velocity squared.
[16]
For instance, half of the velocity goal could correspond to a tunnel a quarter as long needing to be constructed, for the same acceleration.
[16]
For rugged objects, much higher accelerations may suffice, allowing a far shorter track, potentially circular or
helical
(spiral).
[17]
Another concept involves a large ring design whereby a space vehicle would circle the ring numerous times, gradually gaining speed, before being released into a launch corridor leading skyward.
Mass drivers have been proposed for the disposal of nuclear waste in space: a projectile launched at much above Earth's
escape velocity
would escape the Solar System, with atmospheric passage at such speed calculated as survivable through an elongated projectile and a very substantial heatshield.
[10]
[18]
[
verification needed
]
Spacecraft-based mass drivers
[
edit
]
A
spacecraft
could carry a mass driver as its primary engine. With a suitable source of electrical power (probably a
nuclear reactor
) the spaceship could then use the mass driver to accelerate pieces of matter of almost any sort, boosting itself in the opposite direction. At the smallest scale of reaction mass, this type of drive is called an
ion drive
.
[
citation needed
]
No absolute theoretical limit is known for the size, acceleration or muzzle energy of linear motors. However, practical engineering constraints apply for such as the power-to-mass ratio,
waste heat
dissipation, and the energy intake able to be supplied and handled. Exhaust velocity is best neither too low nor too high.
[19]
There is a mission-dependent limited optimal exhaust velocity and
specific impulse
for any thruster constrained by a limited amount of onboard spacecraft power. Thrust and momentum from exhaust, per unit mass expelled, scales up linearly with its velocity (
momentum
= mv), yet kinetic energy and energy input requirements scale up faster with velocity squared (
kinetic energy
=
+
1
⁄
2
mv
2
). Too low an exhaust velocity would excessively increase propellant mass needed under the
rocket equation
, with too high a fraction of energy going into accelerating propellant not used yet. Higher exhaust velocity has both benefit and tradeoff, increasing propellant usage efficiency (more momentum per unit mass of propellant expelled) but decreasing thrust and the current rate of spacecraft acceleration if available input power is constant (less momentum per unit of energy given to propellant).
[19]
Electric propulsion
methods like mass drivers are systems where energy does not come from the propellant itself. (Such contrasts to
chemical rockets
where
propulsive efficiency
varies with the ratio of exhaust velocity to vehicle velocity at the time, but near maximum obtainable specific impulse tends to be a design goal when corresponding to the most energy released from reacting propellants). Although the specific impulse of an electric thruster itself optionally could range up to where mass drivers merge into
particle accelerators
with fractional-lightspeed exhaust velocity for tiny particles, trying to use extreme exhaust velocity to accelerate a far slower spacecraft could be suboptimally low thrust when the energy available from a spacecraft's reactor or power source is limited (a lesser analogue of feeding onboard power to a row of spotlights, photons being an example of an extremely low momentum to energy ratio).
[19]
For instance, if limited onboard power fed to its engine was the dominant limitation on how much payload a hypothetical spacecraft could shuttle (such as if intrinsic propellant economic cost was minor from usage of extraterrestrial soil or ice), ideal exhaust velocity would rather be around 62.75% of total mission
delta v
if operating at constant specific impulse, except greater optimization could come from
varying exhaust velocity
during the mission profile (as possible with some thruster types, including mass drivers and
variable specific impulse magnetoplasma rockets
).
[19]
Since a mass driver could use any type of mass for reaction mass to move the spacecraft, a mass driver or some variation seems ideal for deep-space vehicles that scavenge reaction mass from found resources.
One possible drawback of the mass driver is that it has the potential to send solid reaction mass travelling at dangerously high relative speeds into useful orbits and traffic lanes. To overcome this problem, most schemes plan to throw finely-divided
dust
. Alternatively, liquid oxygen could be used as reaction mass, which upon release would boil down to its molecular state. Propelling the reaction mass to solar
escape velocity
is another way to ensure that it will not remain a hazard.
Hybrid mass drivers
[
edit
]
A mass driver on a
spacecraft
could be used to "reflect" masses from a stationary mass driver. Each deceleration and acceleration of the mass contributes to the
momentum
of the spacecraft. The lightweight, fast spacecraft need not carry
reaction mass
, and does not need much electricity beyond the amount needed to replace losses in the electronics, while the immobile support facility can run off power plants able to be much larger than the spacecraft if needed. This could be considered a form of
beam-powered propulsion
(a macroscopic-scale analogue of a
particle beam
propelled magsail). A similar system could also deliver pellets of fuel to a spacecraft to power another propulsion system.
[20]
[21]
[22]
[23]
Another theoretical use for this concept of propulsion can be found in
space fountains
, a system in which a continuous stream of pellets in a circular track holds up a tall structure.
Mass drivers as weapons
[
edit
]
Small to moderate size high-acceleration electromagnetic projectile launchers are currently undergoing active research by the US Navy
[24]
for use as ground-based or ship-based weapons (most often
railguns
but
coilguns
in some cases). On larger scale than weapons currently near deployment but sometimes suggested in long-range future projections, a sufficiently high velocity
linear motor
, a mass driver, could in theory be used as intercontinental artillery (or, if built on the
Moon
or in orbit, used to
attack a location on Earth's surface
).
[25]
[26]
[27]
As the mass driver would be located further up the gravity well than the theoretical targets, it would enjoy a significant energy imbalance in terms of counter-attack.
Practical attempts
[
edit
]
One of the first engineering descriptions of an "Electric Gun" appears in the technical supplement of the 1937 science fiction novel "Zero to Eighty" by "Akkad Pseudoman",
[28]
a pen name for the Princeton physicist and electrical entrepreneur
Edwin Fitch Northrup
. Dr. Northrup built prototype coil guns powered by kHz-frequency three-phase electrical generators, and the book contains photographs of some of these prototypes. The book describes a fictional circumnavigation of the moon by a two-person vehicle launched by a Northrup electric gun.
Later prototype mass drivers have been built since 1976 (
Mass Driver 1
), some constructed by the U.S.
Space Studies Institute
in order to prove their properties and practicality.
Military R&D on coilguns
is related, as are
maglev trains
.
SpinLaunch
, a company founded in 2014, conducted the initial test of their test accelerator in October 2021.
[29]
See also
[
edit
]
People
[
edit
]
References
[
edit
]
- ^
Pearson, J. (1980-01-16).
"ASTEROID RETRIEVAL BY ROTARY ROCKET"
(PDF)
.
AIAA
.
Archived
(PDF)
from the original on 2022-10-09
. Retrieved
2021-10-18
.
[
dead link
]
- ^
Kolm, H.; et al. (1980).
"Electromagnetic Guns, Launchers, and Reaction Engines"
. MIT.
- ^
Compare:
Henson, Keith
;
Henson, Carolyn
(June 1977).
"1977 Space Manufacturing Facilities Conference"
(PDF)
.
L5 News
.
2
(6). L-5 Society: 4. Archived from
the original
(PDF)
on 2017-05-05
. Retrieved
2017-11-27
.
The stars of this conference [...] were Professor Henry Kolm of Massachusetts Institute of Technology and the group of student volunteers who built the first mass driver [...] In its best test, the mass driver prototype produced an acceleration of thirty-three gravities. This is more than Dr. O'Neill [...] had considered necessary for a lunar surface mass driver. [...] The mass driver was demonstrated several times during breaks between conference sessions, each time with a round of applause for the team who built it in less than four months on a budget of $2,000.
- ^
Compare:
Snow, William R.;
Dunbar, R. Scott
; Kubby, Joel A.;
O'Nell, Gerard K.
(January 1982).
"Mass Driver Two: A Status Report"
(PDF)
.
IEEE Transactions on Magnetics
. Mag-18 (1): 127.
Bibcode
:
1982ITM....18..127S
.
doi
:
10.1109/tmag.1982.1061777
. Archived from
the original
(PDF)
on 2012-07-22
. Retrieved
2017-11-26
.
Mass Driver Two combines for the first time all the essential features of an operational mass driver, with the exception of bucket recirculation and payload handling. Its nominal design acceleration is 5000 m/s2, for a final velocity of 112 m/s.
- ^
IEEE Transactions on Magnetics, Vol Mag-18, No. 1
[
permanent dead link
]
, January 1982. Retrieved May 10, 2011.
- ^
Electromagnetic Launchers for Space Applications
. Retrieved May 10, 2011.
- ^
"High Current, High Voltage Solid State Discharge Switches for Electromagnetic Launch Applications"
(PDF)
.
- ^
"Pulse Power Switching Devices – An Overview"
.
- ^
"Scanning the Technology: Modern Pulsed Power"
. Archived from
the original
on December 1, 2012
. Retrieved
April 27,
2011
.
- ^
a
b
"L5 news, Sept 1980: Mass Driver Update"
. Archived from
the original
on 2017-12-01
. Retrieved
2009-07-28
.
- ^
a
b
c
"StarTram2010: Maglev Launch: Ultra Low Cost Ultra High Volume Access to Space for Cargo and Humans"
. Archived from
the original
on 2017-07-27
. Retrieved
2011-04-28
.
- ^
Kolm, H.; Mongeau, P.; Williams, F. (September 1980). "Electromagnetic Launchers".
IEEE Transactions on Magnetics
.
16
(5): 719?721.
Bibcode
:
1980ITM....16..719K
.
doi
:
10.1109/TMAG.1980.1060806
.
- ^
NASA, 1975: Space Settlements: A Design Study
Archived
2017-06-25 at the
Wayback Machine
. Retrieved 2011-05-09.
- ^
"Magnetic Launch System"
.
The Space Monitor
.
- ^
"Advanced Propulsion Study"
(PDF)
. Archived from
the original
(PDF)
on 2012-12-01
. Retrieved
2011-05-03
.
- ^
a
b
"Constant Acceleration"
.
- ^
"Magnets, Not Rockets, Could Fling Satellites Into Space"
. Archived from
the original
on 2017-12-01
. Retrieved
2008-05-04
.
- ^
Park, Chul; Boden, Stuart W. (1982). "Ablation and deceleration of mass-driver launched projectiles for space disposal of nuclear wastes". In Horton, T. E. (ed.).
Thermophysics of Atmospheric Entry
.
American Institute of Aeronautics and Astronautics
. pp. 201?225.
doi
:
10.2514/5.9781600865565.0201.0225
.
ISBN
978-0-915928-66-8
.
- ^
a
b
c
d
"Physics of Rocket Systems with Separated Energy and Propellant"
.
- ^
Singer, C.E. (1979).
Interstellar Propulsion Using a Pellet Stream for Mass Transfer
(PDF)
(Report).
doi
:
10.2172/5770056
.
Archived
(PDF)
from the original on 2022-10-09
. Retrieved
May 9,
2011
.
- ^
Gilster, Paul (April 20, 2005).
"Interstellar Flight Using Near-Term Technologies"
.
Centauri Dreams
. Retrieved
May 9,
2011
.
- ^
U.S. Patent #5305974, Spacecraft Propulsion by Momentum Transfer
. Retrieved May 9, 2011.
- ^
Matloff, Gregory L. (2005).
"8.5: A Toroidal Ramscoop"
.
Deep Space Probes: To The Outer Solar System and Beyond
. Springer. p. 120.
ISBN
9783540247722
. Retrieved
May 9,
2011
.
- ^
"U.S. Navy"
. Archived from
the original
on 2017-11-08
. Retrieved
2013-06-11
.
- ^
Applications of coilgun electromagnetic propulsion technology
. Retrieved May 9, 2011.
- ^
Affordable Spacecraft: Design and Launch Alternatives, Chapter 5, Page 36
. Retrieved May 9, 2011.
- ^
QDR 2001: Strategy-Driven Choices for America's Security, Chapter 11, Global Reach/Global Power School
Archived
2012-03-23 at the
Wayback Machine
. Retrieved May 9, 2011.
- ^
Pseudoman, Akkad (1937).
Zero to Eighty
. Princeton, New Jersey: Princeton University Press.
- ^
Sheetz, Michael (2021-11-09).
"Alternative rocket builder SpinLaunch completes first test flight"
.
CNBC
. Retrieved
2021-11-11
.
External links
[
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]
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Static structures
| Compressive
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Tensile
| Orbiting skyhooks
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Space elevators
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Dynamic structures
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Projectile launchers
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Chemical
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Mechanical
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Reaction drives
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Buoyant lifting
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Concepts
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Physical propulsion
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Chemical propulsion
| State
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Propellants
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Power cycles
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Intake mechanisms
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Electrical propulsion
| Electrostatic
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Electromagnetic
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Electrothermal
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Other
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Nuclear propulsion
| Closed system
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Open system
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External power
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Related concepts
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