NASA Technical Reports Server (NTRS) 19930007725: Electromagnetic launch of lunar material

19 Pages·0.74 MB·English

by  NASA Technical Reports Server (NTRS)

N93-/G914
Electromagnetic Launch of
Lunar Material
William R. Snow and Henry H. Kolm
Introduction surface to LEO is approximately
5 percent the cost from the surface
Lunar soil can become a source of the Earth to LEO. This small
of relatively inexpensive oxygen percentage is due to the reduced
propellant for vehicles going escape velocity of the Moon
from low Earth orbit (LEO) to compared with that of the Earth.
geosynchronous Earth orbit (GEO) Therefore, lunar derived oxygen
and beyond. This lunar oxygen would be more economical to use
could replace the oxygen propellant even if its production cost was
that, in the current plans for these considerably higher than the cost of
missions, is launched from the producing it on Earth.
Earth's surface and amounts to
approximately 75 percent of the Electromagnetic launchers, in
total mass. Besides the LEO-to- particular the superconducting
GEO missions, a manned Mars quenchgun, provide a method of
mission could benefit from this getting this lunar oxygen off the lunar
more economical oxygen. The surface at minimal cost. This cost
use of such oxygen in a chemical savings comes from the fact that the
rocket would eliminate the need to superconducting quenchgun gets its
develop an advanced nonchemical launch energy from locally supplied,
propulsion technology for this solar- or nuclear-generated electrical
mission. And the shorter trip time power. By comparison, unless
afforded by a chemical rocket hydrogen can be found in usable
would also reduce life support quantities on the Moon, the delivery
requirements. of oxygen from the Moon to LEO by
chemical rocket would cost much
The reason for considering the use more, primarily because of the cost
of oxygen produced on the Moon is of bringing hydrogen for the rocket
that the cost for the energy needed from Earth.
to transport things from the lunar
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Lunar Oxygen Supply The mission scenario starts with
Concept the launching of tanks containing
1metric ton or more of liquid
Various methods by which lunar oxygen from an electromagnetic
oxygen could be delivered from the launcher (superconducting
surface of the Moon to lunar orbit quenchgun) on the lunar surface
and on to LEO have been studied by into low lunar orbit (100-km
a number of investigators (Clarke altitude), as shown infigures 13
1950; Salketd 1966; Andrews and and 14. When the tank reaches
Snow 1981; Snow, Kubby, and apolune (maximum altitude), a
Dunbar 1982; Davis 1983; Bilby et small thruster is fired to circularize
al. 1987; Snow et al. 1988; LSPI its orbit and keep itfrom crashing
1988). A diagram of the Earth-Moon back into the lunar surface. With a
system showing the orbits and launch rate of one every 2 hours,
missions for the lunar oxygen the liquid oxygen tanks collect at
delivery concept that we recommend one spot in lunar orbit. After a
is shown in figure 12. number of these tanks accumulate
i<
Figure 12 __-'_ :
N
Lunar Oxygen Delivery Orbits
and Missions
|
n
i
i|l
E
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m
i
Em
in orbit, they are recovered and the Projectile launched from Periodic lunar
liquid oxygen is transferred to an equatorial site by module return
aerobraked lunar ferry (shown in quenchgun launcher of empty
projectiles
figure 15), which delivers it to low 2° surface
Earth orbit. This lunar ferry returns launch angle
to lunar orbit, bringing back with it
some liquid hydrogen. A lunar
module returns the empty tanks to
the lunar surface so that they can be
reused. This lunar module as well as
the lunar ferry is fueled by the liquid
Inertial
oxygen coming from the lunar ascent Figure 13
surface and the liquid hydrogen
Projectiles in
brought back by the lunar ferry. With Apolune stable orbit Lunar Launcher Mission
the empty tanks now back at the insertion burn awaiting OMV
electromagnetic launcher site, the recovery
process repeats itself.
Figure 14
Lunar.Based Superconducting
Quenchgun
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Figure 15
Aerobraked Lunar Ferry
Artist: Pat Rawlings
E-=
Ii:
i
IE
ii
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_=
__--=
Electromagnetic Launcher the projectile, thus minimizing heat
History losses and being more efficient. This
idea required fast high-power opening
The first reported effort to construct and closing switches, which did not
and test an electromagnetic exist at that time. But the idea would
launcher was that of Professor later be used in the mass driver and
Kristian Birkeland at the University other launcher designs (coilguns) of
of Oslo in 1901 (Egeland and Leer the 1970s. He also recognized the
1986). He received the first world effect of magnetic levitation on the
patent for an electromagnetic projectile; this magnetic force capable
gun and formed a company, of centering the projectile would
"Birkeland's Firearms," to research eliminate friction between the
and produce them. His largest gun, projectile and the barrel. This effect
constructed in 1902, launched would also be used in the 1970s, with
10-kg iron projectiles. The barrel modifications, in the magnetically
was 10 meters long with a bore levitated (maglev) high-speed ground
of 6.5 centimeters and achieved transportation vehicles.
projectile velocities of 80 to
As a variation on Jules Verne's
100 meters per second. He
envisioned building guns that would approach, Northrup proposed using
have ranges of 100 to 1000 km. He an electromagnetic launcher on the
abandoned his efforts due to a lack Earth to send a capsule with two
of funds and his realization that people onboard on a trip around the
there were no available pulsed Moon. In his book this was to have
power sources to operate his guns. taken place in the early 1960s and
This would continue to be the case under the condition of a race with
for the next 70 years. Russia to get to the Moon first.
The next reported efforts were made During World War II, several efforts
by Professor Edwin F. Northrup at were made to use electromagnetic
Princeton University in the 1930s launch technology. In Germany, at
(Northrup 1937). He constructed Peenem_nde in 1943, an electric
a number of electromagnetic catapult for launching V-2 rockets
launchers in the early 1930s. His was unsuccessfully tested. In Japan,
launchers were linear three-phase electromagnetic launchers were
induction motors (like their rotary studied for use as antiaircraft guns,
counterparts), the same type as but they were never constructed. In
Birkeland's guns. He envisioned an the United States, the Westinghouse
ideal electromagnetic launcher in Electric Corporation built a catapult
which only a small part of the barrel (known as the Electropult) for the
would be energized at any one time Navy to launch airplanes. The
and the energized part would be catapult wasn't completed until
synchronized with the passage of after the war, but it successfully
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launched airplanes such as the Norwood's work would lie unknown
B-25. This catapult lost out to until after the concept of mass
the steam catapult which was drivers emerged in the late 1970s.
being developed at that time for
use onboard aircraft carriers. In In the late 1960s and early 1970s,
the late 1940s, electromagnetic electromagnetic launcher technology
launchers were still in their infancy was being developed for high-speed
and were still using the inefficient ground transportation by the United
linear induction motor design States, Japan, and Germany (Kolm
instead of the more efficient linear ancl Thornton 1973). The first
synchronous motor design that repulsively levitated synchronous
would be used in the 1980s. high-speed transportation system
(known as the Magneplane) was
For the next 20 years, electro- developed and tested at 1/25 scale
magnetic launcher technology in the early 1970s as a joint effort
lay dormantexcept for a few efforts by MIT's Francis Bitter National
in building railguns and a small Magnet Laboratory and Raytheon.
coilgun built by Thom and Norwood This concept has been adopted by
at the NASA Langley Research both the German and the Japanese
Center in 1961. Their brush- maglev group, who are continuing
commutated coilgun was a linear their efforts, but U,S. support for
synchronous motor (unlike all maglev research was terminated in
previous electromagnetic launchers). 1975. A Japanese maglev system,
It was proposed for use as a lunar which rides on a cushion of air,
launcher in support of a large base has reached test speeds of
on the Moon. However, Thom and 520 kilometers per hour (325 mph).
Maglev Test Track In Japan
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i
An offshoot of this maglev at MIT and Princeton University
research resulted in the concept of (Snow 1982). The first lunar
the mass driver by Professor launcher proof-of-concept model
Gerard K. O'Neill of Princeton was constructed in 1977 by a
University in 1974. It was based group of students at the MIT
on features of the Magneplane, Francis Bitter National Magnet
like magnetic levitation and Laboratory; it is shown in figure 16.
superconducting armature coils,
but the drive circuit was based on The energy storage capacitors in
the resonant transfer of energy the mass driver dominate its mass
from capacitors rather than on a and cost. And, because capacitors
three-phase power supply. The have a low energy density, they
mass driver was proposed as a are especially unsuitable for an
means for launching raw materials electromagnetic launcher of lunar
(payloads of 1-10 kg size at launch oxygen, facing the requirements of
rates of 1-10 per second) from a a larger payload mass at a lower
lunar base to a construction site in launch rate.
space. The mass driver was
studied extensively for missions of Looking for an alternative way to
launch nuclear waste from the
this type, during three NASA Ames
summer studies in 1975, 1976, and surface of the Earth, Henry Kolm in
1977 (Billingham, Gilbreath, and 1978 developed the idea of the
O'Leary 1979) and subsequently superconducting quenchgun (Kolm
Figure 16
Mass Driver IDuring Construction
WhileGerard K.O'Neill,aPrinceton
physics professor, was on sabbatical as
theHunsaker Professor of Aeronautics at
MITin 1976-77,he and HenryKolm, one
of thecofounders of theFrancis Bitter
NationalMagnet Laboratory, led a team of
students inbuilding MassDriver I. Shown
here are Bill Snow, KevinFine, Jonah
Garbus, O'Neill, Kolm, andEric Drexler.
In 1977itwaswidely befieved thatahighly
advanced mass driver, using themost
sophisticated materials and design,
could achieve atbest 50 gravities of
acceleration. However, even thisprimitive
model, built fromabout $3000worth of
scroungedequipment, demonstrated an
acceleration of over 30 g's.
Courtesy of Space Studies Institute
,_,-_._:NAL PAGE 123
BtACK AND WHITE PHOTOGRAPH
et al. 1979, Graneau 1980). The or coplanar, as long as they are
quenchgun is analogous to the inductively coupled to each other.
Carnot engine inthermodynamics- The thrust generated is simply the
the ideal launcher capable of product Ofthe two co_lcurrents times
achieving the maximum theoretically a proportionality constant. This
possible effic[effcy. Iteliminates the constant is the mutual inductance
need for energy storage capacitors. gradient between the projectile coil
Quenchguns store the entire launch and the barrel coil. The mutual
energy in the superconducting inductance gradient for acoilgun is
barrel coils and transfer it to the typically about 100 times as large as
projectile almost without loss. that for arailgun. As a result, the
coilgun generates 100times more
The quenchgun concept was not thrust for a given heat loss.
pursued in 1978 because it was
considered impractical for any This large thrust isgenerated only
tactical terrestrial applications when the two coils are in close
of interest at the time. High- proximity to each other. Therefore,
temperature superconductors coilguns require that the barrel coil
or better refrigerators would be current must be synchronized with
required. However, the quenchgun the passing projectile. When normal
is practical, even with existing low- conductors are used, this current
temperature superconductors, on must be supplied by a pulsed power
the cold lunar surface. A proof-of- source to minimize energy loss due
concept model of the quenchgun to conductor heating.
was built and successfully tested in
1985 using normal conductors and In the mass driver, the synchronization
silicon-controilea rectifier (_CR) wasaccomplished by triggering the
switches (Snow and Mongeau resonant capacitor discharge to
1985). coincide withthe passage of the
projectile. Capacitors unfortunately
have too low an energy density to be
Electromagnetic Launcher practical, and it becomes necessary
Coilgun Principles to use inductive effergy Storage
when megajoules of launch energy
Coilguns achieve acceleration by are needed.
the Lorentz force exerted by one or
more current-carrying barrel coils Unfortunately it is difficult to
on one or more current-carrying commutate (turn the current in a
projectile coils. The barrel and coil on or off) inductively stored
projectile coils can be coaxial energy. This can be accomplished
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by the use of brushes located on without loss for an indefinite period
the projectile to synchronize the of time. Because of this feature,
barrel current with that in the the superconducting quenchgun
projectile. However, brushes are can be charged up between firings.
not suited to the large energies Thus the superconducting barrel
and vacuum environment of requires only 1/10 000 the power
the lunar launcher mission, and required by a non-superconducting
the wear they would cause is barrel.
unacceptable in such a mission.
The only reasonable option for To provide the very high pulse
this mission is the superconducting power needed in a non-
quenchgun, which is capable of superconducting barrel, the
storing the entire launch energy source would have to be some
in its barrel without loss and of sort of rotating machinery (with
commutating it synchronously bearings that would wear), such as
without brushes. a flywheel/pulsed alternator. The
power for a superconducting barrel
can instead be derived from a much
Quenchgun Principles simpler and smaller solar or nuclear
source. This is the key feature
The quenchgun consists of a that makes the superconducting
superconducting solenoid barrel quenchgun a much more practical
divided up into a number of short, device for lunar launching than any
current-carrying barrel coils. Each other electromagnetic launcher.
of the barrel coils is open-circuited
(after the barrel coil current has The operation of a superconducting
been de-induced) at the instant the quenchgun is illustrated in figure 17.
projectile coil passes through it. It consists simply of a row of short
When the projectile reaches the coaxial superconducting barrel
muzzle, nearly all of the energy coils, with an oversized injection
initially stored in the barrel will coil at the breech. The projectile
have been transferred to the coil is at rest in the breech, as
projectile in the form of kinetic shown in the first of the three
energy. diagrams. It does not need to
be superconducting, as long as
The unique feature of the its characteristic time constant
quenchgun is the superconducting is longer than the launch time. This
barrel coils. Ordinary conductors time constant increases with size,
cannot store the entire launch and at the size proposed aluminum
energy in the barrel coils very or beryllium alloys meet the
efficiently for more than 1 second. requirement if they are precooled
Superconductors, on the other to about 80 K. To initiate the
hand, can store this launch energy launch, it is necessary merely to
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quenchtheinjectioncoil,as
commutation), and the
indicatedintheseconddiagram.
superconductivity of the first coil
Thisinducesacurrentinthe
must be quenched so as to prevent
projectilecoil,whichwillpersist
current from being re-induced in
formorethanthe
duration of the barrel coil as the projectile
the launchl The projectile is now coil passes through it. If the
sucked into the quenchgun, as superconductivity of the barrel
shown in the third diagram. As the coil is not quenched, the re-induced
projectile reaches the first barrel current in it will pull the projectile
coil, it induces a current zero (by backward and reduce its
what is called motion-induced acceleration force.
a. Fully charged--ready to fire
cInojielction --Dt_
r-q
Projectilej r]
b<l D<I1>4I><I
coil _,_
t Superconducting barrel coils
b. Projectile injection
Injection coil _l----_
is manually_ [
quenched. ' '
• Projectile coil is attracted to
v barrel coils.
is established in--" I I I><I b<l [:><1b<] t><l
projectile coil.
¢. Projectile acceleration
Motionofprojectile _-_ ['---] _ _ _ _ ['_
de-inducescurrentin
quenchgun
co J[.
Coil is quenched to -_ Projectile moves to next coil
prevent re-induction LXJ and process repeats.
Figure 17
ofcurrent. _______ [_ [_ _] _] [_
Principles of Ouenchgun Operation
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