By Forrest Bishop
This is an overveiw of a previously unpublished spacecraft launch
system originally conceived and designed in 1981.
There are three major concepts which distinguish this proposal.
Peer review to date suggest they may be original, taken individually
as well as in the aggregate.
The first is to install a vertical launcher near the South Pole,
perhaps on Mt. Erbus. The principle reason is to have launch windows
several hours long for mutually rendevousing projectiles. Launch
windows for Lunar delivery are days long, whereas the "window"
for other missions is continuously open.
The second concept is to boost to nearly Earth escape velocity,
to allow the wide variety of non-planar, near free trajectory maneuvers
that can be performed at the limits of the Earth's sphere of influence.
When a slow moving body (in the Earth frame) is in this region,
the Sun's gravitational field strength is of the same order as the
Earth's. Depending on the time of year, and owing to the Earth's
axial tilt, this means the body is either closer or further from
the the Sun than is the Earth, but traveling at Earth's nominal
orbital velocity. In addition, the body is out of the plane of the
ecliptic. The net force acts in general (and with some nudging)
to move the body toward the plane of the ecliptic, while imparting
a tangential velocity component (relative to Earth). This means
that the payloads can be transfered to Lunar intercept orbit, or
even to an equatorial plane orbit, with very minimal additional
delta V. The traditional apogee burn of Two-Body analysis is replaced
by one or more smaller "nudging" burns. An analogous maneuver
was recently accomplished by the Japanese spacecraft Muses 1.
The third idea is to launch many small projectiles (a few
hundred grams to a few kilograms each) in rapid order. This is done
to keep the bore of the accelerator small (a few centimeters), and
to minimise the peak demand on the power plant. The ratio of mass
to cross section for these bodies is so low that single ones would
not be able to pass throught the atmosphere. A high launch rate
is required to establish and maintain a vertical corridor of rarified
gas (and plasma). This reduces the kinetic energy lost by the projectiles
due to atmospheric drag. The ablation rate is problematic.
A group of these payloads is assembled while en route to the Earth's
field limit, which takes several days. This is to permit applying
the nudging burns to a packet, rather than to each individual payload.
The following subsystems are descibed breifly:
- Electromagnetic accelerator (mass driver) design and installation.
- Projectile/payload types and design.
- Modeling the atmospheric corridor.
(1) Electromagnetic Accelerator
There is a large body of work, both theoretical and experimental,
on the design and construction of these kinds of machines. The launch
velocity is about escape velocity (11.1 km/s) plus on the order
of 1 km/s to overcome atmospheric drag.
In choosing an accelerator, there is a trade-off between the average
acceleration and the length of the accelerator. Something over 6000
g's cuts the length to about 1.5 km.
The launch tube is a vacuum vessel with a diaphragm or iris at
the exit. This is to assist in starting up the accelerator. After
it has begun operating, the projectiles keep the launch tube swept
out, more or less. Vacuum pumps might assist in this. Injecting
gaseous hydrogen at some places along the tube lowers the average
molecular weight of whatever gasses remain, thus reducing drag and
heat transfer. Conditions at the top are a problem. There may be
a requirement for active cooling as well as active cancellation
of noise and vibration.
The upper section has the usual steering and speed adjustments
for the projectiles. The exit velocity vector is very slightly canted
from the vertical. This reduces the danger from possible returning
projectiles (during initialization), as well as permitting an installation
site some distance from the actual Pole.
Sustaining a launch rate in excess of 10 Hertz takes some
very special handling equipment. If it hangs up for more than a
few hundred milliseconds, the flight corridor has to be re-initialized.
The loading equipment at the base of the accelerator has to cool
the reaction coils below the superconducting critical temperature,
charge them with a circulating supercurrent, and load (clips of)
them into the launch tube. Somewhere along this line they are placed
in vacuo. Part of this technology may come from the bottling equipment
industry, and part from military systems.
(2) Projectile design
The size and acceleration limits the kinds of payloads. The most
valuable commodity this system could launch is probably water ice.
Other materials, fuels, and such could also withstand the rigors
The themal protection system could be either insulative, ablative,
Using frozen hydrogen has a distinct advantage besides thermal
protection. As it blows off during the atmospheric passage, it and
its reaction products reduce the average molecular weight of the
gas/plasma in the flight corridor. Water ice can also be used here,
to lesser effect. When the accelerator first starts up, projectiles
consisting mostly of these substances would initialize the corridor.
By allowing the supercurrent (for projectiles with integral coils)
to continue circulating after the projectile clears the accelerator,
its induced magnetic field would deflect the plasma component of
the wake. This may cause more drag and other problems than it's
worth, so provision is made to quench the supercurrent for atmospheric
Some arrangement of auxillary magnetics allows the projectile
to be spun up about its long axis during acceleration, for spin
To facilitate collection, it may be desirable to make the projectiles
in two parts connected by a fiber. Sometime after leaving the atmosphere,
the two pieces separate. The angular momentum of the spun projectile
is transfered to this new configuration, resulting in a flat spin
state roughly perpendicular to the (earth reference) flight vector.
The effective capture cross section is increased as the square of
the fiber length.
It is possible to include an integrated, miniature flight control
system in each projectile. Ground or space based radar can track
the projectiles, and issue serial numbered instructions to individual
members. On board Quartz Rate Sensors, silicon micromachined accelerometers
and valves operate a miniature reaction control system for course
correction and rendezvous. This would obviate the need for the flat
spin idea above.
(3) Modeling the atmospheric corridor
This is a difficult system to properly model. The pulsed nature
of the aerodynamics in the ground reference frame makes time invariant
solutions suspect. The radial variation of density and specific
heats disallows ordinary heat diffusion equations. Aerothermochemicaldynamic
effects add their own non- linearities, as does radiative energy
Prior work indicates the feasibility of successfully launching
single projectiles of a few kilograms through the atmosphere at
10-15 km/sec, with about 10% mass loss. The rarefaction should allow
better performance than this, however the additional heating incurred
may offset the gains.
In addition to the unanswered technical issues, there are the usual
items of environment, politics and finance.
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