8.0 The polar lunar base |
Several writers such as James Burke have discussed the "Merits of a Lunar Polar Base Location" [LB1, p.77-84]. He also cites a half dozen other writers of papers on lunar polar bases and related subjects. From [LB1, p.84] some are: 1. J.R. Arnold, "Ice in the lunar polar regions", J. Geophysics
Res., 84, 5659-5668, 1979.
2. J.D. Burke, "Where do we locate the Moon base?", Spaceflight,
19, 363-366, 1977.
3. J. Green, "The polar lunar base", in "The Future of the United
States Space Program", AAS paper 78-191, Univelt, San diego, 1978.
In "Thoughts on a Lunar Base" [LB1, p.25-30], Edward Teller
also favors a polar lunar base.
Among the attractions mentioned are: (1) possible deposits of
ice, (2) areas where the sun may never fully set, and (3) frequent
access to polar orbiting satellites or space stations. While it
would be helpful to find ice somewhere near the poles, we should
certainly not count on it, and the hope of finding some seems to be
a poor justification for vast expenditures of money.
The availability of permanent
sunlight would be much more useful, but this too seems unlikely.
The inclination of the rotational axis of the moon to the ecliptic
plane is 1.5424 degrees [41, p.68]. This means that if the moon
were a perfect sphere 1738 kilometers in radius, then when the pole
was furthest from the sun, it would be 1.5424 degrees or 46.79
kilometers from the pole to the nearest point where the sun was
visible. If we were to build a ring of solar panels 46.79 kilometers
from the pole, then we could expect to have most of the panels in
sunlight most of the time and thus we would have permanent solar
power. Conversely, if one built a tower 630 meters or 2066 feet
tall at the pole, then sunlight would just strike the top of the
tower in the worst case. Clearly the actual geometry of the poles
will likely determine the final configuration of any polar solar
power arrays which we build.
It is true that a low lunar polar orbitting satellite would
pass over the pole about every two hours, but access from a polar
base would mean rising nearly straight up which probably implies
the use of rocket boosters. That we cannot tolerate because it will
spoil the nearly perfect vacuum present on the moon.
Notwithstanding the previously mentioned reservations, we too
favor a polar lunar base. However, our justification is that the
north pole is the optimal location for the electromagnetic projectile
launcher which will constitute the lunar portion of our momentum
transfer system which will propel spaceships to Mars and elsewhere
(see section 6.4).
8.1 Site selection There is only one north pole of the moon, but it seems to be
right on the northwest shoulder of the 80 km wide Peary crater.
This could make construction very difficult. Perhaps the floor of the
Peary crater would be the best location. Another possibility is
the 80 km wide Byrd crater which is just south of the Peary crater.
The crater floor appears wide and flat, but our projectiles must
clear the surrounding crater rim. From the center of the crater,
the curvature of the moon's surface should give us about 450 meters
(plus the height of the EMPL) of clearance 40 kilometers away, i.e.
at the crater rim. We could knock down part of the crater rim if
necessary, but if nuclear explosives are used, care must be taken to
avoid generating thousands of tons of oxygen which would create an
unwanted artificial atmosphere.
8.2 The lunar polar railroad The following table shows the distance to the pole from various lunar latitudes at which the first lunar base might be located. * Table 8.2-1
Latitude Distance to pole
(deg) (km) (mi)
55 1062 660
57.5 986 613
60 910 566
62.5 834 518
65 758 471
.
From a previous discussion it is clear that we will have copious
amounts of iron available for construction of anything we need. Thus
building a railroad, which is a major user of iron should not be a
problem.
We advocate building an electrified railroad from the first lunar
base north to the north pole. This line will be double track so that
traffic can travel in both directions at the same time and further,
that if necessary, oversized cars stretching between the first and
third or fourth rails could be used. With so much iron available
there is no reason to be chintzy. We will use 100 pound rail (that
means 100 pounds per foot for those not familiar with the business).
The amount of iron required for each kilometer of double track will
be the product of the following factors:
* 100 pounds per foot
x 3.28 feet per meter
x 1000 meters per kilometer
x 4 rails
.
This is 1,312,000 pounds per kilometer. Converted to metric
tons, it is 596.4 MT per kilometer - just for the rails. Counting
the towers needed to suspend the power lines and the contact bars,
it will require roughly 750 MT per kilometer. What about ties?
Ties may not be necessary because the compressive strength of the
lunar surface is much higher than that of the earth. Thus we have
not included any allowance for ties. In any case it matters little
because we will have an infinite supply of iron. Our little railroad
will be 900 to 1000 kilometers long.
The power to run this electrified railroad will come from solar
panels mounted overhead on the cross beams which support the contact
bars.
8.3 Construction of the main electromagnetic launcher The main electromagnetic projectile launcher will be built on
tracks so that it can be rotated between each launch. This is
necessary because of the orbital and rotational motions of the
earth and moon. The earth's orbital velocity around the sun is
about 29.8 kilometers per second, while the moon's orbital velocity
around the earth is about 1.02 kilometers per second. The rotational
period of the moon is 27.322 days. This corresponds to 13.176
degrees per day or 0.0001525 degrees per second. This means that
in the two minutes between the launching of two projectiles, the
moon will move around the earth by about 122.4 kilometers and the
angle that the EMPL is pointing will change by about 0.0183 degrees
if no compensation is made. This will cause an error in the
direction in which the projectiles are going. Of course the
projectiles will carry propellant to allow them to change course,
but we must try to minimize the course corrections they must make.
The pointing error due to the motion around the sun is much smaller,
amounting to 0.9856 degrees per day or about 0.00137 degrees between
shots two minutes apart. Perhaps the most obvious problem is the
fact that it will take days to launch all the projectiles. During
that time the moon will orbit through as much as 90 degrees of its
path around the earth. If the EMPL could not be rotated, then we
couldn't keep it pointed in the direction of its target way out
in the plane of the ecliptic.
There are some precedents for the building of large structures
which are movable. The ones which come immediately to mind are
some types of bridges and in the field of astronomy, some radio
telescopes called "very large arrays" which are mounted on tracks to
permit their accurate movement and placement.
The EMPL will be designed here on earth. The components will be
fabricated on the moon, primarily from iron, titanium, silicon, and
aluminum. The components will be transported via the lunar polar
railroad to the north pole where they will be assembled by a crew
of androids.
8.4 The cost of the primary EMPL Estimating the cost of this EMPL is complicated by three factors which we are not accustomed to here on earth: (1) lunar resources, including unlimited electric power, will be free, (2) the exact ratio of human labor hours to lunar android labor hours is not known, and (3) the cumulative effects of artificial intelligence may, and hopefully will, greatly reduce the number of human labor hours needed. Since the resources are free, the cost of each component will be in direct proportion to the number of human labor hours needed to manufacture it. The more intelligent our androids are, the less everything will cost. Suppose that we decide to build an EMPL that is 10 kilometers long. Then we can make a preliminary estimate based on Sandia's cost estimates [107, p.168-9]. Table 8.4-1 Primary EMPL Costs Sandia Proposed Item Cost ($ M) Times Cost ($ M) Project office 115 1 115 Research & development 410 0 0 Facilities 129 1 129 Launcher system 170 10 1700 Energy storage system 327.8 10 3278 Launch package 413.2 1 413.2 Launcher support systems 5.4 10? 54 Control & monitoring systems 84 1? 84 Installation and testing 12.4 10 124 Operating costs for 7 years 350 1 350 ---- ---- Total 2016.8 6247.2 If you check the previous cost estimate (section 4.4) you will see that we have deleted nearly $400 million from the Project office budget and have given it a multiplier of only one. Why? Because the primary EMPL will just be a larger copy of the earth-to-moon EMPL which has (we hope) by now already been built. Therefore, they will need no more "incremental engineering" (budgeted at $386 million) [107, p.168] and by this time they should know how to run the project. The value of the facility here on earth would be about $6 billion but its construction cost on the moon is unclear. 8.5 Power for the launcher In order to launch one metric ton projectiles at 20 kilometers
per second every two minutes, we need about 2500 megawatts of
power (see section 6.4). That is a lot a power! Fortunately, we
will have about 10 years to provide this power. Nuclear power,
solar photovoltaic power, and solar thermal power are the three
best options available.
Ten years should be sufficient time to build enough solar
panels to run it entirely from sunlight. Normal solar radiation is
1400 watts per square meter. So, the power available from one
square kilometer of photovoltaic solar arrays at 10% efficiency
would be:
140 * 1000 * 1000 = 140 megawatts per square kilometer
So, 17.86 square kilometers would provide 2500 megawatts. This
corresponds to about 6.9 square miles. Remember that all along the
electrified railroad from the initial base to the polar base we
will have mounted photovoltaic arrays overhead on the cross beams
which carry the electric power. How many kilometers of panels 20
meters wide would be required to produce 2500 megawatts?
17.86 square kilometers / 20 meters = 893 kilometers
This means that by simply covering the railroad with solar
arrays, we can generate enough power to run the polar EMPL -
provided that the transmission lines are superconducting so that
there will be no transmission losses.
An estimate of the solar panel manufacturing rate necessary to
satisfy this demand can be calculated in a similar manner. There
are about 31.5 million seconds in a year or 315 million seconds in
10 years. Therefore, a single machine which produced one square
meter every 17.64 seconds (or faster) could do the job. We expect
that there will be many solar panel manufacturing machines, not
just one, although we will begin with just one.
Nuclear power is the other alternative available to us. As was
mentioned before, Brookhaven National Laboratory has built a gas
core particle bed reactor that can produce 200Mw from a 300kg 1.0
by 0.56 meter package [72, p.302]. Presumably, this is thermal,
not electrical power, so there will be a major loss during
conversion. But clearly sufficient units could be built to satisfy
this requirement. These units could be built on the moon from
lunar materials with the possible exception of the fuel pellets.
The pellets would be thrown to the moon with the earth-to-moon
EMPL. They would land on the lunar slide lander with little
danger, almost no propellant, and at low cost. Some studies have
already been done concerning the use of an EMPL to launch nuclear
materials - see for example [SM 2, p.305].
8.6 Perturbations of the orbit of the moon The launching of thousands of projectiles from the north pole
of the moon will have a completely negligible effect upon the
motion of the moon. According to Paul Spudis [3, p.49], the moon
is receding from the earth at about 3 centimeters per year. That
is about 0.00000000095 or 0.95e-9 meters per second.
If we launched 3000 one metric ton projectiles, ALL IN THE
SAME DIRECTION, then the momentum would be:
Momentum = 3000 MT * 20 km/second = 6.0e+10 kg meters/second
The velocity change of the moon would be:
Velocity change = 6.0e+10 / 7.35e+22 = 0.816e-12 meters/second
where 7.35e+22 kg is the mass of the moon.
Clearly, this is negligibly small. Furthermore, we will be
launching the projectiles in thousands of different directions, so
that the overall effect will nearly cancel out.
Of more concern are the perturbations of Phobos due to
activities there. The mass of Phobos is only about 1.08e+16
kilograms or about 0.000000147 of the mass of the moon.
The velocity change of Phobos would be:
Velocity change = 6.0e+10 / 1.08e+16 = 5.555e-6 meters/second
Here too however, the projectiles will be launched in many
different directions so that the overall effect will be signifi-
cantly smaller.
8.7 Timeline The following time estimates are based on the assumed
existence of the earth-to-moon EMPL. It is badly needed to deliver
materials to the moon cheaply.
We estimate that by laying 500 meters of double track per day
for five years, we could build an electrified railroad from the
first lunar base north to the north pole of the moon. This
railroad would be constructed by two large automatic machines (one
to prepare the roadbed and the other to lay the rails) and a small
number of androids controlled from earth. It will require a
significant but "low tech" manufacturing facility at the first
lunar base to make the rails and other components.
The primary EMPL, as described in sections 6.4 and 8.3, would
be constructed at or near the north pole over a period of about
five years subsequent to the completion of the railroad to the
site. This will require a significant crew of androids at the site
and a significant manufacturing capability at the first lunar base
because the components of the EMPL will be more complex than the
components of the railroad.
8.8 Political summary 1. The polar lunar base is needed for the placement of the
primary EMPL because of its unique location. Only the poles of the
moon remain fixed relative to the distant stars during the
rotation of the moon around the earth. Therefore, only those two
places are suitable for the primary EMPL, the key to the momentum
transfer propulsion system.
2. In order to build a polar lunar base it will be necessary
to build an electrified railroad from the first lunar base north
to the north pole of the moon. There will be plenty of iron
available from the maria (about 12% of which is iron) to
accomplish this. This project is expected to take about 5 years -
beginning about a year after the establishment of the first lunar
base.
3. The primary EMPL, as described in sections 6.4 and 8.3,
will be constructed at or near the north pole over a period of
about five years subsequent to the completion of the railroad to
the site. This facility will provide the momentum which will move
our spaceships to Mars or Jupiter or elsewhere.
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