MMM Classics Year 10: MMM #s 91-100 - Moon Society

There are two additional benefit of this system: the introduction of
variety (the same variety we experience by important dates falling
on different days of the week, year after year); and “fairness”, if
you will. By options A and B, some settlements would always
experience sunrise and sunset on their weekends, (some on 3 day
weekends!) others somewhere during the week. As industrial
operations have to shift gear at these two times, the timing will
come with different inconveniences during weekends than during
the week.
The Lunan settlers themselves must consider the merits of
the various proposals above and choose one, or come up
with something different. Please feel free to “vote” for the
solution you like best, or to propose another.
Whatever calendar arrangement settlers eventually
choose, it is sure to reverberate throughout Lunan culture,
adding yet another layer of distinctive and characteristic difference
from the variegated “family” of cultures on Earth.
Physical Calendars
Lunar calendars need to be “perpetual” or recyclable.
Options A and B allow a simple two sunth calendar (the 29, 30
date rotation) to be used indefinitely. A movable accent bar
over a list of sunths on the side or above would be all that was
needed to make it complete. If the day / date squares were
reversible tiles, one side the photo-negative of the other, then
each calendar could be customized easily to the local sunrise /
sunset (dayspan / nightspan) pattern. Materials available are
glass, ceramic, and metal. Recyclable organic art du jour could
take the place of the “scene of the month” on our own paper
calendars. It will be interesting.
Lunar Al minum and O ygen
Propell ants to Support
Lunar & Planetary Fl ght
by Larry Jay Friesen
[A companion paper, “Lagrange Point Staging for Lunar
and Planetary Flight” appeared in last month’s MMM.]
Introduction
It will greatly ease the long-term economics of supporting
a lunar base to produce propellants at the Moon. These
would be used for flights between the lunar surface and any
near-Moon space stations, and from there back to Earth. It has
even been proposed to supply lunar propellants to low Earth
orbit (LEO) to be used for Moonbound ships. This will come as
no surprise to long-term students of lunar base proposals. The
major reason is that traffic models for lunar base show that by
far the largest budget item in mass being moved around
between the Earth and Moon is rocket propellant.
Lunar propellant could also be used to launch interplanetary
space flights. This would be especially advantageous
if those flights were launched from a near Moon staging base,
such as the L1 Lagrange point space station proposed in the
preceding article [MMM #94, April ‘96]. I am going to argue
that the combination of an L1 base and lunar propellants would
make a powerfully synergistic combination for supporting both
lunar and interplanetary ventures.
The most frequently proposed lunar-derived
propellant is liquid oxygen extracted from the oxides and
silicates that make up lunar rocks. This would be burned with
hydrogen provided from Earth. One attraction of this is that the
oxygen/ hydrogen combination provides one of the highest
specific impulse values available from chemical propellants.
Specific impulse is a performance measure for rockets somewhat
analogous to miles per gallon. It is often given in units of
seconds, meaning the number of seconds that one pound of
propellant could produce one pound of thrust, before it is
consumed. The few combinations known that produce higher
specific impulse: (a) produce only slightly higher, not grossly
higher, specific impulse; (b) are composed of more expensive
materials; and (c) are more corrosive and difficult to handle.
One disadvantage of this, if one is trying to minimize
mass lifted from Earth, is that the hydrogen will probably still
have to be supplied from Earth. Hydrogen is extremely rare on
the Moon [Ed. in general. We can hope that Lunar Prospector
will confirm indirect indications from the Clementine mission
that there is economically significant ice in the permashade
areas at the lunar south pole. We should know by early ‘98,
latest.] A minute amount is found implanted in lunar soil by the
solar wind. It is conceivable that this can be extracted in
amounts adequate for life support. However, the amounts of
material that would have to be processed to extract enough
hydrogen to support a reasonable amount of traffic to and from
the Moon are far larger than I, for one, would find attractive.
Other propellant combinations based on lunar materials
have been proposed. Silanes would stretch the terrestrial
hydrogen by combining it with lunar silicon to make compounds
analogous to methane and ethane. This would increase
the proportion of the [total] propellant [combination] supplied
from the Moon. However, it would also reduce specific
impulse. Specific impulses of silanes burned with oxygen are
roughly similar to those of hydrocarbons burned with oxygen,
or in the range of 300+ seconds rather than the 400+ seconds of
hydrogen and oxygen.
Advantages of Lunar Oxygen & Aluminum Together
A particularly appealing propellant combination is
lunar oxygen plus lunar metals, especially lunar oxygen and
lunar aluminum. Aluminum and oxygen alone will provide a
specific impulse somewhat lower than most hydrocarbons.
Brower et al. expect a value of 285 seconds [1]. However, this
should be quite adequate for lunar landing, lunar liftoff, and
departure for Earth from an L1 station using a lunar swingby
trajectory. Lunar escape velocity is only 2.4 km/sec, so we
don’t need an enormous specific impulse for operations in the
lunar vicinity. A big advantage of this propellant combination
is that no terrestrial material at all is required. Keeping down
the mass we have to lift from Earth is likely to be a major
factor in keeping down the operational costs of our missions.
One means of enhancing the performance of lunar
oxygen and aluminum could be to combine them with terrestrial
hydrogen in a tripropellant engine. Andrew Hall Cutler [2]
estimates that [with] an H:O:Al mass ratio of 1:3:3, such an
engine would have a specific impulse exceeding 400 seconds -
only slightly poorer than hydrogen and oxygen alone. This
ratio also manages to decrease slightly the proportion of
Moon Miners’ Manifesto Classics - Year 10 - Republished January 2006 - Page 52