russ
|
|
"Intro to Mars Direct" lecture from Bob Zubrin
| 
Dec 10 04:27 UTC 1998 |
Mars: America's New Frontier
Robert Zubrin
The time has come for America to set itself a bold new goal in space.
The recent celebrations of the 25th anniversary of the Apollo Moon
landings have reminded us of what we as a nation were once able to
accomplish, and by so doing have put the question to us: are we still a
nation of pioneers? Do we choose to make the efforts required to
continue to be the vanguard of human progress, a people of the future;
or will we allow ourselves to be a people of the past, one whose
accomplishments are celebrated not in newspapers, but in museums? There
can be no progress without a goal. The American space program, begun
so brilliantly with Apollo and its associated programs, has spent most
of the subsequent 20 years without a central goal. We need such an
overriding goal to drive our space program forward. At this point of
history, that goal can only be the human exploration and settlement of
Mars.
Some have said that a human mission to Mars is a venture for the far
future, a task for "the next generation." Such a point of view has
absolutely no basis in fact. On the contrary, the United States has in
hand, today, all the technologies required for undertaking an
aggressive, continuing program of human Mars exploration, with the
first piloted mission reaching the Red Planet Mars within a decade. We
do not need to build giant spaceships embodying futuristic technologies
in order to go to Mars. We can reach the Red Planet with relatively
small spacecraft launched directly to Mars by boosters embodying the
same technology that carried astronauts to the Moon more than a
quarter-century ago. The key to success comes from following a travel
light and live off the land strategy that has well-served explorers
over the centuries humanity has wandered and searched the globe.
Going Native: The Fast Track to Mars
Down through history, it has generally been the case that those
explorers and settlers who took the trouble to study the methods of
survival and travel of the wilderness's natives were able to get a lot
farther than those who did not. The reason for this is that indigenous
peoples frequently possessed the best knowledge of how to recognize and
utilize resources present in the wilderness environment.
For example, to the eye of an inhabitant of urban civilization, an
Arctic landscape is desolate, resourceless, and impassable: yet to an
Eskimo it is rich. Thus, during the 19th Century, the British Navy sent
flotillas of steam powered warships, at great expense, to explore the
Canadian arctic for the Northwest Passage. Loaded with coal and
supplies, these expeditions would battle forward against the ice packs
for several years at a time, until shortages would force an about-face
or cause the entire mission to perish.
In contrast, Amundsen, the first westerner to succeed in forcing the
passage, was not afraid to learn from the locals. Operating with an old
sealing boat and a minuscule budget, Amundsen had no choice but to
adopt a live off the land strategy. So he learned the Eskimo way of
Arctic travel - dogsled - which gave him the mobility required to
effectively hunt Caribou. He learned about the anti-scurvey qualities
of Caribou entrails and uncooked blubber, and he learned about the
Eskimo way of building shelters - out of ice. By making intelligent use
of local resources Amundsen not only survived and forced the Northwest
passage on a shoestring, he was even able to explore widely enough to
make some important scientific discoveries, including the fact that
the Earth's magnetic poles move.
Is there a lesson in all of this for space exploration? I think there
is. Now, there are no Martians - yet, but if there are to be, let us
ask ourselves some questions. How will they travel? How will they
survive? Will they import their rocket fuel from Earth? How about their
oxygen?
When on Mars, do as the Martians will do.
To Mars via Dogsled
There have been a large number of concepts advanced for manned Mars
missions that are analogous to the ponderous Royal Navy approach to
arctic exploration cited above. Grand ships are required, hauling out
to Mars all the supplies and propellant that will be needed for the
entire mission. Because such ships are too large to be launched in one
piece, construction on orbit is required, as is long term orbital
storage of cryogenic propellant. Large orbiting facilities are required
to enable both of these operations, and the cost of the whole project
goes out of sight.
However, as in the case of arctic exploration, there is a different way
a Mars mission can be approached, a "dogsled" way if you will, that by
making intelligent use of the resources available in the environment to
be explored, allows the logistical requirements for launching the
mission to be reduced to the point where the endeavor becomes
practical.
This is the spirit of the "Mars Direct" plan. In this plan, no large
interplanetary spaceships are used, and thus no orbiting space bases
are needed to construct and service them. Instead, the astronauts in
their habitat are sent direct to Mars by the upper stage of the same
booster rocket that lifted them to Earth orbit, in just the same way as
the Apollo missions and all unmanned interplanetary probes launched
to-date were flown. While granting the attractiveness of the simplicity
of such a scheme, conventional wisdom would deem it infeasible, as the
mass of propellant and supplies needed for a manned Mars mission is
much too large to be launched in such a way. Conventional wisdom would
be right except for one thing: if done in a clever way, most of the
propellant and supplies needed for the mission do no have to be
launched from Earth at all. They can be found on Mars.
Here's how the Mars Direct plan works. At an early launch opportunity,
for example 2003, a single heavy lift booster with a capability equal
to that of the Saturn V used during the Apollo program is launched off
Cape Canaveral and uses its upper stage to throw a 40 tonne unmanned
payload onto a trajectory to Mars. Arriving at Mars 8 months later, it
uses friction between its aeroshield and Mars' atmosphere to brake
itself into orbit around Mars, and then lands with the help of a
parachute. This payload is the Earth Return Vehicle (ERV), and it flies
out to Mars with its two methane/oxygen driven rocket propulsion stages
unfueled. It also has with it 6 tonnes of liquid hydrogen cargo, a 100
kilowatt nuclear reactor mounted in the back of a methane/oxygen driven
light truck, a small set of compressors and automated chemical
processing unit, and a few small scientific rovers.
As soon as landing is accomplished, the truck is telerobotically driven
a few hundred meters away from the site, and the reactor is deployed to
provide power to the compressors and chemical processing unit. The
hydrogen brought from Earth can be quickly reacted with the Martian
atmosphere, which is 95% carbon dioxide gas (CO2), to produce methane
and water, and this eliminates the need for long term storage of
cryogenic hydrogen on the planet's surface. The methane so produced is
liquefied and stored, while the water is electrolysed to produce
oxygen, which is stored, and hydrogen, which is recycled through the
methanator. Ultimately these two reactions (methanation and water
electrolysis) produce 24 tonnes of methane and 48 tonnes of oxygen.
Since this is not enough oxygen to burn the methane at its optimal
mixture ratio, an additional 36 tonnes of oxygen is produced via direct
dissociation of Martian CO2. The entire process takes 10 months, at the
conclusion of which a total of 108 tonnes of methane/oxygen
bipropellant will have been generated. This represents a leverage of
18:1 of Martian propellant produced compared to the hydrogen brought
from Earth needed to create it. Ninety-six tonnes of the bipropellant
will be used to fuel the ERV, while 12 tonnes are available to support
the use of high powered chemically fueled long range ground vehicles.
Large additional stockpiles of oxygen can also be produced, both for
breathing and for turning into water by combination with hydrogen
brought from Earth. Since water is 89% oxygen (by weight), and since
the larger part of most foodstuffs is water, this greatly reduces the
amount of life support consumables that need to be hauled from Earth.
The propellant production having been successfully completed, in 2005
two more boosters lift off the Cape and throw their 40 tonne payloads
towards Mars. One of the payloads is an unmanned fuel-factory/ERV just
like the one launched in 2003, the other is a habitation module
containing a crew of 4, a mixture of whole food and dehydrated
provisions sufficient for 3 years, and a pressurized methane/oxygen
driven ground rover. On the way out to Mars, artificial gravity can be
provided to the crew by extending a tether between the habitat and the
burnt out booster upper stage, and spinning the assembly. Upon arrival,
the manned craft drops the tether, aero-brakes, and then lands at the
2003 landing site where a fully fueled ERV and fully characterized and
beaconed landing site await it. With the help of such navigational
aids, the crew should be able to land right on the spot; but if the
landing is off course by tens or even hundreds of miles, the crew can
still achieve the surface rendezvous by driving over in their rover; if
they are off by thousands of miles, the second ERV provides a backup.
However assuming the landing and rendezvous at site number 1 is
achieved as planned, the second ERV will land several hundred miles
away to start making propellant for the 2007 mission, which in turn
will fly out with an additional ERV to open up Mars landing site number
3. Thus every other year 2 heavy lift boosters are launched, one to
land a crew, and the other to prepare a site for the next mission, for
an average launch rate of just 1 booster per year to pursue a
continuing program of Mars exploration. This is only about 15% of the
rate that the U.S. currently launches Space Shuttles, and is clearly
affordable. In effect, this dogsled approach removes the manned Mars
mission from the realm of mega-fantasy and reduces it to practice as a
task of comparable difficulty to that faced in launching the Apollo
missions to the Moon.
The crew will stay on the surface for 1.5 years, taking advantage of
the mobility afforded by the high powered chemically driven ground
vehicles to accomplish a great deal of surface exploration. With an 12
tonne surface fuel stockpile, they have the capability for over 14,000
miles worth of traverse before they leave, giving them the kind of
mobility necessary to conduct a serious seach for evidence of past or
present life on Mars - an investigation key to revealing whether lfe is
a phenomenon unique to Earth or general throughout the universe. Since
no-one has been left in orbit, the entire crew will have available to
them the natural gravity and protection against cosmic rays and solar
radiation afforded by the Martian environment, and thus there will not
be the strong driver for a quick return to Earth that plagues
conventional Mars mission plans based upon orbiting mother-ships with
small landing parties. At the conclusion of their stay, the crew
returns to Earth in a direct flight from the Martian surface in the
ERV. As the series of missions progresses, a string of small bases is
left behind on the Martian surface, opening up broad stretches of
territory to human cognizance.
We Can Do It
Such is the basic Mars Direct plan. In 1990, when it was first put
forward, it was viewed as too radical for NASA to consider seriously,
but over the past couple of years with the encouragement of former NASA
Associate Administrator for Exploration Mike Griffin and current NASA
Administrator Dan Goldin, the group at Johnson Space Center in charge
of designing human Mars missions decided to take a good hard look at
it. They produced a detailed study of a Design Reference Mission based
on the Mars Direct plan but scaled up about a factor of 2 in expedition
size compared to the original concept. They then produced a cost
estimate for what a Mars exploration program based upon this expanded
Mars Direct would cost. Their result; $50 billion, with the estimate
produced by the same costing group that assigned a $400 billion price
tag to the traditional cumbersome approach to human Mars exploration
embodied in NASA's 1989 "90 Day Report."
In essence, by taking advantage of the most obvious local resource
available on Mars- its atmosphere- the plan allows us to accomplish a
manned Mars mission with what amounts to a Lunar-class transportation
system. By eliminating any requirement to introduce a new order of
technology and complexity of operations beyond those needed for Lunar
transportation to accomplish piloted Mars missions, the plan can reduce
costs by an order of magnitude and advance the schedule for the human
exploration of Mars by a generation.
Exploring Mars requires no miraculous new technologies, no orbiting
spaceports, and no gigantic interplanetary space cruisers. We can
establish our first small outpost on Mars within a decade. We and not
some future generation can have the eternal honor of being the first
pioneers of this new world for humanity. All that's needed is present
day technology, some 19th century industrial chemistry, and a little
bit of moxie.
|
