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10.0 Phobos and Deimos

       Phobos and Deimos are the two satellites of Mars.  Phobos
   is the larger of the two and its orbit is closer to Mars than
   Deimos' orbit.   What do we know about them?  Not much.  Both
   are believed to be captured asteroids.  The following data were
   obtained from various sources as indicated.
*  Phobos (the closer and larger)
   Datum                      Value      Units       Source
   Mass                       1.08e+16   kg         [3, p.290]
   Mean density               1.95       g/    (1)
   Equivalent radius         10.975      km          author
   Surface gravity            5.98e-3    m/sec/sec   author
   Escape velocity           11.46       m/sec       author
   Mean orbital velocity      2.14       km/sec      author
   Sidereal rotation period   7.65       hours      [17, p.408]
   Sidereal orbital period    7.65       hours        "
   Distance from surface      5984       km           "
   Mean distance from Mars    9380       km         [17, p.95]
   Inclination to equator     0.01       degrees      "
   Size                       20x21x18   km           "
   Orbital eccentricity       0.015                   "
      (1) - Ad Astra, May '90, p.5.
   Datum                      Value      Units       Source
   Mass                       1.8e+15    kg         [3, p.290]
   Mean density               1.7        g/     "
   Equivalent radius          6.323      km          author
   Surface gravity            3.00e-3    m/sec/sec   author
   Escape velocity            6.163      m/sec       author
   Mean orbital velocity      1.35       km/sec      author
   Sidereal rotation period   30.3       hours      [17, p.408]
   Sidereal orbital period    30.3       hours        "
   Distance from surface      20060      km           "
   Mean distance from Mars    23460      km         [17, p.95]
   Inclination to equator     0.92       degrees      "
   Size                       16x12x10   km           "
   Orbital eccentricity       <0.001                  "
       Although Mariner 4 (US) was the first spacecraft to fly by
   Mars, Mariner 9 (US) was the first spacecraft to photograph Phobos and
   Deimos late in 1971.  The US sent two spacecraft called Viking 1 and
   Viking 2 to Mars late in 1975.  A very good account of the Viking
   missions is given in "Solar System Log" by Andrew Wilson [Ref 21,
   p.88-93].  Phobos and Deimos are in nearly circular orbits above
   Mars' equator.  Both satellites are locked in orbit so that the
   same side of each constantly faces Mars.  This makes their rotational
   period equal to their orbital period.  Both are very dark.  They
   reflect only 3-5% of the sun's light [40, p.167].  Spectroscopic
   studies by the Viking spacecraft revealed that their composition
   is similar to carbonaceous chondrites [31, p.149].  Perhaps the
   most important piece of information we have is that their densities
   are less than 2 grams per cubic centimeter.  This is very low and
   strongly indicates that water is present in large quantities.  It
   is difficult to imagine what they could contain if not water - unless
   perhaps they are filled with pockets of gas.   The following table
   shows the required percentage of ice necessary to produce the
   observed densities of Phobos (1.95) and Deimos (1.7) assuming various
   given densities for the remainder of the body.
*  Table 10.0-1  Percent of ice on Phobos and Deimos
   Non-water density   Percent ice
     (gm/cc)           Phobos     Deimos
       2.0               4          27
       2.25             22          40
       2.5              34          49
       2.75             43          56
       3.0              49          61
       Large amounts of ice are also believed to be present on Ganymede
   and Callisto, two satellites of Jupiter.  They both have densities
   which are less than 2 grams per cubic centimeter and both are
   estimated to consist of more than 60% water ice by John
   Lewis and Mark Lupo [3, p.172].
       The Soviet Union sent two probes to Mars in 1988 called
   Phobos 1 and Phobos 2.  Sadly, contact with Phobos 1 was lost within
   a month of launch.  Phobos 2 continued on to Mars arriving in
   February of 1989.  It orbited Mars from February 8 to March 25,1989
   [AA 5, p.5].  A French made near-infrared imaging
   spectrometer (IMS) studied both Mars and Phobos.  "Phobos was found
   to have nearly no water and low surface hydration [chemically bound
   water], reported Y. Langevin of the Institut d'Astrophysique
   Spaciale, even in the interiors of the craters" [AA 5, p.5].
   Contact with Phobos 2 was lost too.
       This lack of evidence of water should not be taken as too
   discouraging because it doesn't change the density.  In fact when
   you consider that the surface of the moon is devoid
   of water, you might expect the surfaces of Phobos and Deimos to
   show no water.  The conclusion is that we will have to dig into
   Phobos to find the water.
   10.1  Asteroids
        Asteroids are known primarily as a group of planetoids
   or planetesimals which orbit the sun between Mars and Jupiter,
   but there are also other groups of asteroids.  There are three
   groups of near earth asteroids.  They are called the Atens, the
   Apollos, and the Amors.  The Atens orbit inside the earth's
   orbit most of the time and thus take less than a year for each
   revolution around the sun.  The Apollos have orbits which cross
   the earth's orbit and the Amors have orbits which vary from
   1.017 AU to 1.3 AU, which is basically the region between the
   orbits of earth and Mars.
       The number of such asteroids is not well known but the
   following estimates were developed by Gene Shoemaker of the USGS.
*  Table 10.1-1  Near-Earth Asteroids
                  Delta V < 6 km/sec
   Class    Known  Est. number  Est. number  Est. number  Est. number
            10/84  dia > 1km    dia > .1km   dia > 1km    dia > .1km
   Aten       5    100+/-40       30,000        20          6,000
   Apollo    37    700+/-300     200,000       140         40,000
   Amor      22    500+/-200     150,000       100         30,000
   totals    64   1300+/-540     380,000       260         76,000
   Source: E.M. Shoemaker, Ann. Rev. Earth Planet. Sci. 1983, 11:461.
           as cited in [14, p.246].
       Since the Apollo asteroids cross the earth's orbit there is
   always the potential of a collision with the earth.  On April 10,
   1972 a house sized asteroid hit the atmosphere over Idaho but
   skipped off and back into space [38, p.105].  Had it hit the
   ground, perhaps somewhere in Alberta, it would have caused a great
   deal of damage.  For a more detailed account see "A Meteorite that
   Missed the Earth", by L. Jacchia in Sky and Telescope 48(1974), p.4.
       Some of these asteroids can be reached more easily than can
   the moon.  Lewis and Lewis give the following delta velocities
   to a few selected Apollo asteroids.  (It takes a delta velocity
   of about 6000 m/s to go from LEO to the surface of the moon.)
*  Table 10.1-2  Delta velocities of Apollo asteroids (from LEO)
   Asteroid    dv out   flight time   dv back  flight time
                m/s       days         m/s       days
   1982 DB     4450       210           60       480
   1982 XB     5300       220          220       470
   1982 HR     5300       180          260       320
   1980 AA     5400       690          360       450
   Anteros     5270       390          390       290
   Source: Lewis and Lewis [14, p.169].
       There are other groups of asteroids one of which is
   called the Trojans.  These are groups of asteroids which orbit
   the sun in the same orbit as the planet Jupiter, but at the L4
   and L5 Lagrangian points of the sun-Jupiter system.  Astronomers
   Dunbar and Helin have searched for earth Trojans from the
   Palomar observatory and have determined that no asteroids
   larger than about 25 kilometers exist at the L4 or L5 points
   of the sun-earth system [48, p.76].
       In 1977 Charles Kowal discovered an asteroid between
   Saturn and Uranus which was named Chiron [36, p.133].  It is
   likely that this is merely the first of many to be discovered
   in this region of the solar system.  They are so distant
   and so small and so dark that they are almost impossible
   to detect from here on earth.
       It seems likely that asteroids are present in significant
   numbers beyond the orbit of Jupiter and that space travelers
   will need to be very observant so as to avoid any collisions.
       In order to determine the composition of asteroids, their
   spectra are compared to the spectra of known groups of meteorites.
   Meteorites are divided into various groups by their composition.
   The most common ones are called ordinary chondrites.  Other groups
   are carbonaceous chondrites, achondrites, irons, and stoney irons.
   The breakdown of these groups by frequency percentage is as
   follows [38, p.97].
*  Table 10.1-3  Meteorite class distribution
   Meteorite class       Percentage (approx)
   carbonaceous chondrite         5
   ordinary chondrite            81
   achondrite                     9
   stoney iron                    1
   iron                           4
       Perhaps the most important of these groups is the carbonaceous
   chondrites.  The reason is that they contain up to 22% water
   [38, p.102] although they average about 10% water [14, p.229].
   Water is extremely important because of its ability to sustain
   life and its potential is a rocket propellant.  These asteroids
   also contain carbon - as their name indicates.  Carbonaceous
   chondrite meteorites contain 3-5% carbon [114, p.31].
       "The chemical composition of chondritic meteorites closely
   matches that of the sun, suggesting that such meteorites represent
   primitive materials that have survived without significant change
   since the formation of the solar system [34, p.42]."
       The class called ordinary chondrites is further subdivided
   into three subgroups depending upon the concentration of iron
   in the meteorite: H - high iron, L - low iron, and LL - very low
   iron.  These meteorites and corresponding asteroids are of
   special interest because of their high concentrations of the
   platinum group metals.  Lewis and Lewis give the following table
   of concentrations of metals in ordinary chondrites [14, p.257].
*  Table 10.1-4  Concentrations of Platinum group metals in ppm
                          chondrite sub-class
   Element     Symbol    LL       L        H
   Ruthenium     Ru      12       8        5.7
   Rhenium       Re       1       0.6      0.5
   Osmium        Os      10       6        4.7
   Iridium       Ir      10       5        4.8
   Platinum      Pt      21       13       11
   total                 54       32.6     26.7
       Consider a one kilometer diameter asteroid.  At a density of
   four grams per cubic centimeter it would weigh about 2 billion
   metric tons.   The metal percentages in ordinary chondrites
   are: H = 16+/-3; L = 9+/-2; LL = 4+/-1 [14, p.257].  Thus this
   sample asteroid would have about 200,000,000 tons of metal.  The
   platinum group metals would weigh about 6520 tons.  Since these
   metals are worth at least $10,000 per kilogram or $10 million
   per metric ton, the total value would be about $65 billion.
   10.2  Visiting Phobos
       Why go to Phobos?  There are at least two very good answers.
   The first is to establish a refueling station there.   If we can
   produce fuel on Phobos, we won't need to carry fuel for the return
   trip. (If the spaceship uses our momentum exchange propulsion system,
   then the fuel produced on Phobos will be used to land on and take
   off from Mars itself.)
       The second answer is that Phobos is a fantastic platform from
   which to observe Mars.  Many people will want to do a detailed survey
   of Mars in order to select optimal landing sites.  From Phobos we
   should be able to see from the equator up to nearly 69 degrees North
   or South latitude.  That should be sufficient to pick out good
   landing sites.
       The velocity change required to go from low earth orbit
   (LEO) to Phobos is about 4.37 kilometers per second [LB1, p.812].
   The velocity change to return to LEO is about 3.54 kilometers
   per second [LB1, p.812].  Thus the velocity change of the
   whole trip from LEO to Phobos and back to LEO is about 7.91
   kilometers per second.  To calculate the mass ratio we use
   equation 6.1-1 again.  First, we will use a propulsion system with
   a specific impulse of 475 seconds (LOX-LH2).  This yields:
*      M = m * exp( dv/g*Isp )         6.1-1
       M = m * exp( 7910/9.8*475 )      or
       M = m * exp( 1.69925 )           or
       M = m * 5.46983
       The mass ratio is 5.4698.  Now we consider using a
   nuclear thermal rocket with a specific impulse of 950 seconds
   to do the same job.  Plugging the numbers in we get:
*      M = m * exp( 7910/9.8*950 )      or
       M = m * exp( 0.849624 )          or
       M = m * 2.33877
       The mass ratio is the square root of 5.4698 or 2.33877.  Now
   consider how much fuel we could save if we could refuel at Phobos.
   The following table shows the mass ratios and the fuel requirements
   for outbound, inbound, and round trip journeys.  The mass ratios
   were calculated using equation 6.1-1 and the fuel ratios were
   calculated using equation 6.1-5 with the tanks and engines estimated
   to be 8% of the weight of the fuel.
*  Table 10.2-1  Phobos mass ratios and fuel requirements
   Delta velocity            Mass ratios        Fuel ratio
   (m/s)                  Isp=475  Isp=950   Isp=475  Isp=950
   4370   (outbound)      2.55685  1.59901    1.778    0.629
   3540   (inbound)       2.13929  1.46263    1.254    0.480
   7910   (round trip)    5.46983  2.33877    6.958    1.499
       The fuel savings for the LOX-LH2 propulsion system would
   be 6.958 - 1.778 = 5.18 tons per payload ton or 74.4% because
   the fuel for the return portion of the trip would come from
   Phobos.  Actually it probably wouldn't be quite that good because
   a multi-stage rocket would probably be used which would need
   less than 6.958 tons of propellant per payload ton.
   The savings for the NTP (Isp=950) system would be 1.499 - 0.629 =
   0.87 tons per payload ton or 58%.  It can also be seen
   from this table that the NTP rocket only needs 35% of the fuel
   that the LOX-LH2 rocket needs for the outbound leg of the journey.
   Thus the fuel cost for the NTP rocket would be about 35% of the
   cost for the LOX-LH2 rocket.
   10.3  The first spaceship to Phobos
       As in the first lunar base, the most important question
   is whether there will be humans on board.  And again the answer
   should be no!  Why not?  There are many good reasons such as:
*  1. Humans need food, water, air, protection from radiation,
      waste facilities, etc. - but androids don't.
   2. In order to sell high priced seats for the first trip to
      Mars, it must actually be the first manned trip there;
      therefore the Phobos trip cannot be manned.
   3. Checkout of the momentum exchange propulsion system
      could be very dangerous and is better done with no
      people on board.
   4. Deployment of the fuel production facility on Phobos
      can be done by the androids - humans are not needed.
   5. Deployment of Mars observation equipment on Phobos or
      the spaceship can be done by androids as well.
   The main components of the Phobos spaceship will probably be:
*      1. Electromagnetic projectile launcher
       2. Projectiles and projectile racks
       3. Nuclear power systems
       4. Hydroponic food production facilities (unassembled)
       5. Crew's quarters (unassembled)
       6. Androids
       7. Fuel production facilities
       8. Mars landing systems (rocket engines, fuel tanks, etc.)
       9. Mars observation equipment
       The following paragraphs will briefly review each of the
   main components.
   10.3.1  The EMPL
       This EMPL will be very much the same as the others mentioned
   previously.  The internal diameter will be about one meter and the
   length will be about 6 kilometers.  As mentioned before, the longer
   the EMPL the lower the power necessary to drive it because the
   projectile takes longer to pass through the launcher.  This also
   means less acceleration and less stress on the structure.
       The following table shows the expected velocity change in the
   spaceship due to each projectile (whose mass is one metric ton)
   for several different projectile velocities and several different
   spaceship masses.
*  Table 10.3.1-1   Spaceship velocity change per projectile
   Projectile        Spaceship velocity change ( m/s )
   velocity      ship mass =4000   4500   5000   5500   6000(MT)
     (km/s)                ----------------------------------
       10                   2.50   2.22   2.00   1.82   1.67
       20                   5.00   4.44   4.00   3.64   3.33
       30                   7.50   6.67   6.00   5.45   5.00
       40                  10.00   8.89   8.00   7.27   6.67
       50                  12.50  11.11  10.00   9.09   8.33
       If the mass of the projectile were two metric tons, then all
   the entries in the table would simply double, and so on.
   10.3.2  Projectiles and projectile racks
       The heaviest part of the cargo of the Phobos spaceship
   will be its projectiles.  They will be used not only to maneuver
   this spaceship, but also to stop and start the manned spaceship
   arriving a few months later.  As mentioned in section 6.4.2,
   stopping and starting the manned spaceship will require several
   thousand projectiles.
       In order to limit the structural elements needed to store
   the projectiles, they will simply be stored in tubes along the
   length of the EMPL. The tubes will be open to the vacuum of space
   because the projectiles are build to survive in space.  All of
   the handling of the projectiles will be automatic.
   10.3.3  Nuclear power systems
       There will be several separate nuclear power systems - perhaps
   as many as 15.  During the arrival and positioning at Mars, they
   will all work together to fire the projectiles with as high a
   velocity as possible to reduce the number of projectiles expended
   for that operation.  The purpose is to save projectiles for
   the arrival of the manned spaceship.
       Each of the Mars landing sites will require its own nuclear
   power supply.  Thus if we plan to have 10 sites, we will need 10
   power systems, but they can small SP-100 systems.  Most of the
   power must remain with the spaceship to drive the EMPL.
       It is safe to assume that the power systems which drive the
   EMPL can also run the fuel production facilities which will be
   deployed on Phobos (or Deimos), but the initial exploration of
   Phobos (and/or Deimos) must have an independent power supply.
       The number of additional power systems needed will depend on
   how many backups are deemed required and how many probes we wish
   to deploy.
   10.3.4  Hydroponic food production facilities (unassembled)
       The hydroponic food production facilities will be carried
   on board the spaceship, disassembled in containers.  When sites
   on Mars have been selected and rocket propellant is available,
   these units will be deployed to the surface along with crew's
   quarters, a power system, and at least one android to set them up.
   10.3.5  Crew's quarters (unassembled)
       The crew's quarters will also be carried on board the spaceship
   disassembled in containers.  When sites on Mars have been selected
   and rocket propellant is available, these units will be deployed to
   the surface along with the hydroponic food production facilities,
   a power system, and at least one android to set them up.
   10.3.6  Androids
       The androids will be our eyes and brains on board the Phobos
   spaceship.  This requires a level of artificial intelligence quite
   a bit advanced from the current technology.  The development of
   that technology will provide thousands of jobs over the next few
   years.  Many groups may view the androids as threats to their jobs
   and indeed if they are in manufacturing - they are!  However, just
   as the computer revolution created more jobs than it destroyed, so
   will the androids.
   10.3.7  Fuel production facilities
       The number of fuel production facilities we need really depends
   on how widely the landing sites are distributed.  If they are more
   than a few miles apart, we will need fuel production facilities
   at all the landing sites.  The type of rocket fuel produced by the
   facilities on Mars may be different than that produced by the
   facilities on Phobos.  In the latter case we are hoping to use
   water as the primary fuel.  On Mars it may be easier to use carbon
   dioxide from the air to produce fuel.  Water may also be available
   in sufficient quantity on Mars either in permafrost under the
   surface or in the water of hydration in the rocks and soil.  If
   a polar site is chosen (which is very unlikely), then water ice may
   be available very easily at that site.
       Since the failure to produce fuel on Phobos (or Deimos) means
   we can't establish bases on Mars, there should be at least one backup
   fuel production facility for use on Phobos.  In addition, both these
   facilities must have the capability to produce some different
   type of fuel if water isn't available.  This fallback position
   could be eliminated if we were prepared to send a separate small
   mission to Phobos to provide this capability if it were needed.
   10.3.8  Mars landing systems (rocket engines, fuel tanks, etc.)
       Since aerobrakes or heat shields are useless to get off Mars,
   there is no reason to have them at all.  We must use ordinary
   rockets to get off Mars and those same rockets can be used to
   land there in the first place.  This implies bringing them down
   from Phobos together with their fuel tanks, guidance systems, and
   so on.
       Obviously the minimum number of such systems is one, but this
   doesn't seem prudent.  Suppose instead that we have one landing
   system for each landing site or 10 systems.  We expect that each
   system (without fuel) will weigh 3-5 tons.  50 tons may be less
   than 1% of the mass of the Phobos spaceship when it leaves earth.
       We also need landing systems for the human crew who will come
   later.  One possibility is to have each Martian fuel production
   facility produce fuel and use that fuel to send the rockets back
   to Phobos.  They could then wait there and be used again to take
   the crew down to the sites.  They could then be used a fourth time
   to return the crews to Phobos.  Another option is to have a second
   set of landing systems for the crews.
       Faced with choosing between the two, I would pick the first
   choice.  The reason is that for each landing system that makes
   it back to Phobos, we could be sure that the entire fuel cycle
   was working without endangering any crew members.  In addition
   we would save the weight and cost of the second set of landing
   10.3.9  Mars observation equipment
       By the time our spaceship reaches Mars, other satellites
   such as the Mars Observer may have already completed much of the
   work necessary to select appropriate landing sites.  However,
   we expect that the androids will deploy some equipment to observe
   Mars and to help in site selection.  Equipment needed to communicate
   with the various landing sites may need to be deployed too.
   10.4  Outline of the Phobos mission
       The primary purpose of the Phobos mission is to set up all
   the infrastructure required to support a major manned mission
   to Mars.  The mission will consist of the following milestones.
       1. Assembly of the spaceship in high earth orbit.
       2. Departure from earth's orbit on a Hohmann trajectory
       3. Checkout of projectile catching during coast phase
       4. Insertion into Martian orbit
       5. Closure on Phobos
       6. Deployment of Phobos investigator
       7. Deployment of Deimos investigator if needed
       8. Closure on Deimos if needed
       9. Landing on Phobos (Deimos)
       10. Deployment of Mars observation equipment
       11. Deployment of fuel production facilities
       12. Assembly of Martian landing units
       13. Selection of landing sites
       14. Deployment of landing units to surface of Mars
       15. Deployment of science experiments and mini-rovers
       16. Deployment of Mars bases' fuel production facilities
       17. Assembly of bases' hydroponic food production facilities
       18. Activation of food production facilities as appropriate
       19. Assembly of bases' crew's quarters
       20. Return of rockets to mother ship
        10.5 Timeline
          Design  and  development  of  the components of the spaceship
     could  begin  at  any time, but actual assembly cannot begin until
     the  lunar  polar EMPL is operational. This will be about 15 years
     after  the beginning of the project. If the earth-to-moon EMPL has
     been  built,  it  could  contribute  to the assembly of the Phobos
     ship, perhaps at an earlier time.
          Construction  of the Phobos spaceship is expected to take two
     to  three  years.  Launch  windows to Mars occur about every 778.7
     days,  so  you  can  not  just  leave  anytime you want to. As was
     mentioned  in  section  6.6,  the Hohmann transfer time to Mars is
     about  257  days.  So, that will be the approximate travel time of
     the Phobos ship.
          There  is  no  need to rush to select landing sites. We could
     allow,  perhaps,  as  much  as 3 years to pick them out. Once they
     have  been  selected, the fuel can be produced and loaded into the
     tanks  of the landers. Deployment of the crew support modules (see
     steps 14 - 19 above) will probably take only a couple of months.

     10.6 Financing
         Estimating the cost of the Phobos spaceship is  complicated by
     several factors which we are not accustomed to here on earth:  (1)
     lunar  resources,  including electric power, will be free, (2) the
     exact  ratio  of human labor hours to lunar android labor hours is
     not  known,  (3) the cumulative effects of artificial intelligence
     will  hopefully  greatly  reduce  the  number of human labor hours
     needed,  (4)  the  difficulty  of  assembling  the  ship  in   the
     microgravity  environment  of  L4  will  surely increase the labor
     required  and  hence  the cost, and (5) the amount of nuclear fuel
     (and  perhaps  other  components)  which will have to be sent from
     earth is difficult to estimate.
          Since lunar resources are free, the cost of each component of
     lunar  origin  will be in direct proportion to the number of human
     labor  hours  needed  to  manufacture  it.  Therefore,  the   more
     intelligent our androids are, the less everything will cost.
          By this time in the project, we expect to be selling helium-3
     to customers on earth. Part of those funds will be used to finance
     the cost of the Phobos spaceship. In the eventuality that helium-3
     is  not  providing  any income, we will rely on the profits of the
     hydroponics and android industries to finance the Phobos ship.