9.0 The design of the spaceship |
The spaceship will consist of three major components: (1) the
nuclear power facility, (2) the electromagnetic launcher/catcher
and (3), the crew's quarters. The momentum transfer propulsion
system requires a very stable spaceship so as to avoid being
hit by any of the high speed projectiles. The best way to do
this is to use spin stablization or what is known as the
gyroscopic effect. The entire spaceship will be spun axially
about the length of the EMPL. An incidental benefit of this
action will be the creation of artificial gravity for the crew.
This is extremely important for the health of the crew. First,
it will allow the crew to function fairly normally. This means
that walking, eating, working, etc. will all be pretty normal.
But the hidden benefits will be that the crew will not suffer
from a debilitating loss of strength and muscle mass (including
the heart), and neither will it be necessary to have long
daily exercise programs. Presumably under artificial gravity
the blood will not deteriorate either. And finally, the crew
won't suffer any bone calcium loss.
The crew's quarters will be built in the shape of a ring
surrounding a small part of the length of the EMPL. The rate
of rotation of this ring is of concern because spinning makes
people dizzy. Spin rates of 3 rpm or less do not cause
dizziness [101, p.236]. The magnitude of the artificial gravity
is given by the equation:
* g = v * v / r; 9.0-1 where "v" is the velocity and "r" is the radius of the ring.
.
A simple program was written which produced the following
sample table for a ring rotating at 2 rpm.
* Table 9.0-1
Radius Circumference Artificial Gravity
(m) (m) (mi) (in gees)
216 1357.17 0.843 0.967
219 1376.02 0.855 0.980
222 1394.87 0.867 0.994
225 1413.72 0.879 1.007
228 1432.57 0.890 1.021
231 1451.42 0.902 1.034
The following was the result at 3 rpm. Table 9.0-2
Radius Circumference Artificial Gravity
(m) (m) (mi) (in gees)
90 565.49 0.351 0.906
93 584.34 0.363 0.937
96 603.19 0.375 0.967
99 622.04 0.387 0.997
102 640.88 0.398 1.027
105 659.73 0.410 1.057
.
It seems prudent to build a multi-layered structure for
three reasons: (1) in case of a solar flare (see below) the
crew can retire to the deepest interior for maximum protection,
(2) in case of an exterior skin rupture and the associated
sealing-off of some portion of the ship, it would still be
possible to detour around the effected area, and (3) the more
floors which are also ceilings or vice versa the more efficient
our structure is.
Our major concern is to protect the crew from radiation. Each
year the average person on earth receives a total radiation dose
of about 200 millirads. It is broken down as follows:
* Table 9.0-3
Radiation source Dosage
Natural sources in the body 34 mr/yr
Cosmic rays (on earth) 30 mr/yr
Natural sources in surroundings 48 mr/yr
Medical X-rays 75 mr/yr
Radioactivity from man-made sources 12 mr/yr
Source: [101, p.126]
.
The primary danger in space comes from solar flares. (Galactic
cosmic rays are discussed below.) The sun has an 11-year cycle of
activity and during peak activity (1991 was a peak year) huge solar
flares can erupt at any time. They spew lethal radiation into space
which could kill an unprotected crew. (The Apollo
crews were just lucky that no big flares erupted while they
were in space.) A radiation dose of 450 rads will be fatal
to 50% of the population (LD50 = 450 rads) [101, p.124]. Lethality
increases to 100% at about 650 rads [101, p.124].
The following is typical of solar activity:
* Tabel 9.0-4
Frequency per solar cycle Dosage
1 or 2 5000 rads(fatal)
2 to 5 500-1000 rads(fatal)
20 to 30 50-100 rads
Source: [17, p.479]
.
A secondary worry is the limited danger from galactic cosmic
rays. According to A.E. Nicogossian, the interplanetary radiation
level is 25-36 millirads per day [17, p.479] and the Martian suface
dose is 12.5-18 millirads per day. (The earth's magnetic field
prevents most of the cosmic rays from reaching the surface.) Imagine
taking a trip to Mars which took two months each way and spent a
year on Mars. The radiation dose from cosmic rays would be roughly:
* Radiation dose for 1 year on Mars (+4 months travel time)
0.75 - 1.0 rads per month in space <= 4 rads
4.5 - 5.5 rads for 1 year on Mars <= 5.5 rads
.
The total galactic cosmic ray dose for the Mars trip would be
less than 10 rads - a safe level. However, one can see that a small
solar flare could hit you with 10 times that - in a couple of days.
Plants are less vulnerable to radiation than people are
so the crew will be located in the middle of a multi-level
design. Imagine a four floor design in which the top and
bottom floors grow plants and the middle two floors house the
crew.
9.1 Apartment size and weight estimates The size of the apartments will be standardized because
everyone will be paying the same price for their billet. There
will be no human staff, i.e. all manual labor will be done by a
few andriods. Clearly the apartment size is limited only by its
mass (weight). We want to have apartments which are as large as
practical without making the voyage substantially longer.
Cabin volume on the Apollo flights was 3.03 cubic meters
per person [112]. "Living Aloft" suggests that 600 cubic feet
or 17 cubic meters are needed per person for voyages lasting
more than 2 months [22, p.61]. This is 10 ft x 10 ft x 6 ft.
We feel this is unacceptable. Our recommendation is a central
hallway with two-person apartments on both sides. Each apartment
would be 9 meters by 5 meters (less wall thickness). The hallway
would be 2 meters wide giving an overall width of 20 meters and
length of 5 meters for 4 people. The height would be 3 meters
less floor thickness and space for lighting fixtures etc. Thus
the overall living volume would be 75 cubic meters (20*5*3/4)
per person.
All floors, doors, and walls will have to be strong enough to
serve as exterior walls (or pressure hulls or bulkheads) because
of the real possibility of a puncture or rupture somewhere. This
means a weight penalty, but we cannot permit a design which could
cause the loss of the entire crew. Clearly all junctions must be
airtight. This includes doors in walls. There will be doors in
hallways between apartments, but since they will be intended for
emergency purposes only, their normal state will be open.
The tentative design calls for four levels, the top and bottom
of which would be used for crops and the middle two would house
the crew. The following analysis will be based on one segment of
the ring which will be four levels (12 meters) high, 20 meters
wide (two apartments), and 5 meters long. The number of occupants
will be 8 ( 4 apartments total, on two floors). In the following
the weight of floor and wall materials is estimated to be 1.0
kilograms per square meter yet it must be able to withstand 0.333
bars of interior atmospheric pressure.
* Table 9.1-1 Weight estimate of apartments
Component Area Weight Per person
(sq m) (kg) (kg/person)
Floor-ceiling 3 * 5 * 20 = 300 300 37.5
Hall wall 4 * 5 * 3 = 60 60 7.5
Exterior wall 4 * 5 * 3 = 60 60 7.5
Apartment wall 2 * 3 * 20 = 120 120 15.0
lighting 8 1
air conditioning 24 3
electronics 80 10
air ( volume ) 100 * 2 * 3 = 600 269.2 33.65
--- ----
totals 921.2 115.15
.
Toilets, showers, and basins will have to be shared because
we cannot afford the extra weight it would require to provide
private facilities. If you assume that each person spends an
hour per day using those facilities, you can see that we would
only need about 1/24 of the number of facilities. We suggest
that there be enough facilities that about 8 people share each
one. Androids will maintain the facilities.
9.2 Hydroponic food production Many different crops will be grown on board the spaceship both to save weight and to provide fresh food for the crew. Fresh food will make the long trip much more bearable. Briggs and Sacco give the following table of human needs and waste production. * Table 9.2-1 Human needs and waste production
Requirement Per man, daily Crew, daily
(kg) (MT)
Metabolic oxygen 0.9 0.9
Drinking water 3.6 3.6
Hygiene water 5.4 5.4
Food 0.6 0.6
Waste production
Carbon dioxide 1.0 1.0
Water vapor 2.5 2.5
Urine 1.5 1.5
Feces 0.16 0.16
Metabolic heat 12,660kj 12,660Mj
Source: M.R. Sharpe, "Living in Space", Doubleday, 1969,
p.107 as cited in [LB1, p.425].
.
From experience one would think that the above food
requirement is too low. Perhaps it is dry weight only. We
shall assume 2 kilograms of fresh food per person per day.
This is about 1.5 pounds per person per meal.
In order to estimate the weight of the hydroponic food
production facilities it is necessary to estimate both the average
growing period of the crops and the average harvest index. The
harvest index is the fraction of the crop which is edible. Corn
for example has a very low harvest index - about 5%, whereas
turnips have a harvest index of 100% because people do eat
turnip greens. We shall estimate 50 days for the average growing
period and 33% for the average harvest index. Thus in order to
harvest 2 kilograms per day per person, we must have a crop
which has an average weight of 1 kilogram for 50 days or a total
weight of 50 kilograms per person. Since only one third is
edible we must grow three times as much or 150 kilograms per
person. Now we can estimate the weight of the hydroponic food
production facilities.
This estimate is based on two levels of the same size (20x5x3)
as used in the previous section for estimating the weights of
personal quarters. Only one floor and ceiling are required because
the others were accounted for in the crew apartment estimate.
* Table 9.2-2 Weight estimate of hydroponic facility
Component Area Weight Per person
(sq m) (kg) (kg/person)
Ceiling (top floor) 5 * 20 = 100 100 12.5
Floor (bottom floor) 5 * 20 = 100 100 12.5
Hall wall 4 * 5 * 3 = 60 60 7.5
Exterior wall 4 * 5 * 3 = 60 60 7.5
Partition 3 * 20 = 60 60 7.5
lighting 24 3
air conditioning 24 3
air ( volume ) 100 * 2 * 3 = 600 269.2 33.65
crops 2 * 5 * 18 = 180 1200 150
water 1120 140
soil ( volume ) 80 * 2 * .25 = 40 1600 200
equipment 150 18.75
--- ----
totals 4767.2 595.9
.
There will be no meat on board with the possible exception
of small amounts that passengers may choose to bring aboard as
part of their personal weight allocation. There are two very
good reasons for this. First, raising animals to be used as food
is a very inefficient way to get nurishment. And second, we
can't afford their weight. It is clear that animals must be fed
and that implies growing food for the animals. Of course in our
situation, the animals could eat the two thirds of the crops
which we would not eat and which represent waste for us. However,
discounting the food the animals need, there still remain two
major problems with animals. First, they must have space to
live in which implies a structure to house them. Second, they
produce waste just like people which implies a significant
additional volume of waste to be handled by our waste recycling
system. This in turn implies more mass.
In summary, the mass penalty of animals is the sum of their
weight plus the weight of their housing (including air) plus
the weight of their waste disposal equipment. Another way of
looking at the situation is that those animals would be displacing
people who could be carried instead. So who would want to buy
million dollar tickets for chickens, rabbits, or goats to fly to
Mars?
9.3 Comparison of grown vs carried food supplies There is a point in terms of crew size and trip duration
where it becomes more economical to grow food for the crew
than to carry it. We saw in the previous section that the
estimated mass of the hydroponic facility was 595.9 kilograms
per person. In addition we must add roughly 20 kilograms per
person of waste processing equipment to recycle the inedible parts
of the plants we grow. That makes the total roughly 620 kg per
person for a trip of unlimited duration.
NASA plans to resupply food to space station Freedom rather
than to grow it on board. The following data comes from Charles
Bourland, Space Station Food Subsystems manager, JSC:
* Table 9.3-1 90-day food supply for a crew of 8
Food type Volume Weight
% (cu m) (kg)
Frozen 56 2.947 985.0
Refrigerated 20 0.992 351.8
Ambient 24 1.247 421.8
total 100 5.186 1758.6
Source: NASA as cited in Ad Astra, Jly '90, p.26.
.
At three meals per day per person this amounts to 0.814 kg
per person per meal or 2.44 kg per person per day. Thus at 254
days the resupply weight will be 620 kg per person. Or in other
words, for any trip longer than about 254 days, it is cheaper to
grow your food than to carry it.
In fact the real breakeven point would be less than 254 days
because we haven't included any weight penalty for storage space to
carry the food or containers to hold it in.
9.4 The spaceship environment The comfort of the crew will be the primary concern of
the design but strong emphasis will be placed on reducing
weight wherever possible. The idea of the crew wearing no
clothing probably would not be acceptable but we can keep
the temperature quite high (say 85F) to encourage people to
wear shorts or other lightweight garments. This will have
several helpful consequences: (1) personal luggage can be
reduced, (2) the mass of clothing washed on a daily basis
will be reduced, (3) water, electricity, and handling needed for
the cleaning of garments will be reduced, and (4) the time spent
by people in dressing and undressing will be reduced.
The individual apartments will be occupied by two crew
members or possibly by a couple and a child. This will permit
privacy and intimacy. Of course intimacy between two crew
members of the same sex will be entirely their own business;
however, AIDS infected people will not be permitted on board.
During the building of the spaceship, couples or pairs of
crew members who will be sharing an apartment will be asked to
either choose an apartment floorplan from a variety supplied
by professional designers or to design their own. This should
quarantee maximum satisfaction with personal quarters. A family
of four would be allocated twice the space and could design
whatever floorplan they wished. Similarly a group of four males
might wish to design a small bunkroom and have the remainder
of their space as a game and TV lounge - maybe they are avid
bridge players. Perhaps a news agency such as CNN would buy
four seats and configure their space as a broadcast station.
The air, at one third of normal air pressure, will be
a mixture of 29.5% nitrogen, 70% oxygen, and 0.5% carbon
dioxide. Normal air would weigh three times as much. Even
so we will be carrying 67.3 MT of "air". Smoking will be
prohibited.
Each person will have a weight allocation of one metric
ton which is 2200 pounds. This allocation will include the
following:
* Table 9.4-1 Overall crew weight estimate
Item Weight(kg/person)
Food production 595.9
Water 10
Food preparation 20**
Waste/wash facilities 50**
Apartment 115.1
-----
subtotal 791.
Body 80 (male; 50 female)
Furniture 50
Personal articles 50 (male; 80 female)
Space suit 50
---
total 1021.
** - SWAG
.
Although we have exhausted our weight allowance, this is not a problem because the momentum exchange propulsion system can handle significantly heavier loads. We will not be at all surprised if some of the estimates are too low. We expect that the mass of the structure may have to be adjusted upward. 9.5 Crew size and composition Perhaps the single most important reason that this space
project will be successful is that we plan to take a very large
crew - namely 1000 people. Now people can say to themselves,
"Hey, I could go on that trip if I wanted to." Past space
flights have been limited to such small crews that selection
was restricted to people with special qualifications. Not only
will that not be the case this time, but we will offer billets
to nearly anyone who can afford the price of the tickets. We
say "nearly anyone" because there will always be some restrictions
such as: no drug addicts, no felons, no people with fatal
communicable diseases, no bedridden people, no insane people
and so on. There will be very limited medical facilities on
board the spaceship so it will be strongly recommended that
babies and other people who need special medical attention not
go. Tickets will be non-transferable to prevent scalping
and there will be both national allocations and limits as to
the number of seats that can be purchased by individuals and
corporations. Some seats may even be sold by lottery.
By opening the doors to people of many different countries
we believe that funds for the project will be much easier
to raise. Of course we expect that about half of the crew will
be women. It is anticipated that anyone who can afford to buy
one such very expensive ticket can very likely afford two - so
that they will also buy one for their spouse. Thus we expect
our apartments to be filled with many married couples of many
different nationalities.
There is no doubt that some women or couples may wish to
have the distinction of producing the first baby in space or on
the moon or Mars. While there will be no prohibition of this,
it will not be recommended for the following reasons: (1) medical
facilities on board the spaceship will be limited thus increasing
the danger to both the mother and baby, (2) the baby will be far
too young to remember the experience when he(she) grows up, and
(3) caring for the baby will greatly reduce the mother's
enjoyment of the trip to Mars (or elsewhere). And finally, (4)
babies (and children) will be charged full fare, thus couples
who have babies will owe additional fares when they return.
9.6 The primary power source - nuclear energy Nuclear fission is the only source of power which is both
powerful enough and light enough to do the job. Some time
in the distant future there may be other alternatives such
as anti-matter or nuclear fusion. As was briefly mentioned in
section 6.4, the particle-bed nuclear reactor appears to be the
best candidate at the present time. 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].
A particle-bed reactor differs from an ordinary nuclear
fission reactor in that instead of fuel rods, the particle-bed
reactor uses tiny fuel pellets. The pellets have a larger
surface area per unit volume than do the fuel rods and thus
increase the rate of transfer of heat energy to the working
fluid [AW 33, p.18-20]. This means a higher power output from
a smaller (and hence lighter) volume. Current experiments
indicate that a power density of 40MW per liter is possible
[AW 68, p.20-1]. This scales up to 40,000 MW per cubic meter.
This much heat should be sufficient to turn the working fluid
into an ionized plasma. The plasma could be run through a
magnetohydrodynamic (MHD) generator to convert it to electricity.
MHD power conversion is about twice as efficient as conventional
power generation equipment [115, p.224]. Greater efficiency usually
but not always implies less weight is required to do the same job.
Soviet researchers are believed to be significantly ahead of the
rest of the world in this field. This is another area where US
taxpayers could save big money if Soviet technology were utilized
to convert the thermal power into electrical power.
Any components of the nuclear reactor and the MHD power
generation system which can be fabricated on the moon will be. The
remainder, perhaps including the fuel pellets, will be "thrown" to
the lunar slide lander, moved to the north pole by railroad and
launched from there to the spaceship assembly site via the polar EMPL.
Although this is a circuitous route, it will use very little
propellant and therefore should be cheaper than other means.
9.7 Spaceship assembly and checkout Perhaps the first decision that needs to be made is where to
assemble the spaceship. The Lagrangian points, L1, L2, L4, and L5
are the only real contenders. They were discovered by the French
mathematician Lagrange in 1772. Points L1 and L2 are unstable
whereas points L4 and L5 are stable. The stability of L4 and L5
are the first reason we prefer them.
The second reason we prefer L4 and L5 has to do with launching
materials from the north pole of the moon to our chosen point of
assembly. Notice that we must launch downward, that is below the
horizon, in order to reach any of these points from the north pole.
We have calculated the launch angle for these points. It is
shown in the following table along with some other interesting data.
The second column was obtained from [61, p.61]. The third column gives
the launch angle from the "top" of the moon - i.e. without regard
to the fact that the north pole is 1.5424 degrees away from the
"top". The fourth column gives the number of meters the projectile
will drop per kilometer of flight as it leaves the EMPL for the
target Lagrangian point. The last two columns give the time in hours
for the projectile to travel from the EMPL to the assembly point
assuming an initial velocity of 5 km per second for column four and
1 km per second for column five.
* Table 9.7-1 Earth-Moon Langrangian Points
Point Distance Launch Drop (m Travel time (in hours)
from moon angle per km) 5 km/sec 1 km/sec
L1 57731 -1.724 30.1 3.2 16
L2 64166 -1.551 27.1 3.6 18
L3 381327 -0.261 4.56 21.2 106
L4,L5 384400 -0.259 4.52 21.4 107
.
Choosing between L4 and L5 is a little more difficult and it
may be possible to use either one. When we leave HEO for Mars or
Jupiter, we will want to point the spaceship such that we cancel
some of the earth's orbital velocity because Mars and Jupiter have
lower orbital velocities. At the same time we want the projectiles
to pick up orbital velocity as they head inside the earth's orbit
so that they will assume a higher velocity orbit around the sun
inside the earth's orbit. It would seem that L4 which is 60 degrees
in advance of the moon, might have a slight advantage in this case.
In any case it will require a very careful plan to determine
the order in which the components of the spaceship should be
launched in order to permit the orderly assembly of the spaceship.
Nearly all material used in the spaceship will originate on the
moon. This will save a lot of money. Assembly will be done
remotely from earth using the androids to perform the work.
9.8 Financing The primary financing for this voyage will come from five
sources: (1) sale of tickets, (2) sale of television broadcast
rights, (3) sale of Martian souvenirs, (4) profits from the android
business, and (5) profits from the hydroponics business. Let's
guestimate how much money each of these sources might raise.
The Soviet space agency, Glavkosmos, has been offering week
long flights in the Mir space station for about $10 million
[71, p.54]. The Tokyo Broadcasting System (TBS) paid upwards
of $12 million to have Toyohiro Akiyama fly on Mir. Liftoff
was Dec. 2, 1990. Two days were spent en route on Soyuz and then 6
days on Mir [AA 5, p.7]. While on board Mir, Akiyama broadcast a
daily commentary on his activities - especially on how sick the
weightlessness made him. A short article in Aviation Week [AW 34,
p.22] of 5/6/91 reported that Helen Sharman of the UK was scheduled
to spend 6 days on Mir with liftoff on 5/18/91. Germany paid Russia
about $12 million for a trip to Mir. Claus-Dietrich Flade, a German
Cosmonaut, spent a week on Mir from March 17-25,1992 in the company
of two Russian Cosmonauts. Austrian and French cosmonauts are
scheduled to fly on Mir too [71, p.56].
The point is that there is a small market already for
joy-rides on Mir for $10 - $12 million a shot. How much would
people pay to go to Mars? Very likely there would be a lot of
people who could and would pay $1 million a seat to go to Mars.
Perhaps we could even sell 1000 seats at $2 million each. There
are more than 250,000 millionaires in the US alone.
* Sales of tickets - $2 billion . The first point to make about broadcast rights is that the market value can be increased significantly by selling the rights on a country by country basis. Television sports contracts give some idea of the value of broadcast rights. * Sport Network Cost Period Source 1988 Summer Olympics NBC $300 M 16 days (1) 1992 Winter Olympics CBS $243 M 16 days (1) 1992 Summer Olympics NBC $401 M 16 days (1) 1994 Winter Olympics CBS $300 M 16 days (1) Baseball ESPN $400 M 4 years USA Today NCAA Basketball CBS $1.0 B 7 years USA Today World Series, etc. CBS $1.08 B 4 years Star Ledger NFL several $3.6 B 4 years USA Today (1):[116] The 1992 Information Please Sports Almanac, p.430. . The value of a live telecast from a spaceship on the way to Mars or from Mars itself is difficult to estimate. None of the three major US networks (ABC, CBS, NBC) responded to my written inquiry regarding their interest in such a venture. But it is clear that its value can be increased by an order of magnitude by timely preliminary "hype". * Broadcast rights (worldwide) - $1 billion . Marketing of souvenirs from the Moon or Mars certainly offers
the possibility of generating some significant revenues, but the
value of such souvenirs is difficult to estimate. The Apollo
program cost the US taxpayers at least $120 billion in 1992 dollars
and it returned 382 kilograms of lunar soil and rocks. Those rocks
cost the US taxpayers about $314 million per kilogram. On a little
more down to earth scale, pieces of the Berlin wall were sold for
$10 in the US.
Perhaps we could get $1000 per pound for moon rocks and $5000
per pound for Martian rocks. If the price is too high, there will
be people defrauding the public by selling rocks from their back
yards. The value per metric ton would be: $2.2 million for moon
rocks and $11 million for Martian rocks. Who knows how many tons
we could sell before the price would drop?
* Martian souvenirs - $11 million per metric ton . Profits from the android and hydroponics businesses will depend on how rapidly they are ramped up to large scale. We believe that both of these industries have the potential of the world automobile industry. The hydroponics business could be ramped up faster because there is no need to wait for product development. On the other hand, hydroponics will have a lower profit margin than the android business. |