Fusion Rocket to the Moon

Nuclear pulse rockets have been proposed as a way to use directly the
energy available from nuclear reactions;

http://en.wikipedia.org/wiki/Nuclear_pulse_propulsion

But the amount of nuclear materials disposed of in the atmosphere
during a rocket's ascent is a problem with these devices. An
uncompressed critical mass of weapons grade plutonium is at least 10
kg. And 1,000 devices are needed to achieve orbit. So, 10 metric
tons of plutonium reaction products would have to be released into the
atmosphere for each flight. Clearly unacceptable.

The amount fissile needed to achieve criticality is inversely
proportional to the square of the density of the material. Since
shaped plastic explosives can compress plutonium to 3x its rest
density, critical mass is reduced to 1.1 kg per device. Reducing the
pollution of each flight by this level.

Density is a function of pressure, and the pressures achieved with
chemical explosives are limited.

Is there a way to increase pressure and therefore density?

Well, there are techniques that have been developed to initiate fusion
reactions in pellets of lithium deuteride. These techniques, ranging
form Zeta-pinch to particle beam compression to inertial compression
(firingpieces at high speeds toward one another) to laser beam
compression - can achieve pressures 3,000 times greater than can be
achieved by chemical explosives. This means that densities of 10,000x
can be contemplated.

When applied to fissile materials this means that the amounts of
materials can be reduced by a factor of 100 million - critical masses
as small as 100 micrograme may be possible in the limit using these
techniques. When system simplicity and ease of manufacture are taken
into account, factors of 400 to 2,000 seem very easily achieved using
Z-pinch technique

http://en.wikipedia.org/wiki/Z-pinch

This implies bomblets using as little as 3 milligrams to 63 milligrams
of fissionable material each. This translates to a release of 3 grams
to 63 grams of fission byproducts per 1000 pulse unit launch.

When these very small fissile devices are used as a primary trigger
for a Lithium-6/Deuteride secondary, a large fusion device can be
contemplated that has very little fissile emissions.

Increasing densities reduces fissile materials required. Replacing
the fissile material with some sort of anti-matter trigger would also
be possible - reducing the use of fissile materials to zero.

Some have reported that by scattering a positron off of a neutron
undergoing decay, anit-protons can be created with far less energy
than they otherwise might by direct creation. This provides total
conversion of mass to energy with only a small input of energy to
create the positron in the first place. This can be used as a sort of
desk top anti-proton generator and when used as an anti-matter spark
plug - sustains desktop fusion or detonation of fusion secondaries in
sequence.

In any event these devices are very small - in the 10 gram to 100 gram
range, and due to fundamental limits of inertial confinement systems
and their triggers - they are limited to 6 kT/kg yeild. About 60 ton
to 600 ton yield. that's 240 GJ to 2.4 TJ per device.

The exhaust speeds achieveable with this sort of device are well above
7,000 km/sec. A continuous fusion rocket is capable of no more than
24,000 km/sec exhaust speed.

Small detonatoin events amounting ot 60 tons of TNT are totally
containable. Impulse units containing 10 grams of fusion material in
a rocket operated at 100 detonations per second totally deflected by
thrust structure, has a propelant flow of 1 kg per second and an
exhaust speed of 7,000 km/sec. That's a thrust of 700,000 kgf - or
700 metric tons of force.

Accelerating at local gravity pluse 1/6th gee from Earth to Moon, with
turn-around halfway there, requires 1-1/6 gee at takeoff from Earth,
1/6th gee through transit, and 1/3rd gee at landing on the moon. The
vehicle detonates 62,516 pulse units massing 6.25 metric tons. The
vehicle masses 400 tons empty and carries 20 tons of pulse units.

It takes 8.5 hours to reach the moon from Earth, and 8.5 hours to
return at 1/6 gee. A total of 17 hours. With a 3.5 hours spent at
each end of the journey, the vehicle can provide daily flight service
to the moon. A fleet of four vehicles can provide a departure every 6
hours. Six vehicles provide spares and reasonable service times to
maintain this flight rate.

6AM 12 Noon 6PM Midnight

Six launch pads, a central control tower and dispatch, a ring of
support hangars, warehouses, and staging areas beyond that, road and
rail feeding into the center - a spaceport at each end of the journey
- one pad for every vehicle at either end.

A structural fraction of 20% - means that 80 tons are vehicle. Leaving
a payload of 320 tons - A total of 1280 tons per day to the moon and
back. At 350 kg per passenger, and 200 passengers per flight a total
of 120 tons per fight for passengers and 250 tons per flight for
cargo.

What could a fleet of six vehicles offering 4 flights per day to the
moon?

A ton of supplies will support 1 person on the moon for a year. So,
without any ability to recycle or make use of lunar resources - 1000
tons per day cargo supply rate could support 365,000 people on the
moon. A balanced allocation to growth and support would allow an
initial city of 100,000 be built in the first year, and support
100,000 tourists - with an average stay time of 4 days then, 200,000
tourists per year would visit the moon and use very little resources,
the remaining 165,000 inhabitants would live in 40,000 high end homes
built on a lunar housing development built over a 3 year period.

The Merrill Lynch World Wealth Report indicates that to maintain this
rate of demand for flights prices in the $100,000 per stay range, and
housing prices in the $10 million per unit range with daily use
charges for air, water, food and so forth. The tourists and luxury
home buyers help support the infrastructure for research and
development, and provide jobs for researcher extended families.

This is sort of the 1950s vision of Luna City - .