Re: Fusion Rocket to the Moon

On Feb 22, 2:24 am, "Williamknowsbest" <William.M...@xxxxxxxxx> wrote:
On Feb 21, 3:15 pm, "Stephen Horgan" <step...@xxxxxxxxxxxx> wrote:

On Feb 20, 1:16 am,Willie.Moo...@xxxxxxxxx wrote:

On Feb 14, 3:54 pm, "Stephen Horgan" <step...@xxxxxxxxxxxx> wrote:

On Feb 14, 7:56 pm, "Williamknowsbest" <William.M...@xxxxxxxxx> wrote:

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 - .

'Small detonatoin [sic] events amounting ot [sic] 60 tons of TNT are
totally
containable.' I would question that assertion, especially in the
context of something designed to fly and with 100 detonations
occurring per second. Most designs for fusion rockets, at least the
ones I have seen, have good deltaV numbers, allowing for high impulse
transfers, but low thrust. The problem of getting out of Earth's
gravity well is a formidable one, especially if you don't want to
spray the launch area with radioactives.- Hide quoted text -

- Show quoted text -

http://www.memagazine.org/backissues/membersonly/sept03/features/cont....

The work on impulsive loads is largely classified and not studied in
the course work of most mechanical engineering and structural
engineering courses. However, since 9/11 that is changing. A
detailed understanding of the mechanics of impulsive forces - even
those known at the time of the construction of the World Trade Center
- may have been sufficient to save that structure from the crash of a
fully loaded airliner into both of the towers.

The reason for this information being classified is obvious. Anyone
with the knowledge of how to build a container for a nuclear explosion
can use that knowledge to create a reinforced shelter proof against an
atomic blast. But, the benefits of securing this sort of generally
useful knowledge is small compared to the long-term benefits of having
this knowledge.

Clearly knowing how to deflect an atomic bomb driven shockwave is not
the same sort of knowledge, which is now possessed by such nations as
North Korea and Pakistan, of creating nuclear weapons in the first
place. So, there should be a general review of such classified
literature in the modern age.

Plainly, we know how to deflect and partially contain small
explosions, and likely small nuclear explosions, in the 60 ton TNT
equivalent range. Such capacity dramatically increases the efficiency
of nuclear pulse propulsion, and creates spacecraft of unprecedented
capabilities.

While the moon is the first and simplest target of such a spacecraft,
since we have experience travelling there already, obviously owners of
such a spacecraft would not stop there, they would move across the
solar system taking stock of the resources of the place, in a manner
similar to Lewis and Clark in early US history, and like the USGS in
later times. A United Nations Solar System Survey (UNSSS) would
collect and correlate all information, and then through some sort of
solar system lease arrangement, provide for the development of
resources found there. The owners of the spacecraft technology and
production infrastructure, would benefit obviously since their
technology would be required to develop such resources. The rate of
import of raw materials from across the solar system by Earth, and the
value it creates to human industry, would set the costs and prices
involved in creating this transport infrastructure. This is well
beyond the science and engineering of such spacecraft, and in the end
gives capacity and cost targets.

A list of strategic materials is given here;

http://www.globalsecurity.org/military/agency/dod/dnsc.htm...

read more »

'Plainly, we know how to deflect and partially contain small
explosions, and likely small nuclear explosions, in the 60 ton TNT
equivalent range.'

It is not at all plain.

Why do you insist this is so?

Because the assertion suggests that the scientific and engineering
knowledge required to do this exists. It does not, for example no
working examples exist.

And the design here calls for containment, not
partial containment,

Yes it does. A parabolic reflector is far more efficient than a
containment that thermalizes the shock and exhausts it through a
nozzle.

As opposed to disintegrating? Containment is required to achieve
fusion in any case.

at 100x60 ton equivalent explosions per second.

Huge thrust, huge reflector.

Huge means massive, and this is in the context of a contained fusion
reaction, which makes all of the other components huge and massive as
well.

It there any actual reference to support this?

What exactly references are you looking for? Thrust containment
references or market efficiency references?

That the engineering problems associated with this have been solved,
because I must have missed them.

Why on Earth would a
United Nations Solar System Survey with de facto ownership of the
entire Solar System make for more efficient space development?
the market was not more efficient why would any nation accept its
decisions?

What are you arguing? Markets are more efficient than what exactly?
You are confused here. You seem to think that establishing the
conditions for efficient markets somehow preclude the operation of
markets. Foolishness.

Markets are more efficient than the sort of central planning for
resource allocation that is being advocated. How does one body with
total control over the resources of the entire Solar System make for
any kind of a market?

Fact is, free markets operate best in a specific context. In a
specific environment. This includes;

1) clear and fairly applied civil laws
2) open information sources
3) strong property laws fairly applied

None of these exist regarding the solar system today.

Many nations on have clear and fairly applied civil laws, which would
apply to space activity in and around earth and the use of
extraterrestrial resources on earth. Information regarding solar
system resources is currently freely available and scientific
information of that type will probably continue to be. Information
relating to prospecting activity will probably be confidential, as
similar information is here on earth. Property laws already apply in
earth orbit and would develop further as exploitation of the Solar
System became a practical proposition.

There is no
generally accepted civil laws markets can rely on to enforce their
rights, or a court that can decide cases even if the laws existed or
an agency to enforce the decisions of such a legal body if it were to
exist. The basic resources of the solar system are largely unknown at
this point. It is at present illegal for nations, corporations, or
individuals to claim ownership of real property off-world.

Given that earth will be the hub of space activity for generations and
that offworld resources will largely be consumed on earth then civil
law and international agreements relating to space will apply.

In this environment there is no opportunity for a market to arise,
investments to be made, or resources to be developed. So your
assertion that markets would be more efficient is just plain missing
the point.

If several nations or companies develop the capability to mine NEAs
then a market in offworld minerals would establish very quickly.

clear and fair rules, open publicly available information regarding
available resources and their value and fair and strong property laws
and a open system of exchange. None of this applies to the solar
system yet. The first step in creating a market is creating a solid
base of information, an clear

Markets do not require that all information relating to commercial
activity be available, just the information that relates to exchanges.
The open system of exchange that would be used would probably be money.

.

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