Space Forum / Space Flight / April 2006

The elevator can always ride up the cable. I would suggest three
habitat modules, connected by cross cables, to maintain a rigid
structure. But there is no need for compression structures.

Agreed, and in different scenarios. What gravity is needed for:

- Convenience for tourists over 1 week
- Comfortable living over six months
- Human pregnancy and birth

The old "Pioneering the Space Frontier" study suggested an orbiting
"variable G research facility" as an early goal, reasoning that the lessons
learned there would affect the mission design of the rest of the program.

Re ion engines- happens I worked on early ion engines.1959-64
NASA used mercury (reason ionizable fluid) AF used cesium metal (pain
in neck to handle as chemicall very acive-) BUT it ionizes on heated
tungesten- the ionization energy of Cs is lower than work function of W
so if you heat  W enough to "boil" Cs off surface, it leaves as
ion)Neat way to get + ION  beam- toss in electrons from TV type gun to
get neutral beam.
BUT
you do not need exotic - say Kr
Anything you can ionize will do just fine
say "lunar" dust powder
H2 and He work (lousy to ionize but work just fine)
UF6 works
the molecular weight doesn't matter at all.
We do not need expensive or rare - the only criteria is energy loss to
ionize it.
With dust you just use electrons on one one pile and accelerate - ions
appropriately.
Strip electron on other pile accelerate to same speed as above and let
them eventually neutralize each other...(total effect is mixd neutral
pair of beams.)
Jim Lawler ("Professor"-) PhD tired aerospace engineer (not re tired
just did it once)
(literally a "rocket scientist"- amused by that jargon)
Re O'neal colonies
U R right on -- if my math holds up there will be more people in space
than on earth in a "couple" (couple meaning more than 2)  of centiries.
And they will be average IQ over 135 in 2006 style measurement. (you
cannot aford to launch welfare basket cases
1) lift energy alone cost too high
2) is someone were stupid enough to do that space would  and will kill
all dummies.
It is not paticlarly safe place to make errors. Usually you get one
chance. No more.
3) fit survive   unfit don't (to coin a "new" phrase vintage
1860's)where did I hear that b 4?

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

The problems of EMP effects from nuclear pulse rockets is overstated.

Let's look at what causes EMP.  This from the FAS;

A high-altitude nuclear detonation produces an immediate flux of gamma
rays from the nuclear reactions within the device. These photons in
turn produce high energy free electrons by Compton scattering at
altitudes between (roughly) 20 and 40 km. These electrons are then
trapped in the Earth's magnetic field, giving rise to an oscillating
electric current. This current is asymmetric in general and gives rise
to a rapidly rising radiated electromagnetic field called an
electromagnetic pulse (EMP). Because the electrons are trapped
essentially simultaneously, a very large electromagnetic source
radiates coherently.

The pulse can easily span continent-sized areas, and this radiation can
affect systems on land, sea, and air. The first recorded EMP incident
accompanied a high-altitude nuclear test over the South Pacific and
resulted in power system failures as far away as Hawaii. A large device
detonated at 400-500 km (250 to 312 miles) over Kansas would affect
all of CONUS. The signal from such an event extends to the visual
horizon as seen from the burst point.

Typical Weapon sizes quoted in such scenarios are in the range of 20
Megatons. This is roughly 1000 times the sizes of the weapons the
United States used in Japan at Hiroshima and Nagasaki which were 20
kilotons.

Nuclear pulse rockets would use explosives that are far smaller still!
Around 200 to 2,000  ton TNT equivalent yeild  And modern microfission
and microfusion concepts would be smaller yet in the 20 ton to 2 ton
yeild range.

The Orion concept involves a pusher plate that does not contain the
blast so, could produced EMP at the altitude range indicated.  Freeman
Dyson proposed the Helios concept where the explosion would be totally
contained in a thrust chamber.

I envision an anti-matter catalyzed fusion bomblets consisting of of
Boron-11 and Protium yeilding He4 and 8.5 MeV per event reacting in a
supersonic nozzle.

http://www.iop.org/EJ/abstract/-search=11301533.3/0029-5515/44/10/004

This nozzle is not the sort of convergent divergent nozzle proposed by
Dyson having such poor performance.  The nozzle I envision is a
parabolic pusher plate that directs the bulk of the blast by reflecting
the shock wave formed deep inside the nozzle at its focal point.  The
tiny bomblet is a point source of alpha particles (He4) radiating in
all directions in a very dense pulse.  They bounce off the nozzle,
scattering propellant that coats the inner surface of the nozzle whose
momentum is conserved.  The interaction time is short, and the entire
output of the pulse unit is deflected into useful thrust.  A thin layer
of propellant - a waxy semi-solid plastic material pumped through pores
in the nozzle surface - pulses from the surface, much as in the Orion
pusher plate - the combined kinetic energy creates a wave of high speed
matter that flows away from the parabolic plate and out of the nozzle
absorbing the output of the entire blast.  Since there is no direct
illumination of the atmosphere there is no compton scattering and no
EMP possible from these tiny 2 ton TNT yeild blasts.  Since the wave
moves through the nozzle in microseconds, dozens of bomblets can be
detonated per second,  2 tons of TNT produce 8.36 x 10^9 joules around
10^10 joules.  At a rate of 20 blasts per second this is a jet power of
200 billion watts of power.  If each blast consumes 1 kg of material,
that's 20 kg/sec mass flow rate.  At this power level the exhaust
velocity is 141 km/sec and the thrust is 2,800 tonnes.  So, this could
lift a vehicle 2,000 tonnes - and only 124 tonnes of propellant would
be needed to blast it into orbit.  Another 300 tonnes of propellant
would be needed to carry this vehicle to the moon and back, after soft
landing there.  A total of 1,000 tonnes of propellant with 1 million
tiny bomblets, and a total of 100 milligrams of anti-matter - would be
sufficient to carry this vehicle on a fast trajectory across the solar
system, landing on any planet and returning to Earth.

Only 3x10^15 anti-protons are required to trigger each blast.  Since
there 6.02x10^17 per microgram - a single microgram of anti-matter
could detonate 200 blasts.  In a 10 minute launch to orbit, at 20
detonations per second, 12,000 micro-fusion blasts would take place.
60 micrograms of anti-protons would be consumed.  This is a rate of 100
nanograms per second.  At 90 kJ per nanogram - this is an anti-matter
power usage of 9 MW. about 1/20,000th the power of the jet.

A Fermi-Lab sized anti-proton maker operating at 9 GW would produce
sufficient anti matter to launch one of these daily.

This is what I'd like to see built over the next few years.  A fleet of
these would scout the solar system and do early exploration.

These could be enlarged, increasing the bomblets to 2 kiloton TNT
equivalent yeild, the same amount of anti-matter per blast to trigger,
and 2 million tonne vehicle, with 1 million tonne payload.  lol.  These
would be the freighter fleet to carry industrial payloads, establish
cities and ports across the solar system - and begin development of off
world resources

They would have the scout class vehicles as ship tender and escape
vessels!  lol.

* * * *

This is the second time I've responded to this - so I don't know what's
up. Seems whenever I talk of things nuclear it gets canned once or
twice before appearing.  lol.

* * *
EMP NOT A PROBLEM

Okay couple of points about EMP.  The problem with EMP is over-stated.
That's because EMP occurs for big blasts - 20 megatons or more -
occuring between 20 km and 40 km altitude in the atmosphere.  At that
pressure and temperature, the big gamma ray burst from the blast
creates a huge number of compton scattered electrons over a wide region
- scattered off the atmosphere, which all interact coherently and
recombine coherently to make a big a.s electromagnetic pulse that can
knock out continental sized areas.  Which is cool, but not what we're
doing with nuclear pulse.

Blasts in the 20 kt range - 1/1,000th the size of the blast we're
talking about, blasts like those in Hiroshima and Nagasaki - which
didn't have EMP - have very limited EMP effects when detonated at the
right altitude.

Blasts in the 2 kt range and below, something the Orion would use,
would have even less effect if any.

And, advanced designs, like the Helios proposed by Freeman Dyson, would
contain the blast effects entirely which means zero EMP at all
altitudes.

Now Helios turned out to have very small thrust to weight and so that's
used to argue against total confinement, but details count!  lol.

An unconventional nozzle that operates like a pusher plate, but shaped
to capture the spherical wave front and redirect it (think of a
parabola being illuminated by a point source wave at its focus)
wouldn't suffer the same performance problems as the publicly released
Helios design - which allowed the heat of the bomblet to thermalize a
working fluid and expand it out of a conventional nozzle.

Finally advanced nuclear engineering can make very interesting
reactions possible.

STRAWMAN DESIGN FOR A PRACTICAL INTERPLANETARY CRUISER

For example, think of Protium (plain vanilla hydrogen without isotopes)
and Boron-10 - heat that sucker up quickly to maintain density -
meeting the Lawson criterion - with a small number of anti-protons
(about 3x10^15) and you've got a nice bomblet that produces nothing but
alpha particles, no neutrons gammas or anything.

And Boron-10 and Protium are easy to obtain, and cheap.  The resulting
alphas (He4) have about 8.54 MeV if I recall correctly.  And a small
quantity produces 2 ton TNT equivalent yeild.  That's about 8.36 GJ per
blast.  Say 10 GJ per blast.

Anti-protons have 90 MJ per micro-gram.  A gram has 6.02x10^23
anti-protons.  So, a microgram has 6.02x10^17 anti-protons.  That's
enough anti-protons to detonate 200 bomblets.

A nanogram has 6.02x10^14 anti-protons - so, you need about 50
nanograms per bomblet to trigger a fusion reaction.  A solid state
-microsized- penning trap can store this easily.

The size of the fusion reaction is determined by the amount of fusion
material you have, since the shock wave created by the anti-proton
blast can propagate once the Lawson criterion is met. The key to this
design is how quickly you can dump your anti-proton pulse, and how
tightly you can focus the beam!

And this is easily achieved with anti-protons at normal pressures and
temperatures.  So, with anti-proton triggered Boron-10/Protium fusion
bomblets each yeilding 2 ton TNT equivalent yeild.   The resulting
alpha pulse flash evaporates a few kg from the shaped pusher plate
(unconventional nozzle) where everything starts out supersonic and
stays supersonic lol - no thermalization, and everything has the same
advantage as the orion plate, but you capture the entire blast as
thrust.

With the evaporated material consisting of waxy semisolid plastic
administered through pores in the underlying shaped titanium plate -
and 20 blasts per second - you'd have a jet power of around 200 GJ,
you'd use antiprotons at a rate of 90 MW - and btw you could easily
replace them with something like the size of Fermi lab in Chicago,
adapted to produce anti-protons exclusive and cool them and capture
them in advanced penning traps - residing at the centers of the
bomblets.  (actually you'd have the traps on the side of the bomblets
and pulse them through a feed line into the center as you compressed
the whole things with explosives - this for safety's sake so you could
have two part bomblet that couldn't detonate until you put the parts
together and launched it into the nozzle)

This system would produce 2800 tonnes of thrust and lift a 2000 tonne
vehicle into orbit by consuming around 12,000 bomblets, and 120 tonnes
of propellant if I did my maths right.

300 tonnes of propllant would allow you to fly to the moon, land and
come back.  900 tonnes of propellant would allow you to fly to any part
of the solar system on a high speed orbit, land at your destination and
come back.

A nice sized scout ship with a crew of 15 to 20 perhaps - judging b the
size of comparable submarines and naval research vessels.  It would
also be a nice 200 foot space yacht for wealthy folks.  lol.  Or if a
latter day Henry Ford could arrange for large scale production, we
could have one at every space yacht club across the world! lol.  People
would rent them the way they now rent yachts for sailing on the weekend
at Chesapeake bay.  lol.

LARGER SHIPS POSSIBLE

Some of the research done by the Orion project, and other research
after suggests that with larger bomblets (but the same sized triggers)
we could increase jet power and so vehicle size, by a factor of 1,000 -
by creating a 2 kt bomblet.  This far larger engine - would lift a
2,000,000 tonne vehicle and allow for the industrial development of
solar system resources.  We could put big chunks of cities and space
ports, bases and industrial systems on the planets with this sort of
vessel.  This would be a freighter sort of vehicle - with perhaps a
crew of 30 to 50 in a freighter mode.  As a cruise liner type ship, one
designed to carry lots of people in comfort - suitable for carryiing
colonists leaving Earth perhaps, or just tourists visiting the planets
- you'd have 5,000 to 10,000 people, and maybe 1,200 service staff - or
by then perhaps robotic staff!  lol.

It would be large enough to carry the scout class vessels as ship
tenders.

A fleet of 1,200 ships of the larger ships operating across the solar
system would be capable of establishing interplanetary nations
throughout interplanetary space.  Construction of a few million a year
of the smaller ships would complete the picture.  Vessels of various
sizes between these two extremes would be constructed, mostly for
police or military or special scientific use.

ENOUGH FUSION FUEL TO POWER LARGE FLEETS

19.8% of all Boron found on Earth is Boron 10.  In 2005 according to
the USGS the US produce 657,000 tonnes of Boric Oxide (B2O3) - and
Boron is 11 and Oxygen is 16 so on a molecular basis we have 22 + 48 =
70, so 22/70th of this amount is Boron itself, so that's  206,480
tonnes of Boron - and 19.8% of that is 44,800 tons of Boron 10.

Boron is found in Borax, and if we paid to process all the Boron 10 out
of the Boron being mined, we could easily achieve 3 to 5 times this
annual production rate from existing resources on Earth.  Of course as
we expanded across the solar system, Boron would be something we'd be
looking for.

Protium isn't a problem, its plain hydrogen and there's lots of that in
water and other things.

We can produce 74.7 GJ per gram of Boron/Protium mix.  So, we use about
1/8th gram of boron per 2 ton blast - about the size of an aspirin
tablet, and 125 grams of boron per 2 kt blast - a bottle of aspirin.
So, a gram produces 8 of the smaller bomblets, a kilogram 8,000, a
metric ton 8 million, 1,000 metric tons 8 billion, 10,000 metric tons
80 billion, and 50,000 metric tons 400 billion - of the smaller ones,
and 400 million of the larger ones.

There are 31.56 million seconds in the year -  that's 12,674 of the
smaller bomblets per second to  achieve 400 billion production rate.
At a rate of 20 per second, that's a continuous firing of 633 scout
class ships - and with a 2% duty cycle - you're thrusting only 2% of
the time during flight - that's a total of 31,685 ships in flight - and
with a 10% flight time to hanger time - comparable to aircraft, that's
a total of 316,850 ships system wide.  If this were larger freighters,
that's only 316 freighters system wide.

If we could increase Boron production on Earth 10x - which should be
aciheveable - and half were allocated to the smaller ships and half to
the larger - we could have 3 million scout class cruisers and 3,000
freighter class cruisers.

Enough to create a sort of sci-fi fantasy world where space travel were
common place.  If 25% of the 3000 freigher class vessels carried
100,000 people per year off world, that's 750 vessels x 100,000 = 75
million people per year.  That's about 1% of the world's population and
equal to the world's population growth rate.

Other trechnologies might be superior.  Solar pumped lasers to support
laser rockets, or tethers, might augment, and surpass the capacity of
fusion powered rockets.  But, we clearly have the technical means, if
we had the will, to create the sort of interplanetary culture space
enthusiasts dream about with fusion rockets today.

* * *

The problem with EMP is over-stated. EMP occurs with very large nuclear
blasts, 20 megatons or more, at an altitude of 20 to 40 km, when a very
large gamma ray burst scatters electrons off the thin atmosphere over a
large area.  Those electrons recombine coherently to make a huge
electromagnetic pulse.

Smaller explosions, Hiroshima and Nagasaki are 20 kt and are 1/1,000th
the size of this explosion, didn't produce EMP.

Explosions of the size of the Orion spacecraft would be less than 2 kt,
and the EMP effects would be nearly non-existant.

Also, Helios type spacecraft, like that proposed by Freeman Dyson,
totally enclose the nuclear explosion in a nozzle that absorbs all the
energy of the propelling explosion.  So, there's no chance at all in
creating an EMP.

Now, Helios had proposed a sort of nuclear pulse thrust chamber that
wasn't every efficient.  And people have said that this inefficiency is
a necessary feature of total enclosure.  That's not exactly true.
Performance, as always, depends on details.

A supersonic nozzle, one where the propellant starts supersonically and
continues flowing supersonically, has many of the features of the Orion
pusher plate, while still affording total enclosure.  Imagine a pulse
from a small bomblet originating at the focal point of a parabola.  The
wave of energetic material strikes the parabolic pusher plate, and
causes a directed wave to exit the base of the nozzle.  This is
distinctly different than say using a nuclear explosion to heat a large
amount of propellant that is then expanded through a conventional
nozzle.  It has many of the advantages of Orion type pusher plates, but
is more efficient in many ways - and totally eliiminates EMP.

By compounding the nuclear pulse WITHOUT a fissile materials, we can
create a relatively clean exhaust.  Boron-10 and Protium ignited by
3*10^15 anti-protons - about 5 nanograms - can generate energetic
pulses of between 2 tonne TNT equiv. to 2,000 tonne TNT equivalent.
Detonating these tiny pulse units at a rate of 20x per second, we can
lift vehicles ranging in size from 2,000 tonnes to 2,000,000 tonnes and
carry 50% of this mass throughout the solar system.

Boron-10 & Protium produce alpha particles only.  No neutrons, no gamma
rays.  Helium-4 that's it, at 8.54 MeV per reaction.

A particle accelerator the size of Fermilab could be built specifically
to produce anti-protons.  Penning traps made of solid state materials
can be made to efficiently store and transport the needed anti-protons,
and deliver them in a form that is concentrated enough - in time and
space - to exceed the Lawson criterion and setup a detonation wave in
the Borton-10/Protium mix.  Since hydrogen and boron can unite
chemically to form borohydrides, these bomblets need not be too
complex.

Since 20% of the world's supply of Boron, extracted mostly from Borax
in Turkey and elsewhere, the world might produce 50,000 tonnes of
Boron-10/Hydride per year at fairly reasonable costs.  At 75 MJ per
gram - equivalent to the energy contained in 12 barrels of oil, this
50,000 tonnes per year of material could yeild 21x more energy than we
now produce by burning oil.

This is enough energy to fly thousands of the very large rockets and
millions of the smaller rockets.  In any case, we have the means to
develop industrially the entire solar system.