starship-design: Fwd: The Nordley Relativistic Particle Beam (RPB) drive requires anumber of beam dr

[KellySt@aol.com]

As to the topic of the cost of a project like this.  Out of the artical I 
attached comes that a 1000-ton RPB-drive ship accelerating at 1 earth gravity 
requires one million drivers,  with a required power input of 3 GW/driver.  
Thats a thousand trillion watts.  At current electric plant costs, that would 
be about a thousand trillion dollars.  Or about 300 years of the the US GNP.  
Given our ships (loaded with deboost fuel) weigh in at 25 million tons, thats 
25,000 times more cost.

Manufacturing cost have to come WAY down.

Kelly


---- Begin included message ----

• To: undisclosed-recipients:;

The Nordley Relativistic Particle Beam (RPB) drive requires a number of
beam drivers "fixed" in the
Solar System, which shoots a relativistic neutral particle beam at a
magsail-equipped spacecraft. The
spacecraft ionizes the incoming particle beam, which is them reflected
by the magsail.

To minimize focusing distance of the beam, Nordley suggests performing
acceleration to terminal
velocity while still close to Sol. This requires accelerations
approaching or even exceeding one earth
gravity, which has the problem of requiring thousands of terawatts of
power for massive (> 1000 tons)
payloads.

A 1000-ton RPB-drive ship accelerating at 1 earth gravity requires a
mass flow of 43 grams/sec from
the beam drivers back home. If split among one million drivers, this
results in 43
micrograms/sec/driver, with a required power input of 3 GW/driver. For
those who think these are
impossible numbers for engineering such a system, Nordley adds:  

    "The point is that a million beam drivers for an interstellar
propulsion system is not
    unreasonable for a civilization that made ten million automobiles a
year before robotics."  

To get a feel for the energy required, he scales the acceleration back
to 0.036 earth gravities and
compares the a 1000-ton RPB-driven probe with a 1000-ton laser lightsail
at the same acceleration. The
RPB-driven probe requires 11 GW/ton to accelerate, as opposed to 65
GW/ton for the lightsail.

Nordley suggests a massive neutral particle, such as a heavy atom or
molecule (C60 or C60F60
surrounding a heavy atom was suggested) for use in an RPB driver.
Massive particles will not be
disturbed by encounters with interstellar hydrogen atoms, but still be
able to be manipulated by light
pressure so as to collimate the beam downrange from the drivers.

The primary reflection scheme Nordley discusses is the magnetic sail
concept developed by Andrews
and Zubrin. He notes that while other reflector concepts (such as an
Orion-style pusher plate and
D-He3 pellets) are readily usable by this system, there would be losses
due to heating of the reflector
which would not translate to propulsion. Magnetic fields are
conservative, require little if any
additional energy (if using superconductors), and have little energy
dissipation upon establishing the
field.

---- End included message ----