John Wheeler wrote:
> IMHO there is a fundamental problem with mass drivers, but
it's economic, not technical. Mass drivers represent a huge
investment, and they will have to transport a lot of cargo to bring
the cost per ton down. However, until the costs come down,
there won't be much demand for space transportation. So you
have a chicken-and-egg kind of problem.

From that permanent page:
The Mass Driver is made of a small variety of parts, all simple
and repeated in a modular way which expedites simple
replacement and maintenance using a small stock of spares in
case of a small failure. It is a lightweight device, which makes
stockpiles of spare parts relatively inexpensive; all of which are
attractive features of a device operating in a remote place like the
Moon.

I'm still thinking of the asteroid retrieval mission. Latch onto an
800 meter stony NEA, and drag it back. (missions like this have
been in the AIAA & such for years. The inventment is under $50
bllion, and the return after a decade is hundreds of billions.)
Send out the parts of the mass driver which aren't just rolled &
stamped metals and concrete & wires,and build up the track
length from local materials making up the bulk.

The question is that I don't know the initial mass needed at the
asteroid. How many (Shuttle-Z?) HLV shots?

John Frazer wrote,

"I'm still thinking of the asteroid retrieval mission. Latch onto an 800
meter stony NEA, and drag it back. (missions like this have been in the
AIAA & such for years. The inventment is under $50 bllion, and the return
after a decade is hundreds of billions.)Send out the parts of the mass
driver which aren't just rolled & stamped metals and concrete & wires,and
build up the track length from local materials making up the bulk."

Suppose that you had available the level of technology and investment
needed to
* Despin the NEA
* Either ship the components of the mass driver to the NEA or build it
there
* Ship the regolith processing or mining equipment to the NEA
* Mine, containerize, and fire off these pellets for as long as it takes to
move the NEA to the desired orbit (possibly years)

If you had available the technology to do that, then why do it in the first
place? Why not instead process the NEO raw material into finished
products right there at the NEO, and ship the finished products back to
HEO? Why is it that you prefer to ship raw material back to HEO rather
than finished products? Why not establish your manufacturing facility at
the NEO?

I've heard from Charles and Mike on this topic; I'd like your view.

Ron Menich

The real position is probably somewhere in the middle. Go to a NEA
start mining operations and producing finished and semi-finished
products and use the waste material as fuel in a mass drive.

Bill

--- In spacesettlers@y..., rmenich@m... wrote:
>
> John Frazer wrote,
>
> "I'm still thinking of the asteroid retrieval mission. Latch onto an
800
> meter stony NEA, and drag it back. (missions like this have been in
the
> AIAA & such for years. The inventment is under $50 bllion, and the
return
> after a decade is hundreds of billions.)Send out the parts of the
mass
> driver which aren't just rolled & stamped metals and concrete &
wires,and
> build up the track length from local materials making up the bulk."
>
> Suppose that you had available the level of technology and
investment
> needed to
> * Despin the NEA
> * Either ship the components of the mass driver to the NEA or build
it
> there
> * Ship the regolith processing or mining equipment to the NEA
> * Mine, containerize, and fire off these pellets for as long as it
takes to
> move the NEA to the desired orbit (possibly years)
>
> If you had available the technology to do that, then why do it in
the first
> place? Why not instead process the NEO raw material into finished
> products right there at the NEO, and ship the finished products back
to
> HEO? Why is it that you prefer to ship raw material back to HEO
rather
> than finished products? Why not establish your manufacturing
facility at

Ron Menich wrote:
> Why not instead process the NEO raw material into finished
products right there at the NEO, and ship the finished products
back to HEO? Why is it that you prefer to ship raw material back
to HEO rather than finished products? Why not establish your
manufacturing facility at the NEO?

In a word: bootstrapping. Ship out a complete factory to make
finished goods?
Far easier to make some concrete rod, brick, or sheet, the rolled
& stamped metals for truss or plate, and wire -or whatever is
needed to build the track length. (Concrete in some form may be
best, if it can be made more simply than all metal structure. An
asteroid mine/ship certainly isn't mass-sensitive! Concrete
structure uses metals in their most effective ways, and uses bulk
rock to do most of the work.)
As I tried to report, ship out the basic parts needed to build up
the capability to build the track. Basic production facilities for the
bulk structure needed for the more complex facility to mass
produce the bigger track.
It all depends on whether this can be made less massive to
ship up from Earth & out to your rock, than the finished mass
driver. (Typical numbers show that over 90% of a production
facility is just dumb bulk structure. Similar numbers for the mass
driver.)

Far simpler is a solar oven based facility, to separate out the
metals & Ices, and just store them for the return trip, and use the
rock dust waste as reaction mass. (the above debate concerns
shipping the finished mass driver)
Typical projections show several hundred tons needed to ship
out, and 8-12 years to bring back about half of the 800m rock
undigested, and hundreds of k-tons+ of bagged raw metals &
ices.
You bring raw materials back to HEEO, because it's easier to
suport the numbers of people here, and to deal with shipping out
replacement parts & people to run a complete factory.

As with much of my meanderings, this stuff is being debated by
those qualified to design the mission. The fact that the AIAA &
SSI haven't decided for sure which way is best, shows that we
here can't decide. (Any more up-to-date info on what's being
decided?) We just need to keep all these possibilities in mind.

> John Frazer wrote,
>> "I'm still thinking of the asteroid retrieval mission. Latch onto
an 800 meter stony NEA, and drag it back...
>Send out the parts of the mass driver which aren't just rolled &
stamped metals and concrete & wires,and build up the track
length from local materials making up the bulk."

Checking for information on Mass Drivers, I find claims that a mass driver can throw objects at 30 Km / s, giving an isp of 3000, as against isp of 400 for LOX / Hydrogen propulsion. Will it be practical to use such mass drivers to move asteroids? And even use them for spacecraft propulsion?

Selvaraj

> From: sraj
> Will it be practical to use such mass drivers to move
> asteroids? And even use them for spacecraft propulsion?

It's pretty much the orrigonal proposal for moving asteroids around. Since
they can use any reaction-mass yoiu can get very good mass ratios, since you
'land' on your fuel rather than putting it in a heavy tank. If the military
ever manages to build a automatic-railgun with a >10kmps muzzle velocity and
a high rate of fire over a period of 8 minutes you might even use it to get
into orbit. ;)

The problem with mass drivers is power, and sometiems the durability of the
'rock crushers' needed to create the reaction mass from raw materials. An
ideal design might be a gas-core reactor with open-system cooling using pure
ice from a comet and dumping the warm water into the mass-driver buckets.
With a 500ton rocket engine and a billion ton iceball you could have a
deltaV of 435kmps - which is a very respectable 0.0015C. Not bad for a
rocket we could actually build.

ANTIcarrot.

Thanks John,

As I understand it, the mass driver is an electric linear motor of considerable length - as much as 2 Km long. Only with such length will it be possible to accelerate a substantial mass. Because it is an electric motor, the magnetic field can be altered suitably as the mass speeds up. Probably the mass will have to be levitated magnetically to reduce friction. I understand the coils will have to be supercooled to increase electrical conductivity..... Wonder whether anyone is attempting to design such a system - even 5Km/s ejection velocity (in vacuum) will be something.

John wrote:

> From: sraj
> Will it be practical to use such mass drivers to move
> asteroids? And even use them for spacecraft propulsion?

It's pretty much the orrigonal proposal for moving asteroids around. Since
they can use any reaction-mass yoiu can get very good mass ratios, since you
'land' on your fuel rather than putting it in a heavy tank. If the military
ever manages to build a automatic-railgun with a >10kmps muzzle velocity and
a high rate of fire over a period of 8 minutes you might even use it to get
into orbit. ;)

The problem with mass drivers is power, and sometiems the durability of the
'rock crushers' needed to create the reaction mass from raw materials. An
ideal design might be a gas-core reactor with open-system cooling using pure
ice from a comet and dumping the warm water into the mass-driver buckets.
With a 500ton rocket engine and a billion ton iceball you could have a
deltaV of 435kmps - which is a very respectable 0.0015C. Not bad for a
rocket we could actually build.

ANTIcarrot.

On Jul 08, 2006, at 18:11 UTC, sraj wrote:

> As I understand it, the mass driver is an electric linear motor of
> considerable length - as much as 2 Km long. Only with such length will it be
> possible to accelerate a substantial mass. Because it is an electric motor,
> the magnetic field can be altered suitably as the mass speeds up. Probably the
> mass will have to be levitated magnetically to reduce friction. I understand
> the coils will have to be supercooled to increase electrical conductivity.....
> Wonder whether anyone is attempting to design such a system - even 5Km/s
> ejection velocity (in vacuum) will be something.

It's not as hard as you make it sound. SSI achieved lunar escape velocity with their "Mass Driver III" demonstrator back in the '80s.

Best,
- Joe

Joe Strout -- joe@...

G'day,

Hmmmm, 20km/per/sec? A one tonne projectile would have the energy equivalent of 10 tons TNT if it hits anything. A mass driver is a pretty good weapon system.

ta

Ralph

--- In spacesettlers, "ralph buttigieg" wrote:

> G'day,
>
> Hmmmm, 20km/per/sec? A one tonne projectile would have the energy
> equivalent of 10 tons TNT if it hits anything. A mass driver is a
> pretty good weapon system.
>
> ta

I think most of the research is built around tossing 1 kg objects at
such speeds. Which still isn't exactly a BB gun.