Bye-bye batteries, hello new tech supercapacitors?

wrote in message
...
In sci.physics Dr J R Stockton wrote:
In sci.space.policy message , Tue,
17
Mar 2009 17:00:01, posted:

No, but unless I dropped a decimal somewhere, it would take a rail
gun
over 3,000 km long to reach the 8 km/s of low Earth orbit at a
constant
acceleration of 5 g.

To reach LEO at a horizontal acceleration of one surface gee takes
half
a radian - URL:http://www.merlyn.demon.co.uk/gravity2.htm#OEV. Now
v^2-u^2 = 2as, so at five gee it should need a tenth of a radian.
The
average radius of Earth is about 6378 km. Such a gun would easily
fit
into the Nullarbor Plain, even if dropped to 3.5 gee. Go up to about
7
gee, and enough straight rail is already in place.

It appears, therefore, that we cannot both be right.

A low Earth orit requires a tangential velocity of about 8 km/s.

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

v = a * t, so,

8,000 m/s = 5 * 9.8 m/2^s * t

t = 8,000 m/s / ( 5 * 9.8 m/s^2) = 163 s

x = 1/2 * a * t^2, so,

x = .5 * 5 * 9.8 * 163^2 = 651 km

Apparently I fat fingered something the first time around.

And that ignores the acceleration due to gravity, which if accounted
for,
means the load actually sees about 5.1 g, and it ignores air drag
losses.

While you could fit such a thing into the Nullarbor Plain, I would
highly doubt the usefullness of the orbits achievable.

If one really wanted to shoot stuff into space, it would make more
sense
to build a much shorter, high g device and use it to shoot the hard
and
heavy stuff into orbit and lift soft stuff, like people, with
conventional
rockets.


--
Jim Pennino

Remove .spam.sux to reply.

===============================================

Numbers! Very useful, especially if you're engineering something. 651
km of railgun; 163 sec, nearly 3 min at 5 g's, for Terran orbital
velocity. It's a useful ballpark number; it says, you're not going to
launch from a railgun on Terra. But railguns elsewhere, that's an
option and that's where you need energy storage.

I notice in his new book, How To Live On Mars, Zubrin doesn't like
Aldrin cyclers nor anything like that. His words lead me to feel he
speaks from some experience, as in one of his Mars Analog experiments.
I think Zubrin is right, here, but wrong: he's right, atmosphere and
station in a cycler are going to have serious problems about sanitation
of the environment. But he's wrong in that somehow we'll have to solve
those problems and when we do, then cyclers are a good way to travel and
to put out new settlements in space. But that's another topic: first,
you have to *get there*.

Having stuck my foot in my mouth, I'm feeling it keenly as I reflect
that given a few minutes of freshman physics, I didn't need to say what
I said. It is the same sort of thing that is dragging down the quality
of discussion in this newsgroup, when we so urgently need to be getting
along somehow and *building those settlements.*

Titeotwawki -- mha [sci.space.policy 2009 Mar 18]

On Mar 19, 1:46*am, Dr J R Stockton
wrote:

Such a gun would easily fit
into the Nullarbor Plain, even if dropped to 3.5 gee. *Go up to about 7
gee, and enough straight rail is already in place.

The Long Straight is only straight in one dimension

Martha Adams wrote:


I notice in his new book, How To Live On Mars, Zubrin doesn't like
Aldrin cyclers nor anything like that.

I suspect he doesn't like anything he didn't come up with himself. :-)

Pat

In sci.space.policy message , Thu,
19 Mar 2009 01:02:47, Martha Adams posted:

Numbers! Very useful, especially if you're engineering something. 651
km of railgun; 163 sec, nearly 3 min at 5 g's, for Terran orbital
velocity. It's a useful ballpark number; it says, you're not going to
launch from a railgun on Terra. But railguns elsewhere, that's an
option and that's where you need energy storage.

Principles are more useful - half-a-radian at one surface gee means
that, even ignoring atmosphere, you won't be able to orbit any sensibly-
evolved native with a railgun whose length is less than an appreciable
fraction of the body's radius. Except maybe by floating the passenger.

--
(c) John Stockton, nr London, UK. Turnpike v6.05 MIME.
Web URL:http://www.merlyn.demon.co.uk/ - FAQqish topics, acronyms & links;
Astro stuff via astron-1.htm, gravity0.htm ; quotings.htm, pascal.htm, etc.
No Encoding. Quotes before replies. Snip well. Write clearly. Don't Mail News.

wrote in message
...
In sci.physics Martha Adams wrote:
"Eeyore" wrote in message
...

Martha Adams wrote:

Not yet mentioned here, and it needs to be, is off-Terra railgun
launchers. Working on a principle like an electric motor, a railgun
launcher imparts an immense amount of kinetic energy to accelerate
something -- a cargo or a ship carrying humans

No, I think you'd crush their internal organs and kill them.

-- to a velocity
appropriate to begin ballistic orbit to another body. To a planet,
an
asteroid, out-of-system, even back to Terra. The great economy to
this
is, the ship doesn't need to carry all that energy nor the machinery
to
convert it into movement. There are two problems about this.

And the practical purpose of this is ?????

Graham

==============================================

1) Will 5g's max crush your internal organs?


No, but unless I dropped a decimal somewhere, it would take a rail gun
over 3,000 km long to reach the 8 km/s of low Earth orbit at a constant
acceleration of 5 g.



I think you dropped something somewhere. To go from standing start to 8000
m/s with 49 m/s^2 acceleration (5 g), would take a little over 163 seconds
(8000 m/s) / (49 m/s^2).

The distance traveled in that time would be 1/2 *a*t^2 = 1/2 * 49 * 164^2 =
658 km.

daestrom

In sci.physics daestrom wrote:

wrote in message
...
In sci.physics Martha Adams wrote:
"Eeyore" wrote in message
...

Martha Adams wrote:

Not yet mentioned here, and it needs to be, is off-Terra railgun
launchers. Working on a principle like an electric motor, a railgun
launcher imparts an immense amount of kinetic energy to accelerate
something -- a cargo or a ship carrying humans

No, I think you'd crush their internal organs and kill them.

-- to a velocity
appropriate to begin ballistic orbit to another body. To a planet,
an
asteroid, out-of-system, even back to Terra. The great economy to
this
is, the ship doesn't need to carry all that energy nor the machinery
to
convert it into movement. There are two problems about this.

And the practical purpose of this is ?????

Graham

==============================================

1) Will 5g's max crush your internal organs?


No, but unless I dropped a decimal somewhere, it would take a rail gun
over 3,000 km long to reach the 8 km/s of low Earth orbit at a constant
acceleration of 5 g.



I think you dropped something somewhere. To go from standing start to 8000
m/s with 49 m/s^2 acceleration (5 g), would take a little over 163 seconds
(8000 m/s) / (49 m/s^2).

The distance traveled in that time would be 1/2 *a*t^2 = 1/2 * 49 * 164^2 =
658 km.

daestrom

Yeah, I know; read the later post.

--
Jim Pennino

Remove .spam.sux to reply.

On Mar 15, 8:40*pm, wrote:
We really don't need better batteries, or anything. *All we need is
the will to do things differently. *We have the technology already in
place.

Electric motors connected to wires built into the roadway are the way
to go. *It was how streetcars worked in the 20s, it is how trams and
trains throughout Europe work today, and it is something that competes
against autos today and back in the 1920s.

That's why the oil and auto companies colluded to destroy the
streetcar companies and replace them with cars and gas stations.

http://en.wikipedia.org/wiki/General...car_conspiracy

If this hadn't happened we'd already have trams superior to that of
Europe *- and we wouldn't be so dependent on oil or automobiles

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

We also would have migrated naturally to powered roadways using more
modern methods developed in the 50s and 60s

Here are some more modern implementation plans;

http://www.peapodmobility.com/

http://www.path.berkeley.edu/PATH/Pu.../PRR-93-19.pdf

http://www.unimodal.com/

And still, your audience is next to zilch.

"Electric motors connected to wires built into the roadway are the way
to go"

Anything is possible, but you've got to be kidding. There's not a
sufficient national grid as is, and roads are dug up and/or dug into
so frequently that at most any time 10% of city roads would be without
live wires to carry the juce.

~ BG