The Next Best Thing to a Space Elevator

On Dec 8, 4:35*am, Quadibloc wrote:
Well, I'm glad that my speculation that a railgun, even on Earth, is a
useful step in obtaining very cheap access to space seems to have some
validity, as the same idea is being studied by those who should know
what they're doing:

http://www.nasa.gov/topics/technolog...tallaunch.html

This news item dates from September.

The scheme proposed, though, appears to involve the railgun-assisted
launch of an aircraft, which will then launch a rocket from a high
altitude. It is not clear to me that a railgun will really benefit an
aircraft that much, since aircraft are already much more economical
vehicles than space rockets. But then, a railgun that accelerates its
payload to 600 miles per hour is much more modest than one that
accelerates it to 16,000 miles per hour.

Just saw this today:

The world's most powerful supergun
15:01 14 December 2010
"A gun the size of a bus has set a new world record, and fired its
payload so fast it broke the speed of sound seven times over.
The railgun was fired by the Office of Naval Research in Dahlgen,
Virginia, on Friday 10 December and has caused a stir with gadget
geeks and sci-fi lovers. In fact, the majority of people who know
anything about railguns have probably seen them in sci-fi films or
video games."
http://www.newscientist.com/blogs/ns...-supergun.html

The best use of this for space purposes would be to launch cargo and
propellant to space. Mach 7 is about 2000 m/s. Cutting off this much
from the required delta-V of a rocket would allow it to be single
stage to orbit after the rail gun launch.


Bob Clark

In sci.space.policy Robert Clark wrote:

Just saw this today:

The world's most powerful supergun
15:01 14 December 2010
"A gun the size of a bus has set a new world record, and fired its
payload so fast it broke the speed of sound seven times over. The
railgun was fired by the Office of Naval Research in Dahlgen,
Virginia, on Friday 10 December and has caused a stir with gadget
geeks and sci-fi lovers. In fact, the majority of people who know
anything about railguns have probably seen them in sci-fi films or
video games."

http://www.newscientist.com/blogs/ns...-supergun.html

The best use of this for space purposes would be to launch cargo and
propellant to space. Mach 7 is about 2000 m/s. Cutting off this much
from the required delta-V of a rocket would allow it to be single
stage to orbit after the rail gun launch.

Well, it would need to be scaled-up - *considerably*. Right now they
are *talking* about not demonstrating ranges in the low hundreds of
miles with something *perhaps* the mass of a naval shell (I'd guess a
five incher but that is just peanut gallery speculation. What you are
hoping for is more the rail-gun version of HARP. And then some.

rick jones
--
It is not a question of half full or empty - the glass has a leak.
The real question is "Can it be patched?"
these opinions are mine, all mine; HP might not want them anyway...
feel free to post, OR email to rick.jones2 in hp.com but NOT BOTH...

On Dec 14, 1:44*pm, Robert Clark wrote:
The railgun was fired by the Office of Naval Research in Dahlgen,

Not funny that Dahlgen sounds like Dahmer, and it deals with guns and
the like...

Danilo J Bonsignore

In sci.astro message
ooglegroups.com, Tue, 14 Dec 2010 10:44:17, Robert Clark
posted:


The best use of this for space purposes would be to launch cargo and
propellant to space. Mach 7 is about 2000 m/s. Cutting off this much
from the required delta-V of a rocket would allow it to be single
stage to orbit after the rail gun launch.


But only if you can design a stage that can accelerate itself by around
6 km/s AFTER being accelerated to 2 km/s in a bus-length. Assuming a
bus 20 metres long, that's an acceleration of 10^5 m/s or 10,000 gee, if
I have it right. Also, the payload needs to survive,

--
(c) John Stockton, near London.
Web http://www.merlyn.demon.co.uk/ - FAQish topics, acronyms, and links.
Correct = 4-line sig. separator as above, a line precisely "-- " (RFC5536/7)
Do not Mail News to me. Before a reply, quote with "" or " " (RFC5536/7)

On Dec 14, 1:44*pm, Robert Clark wrote:
On Dec 8, 4:35*am, Quadibloc wrote:

Well, I'm glad that my speculation that a railgun, even on Earth, is a
useful step in obtaining very cheap access to space seems to have some
validity, as the same idea is being studied by those who should know
what they're doing:

http://www.nasa.gov/topics/technolog...tallaunch.html

This news item dates from September.

The scheme proposed, though, appears to involve the railgun-assisted
launch of an aircraft, which will then launch a rocket from a high
altitude. It is not clear to me that a railgun will really benefit an
aircraft that much, since aircraft are already much more economical
vehicles than space rockets. But then, a railgun that accelerates its
payload to 600 miles per hour is much more modest than one that
accelerates it to 16,000 miles per hour.

*Just saw this today:

The world's most powerful supergun
15:01 14 December 2010
"A gun the size of a bus has set a new world record, and fired its
payload so fast it broke the speed of sound seven times over.
The railgun was fired by the Office of Naval Research in Dahlgen,
Virginia, on Friday 10 December and has caused a stir with gadget
geeks and sci-fi lovers. In fact, the majority of people who know
anything about railguns have probably seen them in sci-fi films or
video games."http://www.newscientist.com/blogs/nstv/2010/12/the-worlds-most-powerf...

*The best use of this for space purposes would be to launch cargo and
propellant to space. Mach 7 is about 2000 m/s. Cutting off this much
from the required delta-V of a rocket would allow it to be single
stage to orbit after the rail gun launch.


Some more info in these articles:

Video: Navy’s Mach 8 Railgun Obliterates Record.
By Spencer Ackerman December 10, 2010 | 6:45 pm | Categories: Navy
http://www.wired.com/dangerroom/2010...erates-record/

US Navy achieves '100 mile' hypersonic railgun test shot
Electro-hypercannon could bring back the dreadnought era
By Lewis Page
Posted in Science, 13th December 2010 12:53 GMT
http://www.theregister.co.uk/2010/12...lgun_test_onr/

The weight of the projectile was 10 kg. The second article gives the
speed more accurately as Mach 7.5. Interestingly this second article
says this test had 3.3 times the energy of the 2008 test, but the
extra energy went to accelerating a heavier projectile, not to
increasing the speed.
Since energy scales as the square of the velocity this suggests that
if they kept the same smaller mass projectile they could have
accelerated it to sqrt(3.3)*Mach 7.5 = Mach 13.6, or about 4,500 m/s.
(The Mach speed depends on temperature and water vapor content. I'm
using the conversion given he
http://www.sciencelab.com/data/conve...nversion.shtml.
)
Or if you wanted to use it to get to orbital velocity of 7,800 m/s
using the same energy, this would be an additional increase in the
speed by a factor of 7800/4,500 = 1.733. To get this using the same
amount of energy would require a smaller mass projectile by a factor
of 1.73^2 = 3. So if say, the 2008 projectile was 3 kg, you could get
orbital speed with a 1 kg projectile. As a practical matter however,
you would lose a great deal of speed when launching from the ground at
this great initial speed due to air drag, not to mention the extreme
heating problem arising from having orbital velocity at ground level,
considering the heating is already significant when entering the
tenuous atmosphere present at orbital altitude.
You would not have this problem if launching from the Moon.
Interestingly, the current installation being able to achieve a 2,400
m/s velocity with a 10 kg projectile means it would suffice for
launching small cargo or propellant to low lunar orbit from the lunar
surface since the delta-V required is 1,870 m/s:
http://en.wikipedia.org/wiki/Delta-v...0.93Moon_space.
And at a slightly smaller mass, about 7.6 kg, it could launch it to
the required delta-V to reach low Earth orbit, about 2,740 m/s with
aerobraking.
This is significant since the biggest bottle neck to getting low cost
transport to the Moon is the cost of just getting the propellant to
LEO. By continual launching of small amounts of propellant we could
build up to having orbital propellant depots.


Bob Clark

On Dec 17, 10:57*am, Robert Clark wrote:
...

Some more info in these articles:

Video: Navy’s Mach 8 Railgun Obliterates Record.
By Spencer Ackerman December 10, 2010 | 6:45 pm | Categories: Navyhttp://www.wired.com/dangerroom/2010/12/video-navys-mach-8-railgun-ob...

US Navy achieves '100 mile' hypersonic railgun test shot
Electro-hypercannon could bring back the dreadnought era
By Lewis Page
Posted in Science, 13th December 2010 12:53 GMThttp://www.theregister.co.uk/2010/12/13/32mj_railgun_test_onr/

The weight of the projectile was 10 kg. The second article gives the
speed more accurately as Mach 7.5. Interestingly this second article
says this test had 3.3 times the energy of the 2008 test, but the
extra energy went to accelerating a heavier projectile, not to
increasing the speed.


Forgot to give the link to the 2008 test:

NAVY TESTS HIGH-POWERED ELECTROMAGNETIC RAILGUN
Friday, February 01, 2008
http://www.foxnews.com/story/0,2933,327205,00.html


Bob Clark