A Railgun on Earth

Some time back, I noted that, as I read in one book that the V-2
levelled off in flight at 20 or 25 miles up, that perhaps a long
horizontal railgun built that high up would be, although a prodigious
engineering feat, a much more reasonable alternative to a beanstalk.

But lately, I thought that depending on going so high that going
through the Earth's atmosphere for a quarter orbit or so wouldn't take
away too much kinetic energy was perhaps unreasonable. Rockets are
launched upwards from the Earth's surface, so why not point a railgun
upwards. That would mean that all the railgun would do is take care of
lofting the spaceship to a high altitude, and rocket engines would
handle the rest of the requirements of putting the ship in orbit.

But then I did some back-of-the-envelope calculations.

Supposing the highest railgun we can reasonably build is one that is 2
1/2 miles high. This assumes it's built on the side of a mountain -
but a typical mountain of 14,000 feet or so, rather than holding out
for Mount Everest. A tunnel down to sea level would be required as
well. This would be 4 kilometers, or 4,000 meters.

To get as good a performance as possible, I will assume a high
acceleration; the passengers would have to endure 5g, so that means
the ship is accelerated at 4g inside the railgun. Round it off to 40
meters/second^2.

Using distance = 1/2 acceleration * time^2, 4,000 divided by 20 is
200, and 14 squared is 198. So our intrepid voyagers into space spend
*14 seconds* in the railgun at 5g. So the spaceship leaves it at a
velocity of 560 meters per second.

Just over half a kilometer per second, when escape velocity is seven
miles per second. A factor of 20 in velocity, and thus one of 400 in
the length of the railgun, at the least, is required. And, so, to
avoid excessive air resistance, heights above that of Mount Everest in
its construction will be needed. So there seems to be no escape from a
truly prodigious feat of engineering being required if one wants to
replace a useful amount of rocket power by electrical power.

John Savard

On Feb 4, 7:16�am, Quadibloc wrote:
Some time back, I noted that, as I read in one book that the V-2
levelled off in flight at 20 or 25 miles up, that perhaps a long
horizontal railgun built that high up would be, although a prodigious
engineering feat, a much more reasonable alternative to a beanstalk.

But lately, I thought that depending on going so high that going
through the Earth's atmosphere for a quarter orbit or so wouldn't take
away too much kinetic energy was perhaps unreasonable. Rockets are
launched upwards from the Earth's surface, so why not point a railgun
upwards. That would mean that all the railgun would do is take care of
lofting the spaceship to a high altitude, and rocket engines would
handle the rest of the requirements of putting the ship in orbit.

But then I did some back-of-the-envelope calculations.

Supposing the highest railgun we can reasonably build is one that is 2
1/2 miles high. This assumes it's built on the side of a mountain -
but a typical mountain of 14,000 feet or so, rather than holding out
for Mount Everest. A tunnel down to sea level would be required as
well. This would be 4 kilometers, or 4,000 meters.

To get as good a performance as possible, I will assume a high
acceleration; the passengers would have to endure 5g, so that means
the ship is accelerated at 4g inside the railgun. Round it off to 40
meters/second^2.

Using distance = 1/2 acceleration * time^2, 4,000 divided by 20 is
200, and 14 squared is 198. So our intrepid voyagers into space spend
*14 seconds* in the railgun at 5g. So the spaceship leaves it at a
velocity of 560 meters per second.

Just over half a kilometer per second, when escape velocity is seven
miles per second. A factor of 20 in velocity, and thus one of 400 in
the length of the railgun, at the least, is required. And, so, to
avoid excessive air resistance, heights above that of Mount Everest in
its construction will be needed. So there seems to be no escape from a
truly prodigious feat of engineering being required if one wants to
replace a useful amount of rocket power by electrical power.

John Savard

NOPE! Use railgun to launch most cargo, components etc. Water doesnt
care how many Gs it endures to orbit,.

Humans and oi-ther delicate cargo still go by rocket.

although a 2 stage spaceplane would be better.

space plane first stage takes off carrying its cargo a smaller space
plane for obital operations.

the carrying craft takes off with little fuel to keep the weight down.
it refuels repeatedly to release altitude, where the carrying craft
flies back to base and the manned portion or g intolerant cargo goes
on its way to orbit.

advantages, all the fuel need no be onboard at launch, refueling is a
common practice with the military, the carrying aircraft uses engines
optimized for air operations, the rocket part is released above most
of the drag inducing atmosphere, the carrying craft can use
afterburners to help the last push for the rocket part.

the carrying aircraft would be near as easy to maintain as a
commercial airliner.

nasa stick concept should remain just that, as a discared concept!

On Feb 4, 8:54*am, " wrote:

NOPE! Use railgun to launch most cargo, components etc. Water doesnt
care how many Gs it endures to orbit,.

This is true. But there's hardly a need to build a railgun for *that*
purpose, because after an initial startup phase, water for space,
nitrogen and hydrocarbons for space, metals for space, silicon for
space... can be obtained from comets and asteroids.

If one wants to send *millions* of people to space, to resettle them
in space habitats (or Mars settlements) that a handful of people
previously launched by rocket (and their descendants) have built, then
one needs to drastically lower the cost of sending people to space.

That's why I'm trying to see if there's an alternative to the hugely
expensive beanstalk.

John Savard

On Feb 4, 5:12�pm, Quadibloc wrote:
On Feb 4, 8:54�am, " wrote:

NOPE! Use railgun to launch most cargo, components etc. Water doesnt
care how many Gs it endures to orbit,.

This is true. But there's hardly a need to build a railgun for *that*
purpose, because after an initial startup phase, water for space,
nitrogen and hydrocarbons for space, metals for space, silicon for
space... can be obtained from comets and asteroids.

If one wants to send *millions* of people to space, to resettle them
in space habitats (or Mars settlements) that a handful of people
previously launched by rocket (and their descendants) have built, then
one needs to drastically lower the cost of sending people to space.

That's why I'm trying to see if there's an alternative to the hugely
expensive beanstalk.

John Savard

you cant start by settling millions, heck explore the moon mars
asteroids and perhaps mercury.

my carrier aircraft launch is a good way to get humans to space,

sorry the costs to mine asteroids is just too high for short term.

besides the world will get nervous about manuvering coments and
asteroids anywehere near the earth, ideal weapon

wrote in message
...
On Feb 4, 5:12?pm, Quadibloc wrote:
On Feb 4, 8:54?am, " wrote:

NOPE! Use railgun to launch most cargo, components etc. Water doesnt
care how many Gs it endures to orbit,.

This is true. But there's hardly a need to build a railgun for *that*
purpose, because after an initial startup phase, water for space,
nitrogen and hydrocarbons for space, metals for space, silicon for
space... can be obtained from comets and asteroids.

If one wants to send *millions* of people to space, to resettle them
in space habitats (or Mars settlements) that a handful of people
previously launched by rocket (and their descendants) have built, then
one needs to drastically lower the cost of sending people to space.

That's why I'm trying to see if there's an alternative to the hugely
expensive beanstalk.

John Savard

you cant start by settling millions, heck explore the moon mars
asteroids and perhaps mercury.

my carrier aircraft launch is a good way to get humans to space,

sorry the costs to mine asteroids is just too high for short term.

besides the world will get nervous about manuvering coments and
asteroids anywehere near the earth, ideal weapon

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

John, I can't see it. All your suggestions are too elaborate and
expensive to operate. The beanstalk will win over the long run owing to
its simplicity. The cost once it's accomplished, will drop away down
and it will be the cheapest way to get up out of Terra's gravity well.

My second point has to do with resettling "millions" of people into
space. If you will just stand around any crowded place and look at the
people, you will see that not as many in one in a hundred of them, maybe
not one in a thousand, has the stuff to go out there and live there.
And further, when they get out there, where do they live? Space is
different from he have you thought about the cost and construction
*per person* of the industrial base required to develop and maintain a
warm moist breathable longlasting life and work space *per person*? It
will not happen. Twice over, however large space is, no large numbers
of Terrans are going to go out there and live there. Thus space cannot
have any impact upon population issues here on Terra. (Able and adapted
humans who were born and grew up there, are another story.)

As for getting water and other life resources from asteroids, hauling
them up out of Terra's gravity well is not an option. It costs too
much. As with the beanstalk, the industrial plant to get those
materials from asteroids, is a new idea to us humans and it will cost
lots of money to get it started, but it will then work better and cost
less than out from Terra.

In all of this, I think it's good to hold up costs of these things vs
the cost of one or two of the wars that Washington likes to do. (For
whatever reason, if any.) Settling space is a much less expensive
enterprise than one of those wars, and where all the money that goes
into a war is dissipated -- and provokes expensive and destabilizing
consequences -- space settlements will pay off in development of new
cultural, technological, and personal resources. As well as by making
some people very rich.

So if you want to work at something offering short-term large rewards,
how about some investigative reporting. Peering behind all the PR about
"what the people want," "domino theory of communism around Vietnam," and
etc, why was Apollo killed when it offered so much to our future? Who
are the people today who could pull together a space settlement program
and make it work? Etc etc.

Titeotwawki -- mha [sci.space.policy 2009 Feb 06]

I agree that moving millions of people into space isn't where we
start.

Rockets are good enough for putting a few dozen or a few hundred
people into space, or on the Moon or Mars, to start a space colony
building program.

For absolutely minimizing costs, could we send remotely operated
robots to the Moon - the time delay not being too great - that could
set up solar collectors to heat rocks and refine metals and so on?

I am making pessimistic assumptions - the program will have to
bootstrap itself, to have minimum start-up costs - and it will still
be so expensive that only the U.S. taxpayer can fund it, not any
private investor. If it can be done in the worst case, then it can
certainly be done if things are easier.

At some point, though, it has to have a payoff for people on the
ground. Sending stuff down Earth's gravity well is one way to do that,
but that should be avoided as far as possible. Moving people up - once
there is somewhere for them to go - is better. For that, really cheap
access to space is needed.

Yes, the beanstalk is conceptually simple. The super-strong and
lightweight materials it needs, though, are anything but simple to
produce, and anything but cheap. Maybe someday it can happen, but I
want to see if I can show that space is possible without depending on
far-off dreams or incredibly advanced technology.

Which is why I'm excited, for example, that while we're waiting for
fusion power - which hasn't been forthcoming on schedule - we have the
thorium breeder reactor as something that could tide us over in the
interim.

John Savard

"Martha Adams" wrote:

Peering behind all the PR about
"what the people want," "domino theory of communism around Vietnam," and
etc, why was Apollo killed when it offered so much to our future?

Why is it "PR" to cite "what the people want"? It was simply political
fact that the "America has to be #1 in space or lose the Cold War"
sentiment of 1957-1961 had weakened considerably by the late 1960s.

The responses to that, _mutatis mutandis_ over four decades since,
fall into three broad categories:

1) Wish for a re-run: a new Sputnik-like scare from Chinese space
activity, a new JFK, whatever. Often bolstered with appeals to claimed
historical or evolutionary precedents: Wright Brothers, the American
frontier, Columbus, Zheng He, hominids out of Africa, lungfish out of
the sea, whatever.

2) Claim that deep down, the American electorate really *does* want
space as much as a handful of space fans does, but since the glorious
1960s has been consistently distracted by spurious ideas: [fill in
here whatever political/social/cultural trends or public figures the
claimant especially dislikes]. Kinda like the Marxist notion of "false
consciousness": the masses really *are* ready for revolution, but
don't know it because they lack the clarity of vision we in the
People's Vanguard enjoy.

3) Chase after the "NewSpace vs. NASA" red herring, which in effect
asserts that we already *have* the technology and experience to pick
up the pace dramatically, but (in the words of St. Ronald) "government
is the problem." As soon as it gets out of the way, Musk or Branson or
Bezos will emerge as the new Thomas Edison or Henry Ford or Jobs &
Wozniak or [back to appealing historical precedents as in (1) above]

4) Recognize that 1957-1968 reflected a unique and transient
confluence of factors... that there ISN'T any "silver bullet" argument
(or "killer app" market) for space that will suddenly open voters'
eyes (or investors' wallets) wide... and settle down to the slow,
costly, patient, incremental task of making space affordable with the
limited resources and political support that *are* available.

Because response (4) doesn't offer either the promise of renewed
thrills in quick succession like the Apollo years, or the consolation
of scapegoating, it naturally has little appeal.

In sci.space.policy message 2dfddc30-3c74-45ca-ae4d-13935e3aa336@g39g20
00pri.googlegroups.com, Wed, 4 Feb 2009 04:16:08, Quadibloc
posted:
Some time back, I noted that, as I read in one book that the V-2
levelled off in flight at 20 or 25 miles up,

Which should one prefer to believe - "one book" or http://en.wikipedia
..org/wiki/V-2_rocket ?


Supposing the highest railgun we can reasonably build is one that is 2
1/2 miles high. This assumes it's built on the side of a mountain -
but a typical mountain of 14,000 feet or so, rather than holding out
for Mount Everest. A tunnel down to sea level would be required as
well. This would be 4 kilometers, or 4,000 meters.

As regards sea level, Israelis can do almost half a kilometre better; or
Jordanians to launch eastwards.

To get as good a performance as possible, I will assume a high
acceleration; the passengers would have to endure 5g, so that means
the ship is accelerated at 4g inside the railgun. Round it off to 40
meters/second^2.

A difference of 1 g applies only for vertical launch.



Note that orbital velocity is reached using 1 g horizontal acceleration
after a distance of half a radian; another half-radian gives escape
velocity.

--
(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.

On Feb 5, 10:38*am, Dr J R Stockton wrote:

A *difference of 1 g applies only for vertical launch.

Yes. Basically, I was discussing a change of mind I had; first, I had
envisaged a horizontal launch from a high altitude, but then, to
achieve greater practicality, at the cost of requiring a larger
portion of the delta-V needed for LEO to be supplied by rocket power,
I considered a switch to a near-vertical launch.

Which I found from back-of-the-envelope calculations to be
impractical.

I didn't try doing the vector addition for the 30 degree launch that
would have doubled the length of the ramp; you are correct there would
be an additional gain of a higher tolerable acceleration.

John Savard