In article ,
says...

On Fri, 14 Sep 2012 09:00:33 -0400, J. Clarke wrote:

In article e204c1ab-9ece-48df-a2bc-2f1b4598d283
@h4g2000yqo.googlegroups.com, says...

Major cool factor....

TMT

NASA funds research into self-building spaceships Technology News Blog

Considering the difficulties of getting even relatively small
spacecraft like the SpaceX Dragon into orbit, the idea of launching
larger interplanetary craft from Earth's surface seems especially
daunting. To address this, NASA thinks that future spacefaring vehicles
could actually construct themselves after they've launched using
onboard 3D printers, eventually transforming into ships much larger and
more complex than anything that could ever be built on the planet.

While I'm all for advances in technology, this makes it clear that NASA
simply DOES NOT UNDERSTAND THE PROBLEM.

If spacecraft are to be "constructed" using 3d printers, you still have
to get the mass needed into orbit.

The problem is that it still costs vastly too much to get a pound of
mass into orbit. As long as we are throwing away a multimillion dollar
booster on each launch, that will continue to be the case. The fuel
cost for an Apollo launch, at today's prices, would be about 5 million
dollars. To put that in perspective, a Falcon 9 launch costs 54 million
dollars to put up less than 1/10 the payload.

I think NASA's point is that the mass needed for a spacecraft that's
constructed in space is a lot lower than the mass needed for a spacecraft
that's constructed here, then needs to withstand 6 or 8 or 10 g's, or
whatever.

But your point about launch costs is well taken. Do you happen to have
about 60km of really strong cable lying around?

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

You need more than 60km. The center of mass of the thing has to be
beyonde Clarke orbit--that means that it has to be more than 25,000
miles long.