# Re: Limits and Capabilities.

From: Dani Eder (danielravennest@yahoo.com)
Date: Wed Jun 12 2002 - 14:20:36 MDT

> > Space exploration.
>
> Due to cost limitations, unless the private sector
> gets its act together
> I don't think we can expect to see much in the way
> of space
> exploration. The except would be if the Chinese
> pump a lot of money
> into their space program, in which case we'll have
> another Space Race
> with the US.
>

The energy cost to put 1 kg in orbit is about 20
kWh, or about \$1 at wholesale rates. It takes
about 1,000 kg per person to transport people to
orbit (body mass + chair + share of pressure
vessel, etc). So an efficient transportation
system should run around \$1,000 per ticket.
At the efficiency of commercial airlines, for
which total costs run around 4 times fuel cost,
that would be \$4,000 a ticket.

The fact that the going rate is about \$20M for
a ticket is a testament to the poor efficiency
of current launch systems. For example, did you
know the fuel efficiency of a commercial jet
engine is twenty times that on the Space Shuttle?

One inexpensive way to send people (and other
stuff) into space would use a large pneumatic
tube. Assume a 30 ton projectile carrying a
3 ton cargo needs to be accelerated at 6 g's
(about the limit for humans). If it's diameter
is 2.5 meters, the operating pressure is only
52 psi. That's why I call it a pneumatic tube
rather than a gun. If located on the big island
of Hawaii (which as a shield volcano has long
stretches of constant slope mountainside), you
can get to 2 km/s this way, which is 25% of the
speed to orbit. The projectile carries a rocket
that does the rest of the job of getting to orbit.

The rather small reduction in the velocity that the
rocket supplies has a dramatic effect on the cost.
Without the boost from the tube, the rocket has
to be 83.7% fuel, 15% structure, and 1.3% cargo.
With the boost, the figures change to 74.4% fuel,
18% structure, and 7.6% cargo. So the fuel-to-
cargo ratio drops from 64:1 to 10:1. But more
importantly, the 20% increase in structural
weight results in 100 times the service life for
the vehicle (the fatigue life for aerospace
structures varies by a factor of 10 for each 10%
change in stress in the region close to yield
strength, which is where most of them operate).
So where the Space Shuttle was designed for 100
flights, the pneumatic-launched vehicle would
be good for 10,000 flights (25 years of daily
launches).

---------------------------------------------

Having pointed out that space travel can be
relatively inexpensive if done right, I think it
will be a moot point to envision a Mars base
in place by 2030 if the Singularity arrives by
2020. Travel will occur at the speed of light