Monetary Cost is not the issue Forum: SSI-List
Thread: Monetary Cost is not the issue
Paul Fernhout wrote a response to my posting about cost that included:
"I think rather than say "cost is not an issue" it would be more
accurate
to characterize my entire point as "launch cost is not the bottleneck"
because rich people could go into space now but mostly have no reason
to.
and..
As for a factor of ten, that's just for putting people in orbit. At
$1000 per pound, the cost of launching a person is around $150K, and
so
about the cost of a mortgage, and so available to most western
people.
and.
As I implied, launch costs really don't matter even at $10,000 per
pound
if you are only going to launch one payload which will self-replicate
and then make wealth the whole human race can share in..
and..
For references, a SSPS could (in theory) just punch down a big laser
beam that could be used to heat propellant in a launch capsule in the
beam, so no need for rectennas etc. on the ground or receiving end in
that model. Of course, such powerful lasers could also be weapons, so
that approach may also assume a certain social advance among all
Earthlings. :-)"
Sorry to be a pedant but your arguments seem to miss the target on a
number of points.
I appreciate that the monetary cost of a single launch (or even a
dozen) is immaterial if that was all that was ever needed but IMHO I
don't think the idea has legs for entirely practical reasons, ie
maintenance and the range of basic materials required etc, etc we
may come tantalisingly close but not close enough for people to put
money on. It is impossible to foresee all possibilities and include
them in a small enough unit. After all, even our planet and the best
computer known (us) are barely up to the task.
However, that's another argument that I really see little point in
following since the goal (as I see it) is not about our taking over
space by machines, I believe its about us humans getting out there
for ourselves and to do that we must obviously leave the ground or do
we perhaps "simply" just send up another Adam and Eve? J]
faring creatures and/or we are going to prevent the complete
destruction of our climate and natural resources in doing so, we must
develop a viable means to reach (and use) space and do so sooner
rather than later.
Since we must eventually do so using renewable resources, why not
start the way we must (eventually) continue anyway. That means
developing our air and space transport on renewable energy NOW. If
it's really not possible (the most unlikely , extreme case), then the
sooner we find out, the better so we can preserve our remaining
resources.
I cannot agree that SPS isn't critical or that space is of little
practical use in our future energy picture as some have implied. The
problem is to work out how and the answer on all counts is beamed
energy.
Energy from space could, quite reasonably, supply an answer to all
our needs, including what is probably the most serious problem we
face transport, particularly flying, for which there is as yet no
local solution proposed that won't pollute us to death and/or consume
our remaining resources within the foreseeable future. As a CPL,
though no longer flying, I consider myself reasonably aware of
aviation matters.
As you say, it is possible, theoretically, to "punch down a big
laser." I take your suggestion very seriously but the method
proposed is totally impractical for half a dozen reasons, including:
1. The human safety "weapons" angle that you so lightly dismiss
which could scuttle the whole project before it starts. The very
prospect of a beam pointed at the ground, strong enough to directly
lift a craft from the ground (~1Mw/m2 or 1000x solar flux) would send
99% of the population into total hysteria (including me). It's a
total no go-er! Don't even think about it. Please!!!
2. Such a beam must be captured from LEO (500 miles, as
suggested by Myrabo) or, more credibly a GEO (23,000miles),
especially the GSO (geostationary orbit).
3. for the direct approach, the beam must be captured within
the radius of a craft a virtually impossible, moving target that
even if ever achievable from that distance is of no great benefit.
The (lightspeed) time delay alone makes it totally impractical.
4. Collecting the beam (from above) and transmitting it through
the craft at sufficient E/D to ionise a reactant below presents an
impossible packaging task. [Some energy could be used to make an Air
Spike but not enough to be useful unless beam strength is off the
planet.]
5. How much easier to transmit to the ground at low E/D, and
then simply reflect the power back up with mirrors to a focus exactly
where it's needed? Beam strength (pointed at the ground) can be quite
low, no more than 5x-10x solar flux levels.
6. The craft would be close overhead (less than 200 miles), the
beam is pointed up, and no one is going to get hurt except the (very)
occasional bird and.
7. Any excess power can easily be converted to other uses.
If we make the logical assumption that beams at high E/Ds would not
be acceptable pointed at the ground, then using lasers is only an
expensive extravagance m/waves would be cheaper, easier, more
efficient and far more flexible and versatile. Except in space-to-
space, long-range applications, m/waves are the go in most situations
for manned air and spacecraft.
Let me return to my "ideal" situation:
We already have the basic technology to beam m/waves (masers) long
distances at high efficiency.
We know that m/waves can be collected in three main ways.
Rectennas useful as a cheap means of collecting low E/D
supply and converting to electricity.
Metal mirrors capable of reflecting high E/D into a highly
tractable focus beneath a craft or into a
Waveguide the simple method of ducting power over short to
medium distances at high E/D.
We know too, that m/waves and/or solar energy can (theoretically) be
used to ionise a reactant, to provide thrust and sustain flight. The
problem is to provide enough energy, focussed at the focal point.
This can be done most efficiently if the energy is only constrained
at the focal point. [ there is a case for passing a part of the beam
through the craft (10%-20%, but not all of it]
According to the figures produced by the Lightcraft tests, a 10kw
laser was able to lift a 50gm craft at 2g's (appx). Do the sums. This
equates (appx) to 100kW/kg thrust to just lift a craft from the
ground (ie 0.1Mw/kg). Far more energy is needed to sustain powerful
acceleration but the initial goal is (obviously) to establish flight
(ie 1g+ anything).
Consider an energy supply from a large SPS in GSO
1. At an anticipated 50% conversion efficiency (solar/m-wave), a
collector array 5km in diameter could transmit 27Gw (appx) toward the
ground. (This may be 25% efficiency, but bear with me)
2. From figures quoted by NASA, at 90% efficiency (from APC page
at islandone, presently down) a ground collector (also 5km diameter)
would collect 24Gw of energy. (it is the overall diameter and E/D
that is critical here, for focusing)
3. Over a diameter of 5km, beam strength at the ground would
vary from 0.5x -10x solar flux. With a rectenna aerial array (as a
background safety measure and to collect low E/D), mirrors and
waveguides would collect energy most efficiently in the central area
where the E/D is at the highest.
4. Depending on the height of the launch platform, energy would
be directed beneath the craft either by direct reflection, by
waveguide or, as a final resort, through energy transducers. Most of
the energy received at the ground would require no conversion
process, it would be used directly.
5. 24Gw of power, over a collector 5km diameter, averages to an
E/D of less than 1.25kW/m2.
If anyone can see any impossible technology here, I would really like
to know about it.
CCMc