On 19/7/21 10:12 am, Kurt Feltenberger - kurt at thepaw.org (via tml
list) wrote:
> I was having a discussion with a friend this afternoon, also a long
> time Traveller player, and the subject of beanstalks came up.  His
> position (he's very influenced by 2300AD/Traveller:2300) is that
> beanstalks are the way to go and they're hands down, better than the
> options of using interface transports or landing a ship on the
> surface.  My position is that they're economically viable, and only
> barely, at a narrow band of tech levels from ~8-9, maybe up to 10, but
> that's pushing it.
>
> My argument is that investors want to see a return on their investment
> while they're still alive and that by about TL10, a 10kdton platform
> could be made and operated in such a way to recoup the investment and
> turn a profit much quicker than a beanstalk without the problem of
> parts/spares availability.  You would need a full fabrication
> shop/factory with the TDP of every part that was used in the beanstalk
> given a potential lifespan of hundreds of years.
>
> Thoughts?
>

Kurt, you seem to be implicitly assuming "on a Garden world that I can't
believe is not Terra" - or have I misread?

Ceteris paribus, a smaller-radius planet would need a less-fancy
beanstalk (such as a being-terraformed Mars).

As Rupert has mentioned, both alternatives (beanstalk and orbital
platform) would have the spares problem.

Part of the disconnect here could be the divergence between OTL nanotech
and Trav nanotech -
http://www.niac.usra.edu/files/studies/final_report/521Edwards.pdf  (c
2003) preferred a carbon nanotube composite ribbon for the real long bit
of the beanstalk and quoting $700/gram (2003 USD) for
commercially-available nanotubes _then_.  In 2004 (quoting from
http://images.spaceref.com/docs/spaceelevator/iac-2004/iac-04-iaa.3.8.2.01.edwards.pdf
),

"At the current time, carbon nanotubes (CNTs) have been measured with
tensile strengths of 200 GPa. CNTs have been spun into yarns of pure
carbon nanotubes and have been implemented in composite fibers. The spun
fibers are a new development (Li, 2004) though CNT composite fibers have
been made with as high as 60% CNTs, strengths comparable to steel (5%
CNTs by weight) and kilometers in length."

I've no idea what TTL that sort of dry nanotech would develop at, but I
suspect it would be a little later than 8.

Take it with the requisite spoonful of salt, but the Edwards report I
linked to first estimates "that the space elevator could be operational
in 15 years for $10B".  That's (I think - it's 4am and I don't know
where my socks are) for a prototype cable where each climber masses 20
metric tonne capacity with a 70% payload fraction and the beanstalk
ribbon itself masses 750 metric tonnes.  Edwards reckons it would take
roughly three years to bootstrap the first such beanstalk to be able to
support kilotonne climbers (presumably with a similar payload fraction).

Further, according to Edwards, beanstalks _do not have to be grounded on
the planet's equator_.  (pp14-15).  The claimed operational cost is 100
USD/lb (or 220 USD/kg) "to any Earth orbit, or location between Venus
and the outer asteroid belt". (p43)
That includes 4 conventional expendable rockets to GEO to loft all the bitz.

The phase 1 Edwards report,
http://images.spaceref.com/docs/spaceelevator/472Edwards.pdf, is an
earlier, more detailed, report that also makes for some fun reading.  It
also estimates the cost of a second beanstalk at approx 35% of the
first, with later cables being even cheaper (p 11.5).  P 7.3 states that
a Martian elevator would be "roughly 1/2 the length and 1/20th the mass
for the same capacity" as the Terran equivalent.

For a comparison, (from https://www.spacex.com/vehicles/falcon-heavy/ ),
SpaceX's Falcon Heavy is stated to be able to loft 63.8 metric tonnes to
LEO, 26.7 metric tonnes to GTO, and 16.8 tonnes to Mars.  A very quick
shufti at a launch cost
(https://twitter.com/elonmusk/status/963076231921938432 - as I said,
_very_ quick shufti) is 150M USD for a "fully expendable Falcon Heavy" -
giving per-kilo payload costs between 2,351 USD/kg to LEO and 8,928
USD/kg.  Admittedly, I am comparing an operational, presumably-debugged,
chemical rocket to a paper design, but I'm working with what I have.

IIRC, that $10B USD price tag for a carbon-nanotube-ribbon beanstalk
works out to approx 3.3 GCr (or 3.57 G$), with no gravitics involved. 
And it's not like power beaming could benefit from cheap fusion power or
transfer efficiencies above 2%, the ribbon itself from  materials
advances, or anything that would drop that overall cost.  </sarcasm>

GURPS Traveller: Interstellar Wars, p22, quoth "By the late 2060s, the
cost of moving a pound of payload from Terra’s surface into orbit had
fallen by a factor of over 100."
Going from those SpaceX costs, that's lift costs dropping to 23 - 89
USD/kg - the upper end could (at a glance) be matched with increasing
power beaming efficiency from 2% to 5%, and the lower by increasing
efficiency to 19.2%

p175 of GT:ISW, for a century later, quotes lighterage fees as "$10/dton
for surface to orbit, $15/dton to a ship at a planet's 100-diameter
limit" - the $ used here being the Terran Confederation solar (1 solar =
2.8 USD as at 2000).

I think those are TTL12 costs (the GURPS 4th to Trav TL conversion is
even rubberier than the GURPS 3rd to Trav TL conversion).
Given the bulk densities given for cargo in GT:FT p58 ("Heavy cargoes"),
topping out at 25 metric tonnes per displacement ton, that places a
lower bound of 0.6 solars/tonne (or 1.68 USD/tonne) for surface-to-100D
lift costs (and thus surface-to-synchronous lift costs would not be
higher for the same bulk density).  Containerised cargoes (p56, GT:FT)
seem to top out at 6 metric tonnes/dton, for a lift cost of 2.5
solars/tonne (or 7 USD/tonne).

GT: Starports, p63, mentions in passing both beanstalks for lifting
cargo in bulk, and mass drivers for durable cargo (not passengers or
fragile kit), but leaves costing up to el GM.  According to GT:SP, these
happen due to "immense traffic patterns, fragile ecologies, or poor
industrial resources for supporting gravitic technology".  The mass
driver approach is "substantially cheaper than shuttle service though
_far_ less environmentally friendly".

I'm not sure if that supports or partly refutes your thesis, Kurt - I'll
have to be more awake.

Alex