[AR] Re: 500,000 tons

  • From: Keith Henson <hkeithhenson@xxxxxxxxx>
  • To: arocket@xxxxxxxxxxxxx
  • Date: Tue, 8 Apr 2014 00:55:15 -0700

On Mon, Apr 7, 2014 at 11:28 PM, David Weinshenker <daze39@xxxxxxxxxxxxx> wrote:

snip
>
> What I think is loony is the assumption of starting at such a large
> scale... it takes time to accelerate the industrial capacity to -build-
> 500,000 tons/year of new "stuff"... what is the current "M-dot" of the
> present US (or global) heavy manufacturing capacity? What are historical
> examples of ramp rates? (e.g., the US industrial activity of World War 2?)

That's an *excellent* question.

The second stage has to fit within the Skylon cargo bay.  It holds
about 10 tons of hydrogen, which takes up most of the space.  Second
stages reach GEO at a rate of 72 per day.  That requires manufacturing
them at a rate of three per hour, a rate that takes several
Panamax-class container ships to deliver about 25,000 of them from
manufacturing plants to the launch site every year.

This shipping requirement is simply the consequence of building 100 GW
of power sats with a mass around 500,000 tons per year, and not using
dedicated transport tugs from LEO to GEO.  Do the numbers make any
sense?  That is, do we have any experience manufacturing aerospace
objects at this rate?  Do we have any related industrial experience?
The answer is "maybe" on both questions.

A B-17 is about the same mass (29,600 kg vs. 30,000 kg) with
equivalent empty and full mass as the proposed second stage.

"At the peak of production, Boeing was rolling out as many as 363
B-17s a month, averaging between 14 and 16 Forts a day, the most
incredible production rate for large aircraft in aviation
history."[al1]

A B-17 is far more complicated than the second stage should be.
Boeing produced B-17s in the 1940s at 20% of the second stage
production rate.

Typical production lines operate at 10-30 units per hour.  Run one
shift, five days a week, the production rate would be 12.6 per hour,
about one every 5 minutes.  The empty mass would be around 10 tons.
The payload (except for fresh food) would probably be preloaded at the
factory, requiring only fueling.  Fueling through the Skylon would
simplify flight operations, though it does present leak hazards.

I don't know the m-dot of current industry, but it's big.  The US has
lost more than half of it's automobile market, but for decades it
produced 10-15 million cars a year.  Most of them were a couple of
tons, making the car production alone 20-30 times the proposed initial
power satellite construction rate.  I worked for a while at the EMD
plant.  A few years before I was there they cranked out over a
thousand locomotives in a year. At 160 metric tons each, that one
factory produced 160,000 tons of product, and it may have been higher.

> It seems like overly ambitious expectations - and the attendant tendencies
> to burn money too fast in the wrong places (and to view realistic outcomes
> as project-invalidating "failures") tend to be a pretty strong risk factor
> for "hard-starting" what could have been feasible industrial undertakings!

If you have specific idea of how to apply this to the power satellite
project, I would be very interested.

> Also, does a power satellite need to be at geosync?

They do.  Anything else is just a nightmare of complications.  Close
in, unless you are using sunsync, the earth eclipses them too much of
the time.

> Seems like a given
> transmitter could deliver better power density at the surface from a
> lower orbital altitude... and it's probably going to want active beam
> aiming in any case (which is one of those things that -can- be "done
> without moving parts, in Software" anymore - i.e., with things like
> phased-array techniques)... so why not just have a constellation
> of the things spinning overhead at low altitude, each scanning its
> beam angle to maintain targeting as it passes over each antenna farm
> (and then switching to illuminate the next one as it came in range).

This means that one of them being out of service give the utilities a
problem of huge blocks of power going in and out of service.  Plus you
can't turn it on till you have a bunch of them.  It's just too
complicated.  At least it is for me.  Royce Jones promotes this
variation.

> My thought would be actual geosync would be undesirable (due to conflict
> with exactly-positioned communications craft);

The communication satellites would be bolted on to power satellite
that would supply power and station keeping.  The comm sat guys like
the idea.

>  it might be better to use
> an orbit that's high enough to avoid the ISS and the air, and low enough
> not to get too much Van Allen exposure...

Thanks for the comments.

Keith

> -dave w
>

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