Re: SPACE: How hard IS it to get off Earth?

Doug Jones (
Wed, 10 Nov 1999 21:50:28 -0800 wrote:
> Here's a question for our aerospace professionals (and space groupies like
> me): How quickly after the development of a general purpose programmable
> assembler could a completely "de novo space program" be developed, and how
> many (or rather, how few) people with what expertise would be necessary to do
> it?

How few? Three people- a brilliant mechanical engineer (Dan Delong), a good all-around systems guy with a mind like a packrat (me), a great engineering manager/engineer (Jeff Greason), and a bunch of design software (petaflops and then some).

How fast? Mighty damn quick. Having incredible materials available would help a lot- just today I was talking with Dan on how much I'd like to have diamondiod materials for rocket engines- great strength combined with the highest thermal conductivity, far better than copper.

Valves, pumps and actuators are idiosyncratic things, bulky and heavy compared to the pipes they join (valves on a small rocket engine often weigh far more than the combustor itself). With nanotech, the pipes would *be* the valves and pumps- no actuators. Control systems would not have noticable mass, those peristaltic pipes would have embedded supercomputers.

I'd choose a light hydrocarbon for fuel, probably propane at the same temperature as the LOX, it's almost as dense as kerosene, but has good Isp. The tanks would be diamond composite, and as Drexler mentioned to me years ago, as the tanks empty, they disassemble themselves and are added to the fuel stream. This drives the non-payload mass delivered to orbit to far less than the payload (of course, since anything no longer in use can be taken apart and reused, everything can be considered payload).

The combustion chamber throat shrinks as the vehicle gets lighter, reducing thrust to limit acceleration. The bell gets larger and larger to maintain ideal expansion until the nozzle extension is less than paper thin (the stress on that part is tensile in the hoop direction and compressive axially).

With improvements to CAD software visible on the horizon, and a complete web source of all engineering data (Quick, what is the enthalpy, heat capacity, thermal conductivity, and density of oxygen at 157 Kelvin and 34.5 Mpa?) engine and vehicle design would be limited more by the imagination of the engineers than by the resources available.

I've been thinking about this question off and on for years, and the timeline keeps shrinking- the only hard limit I can see is the doubling time of the assemblers and the power available for making fuel. With a little bit of design ahead, and a lot of really clever (but non-sentient software), it should only take hours.

As for setting up a spacefaring civilization- the minimum is enough mass to start bootstrapping more from extraterrestrial sources, a Library of Everything (at most a ton or so), a few people, and a good head start.

Drexler wrote of starting a sellar economy by delivering "a hollow shell of strong material several microns in radius and containing about a cubic micron of cargo" to another solar system. See

A few tons and a few people would be more than enough, with hard nanotech.

Bottom line: Give me the right tools and I could be out of here tomorrow.

Doug Jones
Rocket Plumber, XCOR Aerospace