Re: least polluting rocket fuel


psturroc@xxxxxxxxx wrote:
Are there any rocket fuels -- existing or potential -- that are less
polluting than kerosene or hydrogen? If so, are any of them
economically feasible?

Potentially there are an infinite number of rocket propellents with
minimally reacting emissions. A mass ejection system using an
acceleration means to eject any inert mass will obey Newton's law of
equal and opposite reaction. If you were smart enough you could eject
sand, or marshmallows, or watermelons, fast enough to get a forward
thrust from it.

Most people aren't smart enough, so they use chemical explosives to
accomplish the task, beginning with gunpowder being used a thousand
years ago for Chinese rockets for warfare and fireworks displays.
Hydrogen Peroxide is an explosive used by some model rocketeers which
is fairly benign environmentally and quite capable of causing fatal
mishaps to the reckless experimenter.

As pointed out by many posters in this thread, Hydrogen and Oxygen as
fuel is fairly clean under many circumstances, although high volume
traffic in the Ozone layer might present a future problem, as Hydrogen
is very reactive with ozone, so imperfectly burned H2+O2 could
conceivably present a problem at this strata someday bye and bye.

Hydrogen by itself is not flamable. It requires oxidizer. H2+O2 outputs
significant heat, which causes atmospheric Nitrogen to react with
atmospheric Oxygen to make oxides of Nitrogen, called NOX, which
further react to produce photochemical smog.

Any sufficiently hot fire or flame will do this, so all fiery rocket
plumes do this to some extent no matter what is burning as fuel.

The problem is not so much a constant, as it is location dependent.
That is to say a rocket fired from ground level will have ten times the
density of air to react with as a rocket ignited at ten miles in
altitude, so the chemical reaction potential is ten times greater at
sea level.

There are proposals for balloon-assisted launches, or kite-assisted
launches at high altitudes, primarily for the purposs of saving fuel to
orbit, not as "clean" concepts. They would generate less NOX as a
byproduct of saving fuel, but that is not their intent.

NASA was able to loft a 1,600 pound plastic airplane to 96,863 feet in
2001, powered only by solar photovoltaic cells and 28 horsepower of
electric motors. That's 18.5 miles high, so there is some evidence that
high altitude launchpads are worth considering.

SpaceShipOne was launched from 50,000 feet from a flying platform on a
craft named White Knight, although it only attained a maximum height of
one-third the altitude to the International Space Station. That was
also a plastic rocket and plastic carrier plane. Perhaps if it launched
from the peak altitude of the NASA Helios record It might have reached
a low earth orbit.

The Take-Home Lesson should be that when you concern yourself about the
environmental effects you seem to get cheaper launches and better
results as a side-effect, or vice versa. Thinking cheaper produces less
environmental impacts as a side-effect. Ultimately there will be no
mass space transportation until people think a LOT CHEAPER. $10,000 per
pound Space Shuttle cargos is not the route we want to pursue any
longer than required to get the basic science data needed for $10/pound
payloads. Even $10/pound to deliver packages 220 miles is a lot more
than FedEx charges. 2,600,000 pounds of solid rocket exhaust makes a
1,300 tons of pollution. Think "CHEAPER" and you will get cleaner:
think "CLEANER" and you will get cheaper.

.

Relevant Pages