AN EYE ON SPACE (Apr, 1960)


By Dr. Dan Q. Posin


EARTHLINGS ARE PREPARING many kinds of fuels to propel themselves out of this world.

1. Gasoline is inexpensive, and its flow is easy to control. It is, however, hard to store and manipulate. It is not too reliable, as the rocket using it has to be intricate and there are many chances for breakdown. Thrust is moderate to low, amounting to about 270 pounds from one pound of fuel burning per second. Kerosene’s kick also is fairly low.

2. Exotic fuels. Some are common substances difficult to use. Hydrogen could be a powerful fuel if burned, but it is hard to maintain in liquid form. One might liquefy hydrogen by allowing it to combine with an element such as boron, which has a high heat of combustion (25,000 B.T.U.s). So a good exotic fuel is diborane (B2H6), its heat of combustion being 31,000 B.T.U.s per pound. But boron hydrides are poisonous and may explode.

3. Solid fuels are handy, since they can be built into the rocket. Fuel material could be something as simple as rubber burning with the oxygen of some solid compound. But solid-fuel rockets tend to burn unevenly.

4. Nuclear fission engines are under development and, of course, they give high thrust and last a long time. But their radioactive exhaust would contaminate the launching site. The engine may be used after takeoff with safer fuel.

5. Nuclear fusion is something for the future, since controlled fusion has not yet been achieved.

6. Atomic bursts—small atomic blasts will some day be used to propel rockets or spaceships.

7. The ion rocket is one in which charged particles such as cesium ions are accelerated by an electric field and hurled out the nozzle. A cesium atom can easily be made to lose an electron (i.e., become ionized), and then the electric field can act on it. A thrust of more than 20,000 pounds can be obtained for every pound of cesium used up each second, but it is not easy to ionize pounds and pounds of cesium.

8. The plasma-jet rocket operates like this: Some fuel mixture is injected as a vapor, and an electric spark ignites it. The combustion heats up the constituents, and the expanding gases go sizzling out the nozzle.

9. Solar propulsion is of several types. Concave mirrors (or other devices) could absorb sunlight and produce heat to heat some gas, thereby driving it out of the engine. Or, solar heat may spin a turbine which produces electricity to expel ions. Or, sunlight may be used as mere pressure. In regions of vacuum far from restraining gravitational fields, acceleration due to sunlight pressure on a large surface eventually gives the spaceship an enormous velocity.

10. Other energy from space, such as plasma or ion energy belts like the Van Allen belts around Earth, may be used in the future. By ingenious navigation from one belt to another, it may be possible to “sail” almost forever on this fuel just waiting to be tapped.

Some of these may be plucked out of the so-called emptiness of space, for use in helping Earthlings on their way to the stars.

  1. hwertz says: October 30, 20113:04 pm

    So, really what is used now in rockets are:
    1) Liquid oxygen with kerosene. Because it’s easy to handle, mainly.

    2) “Exotic fuels”. Liquid oxygen with liquid hydrogen, or hydrazine, or a few other combinations.

    3) Solid rocket boosters.

    7) Researched recently by NASA and in use by them since about 1999, they are much lighter than conventional hydrazine jets used on satellites for maneuvering. Reportedly the Soviets have used these systems for around 30 years. The article writer’s objections still stand, these engines do not generate large amounts of thrust. But they can make a small amount of thrust for a much larger period of time than a hydrazine jet; for the typical maneuvers of changing a satellite’s orbit or a adjusting a deep space probe’s trajectory, it doesn’t matter if it takes a week instead of an hour to do.

    Not used: #4 is now prohibitive due to environmental concerns. Also, reactors are very heavy, especially given the necessity for shielding for cargo (either human or electronic), to the point that they are not practical even given environmental concerns. Deep space probes due use radioisotope thermal generators for electrical power, but that just uses decay of a radioactive isotope rather than full fission.

    #5 — Still no controlled fusion.

    #6 — Again, shielding, and nobody wants nukes blown up in the atmosphere. This is still the leading possibility for an interstellar drive though, the general assumption is the inhabited bits would be up front, water tanks in the middle would act as radiation shielding from the nukes in the rear. But, of course, no practical design for a interstellar ship exists yet.

    #8 — not sure.
    #9 — Pretty sure NASA built one solar sail prototype, basically on a string to measure how much thrust it generated. None’s been actually used as far as I know.

    #10 — I think there’s been research into using this to power the satellite, but not propel it. However, as the solar wind varies these belts move around to much to be used for a geosynchronous satellite for instance.

  2. Hirudinea says: October 30, 20114:45 pm

    For number 6 check out this video.…

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