Solid Nitrogen Fuel Could Lighten Rocket Load

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To escape the earth's atmosphere, rockets need a lot of fuel. So much, in fact, that much of the volume of current models is devoted to carrying it. If scientists could succeed in synthesizing more efficient propellants, it could lead to smaller spacecraft. To that end, a report published in the current issue of the journal Physical Chemistry A may help. The findings suggest that the production of a solid form of nitrogen that packs twice the energy punch of current space propellants is feasible.

Rodney J. Bartlett and his colleagues at the University of Florida ran computer simulations to investigate the properties of a new form of nitrogen known as N₅⁺N₅^-. An ionic bond between a negatively charged group of five nitrogen atoms and a second group of positively charged ones holds the compound together, making it a solid crystalline salt. The positively charged half of N₅⁺N₅^- has been manufactured in a lab, but N₅^- so far remains in the realm of conjecture.

The Florida team posits that N₅^- should form a ring of five nitrogen atoms that share the negative charge equally among themselves. Their calculations further indicate that it should be stable enough to manufacture it experimentally, though the effects of the crystal's framework on the stability of the molecule remain unsolved. According to the report, N₅⁺N₅^- could release a comparable amount of energy per gram as hydrazine, a liquid comprised of hydrogen and nitrogen that powers many current spacecraft. But because the density of the solid fuel is calculated to be twice that of hydrazine, only half the volume would be required to carry it, "which might allow for smaller and therefore lighter rockets."

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