Antimatter ain’t what it used to be…

Antimatter annihilation propels the most memorable SF starship of all – the USS Enterprise – between the stars at FTL speeds by powering the manipulation of “subspace”. But what can real matter annihilation do? A naive view would claim an antimatter drive is a photon rocket with an exhaust velocity of lightspeed. The problem with that is that antimatter and matter turn into some seriously nasty gamma-rays. And nothing known can reflect a mega-electron volt gamma-ray. Is antimatter annihilation a hopeless cause then?

Several analyses say otherwise. Robert Frisbee studied the concept a bit more closely for NASA…

Systems-Level Modeling of a Beam-Core Matter-Antimatter Annihilation Propulsion System (Robert H. Frisbee)



…basically concluding that building the thing was possible, but the performance somewhat poorer than first imagined. So much energy is lost as gamma rays that the effective exhaust velocity he computed was 0.33 c. That’s way, way above the piddling 0.01-0.05 c hoped for from fission or fusion reactions, but a long way from ideal. A major problem was storing the antimatter – very cold anti-hydrogen ice could be levitated due to the residual magnetic field of hydrogen (and anti-hydrogen) molecules, but the storage density had to be very low, maybe 1/10th the density of hydrogen ice (itself just 75 kg/cu.metre.) Another problem was cooling off systems exposed to the gamma-rays produced by the engine. Frisbee’s starship design is very narrow, and very, very long. But he believed a transit speed of 0.25 c was feasible, and allowed a return mission design.

A slightly poorer performance, just 0.2083 c, was derived by Ulrich Walter in his text Astronautics (from Google book preview.) Not bad, but no one is likely to be powering to near lightspeed with any reasonable amount of antimatter. At least with normal matter structures.

Hans Moravec speculated on an interesting material over 20 years ago… Higgsinium …which is composed of heavy, charged supersymmetric versions of the Higgs boson (still undiscovered.) If such could be made in sufficient amounts it could be used as a gamma-ray reflecting material and enable true antimatter/matter photon rockets. However such SUSY particles have yet to be observed – maybe they exist, maybe they don’t. Once the Large Hadron Collider has obliterated enough particles in the TeV range of energies we may well know. Watch this Space for an update in ~2 years.