With all the rockets that we have looked at there are advantages and disadvantages that we have discussed, some relatively near term ideas have been proposed consisting of a hybrid of the rockets.
These attempt to gain the advantages of other systems while offsetting the disadvantages.

An example of these systems is the Hybrid Nuclear-Thermal / Nuclear-Electric Propulsion. This system takes advantage of the high thrust of the nuclear-thermal system (>0.1) and the high specific impulse of the Nuclear-Electric system (2000-5000secs).

There are several near term proposals for high performance rockets. These are revolutionary ideas that use nuclear technologies but gain huge performance advantages over standard systems by introducing antimatter. This results in significant improvements over standard nuclear rockets and requires much less antimatter than would be required for a pure antimatter rocket, which is important because only very small amounts of antimatter can be produced with today's methods.
While the performance may be inferior to pure antimatter rockets, the proposals represent interesting and valuable projects for the near term while we wait for superior methods of antimatter production.

It should be noted that the following proposals would be no use for energy production as there is a net energy loss, but with propulsion we are only concerned with providing thrust, not producing energy.

ICAN-II

The Antimatter Space Propulsion team at Pennsylvania State University (PSU) have developed ICAN-II. This utilises a combination of antimatter and nuclear fission, using the antimatter to induce fission by allowing the antiprotons to penetrate the fissionable nuclei where they will annihilate with protons. This release of energy causes the nucleus to split, with the result of a greater release of energy than with standard fission. It is estimated that only 140 ng of antimatter will be required for a 30-day trip to Mars, which is significantly less than a beam core antimatter rocket.

The ICAN-II	The AIMStar
Courtesy: Penn State University Antimatter

Antiproton Initiated Microfission/fusion (AIM) and AIMStar

Following the ICAN-II will be AIM and AIMStar, again proposed by PSU and these will be the next step towards a beam core engine, when slightly more antimatter is available. Here again antimatter is used to enhance a fission reaction but this time the fragments would then be used to heat the fusion fuel, inducing fusion. There is an increased requirement of antimatter, but less fissionable material and higher specific impulse at around 61,000secs.

The combination of fusion and antimatter

Again this is another attempt at utilising such small amounts of antimatter for near term proposals, though more would be required here than in AIM. Here we effectively cut out the fission process and use the annihilation reaction to provide the energy to induce ICF directly (i.e. using antimatter instead of lasers). Estimates suggest this system would be able to reach Mars in well under a month.

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