A Plateau-Burning, Low Temperature-Operable Solid Propellant for Mars Sample Return

The Mars ascent vehicle (MAV) is required to endure a long space transit time, high-g loading during planetary entry, and high launch loads, all at low temperatures of approximately -40 Deg C. Additionally, low-temperature motors like the MAV are often tested at room temperature, since testing at temperatures of -40 Deg C or lower is both difficult and expensive. Since testing at higher temperatures results in higher burn rates for typical propellants, and thus higher working pressures, ambient tests result in a motor case that is heavier than required for a low temperature mission, because ambient testing results in a higher maximum expected operating pressure. Our proposed technology alleviates that problem by using a plateau-burning composite propellant that will substantially lessen the burn rate sensitivity to temperature. As such, the MAV operating pressure in ambient conditions will more closely resemble those on the Mars surface, allowing for a lighter motor case resulting in reduced weight, smaller volume and greater propellant mass fractions. Additionally, our plateau burning formulation will include a low temperature binder with a high density fuel additive, in order to alleviate the loading stresses at low temperatures and further increase the motor density-Isp. This may allow us to eliminate the need for the MAV launch erection equipment currently baselined for the MSR mission.

The primary benefit of using a plateau-burning composite propellant formulation on the MAV is an increase in solid rocket motor (SRM) propellant mass fraction. Further, using a low temperature binder with a high density fuel will increase the overall motor performance, as well as its capability to withstand stresses at low temperatures. As such, potential NASA applications include SRMs used in space exploration systems, as well as earth and planetary launch vehicles where high performance is a major performance objective.

The application of our technology can be extended to missile defense programs such as THAAD, Patriot, and the SM-3/6, where low temperature missile requirement are on the order of -65 Deg F. Those programs can also benefit from the high density-Isp of the propellant to increase ??V performance. In addition, the low sensitivity of burn rate to temperature provided by our novel propellant formulation can also be advantageous, providing uniform performance over a wide range of operating conditions. Further, our high-density propellant would also be beneficial for a ramjet, where high density-Isp performance and high burn rates are desirable.

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