ALBERT

Description: A new family of environmentally friendly, low-freezing-point, high-density monopropellants is being developed under a NASA Glenn technology program. New monopropellant technology would greatly benefit a range of small (〈100 kg) satellites and spacecraft missions. These monopropellants are mixtures of hydroxylammonium nitrate (HAN), fuel, and water. Primex Aerospace Company, under contract to the NASA Glenn Research Center at Lewis Field, tested a 1-lbf thruster using a HAN-based monopropellant formulation. Over 8000 sec of total test time was accumulated on a single thruster using the blowdown duty cycle typical of state-of-the-art monopropellant systems.

Description: The NASA Glenn Research Center is sponsoring efforts to develop advanced monopropellant technology. The focus has been on monopropellant formulations composed of an aqueous solution of hydroxylammonium nitrate (HAN) and a fuel component. HAN-based monopropellants do not have a toxic vapor and do not need the extraordinary procedures for storage, handling, and disposal required of hydrazine (N2H4). Generically, HAN-based monopropellants are denser and have lower freezing points than N2H4. The performance of HAN-based monopropellants depends on the selection of fuel, the HAN-to-fuel ratio, and the amount of water in the formulation. HAN-based monopropellants are not seen as a replacement for N2H4 per se, but rather as a propulsion option in their own right. For example, HAN-based monopropellants would prove beneficial to the orbit insertion of small, power-limited satellites because of this propellant's high performance (reduced system mass), high density (reduced system volume), and low freezing point (elimination of tank and line heaters). Under a Glenn-contracted effort, Aerojet Redmond Rocket Center conducted testing to provide the foundation for the development of monopropellant thrusters with an I(sub sp) goal of 250 sec. A modular, workhorse reactor (representative of a 1-lbf thruster) was used to evaluate HAN formulations with catalyst materials. Stoichiometric, oxygen-rich, and fuelrich formulations of HAN-methanol and HAN-tris(aminoethyl)amine trinitrate were tested to investigate the effects of stoichiometry on combustion behavior. Aerojet found that fuelrich formulations degrade the catalyst and reactor faster than oxygen-rich and stoichiometric formulations do. A HAN-methanol formulation with a theoretical Isp of 269 sec (designated HAN269MEO) was selected as the baseline. With a combustion efficiency of at least 93 percent demonstrated for HAN-based monopropellants, HAN269MEO will meet the I(sub sp) 250 sec goal.

Description: The capabilities and performance of an aircraft depends greatly on the ability of the propulsion system to provide thrust. Since the beginning of powered flight, performance has increased in step with advancements in aircraft propulsion systems. These advances in technology from combustion engines to jets and rockets have enabled aircraft to exploit our atmospheric environment and fly at altitudes near the Earth's surface to near orbit at speeds ranging from hovering to several times the speed of sound. One of the main advantages of our atmosphere for these propulsion systems is the availability of oxygen. Getting oxygen basically "free" from the atmosphere dramatically increases the performance and capabilities of an aircraft. This is one of the reasons our present-day aircraft can perform such a wide range of tasks. But this advantage is limited to Earth; if we want to fly an aircraft on another planetary body, such as Mars, we will either have to carry our own source of oxygen or use a propulsion system that does not require it. The Mars atmosphere, composed mainly of carbon dioxide, is very thin. Because of this low atmospheric density, an aircraft flying on Mars will most likely be operating, in aerodynamical terms, within a very low Reynolds number regime. Also, the speed of sound within the Martian environment is approximately 20 percent less than it is on Earth. The reduction in the speed of sound plays an important role in the aerodynamic performance of both the aircraft itself and the components of the propulsion system, such as the propeller. This low Reynolds number-high Mach number flight regime is a unique flight environment that is very rarely encountered here on Earth.

Description: On-board propulsion functions include orbit insertion, orbit maintenance, constellation maintenance, precision positioning, in-space maneuvering, de-orbiting, vehicle reaction control, planetary retro, and planetary descent/ascent. This paper discusses on-board chemical propulsion technology, including bipropellants, monopropellants, and micropropulsion. Bipropellant propulsion has focused on maximizing the performance of Earth storable propellants by using high-temperature, oxidation-resistant chamber materials. The performance of bipropellant systems can be increased further, by operating at elevated chamber pressures and/or using higher energy oxidizers. Both options present system level difficulties for spacecraft, however. Monopropellant research has focused on mixtures composed of an aqueous solution of hydroxl ammonium nitrate (HAN) and a fuel component. HAN-based monopropellants, unlike hydrazine, do not present a vapor hazard and do not require extraordinary procedures for storage, handling, and disposal. HAN-based monopropellants generically have higher densities and lower freezing points than the state-of-art hydrazine and can higher performance, depending on the formulation. High-performance HAN-based monopropellants, however, have aggressive, high-temperature combustion environments and require advances in catalyst materials or suitable non-catalytic ignition options. The objective of the micropropulsion technology area is to develop low-cost, high-utility propulsion systems for the range of miniature spacecraft and precision propulsion applications.