3.3 Space Propulsion

3.3.1 Warfighter Needs

The goals of the Integrated High-Payoff Rocket Propulsion Technology (IHPRPT) program, under DoD/NASA sponsorship, translate into payoffs to the warfighter in terms of increased capabilities. Payoffs to launch vehicle systems include performance, cost, and reliability improvements to existing launch systems, expendable launch systems, and new reusable vehicles. The operational increases for boost and orbit transfer propulsion systems by the year 2000, 2005, and 2010 include 7%, 12%, and 18% increases, respectively, in payload capability for new expendable boosters (over the 25,000-lb baseline to LEO). An alternative to increasing the payload on a lift vehicle would be to launch payloads on smaller, more capable vehicles to reduce the need for costly heavy-lift vehicles. The resulting launch cost reductions would equate to savings of 12%, 20%, and 27% in cost-per-pound to orbit. These savings are in addition to the savings seen from design and process changes. For a new reusable launch system, the payload improvements by 2000, 2005, and 2010 approach 69%, 121%, and 170% over the life of the vehicle with cost reductions of 57%, 78%, and 90%, respectively.

Spacecraft goals will result in increased warfighter payoffs through reliable critical information gathering and global communication capabilities at reduced costs. Space vehicles in geosynchronous orbit will be able to extend their on-orbit life up to 45%, increase repositioning capabilities by a factor of 2 to 5, or increase useful mission payload mass by 10% to 30%. This last capability can mean an ability to increase the number or types of transponders, potentially manifest the same payload on less expensive launch vehicles, or increase the survivability of the satellite by allowing for increased shielding material. Communication and reconnaissance payloads will be able to reposition more often and more rapidly to support the warfighter needs in local theaters of operation without significantly sacrificing satellite life. More reliable deployment and on-orbit operation throughout the life of the satellite will provide greater assurance in asset availability. Higher performance compact propulsion systems will also enable the deployment of smaller payloads into higher energy orbits. For medium-lift vehicle class geosynchronous space vehicles launched at a conservative rate of six per year, meeting the IHPRPT goals would result in cost savings of $60 million, $130 million, and $240 million by 2000, 2005, and 2010, respectively.

Tactical missile propulsion systems will have increased range, increased maneuverability for flexible targeting opportunities, or increased kill effectiveness with decreased size providing greater weapons carriage capability under the IHPRPT program. For size-constrained systems, an alternative to decreasing the weapon size could include increasing the warhead payload or increasing the range by increasing the amount of loaded propellant. For tactical missile systems, a 10%, 25%, and 100% increase in payload capabilities can be achieved for the three IHPRPT phases (2000, 2005, and 2010). For divert propulsion systems, the number of theater missile defense systems needed to cover a given area can be reduced by 26%, 45%, and 60% through the three phases.

3.3.2 Overview

3.3.2.1 Goals and Timeframes. The IHPRPT initiative was started in FY94, with primary program impacts beginning in FY95. The program is based on achieving the goals (with respect to 1993 state-of-the-art baselines) shown in Table VIII-8 for boost and orbit transfer (B/OT), spacecraft (S/C), and tactical (T).

^* All percentage goals are percent change from the baseline.

^** An additional goal for reusable propulsion systems of 20 missions between removal is also included in B/OT propulsion.

^*** B/OT Isp goal represents a combination of specific propulsion improvements at the following respective levels:

Cryogenic Engine: 1% (2000), 2% (2005)
Hydrocarbon Engine: 13% (2000),15% (2005)
Solid Motor (Castor 120 Propellant): 2% (2000), 4% (2005)
Hybrid Motor: 8% (2000), 11% (2005).

3.3.2.2 Major Technical Challenges. The doubling of rocket propulsion system capability will be achieved through a combination of technology initiatives. To meet the propulsion system goals, investigations to increase the energy of propellants, increase the efficiency of combustion processes, increase the combustion chamber operating pressures, decrease the inert weight of propulsion systems, and improve the efficiency of thrust magnitude/vector control systems will be concurrently developed and consolidated. Specifically, propellant developments involve increasing performance (energy, density) and reducing costs (manufacture, storage, handling, testing) while improving the environmental acceptability.

For all rocket propulsion systems, the IHPRPT initiative will provide cost reductions in a system while improving payload capability. Achieving this goal will require significant performance improvements. Future propellant requirements include improved reliability and environmental acceptability, increased safety, greater performance, longer service life, and lower life-cycle costs. Propellant management devices, combustion and energy conversion devices, and control systems require innovative subcomponent and component design methods, manufac-turing techniques, and materials for the respective component and application area developments. The major advances required in liquid propellant combustion devices include an increase in theoretical-specific impulse (Isp) by increasing chamber pressure, increases in Isp efficiency as measured by Isp actual/Isp theoretical, reductions in weight, reductions in cost, and increases in reliability (measured by decrease in part count).

The solid propulsion area consists of nozzles and the igniter. In solid propulsion, the major advances required are in increasing Isp efficiency, decreasing component weight and volume, decreasing component cost, and increasing reliability. The electric propulsion area of satellite propulsion includes the power processing components and the thrust chamber assembly, including the electrode. Major advances are needed in improving the power processing efficiency, the energy conversion efficiency, and combustion chamber life.

The wide range of missions for tactical systems require multifaceted technology applications to address the higher performance needs with improved survivability and environmental compliance—at no compromise to cost or safety. Increasing propellant energy for the under 10,000 lb-s total impulse motors, 10,000-75,000 lb-s total impulse motors, over 75,000 lb-s total impulse motors, gun-launched motors, and assist boost motors requires development and application of new propellant ingredients (for smoky, reduced smoke, and minimum smoke propellants). These ingredients (fuels, oxidizers, and binder systems) will have to be of higher heats of formation or higher density. Near-term approaches include GAP, ADN, CL20, and perhaps metallic hydrides.

Propellants will have to be formulated to eliminate current burn-rate and combustion stability problems at pressures above 3,000 psi and with greater strength than currently available to allow higher volumetric loading. One approach to this may be the incorporation of ingredients such as GAP-Azide. In addition, tactical systems will no longer be limited to solid-propulsion concepts. Liquid and especially gel propellants will be investigated for possible use. Propellant development for divert propulsion (with emphasis on minimum smoke propellants) involves adding ingredients to cool the flame temperature. Additional work is needed to reduce the oxidation index of the propellant. Reducing or eliminating the amount of oxygen produced in the exhaust is the only way to achieve this. Tailoring propellant chemical properties to reduce the oxidation characteristics of the propellant gases is necessary to meet the cost and safety goals in divert propulsion. These cooling ingredients already exist and further development is not required.

In all tactical applications, meeting environmental regulations as well as safety/ survivability requirements will continue to be a major technical challenge. High-pressure operation will be investigated through propellant ballistic modification for intercept applications.

3.3.2.3 Related Federal and Private Sector Efforts. All DoD agencies, NASA, and industry participate in IHPRPT. Industry rocket propulsion IR&D investment for FY96 is approximately $50 million. NASA FY96 investment for IHPRPT-related programs for the RLV is approximately $20 million.

3.3.3 S&T Investment Strategy

The key to the IHPRPT process is the simultaneous achievement of the goals. Technology demonstrations conducted during each of the three phases will quantify the degree of success in reaching the goals. The technology demonstrators do not have to be a complete propulsion system demonstration. They may be individual components or a combination of components. The requirement is to prove justifiable, analytical connectivity that the compilation of the demonstrated technologies would work together as an acceptable propulsion unit. As a metric, the empirical or analytical data will be compared to baselines identified at the initiation of IHPRPT. Following demonstration, the technologies may transition economically to new propulsion systems or to improvements to current propulsion systems.

3.3.3.1 Technology Demonstrations. Technology demonstrations for IHPRPT are divided into three fundamental propulsion classes. Each class is a separate family of demonstrations.

Boost and Orbit Transfer Propulsion. These demonstrations, when successful, fulfill DTO (SP.10.06.F). The demonstrators for this mission application area are divided into (1) propulsion systems that lift payloads from ground level to orbit elevation (boost propulsion), and (2) propulsion systems (orbit transfer) that move payloads from one orbit (such as LEO) to another orbit elevation (GEO). Specific boost demonstrations will occur at the end of each IHPRPT phase. In 2000 the component improvements will feed into an integrated demonstration. In 2005 further component improvements will integrate into a high-performance (4,000-psi chamber pressure) booster class demonstration. Orbit transfer component improvements will feed into a FY00 high-performance (1,200-psi chamber pressure) upper stage/orbit transfer demonstration and a FY05 high-performance (1,500-psi chamber pressure) upper stage/orbit transfer demonstration.

Spacecraft Propulsion. The technology demonstrators for this mission application include two areas: chemical propulsion (e.g., solar electric) and nonchemical propulsion (e.g., solar thermal). In all cases, these system demonstrations will be conducted at simulated altitude conditions permitting direct measurement of performance at space conditions. Solar electric demonstrations (pulsed plasma thruster and hall thruster) by 2000 and 2005 will integrate all developments for satellite stationkeeping and repositioning. By 2010 advanced solar thermal propulsion systems and advanced solar electric propulsion systems (ion thrusters) for orbit transfer missions will be demonstrated.

Tactical Propulsion. These demonstrations, when successful, fulfill several DTOs. The extensive, integrated, full-scale propulsion system evaluations begin with sea-level evaluations of the delivered performance in a rocket engine/motor. Next, evaluations are performed to demonstrate performance at environmental conditions simulating captive flight and launch conditions for tactical missiles. Divert and gun-launched propulsion system evaluations include hover, quick-response maneuvering conditions, and high-acceleration environments.

3.3.3.2 Technology Development. Once the goals and payoffs have been established and confirmed as worthwhile, the technology advancements needed to achieve the goals are determined. The propulsion technologies in BO/T and S/C are divided into the same four component technology areas. These four areas, which represent the rocket propulsion system technology improvement areas, are propellants, propellant management devices, combustion and energy conversion devices, and control systems. The efforts in the propellant area include solid, liquid, hybrid, gels, and liner development. Propellant management efforts include work in tanks, feed systems, bladders, turbomachinery, thermal protection systems, cases, pressurization systems, and insulations. Combustion and energy conversion efforts include work in injectors, igniters, combustion chambers, nozzles, gas generators, preburners, and all components of electric and solar propulsion systems (except the propellant). Control system work includes actuator, health monitoring, thrust management, ordnance, valve, and thrust vector control system development.

The projects are technology specific as opposed to being system specific, allowing for global propulsion system improvements applicable to all rocket propulsion systems. Goals within each application area address where the R&D specialists will overcome operational deficiencies and meet requirements and needs defined by the propulsion system users. Subsequently, goals are subdivided into the component technology improvements needed to meet the goals. These component improvements are identified and represent component area objectives toward which the technologists will work in laboratory R&D projects.

This goal-objective relationship connects the R&D laboratories to the user community in a way that streamlines the work done by both communities and enables the needs of both groups to be satisfied. The result of the IHPRPT process is the fulfillment of a set of goals that integrates the technologists with the user community and provides maximum payoffs for future space systems.

3.3.3.3 Basic Research. The Phillips Laboratory Propulsion Directorate has several basic research projects supporting development in boost and orbit transfer and in spacecraft propulsion. In B/OT, one combustion development project (supercritical combustion), two propellant development projects (chemically bound excited states and nonequilibrium flow characteristics), and three materials development projects for rocket components (synthesis, carbon materials research, and material mechanics research) exist. In spacecraft propulsion, the plasma diagnostics project supports electric propulsion development.