Scott W. Benson

NEXT Ion Propulsion System Development Status and Performance

*† NASA’s Evolutionary Xenon Thruster (NEXT) project is developing next generation ion propulsion technologies to provide future NASA science missions with enhanced mission performance benefit at a low total development cost. The objective of the NEXT project is to advance next generation ion propulsion technology by producing engineering model and prototype model system components, validating these through qualification-level and integrated system testing, and ensuring preparedness for transitioning to flight system development. This paper describes the NEXT ion propulsion system development status, characteristics and performance. A review of mission analyses results conducted to date using the NEXT system is also provided.

Radioisotope Electric Propulsion for Fast Outer Planetary Orbiters

Recent interest in outer planetary targets by the Office of Space Science has spurred the search for technology options to enable relatively quick missions to outer planetary targets. Several options are being explored including solar electric propelled stages combined with aerocapture at the target and nuclear electric propulsion. Another option uses radioisotope powered electric thrusters to reach the outer planets. Past work looked at using this technology to provide faster flybys. A better use for this technology is for outer planet orbiters. Combined with medium class launch vehicles and a new direct trajectory these small, sub-kilowatt ion thrusters and Stirling radioisotope generators were found to allow missions as fast as 5 to 12 years for objects from Saturn to Pluto, respectively. Key to the development is light spacecraft and science payload technologies.

NASA's Evolutionary Xenon Thruster (NEXT) Phase 2 Development Status

** The NEXT (NASA’s Evolutionary Xenon Thruster) project is currently in the second year of the Phase 2 technology development project. This paper presents a summary of the overall NEX T project status, highlighting key accomplishments to date. The characteristics and flexibility of the NEXT system configuration are described. NEXT can be configured from simple configurations supporting single thruster operations through more complex fou r thruster systems. Results of recent in -space propulsion technology assessment analyses conducted by NASA are presented. To augment prior outer planet reference missions, extensive mission analyses have illustrated NEXT benefits to a variety of mission cl asses, including Discovery and New Frontiers. The resulting impacts on system requirements are described. NEXT ion thruster, power processing unit, propellant management system and gimbal design, fabrication and test status are provided, with summaries of results achieved to date. Status of thruster life evaluation is also summarized. Finally, plans for the completion of the second phase of the NEXT project are described.

NEXT Ion Propulsion System Configurations and Performance for Saturn System Exploration

*† ‡ The successes of the Cassini/Huygens mission have heightened interest to return to the Saturn system with focused robotic missions. The desire for a sustained presence at Titan, through a dedicated orbiter and in-situ vehicle, either a lander or aerobot, has resulted in definition of a Titan Explorer flagship mission as a high priority in the Solar System Exploration Roadmap. The discovery of active water vapor plumes erupting from the “tiger stripes” on the moon Enceladus has drawn the attention of the space science community. The NASA’s Evolutionary Xenon Thruster (NEXT) ion propulsion system is well suited to future missions to the Saturn system. NEXT is used within the inner solar system, in combination with a Venus or Earth gravity assist, to establish a fast transfer to the Saturn system. The NEXT system elements are accommodated in a separable Solar Electric Propulsion (SEP) module, or are integrated into the main spacecraft bus, depending on the mission architecture and performance requirements. This paper defines a range of NEXT system configurations, from two to four thrusters, and the Saturn system performance capability provided. Delivered mass is assessed parametrically over total trip time to Saturn. Launch vehicle options, gravity assist options, and input power level are addressed to determine performance sensitivities. A simple twothruster NEXT system, launched on an Atlas 551, can deliver a spacecraft mass of over 2400 kg on a transfer to Saturn. Similarly, a four-thruster system, launched on a Delta 4050 Heavy, delivers more than 4000 kg spacecraft mass. A SEP module conceptual design, for a two thruster string, 17 kW solar array, configuration is characterized.

Advanced solar cell and array technology for NASA deep space missions

A recent study by the NASA Glenn Research Center assessed the feasibility of using photovoltaics (PV) to power spacecraft for outer planetary, deep space missions. While the majority of spacecraft have relied on photovoltaics for primary power, the drastic reduction in solar intensity as the spacecraft moves farther from the sun has either limited the power available (severely curtailing scientific operations) or necessitated the use of nuclear systems. A desire by NASA and the scientific community to explore various bodies in the outer solar system and conduct “long-term” operations using smaller, “lower-cost” spacecraft has renewed interest in exploring the feasibility of using photovoltaics for missions to Jupiter, Saturn and beyond. With recent advances in solar cell performance and continuing development in lightweight, high power solar array technology, the study determined that photovoltaics is indeed a viable option for many of these missions.

Electric Propulsion for International Space Station Reboost: A Fresh Look

Abstract Electric propulsion has recently been revisited for reboost of space station due to its high fuelefficiency. This paper focuses upon the propulsion system and orbit analysis trades undertaken at thebeginning of a study to show the relative performance of potential electric propulsion system. A codewas developed to analyze continuous low thrust reboost of space station with various electricpropulsion systems at various power levels. Analysis showed that a major portion of reboost of spacestation can be made using electric propulsion systems with 0.5 N of continuous thrust. 1.0 N of EPthrust can provide almost the entire reboost mission. Three electric propulsion systems at various totalpower levels were chosen for further investigation: N2H4 arcjets at 5 kW, xenon Hall at 10 kW, andxenon ion thrusters at 20 kW. They were chosen for their ability to reduce the internationallylaunched chemical reboost fuel by 50% or more. Introduction Electric propulsion has been explored in thepast for reboost of space station.

Technology Readiness of the NEXT Ion Propulsion System

The NASAs evolutionary xenon thruster (NEXT) ion propulsion system has been in advanced technology development under the NASA in-space propulsion technology project. The highest fidelity hardware planned has now been completed by the government/industry team, including: a flight prototype model (PM) thruster, an engineering model (EM) power processing unit, EM propellant management assemblies, a breadboard gimbal, and control unit simulators. Subsystem and system level technology validation testing is in progress. To achieve the objective Technology Readiness Level 6, environmental testing is being conducted to qualification levels in ground facilities simulating the space environment. Additional tests have been conducted to characterize the performance range and life capability of the NEXT thruster. This paper presents the status and results of technology validation testing accomplished to date, the validated subsystem and system capabilities, and the plans for completion of this phase of NEXT development. The next round of competed planetary science mission announcements of opportunity, and directed mission decisions, are anticipated to occur in 2008 and 2009. Progress to date, and the success of on-going technology validation, indicate that the NEXT ion propulsion system will be a primary candidate for mission consideration in these upcoming opportunities.

Breakthrough capability for the NASA astrophysics explorer program: reaching the darkest sky

We describe a mission architecture designed to substantially increase the science capability of the NASA Science Mission Directorate (SMD) Astrophysics Explorer Program for all AO proposers working within the near-UV to far-infrared spectrum. We have demonstrated that augmentation of Falcon 9 Explorer launch services with a 13 kW Solar Electric Propulsion (SEP) stage can deliver a 700 kg science observatory payload to extra-Zodiacal orbit. This new capability enables up to ~13X increased photometric sensitivity and ~160X increased observing speed relative to a Sun- Earth L2, Earth-trailing, or Earth orbit with no increase in telescope aperture. All enabling SEP stage technologies for this launch service augmentation have reached sufficient readiness (TRL-6) for Explorer Program application in conjunction with the Falcon 9. We demonstrate that enabling Astrophysics Explorers to reach extra-zodiacal orbit will allow this small payload program to rival the science performance of much larger long development time systems; thus, providing a means to realize major science objectives while increasing the SMD Astrophysics portfolio diversity and resiliency to external budget pressure. The SEP technology employed in this study has strong applicability to SMD Planetary Science community-proposed missions. SEP is a stated flight demonstration priority for NASAs Office of the Chief Technologist (OCT). This new mission architecture for astrophysics Explorers enables an attractive realization of joint goals for OCT and SMD with wide applicability across SMD science disciplines.

Breakthrough capability for UVOIR space astronomy: reaching the darkest sky

We describe how availability of new solar electric propulsion (SEP) technology can substantially increase the science capability of space astronomy missions working within the near-UV to far-infrared (UVOIR) spectrum by making dark sky orbits accessible for the first time. We present two case studies in which SEP is used to enable a 700 kg Explorer-class and 7000 kg flagship-class observatory payload to reach an orbit beyond where the zodiacal dust limits observatory sensitivity. The resulting scientific performance advantage relative to a Sun-Earth L2 point (SEL2) orbit is presented and discussed. We find that making SEP available to astrophysics Explorers can enable this small payload program to rival the science performance of much larger long development-time systems. Similarly, we find that astrophysics utilization of high power SEP being developed for the Asteroid Redirect Robotics Mission (ARRM) can have a substantial impact on the sensitivity performance of heavier flagship-class astrophysics payloads such as the UVOIR successor to the James Webb Space Telescope.