John Ziemer

Colloid Micro-Newton Thrusters for the space technology 7 mission

Two flight-qualified clusters of four Colloid Micro-Newton Thruster (CMNT) systems have been delivered to the Jet Propulsion Laboratory (JPL) and subsequently delivered to ESA for spacecraft integration. The clusters will provide precise spacecraft control for the drag-free technology demonstration mission, Space Technology 7 (ST7). The ST7 mission is sponsored by the NASA New Millennium Program and will demonstrate precision formation flying technologies for future missions such as the Laser Interferometer Space Antenna (LISA) mission. The ST7 disturbance reduction system (DRS) is a payload on the ESA LISA Pathfinder spacecraft along with the European gravitational reference sensor (GRS) as part of the ESA LISA Technology Package (LTP). To achieve the nanometer-level precision spacecraft control requirements, each of eight thruster systems is required to provide thrust between 5 and 30 µN with resolution ≤0.1 µN and thrust noise ≤0.1 µN/vHz. Developed by Busek Co. Inc., with support from JPL in design and testing, the CMNT has been developed over the last six years into a flight-ready and flight-qualified microthruster system, the first of its kind. Recent flight-unit qualification tests have included vibration and thermal vacuum environmental testing, as well as performance verification and acceptance tests. All tests have been completed successfully prior to delivery to JPL. Delivery of the first flight unit occurred in February of 2008 with the second unit following in May of 2008. Since arrival at JPL, the units have successfully passed through mass distribution, magnetic, and EMI/EMC measurements and tests as part of the integration and test (I&T) activities including the integrated avionics unit (IAU). Flight software sequences have been tested and validated with the full flight DRS instrument successfully to the extent possible in ground testing, including full functional and 72 hour autonomous operations tests. In the summer of 2009 the cluster assemblies were delivered to ESA along with the IAU for integration into the LISA Pathfinder spacecraft. Spacecraft-level testing will include magnetics, acoustic, and thermal vacuum environmental testing with a planned launch and flight demonstration in April 2012. 1 2

Space Mission Concept Development Using Concept Maturity Levels

Over the past five years, pre-project formulation experts at the Jet Propulsion Laboratory (JPL) has developed and implemented a method for measuring and communicating the maturity of space mission concepts. Mission concept development teams use this method, and associated tools, prior to concepts entering their Formulation Phases (Phase A/B). The organizing structure is Concept Maturity Level (CML), which is a classification system for characterizing the various levels of a concepts maturity. The key strength of CMLs is the ability to evolve mission concepts guided by an incremental set of assessment needs. The CML definitions have been expanded into a matrix form to identify the breadth and depth of analysis needed for a concept to reach a specific level of maturity. This matrix enables improved assessment and communication by addressing the fundamental dimensions (e.g., science objectives, mission design, technical risk, project organization, cost, export compliance, etc.) associated with mission concept evolution. JPLs collaborative engineering, dedicated concept development, and proposal teams all use these and other CML-appropriate design tools to advance their mission concept designs. This paper focuses on mission concepts early Pre-Phase A represented by CMLs 1- 4. The scope was limited due to the fact that CMLs 5 and 6 are already well defined based on the requirements documented in specific Announcement of Opportunities (AO) and Concept Study Report (CSR) guidelines, respectively, for competitive missions; and by NASAs Procedural Requirements NPR 7120.5E document for Projects in their Formulation Phase.

Colloid Microthrust Propulsion for the Space Technology 7 (ST7) and LISA Missions

For future applications to precision formation flying missions, NASA’s New Millennium Program is scheduled to test Colloid Micro‐Newton Thrusters (CMNTs) on the ST7 technology demonstration mission. These CMNTs are part of a disturbance reduction system (DRS) on the ESA SMART‐2 Spacecraft or LISA Pathfinder. The goal of the ST7 DRS is to demonstrate technologies necessary to meet the nanometer precision positioning control requirements of the LISA mission. In order to achieve these goals, the CMNTs are required to demonstrate a thrust resolution of less than 0.1 μN and a thrust noise of less than 0.1 μN/√Hz for thrust levels between 5 and 30 μN. Developed by Busek Co. with support from JPL in testing and design, the CMNT has been developed over the last four years into a flight‐ready microthrust system. The development, validation testing, and flight unit production of the CMNTs are described. Development tests and analysis include preliminary wear tests, propellant loading process verification, flow test...

Development of a Rapid Electric Propulsion System Preliminary Design Tool

A tool that provides a means of performing rapid mission studies using electric propulsion system technologies is developed to simplify the complex multidisciplinary problem of simultaneously optimizing low-thrust trajectories, propulsion, and power systems. The tool implements analytic expressions for optimized low-thrust trajectories and combines them with electric propulsion system performance and mass models. The tool then finds the maximum delivered payload mass and the corresponding optimum power and specific impulse. The tool uses existing technology as a baseline but permits tweaking technology parameters to help identify sensitivities and mission enabling technologies. Design scaling curves for technology parameters are examined. In addition, electric propulsion engine lifetime limitations are included. This identifies optimum flight times for given missions. A study for Earth-Jupiter transit is presented to demonstrate rapid system level trade studies and examination of limits in current electric propulsion technology.

Space Technology 7 -- Micropropulsion and Mass Distribution

The NASA New Millennium Program Space Technology 7 (ST7) project will validate technology for precision spacecraft control. The ST7 distrubance reduction system (DRS) will contain new micropulsion technology to be flown as part of the European Space Agencys LISA (laser interferometer space antenna) Pathfinder project. After launch into a low Earth orbit in early 2010, the LISA Pathfinder spacecraft will be maneuvered to a halo orbit about the Earth-Sun LI Lagrange point for operations. The DRS will control the position of the spacecraft relative to a reference to an accuracy of one nanometer over time scales of several thousand seconds. To perform the control the spacecraft will use a new colloid thruster technology. The thrusters will operate over the range of 5 to 30 micro-Newtons with precision of 0.1 micro-Newton. The thrust will be generated by using a high electric field to extract charged droplets of a conducting colloid fluid and accelerating them with a precisely adjustable voltage. The control position reference will be provided by the European LISA Technology Package, which will include two nearly free-floating test masses. The test mass position and attitude will be sensed and adjusted using electrostatic capacitance bridges. The DRS will control the spacecraft position with respect to one test mass while minimizing disturbances on the second test mass. The dynamic control system will cover eighteen degrees of freedom, six for each of the test masses and six for the spacecraft. In the absence of other disturbances, the test masses will slowly gravitate toward local concentrations of spacecraft mass. The test mass acceleration must be minimized to maintain the acceleration of the enclosing drag-free spacecraft within the control authority of the micropropulsion system. Therefore, test mass acceleration must be predicted by accurate measurement of mass distribution, then offset by the placement of specially shaped balance masses near each test mass. The acceleration is characterized by calculating the gravitational effect of over ten million modeled points of a nearly 500-kg spacecraft. This paper provides an overview of the mission technology and the process of precision mass modeling of the DRS equipment.

Mars Aeronomy Explorer (MAX): study employing distributed microspacecraft

An overview of a Mars Aeronomy Explorer (MAX) mission design study performed at NASAs Jet Propulsion Laboratory is presented herein. The mission design consists of ten microspacecraft orbiters launched on a Delta IV to Mars polar orbit to determine the spatial, diurnal and seasonal variation of the constituents of the Martian upper atmosphere and ionosphere over the course of one Martian year. The spacecraft are designed to allow penetration of the upper atmosphere to at least 90 km. This property coupled with orbit precession will yield knowledge of the nature of the solar wind interaction with Mars, the influence of the Mars crustal magnetic field on ionospheric processes, and the measurement of present thermal and nonthermal escape rates of atmospheric constituents. The mission design incorporates alternative design paradigms that are more appropriate for - and in some cases motivate-distributed microspacecraft. These design paradigms are not defined by a simple set of rules, but rather a way of thinking about the function of instruments, mission reliability/risk, and cost in a systemic framework.