Technical Sessions

Session VI: Advanced Technologies 2

Chair: Jana Schwartz, The Charles Stark Draper Laboratory

Tuesday, August 11, 2009

4:15 p.m. 3Dwheel: 3‐Axis Low Noise, High‐Bandwidth Attitude Actuation from a Single Momentum Wheel Using Magnetic Bearings

Jon Seddon, Alexandre Pechev – Surrey Space Centre

ABSTRACT: This paper proposes a new concept for attitude actuation for small satellites that uses active magnetic bearings to support and tilt a spinning rotor to provide 3‐axis attitude control of the satellite using a single actuator. A controlled 3D motion in the spinning rotor provides a conventional torque output about the momentum axis and a gyroscopic torque output about any direction in the plane normal to the spinning axis. Therefore, a single tilting momentum‐wheel can generate torque along the three principal axes of the satellite, providing mass and power savings, or redundancy.

In this paper we present a model of, and results from the engineering model that has been built of the tilting magnetically‐levitated momentum‐wheel. The control loop that levitates and tilts the rotor is discussed. The 3‐axis actuation of this wheel is demonstrated with simulations of the wheel fitted to the TopSat small satellite. The bandwidth and torque output of the wheel are compared with a conventional momentum wheel’s. The power consumption, operation and stiffness of the magnetic bearing are discussed. The 2.5 micrometre translational and 0.1 milliradian rotational control of the wheel obtained in experiments with the engineering model are demonstrated.

4:30 p.m. Plug‐and‐Play (PnP) Micro‐Electro‐Mechanical System (MEMS) Inertial Measurement Unit (IMU) an Enabling Technology for Small Satellites

Jon Pollack, Jane Hansen – HRP Systems, Inc; Dan Cardarelli – MilliSensor Systems and Actuators, Inc. (MSSA); Paul Graven – Microcosm, Inc.

ABSTRACT: Great strides are being made toward a standardized Spacecraft PnP Avionics (SPA) protocol and, at the same time, Micro‐Electro‐Mechanical System (MEMS) technologies are being developed and exploited by small uninhabited aerial vehicles (UAVs). The integration of the PnP capability with the MEMS technologies, implemented at lower costs while being designed for use in the space environment, will move the spacecraft component industry toward supporting the next generation of small, highly capable satellites. Microcosm, in conjunction with MilliSensor Systems and Actuators, Inc. (MSSA) and HRP Systems, is creating a PnP MEMS Inertial Measurement Unit (IMU) for spacecraft applications that will ultimately have performance comparable to today’s mid‐range IMUs, such as Northrop Grumman’s LN‐200. The combination of low cost, low mass, low power, and high performance expected from the PnP MEMS IMU is enabling technology for accurate pointing knowledge and control for the next generation of small satellites. This paper will address the state of the technology development to date for the PnP MEMS IMU, as well as presenting an estimate of the performance that is anticipated in future design iterations.

4:45 p.m. Improving Angles‐Only Navigation Performance by Selecting Sufficiently Accurate Accelerometers

Jason Schmidt, David Geller – Utah State University; Frank Chavez – Air Force Research Laboratory/SVD

ABSTRACT: In order to make future satellites both smaller and smarter, more navigation information must be extracted from simpler, smaller sensors. One of the simplest sensors is an optical or infrared camera. With a camera, a satellite can track a second satellite located within its field‐of‐view. This simple measurement is the foundation of angles‐only navigation. By its very nature, angles only navigation cannot determine the relative range to an object. Even as the dynamics associated with orbital rendezvous and proximity operations unfold, the relative range will generally remain unobservable. In this paper we confirm that an angles only navigation system can observe range if small maneuvers can be executed, and we show that the level of accelerometer accuracy determines how well the range can be observed.

5:00 p.m. Plug and Play Spacecraft Evolution

Don Fronterhouse – PnP Innovations, Inc

ABSTRACT: The space community, led by AFRL, started developing spacecraft plug and play concepts and standards in 2004 and has resulted in the Space Plug and play Avionics (SPA) Standards. AFRL has undertaken two efforts in small satellite development to both solidify the technology and to demonstrate the benefits. The Plug and Play Satellite (PnPSat) utilizes the SPA‐S interface standard and demonstrated that rapid development, integration and testing is possible. The second effort is PnPSat‐2 that uses the next generation of SPA components for a larger bus focused on ORS needs to make real the promise of custom performance at commodity prices. The SPA standard interface has proven critical to the development of design tools that both select (based upon performance requirements) and place (based upon restrictions such as mass and power balance) components. The Satellite Data Model (SDM) method of query and discovery enables the development of modular, single purpose applications that support autonomous flight software in a distributed computing system. The utilization of a data centric architecture (as opposed to component centric) insolates software developers from both specific hardware components and data network topology. The SPA standard interface reduces the need for many specialized test methods resulting in major reductions in test time. This paper will present the steps used in designing, building, and testing SPA PnP satellites and the current status of PnPSat and PnPSat‐2.

5:15 p.m. Self Deploying Nitinol LHP Radiator for Small Spacecraft

Alfred Phillips – Thermacore, Inc.; Jentung Ku – NASA Goddard Space Flight Center

ABSTRACT: The use of nitinol (shape memory alloy) tubing for an LHP condenser allows a passive, self deploying heat rejection radiator for small spacecraft. The tubing is “trained” to its deployed configuration, then compactly coiled for launch. When the payload is energized and the condenser heats up, the shape memory alloy changes phase and returns to its trained shape. This paper reports on a NASA sponsored SBIR Phase I program that established the feasibility of the concept. Nitinol tubing was made from available material which had a phase change temperature much higher than desired. It was trained to a simple deployed shape. Since the ends of the LHP condenser are constrained, there are a limited number of basic, possible coiling arrangements. Early experiments used a loop thermosyphon with water working fluid to provide condensing vapor to heat the tubing internally and actuate the shape change. The later experiments used an ammonia loop heat pipe to successfully demonstrate deployment that was actuated by the heat being rejected.

Alternate  Collision Probability Estimation

Michael Phillips, David Geller, Frank Chavez – Utah State University

ABSTRACT: As small satellites become more common and are assigned increasingly sophisticated missions, their role in proximity operations is also increased. An estimate of the current relative state (position, velocity and often attitude) as well as a prediction of the future relative state is important in close proximity operations. However, it is often insufficient to rely solely on this estimate to predict a collision due to the errors involved in the state estimate. An alternative approach is to determine the probability of a collision. In order to do this, the covariance of the state estimate must also be taken into account. For this reason, it is therefore important to determine a measure of the uncertainty of the position and velocity of both spacecraft. One approach is to conduct a Monte Carlo analysis either onboard or on the ground. Implementing this approach is time consuming and most likely not feasible with current technology. This paper explores the possibility of using covariance propagation onboard a small satellite to perform this uncertainty analysis. Covariance propagation has been shown to be one or two orders of magnitude faster than Monte Carlo analysis. This paper will show how this type of analysis can be used by small satellites for hazard avoidance.