A Power Control and Distribution Unit for Small Satellite Platforms

The chapter contains first an overview on the power supply subsystem and discusses all the components. These are the solar panels including the deployment mechanism, the battery and in particular the Power Control and Distribution Unit (PCDU). The PCDU modes and its particular functions in the frame of the Combined Data and Power Management Infrastructure (CDPI) are explained. The last part comprises the onboard software elements and functions for control of the power supply subsystem. Additional tables are provided in the book’s annexes.

“Model Philosophy”, the commonly accepted methodology for the levels of reliability of space missions, minimizes risks with a staged development schedule of sequential prototypes that mimic different and crucial aspects of the design. Depending on the mission objective, the classical flow of Bread Board, Engineering, Qualification, and Flight models, may vary. In this work, we introduce the magnetic model, representative of magnetic moment, as a key property in scientific missions such as the ESA'Jupiter Icy Moons Explorer. The approach intends to minimize the magnetic momentum of the complex Power Control and Distribution Unit (PCDU) at the early stages of the project, to avoid test non-compliance or the need of critical changes in the late stages. We calculate the PCDU magnetic moment based on the properties and distribution of the numerous individual components, between -50 and 50°C, and we determine magnetic moment experimentally, which we use to validate the model.

This paper presents a general approach to solve multi-client space logistics path optimization problems in the case of low-thrust propulsion. The methodology accounts for key time-dependent factors, including secular J 2 and drag perturbations, eclipse propulsion constraints, and servicer fuel mass depletion. A low-thrust transfer strategy, consisting of three phases (thrust-coast-thrust), is employed, utilizing a drift orbit to correct the difference in Right Ascension of the Ascending Node. The drift orbit parameters are optimized by using a nonlinear programming algorithm to minimize the fuel cost associated with the transfer while satisfying a maximum time of flight constraint. An optimization is conducted for all possible transfers between the satellites of a dataset on a two-dimensional discrete grid of initial servicer mass and departure time. This procedure creates two four-variable arrays representing the cost of each possible visitation in terms of fuel consumption and time of flight. The arrays are then interpolated to efficiently solve a general path optimization problem by using a genetic algorithm. Two test cases are analyzed for datasets consisting of 12 and 20 satellites in low Earth orbit, respectively. The first addresses an optimal open tour problem where the servicer must visit all satellites once while minimizing total fuel consumption. The second addresses an on-orbit refueling problem where the servicer must refuel as many satellites as possible. The mission scenario is generalized to consider a priority index associated with each client; servicing time and fuel mass constraints are also taken into account.

Precise relative GPS navigation is essential technology for rendezvous and formation flying of spacecraft in Low Earth Orbit. Key design issues of precise relative GPS navigation software are studied and a novel formulation is proposed for the mission which requires high accuracy when the separation distance is up to several km. The navigation filter estimates float navigation solutions by extended Kalman filter with elaborate dynamics models, and resolves ambiguities of integer carrier phase biases to achieve high accuracy fix navigation solutions. A relative navigation software with the proposed formulation is implemented and evaluated in two different ways. One is a test using spacebourne GPS receivers and a GPS signal simulator to evaluate the performance and sensitivity of the software against variation of parameters. The other is a test using actual telemetry data from Gravity Recovery and Climate Experiment (GRACE) to demonstrate the software performance. The design, implementation, and results of the evaluation are presented and discussed on this paper.

Satellite Power subsystem is one of the critical subsystems of satellite. The purpose of power subsystem is to generate, store and distribute the conditioned power to all subsystems. This paper focuses on modular design methodology of COTS based small Satellite Power System (SPS). SPS has five main parts Power generation Unit (PGU), Battery Unit (BTU), Power Control Unit (PCU), Power conditioning Unit (PCNU) and Power Distribution Unit (PDU). According to the mission requirements centralized, fully regulated bus architecture is developed using modular approach. The SPS is scalable starting from 200 watt to 1000 watt. It is aimed for experimental LEO mission. The duration of the mission is one year.

Robust and precise baseline determination of distributed spacecraft in LEO

The Power Control Unit (PCU) in Micro-satellites program proposed to develop by NSPO, acts as the satellite power control and distribution center. One of the modules in the PCU, named the Power Distribution (PD), the main function provides the rated voltage and current of each power outlet for the satellite subsystem. When overload or short-circuit happens and persists for a time period, PD will limit the load current in a pre-designed value, and shut off the load to avoid damage on essential devices. In this paper, we will introduce the PCU EBB function and circuit design of PD.

The Power Control Unit (PCU) in FORMOSAT-7 NSPO-Built satellite mission acts as the satellite power control and distribution center, is similar to a human heart. One of the modules in the PCU, named the Power Distribution module (PDM), the main function provides the rated voltage and current of each power outlet for the satellite unit. When overload or short-circuit happens and persists for a time period, PDM will limit the load current in a pre-designed value, and shut off the load to avoid damage on essential devices. In this paper, we will introduce the PCU function and circuit design of PDM.

The PROBA-2 microsatellite of the European Space Agency (ESA) is equipped with a novel single frequency global positioning system (GPS) receiver, which combines low resource requirements with a high navigation performance. Aside from supporting the spacecraft and mission operations, the Phoenix GPS receiver on PROBA-2 is used to study realtime and offline navigation using single-frequency GPS measurements. A 1 m accuracy is targeted for both applications which has so far been the domain of dual-frequency receivers. Following a mission overview, the achievable performance for ground-based orbit determination and real-time onboard navigation is discussed for different processing concepts based on flight data collected during the first half year of mission operations. It is shown that a 1 m or better accuracy can be achieved in either case, despite sub-optimal GPS tracking conditions induced by the mission specific attitude profile. Besides self-consistency checks and comparisons with independent GPS based orbit determination solutions, the accuracy is evaluated using satellite laser ranging (SLR) measurements as an external reference. The results show that single-frequency GPS tracking is sufficient to meet the navigation requirements of even advanced remote sensing missions in low Earth orbit, if their accuracy potential is properly exploited.

THERE is a growing trend toward distributed missions for scientific and remote sensing applications where large\nnumbers of satellites are required. Analogous to proliferating terrestrial wireless sensor networks, space sensor\nnetworks could provide an unprecedented capability to investigate widespread phenomena. For example, several\nimportant space weather missions have yet to be realized due to the present inability to take simultaneous\nmeasurements of a phenomenon over a large volume. Space economics and environmental concerns dictate a costeffective mass-producible low-mass satellite for such massively distributed missions in low Earth orbit (LEO).\nAn investigation of very small (sub-kilogram) satellite miniaturization techniques has been undertaken, focusing\non enabling technologies targeted at space sensor network applications. Existing and emerging very small satellite\ntechnologies have been assessed and compared with power generation and payload volume being the key\nperformance metrics. Two novel design methodologies have been developed, simulated, and verified through\nfunctional and environmental testing of hardware prototypes. SpaceChip, inspired by the satellite-on-a-chip vision,\nis a monolithic heterogeneous system-on-a-chip (SoC) integration approach.\n1,2 PCBSat is a proposed miniaturization\napproach, which is based on printed circuit board (PCB) substrates.\n3\nPCBSat is focused on deriving the smallest\npractical satellite within the context of space sensor networks, and constrained to the use of commercial off the shelf\n(COTS) components, processes, and deployment systems.

ESA's current approaches to end-of-life strategies for HEO missions

Detailed knowledge of the radiation environment in space is an indispensable prerequisite for space missions in low Earth orbit and beyond. The RadMap Telescope is a compact radiation monitor that can characterize the radiation environment aboard spacecraft and determine the biologically relevant dose received by astronauts. Its main sensor is a tracking calorimeter made from 1024 scintillating-plastic fibers of alternating orientation and silicon photomultipliers. It allows the three-dimensional tracking and identification of cosmic-ray nuclei by measurement of their energy-deposition profiles. The properties of nuclei traversing the detector are reconstructed using a neural-network-based analysis framework. In this contribution, we describe the three consecutive convolutional networks that we use to determine the track parameters, charge, and initial kinetic energy of each nucleus as well as the challenges of a network-based analysis approach. We demonstrate the capabilities of our framework with networks trained and evaluated on simulated data and show that the achieved performance is in agreement with the requirements of radiation monitoring. Finally, we discuss the significance of our results and the limitations of both the analysis framework and the detector.

The NASA Hubble Space Telescope (HST) was designed to be deployed and later serviced for maintenance and upgrades, as required, by the space shuttle fleet, with a 5-year mission life for the batteries. HST was deployed 380 miles above the Earth, from Space Shuttle Discovery, on April 25, 1990. Four servicing missions, (SM1, SM2, SM3A, AND SM3B) have been performed. Astronauts have replaced or modified optics, solar arrays, a power control unit, and various science packages. A fifth servicing mission, SM4 scheduled for early 2004, is planned to replace the batteries for the first time. The HST is powered by solar array wings and nickel hydrogen (NiH/sub 2/) 22-cell batteries, which are grouped into two parallel battery modules of three parallel batteries each. With a design life of 7 years at launch, these batteries have surpassed 12 years in orbit, which gives HST the highest number of charge/discharge cycles of any NiH/sub 2/ battery currently in low earth orbit (LEO) application. Being in a LEO orbit, HST has a 36-minute umbra period, during which spacecraft power requirements normally force the batteries into discharge, and a 60-minute sun period, which is available for battery recharge. The intent of this paper is to address the issue of NiH/sub 2/ battery reliability and how battery capacity degradation can impact scheduling of a servicing mission to bring replacement batteries to HST, and extend mission life until deployment of Next Generation Space Telescope (NGST), planned for 2010 at the earliest.

This paper presents various control strategies to improve operations in two interconnected areas connected by a VSC‐HVDC transmission line. The main focus is on designing a central control system (CCS) that coordinates control units in both areas. In area 1, an AC voltage control unit is connected to the CCS. In area 2, three control units including a load power control unit, a fault detection unit, and an AC voltage control unit are also connected to the CCS. The CCS receives inputs from these units and generates commands for the DC voltage and active/reactive power control units on both sides of the DC line. The first proposed strategy addresses permanent voltage drops caused by load fluctuations in area 2. It adjusts the transmitted power from area 1 based on voltage variations in area 2. The second strategy focuses on mitigating faults in area 2 by injecting active and reactive power from area 1 during such events. The third strategy resolves transient voltage oscillations in both areas by controlling the reactive power of stations on either side of the DC line. Simulations using MATLAB‐SIMULINK demonstrate that these mechanisms successfully achieve their objectives.

A combination of an on-chip power control and a closed loop power control for inductively powered biomedical implants using inherent inverse load modulation as back channel is presented. Inverse load modulation is realized using an innovative internal on-chip power control. By shorting the secondary receiving coil to ground using varying switching pulse repetition rates the magnetic field is diminished and the load is nearly canceled. This reduces the energy absorbed by the implant and consequently the transmitted power decreases with a slight increase of the voltage amplitude in the primary transmitting coil. The increased amplitude peaks on the transmitter side are measured in order to decrease the on-chip power control state. Finally the transmitting power is adjusted in a way to transmit only sufficient power for chip operation. This reduces the transmitting power. Therefore the power control unit in the implant has to control less excessive power.