GYRO BIAS ON-ORBIT CALIBRATION FOR MICRO SATELLITES

According to gyro application in micro-satellites, a new gyro bias real-time on-orbit calibration technology is presented and it is independent of any other sensors. The approach relies on gyro on-orbit measurements restricted by satellite attitude dynamics and estimates the gyro bias generated when the gyro is electrified. Observability of the calibration model is analyzed and applicable conditions of the technology are derived. Simulation results indicate that the calibration algorithm is accurate and robust at gyro sampling rate, and its convergence speed is fast. Within the given attitude dynamics model error, the convergence time is less than 100 s and the convergence accuracy is about 1.0 （°）/h. Calibration performance can meet requirements of spacecraft operations.

Ignition processes and characteristics of charring conductive polymers with a cavity geometry in precombustion chamber for applications in micro/nano satellite hybrid rocket motors

The arc ignition system based on charring polymers has advantages of simple structure,low ignition power consumption and multiple ignitions,which bringing it broadly application prospect in hybrid propulsion system of micro/nano satellite.However,charring polymers alone need a relatively high input voltage to achieve pyrolysis and ignition,which increases the burden and cost of the power system of micro/nano satellite in practical application.Adding conductive substance into charring polymers can effectively decrease the conducting voltage which can realize low voltage and low power consumption repeated ignition of arc ignition system.In this paper,a charring conductive polymer ignition grain with a cavity geometry in precombustion chamber,which is composed of PLA and multiwall carbon nanotubes(MWCNT)was proposed.The detailed ignition processes were analyzed and two different ignition mechanisms in the cavity of charring conductive polymers were revealed.The ignition characteristics of charring conductive polymers were also investigated at different input voltages,ignition grain structures,ignition locations and injection schemes in a visual ignition combustor.The results demonstrated that the ignition delay and external energy required for ignition were inversely correlated with the voltages applied to ignition grain.Moreover,the incremental depth of cavity shortened the ignition delay and external energy required for ignition while accelerated the propagation of flame.As the depth of cavity increased from 2 to 6 mm(at 50 V),the time of flame propagating out of ignition grain changed from 235.6 to 108 ms,and values of mean ignition delay time and mean external energy required for ignition decreased from 462.8 to 320 ms and 16.2 to 10.75 J,respectively.The rear side of the cavity was the ideal ignition position which had a shorter ignition delay and a faster flame propagation speed in comparison to other ignition positions.Compared to direct injection scheme,swirling injection provided a more favorable flow field environment in the cavity,which was beneficial to ignition and initial flame propagation,but the ignition position needed to be away from the outlet of swirling injector.At last,the repeated ignition characteristic of charring conductive polymers was also investigated.The ignition delay time and external energy required for ignition decreased with repeated ignition times but the variation was decreasing gradually.

Tsinghua-1 Micro-Satellite Power System Architecture and Design

The Tsinghua 1 Micro satellite, the first satellite made by Tsinghua University, was launched in 2000. The power system of the Tsinghua 1 Micro satellite is one of the most important subsystems. It provides all the power for the satellite platform and the payloads. The power system design includes the regulation, protection and distribution of a 4×35 W solar array and 7 Ah NiCd batteries. This subsystem essentially offers two buses: an unregulated 14 V bus and a regulated 5 V bus. All distributed power lines to the users are protected by current tripping switches. In addition, some essential loads, such as the tele command system, are supplied through fuses. The Tsinghua 1 Micro satellite power system provides an efficient, flexible, reliable, and cost effective solution for small satellites in low earth orbit. A better maximum power point tracking method has been used to increase reliability margins and to increase the efficiency of the power system. The power system reliability was evaluated using several different tests, such as the power board test, the assembly integrate test (AIT), the electromagnetic compatibility (EMC) test and the thermal vacuum test (TVT).

Investigation on ignition characteristics of charring conductive polymers stimulated by electric energy

The arc ignition based on charring conductive polymers has advantages of simple structure,low ignition power consumption and restart capacity,which bringing it broadly application prospect in hybrid propulsion system of micro/nano satellite.In order to optimize the performance of arc ignition system,it is essential to have a deeper understanding of the ignition processes and ignition characteristics of charring conductive polymers.In this paper,the thermal decomposition,electrical conductivity and thermal conductivity characteristics of charring conductive polymers with different conductive additives and matrix materials were comprehensively evaluated.An experimental investigation was conducted to determine the ignition behaviors and characteristics of different charring conductive polymers in a visual ignition combustor.The experiment result showed that the ignition delay and external energy required for ignition are negatively correlated with voltage and initial temperature of the ignition grain,but positively correlated with oxidizer flow velocity.Compared with charring conductive polymers containing multi-walled carbon nanotube,the ignition delay of charring conductive polymers with carbon black is significantly higher and the pyrolysis time is relatively longer.However,the ignition and initial flame propagation of charring conductive polymers with carbon black is more violent and more inclined to carbon particle ignition.Finally,the restart characteristic of different charring conductive polymers was studied.The ignition delay and external energy required for ignition of different charring conductive polymers all reduced with the increasing of the number of ignitions.However,the ignition characteristics would not change a lot after repeated ignition.