By Jeremy Seiden (Mission, Systems, and Test)

This study weighs the benefits and drawbacks of a discrete component based high voltage supply circuit, and an IC based high voltage supply circuit. The purpose of this study was to determine the most radiation hardened high voltage power supply method.

Introduction

The intent of the SPARCSS satellite is to complete a specific mission of collecting data on radiation doses present in geosynchronous orbit with the intention to study radiation ionization charging. To do this, the SPARCSS satellite will contain instruments designed to detect radiation dose (dosimeter) and a single even upset monitor. The dosimeter will require a high voltage on the order of 500VDC to operate and collect data. As the instrument is supplied with 5VDC, a voltage converter must be included onboard the instrument. Determining the best method for high voltage DC-DC conversion requires an in depth analysis of system requirements.

Background Information

Without an atmosphere to protect them, spacecraft experience much greater doses of radiation from a variety of sources during spaceflight. This ionizing radiation can have detrimental effects on spacecraft. Ions present in large quantities cause charge to accumulate across the chassis of a spacecraft. Excess charge can result in arcing and damage to onboard electronics. As mission success of spacecraft is of critical importance, the effects of this charging radiation must be studied to better prepare spacecraft for the environment they must operate in. The study of this environment is the purpose of the SPARCSS mission.

Purpose of Study

As the SPARCSS satellite will be exposed to radiation, multiple solutions for onboard voltage conversion components shall be considered to achieve the most reliable, efficient, and cost effective solution. This study shall analyze the benefits and detriments of different voltage conversion solutions to form a conclusion of which solution shall be included onboard the SPARCSS satellite instrumentation.

Instrumentation Requirements

Due to the relatively small size of the SPARCSS satellite, stringent size, weight, cost, and power requirements have been put in place. As can be observed directly from our project objectives, the PCB containing our instruments shall be confined to 89mm by 92mm board, shall not exceed 500g, and shall not use more than 500mW on average. At 5V, due to the USB connection, the instrument shall not draw more than 100mA. The restriction on power is the most stringent requirement and therefore, is the largest consideration when determining appropriate solutions. Another aspect of employing a successful solution is the availability of radiation hardened component options for the employed hardware.

Solution Options

Discrete

This method utilizes a small transformer and support hardware for safe and efficient operation. This is also hardware that is currently in our possession, which presents a significant advantage when considering the cost of the solution. The transformer with support hardware is capable of providing a constant 560VDC, which is the optimal operating voltage for the Geiger tube to be used. At this voltage, the transformer, support hardware, and Geiger tube together draw roughly 20-25mA when supplied with 5VDC during constant use. This operational current draw is well within the 100mA limit and leaves significant draw to support other onboard systems such as the microcontroller and single event upset (SEU) monitor. The weight of the transformer itself is nominally 1g and support hardware weighs roughly 15g, which will help keep the entire instrument within the 500g limit. However, the transformer does not provide any shielding from radiation. Shielding will require providing additional material resulting in an increase in weight with unknown improvements in radiation shielding.

IC

This method utilizes an integrated circuit (IC) component accompanied by support hardware to essentially create a boost converter to step-up the supply voltage to the proper operating voltage for the Geiger tube. These IC step-up converters can cost anywhere from $10 to $100 and more for custom produced models. The efficiency of these boost converters is around 50% and many models available on the market require an excess of 1W of power, which is roughly 200% of our allotted value. However, these efficiency values are for peak usage. If a converter is selected so that the output is not close to peak value, the efficiency will be greater and therefore the power consumption would be feasible for use on the instrument. The IC components can weight up to 30g. However, these IC’s do not require as much support hardware as the discrete solution and come with much more robust shielding including multiple layers of nickel or aluminum plating, making the IC a much more radiation hardened component when compared with the discrete solution.

Conclusion

In conclusion, this SPARCSS project requires an instrument capable of measuring the total ionizing dose of radiation present in the satellite’s intended environment. A Geiger tube has been selected for this task. The Geiger tube requires an operating voltage between 500-600VDC, with the optimal voltage being 560VDC. To supply this voltage from the 5V USB connection provided by other divisions of the SPARCSS project, a step up voltage converter must be used. Ideally this component will exhibit space-ready qualities, specifically a compact, efficient, and radiation hardened package. As a result, an IC solution shall be utilized for the Spring 2016 SPARCCS instrument.