Study On Atomic Oxygen Detector Based On Carbon Films

Atomic oxygen（AO）is a major content of atmosphere environment of space Low Earth Orbit,which with high oxidizability,high density and relative energy,surface materials used on satellites are eroded deeply by atomic oxygen and then performances of optic,electric and mechanics will be degraded.Therefore,atomic oxygen is a threat for satellites.With the help of the atmosphere model,such as MSIS,which were based on data from exploration of satellites,rockets and ground test,the density or fluence of space AO can be calculated.The distribution and fluence of AO is affected by solar activity,seasons and day and night.There is a big distance between the data from the model and the actual density of AO.It is necessary and significate to detect the density of AO by use of kinds of sensors or detectors.Researching on AO effects was begun with detection of AO in the foreign.So far,detection on orbit is also the most important part in researching of AO.Ground testing is the major form on AO investigation in our country.There is a big boundedness on AO effects investigation by lack of the experience of space detection.It will be broadened the domain of AO effects investigation to develop detection of AO in orbit.It is meaningful for satellites in LEO with long life and high reliability.There are many kinds of methods to detect AO in orbit,such as mass spectrometry,retrieving of samples,quartz crystal microbalance（QCM）,chemical thermal detection,semiconductors and resistance measuring,etc.Each of them has advantages and disadvantages.Based on the principle of measuring the resistance under the condition of atomic oxygen,three kinds of film sensors used of carton were designed,with the thickness of 2.5μm,25μm and 50μm and the size of 30mm×7mm and 30mm×7mm.A suite of measuring system for measuring the resistance of the sensor were designed and made,in which AD 7767 was used for ADC,FPGA BQR2V3000 was used for controller,LFSA/（20-50）-461-40 was used for filter and LDCD/（20-50）-515-15F/T1 was used for DC/DC。The thinner carbon film with the thickness of 2.5μm was prepared by cathode arc discharge.The surface and fracture morphology were tested by SEM.It showed that the film had a single layer with the smooth surface,carbon particles which had the diameter of about 2.0μm were in regular arrange.Two kinds of thicker carbon films were made by silk-screen printing.All the carbon films were tested in the Atomic Oxygen simulation and test equipment.It showed that the erode yield of the thinner and the thicker film were 2.16×10^-25cm³/a和4.8×10^-25cm³/a,were superior to the value recorded in the literatures.The ratio of the resistances of carbon films before and after impacted with atomic oxygen beam was linear with the time although the films had different thickness.A conclusion was made that all the carbon films could be used for detection the fluence or the flux of the atomic oxygen in LEO.The fluence up to 5.1×10²¹a/cm² and1.0×10²²a/cm² could be measured by using of the thinner film and the thicker film,and the thinner and the thicker film may had 2 years and 4 years life in the orbit of 400km.