BUILDING LOW-COST NANO-SATELLITES: THE IMPORTANCE OF A PROPER ENVIRONMENTAL TESTS CAMPAIGN Jose Sergio Almeida INPE (Brazil) 1 st International Academy of Astronautics Latin American Symposium on Small Satellites: Advanced Technologies and Distributed Systems 7-10 March 2017 San Martin, Buenos Aires - Argentina LABORATÓRIO DE INTEGRAÇÃO E TESTES
The spacecraft may be: - Simplified in its design - Miniaturized in its size - significantly reduced in its total cost but the harsh of the launching stresses and the space environment of the orbit still remains virtually the same!
past few years: increase interest in very small satellites Possible from: miniaturization and better performance of electronic and some mechanical components also because of relatively lower costs associated to project, production and launching of these tiny spacecraft nano-satellites proved valuable for students opportunity of better understanding and learning details of design, construction, tests, launching and operating a real spacecraft also very useful in terms of low-cost platform for qualification, in orbital flight, of new technologies for space application
with typical low-budget, short time of design, construction and production significant risk of underestimating importance of environmental tests the spacecraft has to be submitted to increase probability of operational success during launching and orbital flight typically CubeSats and other relatively lower-cost nano-satellites make use of COTS components, and frequently include new kinds of payload equipment more attention and more severe ground environmental tests shall be recommended
The Vibration and Shock Environment Current launching vehicles are powered by solid boosters or liquid-injection operating engines, vigorous burning of fuel inducing significant levels of vibration in structural elements and equipment of spacecraft Also, the rocket high-speed crossing along atmosphere generates shock waves producing significant noise and vibration on top of tiny passenger spacecraft computer-based structural modelling to analyse that mechanicdesigned spacecraft will withstand and remain healthy and safe
But: Although computer modelling are producing more accurate output data, they are not perfect (and also depend on Engineer for correct inputs and data) Building materials, including metallic and structural parts, resins, fasteners etc. may not be produced exactly as theoretically proposed and expected Even with the well-qualified assembly and integration procedures, and even with proper training, the hand-operation of the technician can not guarantee that all the details of the procedure were executed exactly as programmed and expected So, the best way to confirm that it is ready for launch and orbital flight is submitting the hardware to real, actual laboratorial environmental tests
Nano-satellite instrumented with vibration sensors (accelerometers) able to read acceleration taking place at the location and direction(s), along the frequency sweeps Nano-satellite installed inside ejection device, all properly installed on top of the laboratory Shaker, accelerometer cables taken to a Data Acquisition System for real-time reading and recording for post analysis
The Environment of High-Vacuum and Temperature Extremes when spacecraft reaches orbital altitude it confronts with the high vacuum and soon with the temperature extremes of the space environment all materials that compose the spacecraft (metals, fibres, special painting, surface finishing, cabling etc.) shall be fully compatible in terms of material stability with the harsh of the very low pressure of the space environment If not compatible occurrence of outgassing phenomenon Outgassing: if gas releasing rate significant risk the material or component may change physical or chemical properties, possible degradation on its operational or functional demand within the spacecraft
The Environment of High-Vacuum and Temperature Extremes Traditionally, CubeSats tend to adopt COTS (Commercial Off-The-Shelf) components usually do not have the tight technical qualification for space application Usually they have lower costs and shorter delivery time when compared to their space-qualified counterparts Also, nano-satellites in many cases are launched into space as a second payload (piggy-back), together with high-cost large spacecraft significant additional concern in terms of chemical contamination from the nano-satellite to the main payload
The Environment of High-Vacuum and Temperature Extremes Outgassing rate verification under high vacuum conditioning: Spacecraft is put in a vacuum chamber, clean high-vacuum conditioning, mass spectrometer used to analyse, to identify and estimate the rate of any significant gas releasing from the spacecraft Bake-out Procedure: Spacecraft in a vacuum chamber, clean high-vacuum conditioning, warming up the whole satellite to tolerable high temperature, keep in the condition for a period of time (e.g. 24h or 48h). This accelerates releasing of gases from spacecraft, making it cleaner and more appropriate to be launched together with higher-costs satellites. Usually this is a call from the launch vehicle authorities.
The Environment of High-Vacuum and Temperature Extremes The issue of High and Low Temperatures Outside the atmosphere, when satellite is within Sun s sight, quite significant rate of solar radiation impinges its surfaces may generate significant amount of heat When the spacecraft goes to Earth eclipse mode spacecraft can lose heat, for small satellites this can take place in a very fast mode
The Environment of High-Vacuum and Temperature Extremes The issue of High and Low Temperatures Components adopted for nano-satellites (CubeSats) not necessarily are fully qualified to endure stress of high and low temperatures Recommended computer thermal modelling of spacecraft to optimize thermal design, aiming to moderate extremes of high and low temperature during orbital flight, in this way keeping it inside the operational temperature range.
But: The best computer-assisted thermal modelling of the satellite will not guarantee that: the thermal design and control will work perfectly and that the several parts of spacecraft will operate between safe extremes of temperature the spacecraft components and subsystems will operate accordingly and successfully when submitted to the high and low temperatures during the orbital flight The workmanship produced by technicians during assembling & integration (also involving thermal aspects and peculiarities), cannot be taken as exact the way it was specified in the procedures So, the best way to confirm that it is ready for orbital flight is submitting the hardware to real, actual laboratorial environmental tests
The Environment of High-Vacuum and Temperature Extremes Spacecraft instrumented with temperature sensors, quantity and location according to monitoring requirements Spacecraft installed in a thermal-vacuum chamber, all test cabling including any harness for functioning tests if the case, is connected to DAS or EGSE, chamber closed High vacuum conditioning, thermal shroud produce heat to warm-up spacecraft to hot-case condition where electrical functional tests can be performed on S/C Tvac chamber shrouds cooled down, by radiative heat transfer the S/C is also cooled down to specified cold-case condition where electrical functioning tests are performed on S/C. Depending on specification, more than one thermal cycle may be executed
The Environment of High-Vacuum and Temperature Extremes A nano-satellite being prepared for Thermal-Vacuum Tests
The Matter of Electromagnetic Compatibility Virtually all nano-satellites carry some kind of communication subsystem (send signal and/or data to ground stations, communication among other satellites for instance) Also, nano-satellites may carry sensitive on-board electromagnetic equipment To ensure the on-board equipment is safe against possible interferences, and also safe against players as the launching vehicle communication system or launcher main payload(s), computational electromagnetics simulations are performed But, still, tests related to possible electromagnetic interference are recommended to be executed in the Laboratory
The Matter of Electromagnetic Compatibility Emission Testing Nano-satellite positioned in Anechoic Chamber, put into operation and the levels and characteristics of the emitted electromagnetic waves are analysed to verify if they are within safe range. Susceptibility Testing Spacecraft positioned nearby a well-defined source of RF or electromagnetic pulse energy, so radiating antenna can direct energy at spacecraft, so measurements are performed to analyse the results in terms of how much it may be affected.
Mass Properties Measurements No spacecraft may be launched into space without precisely knowing its physical characteristics. This includes: measurement of its mass (M) centre of gravity location (C.G.) moment of inertia (MOI) and others These can be accomplished by using dedicated facilities provided by the testing laboratory Mass Properties Measurements of a nano-satellite give the spacecraft its characterization in terms of actual physical properties, absolutely mandatory for its launching campaign
Conclusion New technologies, lower-cost components and materials that may be typically connected to CubeSats may have significant probability of presenting some kind of premature malfunction Significant amount of time and resources shall absolutely be allocated in order to support and to assure a proper spacecraft environmental testing campaign If CubeSat is conceived inside the Academia, students naturally hold very high expectation to witness their space product operating accordingly in orbit. big frustration if happens a premature mal-function The bottom line: if the nano-satellite has to use components that do not hold full, proved, space qualification, so a higher reason that laboratory environmental tests are absolutely required, aiming to mitigate chances of failure
Conclusion Contrary to that many project managers may presume, lower-cost and perhaps simpler spacecraft definitely will require still more attention in terms of hardware qualification against the very tight stress of the launching and space environment, before it can be considered as ready to initiate its mission in space. Thank you for your attention!