NASA describes a spacecraft as “a vehicle or device designed for travel or operation outside the Earth’s atmosphere.” A satellite is described as “a type of spacecraft that orbits the Earth, the moon or another celestial body.” Over the past several decades of years the small satellite mission market has been experiencing an advanced rate of growth in capabilities, number of missions and user investments due to the increasing demand of small satellite applications among end users within academia, commercial, defense, and government.
There is growing utilization of miniaturized satellites for military and defense applications. Defense organizations have been launching communication nanosatellites and microsatellites to provide communication signals to soldiers stationed in remote locations or in dense forests. The military needs more data bandwidth and reliable communications infrastructure for its UAVs, which can be fulfilled using constellations of nano and microsatellites.
However, a large percentage of missions are found to fail on launch or during early operations, particularly missions from university teams rather than those from commercial groups or space agencies. This is likely attributed to a lack of verification and validation (V&V) activities due to constraints on resources, experience, or schedule within these small scale projects
Satellite manufacturers must create a reliable product that supports these critical functions. Whether the satellite is for the government, the military or private industry, the need for rigorous testing remains the same. If a private company is going to build satellites for the government or commercial concern, they won’t retain that business for very long if the satellites they build don’t operate appropriately after launching into orbit.
Therefore all involved in the satellite industry, the government or private, needs vigorous satellite testing. It is also vital to test satellites properly because they are so expensive. For instance, a typical weather satellite that provides information to forecasters across the country can cost as much as $290 million. While the high cost of satellites and advances in miniaturization have led companies to develop smaller satellites for low and medium orbit, larger satellites should last at least 15 years before they need replacing. Governments or private companies that spend millions or even billions of dollars a year on satellite technology need to know their investments will not evaporate because the satellite failed during or the following launch.
Currently, NASA and some other private companies are exploring the idea of building smaller vehicles that could be capable of repairing satellites. Other ideas include assembling satellites in space. However, for now, once satellites are in orbit, they’re normally beyond the reach of repair. That is why companies that design and test satellites must consider every contingency, and examine everything that can possibly go wrong multiple times. Even if part of the satellite fails after launch, that does not mean the entire unit will get abandoned. If other components that are providing critical information are still operational, the satellite will remain in use until it has reached the end of its lifecycle.
The basic elements of a spacecraft are divided into two sections: the platform or bus and the payload. The platform consists of the five basic subsystems that support the payload: the structural subsystem, the telemetry subsystem, tracking and command subsystems, the electric power and distribution subsystem, the thermal control subsystem, and the attitude and velocity control subsystem. The structural subsystem is the mechanical structure and provides stiffness to withstand stress and vibration. It also provides shielding from radiation for the electronic devices.
The telemetry, tracking, and command subsystems include receivers, transmitters, antennas, sensors for temperature, current, voltage, and tank pressure. It also provides the status of various spacecraft subsystems. The electric power and distribution subsystems convert solar into electrical power and charge the spacecraft batteries. The thermal control subsystem helps to protect electronic equipment from extreme temperatures.
And finally, the attitude and velocity control subsystem is the orbit control system that consists of sensors to measure vehicle orientation and actuators (reaction wheels, thrusters), and to apply the torques and forces needed to orient the vehicle in the correct orbital position. Typical components of the attitude and control system include Sun and Earth sensors, star sensors, momentum wheels, inertial measurement units (IMUs), and the electronics required to process the signals and control the satellites position.
RF Payload Systems deals with not only the specific radio technologies, equipment (low and high power amplifiers, filters, frequency converters) and systems aboard a spacecraft tasked with delivering mission objectives, but also the supporting ground equipment and telecommunication systems through which spacecraft payloads are controlled and results communicated to mission control.
Assembly, Integration & Verification (AIV) or Satellite integration and test (I&T)
Satellite production doesn’t begin in earnest until a program has successfully passed its critical design review (CDR), a point at which most design details have been finalized and the customer has given their approval for production to begin. But the actual space vehicle I&T process doesn’t start until all of the satellite’s structural and electronic components have been fabricated, assembled and individually tested, a process that can take a year or more.
The procurement of the major components that make up a satellite is typically handled by a joint manufacturing and space vehicle team. This team acquires major satellite support subsystems such as propulsion, electrical power, and command and data handling, and fabricates the satellite bus, i.e. the physical structure that houses these subsystems and the mission payloads. The team is also responsible for the fabrication of hinges, gears, and gimbals used in movable or deployable subsystems; antenna and solar array structures; and radiators, which provide thermal control for different zones of the spacecraft.
Mechanically Integrate S/C
Spacecraft boxes or units are fabricated, assembled and tested either by outside vendors or by manufacturing organizations within the spacecraft contractor’s company. “We start fabricating circuit boards as soon as possible after CDR,” explains Ken Weber, communications payload deputy for a current Northrop Grumman satellite program. “Each board is populated with components, tested at the board level, then inserted into a mechanical frame to create what we call a slice, or plugged into a backplane that holds multiple circuit cards. The slices – the backplane and its plug cards – are then bolted together or enclosed in a housing and then tested as a single unit.”
For boxes manufactured in-house, Weber adds, unit-level testing is done under the supervision of the engineer responsible for the design of that unit. For units produced by outside vendors, the spacecraft contractor will typically send a team to the vendor’s site to inspect each flight unit, review its test data and confirm its readiness to be delivered to the contractor’s I&T facility.
Mechanically Integrate S/C
Before a new spacecraft can be launched, its main structural, electronic and propulsion components must be attached to the satellite structure, connected to each other electrically, and then tested as an integrated system, a process called integration and test (I&T). In the very competitive aerospace industry, it’s no surprise that the planning behind these steps begins long before the space vehicle has even been designed. After all, you can’t afford to design a spacecraft that can’t be assembled, integrated and tested in a straightforward and cost-effective manner.
“Typically, a few members of the integration and test team come on board a program very early to support the initial requirements development and flow-down process. We’re there to identify and help reduce or ‘burn-down’ risk for the program,” says Marty Sterling, a director of engineering for integration and test for Northrop Grumman. “We also work with the design folks on issues such as accessibility and testability, and help them by laying out notional test schedules which we will mature as the design matures.”
Once a company wins a spacecraft production contract, she adds, the I&T process begins to gain momentum. Her team begins working closely with the systems engineering and space vehicle engineering teams, helping them write the I&T plans and recommending small design changes to flight hardware that will allow I&T to proceed more smoothly. “In those early days, we’ll also be designing the electrical ground support equipment used to test the space vehicle, and the mechanical ground support equipment used to support the structural build of the satellite and any ground testing prior to launch,” says Sterling.
The AIT process takes modules, software & mechanical components & transforms them into a stable, integrated spacecraft ready for EVT. It is the real-world implementation of systems engineering and the start of the execution & formal recording of the verification process. AIT testing starts following the completion of module-level tests, Module Readiness Review (MRR), and prior to the EVT campaign. Each module engineer supports AIT throughout their module test at AIT level.
Electrical power subsystem (EPS)
The same is generally true of a satellite’s electrical power subsystem (EPS), which comprises of solar arrays, batteries and electronic units that generate, store, process and distribute power within the spacecraft. “It can take about 18 to 24 months to fabricate, assemble and test the electrical boxes, both functionally and environmentally,” says Tommy Vo, the EPS manager for a current Northrop Grumman satellite program. “Assembly and test of a satellite’s solar arrays can take upward of 54 months.” Vo’s team tests EPS boxes and solar arrays vigorously to ensure that each one meets its specification — a process called unit verification — before delivering them to the integration and test team.
Integrate Propulsion System
A satellite’s propulsion system, which includes propellant tanks, thrusters, valves, heaters and precision metallic fuel lines, is treated differently from other subsystems, partly because of its critical role in satellite operations. As such, it is assembled and integrated with the bus by a team of propulsion specialists before the bus is delivered to the I&T team.
“The propulsion assembly team provides special expertise in handling, installing and welding the system together,” explains Arne Graffer, a senior satellite propulsion specialist with Northrop Grumman. “This work includes alignment of thrusters, electrical and functional checkouts, and proof and leak testing of the completed system. We have to demonstrate that the system will perform reliably under all flight conditions.”
Once the propulsion system has been installed in the satellite bus, the integrated structure is delivered officially to the integration and test team. “Typically, the bus is delivered to us as a main structure and a series of panels that form the outer ‘walls’ of the bus,” explains Sterling. “We begin by installing bus electronics into the bus structure, and attaching payload electronics onto these individual panels.” This process includes installing all the cabling required to interconnect the satellite’s electronics, she adds.
“We start the integration process by flowing voltage through one of the cables to make sure we get the expected signal out the other end,” says Sterling. “If it all looks good, we know it’s okay to mate that cable to the next box. Then we check the signal coming out of that box to make sure it’s what we expect.”
This validation process continues, she adds, until all the bus electronic units and wire harness cables have been tested and mated. Sterling’s team next performs a series of functional checks on the integrated system, still at ambient temperature, to make sure that all of the bus electronics units are communicating and interacting with each other as expected. The integration process is then expanded to include auxiliary payloads such as sensors and other mission-specific electronics.
Sterling’s team conducts this satellite checkout process with the aid of ground support test equipment. The test equipment functions, in effect, like a “ground station” sending and receiving data to and from the satellite. This communication also helps verify, therefore, the ability of the satellite bus and mission payloads to talk to the “Earth.”
Install Solar Arrays and Deployables
The integration and test team also installs a satellite’s mechanical systems, such as its solar arrays, antennas, radiators and launch vehicle separation system, and then tests the ability of these systems to deploy properly. To ensure their proper operation on orbit, the team aligns these systems with a precision of .002″ or about half the thickness of a standard sheet of paper.
Robust Verification and validation
Similar to any large-scale satellite, albeit on a scaled down level, CubeSats should undergo robust V&V to reduce the risk involved in a space mission. This refers to verifying that the system conforms to a predefined set of requirements and validating that the system can perform the intended mission. Key phases in the life cycle of any space mission are ‘Phase C–Detailed Definition’ and ‘Phase D–Qualification and Production’. During these phases, the development of the system through qualification or acceptance verification and testing is performed and the preparation for mission operations is finalised.
Full functional test (FFT)
A core activity during these phases includes functional testing. Defined by ECSS standard ECSS-E-ST-10-03C , a full functional test (FFT) is a “comprehensive test that demonstrates the integrity of all functions of the item under test, in all operational modes” whose main objectives are to “demonstrate absence of design manufacturing and integration error”. It demonstrates the ability of the spacecraft to conform to its technical requirements and verifies the overall functionality of the system. Therefore, a robust and detailed functional test, supported by mission, performance, or end-to-end testing, can lead to increased mission survival rates.
The importance of the V&V process for CubeSat projects is becoming more apparent among missions, including university projects, and is reflected in the reduced failure rates of CubeSat missions in recent years and the adaptation of ECSS Standards for CubeSat missions. Multiple university projects are implementing robust testing methods to provide reliability to their mission and ensure mission success.
One method suggested is a fault injection technique, implemented by NanosatC-BR-2, whereby software and hardware faults are injected into the system and subsequently cause a failure from which it has to recover. Cheong et al. propose a minimal set of robustness tests that were developed following their experience with a communication failure at the early stage of the mission that lead to a root cause analysis investigation and recovery of the spacecraft.
Multiple projects report using hardware-in-the-loop (HIL) methods to verify the full functionality of the system while InflateSail at the University of Bristol perform functional and qualification testing on individual subsystems prior to integration at system level.
Various CubeSat projects implement risk reduction processes such as fault tree analysis (FTA), failure mode and effects analysis (FMEA), failure mode, effects, and criticality analysis (FMECA), or risk response matrix (RRM) . It also includes maintaining a risk register, whose purpose is to identify risks, and develop strategies to mitigate them, conducting structural and thermal analysis, and implementing fault detection, isolation, and recovery (FDIR) methods during the software development and mission test to manage risks for the mission.
AIT process and testing
All integration & testing is facilitated by the AIT team
■ Controls Spacecraft configuration
● Spacecraft build schedule
● Module Integration Schedule
● Software deployment schedule
■ Test scheduling
■ Coordination of activities with other facility and equipment users
■ Designation of spacecraft operators (personnel from AIT team)
Challenges of Space
Those can be listed as vacuum, high temperature changes regarding nonconductive thermal feature of vacuum typically between −150 and 150°C, outgassing or material sublimation which can create contamination for payloads especially on lens of cameras, ionizing or cosmic radiation (beta, gamma, and X-rays), solar radiation, atomic oxygen oxidation or erosion due to atmospheric effect of low earth orbiting.
The first hurdle for space systems to overcome is the vibration imposed by the launch vehicle. Rocket launchers generate extreme noise and vibration. When a satellite separates from the rocket in space, large shocks occur in the satellite’s body structure. Satellite must survive the extreme vibrations and acoustic levels of the launch. Pyrotechnic shock is the dynamic structural shock that occurs when an explosion occurs on a structure. Pyroshock is the response of the structure to high frequency, high magnitude stress waves that propagate throughout the structure as a result of an explosive charge, like the ones used in a satellite ejection or the separation of two stages of a multistage rocket. Pyroshock exposure can damage circuit boards, short electrical components, or cause all sorts of other issues.
Then, as it quietly circles the earth doing its job, it has to operate in very harsh conditions. It must function in an almost complete vacuum, while handling high levels of electro-radiation and fluctuation in temperatures that range from the hottest to the coldest. Outgassing is another major concern. The hard vacuum of space with its pressures below 10−4 Pa (10−6 Torr) causes some materials to outgas, which in turn affects any spacecraft component with a line-of-sight to the emitting material. Plastics, glues, and adhesives can and do outgas. Vapor coming off of plastic devices can deposit material on optical devices, thereby degrading their performance.
High levels of contamination on surfaces can contribute to electrostatic discharge. Satellites are vulnerable to charging and discharging. Discharges as high as 20,000 V have been known to occur on satellites in geosynchronous orbits. If protective design measures are not taken, electrostatic discharge, a buildup of energy from the space environment, can damage the devices. A design solution used in geosynchronous Earth orbit (GEO) is to coat all the outside surfaces of the satellite with a conducting material.
The atmosphere in LEO is comprised of about 96% atomic oxygen. Atomic oxygen can react with organic materials on spacecraft exteriors and gradually damage them. Plastics are considerably sensitive to atomic oxygen and ionizing radiation. Coatings resistant to atomic oxygen are a common protection method for plastics.
Another obstacle is the very high temperature fluctuations encountered by a spacecraft. Because it is closer to the Sun, the temperature fluctuations on a satellite in GEO stationary orbit will be much greater than the temperature variations on a satellite in LEO. Thermal cycling occurs as the spacecraft moves through sunlight and shadow while in orbit that can cause cracking, crazing, delamination, and other mechanical problems, particularly in assemblies where there is mismatch in the coefficient of thermal expansion.
Radiation effects (total dose, latchup, single event upsets) are one of the main concerns for space microelectronics. The design of radiation-hardened integrated circuits ( RHlCs ) involves four primary efforts. First is the selection of a technology and process which are relatively insensitive to the projected application environment of the IC.
Therefore satellite parts representative of the selected technology must be characterized in a simulated environment that models the RHIC’s application environment in order to quantify the effects of the environment on material and device characteristics. In the third phase, the circuit design techniques which make device responses most insensitive to the radiation are selected based on the technology analyses, and implemented in an IC design. The fourth phase actually occurs throughout the design process. Computer simulations of the chip response in pertinent environments should be performed as a part of each cycle of the design, manufacture, and testing processes, write Sherra E. Kerns, Senior Member, IEEE, And B. D. Shafer, Department of ElectricalEngineering, Vanderbilt University, Nashville, TN 37235, USA.
Multiplication and corona discharge
Multipaction is, basically, an event that can be reason of breakdown because of high power RF signal in a vacuum or near vacuum medium. It can reduce RF output power of device, cause noise in RF signal and even corona discharge because of ionization in presence of electromagnetic wave. Therefore, it can result a catastrophic failure of an antenna, RF component and even another payload module. There are two main factors for multipaction: high RF power and vacuum medium. Thus, related RF components including antennas should be either analyzed or tested for these phenomena. There is an analysis tool designed by ESA/ESTEC named as “ECSS Multipactor Tool”. By using this tool one can calculate threshold and safety margin levels for pre-defined structures according to the operating frequency, impedance, RF power level, material finishing and minimum distance between metal tips or edges.
As is known, in active RF devices there can occur intermodulation products of applied two or more tones at the output of the device. Similar phenomenon can be seen at antennas because of two main reasons: nonlinearity of material and nonlinearity of contact.
To avoid multipaction and passive intermodulation there are some published standards for design and verification phases. One of them is ECSS-E-20-01A Rev.1—multipaction design and test.
Space puts all materials under severe stresses, allowing only the most robust products to survive. Testing materials for space is crucial to ensuring the devices that use them will last in the worst conditions known to humanity without a repair service anywhere in sight. Without testing, the efforts of putting satellites into orbit are for naught when the devices fail in the heat of the atmosphere or the cold of space.
It’s required to test every satellite before it goes into orbit. Testing must begin at the initial phase of construction with each component. As these parts get assembled into larger pieces, they must undergo additional tests. Finally, once the final phases of satellite construction conclude, the entire unit needs to undergo rigorous testing. Other elements of the satellite that need testing, depending upon its construction, design and payload, includeing Solar panels, Antennas, Batteries, Electrical checks, Center of gravity and mass measurements, communication and telemetry systems and Fuel cells.
Assembly and Integration activities are followed by “Functional Performance Test” activities to generate all possible satellite mission scenarios. The purpose of the functional tests is to ensure that both satellite hardware and software is well functioning with respect to requirements/specifications based on the developed test scenarios related to the mission of satellite in space and performance verification of satellite components.
Satellite testing presents unique challenges. Unlike testing in the automobile industry or the appliance industry, you don’t get to test a prototype before constructing the final version. When you test a satellite, you are often testing the one that will eventually go into orbit. Therefore, while the tests need to be meticulous, the testing itself cannot damage the satellite in any way.
The following infographic takes a closer look at the test phases of a spacecraft and describes why functional and environmental tests (like electromagnetic compatibility EMC and telemetry, tracking, command TT&C) are essential to make sure that the satellites you are launching work perfect.
Testing Complete Satellite
When the satellite arrives at the testing facility after its construction, it must get unpacked in a clean room as many of the satellite tests must take place in a clean-room environment. That’s because it only takes one tiny outside contaminant to have a drastic effect on a satellite.
What is an ISO Clean Room?
AIT tests are carried out in the AIT cleanroom facility under the responsibility of the AIT Lead. The Module Engineer is responsible throughout AIT for testing their module & providing support to AIT at system level testing.
Once launched into space, satellites can no longer be serviced and contaminations increase the probability of malfunctions occurring during the planned lifetime. Even a single dust particle can interrupt a circuit. Dust is ubiquitous on Earth. In fact, it is so omnipresent that there are no completely dust-free environments. And not all dust is the same. There is an unimaginable amount of natural and man-made dust sources.
In addition, the mechanics of satellites are also prone to failure due to contamination, as conventional lubricants cannot be used when operating in space. In the case of payloads, a foreign object adhering to a mirror or sensor can render entire instruments unusable. To avoid this, satellites are manufactured in clean rooms.
A cleanroom is a specially engineered and carefully designed enclosed area within a manufacturing or research facility. These rooms allow for precise control, monitoring, and maintenance of an internal environment. The numerous ISO classifications are specifically designed to regulate: Temperature, Humidity, Airflow, Filtration, Pressure. Each room requires a different level of cleanliness depending on the industry and application.
This state-of-the-art AIT Center serves for more than one satellite up to 5 tons simultaneously by means of 3,800 m2 ISO-8 grade cleanroom and specific ground support equipment within the 10,000 m2 under roof approximately. Besides, ISO-6 grade mobile cleanroom offers high precision activities such as optical equipment/sensors, circuit board operation etc.
The satellite’s assembly team is the first group to test it. Next, a quality control team must conduct a separate series of tests before declaring the satellite ready for flight. The teams often repeat many of these tests to gather enough data to decide whether or not the satellite is ready to go into orbit.
Testing the Extremes of Space
Once a satellite is fully assembled, and its electrical systems have been proven functional at ambient temperature, the I&T team begins a series of rigorous environmental stress tests. Collectively, these tests are designed to prove (1) that the satellite can survive the extreme acoustic and vibration environment of launch, (2) that it can sustain the explosive shock associated with separation from the launch vehicle, and (3) that once on orbit, its electronic subsystems can operate successfully in the extreme temperature and radiation environments of space.
Another key phase of environmental testing within integration and test is called thermal vacuum (thermal vac) testing. For this testing, the entire satellite is placed in a special chamber that can be pumped down to near-vacuum conditions. The chamber also includes high-performance heating and cooling equipment. As the I&T team “exercises” the satellite’s electronics functionally, the temperature inside the chamber is cycled repeatedly — typically six or seven times — between extremely hot and cold temperatures (+180 to -200 degrees C) over the course of several days.
In conjunction with thermal vac testing — either before or after — the I&T team also conducts electromagnetic interference/electromagnetic compatibility (EMI/EMC) testing to ensure that no devices on the satellite are emitting significant amounts of electromagnetic energy. Such emissions could interfere with the proper operation of the satellite bus or its mission payloads.
Simulating Launch and Deployment
During vibration testing, the satellite is placed on a large shaker table and shaken for several minutes at frequencies expected during launch. For acoustic testing, the satellite is placed in a large chamber, then exposed to high-intensity sound waves that simulate the acoustic environment of launch. Shock testing involves exploding the ordnance that’s used on orbit to release the mechanical pins that hold deployable devices in their stowed position.
During acoustic, vibration and shock testing, Sterling noted, the satellite’s electronic systems are all placed in their launch configuration. For many of the satellite’s systems, such as mission payloads, that means the electronics are switched off completely.
Since satellites cost so much to build, vibration tests have become not only vital, but also highly monitored. It’s common for the testing team to gather hundreds of data points from the vibration test, which allow them to scrutinize every inch of the satellite and locate any possible weak points. A key satellite test procedure in qualifying a satellite for launch is swept sine testing — a variety of vibration test that uses a single frequency to test a specific structure within the satellite. During a swept sine test, the sine tone ranges up and down through various frequencies, and always for a specified rate of vibration and duration.
In situations where a controller system for vibration does not include a channel count that is high enough for a specific test, or that require the use of an independent analysis system, it is possible to use a dynamic signal analyzer. This analyzer provides software that allows the testing team to measure multiple channels of sine data simultaneously.
Recording all this data is one of the most essential parts of satellite testing. Scientists can monitor and collect all the various channels of sine data at once when a satellite is undergoing vibration testing. This data will provide the satellite testing team with clues about the construction of the satellite and whether there are any weak spots that pose a potential problem during launch.
Since scientists carry out all these vibration tests on the real satellite, however, it is crucial not to over-test. A critical part of the test is also to apply limited channels during the testing. These channels have a maximum allowable vibration level that gets assigned to certain structures within the satellite. If the testing reaches these levels, the team must reduce the test vibrations.
Being able to accurately locate weak spots during vibration testing ensures a longer life for the satellite once it is in orbit — which is why there is no room for error. If the vibration testing misses a troublesome location on the satellite, and the satellite then gets damaged by the extreme shaking and violence of the launch itself, it could greatly shorten the life of the satellite and result in the loss of millions of dollars.
With new technologies such as 3D printing and artificial intelligence lending themselves to the improvement of the manufacturing process, we could be about to witness an emergence of a production line-type assembly process for satellites. Historically, satellites were built as a one-off design – customised and handmade. But with whole constellations being planned for launch, space companies are looking at how to stamp out identical satellites using the latest design tools in the same way as Henry Ford did with his cars in at the beginning of the last century.
Additionally, in the development phase, space companies will use simulated data to test their designs on a more frequent basis. Using this method means reducing the need to do expensive hardware testing. What’s more, ongoing advances to mathematical computing will enable faster design and simulation. For engineers, that means that they will be able to accomplish more in a narrower period of time, allowing design of more complex systems in a shorter timeframe.
EDU vs Flight Unit
If a project has enough money, the engineers will buy duplicate units. One unit is dedicated to engineering development (EDU) and the other to flight. The EDU is identical in hardware and software, functionally equivalent, but may not have been environmentally tested. The EDU may be cheaper during procurement due to less rigorous or complex manufacturing and testing standards. The EDU is meant to be exercised in functional tests at the component to system levels. The idea is to rigorously test this less expensive unit and reduce wear-and-tear on the unit that will actually go into space, the flight unit. Before delivery, the flight unit’s health is checked out by engineers/scientists and lightly exercised to ensure system functionality. The majority of the flight unit’s operations are reserved for in-space nominal operations.
Here is a real-life example of a satellite test
The National Oceans and Atmospheric Administration tested its Geostationary Operational Environmental Satellite-S (GOES-S) in March 2017, ahead of its launch a year later under the new name of GOES-17. As part of that testing, the team placed GOES-S in a thermal vacuum chamber to determine its ability to operate in the extreme cold of space.
The vacuum chamber tested the satellite across four different cycles that ranged from intense cold to intense heat. Severe temperature fluctuations in the airless vacuum chamber gave scientists a chance to check how the satellite’s sensitive instruments performed in these harsh conditions. Satellites also need to get tested for shielding against external radio signals. The testing team must ensure the satellite’s antennas unfold properly and are compatible with the satellite’s other systems, as well.
Additional tests will include measurements to learn each satellite’s exact center of gravity and mass, which will ensure the satellite is compatible with its launch vehicle. It also helps control the orientation when the satellites are in orbit, which can lengthen how long they will operate in space. Scientists will need to test satellite thrusters, too, which will help orient its orbit after its launch vehicle releases it.
Verification for launch and environmental effects
In order to verify that antennas can perform functionally in space environment and withstand launch effect mentioned above, some tests should be performed as addition to functional tests before mission started. These environmental verifications can be listed as: thermal qualification, sine vibration, random vibration or acoustic, quasi-static acceleration, stiffness measurement, and low outgassing compatibility.
To verify the modules, requirements and tests have been defined by NASA and ESA in their published standards. For space programs, the related requirements and tests are prepared based on those standards. Some important and general ones can be listed as:
Published by ESA
- ECSS-Q-ST-70-02—thermal vacuum outgassing test for the screening of space materials
- ECSS-Q-ST-70-71C Rev.1—materials, processes and their data selection
- ECSS-Q-ST-70-04C—thermal testing for the evaluation of space materials, processes, mechanical parts and assemblies
Published by NASA.
- GSFC-STD-7000A—General Environmental Verification Standard (GEVS) for GSFC Flight Programs and Projects
- Outgassing Data for Selecting Spacecraft Materials
- NASA-STD-7002B—Payload Test Requirements
- NASA-STD-5001—Structural Design and Test Factors of Safety for Spaceflight Hardware
- NASA-STD-7001—Payload Vibroacoustic Test Criteria
- NASA-STD-7003—Pyroshock Test Criteria
For many years, the government was the primary industry interested in the construction and testing of satellites. These days, however, large and small private companies are increasingly investing in satellites. Commercial concerns have a greater hand in the construction of satellites for television and radio signals, telecommunications and military applications.
Companies like NTS maintain a network of facilities across the United States to conduct the necessary tests, including building gigantic climate chambers to analyze how a satellite responds to the vacuum of space or to extreme changes in temperature. Other centers may conduct tests for vibration, solar radiation, dealing with the dust of space or with pyroshock, which might occur during the booster separation stage or the satellite separation stage from explosive bolts. The explosive shock of booster seperation can damage circuits, dislodge contaminants in the satellite or short-circuit electrical components.
In other facilities, such as the NTS satellite testing facility in Santa Clarita, Calif., satellites get tested in a 5,000-cubic-foot acoustic chamber to learn about how the satellite reacts to heavy vibration, as well as the deafening noise of a launch. Because these tests are so rigorous — and costly to carry out — they are among the most crucial checks to conduct. The facilities needed to test satellites adequately can be enormous. For instance, the Santa Clarita facilities cover more than 150 acres.
When all of the functional and environmental tests are complete, the I&T team puts the satellite into its shipping configuration with all mechanical appendages stowed, tests it one last time for electrical “aliveness” and then packs and ships the satellite by truck or cargo plane to the launch site. But the I&T team’s work doesn’t end when the satellite leaves the factory.
At the launch site, explains Sterling, the I&T team unpacks the satellite and performs post-delivery health checks on its bus electronics and payloads to verify that the transportation process didn’t harm them. Then her team works closely with the launch vehicle team to integrate the satellite to the launch vehicle in preparation for launch. “I think it’s safe to say that the I&T process never really ends until the launch vehicle clears the tower,” she advises.
References and Resources also include: