Satellites are man-made objects that orbit the Earth in various orbits. They send important data such as weather data and remote sensing data while enduring the harsh, cold, and icy space environment. But have you ever wondered how they are able to survive this? Let's dive deeper into the journey of satellites before launch.
Introduction
It's a fine winter evening at U R Rao Satellite Centre (URSC) in Bangalore, and the satellite has already been fabricated. Before it is transported to Satish Dhavan Space Center (SDSC) SHAR for launch, ISRO's scientists must ensure that it can withstand the harsh space environment, including solar storms, extreme temperatures, vacuum, microgravity, micrometeoroids, and high-speed debris.
If you have witnessed a space launch from the launch viewing gallery at SDSC SHAR, you know how loud the sound from the launch pad can be. This generates significant vibrations on the launch vehicle.
Therefore, this newly fabricated satellite must be able to withstand these high vibrations in order to reach its desired orbit and function properly. The satellite is designed to fit inside the payload fairing of the launch vehicle, so its antenna and solar panels are folded.
Once it reaches its desired orbit, scientists will unfold the solar panels and antenna. Therefore, it is important to test whether our newly fabricated satellite can handle all of these conditions.
How can we Validate ?
Solar Panel Deployment Test
Since our satellite will be exposed to harsh space environments, we need to create an artificial space environment on Earth in laboratories. Here's how we will proceed:
Place the fabricated satellite into a vacuum chamber that simulates the space environment, including the vacuum and absence of gravity.
Remotely send the deployment command to the satellite and observe the programmed unfolding of the solar panels.
Monitor the deployment process using video cameras and telemetry data to ensure that the panels fully extend and lock into their operational position.
After successful deployment, visually inspect the solar panels for any damage or irregularities and confirm proper alignment and operation.
By following these steps, we can successfully test the solar panel deployment of our newly fabricated satellite.
Antenna deployment test
After completing the Satellite deployment test, we will now proceed with the Antenna deployment test. Typically, Antenna deployment and solar panel deployment are programmed as an automatic sequence task once the satellite is ejected from its launch vehicle. To begin, we need to place our newly fabricated satellite into a vacuum chamber that simulates the space environment, including the vacuum of space and the absence of gravity.
Next, we will remotely send the deployment command to the satellite and observe the antennas unfold according to the program. The deployment process will be monitored through video cameras and telemetry data, ensuring that the panels fully extend and lock into their operational position. Once the deployment is successful, we will conduct performance testing to verify the efficiency of the antennas in transmitting and receiving signals. This will involve measuring the signal strength, gain, and pattern under simulated operating conditions.
By completing these steps, we will have successfully validated the Solar Panel deployment test and the Antenna Deployment test.
Vibration Test
Now that we have completed two tests, our third task is to ensure that our satellite does not get damaged by the low-frequency vibrations caused by the rocket during its launch. To achieve this, we will place our newly fabricated satellite into the Vibration Test Facility.
In the Vibration Test Facility, the satellite will undergo a vibration test.
This facility is equipped with electrodynamic shakers, a digital vibration control system, a data acquisition system, and a sufficient number of accelerometers. Additionally, the satellite will undergo a test using a drop shock machine.
This test is used to perform high 'g' shock tests on components and small subsystems. These tests help us verify whether the satellite can function normally after enduring such vibrations. They also help verify that the designs and analysis of the satellite structure meet the vibration requirements.
Acoustic Test
After completing the previous tests, it is time for the Acoustic Test. We will place our newly built satellite into an acoustic chamber to simulate the launch process. During this process, the rocket generates noises that create a vibration environment.
First, we will conduct the Random Acoustic test. This test exposes the satellite to a complex acoustic environment with varying sound pressure levels and frequencies, replicating the random nature of launch acoustics. It ensures the structural integrity and functionality of the satellite under realistic conditions.
Once the Random Acoustic test is completed, we will proceed with the Sine Sweep Acoustic Test. During this test, the satellite is exposed to a sinusoidal sound wave that gradually increases in amplitude while sweeping across a range of frequencies. This helps us identify any resonance frequencies that could be amplified by specific acoustic tones during the launch.
Thermal vacuum Test
After completing the aforementioned tests, it is now time to test our satellite in the space environment, specifically in near vacuum conditions with significant temperature fluctuations. To do this, we will conduct a Thermal Vacuum Test. In this test, the satellite will be placed inside a chamber where all the air is drawn out using a pump.
The environment inside the chamber is controlled through the use of liquid nitrogen and a heater, which regulate the temperature through radiation. This test is crucial in ensuring that the satellite's components can withstand thermal expansion or contraction during launch and operate effectively in space.
Mass property Test
After completing the above tests, it is now time to test the centroid of a satellite, moment of inertia, and product of inertia. These tests are necessary to provide control for satellite positioning during orbit insertion and attitude adjustments.
To perform these tests, we will mount the satellite on a motor that will slowly move it. Air bearings will be used to reduce friction and resistance. A sensor will measure the power created due to these movements. The data obtained from this measurement will then be used by the data processing system to calculate the position of the satellite's centroid and its moment of inertia.
Electromagnetic Compatibility tests
Once we have completed all the tests mentioned above, it is time to check for the presence of electromagnetic interference phenomena among various satellite subsystems. To do this, we will place our satellite into an Anechoic chamber.
An anechoic chamber is a specially designed room that absorbs all reflections of electromagnetic waves. It allows us to measure radiation patterns and ensures that there is no negative impact on the performance of the antenna and payload.
By characterizing the antenna performance on the ground, we can confirm that it meets the design specifications. This combination of factors helps us simulate a quiet open space of infinite dimensions, which is ideal for testing communication antennas intended for use in space.
Hardware In-Loop Simulation Test
After completing the above tests, it is now time to test for deficiencies in the spacecraft's hardware, software, interfaces, etc. This will be done through the Hardware In-Loop Simulation Test (HILS). The HILS facility is used to test the Attitude and Orbit Control System (AOCS) of satellites in a closed loop, with all AOCS hardware in the loop.
It caters to the stringent requirements of the spacecraft mission. The facility includes various key elements such as 3-axis Motion Simulators, Earth Simulators, Sun Simulators, and Star Simulators to stimulate optical sensors, computing workstations, closed loop dynamics software, data acquisition, and related display and plotting software.
Now that our satellite is ready, it can be transported to Sriharikota for launch. This concludes today's topic. If you enjoyed it, please follow zetagravit on X and Insta for daily space updates. You can also subscribe to our newsletter with your email to receive new articles directly into your inbox.
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