Analysis

Satellite is placed in the required orbit by the launch vehicle. During launch, the satellite undergoes high levels of acceleration, vibrations and shock. Loads include vibration, shock and acoustic loads. Satellite structure should be made in such a way that it can withstand such high level of loads. Launch loads depend on the launch vehicle.
We can only analyse structural integrity of satellite, we can’t comment on functional integrity.
To test functionality along with structural stability on software requires high computational power. It is more preferable to do functionality test on hardware rather than on software because it provides more visual information than software and also helps to examine practical problem more conveniently. Listed below are typical analyses usually performed to ascertain structural stability:

Static Analysis

Static loading occurs due acceleration of launch vehicle.

• We need static analysis to verify and test the structure of satellite.
• We need to ascertain that the maximum stress on the components will not be greater than the yield strength of material. More precisely maximum stress should be within some factor of safety of the yield strength.
• If maximum stress exceeds yield strength then we have to make changes to the structure to maintain maximum stress in certain desired range.

Shock Analysis (Shock Response Spectrum)

A shock response spectrum(SRS) is a response of single degree of freedom(SDOF) system to a shock or any other transient acceleration. It is depicted by a graphical representation.
Shock loading also occurs due to the acceleration of launch vehicle but just to get an idea, consider that you are sitting in a bus and it starts accelerating and you just get pushed backwards. What happens to you in the bus is just a very miniature version of what happens on the launch vehicle.
Launch vehicle experiences increasing acceleration along with vibration. Satellite acceleration changes with frequency of vibration of satellite. Things we have to analyse when performing Shock Analysis are the same as Static Analysis.

• We need to ascertain that the maximum stress on the components is not greater than the yield strength of material. More precisely maximum stress should be within some factor of safety of the yield strength.
• If maximum stress exceeds yield strength then we have to make changes to maintain maximum stress within the desired range.

Modal Analysis

Modal analysis involves the determination of fundamental frequency of satellite.
Launch vehicle puts a lower limit on the fundamental frequency of the satellite. So satellite must be design to keep its fundamental frequency above the lower limit to maintain the integrity of satellite. If the satellite fundamental frequency is lower than the lower limit in any direction, then the satellite can be severly damaged due to resonance since maximum energy transfer takes place during resonance. We need to check whether the fundamental frequency is higher or lower than the lower limit in each direction.

Harmonic Analysis

Harmonic analysis gives the steady-state response of a linear structure to loads that are harmonically varying with time. Harmonic analyses are done to determine whether a structure can survive the loads appearing during resonance resulting from the forced vibrations. It also helps in ensuring whether the structure will survive through fatigue. In the case of a satellite the harmonic loads are applied by the launch vehicle. The structure of the satellite - its side panels, PCBs, screws etc must not get damaged during this loading. This analysis will also help determine the appropriate torque needed to be applied to the screws to not come off or fracture during launch.

If you are done reading this page, you can go back to Mechanical Subsystem