## General Mechanical

#### Thermal Radiation Flux In Spacecraft Orbit Simulation

• markg0311
Subscriber

Hi all,

I'm looking to preform thermal analysis on a spacecraft/spacecraft components over the course of an orbit. This means radiative heating from the Earth and Sun must be taken into account. Currently the heat flux from these objects can be determined, aswell as a vector describing the direction from which they originate at each time in an orbit. To determine the incident flux on the surfaces of the spacecraft, the view factor of these objects from each surface on the spacecraft needs to be caluclated. I would like to take advantage of the fact that the ANSYS radiosity solver method can compute these view factors for me, correctly accounting for the sizes of these objects, and shadowing. However, in ANSYS, only direct surface flux, and radiation between objects can be defined. I am having some trouble determining how to incorporate the incoming flux from the Earth and Sun.

Roughly, the radiation from the sun can be treated as parallel from a source, but from the Earth, the situation is different since the Orbit is low, and the Earth is large. Somehow the view factor for each surface to the earth needs to be calculated. My current solution is to encompass the satellite in a large hollow sphere, mesh it with shell elemnts, and set the temeprature on the regions of the sphere corresponding to the projections of the Earth and Sun onto the sphere as the effective temperature of these objects. The sphere would be meshed with SHELL132 elements, with emissivity 1, and the temperature would be set as a DOF contraint. The effective temperature at each point on this sphere would change with each timestep to reflect the change in position of the Sun and Earth. So essentially what is being done is placing the spacecraft in an enclosure, and heating the walls of the enclosure to mimic the heating that would come from the Sun and Earth. The analysis will be done within ANSYS Mechanical APDL.

Is this the correct way of approaching the problem? This method seams a little bit ad hoc, and I feel there should be a better way. Is there other functionality within ANSYS that can do what I'm looking for/acheive the same resutls in a simpler way. I am aware that other software is available for this analysis, but it is not available to us. Any help is appreciated.

Regards

• 1shan
Ansys Employee
As mentioned in your previous post https://forum.ansys.com/discussion/29549/external-radiation-sources-for-thermal-analysis#latest, a better way would be to use SURF152 element which also allows you to set a user defined view factor using keyopt(9) = 1.
Regards Ishan.
• markg0311
Subscriber
Thanks for getting back to me Ishan. I still have a few questions on how this would work in my situation. This seems like a good way to incorporate radiation incoming from the sun, which would have a cosine effect view factor. However the radiation coming from the Earth is a bit more tricky. The view factor depends still on the angle between the surface and the source, but not just as a cosine, but other functions of that angle. It seems that only a constant view factor can be use with surf152.
Is it possible to define a view factor that depends on the angle between the element normal and the extra node? Furthermore, if there are other objects in between the element and the extra node, does the SURF152 element account for the shadowing of that object?
Furthermore, I wish to do a transient analysis, where the position of the Sun and Earth change over time. How would this be incorporated? Would I use multiple extra nodes and switch between them somehow. As far as I understand, only a single extra node can be used.
Again, thanks for you help so far Mark