Most crashes of Celestia are caused by bugs in the computer's OpenGL graphics driver. Loading many large Addons is likely to exercise the driver in ways unanticipated by its authors.
First, update the graphics driver using the latest version available from the manufacturer of your graphics chipset -- usually Nvidia, AMD or Intel. Drivers can be downloaded for free from their Web sites. Some laptops require drivers with proprietary modifications made by the manufacturer of the computer. They have to be downloaded from the Web site of the company that made the computer. OpenGL graphics drivers obtained from Microsoft's update service tend to be obsolete and buggy.
If you still have crashes after updating the graphics drivers, then you will have to disable individual Addons until you find the culprit. Please let us know which one it is and where you got it.