Update setup.py

Author: Sceki

setup.py

@@ -30,7 +30,7 @@ def read_package_variable(key):
     author='ESA FDL Europe Constellations Team',
     # author_email='',
     packages=find_packages(),
-    install_requires=['numpy', 'matplotlib', 'torch>=1.5.1', 'pykep>=2.5', 'skyfield>=1.26', 'kessler', 'pandas'],
+    install_requires=['numpy', 'matplotlib', 'torch>=1.5.1', 'pykep==2.5', 'skyfield>=1.26', 'kessler', 'pandas'],
     extras_require={'dev': ['pytest', 'coverage', 'pytest-xdist'],
                     'docs': ['sphinx==3.2.1', 'sphinx_rtd_theme==0.5.2', 'jupyter-sphinx==0.3.2', 'myst-nb==0.12.3']},
     # url='https://github.com/kessler/kessler',