This was one of my first 3D cutaways once learning Blender in 2020. Its not supposed to be mechanically or scientifically accurate in any way, but I have generally tried to keep the science grounded at least with exisiting or in development technologies.
The idea of the design was based on a sketch by the great Dipo Muh.
Below are some illustrations from my own collection I studied for some of the details on this design.

Fictional History
The SAAB Heimdallr has been the mainstay of the Swedish Orbital Deterrence mission since 1988. The squadrons rotate on deployment providing a constant overwatch on potential Soviet ICBM’s.
The crew of two, a Commander and Weapons System Officer enjoy quite a large space, larger than the Apollo capsules decades before. They are able to stay in orbit for up to 10 days but this can be extended if needed.
Powered by a combined cycle precooled jet engine and closed cycle rocket engine (SABRE) running on an air and Liquid Oxygen/Hydrogen mix. They are able to achieve SSTO and land conventionally at the end of the tour, on an improvised runway if needed.
The spacecraft contains a miniaturized reactor supplying electricity to a high output laser, its offensive means to counter enemy missiles in the boost and mid course stages. A radiator array is deployed in orbit to provide cooling for these systems..