Matter Beam, the author of the toughSF blog, has published a great article explaining how to design a spacecraft that has optical, infrared and radar stealth. It’s quite technical and relies on advanced technologies, but it shows that stealth in space is achievable:

“Despite the commonly accepted truth in Hard Science Fiction, spacecraft are able to evade detection in space in many circumstances. The Hydrogen Steamer was a design that used liquid hydrogen evaporative cooling to keep a non-reflective surface practically invisible.

However, it was vulnerable to RADAR and had extremely poor manoeuverability, as it was meant to demonstrate how long it could stay cool. This time, we will design a more advanced, functional and performant stealth spacecraft.

This post builds upon the conclusions drawn from the Stealth in Space is Possible series found here (Part I, II, III and IV). A useful read is the page on the Hydrogen Steamer design.”

The rest is at toughSF: https://toughsf.blogspot.com/2018/04/permanent-and-perfect-stealth-in-space.html

Also relevant to the subject are two files I created to design stealth spacecraft and evaluate the range at which they are detected.