Beautiful, creepy, heart pounding... I love a good newtonian physics sim and this does quite a lot with comparatively very little!
I love the way the sonar (in space?) heart beat matches your own as you get closer to the astronaut.
I can imagine this being expanded on with different types of hazard, functions like shields or gravity tractors, even some orbital mechanics? Or maybe just a way to shut off the damage alarm. :P
Great stuff!