Artist's rendering of the NICER instrument. Source
One of several projects currently being considered by NASA proposes to send a special instrument to the International Space Station to monitor x-ray emissions from pulsars (neutron stars), the super dense remnants of dead stars that are almost, but not quite, black holes. This device is called the Neutron Star Interior Composition Explorer (NICER, for short). Due to their relative darkness and diminutive size, we have been unable to accurately gauge the size of neutron stars, but NICER proposes to change this. The device will measure the light emitted from the poles of these dead stars and scientists will use their knowledge of relativity to measure their actual size. Ultimately, this study would provide us with a knowledge of just how compressible matter really is.
It's all very complicated, but if you want a better explanation of what NICER is and what neutron stars are, check out NASA's article. If NICER is accepted, it will be launched in 2016.