I am trying to merge a series of 20 second exposure shots of the space station, so that the space station presents as a white line throughout the photo. The shots were taken successively so as to avoid star shake. However, when merged it seems only the last photograph is visible thereby not providing the desired effect. Any ideas would be greatly appreciated!
Make sure you don't have the dehosting option turned on. This option masks out changes between images. If that doesn't Work you should try stacking the layers in photoshop with a Lighter color blend mode.
This is not something that Lightroom can do. Lightroom can merge to panorama, but this is not a panorama so only one image will show. And Lightroom can merge to HDR, but because these are not exposure brackets it is not an HDR series either, so you will probably get the same problem. You need to use Photoshop for this.