I found this guide usefull. Unlike the s++ guides that are difficult for most people to follow, this is a more modest s rank done on easy.
I'd been stuck in the habit of always playing on normal due to the suicide bullets charging up your homing missiles. After seeing this video I forced myself to play it on easy and got it after about 5 tries.
A few things to note: It is MUCH easier to keep your chain going through the second part of the satellite on easy than on normal, so if that was a problem for you, try easy.
The boss is also much easier, obviously.
Lastly, keep in mind you only need 4 million to get 'A' rank. The video is a score of over 5million so there is a lot of room for error.