Dead Space contains various unlockables, most of which are acquired after beating the game on default difficulty. The unlockable items are designed to give you backstory to the game and encourage you to play through the game again on a harder difficulty.CheatCodesGuides.com: Dead Space Unlockables

After completing the game on the normal difficulty, the following gameplay elements will be unlocked:

1. Impossible mode
2. Backstory log entries
3. 10 Power Nodes
4. 50,000 credits
5. Level Six Suit SchematicCheatCodesGuides.com: Dead Space Unlockables

Once the player has unlocked Impossible Mode, they must start a new game in that mode and save it in order to keep the mode unlocked.CheatCodesGuides.com: Dead Space Unlockables

One of the unlockable elements in Dead Space is 10 free Power Nodes, but if you play the game smartly, a lack of Power Nodes should never be a problem. One trick is to always keep at least one Node on-hand. There are special rooms scattered throughout the game that can only be unlocked with a Node, but the treasure you'll find inside can you tons of credits, making it easy to purchase extra Nodes for upgrades.IGN: Dead Space Strategize