Protoss power unit
Five power cells were located around Khor-shakal to power the dormant arkship Spear of Adun for the day when it would be needed. In 2506, Hierarch Artanis, phase-smith Karax and a group of freed Khalai protoss came to Khor-shakal to activate the cells. They destroyed the zerg infestation restricting the cells and evacuated the planet within the Spear of Adun.
The power cells are invincible structures that are covered by zerg constriction. Destroying the zerg constriction activates the cells. All five must be freed to win the mission. They also generates Psionic matrix around them, allowing units to warped in and buildings to be build around them.