Played: 2688837 times since May 1, 2008.

PlanetDefender was inspired by the popular "Tower Defense" flash games like Elements TD, Desktop Defense or Vector Defense. The objective is to survive the onslaught of alien invaders by building a variety of weapons, defenses and other structures. Initially you can only build Ion Cannons (for attack) and Bunkers for protecting your population, but further structures become available with research.

See here for help and tips.
See here for release notes.


The game is played by building structures. To build a structure, click on the desired structure from the available structures on the right side of the screen. A grid of available slots will appear over the planet. If you have sufficient funds, you will be able to purchase the structure by clicking on any open slot. New structures become available when prerequisite technologies have been researched. Begin researching technologies by clicking on the Research tab above the structure list.


Ion Cannon

Ion Cannons

Ion Cannons are your basic attack weapon and should be built right away to destroy incoming ships. It takes them a few shots to take down even the weakest enemy ships, but they fire quickly and upgraded versions can fire faster, more accurately and for greater damage.


Fortified Bunkers

When alien attackers rain down plasma bursts from above, your population will be safer deep underground. Every alien attack reduces your population, these fortifications decrease how many people you lose. Watch where the enemy is attacking and build bunkers next to those locations. The effect is cummulative so multiple bunkers next to the same location provide even greater population defense. Upgraded bunkers decrease population loss from alien attack even further.

Economic Center

Economic Centers

Available only after researching Advanced Economics, Economic Centers provide increased revenue based on your population. While it takes some time for them to pay for the cost of their initial construction, after that point it's all profit.

Repair Base

Repair Bases

Repair Bases dispatch robotic engineering teams to nearby structures, greatly increasing the rate at which they recover from damage. A structure protected by multiple upgraded repair bases can withstand all but the most concerted alien attack.

Missile Complex

Missile Complexes

Missiles are the ultimate weapon against alien capital ships. While they fire much more slowly than Ion Cannons, their fusion warheads pack a wallop. Basic missiles suffer from the disadvantage that if their target is destroyed while they are enroute, they're wasted. Level 2 missiles and above can not only fire faster and for more damage, they can retask to a new target if their current target is destroyed.


Anti-Missile Defense

Some Alien ships are nuclear capable as well. Anti-missile defenses use a highly accurate beam weapon to destroy incoming warheads. Upgraded versions can fire faster, allowing for the defense against multiple inbound weapons.



Advanced Economics

This technology increases your global revenue rate, so get it early if you want to be able to produce lots of structures. It also allows for the construction of Economic Centers, which bring in even more money.



All structures slowly repair damage over time, but with Robotics, they repair twice as fast. Not only that, but they allow the construction of Repair Bases (see above).


Nuclear Fusion

This technology provides no advantages on its own, but allows the construction of Missile Complexes, a critical weapon against the larger alien ships.

Adv. Energy

Advanced Energy

Advanced Energy enables the construction of anti-missile defense weapons.

Planet Shields

With this technology, your planet's Van Allen belts are charged to deflect the majority of incoming energy attacks. No corresponding structure is required, when the research is completed, shields are raised.


  1. Your population is the key to victory. Your revenue is determined by the size of your population. To protect your population, make sure areas under attack are protected by fortified bunkers. Late in the game, you'll want every location protected by at least one upgraded bunker.
  2. The alien attackers are fairly intelligent-- they will attack structures based on strategic importance, as well as how defended it is-- both the structure itself (by Repair Bases) and the population (by Bunkers).
  3. Economic Centers will allow you to generate the revenue you need, but since it takes time for them to pay for their initial investment, build them early on.
  4. Bunkers and Repair Bases have a strong effect on adjacent (green) squares and a weak effect on diagonal (blue) squares. A structure that's diagonal from two fortified bunkers will have the population defense bonus as if it were directly adjacent to one.

Release Notes