Planet Cybertron is in Grave Danger: Part 1

Thanks to the efforts of Optimus Prime, the Vector Sigma computer has been put in a stable condition again and works to help the Autobots. The episode starts off with Vector Sigma creating something new which could really assist the Autobots in defeating the Decepticons for good, but this is seen by Soundblaster and his cassettes who return to Charr.
 

Soundblaster tells Galvatron about how Vector Sigma has created something called "Cybertonuron", a new type of metal which is much stronger than Cybertronium (Cybertronium was the substance in the season 2 episode Desertion of the Dinobots) and that it could be used to make the Autobots much more powerful in terms of both defense and attack. Galvatron says that they must get a hold of it and then fantasises about using the new metal to make himself a large sword to slay Rodimus Prime and destroy Fortress' ship.
 

Soundblaster goes on to tell Galvatron about how this new metal can only be created by Vector Sigma itself and that if the Decepticons got a hold of it they could conquer the entire universe. Galvatron decides that they must invade Cybertron yet again and take the new metal for themselves and so tells Soundblaster they will take the metal by force. Meanwhile on Athenia Twincast reports to Rodimus about the metal as well.
 

Galvatron orders the Predacons to go to Cybertron and not be spotted by the Autobots. They leave and Galvatron has a brief chat with Zarak, who is concerned about Galvatron's plans. Zarak doesn't want to have to make any sacrifices for the Decepticons to get this new miracle metal, but Galvatron basically tells him to piss off and get ready to attack.
 

Galvatron takes Soundblaster, Zarak and the Decepticon Headmasters to Earth via Astrotrain to meet up with Sixshot. What they don't know is that their movements are being tracked by the Autobot cassettes, who report back to Twincast. Twincast sends a transmission to Rodimus and says how the Decepticons are on the move although he doesn't know what they're up to exactly. Chromedome and Hardhead volunteer to go out on a little spying of their own.
 

On Cybertron a couple of the newly introduced generic Autobot warriors find the Predacons and wonder what they are up to, but they are then spotted and shot at. One of them is hit and tells his friend to go and tell the others that they are under attack by the Decepticons.
 

Galvatron assembles all of his warriors together and gets ready to invade Cybertron. In another room, Sixshot explains to Zarak that they will be able to not only crush the Autobots but also take back Cybertron, as well as being able to get their hands on this new metal. Outside the base Chromedome and Hardhead show up but are surprised to see that there are no guards outside and wonder where the Decepticons are.
 

The reason the Decepticons aren't at their Earth base is because they've taken the space bridge and invaded Cybertron. Galvatron's assault force consists of himself, Soundblaster, Astrotrain, Weirdwolf, Mindwipe, Skullcruncher, Combaticons and the Stunticons, as well as the Predacons who are already there. Galvatron tells everyone to move out and the Decepticons start to tear the place apart.
 

The Autobot guard robots appear and do their best to counter attack but are slaughtered quickly by the Decepticons, so the remaining ones go and alert Rodimus Prime on Athenia.
 

Rodimus gets the message and tells Arcee to contact Ultra Magnus on Earth and get him to send over as many Autobots as he can spare. Rodimus prepares to depart for Cybertron but Fortress briefly stops him and strangely requests that Rodimus doesn't send over any troops as they shouldn't risk any more deaths. Thankfully Rodimus completely disagrees and says that they cannot let the Decepticons take over Cybertron. Meanwhile on Earth the Trainbots, Protectobots, Aerialbots, Chromedome and Hardhead all use the space bridge and head to Cybertron. Fortress decides to go to Cybertron as well and takes his battleship there along with Brainstorm and Highbrow.
 

All of the Autobots arrive on Cybertron and the tide turns on the battle since the Decepticons suddenly find that their enemies are actually putting up a fight. Rodimus finds Galvatron and the two fight each other, but Galvatron punches Rodimus into a wall and then...

...transforms into his cannon mode and blasts the wall. A load of debris falls down and hits Rodimus, knocking him down. Galvatron blasts the wall again causing more debris to drop and with Rodimus down Galvatron transforms back and prepares to finish him off, but Soundblaster appears demanding that Galvatron has to hear some important news he has, and that he can't say it here because there are Autobots present and he doesn't want them to hear it. Galvatron is angry but he agrees and the two walk off, giving Kup, Blurr and Arcee enough time to get Rodimus.

Soundblaster's important news is that Vector Sigma has finished research on Cybertonuron and that production could start at any moment. Galvatron says they will crush the Autobots and take the metal. Elsewhere Zarak has also found out about Cybertonuron's status but is worried that if Galvatron fails then the Autobots would be unbeatable and that all of the Decepticons will be destroyed, and so, he has a plan: destroy Vector Sigma and destroy Cybertron.

Zarak thinks how the destruction of Vector Sigma would mean that Cybertron itself would self destruct and be completely destroyed. He then uses his telepathic powers to contact Weirdwolf, Mindwipe and Skullcruncher and has them all meet up with him.

Zarak reveals his plan to the Decepticon Headmasters, and shows them three explosive devices. Zarak says that Mindwipe will take these bombs and plant them on Vector Sigma whilst Weirdwolf and Skullcruncher cover him. Once the bombs are set they cannot be stopped from exploding, although Zarak assures them that they and all the other Decepticons will have enough time to escape. The episode ends with the narrator asking it this scheme will succeed and what the fate of the Autobots will be.

Why didn't Galvatron and the others take the space bridge to Earth instead of taking the slower route of using Astrotrain to get there?

And why on Earth did Fortress suggest to Rodimus that they shouldn't counter attack the Decepticons? In other words, he basically wanted the Decepticons to reclaim Cybertron. Although the bigger question is that you'd think that Rodimus would stay on Cybertron, not Athenia.