CT How did Vader know that Princess Leia would travel to Tatooine?

With Rogue One showing in theaters December this year we might get an answer, but as it still stands that the opening scene in ANH begs for Explanation, IMHO.

Princess Leia has received the plans of the Death Star, but it's obvious that she neither takes these straight to Alderaan but makes a stop to pick up General Kenobi on Tatooine.

Apparently and after she received the plans, she was instructed to bring him along:

I regret that I
am unable to present my father's
request to you in person, but my
ship has fallen under attack and I'm
afraid my mission to bring you to
Alderaan has failed. I have placed
information vital to the survival of
the Rebellion into the memory systems
of this R2 unit. My father will know
how to retrieve it. You must see
this droid safely delivered to him
on Alderaan.

According to the radio drama, there was a considerable amount of wondering, how Vader's Devastator Star Destroyer could possibly knew where she'd be heading. I believe we are looking at various explanations:

1. Vader had intercepted her mission update and thus knew where she was heading next (unlikely considering that the message to Leia was probably encrypted to prevent this from happening)
2. The Devastator had correctly calculated their hyperspace jump trajectory and concluded that Tatooine was the destination
3. The hyperdrive of the Tantive IV had been damaged and Vader followed them, but stayed out of their tracking instruments' range
4. It happened to be the anniversary of Shmi Skywalker's death and Vader coincidentally happened to be in orbit to remember his mother when Leia's ship showed up

 

Presumably somewhere between 3 and 4. They found out somehow (the Force moves in mysterious ways I guess) that Leia had the plans and were chasing her and followed her all the way to Tattooine instead of intercepting her there is my best guess.

 

The simplest answer is the best: the Devastator followed the Tantive IV from Toprawa to Tatooine.

 

Perhaps we will find out in Rogue One. I believe that it is 2. of your list. Plus, Vader said that transmissions from Rebel spies had been sent to Leia's ship. That was a large clue, of course. I imagine that Vader personally destroyed the spies and his men were able to track the destination of the plans from the spies' computer. He then promptly left to retrieve them.

 

I see, you are suggesting that the spies' transmitter was aimed at the Tatooine system and thus Vader knew what to look for. He arrived, found the Tantive IV to be the only ship presently in orbit and therefore concluded that must have been the recipient of the messages? (Hadn't thought of this one, yet)

 

2& 3 make the most sense. I never really thought about it that much though. Vader does have the force on his side so he can make pretty good judgments

 

If I remember correctly, in the ANH radio drama Capt. Antilles figures they had an Imperial spy on board with a transmitter/homer, allowing Devastator to track them.

 

Eventually, the EU identified that spy as being a movie character - the other 3PO unit seen aboard the ship in the opening scenes of ANH:

http://starwars.wikia.com/wiki/U-3PO

 

I'm going to go with it being an inside job - Leia was clearly betrayed by one of her Ambassador Guards. This guy on the right looks far too happy to see the Stormtroopers arriving:

 

Mm. I recall from the radio series, that the Devastator tried to initiate a traffic stop over Toprawu, and mention of a tracking device.

At the time, I just assumed Vader had used the Force to divine their heading.

 

I'm not sure if Vader used the Force for finding the plans (or where he'd left his TIE fighter keys that morning for that matter). Seems just as likely he was merely following leads given to him by Imperial Counter Intelligence forces as he chased down Leia's ship. And the Force simply helped him after the fact.

If he had a rebel by the throat I can certainly see him easily peering into their mind to determine if he was on the right track. But he didn't seem to know the plans weren't on the ship even when he was on that very ship. He quickly deduced they were on Tattooine after being told a pod with no lifeforms had been jettisoned. Seems to me if he was using the Force he wouldn't have bothered telling his troopers to tear the ship apart looking for the plans. He'd have just sent them straight down to Tattooine. So I always assumed the Force was more about sensing disturbances, readings signs with heightened intuition, and detecting the presence of other users such as Luke across space during the Battle of Yavin.

Makes me think of how they found the rebel base on Hoth. The Force gave Vader no clue where the base was. But after the planet was suggested to him via droid intelligence, he knew they were there.

 

I honestly think it's going to be like the Heroic Dying Person in Rogue One transmits the plans to Princess Leia with their dying breath, Vader is on their tail, end up above Tatooine.

 

I'm placing a bet right now that the last scene of Rogue One will end mere seconds before A New Hope begins.

 

I hope it ends with the successful heist crew enjoying some well earned rnr on Aldreaan!

 

We can bet there was some sort of secret facility where the plans for the Death Star were being held. Someone betrayed by the Empire knew of the Rebellion and secretly made contact to some of their informants about the nature of the weapon. This traitor caught the detection of higher ups, all the way to the Emperor because of what he knew. The Emperor had Vader begin to investigate this matter personally because the Death Star could be vulnerable. Vader eventually tracks down one the spies or informants working for the Rebellion. For all we know they will be hunting the crew of the Ghost and catch up with them aboard his Star Destroyer. Just before these informants are destroyed, the transmission is made in desperation to Princess Leia above the Tantive IV through an encrypted signal. It is made to her because of urgency of the nature of its contents and also that the station will soon be ready to operate. The Empire is able to break through the signal and intercept the transmissions. They track the signal of the ship and begin pursuit. Leia knows that the Empire is aware of her location and decides she must use the closest contact she has, which is General Obi-Wan Kenobi. She heads to Tatooine to find him, but is intercepted in the attempt just above orbit.

 

Nah. My second bet is that most of the good guys will end up dead by the time this movie is over.

 

Well that is the key.

How does Leia get the plans?

They make a point of no transmissions in ANH so that they received a transmission (which may be how they traced it to the Tatooine system) then saw the Tantive IV which they knew to be her's is why they attacked.

They were surprised the Imperials showed up otherwise they wouldn't have bothered going to Tatooine to get Obi-Wan but go straight to either Alderaan or the Rebel base.

 

Qui-Riv-Brid

I think it's a bit more "complicated".

Leia said in Artoo's holo message that it was (or became) her mission to go to Tatooine and pick up General Kenobi.

That somewhat doesn't make sense in the context of the later (extended) Kenobi-Luke Scene in ROJ, according to which Leia was supposed to contact him in times of trouble.

Because going to Tatooine to pick General Kenobi up caused the real trouble.

 

If ISDs are faster than corvettes in hyperspace, Vader could have "calculated their destination along the last known trajectory" (after they passed through a restricted system, received transmissions, and jumped to hyperspace) - outran them there, and waited for them to show up.

 

But would the presence of Vader's Devastator not have alerted Captain Antilles and crew, that would then have made a turn around and go for open space?

It rather looked to me that the Tantive IV was preparing to land on Tatooine, then got ambushed by the Devastator but was crippled before it could escape.

 

Depends how close the Devastator is when they drop out of hyperspace, and what speed differential if any, there is.

 

hahah, pan up from the Blockade Runner arriving at Tatoonie and you see the crawl to ANH above in floating in space.

 

In the other message board a poster suggested that Rogue One could actually end with the (previously) deleted scene of Luke working on the vaporator with his Treadwell, taking his macrobinoculars and looking into the Tatooine sky and then taking off - towards ANH (starting at 0:30):



The actual scene might require some editing, but I'd say this would be perfect and a great opportunity to restore the original ANH film negatives.

 

The most likely explanation is the EU one where they had a spy droid on board, got the position of the ship and then waited until they were above Tatooine then came out of hyperspace to surprise them.

 

As others have said, I think Rogue One will address this. Vader either had a spy on board or was in pursuit