Why didn't the Prometheus pick up the signal from LV-426 that the Nostromo investigated?

On the Prometheus Blue-Ray, the Peter Weyland Files say the Weyland knew of the signal and that David was the only one on board who knew of the signal emitting from the derelict's beacon. I would imagine they kept this a secret from the rest of the crew. However, this tid bit of info was not placed on the blue ray by Scott or the writers of Prometheus, therefore it is not to be considered canon.

Because Peter Weyland had already obtained the co-ordinates from the beacon/signal for the location of LV-426, using ECIU software, apparently stolen from his rivals Yutani Corp; before Shaw and Holloway ever explained their thesis to him charting the location of LV-223 from what they referred to as a "Star Map".  

    Weyland would then embbed a David-8 android with the Prometheus crew as per-standard protocol, ofwhich only this particular android and himself would ever know of the loction of LV-426. Weyland planned to head there next, IF he did not find what he was looking for on LV-223.

I thought LV-426's xenomorphs were supposed to have been created after Prometheus' time.

In certain extent I hope the mystery of Space Jockey will never be revealed on future sequels. The engineer concept is interesting but it somehow ruins the imagination. 

Wasn't the Prometheus like 20 or so years before the Nostromo events?

I think the timeline is too tight.  It will look funny when our descendants watch these movies in the year 2100 or so, just as we find 1960's sci fi movies set in the 21st century funny.

Even Blade Runner looks funny now.  We tend to overestimate scientific progress.

I hope they leave some mystery to the original movie. I hope they don't reveal (at some point) that the engineer in the chair (Alien 1979) is David or some other future character. It's nice to not know how that ship crash landed on LV-426. 

"Even Blade Runner looks funny now.  We tend to overestimate scientific progress.

Exactly. It's like going to Disney World to ride Space Mountain. I love hearing the robot voice say "In the year 2000, we'll all be living on Mars." Whoops!

There's a LOT of things that can totally bollix a radio signal. There's a gas giant with rings in that area, and it's magnetic field flux alone could stifle the signal for decades or centuries at a time until it fluctuates and a 'window' opens randomly. Orbital positions also factor in as well.

The beacon may also operate in a non-continuous mode to conserve power, say operates for five years, then shuts off for 5 years.

There might have been some pre-programming aboatd the ship's computer to 'not register it', thus the signal IS there but the computer says 'Nope, nothing to see here'.

The derelict was there a very very long time by the look of it and the space jockey, i think, but just a theory, it ties in with what went down with the engineers on LV-223 and their fates. 

I hope they leave some mystery to the original movie

Agree AcidBlood. Seeing David get into the Derilect pilot seat and having it end there would make things too "spoon fed" imo.

Thank you Ryan_C, I should have included a more clear timeline.

The events of Prometheus were around the end of the year 2093. 

The Engineer transmission was picked up by the Nostromo crew in 2122.

So, my point was they were looking for a signal from the Engineers on the way to LV-223 on the Prometheus but were unable to pick up the Engineer signal that caught the Nostromo A.I.'s attention on LV-426 in 2122. And this signal is supposed to be "thousands" of years old.

To summarize, the signal on LV-426 that Nostromo checked out looks like it began to transmit after the events of Prometheus or A.I. or corporate kept the information "compartmentalized". 

Weyland Industries had been looking at the system since 2039.

When viewing the Space Jockey, the Nostromo crew theorized that the Space Jockey (below) was thousands of years old and fossilized. 

Why hadn’t the colonists on LV-426 picked up the signal from the juggernaut in 2157?

“Although there are unsubstantiated reports that the beacon was deliberately turned off in 2135 (see Report REF#MARLOW58821). What could still be seen of the ship by 2157 was believed to be part of the Ilium Mountain Range, nearly 30KM from the terraformers’ compound."

Weyland-Yutani Report (page 83)

I'm sure this report above is in reference to Henry Marlow, the captain of the salvage vessel Anesidora around the year 2135.

This vessel discovered the juggernaut on LV-426 and Marlow said to his crew:

"I'll find the beacon and shut it off. Don't want anybody else finding this place."

(Source: Alien: Isolation)

Hi, Ingeniero, where have you been?

What does the WY report write about the position of LV-426 and LV-223? Are they in the same solar system (around the same planet known as Calpamos)?

The Nostromo crew theorized the derelict was thousands of years old, but they had no way of knowing its age and did not run any type of tests in the movie to determine its age.

It is a common error to assume that LV 223 and LV 426 are moons orbiting a planet (a gas giant named Calpamos) in the Zeta Reticuli star system.

According to Wikipedia, Zeta Reticuli is a binary star system/double star without planets. As of today, no planets orbiting the two stars of Zeta Reticuli have been discovered. Zeta Reticuli is close enough to earth to be visible with the naked eye from the southern hemisphere in very dark skies.

In "Prometheus" it is never explicitly stated or shown that Zeta Reticuli is the destination of the mission. During the briefing Holloway shows an unnamed star system that consists of a single sun orbited by several planets. This cannot be Zeta Reticuli.

The Prometheus didn't pick up the signal which the Nostromo received because LV 223 and LV 426 are not in the same star system. LV 426 is located "just short of Zeta 2 Reticuli" (according to Lambert in "Alien"). LV 223, the destination of the Prometheus mission, must be located somewhere else.

If LV 223 and LV 426 were close to one another, if they were moons orbiting the same planet then it would be strange that LV 426 is chosen for colonization in the middle of the 22nd century while LV 223 remains uncolonized. LV 426 has no atmosphere, hence the need for an atmosphere processing station ("Aliens"). LV 223 has an atmosphere and even primitive organic life ("Prometheus"). Furthermore, it would be stranger still that LV 426 is colonized while neighboring moons remain unexplored. We can safely assume that all planets, planetoids and moons of a given star system are carefully explored (with technical means or even by human expeditions) before one of them is chosen for colonization. If LV 223 were located in the vicinity of LV 426, it would be explored at the same time as LV 426, and the abandoned installation of the engineers and maybe even the remains of the Prometheus would probably be discovered. But at the time of "Aliens" (2179) mankind has no knowledge of engineers and xenomorphs. Ripley's report about both is met with incredulity during the hearing in "Aliens". When she mentions a "derelict spacecraft" nobody is astonished and bothers to ask questions. The members of the commission seem to think that Ripley is talking nonsense. This means that LV 223 and LV 426 are not close to one another and that after the disappearance of the Nostromo mankind has had no further encounters with engineers (living or dead) and xenomorphs, at least no encounters that became common knowledge. The colonists on LV 426 didn’t even discover the engineer spacecraft themselves although at the time of "Aliens" they had been living on the moon for over 20 years.

@Andrew 1976

Correct that it is never explicitly stated Prometheus that Zeta 2 Reticuli is destination of the Prometheus mission, but Ridley himself explicitly stated that was the location in a 2012 interview and in the "Origins" featurette. The official Weyland Industries Timeline on the Blu Ray, written by Damon Lindelof, also states "Weyland astronomers discover MULTIPLE moons and a ringed planet just outside the Zeta 2 Reticuli System, which are possibly able to support life. Weyland expects to travel there within the century." The expedition to go there was the Prometheus. It was also named as the system the Engineers gave directions to in Spaith's script. It's laso shown on one of the Blu Ray menus, and listed several times in the Wyland Yutani Report book.

When the director, writers, marketing campaign, and supplemental products are all saying that is where it is, then that is where it is.

It may seem to conflict with Aliens story line, but Aliens also seems to contradict Alien by making the company seem unaware that there is an alien ship on LV-426, when they actually knew all about it and sent the Nostromo there. Of course, those contradictions can be explained in several different ways, but there it is.

Also, minor point, but LV-426 does have an atmosphere. You can't have the severe wind we saw blowing in Alien without something to blow :)

It is fun watching people tying to piece together a universe / story that's so fragment not even the creator knows what's up :D .

But using what we do have... yes  supposedly Prometheus is before AC and AC before other films before alien.  So maybe its not crashed yet. And yes the outside looks fossilized of the jockeys suit but maybe not inside as such. That was one of the best bits for me the fossilized bit. It brought up thoughts of wow it's 100s of thousands of years old or been there for millions? And eggs still alive? Vast and the crazyness of what might be out there captured... possibly about to become stale and  small  :( ...

We have to remember that the system ZIIR was largely fictionalised for the movies. WHen it comes to fiction, all bets are off, except for what is considered canon within the films.

Thank you for noticing Ati. I was traveling with family and out of touch for a little while. I'm finishing up a few new topics and will post again soon.

Thank you everyone for your comments.