Factual error: The whole conspiracy is doomed from the start! They show a Lunar Module on the set representing Mars; the astronauts were supposed to use this to 'land' on the Martian surface. This is insane. The Lunar Excursion Module cannot operate in an atmosphere; it would burn up on entry. It has no heat shield - the engine nozzle and landing legs would have to poke through it if it had. Exterior protrusions like antennae and steering engines would burn off during descent through the Martian atmosphere. While Mars' atmosphere is thin, it is still more than sufficient to burn up a Lander designed this way. All three recent Mars Landers, Spirit, Opportunity, and Phoenix, had heat shields and parachutes to facilitate safe re-entry. This is not a radical redesign of the LEM; it simply cannot be the shape it is if it is to work in an atmosphere. Any schoolkid would know that, and the world's media would not be fooled for a second.
Factual error: If one person (at NASA) was able to calculate the distance between the returning Mars capsule and Earth based on their radio signals, then everyone with basic radio receiving equipment would be able to. The Russians routinely track American spacecraft and publish details of their trajectory in Pravda, and amateur astronomers throughout the world do so, too. This all comes from triangulation of their radio signals. There is no way that NASA could hide this simple fact from their worldwide audience.
Factual error: In the beginning of the movie, a Saturn V is seen representing the launch vehicle that will take Capricorn One to Mars. This is downright ridiculous. A Saturn V's third stage (that would insert into orbit and make the injection burn) does not have nearly enough Delta-V to make a Trans-Martian Injection from low Earth orbit.
Factual error: When Caulfield is looking at the address on the woman's magazine (when he's at Elliot's apartment) the Houston zip code is listed as 80144. Houston zip codes start with "77."
Factual error: A round-trip voyage between Mars and Earth would take about two years. Although the movie's timeline is compressed, from when the astronauts supposedly leave Earth to them supposedly returning (and dying) and then Caulfield rescuing Brubaker, the entire plot implausibly takes place in only eight months. It is mentioned at the memorial that they "left" Earth eight months earlier. The military memorial is held at least a month after the "tragedy" so that would mean they made the trip in seven months, which is impossible. The film is not set in the future when technology would be more advanced.
Suggested correction: You're assuming they travelled from Earth to Mars in the lander alone. The astronauts didn't do this when they went to the moon. The Lunar Lander was attached to the command module during the 3-day journey. When the astronauts reached the moon, they detached the lander from the command module and landed on the surface. It is reasonable to believe the astronauts for Capricorn One did the same thing, except on a much bigger ship for a journey that lasted over a year. We just never saw it.
Mike Lynch
The posting did not refer to the Lunar Lander, it referred to the tiny Lunar Command Module, the only part of the Saturn V that returned to Earth. From 44:00 to 48:08 of the film we see a live broadcast, supposedly from Martian orbit, showing all three astronauts crammed into a Lunar Command Module. The posting is absolutely correct.
This is another Deus ex Machina explanation for a blatant film mistake. The astronauts launched into orbit in a standard Saturn V rocket which could not possibly carry anything like a spacecraft large enough to make the trip to Mars. There is nothing in the film to suggest that there was a "much bigger ship" involved.
They are also shown seated in the tiny Apollo command module, supposedly transmitting messages from orbit around Mars. The posting is absolutely correct.
You're assuming the astronauts were launched in a standard Saturn V rocket, but with all the resources needed for a journey to Mars that took 18 months round trip, NASA would have to send them on a larger rocket to accommodate the required oxygen, water, food, spare parts, supplies, etc. needed to bring them back safely.
Mike Lynch
Did you watch the film? From 1:54 to 2:25 we see an establishing shot of a perfectly ordinary Saturn V rocket on the launch pad. From 6:05 to 6:43 we see all three astronauts strapped into the tiny, Lunar Command Module. As has already been pointed out from 44:00 to 48:08 we see a live broadcast, supposedly from Martian orbit, showing all three astronauts crammed into a Lunar Command Module. There is absolutely no mention of a larger spacecraft and none is ever shown.