In the year 2050, dark energy is destabilizing the sun, threatening all life on Earth. Scientists conclude that an experimental stellar bomb payload, with a mass equivalent to Manhattan Island, will flush out the infection and restabilize the sun. An experimental spacecraft, Icarus I, is designed to transport the stellar bomb payload to the sun. Unfortunately, the mission fails. Seven years later, a second attempt is made with the Icarus II.
The crew consists of (left to right):
Harvey - the first officer and communication specialist; Dr. Robert Capa - the physicist overseeing the payload's deployment and detonation; Corazón - the botanist who maintains the oxygen garden; Cassie - the pilot who serves as the crew's emotional tether; Dr. Searle - the ship's counselor and medical officer; Trey - the tech savvy navigator; Mace - the engineer who lends a military perspective to the mission; and Captain Kaneda (not shown) - the focused, determined mission leader.
It takes 16 months for them to get close to the sun, as mentioned in the introduction voice over by Capa. As the ship nears the sun, solar noise known as "the [communications] dead zone" begins to interfere with radio communications to Earth. As the ship encountered the "Dead Zone" seven days earlier than expected, the crew is now left with just 24 hours to collect all of their individual thoughts and send each of them off to their loved ones in a last message "packet".
Capa has difficulty in finding his words, and makes several different attempts at his message, accidentally "running out the clock" on Mace. A fight breaks out between Capa and Mace, which lingers as open animosity between the two, despite Mace's apology. Searle has Mace spend a couple of hours in the "Earth" room, which simulates sensual experiences on Earth. Afterward, Mace apologizes to Capa and they become civil toward each other.
The ship has an oxygen garden, tended to by Corazón, to provide both food and carbon to atmosphere recycling during the trip. It is noted that while the ship is only about two-thirds of the way to its destination [the sun], the garden has been producing oxygen at better than expected rates - the ship already has enough oxygen stored up for the delivery, and a quarter of the return trip.
Searle has become fascinated at looking out from the ship's viewport at the approaching sun and is curious what it would be like to experience the unfiltered view. The Icarus' computer (the voice of Chipo Chung) warns him that he can only tolerate 3.1% of the actual light, and Searle has Icarus set the system for 30 seconds of viewing at this 3.1% rate.
The result has some kind of effect on Searle, who begins to spend many hours in the viewing room, repeating his exposures to the sun so often that his skin eventually peels away and sores cover his face. Captain Kaneda has been researching the video logs of Captain Pinbacker, the commander of Icarus I, in an attempt to discover what went wrong, and thereby prevent his crew from making the same errors.
He plays one where Pinbacker describes a small meteor storm that did superficial damage, and is perplexed by Pinbacker's aloof reaction to the event. As the ship approaches Mercury, Harvey picks up a signal from the Icarus I's distress beacon, only hearing the faint signal because it was amplified by the iron in Mercury's mass.
Emphasizing that some of those aboard Icarus I could still be alive, Captain Kaneda explains this point to the crew, and begins a discussion as to whether the current mission should be altered in order to check on the Icarus I's distress beacon. Mace is not happy with the choice to divert from their flight path because their mission has the utmost priority.
Dr. Searle says that he agrees with Mace's assessment, but adds that diverting to the Icarus I could possibly add a second payload [bomb]. He argues that since the Icarus bombs have never existed before and therefore have never been actually detonated either, their existence is "entirely theoretical" and having two could be advantageous if something went wrong with the first one.
There is further heated discussion, which Captain Kaneda finally stops by saying he is handing the decision to the ships most informed person in these matters, their nuclear physicist, Capa. Capa is troubled by being asked to make this decision. He explains to the captain that he simply doesn't have enough information to make an informed and rational decision, and the best he can do is to "flip a coin".
When Kaneda asks "So? heads or tails", Capa replies "Heads: two last best chances are better than one." Capa's decision is finalized by the captain: both Icarus crafts will rendezvous together. Trey plots the course, checks it three separate times, and is satisfied he has been accurate. Trey shifts the Icarus II's course to intercept the Icarus I.
In the many calculations, Trey misses one - the need to readjust the heat shield that protects the ship from the sun's radiation. This error is discovered when there is an emergency declared by the computer after slight damage to the heat shield results from Trey's mistake. The true extent of the damage can only be assessed, and then repaired, by leaving the ship and working directly in space.
Captain Kaneda asks for a volunteer to accompany him and, after refusing to allow the second in command to join him, Capa is volunteered by Mace - this is Mace's way of stating that the current events are a direct result of Capa's decision to alter the original mission, and the "volunteering is clearly made in anger and not by deciding if Capa was the best man for the job."