Factual error: After Watney patches the blow out of one of the HAB's airlocks with plastic sheeting, tie down straps, and duct tape, he pressurizes the HAB and the plastic sheeting pushes out like an inflated balloon. Assuming the plastic and duct tape would hold this is correct, however the plastic would be much more taut given the pressure difference inside and outside. The real mistake is later in the scene during a sand storm the plastic flops in and out. The plastic would remain tautly inflated, since the inside pressure is much greater than outside, and since the HAB is airtight the storm would have no equalizing effect to cause the plastic to be sucked inward.
Factual error: Lewis replaces Beck on the EVA to rescue Watney. On a NASA mission, each crewman is a specialist in several areas. While all of the crew have trained on EVA, Beck is the specialist for Ares III meaning he practiced EVA protocol and maneuvers 2-3 times as much as any other crew member. So while it is a nice dramatic moment for Lewis to replace him, a real mission commander would trust the best trained personnel to do their jobs, as she is actually lowering the chances of success by replacing Beck.
Add timeGrumpy Scot
Factual error: When the crew is walking around the area of the Hermes with artificial gravity created by spinning the ship, the angle of the crew members' bodies should be perpendicular to the curved floor of the ship. However, in multiple shots, the crew standing at different locations of the room are seen standing at the same angle, directly upright.
Factual error: When Commander Lewis in the tethered MMU jet-pack-chair is catching Mark Watney flying Iron-Man style via air jets from the hole in his glove, Mark misses Lewis' hand and grabs the tether, with some angular velocity relative to Lewis. As Lewis pulls the tether hand-over-hand to bring Mark closer, the angular momentum should spin them faster and faster like ice skaters pulling their arms in or Argentinian bolas (weighted balls connected by a cord) winding faster and faster around a target. Only when solid contact is made would Lewis' MMU be able to counteract the spin. The expected rotational speed-up effect is not seen.
Factual error: In the scene near the end where Mark is blasting off from Mars and before second stage engine cut-off, loose bolts are floating around the MAV cabin as if in zero G. With the engines still firing the acceleration would be pinning them to the deck. Even after SECO, it would take some time for the bolts (and probably a lot of Mars dust too) to jostle away from the floor and distribute evenly and randomly through the volume of the cabin.
Factual error: Prior to and during the orbital rendezvous rescue scene, the dialog states that a) the capsule with Watney is on a parabolic trajectory and will drop back to Mars b) the Hermes is on a swing-by trajectory that will carry it past mars c) the Hermes doesn't have the fuel to spare to do more than swing-by, i.e. They can't brake enough to even enter an orbit (yes, when one is on a fly-by, one has to brake to get into an orbit. Watney would be way slower still) d) the relative speed of the spaceships at the time of rendezvous is less than 20 m/s e) the spaceships are at a distance of less than 200m. All those statements can't be true at the same time. What orbit you are on is pretty much defined by your altitude and speed. If the speed and altitude of two spacecraft are the same, they are on the same (general shape of) orbit. Conversely, if they are on the same altitude but one is on a suborbital trajectory and one doing a swing-by, the latter is faster than the former by hundreds, if not thousands of m/s. By comparison, the rendezvous depicted in that scene would be like granny with her walker trying to "rendezvous" with an Amtrak train at full speed.The dialog states explicitly that the Hermes can't brake into orbit of Mars to pick up Watney because it doesn't have the necessary reaction mass to do that and get home too. If they can't even brake into orbit, they can brake to match Watney's speed even less. Even without that dialog, it wouldn't make sense either way. The acceleration required to do that would be measured in thousands of m/s. Translated into fuel, that would be dozens, if not hundreds of tons. No spacecraft this side of complete science fiction carries that much spare fuel, for the simple reason that lofting the extra weight to orbit would be prohibitively expensive.
Factual error: Towards the end of the film Watney is told to discard the heavy nose cone of the Martian Ascent Vehicle and replace it with a flimsy plastic sheet because the atmosphere is so thin that it will not be damaged despite the vehicle being accelerated to Martian escape velocity - nearly 14,000 kmh. But the storm caused massive damage earlier. It cannot work both ways - if the atmosphere is so thin that it won't dislodge a jury rigged plastic canopy from an accelerating spacecraft, it cannot possibly whip up a storm like the one we see.
Factual error: When Teddy is announcing Mark Watney's "death," the American flag is on the wrong side of the podium. This would be quite a goof for a government agency, especially one as image-conscious as NASA. Even in subsequent press conference scenes, the American flag is consistently to the left of the speaker, when it should be to the right.