Spacesuits must support the biological functioning of the astronaut. There are probably damned fine psychological reasons to not show astronauts their own biometric data while on stressful extravehicular missions, but there is the issue of comfort. Even if temperature, pressure, humidity, and oxygen levels are kept within safe ranges by automatic features of the suit, there is still a need for comfort and control inside of that range. If the suit is to be warn a long time, there must be some accommodation for food, water, urination, and defecation. Additionally, the medical and psychological status of the wearer should be monitored to warn of stress states and emergencies.
Unfortunately, the survey doesn’t reveal any interfaces being used to control temperature, pressure, or oxygen levels. There are some for low oxygen level warnings and testing conditions outside the suit, but these are more outputs than interfaces where interactions take place.
There are also no nods to toilet necessities, though in fairness Hollywood eschews this topic a lot.
The one example of sustenance seen in the survey appears in Sunshine, we see Captain Kaneda take a sip from his drinking tube while performing a dangerous repair of the solar shields. This is the only food or drink seen in the survey, and it is a simple mechanical interface, held in place by material strength in such a way that he needs only to tilt his head to take a drink.
Similarly, in Sunshine, when Capa and Kaneda perform EVA to repair broken solar shields, Cassie tells Capa to relax because he is using up too much oxygen. We see a brief view of her bank of screens that include his biometrics.
Remote monitoring of people in spacesuits is common enough to be a trope, but has been discussed already in the Medical chapter in Make It So, for more on biometrics in sci-fi.
There are some non-interface biological signals for observers. In the movie Alien, as the landing party investigates the xenomorph eggs, we can see that the suit outgases something like steam—slower than exhalations, but regular. Though not presented as such, the suit certainly confirms for any onlooker that the wearer is breathing and the suit functioning.
Given that sci-fi technology glows, it is no surprise to see that lots and lots of spacesuits have glowing bits on the exterior. Though nothing yet in the survey tells us what these lights might be for, it stands to reason that one purpose might be as a simple and immediate line-of-sight status indicator. When things are glowing steadily, it means the life support functions are working smoothly. A blinking red alert on the surface of a spacesuit could draw attention to the individual with the problem, and make finding them easier.
One nifty thing that sci-fi can do (but we can’t yet in the real world) is deploy biology-protecting tech at the touch of a button. We see this in the Marvel Cinematic Universe with Starlord’s helmet.
If such tech was available, you’d imagine that it would have some smart sensors to know when it must automatically deploy (sudden loss of oxygen or dangerous impurities in the air), but we don’t see it. But given this speculative tech, one can imagine it working for a whole spacesuit and not just a helmet. It might speed up scenes like this.
What do we see in the real world?
Are there real-world controls that sci-fi is missing? Let’s turn to NASA’s space suits to compare.
The Primary Life-Support System (PLSS) is the complex spacesuit subsystem that provides the life support to the astronaut, and biomedical telemetry back to control. Its main components are the closed-loop oxygen-ventilation system for cycling and recycling oxygen, the moisture (sweat and breath) removal system, and the feedwater system for cooling.
The only “biology” controls that the spacewalker has for these systems are a few on the Display and Control Module (DCM) on the front of the suit. They are the cooling control valve, the oxygen actuator slider, and the fan switch. Only the first is explicitly to control comfort. Other systems, such as pressure, are designed to maintain ideal conditions automatically. Other controls are used for contingency systems for when the automatic systems fail.
The suit is insulated thoroughly enough that the astronaut’s own body heats the interior, even in complete shade. Because the astronaut’s body constantly adds heat, the suit must be cooled. To do this, the suit cycles water through a Liquid Cooling and Ventilation Garment, which has a fine network of tubes held closely to the astronaut’s skin. Water flows through these tubes and past a sublimator that cools the water with exposure to space. The astronaut can increase or decrease the speed of this flow and thereby the amount to which his body is cooled, by the cooling control valve, a recessed radial valve with fixed positions between 0 (the hottest) and 10 (the coolest), located on the front of the Display Control Module.
The spacewalker does not have EVA access to her biometric data. Sensors measure oxygen consumption and electrocardiograph data and broadcast it to the Mission Control surgeon, who monitors it on her behalf. So whatever the reason is, if it’s good enough for NASA, it’s good enough for the movies.
Back to sci-fi
So, we do see temperature and pressure controls on suits in the real world, which underscores their absence in sci-fi. But, if there hasn’t been any narrative or plot reason for such things to appear in a story, we should not expect them.