Users of "MARS - the arrival" often experience a lack of modules at some time in the settlement process. As a result they run into the problem that maintaining or even repairing buildings is not possible any more because the supply of a certain type of module has run dry.
To a certain degree this is by design since the intention of the app is a simulation of the harsh environment real settlers would encounter when starting to claim the Red Planet. So coping with the lack of everything and still surviving somehow is part of the mission.
There are many ways to minimize consumption of modules:
Don't necessarily construct new buildings until you are out of modules. Construct only those buildings you think are needed right now. Start constructions only if you have enough modules left for maintenance and the occasional repair in the coming days/weeks.
Prioritize maintenance as #1. As soon as the maintenance button appears next to a building, consider starting this action. When several different building actions (maintenances, repairs, enhancements, constructions) are possible, performing maintenances is normally the best choice.
Keep conditions over 80%. If the condition of a building falls below that threshold, there is a daily chance for a break-down. The further below 80% the higher the chance. Break-downs make module-costly repairs necessary.
Deactivate unused buildings. There is no wear & tear on buildings that are not active. This reduces the modules needed for maintenance. But try to keep the balance and make sure you produce enough of the essential resources energy, oxygen, water and food!
But there are also several ways to increase the inflow of modules:
Prioritize explorations. From "Expansion Phase" on you can R&D the needed techs for sending exploration teams on their way. The soil samples those teams will find can be sent back to MAA on Earth. As a reward modules (and sometimes settlers) are added to your shipment currently in preparation. You can see them in the "Bonus part (MAA)" of the shipment. This is very effective in terms of module supply for your settlement. Downside is, that turn-around times are quite long.
Dismantle buildings. When the lack of modules is severe you should consider dismantling buildings that are not critical for your settlement. Dismantling returns 50% of the originally spent modules for construction back into your cargo hold and can be used for e.g. maintaining or repairing other buildings that are more critical.
Watch reward videos. Beginning in "Resource Gathering Phase" from time to time watching a video is offered. This adds modules (and sometimes settlers) to your shipment currently in preparation. Those rewards can be seen in the "Bonus part (sponsors)" of a shipment.
Close a logistics contract. Normally only one specific module type is really low on supply. Check your shipment in preparation and see if it contains enough modules of the lacking type. If not hit the "Influence shipment content" button. This randomly reassembles the entire shipment. You can repeat this until you are satisfied with the amount of the lacking module type. Influence shipment content is only available if a logistics contract (In-App-Purchase) has been closed before .
Close a sponsors contract. Watching reward videos takes time. Closing a sponsors contract (In-App-Purchase) automatically pumps up the "Bonus part (sponsors)" of the shipment in preparation to the full daily maximum for the next 36 days (real-time). This has the same effect as watching every reward video offered within a real day.
And should there still occur module shortages that brings down health and happiness of your settlement, don't get discouraged. Even if some settlers leave or even die, the stress on the remaining/surviving settlers is reduced and the downfall of your settlement will come to a halt eventually.
We hope this helps you in building a big and flourishing settlement on Mars!