What the Experiment Storage Unit Does

The Experiment Storage Unit (or ESU) is a container that holds completed science experiments so you can bring them back to Kerbal Space Center without transmitting them. Once you run an experiment with a science instrument—like a thermometer, barometer, or seismic sensor—the data sits inside that instrument and takes up space. The ESU lets you store that data in a separate module, freeing up the instrument to run again. This matters because some experiments can only run once per location, and storing the data lets you gather multiple readings before returning home.

Think of it as a cargo hold for invisible data. You fill it by transferring completed experiments from instruments into the unit, then fly the whole unit back to the Space Center. The game rewards you with science points when the data arrives home—more points than you would get from transmitting, but you have to complete the journey.

Key Takeaways

  • The Experiment Storage Unit stores completed experiment data from science instruments, letting you run the same instrument multiple times in one location.
  • You transfer data from an instrument to the ESU by right-clicking the instrument, selecting "Store Experiment", and choosing the ESU as the destination.
  • Each ESU has a storage capacity measured in "Mits"—the standard unit holds 750 Mits, and larger variants hold more.
  • You must physically return the ESU to the Space Center and recover it to receive the science points; transmitting data from the ESU does not work.
  • The ESU is most useful on long missions where you want to gather multiple readings from the same location before leaving.

Transferring Experiments Into the Storage Unit

To move experiment data from an instrument into the ESU, you need to be in the same vessel and have both modules intact. Right-click on the science instrument that holds the completed experiment—for example, a thermometer or barometer. A menu will appear with several options. Look for the button labeled "Store Experiment" (the exact wording may vary slightly depending on your game version).

When you click "Store Experiment", the game will show you a list of available storage units in your vessel. Select the Experiment Storage Unit you want to use. The data transfers when ready, and the instrument becomes empty and ready to run again if the location allows it. If the ESU is full, the transfer will fail and the game will tell you there is not enough storage space.

You can repeat this process as many times as you want, moving data from the same instrument into the ESU each time you run it. This is the main reason to use an ESU: it lets you gather five or six readings from one location instead of just one.

Understanding Storage Capacity and Unit Variants

Every Experiment Storage Unit has a storage limit measured in units called Mits. The standard ESU holds 750 Mits. Different experiments take up different amounts of space—a straightforward temperature reading might use 8 Mits, while a more complex experiment like a seismic reading uses 40 or 50 Mits. You can see how much space each experiment uses by looking at the experiment's description in the VAB or by checking the stored data in the ESU itself.

Kerbal Space Program includes larger variants of the ESU. The bigger versions hold 1500 Mits or even 3750 Mits, giving you room for many more experiments. Choose the size based on how long your mission will be and how many readings you plan to gather. A short trip to the Mun might need only the standard unit, but a long-term base on another planet should use a larger one.

You can also carry multiple ESUs in the same vessel if you need extra capacity. There is no penalty for doing so beyond the added weight and cost.

Returning Data to the Space Center

The ESU must physically return to Kerbal Space Center to deliver its data. You cannot transmit the contents of an ESU like you can with some other science modules—the game requires you to recover the vessel or dock it at the Space Center. This is by design: transmitting data gives you fewer science points than returning it, so the ESU rewards you for the extra effort of bringing it home.

When your vessel lands at the Space Center and you recover it, the game automatically processes all the data in the ESU and awards you the science points. The amount you receive depends on the experiment type and where you gathered it. Data from distant locations (like other planets) is worth more than data from Kerbin's surface.

If you dock your vessel at the Space Center's orbital station instead of landing, you can transfer the ESU to another vessel and send it down separately. This is useful if you want to keep your main ship in orbit while sending a small lander home with the data.

Common Mistakes and How to Avoid Them

The most frequent error is forgetting that the ESU must come home with you. New players sometimes gather data, store it in the ESU, and then leave the ESU behind on the Mun or in orbit. The data is lost because the unit never reaches the Space Center. Always plan your return journey with the ESU in mind, and make sure it has enough fuel or a way to get home.

Another mistake is overfilling the ESU. If you try to store an experiment and the unit is full, the transfer fails silently in some cases. Check the remaining capacity before each transfer, especially on long missions. You can see how much space is left by right-clicking the ESU and looking at the storage bar.

Some players also confuse the ESU with the Mobile Processing Lab, which is a different module that can process raw experiment data into science points while in space. The ESU only stores data; it does not process it. If you want to convert data to science before returning home, you need the lab instead.

When to Use the Experiment Storage Unit

The ESU is most valuable on missions where you plan to stay in one location for a while and run multiple experiments. A base on the Mun, a long-term orbital station, or a multi-day rover mission all benefit from having an ESU. You gather more data per trip, which means more science points per mission.

It is less useful for quick flyby missions where you only have time to run each experiment once. In those cases, transmitting the data directly from the instrument is faster and simpler, even though you get fewer science points.

The ESU also helps when you are exploring multiple biomes in one region. You can move the ESU from one location to another (by rover, aircraft, or ship) and keep filling it with data from different biomes. This is especially efficient on the Mun or Minmus, where you can drive between biomes and gather readings at each one.

Frequently Asked Questions

Can I transmit data from the Experiment Storage Unit?

No. The ESU can only deliver its data when the vessel is recovered at the Space Center. Transmitting from an ESU does nothing. If you need to send data home without returning the vessel, use the Mobile Processing Lab to convert the data to science points while in space, then transmit those points.

What happens if the ESU is destroyed before I return home?

All the data inside is lost. The game does not save experiment data separately from the vessel that holds it. Always protect your ESU during re-entry and landing, and make sure it is mounted securely so it does not detach during flight.

Can I use the ESU on Kerbin, or only on other worlds?

You can use it anywhere. However, Kerbin has many biomes and locations where you can run experiments, so the ESU is less critical there. It becomes much more valuable on the Mun, Minmus, and other planets where biomes are spread out and you want to gather multiple readings before leaving.

How much does the Experiment Storage Unit cost?

The standard ESU costs 1,600 Funds in the VAB. Larger variants cost more. The cost is worth it if you plan to gather science efficiently, but early in the game you might want to transmit data directly until you have more Funds available.

Can I transfer experiments between two Experiment Storage Units?

No. You can only move data from an instrument into an ESU, not from one ESU to another. If you need to consolidate data, you must use the Mobile Processing Lab, which can accept data from both instruments and other storage units.