### *Mage hand* is intended to be able to perform simple manual tasks. 

From the spell description of [*mage hand*](https://www.dndbeyond.com/spells/mage-hand):

>You can use the hand to manipulate an object, open an unlocked door or container, stow or retrieve an item from an open container, or pour the contents out of a vial.

Some other examples of manipulating an object can be found [here](https://www.dndbeyond.com/sources/basic-rules/combat#InteractingwithObjectsAroundYou) in the basic rules. 

It is important note the *simplicity* of these actions. Actions requiring more dexterity are not intended to be doable with *mage hand* - this is evident in the [Arcane Trickster](https://www.dndbeyond.com/classes/rogue#ArcaneTrickster)'s ability Mage Hand Legerdemain:

>Starting at 3rd level, when you cast mage hand, you can make the spectral hand invisible, and you can perform the following *additional tasks* with it:
>
> * You can stow one object the hand is holding in a container worn or carried by another creature.
> * You can retrieve an object in a container worn or carried by another creature.
> * You can use thieves’ tools to pick locks and disarm traps at range.

By using the phrase "additional tasks", this ability description implies that the list given in the *mage hand* spell description is intended to be a more restrictive list. A *broad* reading of *mage hand* would seem to imply anyone could do these things anyway, yet the Arcane Trickster has an entire class feature dedicated to them. 

But what about operating [siege equipment](https://www.dndbeyond.com/sources/dmg/running-the-game#SiegeEquipment)? 

### It's up to the DM. 

Keeping in mind the intended limits of *mage hand*, it's going to be up to the DM to determine if we can fully operate the ballista with *mage hand*. *Load* and *Fire* seem to be, at least to this DM, simple enough manipulations that a *mage hand* could perform, assuming that the ammunition and reset force is less than 10 pounds and the firing mechanism is simple like a trigger or button - more complex machinery will likely fall afoul of the arguments made in the previous section. 

But, I would rule that aiming is beyond the limitations of *mage hand* for a few reasons. First, siege equipment is quite large, and often lacks fine manipulations for aiming, and where there are fine aiming instruments, they may require a dexterity that *mage hand* is not intended to offer.  I would rule that it takes more strength than a mage hand can muster to aim siege equipment. Further to this, there is also the matter of what aiming entails. It requires a field vision that *mage hand* doesn't afford. If you are in a position with field of view to meaningfully be able aim the siege equipment, you're probably not using *mage hand* anyway, you're moving it yourself. 

### Conclusion: You might be able to load and fire, but probably can't aim with *mage hand*.