TL;DR
Why wouldn't we be able to power a rocket with normal nuclear fuel (not uranium fuel cell), or even maybe legendary coal ?Replace rocket part's Rocket Fuel requirement with a Special Burner Fuel requirement.
What?
Now that launching a rocket has been moved to the early-mid game, the rocket part's restriction of only using rocket fuel feels very un-Factorio-like.And with the addition of Quality, an extra possibility for balancing it presents itself :
make the rocket silo accept most fuels, albeit with minimum restrictions, but which wouldn't be (directly) dependent on item type.
(A bit like how a steam engine can only accept a maximum of 165°C steam, or how a heat exchanger needs a temperature of at least 500°C.)
These restrictions could be one of these, having a minimum value to be accepted by the silo :
- Area (on belt) : energy content of a single item
- Volume (in inventory) : energy content of a single stack of items
- Mass (in rocket) : energy content of the cargo that a single rocket can carry
- Vehicle acceleration
- Vehicle top speed
(or maybe it could even be a combination of several minimum requirements above ?)
(- If some fuels are still too problematic to balance for this, even if restricted to their higher quality versions : Item type)
Higher quality rocket parts, if/when vanilla or mods get these, could be even more restricted in the above.
One remaining question is how to power the silo itself, IMHO it should still be restricted to electricity instead, to separate these requirements, but I could see it going either way... (especially if it's hard to implement)
It might also be interesting if the vehicle speed and/or acceleration bonuses of the fuels (averaged over the course of the recipe ?) also had an effect (besides potentially clearing the minimum bar for viability), for instance :
- vehicle acceleration bonus would increase rocket's max cargo weight
- vehicle top speed would decrease time between launch and arrival
(This one would I guess speed up the animations of the rocket itself, including its cargo mini-rocket landing faster on the space platform ?)
(The silo animation would probably be left out of it, affected by speed modules in or near the silo instead.)
Then fuels would be rebalanced : some fuels to be better at acceleration, others at top speed, and their increases in quality would also be rebalanced to affect these values differently per fuel type.
See also :
Burner Fuel Bonus mod.
More rocket types
Why?
This would bring the rocket silo closer to how other vehicles (and burners) operate and would allow for more options in the mid-late game, while still retaining minimum requirements for balance, especially in early game.Somewhat related :
Allow higher quality rocket fuel for rocket silo recipe
Allow us to make rocket parts with quality components OR give as a method to lower quality of resources
And maybe :
Allow Boilers to be used in space with Rocket fuel
I guess this would also change the amount of fuel you use compared to blue circuits and low density structural, which might be a nice bonus for later-game players. Maybe the fuel could change the maximum payload? This seems like maybe rocket silos could have different rocket recipes with different trade-offs.