This guide mostly applies to farming Protea parts from the Granum Void but you may also find it useful for quickly cycling through Tenet Weapons to Valence Fusion, or spawning a Sister with a Radiation Progenitor.

To farm Protea, you need to reach rotation C in each tier of the Granum Void (Neuroptics in T1, Systems in T2, Chassis in T3). The easiest way to do this is with an Octavia modded mostly for Range and Duration and some Strength.

When you spawn into the Void, you want to find an edge of the map with few obstructions on the ground (Mallet requires Line of Sight) and throw Octavia's Mallet and Amp between you and the rest of the map.
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By being on the edge of the map you've restricted the spawning area of the Void Specters, and they should all be forced to spawn within Mallet's range.

My preferred mission for farming the Void would be Capture. From testing, the capture target can not escape on the Corpus Crewship Tileset (or the tile required for that fail-state just never spawned). Do not Capture the target until after after you've completed the Granum Void side mission as enemy spawning is disables shortly after completing the main objective and may cause issues if you're waiting for the Treasurer to spawn to drop a new Granum Crown. Once you're finished in the void it is safe to complete the mission's main objective, wait around until the Treasurer spawns to replace the Crown you spent to enter the Void.

Farming Tier 1:

(Neuroptics)
For this part, I would farm the Capture mission on Phobos>Skyresh. A "Granum Crown" (Tier 1) is required for drop table containing the Neuroptics. The Treasurer also drops this same Crown, so you only really need the initial coin to begin farming.

Farming Tier 2:

(Systems)
The "Exemplar Granum Crown" is required for this drop. The Rescue mission on Neptune>Triton is probably the easiest one to perpetually farm the Void. Be sure to complete the void first before saving the Rescue Target, or you may run into issues with the Treasurer not spawning, and the rescue target dying within the Void.

Farming Tier 3:

(Chassis OR Tenet Weapons)
"Zenith Granum Crown" is required for the Chassis to drop. The best mission for this is Pluto>Hydra, and everything mentioned earlier about farming Capture missions applies here, the capture target can't escape as far as I can tell, and completing this objective before the Void can cause issues with the Treasurer/Candidate not spawning before spawns stop.

For the Main Protea Blueprint, you either need to pick that up from completing the Deadlock Protocol (Don't think you even have access to the void without this mission completed), or from Simaris for 50,000 standing.

Some notes about farming Tenet Weapons this way:

• You technically only need 25 kills (solo) to spawn a Candidate, but I found reaching the 75 Kill Cap was faster than waiting out the timer. Complete the mission after downing the Candidate (without mercy killing) to add the previewed weapon to a blacklist.
• A Radiation based Sister is probably the most annoying to fight because of all the ways it enables Friendly Fire; All Tenet Weapons will be able to proc Radiation status, instead of only the weapons that have base Radiation like the Tenet Arca Plasmor. Arcane Healing, or an ability with Status Cleanse/Immunity works fine to mitigate this, but it still makes it extremely easy to fail a mission like Defense.
• A Sister spawned from a Radiation Progenitor also has the ability Magnetize, like Malice any shots fired will be redirected at whoever has Magnetize on them. It is possible to roll out of it, but the ability is not very visible from inside the bubble, so there is a very good chance that you will end up downing yourself before you notice you've had Magnetize cast on you.

*I've tried to keep this guide as brief as possible while still explaining everything, if you run into issues or think I've missed something, let me know and I'll work on correcting the guide.

You can Bring the Xoris, and use it to free the Solaris Prisoners if you need a little more time in the Void. Collecting Spectral Debris will also increase the time you can spend in the Void.

Currently the easiest ways to get an Octavia if you don't currently have one is to check the Duviri Circuit as it is one of the possible Warframes on Week 9. (It can take a while to farm for her Neuroptics through Survival if you're really unlucky, and requires you to do her quest/pick up the main blueprint and Mandrachord from Simaris if you no longer have base Octavia.)

The other ways to get Octavia would be to wait for Prime Resurgence or selling your extra prime parts on https://warframe.market and finding someone selling her set for a reasonable price.