Reaching Top standing with Solaris United means reach lv.5 from their "main syndicate" on Fortuna.
To increase in levels, you'll need to interact with Eudico, which is located near the main door to Orb Vallis.
In order to increase in levels, you'll need to reach a certain amount of reputation at each level of standing. To gain reputation, there are 2 main ways :
- Complete Orb Vallis bounties, which will grant you between 1k and 5k reputation for a completed bounty (splitted for each part of the bounty, to still reward you a bit if you fail it through)
- Sell fishes/gems to Fortuna NPCs
In my opinion, it's best to farm the second way, since with some booster, it's way easier. But you're free to choose your own torture. Also, the second method has a great advantage : You can farm a lot of gems at once, then just log in everyday to sell them.
1st way tips : - Gather a group of people, you'll be stronger and faster to complete missions. Also, this could help you unlock another achievement (Complete 6 bounties in Orb Vallis in under 60 minutes). Try using a strong defensive warframe (Frost or Gara for example), and good weapons to make this easy, and a fast archwing will be perfect to navigate through the objectives.
2nd way tips : - Look at your maps to find caves, you'll want to go for gems, since the rarest reward a lot. Bring a Smeeta Kavat if you can to potentially increase your gems, and use a stealth warframe (Loki or Ivara for example) so you'll avoid fighting nearby ennemies. Using a double ressource booster will greatly help to gather more gems, and a rare ressource booster helps to find rarer gems. You might want to focus on Blue minerals, since they yield gems 100% of the time, but mining Red minerals will sometimes give you gems too depending on how you managed to mine them.
Once you reach max reputation for your current level, you'll need to do a "sacrifice" in order to level up. You'll need to give some Debt-bonds. There are also two ways to get them, but clearly one is easier.
1st way : Praying RNG to have 1-2 Debt-bonds dropping as bounty rewards.
2nd way : Buying them to Ticker, a hidden NPC on Fortuna (Start menu > Fast Travel > Ticker). He'll sell you Debt-bonds for some ressources and credits. Be sure to meet him as soon as you can to gather the required amount of Debts for each level asap. The higher the debt-bond, the more expensive it will cost to Ticker
Here's the list of the debts required for each rank :
0 -> 1 : [13 Training Debt-bonds]
1 -> 2 : [12 Training Debt-bonds, 15 Shelter Debt-bonds]
2 -> 3 : [10 Training Debt-bonds, 15 Shelter Debt-bonds, 13 Medical Debt-bonds]
3 -> 4 : [12 Shelter Debt-bonds, 10 Medical Debt-bonds, 13 Advances Debt-bonds]
4 -> 5 : [12 Medical Debt-bonds, 12 Advances Debt-bonds, 10 Familial Debt-bonds]
Which is a total of : 35 Training ; 42 Shelter ; 32 Medical ; 25 Advances ; 10 Familial
Each level you'll need more and more reputation : 5k ; 22k ; 44k ; 70k ; 99k.
Depending on your Mastery Rank, this will take some time, because of your daily limit. Your daily limit is defined as : (Your Mastery Rank + 1) * 1000.
Being a MR5, your daily limit is 6k. Being a MR15, your daily limit is 16k.
Finally, the daily limit do not depend on the way you're levelling up. If you combine gems and bounties, it will be the same limit. So if you know you're going to do some bounties, don't sell your gems before, otherwise you'll waste daily reputation.
Once you get to lvl.5 the achievement should unlock and you'll reveal Fortunas NPC secret. Also, you'll be able to take part in Vox Solaris syndicate in their secret room if you're enjoying Fortuna/Orb Vallis.