The Salvation’s Grip is a new Exotic Rocket Launcher in Destiny 2 that was introduced with the Beyond Light expansion. To get access to the Stasis Prototype quest that rewards you with this weapon, you will need to complete the Beyond Light story campaign.
When that is done, visit the Drifter in the Tower and you will be able to start the quest.
Stasis Prototype Quest Steps
Step 1 – Gathering Intel
You will need to defeat Fallen Captains and Servitors on Europa to collect intel. It is a good idea to do this around the Eventide Ruins area, where both enemies are common.
Step 2 – Locating the Prototype
For this step, you will need to complete an Empire Hunt. These are another fight with the bosses from the story campaign. You should have the Dark Priestess mission available, so that will satisfy this requirement.
Step 3 – Stasis Practice
The Drifter shows an unusual amount of caution, and wants you to practice taking out enemies with Stasis. You can either directly kill enemies, or affect them by freezing them, then kill them by any means.
Step 4 – Lost Sector Rendezvous
You will need to make your way to the Concealed Void Lost Sector. You may need to bump up your Power, as this one is at 1210 recommended Power. Talk to the strange NPC at the end.
Step 5 – Rendezvous with the Drifter
It is time to head back to the Tower and speak with Mr. Mysterious.
Step 6 – Stealing Stasis
You will need to complete a mission at Charon’s Crossing called The Stasis Prototype. It is quite straightforward.
Step 7 – Drift back to the Drifter
Return to the Drifter and the mission is complete, and the Salvation’s Grip will be yours.