Raycast between frames

You simply can't.

However, each frame, you can :

1. Cast a ray with a given origin and direction

2. Store the "result" (meaning the hit object) as a member of your class

3. Reuse the result stored in the last frame into the current frame, and cast a new ray for the current frame.

Pseudo-code :

 private RaycastHit lastFrameRaycastHit = null ;
 
 private void Update()
 {
     if( lastFrameRaycastHit != null )
     {
           // Do something with the raycast hit
           // All the data inside lastFrameRaycastHit comes from the last frame
     }
 
     if ( !Physics.Raycast(transform.position, -Vector3.up, out lastFrameRaycastHit , 100.0f))
             lastFrameRaycastHit = null ;
 }