Jean-Baptiste Bayle
--- a/lisainstrument/indexing.py 0 → 100644
+++ b/lisainstrument/indexing.py 0 → 100644
+
+    return np.stack(tuple(x_int[sc] for sc in keys), axis=axis)
+
+
+def dict2mosa(x, axis=0):
+    """Return a new array whose `axis` is for spacecraft and `axis + 1` for MOSAs, with content of `x`.
+
+    The keys of `x` should be [12, 23, 31, 13, 32, 21] (or convertible to those), and values array-like.
+
+    Note that all values of `x` should have the same shape, or can be automatically broadcasted.
+    If they have shape (N), the resulting array will be of shape (3, 2, N) by default (first axis).
+
+    Args:
+        x: input dictionary
+    """
+    mosas = [12, 23, 31, 13, 32, 21]
--- a/lisainstrument/indexing.py 0 → 100644
+++ b/lisainstrument/indexing.py 0 → 100644
+
+def sc2dict(x, axis=0):
+    """Return a dictionary whose keys are spacecraft indices, from array `x`.
+
+    The array `x` must have `axis` of dimension 3, ordered as [SC1, SC2, SC3].
+
+    The output dictionary containes the keys [1, 2, 3].
+
+    Args:
+        x: array-like input
+    """
+    if x.shape[axis] != 3:
+        raise IndexError(f"invalid size '{x.shape[axis]}' for spacecraft dimension '{axis}'")
+
+    return {
+        1: np.take(x, SC1, axis=axis),