Complex sentence: The orbit and the design of GRACE-FO will be very similar to GRACE; the distance between the two spacecraft of GRACE-FO will be measured with lasers (the original GRACE used microwave ranging) as a technological experiment in preparation for future satellites.
Split into simpler sentences: The orbit and the design of GRACE-FO will be very similar to GRACE. In addition to the proven microwave ranging system used on the GRACE mission, the distance between the two spacecraft of GRACE-FO will also be measured with laser ranging as a technological experiment in preparation for future satellites.