A tethered spacecraft has a first endmass and a second endmass with a telescoping stacer spring and a tether arranged between the endmasses. The spring is coiled around a center rod and initially contained within a housing, the spring being biased to push the first endmass away from the second endmass. The spring housing is affixed to the first endmass, a first end of the spring being affixed to the spring housing, and tether are affixed to spring at one end and to the second endmass at the other end. A pretensioned loop holds the endmasses abuttingly together, and a burnwire release mechanism cuts the loop to deploy the spring. Upon deployment, the spring extends to its full length to form a cylindrical boom, and the endmasses continue to move outward along the spring centerline until stopped by the tether.