The harness holds the rocket sections and parachute together during descent. Small (low mass) rockets may use an elastic cord to absorb forces created when the parachute is ejected and inflates. A recovery system for large rockets should be designed to reduce the forces that occur rather than try to absorb them. An elastic harness will not withstand the forces created with large rockets. A failed harness creates a dangerous situation with rocket parts falling from a high altitude.
A long harness, about 20’ or more, is used so that rocket parts decelerate from air friction after a pyrotechnic charge separates the airframe into two pieces, or deploys the main parachute. Common materials are tubular nylon and tubular kevlar. The latter material is fire and heat resistant. Nylon is affected by fire and heat and must be periodically replaced.
Tubular nylon and kevlar are wolven into a tube, then made flat like a strap. The material can be pressed with the fingers to form a tube, which will return to a flat shape when pressure is removed.
No single recovery technology works for all situations. Available technologies need to be reviewed and the one that best suits the problem chosen. The technique of using a harness to hold rocket parts together during descent may not work for high mass rockets and high altitudes. A long harness is used to allow air resistance to slow rocket parts when they are separated by a pyrotechnic charge during drogue and/or main parachute deployment. This technique depends upon air density. A 20’ harness may not be sufficient at 50,000’ where air density is lower than at 1,000’ or 5,000’. Very high altitudes and rocket mass may neccessitate a different recovery solution.
An elastic cord harness (“shock cord”) can work with low mass rockets, such as those weighing less than three pounds. The harness should be 2 to 3 times the rocket’s length, or about 6’ for rockets 1 pound or less, and 12’ for rockets 1 to 3 pounds. However, tubular nylon is probably a better choice. Small tubular nylon is sold by the yard by some stores that sell camping supplies and boots. Another use for it is boot laces. Low weight high power rockets may be able to use less than 20’ of cord, such as 12’.
Submitted by: Dean A. Roth