P % the Stacer via a woven Dacron (parachute shock) cord. Similar to the device found on (old) dial  telephones that prevented the dial from being rotated faster than an old telephone exchange could count,  the flyweight brake supplies braking force proportional to the rotational speed of its weight assembly. If  the force (speed) increases, the brake shoes are centripetally accelerated against the brake drum,  increasing the braking force and slowing the rotational velocity. Over a wide range of forces, the brake  typically can control the speed to *lo%. For the Boom, a deployment  velocity of -0.5 m/s was chosen. This allows a certain momentum to  build, but is slow enough to avoid shearing damage to the lock pins at  the end of travel.  Harness and SDOOI  The power and electrical signals between the data processing unit and  the instruments are carried by a cable routed down the center of the  tubes, and is stowed on a spool for launch. This harness is a custom-  fabricated conductor assembly consisting of seven coaxial cables and  five twisted shielded pairs. Built of silver-plated copper with Gortex@’  dielectric, the harness is wound onto a bobbin when stowed and is  pulled off when the boom deploys. This ‘straight through’ design  provides greater signal strength, higher reliability and allows longer  harness length as there are no slip rings or other connections between  the data processing unit and the instruments. Care is taken to prewind  the harness to avoid kinking or ‘birdnesting’ when stowing. I  Figure ,,. Flyweight  Brake 81 Harness Spool  The Stacer  The Stacer is a rolled, constant helical pitch, fixed diameter flat spring. The strip width, thickness, roll  diameter, and helical pitch are selectable for each application, allowing each Stacer to be tailored for  optimum properties. Stacers range in size from <1 m to >10 m in length, from 4 mm to 55 mm in diameter  at the tip, and can provide extensive force from almost nothing to 200 N. Trade studies can balance mass  versus length, force, etc. In the last 30 years, more than 650 units have been utilized in aerospace  applications, from sounding rocket sensors to gravity gradient booms with large masses on the end. What  makes the Impact Boom unique is the use of the Stacer as a spring ‘motor’ without using it as the  structure or sensor surface. Most applications have the Stacer with the sensor(s) mounted directly on it,  or the Stacer as the sensor, for example as an antenna (a total of six 6-m-long beryllium copper Stacers  are used on the Stereo satellites for the Swaves experiment in this manner).  I  .- -I  Figure 12. Picture of a Stacer  To accommodate the Mag requirement of low magnetic signature for the boom, Elgiloy@ was selected as  the spring material over the more traditional beryllium copper (Be-Cu). This alloy was chosen to minimize  any eddy currents that could be developed between the SWEA / STE and the spacecraft. Originally  invented in the late 1940’s in Elgin, IL for use in watches, it has been used for exacting Stacer  applications several times. Its internal resistance is higher than copper, and cuts down the eddy currents  accordingly. It has a higher modulus (E), and can provide greater force in the same physical volum7e as  the Be-Cu. Elgiloy is a cobalt ‘super-alloy’, having an E -1 90 GPa and a yield strength of -1 600 MPa .  7 Matweb, http://www.matweb.com/search/SpecificMaterial.asp? = Elgiloy  56