requirements for operational tests on the ground, the HGAS g-negation system was required to enable  vertical deployments. Other options such as deploying perpendicular to gravity (horizontally) on a low friction surface were not compatible with GPM program requirements. The g-negation scheme utilizes three discreet counter mass elements sized to g-negate individual  sections of the HGAS. The system is comprised of a four-bar mechanism, a concentrated mass/moment arm, and a counter mass connected by cables and pulleys through an overhead gantry. The g-negation  system, attached to the HGAS, is sketched in Figure 3. Ground Support Equipment (GSE) is drawn in  bold lines, while the HGAS flight hardware is drawn in thin lines. Shown partially deployed, heavy solid  arrows indicate the direction of motion of the moving parts of the g-negation system. Counter Torque Assembly The Counter Torque Assembly (CTA)  imparts a torque to the HGAS shoulder hinge line. The intent of the CTA is to negate the effects of gravity on the lower boom of the HGAS assembly as it rotates  through its 90 degree deployment. The torque is produced by an adjustable mass mounted to a moment arm. The torque is  transmitted to the shoulder hinge line via a  four-bar linkage. The magnitude of the torque decreases as the moment arm rotates through 90° from horizontal to vertical. In the absence of the deployable portion of HGAS above the elbow hinge, the  CTA would negate the force of gravity on the lower boom throughout its rotation, assuming no applied torques from the harness or deployment springs.  Elbow Counter Mass The elbow counter mass balances the  upper boom and gimbal assembly about the C-hook pickup axis. It consists of a mass block and a ‘U’-shaped bracket; the mass of each may be adjusted. Were the lower boom absent, the  upper boom and gimbal/HGA assembly would be torque balanced about the C-hook pickup axis,  assuming no applied torques from the harness or deployment springs. The addition of the elbow counter mass to the upper boom requires that this mass is also negated by the C-hook counter mass. Gantry/C-Hook Counter Mass The gantry/C-hook counter mass assembly is intended to negate the effects of gravity on the mass of the  upper boom, gimbal assembly, and the elbow counter mass. The system consists of a modified  commercial off-the-shelf gantry, a ‘C’-shaped link (C-hook), a counter mass and a cable/pulley system. The gantry, in its configuration to support spacecraft integrated HGAS deployments, measured 7.6-m (25ft) tall by 6.1-m (20-ft) wide and 3.6-m (12-ft) deep. It includes a substantial amount of ballast mass at its  base to meet stability requirements. The total mass of the upper boom, gimbal/HGA assembly, and elbow  counter mass is g-negated by the C-Hook counter mass. Assuming a 2:1 ratio between the shoulder and elbow hinge angles is properly maintained and the HGAS  mounting plate is parallel to the ground, the C-hook pick up axis on the upper boom should stay directly over the shoulder hinge axis. This allows a vertical cable to provide the g-negation for the upper boom/gimbal assembly through the C-hook pickup axis. The C-hook link allows the load path to go  

Figure 3. HGAS G-Negation System   48