in most cases the strut could be saved by simply reworking or replacing the defective parts. In addition,  since the struts are inert until they are pressurized, ground handling hazards are eliminated, making handling a low-cost operation.   Parametric cost modeling bases the estimated cost on weight and similarities to selected components for which cost are available. Since the struts are half the weight of BDMs, they would be half the cost assuming equal complexity. This is the only level of cost analysis that is possible given the maturity of the MAG Strut design. Actual per-unit cost would need to be reevaluated after developed units have been fabricated and the design finalized.    MAG Strut Design   The MAG Strut struts are designed to take advantage of the increase in payload to orbit by separating at 356-kN residual first stage thrust. To achieve this, a significant force is required. Consequently, the struts can place a substantial bendi ng moment into the edge of the aft skirt, increasing the potential for buckling  during ascent. Also, sudden release of the energy stored in the struts could result in a significant jerk to the upper stage, which could affect propellant quality and tank pressure. The MAG Strut design is proposed in order to counter these effects. During ascent, only a low pressure acts against the upper stage aft skirt. At separation, the force applied increases gradually, which minimizes potential for skirt buckling and mitigates concerns about sloshing induced in the propellant tanks.  The MAG Struts are designed with two chambers as shown in Figure 7. The low-pressure chamber is meant to provide the initial force requirement for separation. The initial force calculation for each strut would be as follows:  

N kPacm cmkPacm124,68 034,1**4) 62.7 78.17(342,10**4) 62.7(2 2 2 /g32 /g176/g191/g176/g190/g189 /g176/g175/g176/g174/g173 /g187 /g188/g186 /g171 /g172/g170 /g16/g14 /g176/g191/g176/g190/g189 /g176/g175/g176/g174/g173 /g187 /g188/g186 /g171 /g172/g170/g83 /g83  

With 8 struts, the force of 545 kN is more than sufficient to overcome a SRM residual thrust of 356 kN and the transient oscillatory force from the SRM, and therefore preventing re-contact of the two stages during separation. (See Figure 8 for a plot of the transient oscillatory thrust of the Ares 1 first stage.) The high-pressure chamber is intended to store the gas needed for the main part of the strut stroke. After 40 cm of stroke, this force reaches 1,495 kN. This force is capable of driving the first stage and upper stage apart with sufficient velocity margin to achieve separation with a residual first stage thrust of 356 kN.   

Figure 7 – Schematic of the Proposed MAG Strut Design    The metering rod has a pattern of holes that are exposed as the strut strokes, providing a gradual force buildup that will minimize impulse on the upper stage. Figure 9 shows a computer-aided design (CAD)  rendering of the strut in the collapsed position. Figure 10 shows a CAD rendering of the strut in the  extended position. Initially no holes are exposed. Once the strut has stroked 2.54 cm, 6 holes are exposed. Figure 11 shows the cumulative area for the exposed holes as  a function of stroke. Every   2.5 cm of additional stroke exposes more holes to achieve the gradual force build-up. (The summation of  336