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Overcarriage

Fisher Space Systems LLC

Space Track Launch System

     A more detailed discussion of ribbon displacement during launch is found in the Proof of Concept paper. A review of the overcarriage can be found in the STLS Overcarriage paper.  Use the comment form on the contact page if you wish to comment on the STLS concept. Be sure to review the creative commons licenses. All comments and suggestions will be shared equally throughout the space access community.
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     The overcarriage rest on top of the ribbon and carries the launch vehicle down the ribbon to the launch point. At the launch point, the overcarriage ejects the launch vehicle, is thrown clear of the ribbon, and returns to the launch point to be refurbished and reused. The overcarriage is approximately 25% of the combined mass of the overcarriage and launch vehicle. For example, for a 100 ton overcarriage and launch vehicle, the mass of the overcarriage is 25 tons and the mass of the launch vehicle is 75 tons. This ratio is important because after launch the overcarriage continues to accelerate down the ribbon. The Coriolis force continues to act on the overcarriage retarding the ribbon. As such, the impulse on the ribbon and tower are much lower than would be if the launch vehcile is released from the end of the ribbon.

     The displacement of the ribbon from its normal position (indicated by the dotted line) is shown here. The displacement is due to the Coriolis force on the launch vehicle and overcarriage as it travels down the ribbon to the launch point. At launch, the mass on the ribbon drops to 25% of the combined launch vehicle/overcarriage mass. As such, the Coriolis force still acting on the overcarriage is greatly reduced. The force acting in the opposite direction due to the tension in the ribbon accelerates the ribbon and overcarriage back toward its normal position. The ribbon accelerates to a peak velocity. As the Coriolis force becomes greater than the tension force, the ribbon begins to slow down. The ribbon comes to rest on the other side of normal. At this point, the overcarriage launches off of the ribbon and returns to the launch site. The remaining oscillations are dampened by the counterweight.

     The overcarriage is itself a reentry vehicle. The super structure for the overcarriage is shown here. In operation, it will have an aerodynamic shell to protect the structure during reentry, body flaps for attitude control in the atmosphere, reaction control system for attitude control in space, prime power and avionics, landing gear, and a parafoil for landing.
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Updated Aug 2012