ASCENT GUIDANCE COMPARISONS

This paper contains results from ascent guidance studies conducted at the NASA Marshall Space Flight Center. The studies include investigati on of different guidance schemes for a variety of potential launch veh icles. Criteria of a successful ascent guidance scheme are low operati ons cost, satisfaction of load indicator constraints, and maximization of performance. Results show that open-loop designs as a function of altitude or velocity are preferable to designs that are functions of t ime. Optimized open-loop trajectories can increase performance while m aintaining load indicators within limits. Closed-loop atmospheric sche mes that involve linear tangent steering or feedback of velocity terms for trajectory modification did not yield any improvement. Early rele ase of vacuum closed-loop guidance, including use during solid rocket booster operation, yields some improvements. Evaluation of a closed-lo op optimization scheme for flying through the atmosphere shows no adva ntages over open-loop optimization. Dispersion study results for sever al potential guidance schemes and launch vehicles are included in the paper and are not a discriminator between guidance schemes. The primar y cost driver is mission operations philosophy, not choice of guidance scheme. More autonomous guidance schemes can help in movement towards a philosophy that would reduce operations costs.