An Optimal Strategy For Day Of Launch Wind Biased Steering Design And Onboard Implementation
- Paper number
IAC-07-C1.3.07
- Author
Dr. K. Sivan, Indian Space Research Organisation (ISRO), ISAC, India
- Coauthor
Mrs. V.R. Lalithambika, Indian Space Research Organisation (ISRO), India
- Coauthor
Mr. C. Geethai krishnan, Indian Space Research Organisation (ISRO), India
- Coauthor
Mr. D.S. Antuvan, Indian Space Research Organisation (ISRO), India
- Coauthor
Mrs. G. Thangavelammal, Indian Space Research Organisation (ISRO), India
- Coauthor
Mr. Joyas Jose, Indian Space Research Organisation (ISRO), India
- Coauthor
Mrs. A. Sreelatha, Indian Space Research Organisation (ISRO), India
- Year
2007
- Abstract
The primary criterion for launch vehicle steering program design, during its atmospheric flight, is to maintain the structural loads within design limits. Launch vehicles generally follow predefined ground computed attitude steering during atmospheric flight and subsequently use Closed Loop Guidance (CLG) algorithm for onboard steering computation till the end of the mission. The state vector of the end point of open loop steering phase is taken as the initial conditions for CLG phase. So, any change in open loop steering calls for changes in CLG algorithm and onboard data and all validation studies are to berepeated. This design and validation cycle takes about three months time period. During atmospheric flight, wind is the major factor that contributes to the aerodynamic loads acting on the vehicle. Therefore, the winds are closely monitored and predicted by trend analysis from the beginning of the launch campaign till lift-off and go-ahead decision is taken before every critical operation. Thus, wind plays a critical role in launch clearance and in some cases it leads to the risk of launch postponement, which increases the cost enormously. This scenario is undesirable in advanced space vehicles operational phase which desires all-weather launch. One common practice, that reduces the criticality due to winds, is to bias the steering program to the mean wind profile of the season of the launch. Though this scheme increases the launch probability, it does not take care of the variations between the mean wind and that prevails during launch. The scheme will not be effective for the seasons with large wind variations and large wind shears and during transition periods. Also, in case of slippage in the launch schedule to the next season, the entire design and validation cycle has to be repeated. In order to overcome the above drawbacks and to achieve all-weather launch, open loop steering program needs to be biased to the wind that prevails during Day-Of-Launch(DOL). The major challenge in implementing DOL Wind Biasing(DOLWB) is minimizing the considerable lead-time required for wind data collection, processing, steering program generation, CLG design, validation and onboard implementation. Of all the processes involved, the wind data collection and processing requires a stipulated time of one and half hour. So, a scheme that consists of an advanced steering program generation strategy which eliminates CLG design and validation cycle is envisaged. This scheme also involves automation of the all the processes. This paper describes this novel scheme for implementation of DOLWB. A reference trajectory is designed for a mission and CLG is designed for the reference trajectory. The CLG design is validated through various phases of simulations and stored as flight data. The CLG initiation conditions of the reference trajectory is set as the open loop steering target conditions. On the DOL, open loop steering program is generated, by biasing to the pre-launch wind, to achieve the CLG initial conditions within prescribed tolerances. This strategy makes CLG algorithm unique and insensitive to wind conditions and optimizes the lead-time. A scheme to specify the tolerance levels in terms of state vector is also worked out. In order to ensure the integrity of the open loop steering design, unaltered flight data and the onboard systems to meet the mission specifications, detailed simulation studies need to be carried out with flight onboard equivalent systems. So, the complete process of DOLWB implementation involves wind soundings, wind data processing, steering program generation, its validation along with CLG parameters in digital simulation mode with vehicle flexibility in two different test beds, onboard data generation, validation of onboard data in an integrated onboard equivalent system, onboard implementation and launch clearance studies. These simulation tasks are to be carried out, due to logistic limitation, in the laboratory which is typically located about 1000km away from the launch station. The seamless integration of various functionalities in this process has enabled successful operation of the scheme, which has drastically reduced the total design and validation cycle for each mission and the lead-time is optimized as five and half hours. This DOLWB scheme has been successfully implemented for three different types of ISRO missions. One of the missions had an inclement wind conditions during launch which, but for DOLWB, would have called for launch postponement. These flight performances establish that this DOLWB implementation scheme completely eliminates the risk of launch postponement due to winds and ensures benign load conditions during flight.This paper consists of studies on the requirement of DOLWB, the novel idea of steering program generation, implementation methodology and typical results.
- Abstract document
- Manuscript document
IAC-07-C1.3.07.pdf (🔒 authorized access only).
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