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Bhilawe et al. LESSONS LEARNED CONCLUSION MOM was challenging as the mission plans used to change depending on the current situation and inputs from the review committee. There were few observations related to mission operations. The observations and the lessons learned are listed below. During one of the maneuvers, the LAM could not give the expected performance. The spacecraft could not achieve the expected delta velocity due to under-performance of the LAM. After the analysis of the observation, it was found that the mission plan executed on that day was never tested in checkout. Therefore, it is better to avoid the operations that are never tested at ground checkout. The Mars Orbiter has many autonomy logics onboard. One of the logics, TWTA autonomy, changes the transmission chain automatically if the current transmission chain lands into a problem to ensure continuous telemetry transmission to ground station. When the logic was enabled, complete telemetry was lost as the TM channel programmed for detecting TWTA failure was wrong and the logic misfired. The TWTA autonomy logic could not change the transmission chain as the actions (commands) uplinked were not correct. The review committee advised to simulate the commands on the setup shown in Figure 12 before sending the commands to the spacecraft to avoid such mistakes. We also faced a few problems in thermo-vacuum and interface testing. The observations and lessons learned during the development phase are listed below. During the development, one of the Low Voltage TransistorTransistor Logic Bus Hold (LVTH) [22] inputs was floating (inputs that are not pulled up or down) and LVTH output was a part of bus arbitration logic. At room temperature, the system passed all of the tests. When the system was switched off and on at low temperature (-18 degrees Celsius), the bus arbitration logic misbehaved; it was due to LVTH output which toggled its state at that temperature. The processor could not initialize the software properly due to the failure of bus arbitration logic and in turn behaved like it was hanged. Therefore, it is better to avoid floating inputs. These kinds of observations are very difficult to analyze as it takes time to bring the thermo-vacuum chamber to -18 degrees Celsius if one wants to repeat the observation. Interface tests with other subsystems are very important. The MTcP transfers the executed commands history to BDH over 1553B bus. During the transfer, BDH receives the valid number of words followed by the data (TC history) in a sub-address and it stores the TC history. The number of words is a 5-bit field. 1-31 is represented as 1-31 and 32 is represented as 0. This representation is same as the number of words field in the command word of 1553B protocol. The BDH software was expecting number of words to be 32 when the data has 32 valid words but the MTcP software was giving it as 0 as it was a 5-bit field. Therefore, when the valid number of words was 32, BDH was missing the data which we observed during interface test. There were no observations in the software performance after it was delivered for flight. All the functionalities worked per the defined requirements. The mission was perfect from the software point of view. AUGUST 2016 The MTcP software design concepts presented in this article are successfully flown in MOM. The software is working well onboard the Mars Orbiter. The software design presented in this article is simple, general purpose, and database driven. The design is robust and can withstand the main system failure by changing over to a redundant system automatically. The configurable features provided can be used to achieve autonomy in spacecraft. Due to programmability provided in the software, the same features can be used for different purposes in different phases of a mission. ACKNOWLEDGMENTS The authors would like to thank and acknowledge the support and encouragement received from Mr. E. Vasantha, Deputy Director, Digital and Control Area (DCA) and Dr. Shivakumar S. K., Director ISRO Satellite center (ISAC), Bangalore. They would also like to acknowledge the contribution of the hardware design team of telecommand for their contribution towards understanding the hardware interfaces and the contribution of test system team for designing a new, advanced test station for Mars Orbiter Mission. REFERENCES [1] [2] [3] [4] [5] [6] [7] [8] [9] [10] IEEE A&E SYSTEMS MAGAZINE Mars Orbiter Mission. Nov. 5, 2013. [Online]. Available: http://www. isro.gov.in/pslv-c25-mars-orbiter-mission, last access Aug. 5, 2015. Mars Orbiter Mission. Aug. 4, 2015. [Online]. Available: https:// en.wikipedia.org/wiki/Mars_Orbiter_Mission, last access Aug. 5, 2015. Kramer, M. Liftoff! India's first mars probe launches toward the red planet. Nov. 5, 2013. [Online]. Available: http://www.space. com/23464-india-launches-mars-orbiter-mission.html, last access Aug. 5, 2015. Payloads. Nov. 5, 2013. [Online]. Available: http://www.isro.gov.in/ pslv-c25-mars-orbiter-mission/payloads, last access Aug. 5, 2015. Condor Engineering. MIL-STD-1553 tutorial. Condor Engineering. Oct. 3, 2000. [Online]. Available: http://microsat.sm.bmstu.ru/ e-library/military%20standatds/MIL-STD-1553Tut.pdf, last access Dec. 3, 2014. MIL-STD-1553B: Digital time division command/response multiplex data bus. United States Department of Defense, Sept. 1978. Data Device Corporation. MIL-STD-1553 designer's guide sixth edition. Data Device Corporation, Aug. 12, 2003. [Online]. Available: http://www.ddc-web.com/Documents/dguidehg.pdf, last access Aug. 1, 2015. ISRO. Mars Orbiter spacecraft successfully inserted into Mars orbit. isro.org, Sept. 24, 2014. [Online]. Available: http://www.isro.org/ update/24-sep-2014/mars-orbiter-spacecraft-successfully-insertedmars-orbit, last access Aug. 5, 2015. Mars Orbiter mission successfully enters Red Planet orbit. India Today, Sept. 24, 2014. [Online]. Available: http://indiatoday.intoday.in/story/ mars-mission-mars-orbit-insertion-mom-isro-india-m-annaduraibaylalu-red-planet/1/384723.html, last access Aug. 5, 2015. Kulkarni, S., Sharma, S., Pujari, V., Lakshminarsimhan, P., and Seshaiah, R. 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Table of Contents for the Digital Edition of Aerospace and Electronic Systems Magazine August 2016