LAUNCH WINDOW ANALYSIS FOR MARS ORBITER MISSION Kiran B S(1), Kuldeep Negi(2) (1)Flight Dynamics Group (FDG), ISRO Satellite Center (ISAC), Old Airport Road, Bengaluru - 560017, India, +918025084423, [email protected] (2)FDG, ISAC, Old Airport Road, Bengaluru - 560017, India, [email protected]

Abstract Mars orbiter mission (MOM) is India’s first interplanetary endeavor. The objectives of this mission were mainly to develop the technologies required for design, planning, management and operations of an interplanetary mission. MOM Project proposed the mission employing the limited capacity PSLV launcher. MOM mission scenario is unique, involving transfer of the spacecraft from earth parking orbit phase to Mars transfer trajectory phase and finally to Martian orbit phase. The PSLV would put MOM, weighing about 1350 kg, into an Elliptic Parking Orbit (EPO) of size 250 x 23000 km and inclination of 18 deg. The target orbit around Mars considered is a highly elliptic orbit of size 500 x 80000 km. This paper covers the studies that were carried out on the Earth-Mars transfer trajectory design, delta-V requirements, EPO requirements, departure trajectory characteristics, launch opportunities, periods and launch window. The optimal launch opportunity is a function of the trans-Mars delta-V, the MOI delta- V, the declination of the departure V-infinity and launcher constraints. The launch opportunities were worked out for the years 2013, 2016 and 2018. PSLV had initially constrained the EPO argument of perigee (AOP) in their launch vehicle trajectory design. It was shown that the spacecraft mass in Martian orbit could be increased by about 100 kg and a useful mission would be possible if the launch vehicle provided the desired optimum EPO AOP. PSLV came up with a solution to provide the desired EPO AOP by introducing an appropriate coasting phase in the launch trajectory. The overall optimal departure date for the year 2013 was Dec 4, with a V- infinity declination of 24.5 deg, which called for EPO inclination of 23.5 deg accounting for effect of perturbations in the EPO phase that was favorable in taking the inclination towards the required V-infinity declination. After negotiations with PSLV, the launch vehicle team increased the launch azimuth from 102 deg to 104 deg, satisfying all their range safety constraints, giving an EPO inclination of 19.2 deg, which fell in the relatively flat minimum delta-V cost region. The optimal departure date for this case was Nov 30, with a V-infinity declination of 20.2 deg. The launch period was fixed from 2013 Oct 15 to Nov 15 after analysis of the maneuver strategy considering operational constraints for each day in the launch period, holding departure date as Nov 30. The EPO optimum requirements of AOP and launch time, specifying right ascension of ascending node (RAAN), which minimize the total delta-V cost of the mission, were provided to PSLV for each day in the launch period. The launch window duration was restricted to five minutes to minimize deviation of RAAN from the optimum value which would result in propellant penalty for the Mission. The total maneuver strategy was designed and the mission profile was studied for each launch date of the launch period. The effect of delay in launch time was studied and resulting penalties were worked out. MOM was successfully launched at 09:08 UTC on 2013 Nov 5, as per the launch window, from Satish Dhawan Space Center, Siharikota, India into the expected EPO and all orbit/trajectory maneuvers were successfully carried out and the spacecraft was captured into the desired target Martian orbit on 2014 Sep 24 around 02:00 UT as per plan.