Trans. JSASS Aerospace Tech. Japan Vol. 14, No. ists30, pp. Pk_9-Pk_15, 2016 Orbit Plan and Mission Design for Mars EDL and Surface Exploration Technologies Demonstrator By Naoko OGAWA,1) Misuzu HARUKI,2) Yoshinori KONDOH,3) Shuichi MATSUMOTO,2) Hiroshi TAKEUCHI4) and Kazuhisa FUJITA5) 1)Space Exploration Innovation Hub Center, Japan Aerospace Exploration Agency, Sagamihara, Japan 2)Research and Development Directorate, Japan Aerospace Exploration Agency, Tsukuba, Japan 3)Human Spaceflight Technology Directorate, Japan Aerospace Exploration Agency, Tsukuba, Japan 4)Institute of Space and Astronautical Science, Japan Aerospace Exploration Agency, Sagamihara, Japan 5)Research and Development Directorate, Japan Aerospace Exploration Agency, Chofu, Japan (Received August 1st, 2015) Mars EDL (entry, descent and landing) and surface exploration demonstration working group in Japan Aerospace Exploration Agency (JAXA) has assessed and discussed feasibility of a Martian rover mission to be launched in early 2020s. The primary objectives of this mission are to demonstrate technologies required for EDL and surface exploration of a massive planet with an atmosphere, to investigate Martian geochronology and to search for signs of lives, past or present, and to determine when the ocean was lost in the Martian history. The launch date is targeted in early 2020’s in our study. In this paper, we investigate launch opportunities during 2020’s and propose several launch windows considering some system requirements. Feasible interplanetary transfer trajectories from Earth to Mars are proposed. Assuming direct entry and following aerodynamic guidance in Martian atmosphere, we connected interplanetary and aerodynamic trajectories so as to land on an aimed point. Precision analysis of orbit determination at the entry and landing is also shown. Key Words: Mars, EDL, Orbit Plan, Orbit Determination, Aerodynamic Guidance 1. Introduction Space Center as the launch site, and coasting flight on the 300- km parking orbit followed by injection into the interplanetary Mars EDL (entry, descent and landing) and surface explo- orbit by the upper stage. ration demonstration working group in Japan Aerospace Explo- 2.2. Launch windows ration Agency (JAXA) has assessed and discussed feasibility of Figure 1 shows windows for Earth-Mars transfers between a Martian rover mission to be launched in early 2020s. 1) The 2015 and 2025. The blue line shows the sum of hyperbolic primary objectives of this mission are to demonstrate technolo- excess velocity in Earth departure and Mars arrival. The red gies required for EDL (entry, descent and landing) and surface line indicates how many times the spacecraft will go around the exploration of a massive planet with an atmosphere by driving sun. The launch opportunities which requires rational energy an autonomous rover, 2) to investigate Martian geochronology and flight time are 2018, 2020, 2022 and 2024. Launch after and to search for signs of lives, past or present, and to deter- 2020 is reasonable from the viewpoint of development sched- mine when the ocean was lost in the Martian history. The space- ule. Among of all, the window in 2020 allows us to go to Mars craft system consists of ICM (interplanetary cruise module) and with small energy. Windows in 2022 and 2024 require more en- AEM (atmospheric entry module), and AEM is composed of ergies because of high declination of launch asymptote and high AM (aeroshell module), LM (landing module) and a rover. excess velocity. Thus it can be a good strategy to set 2020 as the In this paper, results of our feasibility study on the prelimi- nominal window, and to regard 2022 and 2024 as back-up win- nary trajectory plan, mission design and interface condition for dows. Another strategy for back-up windows can be also fea- aerodynamic guidance of this mission as of 2015 are described. sible by using interplanetary parking orbits followed by Earth gravity assist for trans-Mars injection. 3) 2. Launch Window Assessment and Trans-Mars Orbit De- 2.3. Mission requirements and constraints sign Next, we assessed each windows, and decided preliminary departure and arrival dates considering the following require- In this section, we describe launch window assessment and ments; trans-Mars orbit design. Mission Requirements 2.1. Launch vehicle Melas Chasma (291.48◦E, 11.47◦S) is the prime candi- • The nominal squared hyperbolic escape velocity (C3) for date of landing sites. Juventae Chasma (298.22◦E, 4.80◦S) 2 2 transfer from Earth to Mars is around 8 to 21 [km /s ]. In and Marte Vallis (105.6◦E, 8.0◦N) are also possible. Sev- this feasibility study, we assumed H-IIA series capable of such eral possible signs of water have been found around these launch requirements as of 2015. We also assumed Tanegashima points, thus we think that they are suitable for life search. Copyright© 2016 by the Japan Society for Aeronautical and Space Sciences and ISTS. All rights reserved. Pk_9 Trans. JSASS Aerospace Tech. Japan Vol. 14, No. ists30 (2016) 8 6 7.5 5 7 4 6.5 3 Revolution about Sun Revolution about 6 2 Vdeparture + Varrival (km/s) 5.5 1 5 0 2015 2016 2017 2018 2019 2020 2021 2022 2023 2024 2025 Launch Date Fig. 1. Launch windows to Mars between 2015 and 2025. The blue line shows the sum of hyperbolic excess velocity in Earth departure and Mars arrival. The red line indicates how many times the spacecraft will go around the sun. Time of flight should be within one Earth year, because too and the vehicle. • long flight may decrease scientific value of this mission. 2.4. Assessment of launch windows 45-min or more Direct-To-Earth (DTE) communication • DTE communications, Sun elevation, Earth distance and Ls between Earth (tracking stations in Japan if possible) just after landing on Mars are essential requirements in this should be ensured just after landing on Mars, because they mission. They depend on Sun, Earth and Mars position rela- have to confirm the success of landing and supervise the tionship, and therefore on departure/arrival dates. We assessed lander to acquire power supply and communication as soon suitable launch and arrival windows to satisfy landing require- as possible. There may be no guarantee for communication ments. relay orbiters dedicated for Japanese Mars missions. For example, Fig. 2 shows departure/arrival window candi- The rover should have capability to communicate to Earth • dates superimposed on the porkchop plot for 2020 launch op- ffi for at least 70 sols after landing for su cient mission ac- portunities. Red and blue contours are departure and arrival C3 tivities. respectively. Points A to I are candidates. Departure C3 (red) & Arrival C3 (blue) (km2/s2) System Requirements 2021-05 1 12 8 24 36 16 C3 values for departure and arrival should be small as much 28 24 • 12 24 Earth 24 8 Ls Dist as possible to maximize the probe mass. 8 Sun Elv 20 (au) 2 2 2021-04 12 C3 on Mars arrival should also be within 36 m /s for ther- 20 36 20 G 23 1.71 • 8 mal protection system on entry. 16 16 A 15 1.55 Martian solar longitude (Ls) less than 10 at landing is 2021-03 H 11 1.48 • I preferable to avoid mission phase in winter, if the landing 12 8 16 36 24 FE16 site mentioned above is in the southern hemisphere. This 3 1.32 12 20 12 2021-02 8 B 8 3571.20 is because winter on Mars is too severe thermal condition 16 12 for the rover. 24 Arrival 8 20 16 12 Consecutive 15-days should be ensured for launch, be- C D 24 3430.94 • 2021-01 16 cause there is a risk for launch postponement due to 12 20 28 32 36 16 20 2420 24 16 weather or other problems. 16 24 3236 20 28 Sun elevation should be about more than 30 degrees just 12 20 • 2020-12 32 36 after landing on Mars to ensure sufficient power supply for 24 28 24 Departure C3 the rover. 32 36 Arrival C3 A Candidates Earth distance on Mars arrival should be within 1.8 au, re- 2020-11 Ls • 32 Earth Dist quired by communication system during cruising. 36 Earth distance 70 sols after landing should be within 2.1 2020-05 2020-06 2020-07 2020-08 2020-09 • Departure au for the rover to communicate to Earth by the low gain Fig. 2. Departure/arrival window candidates (A-I) superimposed on antenna during the mission phase. the porkchop plot for 2020 launch opportunities. Constraint Conditions Table 1 is a case study result for each 2020 windows for land- C on Earth departure should be within 21 m2/s2 con- ing on Melas Chasma. Note that “local time” used here is de- • 3 strained by launch vehicle capabilities. rived by assuming that 1 sol is 24 hours, thus one second is Declination of launch asymptote (DLA) should be within longer than on Earth. You can see that late arrival allows earlier • 60 degrees constrained by the launch site (Tanegashima) landing in the afternoon with higher Sun and Earth elevation, ± Pk_10 N. OGAWA et al.: Orbit Plan and Mission Design for Mars EDL and Surface Exploration Technologies Demonstrator Table 1. Assessment results for 2020 windows. Case Entry date Sun Earth Landing Earthset Sunset Earth Ls Elv Elv Local Local Local Dist [deg] [deg] Time Time Time [au] A 2021-03-09 16:50:31 58.9 32.4 13:42 17:54 15:55 1.55 15 B 2021-02-01 19:42:25 38.0 5.6 15:25 15:49 18:00 1.20 357 C 2021-01-05 02:49:07 27.4 5.4 16:13 15:49 18:05 0.94 343 − D 2021-01-05 03:01:09 24.5 8.0 16:25 15:49 18:05 0.94 343 − E 2021-02-14 03:07:23 43.5 12.3 14:59 15:51 17:58 1.32 3 F 2021-02-14 02:06:10 57.5 26.5 14:00 15:51 17:58 1.32 3 G 2021-03-26 02:35:39 64.2 43.5 13:01 15:59 17:52 1.71 23 H 2021-03-02 12:40:58 54.5 26.0 14:07 15:54 17:56 1.48 11 I 2021-02-27 10:57:01 51.8 22.5 14:20 15:53 17:56 1.45 10 which is desirable for DTE communications and power supply 90 just after landing.