Trans. JSASS Aerospace Tech. Japan Vol. 8, No. ists27, pp. Tk_7-Tk_12, 2010 Topics Preliminary Mission Analysis and Orbit Design for Next Mars Exploration By Naoko OGAWA 1), Mutsuko Y. MORIMOTO1), Yuichi TSUDA1,2), Tetsuya YAMADA1,2), Kazuhisa FUJITA1,3), Tomohiro YAMAGUCHI4), Yasuhiro KAWAKATSU1,2), Takashi KUBOTA1,2) and Jun’ichiro KAWAGUCHI1,2) 1)JAXA Space Exploration Center, Japan Aerospace Exploration Agency, Sagamihara, Japan 2)Institute of Space and Astronautical Science, Japan Aerospace Exploration Agency, Sagamihara, Japan 3)Aerospace Research and Development Directorate, Japan Aerospace Exploration Agency, Tokyo, Japan 4)The Graduate University for Advanced Studies, Sagamihara, Japan (Received July 21st, 2009) Japan has launched many interplanetary spacecraft for exploration of solar system bodies including Mars. Now we are planning the next Mars mission in the late 2010’s. This paper describes the preliminary mission analysis and orbit design for this plan. The combined exploration by several spacecraft requires complicated and careful consideration, different from those for single-probe missions. Mission plans to realize required configuration by a single launch and simple simulation results are reported. Key Words: Mars, Mission Analysis, Orbit Design, MELOS 1. Introduction 2.1.1. Meteorological orbiter for martian climate One orbiter of the two, called hereafter as the meteorological In 2008, Japan Aerospace Exploration Agency (JAXA) orbiter, aims understanding of the interaction between the has established a novel working group toward a novel Mars atmosphere and subsurface ice, and atmospheric dynamics. exploration program named MELOS, an acronym for “Mars Global, high-resolution and continuous mapping of water vapor, Exploration with Lander-Orbiter Synergy”1). As its name clouds, dusts and atmospheric temperature will be performed indicates, this is an ambitious mission composed of several with imaging cameras from the apoapsis of its highly elliptic landers and orbiters, schematically illustrated in Fig. 1. orbit. At lower altitude, a sub-millimeter sounder will also be Combined and networked exploration by multiple spacecraft is used for three-dimensional mapping of water vapor and winds. one of notable features of the MELOS mission, compared to Knowledge of Martian climate with the meteorological several missions to be launched in 2010’s 2–5). A working group orbiter will allow us to establish comparative meteorology for the MELOS mission has been established in 2008, and more of terrestrial planets such as Earth, Venus and Mars by than 100 researchers have joined discussing the details of the incorporating Earth climate data and those from Akatsuki, mission toward the launch in late 2010’s. JAXA’s Venus Climate Orbiter launched in May 20106). Both This paper describes the preliminary mission analysis and scientific data and engineering designs of PLANET-C will be orbit design for the MELOS mission. The combined inherited to the meteorological orbiter. exploration by several spacecraft requires complicated and 2.1.2. Atmospheric escape orbiter for escaping atmo- careful consideration, different from those for single-probe sphere missions. Mission plans to realize required configuration by a The other orbiter, here we call it the atmospheric escape single launch and simple simulation results are reported. orbiter, performs in-situ observations of escaping atmosphere in a low-Mars orbit, which was one of science objectives in 2. Mission Overview Nozomi – Japan’s past Mars orbiter mission7). It is now almost certain that Mars once had duration of warm In this section, overview and scientific basis of the MELOS and wet climate. The aim of the observation of atmospheric mission are introduced. escape is to obtain a clue of how and why the atmosphere 2.1. Scientific objectives and climate of Mars have evolved with time. Our target This mission is expected to consist of two orbiters and several is to elucidate non-thermal escape processes, in particular, landers, as implied by its name, MELOS, an acronym for solar wind-induced escape processes, which are pointed out to “Mars Exploration with Lander-Orbiter Synergy”. Two orbiters involve substantial uncertainties by previous measurements and and landers will perform cooperative and combined exploration theoretical studies. of Martian atmosphere, climate, interior structure and surface Elucidation of atmospheric escape will be strongly supported environment for understanding and elucidation of the evolution also by the meteorological orbiter in two ways. First, simul- of Mars environment. The MELOS mission challenges the taneous observation will be performed by the meteorological following three science objectives. orbiter to grasp global structures of escaping ions, and by the atmospheric escape orbiter to investigate the escape processes through in-situ measurements. Second, it will monitor solar Copyright© 2010 by the Japan Society for Aeronautical and Space Sciences 1and ISTS. All rights reserved. Tk_7 Trans. JSASS Aerospace Tech. Japan Vol. 8, No. ists27 (2010) winds, which is crucial to understand present escape processes or fluxes as well as their dependencies on the external condi- Arrival 1.0e+08 Dec 2018 tions. 2.1.3. Landers for internal structure and surface envi- ronment 0.0e+00 MELOS surface landers will scope several scientific topics such as mass spectrometry, seismology, geochemistry, thermal Y [km] activity, crater chronology and atmospheric electricity. They Launch -1.0e+08 will carry several science packages for measurement of these May 2018 properties. It is noteworthy that we are planning networked exploration by several landers distributed in the wide area on -2.0e+08 Mars Mars. They can benefit from network science with ESA’s Mars Earth S/C NEXT mission. -1.0e+08 0.0e+00 1.0e+08 2.0e+08 3.0e+08 Accumulation for surface science and landing technologies X [km] through recent ambitious missions such as Hayabusa (JAXA’s Fig. 2. The transfer orbit from Earth to Mars in the inertial ecliptic asteroid sample return mission)8) and its follow-ons, and coordinate system (case 1, launched in 2018). SELENE-2 (JAXA’s lunar lander)9) will be of great use for Mars landers. Experience of reentry into the atmosphere and knowledge of aerodynamics cultivated through Hayabusa’s 2.0e+08 reentry will be also inherited. 3. Orbit Sequence 1.0e+08 3.1. Launch opportunities We are planning the launch of the all spacecraft in the late Launch 2010’s by a single H-IIA rocket, aiming data acquisition under May 2018 conditions of high solar activity expected to be maximized 0.0e+00 Y [km] Sun around 2022. There will be several launch windows toward Mars around 202210). In one case, for example, the spacecraft will depart Earth in May 2018 and arrive at Mars in December 2018, after a half revolution around the sun. The total delta-V -1.0e+08 for the departure and the arrival is 5.75 km/s. In other case, the Arrival departure from Earth will be in October 2017, and the arrival at Dec 2018 Mars Mars will be February in 2020. Though it requires one and a S/C -2.0e+08 half revolutions around the sun, the total delta-V is 5.59 km/s, 0.0e+00 1.0e+08 2.0e+08 3.0e+08 less than that for the former case. Figs. 2-5 show transfer orbits X [km] from Earth to Mars in the inertial ecliptic coordinate system Fig. 3. The transfer orbit from Earth to Mars in the Sun-Earth fixed (J2000) and Sun-Earth fixed ecliptic coordinate system. ecliptic coordinate system (case 1, launched in 2018). 3.2. Orbital design around mars After the cruising phase around the sun, the spacecraft is 3.0e+08 injected to the orbit around Mars. Two orbiters are then 2.0e+08 1.0e+08 Launch Mars Exploration Oct 2017 with Lander-Orbiter 0.0e+00 Synergy (MELOS) Y [km] -1.0e+08 -2.0e+08 Arrival Feb 2020 Mars Earth S/C -3.0e+08 -3.0e+08-2.0e+08-1.0e+08 0.0e+00 1.0e+08 2.0e+08 3.0e+08 X [km] Fig. 4. The transfer orbit from Earth to Mars in the inertial ecliptic Fig. 1. Concept of MELOS. coordinate system (case 2, launched in 2017). 2 Tk_8 N. OGAWA et al.: Preliminary Mission Analysis and Orbit Design for Next Mars Exploration 3.0e+08 Atmospheric Escape Orbiter 2.0e+08 Arrival Feb 2020 1.0e+08 Landers Meteorological Launch Orbiter Oct 2017 0.0e+00 Y [km] Sun -1.0e+08 Fig. 6. Orthogonal constellation required for two orbiters. -2.0e+08 Mars Table 1. Examples of orbital elements of the two orbiters. S/C -3.0e+08 -3.0e+08-2.0e+08-1.0e+08 0.0e+00 1.0e+08 2.0e+08 3.0e+08 Meteorological Atmospheric X [km] Orbiter Escape Orbiter Fig. 5. The transfer orbit from Earth to Mars in the Sun-Earth fixed Apo. Alt. 6.9 Rm 7,000 km ecliptic coordinate system (case 2, launched in 2017). Peri. Alt. 300 km 300 km Incl. 8.67 deg 102.09 deg Period 16 hrs (3 revs in 2 5 hrs separated, and several maneuvers are performed to establish the days) constellation appropriate for the combined observation of Mars. RAAN Rate 0.4142 deg/day 3.2.1. Mission requirements for orbits around mars As mentioned above, simultaneous observation of the Martian atmosphere by two orbiters is one of the most important 3.2.2. Mars orbit insertion and initial orbit phase goals in the MELOS mission. The atmospheric escape orbiter After about a 7-month voyage at shortest along the Mars has to be in a low-altitude polar orbit for in-situ and local transition orbit, the spacecraft will be inserted into a Mars observation of the Martian atmosphere. The meteorological orbit by an orbit maneuver engine (OME) mounted on the orbiter needs to capture global images from the distance of atmospheric escape orbiter, with the initial periapsis altitude of several radii of Mars.