Messenger and New Horizon Planetary Missions

MESSENGER and New Horizon Planetary Missions

Planetary or Interplanetary missions are trips through outer space involving several planets. Currently, all missions operated by man have been in Earth's orbit or on the moon. However, NASA, ISRO, the Soviet Union, and the European space agency have performed several robotic interplanetary missions. To decide on the planetary missions to approve or disapprove is always a daunting problem since missions’ goals and requirements are always different. A good example is the MESSENGER mission and the New Horizons journey to Pluto. The two current missions have closely related goals and scientific objectives. This paper will compare the two planetary missions by focusing on their orbital plans, fuel sources, and scientific objectives. The paper will further explore their significance in NASA's overall solar system exploration objectives.

MESSENGER Mission

Launched on 3ard August 2004, MESSENGER, NASA's robotic space probe, managed to orbit the planet Mercury until 2015, and its cost was 450 million dollars to launch. The planetary mission studied the chemical composition of the planet Mercury, magnetic field, and geology. The acronym MESSENGER stood for “MERcury Surface, Space Environment, GEochemistry, and Ranging." The name referenced the Roman mythology’s messenger god Mercury. Its path was involving a complex flyby series (NASA, 2020a). The MESSENGER spacecraft flew once by Earth, twice in Venus, and finally three times in Mercury. That allowed it to decelerate relatively to Mercury, minimizing the fuel consumption. It became the first spacecraft to enter Mercury orbit by March 2011. In 2012, the MESSENGER completed its main mission. However, following two extensions of the mission, the spacecraft deorbited by using its last maneuvering propellant, impacting the Mercury surface in April 2015. MESSENGER's stay in Mercury orbit yielded important data that included the characteristics of Mercury's magnetic field patterns. Besides, its stay led to the discovery of water ice at Mercury's North Pole, as was previously suspected based on Earth's radar data.

Before its launching, the MESSENGER mission passed through a critical design review in four days. During the review, the project advisory panel, together with the NASA assessment team, took time to examine every fine detail of the mission and the space craft's design. Fortunately, both teams confirmed that the design was meeting the mission's engineering and scientific requirements. Its key design features were to deal with the intense heat at Mercury since the sun is almost eleven times brighter at Mercury than it is on Earth's surface. That would mean that Mercury's temperature could reach 450 degrees Celsius. That required the MESSENGER instruments to be shielded from such overheating in addition to limiting the passage of the spacecraft over the hottest parts of the surface. Putting these factors into consideration, two teams approved the mission launch. Therefore, NASA selected MESSENGER to be the seventh mission in its lower cost, highly focused space science investigations innovative discovery programs.

The MESSENGER mission was designed primarily to study the characteristics of Mercury and the environment from the orbit around Mercury (Genova et al., 2018) . Besides, there are also several scientific objectives for the mission. These include characterizing the Mercury surface’s chemical composition, studying Mercury's geological history, and elucidating the global magnetic field nature. The global magnetic field is an important factor for scientists since life on Earth was initially developed and is continually sustained under the protection of these magnetic environments. Therefore, knowing much about the magnetosphere is important since it helps shield people's home planet from cosmic particle and solar radiation and erosion, shielding the atmosphere's erosion by the solar wind. Furthermore, other scientific mission objectives were to determine the state and the core's size, determine the volatile materials at the poles, and study the nature Mercury's exosphere. 

NASA's MESSENGER spacecraft significantly contributed to NASA's overall solar system exploration goals. For instance, among its accomplishments, it determined the surface composition of planet Mercury, discovered the internal magnetic field within Mercury, and also helped in revealing Mercury's geological history. Besides, the mission verified that Mercury's polar deposits are dominant water ice. In the later years, the MESSENGER mission provided tangible evidence of the volcanic activity on the surface of mercury, adding to the pre-existing evidence of liquid iron planetary core. Another benefit that NASA got from the mission was its construction of a more detailed and accurate Mercury maps, which NASA uses till date. NASA uses these discoveries to help achieve its targeted solar system exploration goals.

In 2014, MESSENGER was in its expected last period of orbital decay after running out of course adjustment propellant. The need to explore its remaining Helium gas supply led to its extended operation by several weeks. The helium gas was used in pressurizing its propellant tank as reaction mass. Furthermore, according to NASA Solar System Exploration (2020a), the main propulsion for MESSENGER was availed by the 645-newton unit, 317 sec. Specific impulse bipropellant large velocity assist thruster. Besides, it was also noted that the spacecraft was designed to have the ability to carry approximately 600 kg of propellant and also a Helium pressurizer for the large velocity assistant.

New Horizon Mission

New Horizon was also an interplanetary spacecraft that was part of NASA's new frontiers program. According to NASA Solar System Exploration (2020b), the mission was launched in January 2006 by an Atlas V rocket directly into space with an Earth-and-Solar escape trajectory velocity of approximately 16000 meters per second. Its primary mission was to do a flyby Pluto system study by 2015. Besides, its secondary mission was to study the Kuiper Belt objects (KBOs) in the following decade. New Horizon's mission is the 5th spacecraft to achieve the escape velocity needed to leave the solar system.

New Horizon's mission cost was approximately 700 million dollars over fifteen years (from 2001 to 2016). The cost included developing spacecraft and instruments, data analysis, and the cost of public education on the same. New Horizon's goal was to understand the Plutonian system formation, Kuiper Belt formation, and help understand the early solar system formation (Stern et al., 2018). The mission collected data from the surface, atmosphere, environment, and interior parts of Pluto and its moon. These data are targeted at knowing Pluto's atmosphere and how it behaves. The data will also help understand Pluto's surface looks and some sizeable geological structures. Besides, the mission had some scientific objectives. Some of these are to map Pluto and Charon's surface composition, identify the geological and morphological characteristics of Pluto and Charon, and identify the traits of Pluto's neutral atmosphere and how it escapes. Additionally, some other scientific objectives include searching for an atmosphere around Charon, rings and additional satellites around Pluto, and mapping the temperature on Pluto and Charon's surface, and conducting the same investigation on one or more objects of the Kuiper Belt.

New Horizon carried with it a radioisotope thermoelectric generator that is cylindrical. The generator provided approximately 250 watts of power during its launch. That was set to decay to 200 watts by the time it encounters Pluto. The spacecraft had both spins stabilize, and a three-axis stabilize modes, which controlled hydrazine monopropellant. A 77-kilogram tank found in the inner side provided an excess velocity of 290 meters per second. The spacecraft used Helium to supply pressure with an elastomeric diaphragm that helped in expulsion.

By April 2015, Pluto's pictures started revealing distinct features with weekly increasing details into the approach. However, a concern arose in July the same year when New Horizon was forced to enter a safe mode as a result of its command sequence timing flaw. Fortunately, the spacecraft returned to regular scientific operation after three days. Data from New Horizon was later used to help inconclusively answer one of the essential mysteries about Pluto's size. The data concludes that Pluto is approximately 1470 miles in diameter (NASA Solar System Exploration, 2020b). That conclusion was slightly larger than estimations made before. Additionally, the data indicated that its moon Charon is approximately 750 miles in diameter.

The New Horizon mission was essential for NASA's main solar system exploration goal. For instance, the data from the spacecraft showed that Pluto and its satellites were more complex than the scientists could have imagined. The scientists were therefore surprised by the current activity degree on the surface of Pluto. Pluto gives evidence of enormous atmospheric pressure changes. The planet Pluto had possibly run or even stagnant volatiles of liquids on its surface in the past. Hints are that today Pluto could be having internal water ice currently. Furthermore, the New Horizon mission helps NASA better understand the world at the solar system's age by making the first dwarf planet Pluto reconnaissance (NASA, 2020b). It makes that possible by venturing more in-depth into the distant and mysterious Kuiper Belt, a solar system relic.

According to NASA Solar System Exploration (2020b), after the New Horizon encounter with Pluto, mission planners started to redirect the New Horizons for the beginning of 2019 flyby of Ultima Thule, a Kuiper Belt object that is approximately four billion miles from the Earth. The scientists implemented four-course corrections in the fall of 2015. The encounter's main goal was to study the Ultima Thule object's surface geology, measure its surface temperature, search for activity signs, measure its mass, and detect any satellites or rings around the item. By 2017, the spacecraft was on its way to the targeted object, halfway from Pluto. That indicates a significant contribution that the New Horizon mission contributed from its first time launch on the effort to explore the solar space.

Comparison

New Horizon seems to yield a higher significance than MESSENGER. After helping the scientists answer some of Pluto's complex issues and its surroundings that they could not understand, the New Horizon further helped them identify the existence of another object that then called for further exploration. On the other hand, the MESSENGER mission only ended after studying planet Mercury. Even though they had closely related main goals, the New Horizon mission further paved the way for more solar space exploration. Furthermore, New Horizon had several scientific objectives compared to the MESSENGER mission. However, the two missions were beneficial to NASA since they played an essential role in helping NASA explore the solar system space. Additionally, the obtained data from these two missions were necessary to plan other new missions intended to explore the planets. Concerning their cost, MESSENGER incurred approximately 450 million dollars to be launched while New Horizon incurred about 700 million dollars to launch. 

Conclusion

The above premises shows that one must consider several factors to decide whether to approve or disapprove any planetary mission's planned to be launching. MEESENGER mission portrayed several essential benefit for the NASA’s main solar system and exploration goals compared to the New Horizon mission. However, each mission’s scientific objectives were closely related. Therefore, it is crucial to focus on the contribution the mission will bring to NASA’s solar exploration goals rather than the individual mission’s goals to decide on which mission to launch.

References

Genova, A., Mazarico, E., Goossens, S., Lemoine, F., Neumann, G., Smith, D., & Zuber, M. (2018). Solar system expansion and strong equivalence principle as seen by the NASA MESSENGER mission.  Nature Communications ,  9 (1). https://doi.org/10.1038/s41467-017-02558-1

NASA Solar System Exploration. (2020a).  In Depth | MESSENGER – NASA Solar System Exploration . NASA Solar System Exploration. Retrieved 1 November 2020, from https://solarsystem.nasa.gov/missions/messenger/in-depth/ .

NASA Solar System Exploration. (2020b). In Depth | New Horizons – NASA Solar System Exploration . NASA Solar System Exploration. (2020). Retrieved 1 November 2020, from https://solarsystem.nasa.gov/missions/new-horizons/in-depth/.

NASA. (2020a).  MESSENGER . NASA. Retrieved 1 November 2020, from https://www.nasa.gov/mission_pages/messenger/main/index.html .

NASA. (2020b).  New Horizons . NASA. Retrieved 1 November 2020, from https://www.nasa.gov/mission_pages/newhorizons/main/index.html .

Stern, S., Weaver, H., Spencer, J., & Elliott, H. (2018). The New Horizons Kuiper Belt Extended Mission.  Space Science Reviews ,  214 (4). https://doi.org/10.1007/s11214-018-0507-4