BepiColombo

BepiColombo
Operator European Space Agency, Japan Aerospace Exploration Agency
Major contractors For ESA: EADS Astrium
For JAXA: ISAS
Mission type Two orbiters
Launch date April 2018 (planned[1]) from Guiana Space Center[2]
Launch vehicle Ariane 5
Mission duration >1 year science phase
Flyby of Earth, Venus, and Mercury
Satellite of Mercury
Orbital insertion date 1 January 2024 (planned)
COSPAR ID BEPICLMBO
Homepage ESA JAXA ISAS
Mass at launch: 4,100 kg[3]
MPO: 1,150 kg
MMO: 275 kg[3]
Power MPO: 150 W
MMO: 90 W
Orbital elements
Inclination Polar orbit (90°) both elements
Apoapsis MPO: 1,508 km
MMO: 11,824 km
Periapsis MPO: 400 km
MMO: 400 km
Orbital period MPO: 2.3 h
MMO: 9.3 h

BepiColombo is a joint mission of the European Space Agency (ESA) and the Japan Aerospace eXploration Agency (JAXA) to the planet Mercury.[4] The mission comprises two satellites to be launched together: the Mercury Planetary Orbiter (MPO) and the Mercury Magnetospheric Orbiter (MMO). The mission will perform a comprehensive study on Mercury, including its magnetic field, magnetosphere, interior structure and surface. It is scheduled to launch in April 2018.[1] The mission was approved in February 2007 as part of the Cosmic Vision programme.[5]

Mission

BepiColombo is named after Giuseppe (Bepi) Colombo (1920–1984), scientist, mathematician and engineer at the University of Padua, Italy, who first implemented the interplanetary gravity-assist maneuver during the 1974 Mariner 10 mission, a technique now commonly used by planetary probes.

The mission involves three components:[6]

The prime contractor for ESA is Airbus Defence and Space.[7] ESA is responsible for the overall mission, the design, development assembly and test of the propulsion and MPO modules, and the launch. The two orbiters are planned to be launched together on an Ariane 5 launch vehicle in April 2018. The spacecraft will have a six-year interplanetary cruise to Mercury using solar-electric propulsion (ion thrusters) and gravity assists from Earth, Venus and eventual gravity capture at Mercury.[3] ESA's Cebreros 35-metre ground station is planned to be the primary ground facility for communications during all mission phases.

Planned orbits for MMO and MPO satellites, the two probes of the BepiColombo mission.

Arriving in Mercury orbit on 1 January 2024, MMO and MPO satellites will then separate and observe Mercury in collaboration for 1 year, with a possible 1-year extension.[3] The orbiters will be equipped with scientific instruments provided by various European countries and Japan. It will characterise the huge liquid iron core (¾ of the planet radius) and will complete gravity and magnetic field mappings. Russia will provide a gamma ray and neutron spectrometers to verify the existence of water ice in polar craters that are permanently in shadow from the Sun's rays.

Mercury is too small and hot for its gravity to retain any significant atmosphere over long periods of time; it does have a "tenuous surface-bounded exosphere"[8] containing hydrogen, helium, oxygen, sodium, calcium, potassium and others. Its exosphere is not stable; atoms are continuously lost and replenished from a variety of sources, and the mission will also study its composition and dynamics, including generation and disappearance.

Objectives

The main objectives of the mission are:[3][2]

Mission design

The spacecraft will have a 7-year interplanetary cruise to Mercury using solar-electric propulsion and eight gravity assists, flying past the Earth and Moon in July 2018, Venus in 2019 and 2020, and five Mercury flybys between 2020 and 2023.[10]

The spacecraft will leave the Earth with an hyperbolic excess velocity of 3.475 km/s. After two years, it returns to Earth to perform a gravity-assist manoeuvre and is deflected towards Venus. Two consecutive Venus flybys reduce the perihelion to Mercury distance with almost no need for thrust. A sequence of five Mercury flybys will lower the relative velocity to 1.76 km/s. Four final thrust arcs further reduce the relative velocity to the point where Mercury will capture the spacecraft on 1 January 2024 into polar orbit; the spacecraft then will be lowered using chemical thrusters.[10][11]

The BepiColombo heliocentric cruise will use gravity assists around the Earth, Venus and Mercury and will last 6 years

The planned mission schedule is:[3]

Date Event
April 2018[1] Launch
25 July 2019 1st Venus flyby
20 May 2020 2nd Venus flyby
9 April 2021 1st Mercury flyby
27 March 2022 2nd Mercury flyby
16 December 2023 3rd Mercury flyby
24 January 2024 4th Mercury flyby
18 December 2024 Mercury orbit insertion
27 March 2025 in final science orbit
1 May 2026 end of nominal mission

Components

Propulsion: Mercury Transfer Module (MTM)

Mercury Transfer Module in ESTEC before stacking

The Mercury Transfer Module is at the base of the 'stack' and provides propulsion for Earth-Mercury transfer and to slow down its approach to Mercury. It carries no significant scientific instruments.

The Transfer Module is equipped with two propulsion systems: a solar electric ion drive engine and a standard chemical propulsion system which is bipropellant using MMH/MON3. The CPS will be used for Earth escape and then it will be pyrotechnically isolated, and the solar electric ion engine will take over for the cruise phase. The twin 'QinetiQ T6' ion thrusters operate at maximum combined throttle of 290 mN.[12] The MTM supplies electrical power for the two hibernating orbiters, as well as for its solar electric propulsion system.[13]

The spacecraft will be propelled in cruise by a form of ion drive dubbed solar electric propulsion, which has a very high specific impulse and very low thrust. Unlike a chemical rocket which fires for several seconds, it will keep propelling the craft for years, building up far more speed per mass of fuel as the years go by. This will be ESA's first mission outside the Earth–Moon system using such a form of propulsion. This drive will actually push against the direction of travel, instead of with it; the spacecraft will be falling toward the Sun, accelerated by its gravity, and will have to slow down enough to eventually enter Mercury's orbit. Moments before Mercury orbit insertion, the MTM will be jettisoned from the spacecraft stack.[13]

Mercury Planetary Orbiter (MPO)

Mercury Planetary Orbiter in ESTEC before stacking
Radio testing of BepiColombo orbiter

The Mercury Planetary Orbiter will have a mass of 1,150 kilograms (2,540 lb) and will have its sides covered with solar cells providing 150 W at perihelion. A radiator with an area of 1.5 m2 is mounted on one side to provide thermal control. The radiator is always pointed away from the Sun and is protected from planetary IR heat with a 3.4 m2 shield. High efficiency insulation is also used. The configuration and thermal design will provide a stable temperature for internally mounted instruments.

A high-temperature resistant 1.0 m diameter high-gain antenna is mounted on a short boom on the zenith side of the spacecraft. Communications will be on the X and Ka band with an average bit rate of 50 kbit/s and a total data volume of 1550 Gb/year. After the arrival, the MMO will be separated by spin-ejection, will be 3-axis stabilized and nadir pointing. Navigation is facilitated by 3 star sensors. After its release in Mercury orbit, the MPO will be operated by Sagamihara Space Operation Center using Usuda Deep Space Center's 64 m antenna located in Nagano, Japan.[14]

Scientific payload

The scientific payload in the Mercury Planetary Orbiter consist of eleven instruments:[14][15]

Mercury Magnetospheric Orbiter (MMO)

Mercury Magnetospheric Orbiter in ESTEC before stacking

The Mercury Magnetospheric Orbiter has the shape of a short octagonal cylinder, 180 cm long from face to face and 90 cm high.[2][16] It has a total mass of 285 kg (628 lb), including a 45 kg scientific payload.[2][17]

The MMO is spin stabilized at 15 rpm with the spin axis perpendicular to the equator of Mercury and it will enter polar orbit at an altitude of 400 km × 12,000 km - outside the MPO's.[17] The top and bottom of the octagon act as radiators with louvers for active temperature control. The sides are covered with solar cells which provide 90 W. Communications with Earth will be through a 0.8 m diameter X band phased array high-gain antenna and two medium-gain antennas operating in the X band. Telemetry will return 160 Gb/year, about 5 kbit/s over the lifetime of the spacecraft, which is expected to be greater than one year. The reaction and control system is based on cold gas thrusters.

Scientific payload

The Mercury Magnetospheric Orbiter (MMO), being developed and built mostly by Japan, will carry five groups of instruments with a total scientific payload mass of 40 kg:[2][14]

Mercury Surface Element

The Mercury Surface Element (MSE) was cancelled in 2003 due to budgetary constraints.[5] At the time of cancellation, MSE was meant to be a small (44 kg) lander designed to operate for about one week on the surface of Mercury.[18] Shaped as a 0.9 m diameter disc, it was designed to land at a latitude of 85° near the terminator region. Braking maneuvers would bring the lander to zero velocity at an altitude of 120 metres at which point the propulsion unit would be ejected, the airbags inflated, and the module would fall to the surface with a maximum impact velocity of 30 m/s. Scientific data would be stored onboard and relayed via a cross-dipole UHF antenna to either the MPO or MMO. The MSE would have carried a 7 kg payload consisting of an imaging system (a descent camera and a surface camera), a heat flow and physical properties package, an alpha particle X-ray spectrometer, a magnetometer, a seismometer, a soil penetrating device (mole), and a micro-rover.[19]

See also

References

  1. 1 2 3 "BEPICOLOMBO - Fact Sheet". ESA. 20 April 2016. Retrieved 2016-05-03.
  2. 1 2 3 4 5 Staff (2008). "MM - BepiColombo". Japan Aerospace Exploration Agency. Retrieved 2014-02-07.
  3. 1 2 3 4 5 6 "ESA Science & Technology: Fact Sheet". ESA. Retrieved April 5, 2015.
  4. ↑ Amos, Jonathan (2008-01-18). "European probe aims for Mercury" (web). The European Space Agency (Esa) has signed an industrial contract to build a probe to send to the planet Mercury. BBC News. Retrieved 2008-01-21.
  5. 1 2 "Europe Scaling Back". NASA News & Events (NASA). 6 November 2003. Retrieved 2014-02-07.
  6. ↑ Hajime Hayakawa: BepiColombo Mercury Magnetospheric Orbiter (MMO)
  7. ↑ "BepiColombo To Enter Implementation Phase". ESA. 26 Feb 2007.
  8. ↑ Domingue DL, Koehn PL, et al. (2009). "Mercury's Atmosphere: A Surface-Bounded Exosphere". Space Science Reviews 131 (1–4): 161–186. Bibcode:2007SSRv..131..161D. doi:10.1007/s11214-007-9260-9.
  9. ↑ "BepiColombo - Testing general relativity". ESA. 4 July 2003. Retrieved 2014-02-07.
  10. 1 2 "NASA Data Center: BepiColombo". 26 August 2014. Retrieved 2015-04-06.
  11. ↑ Staff. "BepiColombo Mission Operations - Getting to Mercury". ESA. Retrieved 2014-02-07.
  12. ↑ Clark, Stephen D. (October 6–10, 2013). "BepiColombo Electric Propulsion Thruster and High Power Electronics Coupling Test Performances". 33rd International Electric Propulsion Conference.
  13. 1 2 Staff (20 October 2011). "Mercury Planetary Orbiter - spacecraft". European Space Agency. Retrieved 2014-02-06.
  14. 1 2 3 "MMO (Mercury Magnetospheric Orbiter) : Objectives". JAXA. 2011. Retrieved 2014-02-07.
  15. ↑ Staff (15 January 2008). "The Mercury Planetary Orbiter - Instruments". European Space Agency. Retrieved 2014-02-06.
  16. ↑ H. Yamakawa; H. Ogawa; Y. Kasaba; H. Hayakawa; T. Mukai; M. Adachi (2004). "Current status of the BepiColombo/MMO spacecraft design". Advances in Space Research 33 (12): 2133–2141. Bibcode:2004AdSpR..33.2133Y. doi:10.1016/S0273-1177(03)00437-X.
  17. 1 2 "Mercury Exploration Project "BepiColombo"" (PDF). Japan Aerospace Exploration Agency (JAXA). JAXA. 2014. Retrieved 2015-04-06.
  18. ↑ "BepiColombo". ESA. NASA. 2004. Retrieved 2014-02-07.
  19. ↑ "BepiColombo's lander". ESA. 2001. Retrieved 2014-02-07.

External links

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