Is there life on the satellite of Jove - Europe? Does its ice shell really hide liquid ocean of salted water? Not only NASA and ESA, but also Roscosmos also looks for answers to these question. In order to carry out Russian mission to Jove SINP scientists solve one of the basic problems - what are the ways for diminishing of the level of radiation accumulation onboard pilotless spacecraft in order to extend its lifetime.
Mikhail Podzolko, scientist of SINP MSU, one of the developersof Jovian mission, told us: "Radiation dose accumulated onboard a spacecraft protected with a shielding of 8 mm Al at Europa's orbit will be about 1 million rad. As a comparison such radaition dose will be accumulated at the orbits of the Earth's satellites GLONASS even over twice thinner shielding during 25 years. Such level of radiation is extremely high even for electronics of "the military class"."
Radiation doses of the spacecraft protected with radiation shielding of different thickness depending on the distance from Jove in equatorial plane. At the orbit of Europa behind the shielding of 1 mm Al radiation dose is about 100 thousands rad/day, behind 4 mm Al - 30 thousands rad/day, behind 8 mm Al - 15 thousands rad/day, behind 2 cm Al - 3.5 thousands rad/day. At Ganymede's orbit doses are 50-100 times lower.
If life exists in the subglacial ocean of Europa, it is protected from external radiation by ice up to 10 km thick. There is a supposal that some substance, probably containing signs of organic life, can penetrate to the surface of the satellite through the crashs in ice, which appear due to the inner tidal currents formed by powerful gravitation of Jove.
In order to study Europa and other Jovian satellites, Russian scientists started the development of "Laplace" mission, named after great scientist developed detailed theory of Jovian satellites' movement. Currenty foreign space agencies also develop new projects of flights to Jove. Within the frames of the recent variant of NASA mission «Europa Clipper» it is supposed to organize several dozens of spacecraft's flights near Europa. ESA scientists are concentrated on the project JUICE (Jupiter Icy Moon Explorer) - mission to another Jovian satellite, Ganymede.
One of the variants of Russian mission suggests launching of an unmanned spacecraft to the orbit around Europa and landing to Europa during this and following missions (for comparison variant of landing to Ganymede is also under development). The project is developed by collaboration consisted of scientists from the Space Research Institute RAS, S.A. Lavochkin Scientific and Production Association, D.V. Skobeltsyn Institute of Nuclear Physics of MSU (SINP MSU), M.V. Keldysh Institute of Applied Mechanics RAS and other institutes.
There are regions, called radiation belts, around Jove, like around the Earth. They are filled with high-energy charged particles, mainly protons and electrons, captured by the planet's magnetic field. Fluxes of charged particles in the Jovian radiation belts are hundreds times higher than near the Earth. Besides, in contrary to the Earth, in the Jovian radiation belts there are significant fluxes of electrons of very high “relativistic” energy (up to 100 MeV), i.e. whose speed is close to the light velocity.
Inside the Jovian radiation belts there are orbits of three big satellites – Io, Europa and Ganymede. Radiation situation varies from one satellite to another, depending on the distance from the planet – nearer is more dangerous. Io is the nearest to Jove satellite, Europa is a bit farer from it, and Ganymede is at the greater distance. As we can see the planned flight to Europa is high radiation risk bearing.
It is worth mentioning that NASA spacecraft “Galileo” became the first artificial satellite of Jove. Its flight in Jovian system included 35 eccentric circuits and lasted from 1995 to 2003. Totally the spacecraft spent about 2 months inside radiation belts of the planet, and accumulated radiation dose over 650 thousands rad behind the shielding of 8 mm (or 2.2 g/cm2) Al. When approaching to Jove the spacecraft studied its satellites – Callisto, Ganymede, Europa, Io, Barnard's satellite.
So, what is the way for minimization of radiation risk for a spacecraft? It was found out that in part high-energy charged particles' fluxes near Europa are shielded by Europa itself. “By means of simulation of trajectories of high-energy chanrged partciles' movement in the magnetic field of Jove relating to Europa we succeeded in recognizing the areas of low radiation at the surface of Europa and at the orbit around it”, - Mikhail Podzolko told us.
High-latitude areas and “front” side of Europa regarding direction of its movement along the orbit are found to be the most safe places for spacecraft's landing. There radiation dose is about 10 times lower. For an orbital spacecraft at the altitude of 100 km over the surface of Europa an orbit with high inclination is the most safe. At this orbit the spacecraft will accumulate radiation dose of about one forth of maximum, i.e. about 250 kilorad during 2 months with the same shielding as “Galileo”. Russian spacecraft “Laplace” will be equipped with shielding of double thickness, and it will additionally decrease radiation load.
It is necessary to take into account that the spacecraft will not enter an orbit around Europa directly after arrival to Jove – it would need great amount of fuel for breakdown. First it will enter an eccentric orbit around Jove, then it will make several circuits passing near Ganymede and, probably, Callisto, using their gravitation for gradual slowdown. Total time for gravitation evolutions can be over one year. During this time due to the paasing through Jovian radiation belts the spacecraft will be also exposed to significant radiation danger. In order to diminish both radiation load and energy consumption the scientists of SINP MSU, IKI RAS, IAM RAS and other developers solve a complicated problem of trajectory's optimization.
Mikhal Podzolko told us: «Mission to the satellite of Jove, Europa, changes from “egg-dance” to complicated, but executable task». Start of Jovian mission is planned for 2026.