Artist impression of ESAs EnVision objective at Venus. EnVision needs to aerobrake through Venus atmosphere. Credit: ESA/VR2Planets/DamiaBouic
EnVisions predecessor spacecraft, Venus Express, carried out speculative aerobraking throughout the final months of its objective in 2014, gathering important data on the method. Aerobraking was used operationally for the first time in 2017 by ESAs ExoMars Trace Gas Orbiter (TGO) to decrease its orbit around the Red Planet over an 11 month duration.
Samples of candidate products for various parts of the EnVision spacecraft went through simulated aerobraking conditions consisting of orbital-velocity atomic oxygen and heat flux utilizing ESAs LEOX facility. Credit: ESA
To start with, the gravity of Venus is about 10 times greater than that of Mars. Accordingly, EnVision has to target a lower aerobraking regime, resulting in an aerobraking phase twice as long.
” On top of that, we are also going to be much closer to the Sun, experiencing around double the solar intensity of Earths, with the thick white clouds of the environment reflecting a great deal of sunshine directly back to space, which additionally requires to be taken into consideration. On top of all that, we understood we had to reckon with another factor over the thousands of orbits we imagine, formerly just experienced in low Earth orbit: highly-erosive atomic oxygen.”
This specific phenomenon stayed unidentified during the very first decades of the space age. It was only when early Space Shuttle flights returned from low orbit in the early 1980s that engineers received a shock: the spacecrafts thermal blankets had been badly eroded.
The offender turned out to be extremely reactive atomic oxygen– private atoms of oxygen at the fringes of the atmosphere, the outcome of standard oxygen molecules of the kind found just in the air being disintegrated by effective ultraviolet radiation from the Sun. Today, all objectives listed below about 1,000 km (~ 620 miles) need to be created to resist atomic oxygen, such as Europes Earth-watching Copernicus Sentinels or any hardware constructed for the International Space Station.
Area Shuttle Endeavours tail aglow with atomic oxygen, as seen during the STS-99 objective in February 2000. Extremely erosive atomic oxygen turned out to gnaw at unprotected thermal blankets during early Shuttle objectives, up until countermeasures were put in location. Credit: NASA
Spectral observations by previous Venus orbiters of airglow above the planet confirm that atomic oxygen is widespread at the top of the Venusian environment too, which is more than 90 times thicker than Earths surrounding air.
Thomas states: “The concentration is rather high, with one pass it doesnt matter a lot but over thousands of times it starts to collect and ends up with a level of atomic oxygen fluence we have to take account of, comparable to what we experience in low-Earth orbit, but at higher temperature levels.”
LEOX produces atomic oxygen at energy levels that are comparable to orbital speed– 7.8 km/s– to mimic the space environment as carefully as possible. With a purple flash each time the laser is fired, the oxygen is transformed into a hot plasma whose rapid growth is channeled along a cone-shaped nozzle. It then dissociates to form an extremely energetic beam of atomic oxygen.
The EnVision group relied on an unique European facility specifically developed by ESA to mimic atomic oxygen in orbit. The Low Earth Orbit Facility, LEOX, is part of the Agencys Materials and Electrical Components Laboratory, based at ESAs ESTEC technical center in the Netherlands.
ESA materials engineer Adrian Tighe discusses: “LEOX generates atomic oxygen at energy levels that are equivalent to orbital speed. Cleansed molecular oxygen is injected into a vacuum chamber with a pulsing laser beam focused onto it. This transforms the oxygen into a hot plasma whose rapid expansion is directed along a conical nozzle. It then dissociates to form a highly energetic beam of atomic oxygen.
EnVision candidate materials samples exposed to atomic oxygen in ESAs LEOX generator. Credit: ESA
” To work reliably, the laser timing must remain precise to millisecond scale, and directed to a precision measured in thousandths of a millimeter, throughout the four-month period of this existing test project.
” This isnt the first time that the center has been utilized to mimic an extraterrestrial orbital environment– we have actually previously performed atomic oxygen testing on candidate solar variety products for ESAs Juice objective, since telescopic observations recommend atomic oxygen will be found in the atmospheres of Europa and Ganymede. For EnVision the increased temperature throughout aerobraking presents an additional challenge, so the facility has been adapted to mimic this more extreme Venusian environment.”
EnVision prospect materials sample observed by infrared camera. The samples are also heated up as they are exposed to atomic oxygen by the LEOX generator to much better imitate aerobraking through the atmosphere of Venus. Credit: ESA
A series of products and coatings from different parts of the EnVision spacecraft, consisting of multi-layer insulation, antenna parts and star tracker components are positioned within a plate to be exposed to the purple-glowing LEOX beam. At the very same time this plate is being heated to simulate the anticipated thermal flux, up to 350 ° C 662 ° F).
Thomas includes: “We wish to examine that these parts are resistant to being deteriorated, and likewise preserve their optical residential or commercial properties– indicating they do not break down or darken, which might have ripple effects in terms of their thermal habits, due to the fact that we have delicate clinical instruments that must maintain a set temperature. We also require to prevent flaking or outgassing, which cause contamination.”
This present test project belongs to a larger panel looking into EnVision aerobraking, consisting of the usage of a Venus climate database developed from previous mission results to approximate the local variability of the worlds environment to set safe margins for the spacecraft.
The results of this test project are anticipated at the end of this year.
The EnVision mission to Venus will explore why Earths closest neighbor is so various. Credit: NASA/ JAXA/ ISAS/ DARTS/ Damia Bouic/ VR2Planets
About EnVision
EnVision is an ESA-led objective in collaboration with NASA, supplying its Synthetic Aperture Radar instrument, VenSAR, and Deep Space Network support for crucial mission phases. EnVision will utilize a range of instruments to carry out holistic observations of Venus from its inner core to upper atmosphere to better comprehend how Earths closest neighbor in the Solar System progressed so in a different way.
EnVision has been chosen by ESAs Science Program Committee as the 5th Medium-class mission in the Agencys Cosmic Vision plan, targeting a launch in the early 2030s.
EnVision, a project of the European Space Agency (ESA), is a mission to Venus that will perform optical, spectral and radar mapping of Earths sibling planet. Artist impression of ESAs EnVision objective at Venus. Space Shuttle Endeavours tail aglow with atomic oxygen, as seen throughout the STS-99 objective in February 2000. ESA products engineer Adrian Tighe discusses: “LEOX creates atomic oxygen at energy levels that are comparable to orbital speed. The samples are also heated as they are exposed to atomic oxygen by the LEOX generator to much better simulate aerobraking through the environment of Venus.
EnVision aerobraking in Venus environment. Credit: ESA/ Paris Observatory/ VR2Planets/ Damia Bouic
EnVision, a project of the European Space Agency (ESA), is a mission to Venus that will perform optical, spectral and radar mapping of Earths sister planet. However, before coming down to work the van-sized spacecraft requires to aerobrake– decreasing its orbit with thousands of passages through the worlds hot, thick environment for approximately two years. An unique ESA center is currently testing prospect spacecraft materials to verify if they can securely endure this challenging process of climatic browsing.
” EnVision as currently developed can not happen without this prolonged stage of aerobraking,” describes ESAs EnVision study manager Thomas Voirin.
Artist impression of ESAs EnVision objective. Credit: ESA/VR2Planets/Damia Bouic
” The spacecraft will be injected into Venus orbit at a very high altitude, at around 250,000 km (~ 150,000 miles), then we require to come down to a 500 km (~ 300 mile) elevation polar orbit for science operations. Flying on an Ariane 62 rocket, we can not pay for all the extra propellant it would take to lower our orbit. Rather we will slow ourselves down through repeated travel through the upper environment of Venus, coming as low as 130 km (80 miles) from the surface area.”
