ESA’s EnVision mission will present optical, spectral and radar mapping of Earth’s sister planet to Venus. However earlier than it will get to work, the minivan-sized spacecraft should do an “aerofoil” — a two-year orbit that may take 1000’s of passes via the planet’s sizzling, thick ambiance. ESA’s distinctive facility is presently testing spacecraft supplies to make sure that spacecraft can stand up to this difficult strategy of atmospheric browsing.
“EnVision because it stands in the present day wouldn’t be attainable with out this lengthy part of aerobraking,” explains Thomas Voirin, ESA’s EnVision analysis supervisor.
“The spacecraft might be inserted into the orbit of Venus at a really excessive altitude, about 250,000 km, after which we should descend to a polar orbit at an altitude of 500 km for scientific operations. Flying on Ariane 62, we will not afford all the additional gas we have to decrease our orbit. As an alternative, we sluggish ourselves down by repeatedly passing via the higher ambiance of Venus, about 130 km under Earth’s floor.
EnVision’s earlier spacecraft, Venus Categorical, carried out an experimental aerobraking within the remaining months of its 2014 mission, gathering invaluable info on the approach. Aerobraking was first utilized in 2017 by ESA’s ExoMars Hint Fuel Orbiter (TGO) to decrease its orbit across the Pink Planet for 11 months.
Thomas notes, “Aerobraking round Venus might be way more troublesome than TGO. For starters, the gravity of Venus is about 10 instances stronger than that of Mars. Which means the spacecraft will expertise twice the pace of the TGO because it passes via the ambiance, and the warmth is generated because the dice of the pace. Due to this fact, EnVision should scale back the air braking mode, ensuing within the air braking part lasting twice as lengthy.
“As well as, we’re a lot nearer to the Solar and expertise photo voltaic depth practically twice that of Earth, and the thick white clouds of the ambiance mirror a lot of the daylight instantly into house. taken under consideration. As well as, we realized that over 1000’s of orbits we thought we needed to account for one more issue that had beforehand solely existed in low-Earth orbit: extremely erosive atomic oxygen.
It is a phenomenon that remained unknown within the early many years of the house age. It wasn’t till the primary Area Shuttle flights returned from low orbit within the early Nineteen Eighties that engineers have been hit onerous: the spacecraft’s thermal blankets have been severely eroded.
The wrongdoer turned out to be extremely reactive atomic oxygen – particular person oxygen atoms on the edges of the ambiance, the results of the breakdown of ordinary oxygen molecules discovered simply above Earth by highly effective ultraviolet radiation from the Solar. Immediately, all missions under about 1,000 km have to be designed to face up to atomic oxygen, akin to Europe’s Copernicus Sentinels, or any gear constructed for the Worldwide Area Station.
Spectral observations of previous Venusian orbits of the airglow above the planet affirm that atomic oxygen can also be widespread within the higher ambiance of Venus, which is greater than 90 instances thicker than the air surrounding Earth.
Thomas says, “The focus is so excessive that it would not matter a lot in a single move, nevertheless it begins to build up 1000’s of instances and finally ends up with atomic oxygen ranges that we’ve got to keep in mind. Expertise in low orbit, however at excessive temperatures.’
The EnVision crew turned to a singular European facility constructed by ESA particularly to simulate atomic oxygen in orbit. Low Earth Orbit is a part of the Company’s Supplies and Electrical Elements Laboratory based mostly at ESA’s ESTEC Technical Middle in LEOX, the Netherlands.
ESA Supplies Engineer Adrian Tighe explains: “LEOX creates atomic oxygen at power ranges equal to orbital velocity. Purified molecular oxygen is injected right into a vacuum chamber with a pulsed laser beam. This turns the oxygen right into a sizzling plasma, the speedy growth of which is directed via a cone-shaped nozzle. It then dissociates to provide a extremely energetic beam of atomic oxygen.
“For dependable operation, laser timing have to be correct on the millisecond scale and aimed to an accuracy measured in thousandths of a millimeter over the four-month period of this present check marketing campaign.
“This isn’t the primary time that this facility has been used to simulate an extraterrestrial orbital atmosphere – we’ve got already carried out atomic oxygen checks on candidate photo voltaic array supplies for ESA’s Juice mission, as telescopic observations have proven that atomic oxygen will be discovered within the ambiance. Europa and Ganymede. Nonetheless, for EnVision, the elevated temperature throughout air braking poses an extra problem, so the ability is designed to simulate the intense atmosphere on Venus.
A variety of supplies and coatings from varied components of the EnVision spacecraft, together with multilayer insulation, antenna components and star tracker parts, are positioned on a wafer to be uncovered to the violet-bright LEOX beam. On the identical time, this plate is heated as much as 350°C to simulate the anticipated warmth circulate.
Thomas provides: “We need to guarantee that these components are proof against erosion and in addition preserve their optical properties, that means they do not degrade or darken, which might have a huge impact on their thermal habits as a result of we’ve got a fragile set temperature maintain. Scientific devices that ought to be saved. We must also avoid the bark or fuel that causes air pollution.
This present check marketing campaign is a component of a bigger panel EnVision aerobraking, together with utilizing the Venus local weather database developed from earlier mission outcomes to estimate the native variability of the planet’s ambiance to set protected limits for the spacecraft.
The outcomes of this check marketing campaign are anticipated later this yr.
EnVision is an ESA-led mission in partnership with NASA, with help from its Artificial Aperture Radar instrument, VenSAR and the Deep Area Community for mission milestones. EnVision makes use of a sequence of devices to hint Venus from its interior core to its higher ambiance to raised perceive how Earth’s closest neighbor within the Photo voltaic System has advanced otherwise.
EnVision was chosen by ESA’s Science Program Committee because the fifth medium-class mission within the Company’s Area Imaginative and prescient Plan, with a goal launch within the early 2030s.