Zephyr (rover)
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''Zephyr'' is a concept of a robotic
Venus Venus is the second planet from the Sun. It is sometimes called Earth's "sister" or "twin" planet as it is almost as large and has a similar composition. As an interior planet to Earth, Venus (like Mercury) appears in Earth's sky never fa ...
rover for a mission called Venus Landsailing Rover. This mission concept would place a rover on the surface of Venus that would be propelled by the force of the wind. The rover would be launched together with a Venus orbiter that would perform both communications relay and remote atmospheric studies. The rover would be designed to operate on the surface of Venus for 50 Earth days, and navigate sandy plains bathed in heat and dense
sulfuric acid Sulfuric acid (American spelling and the preferred IUPAC name) or sulphuric acid ( Commonwealth spelling), known in antiquity as oil of vitriol, is a mineral acid composed of the elements sulfur, oxygen and hydrogen, with the molecular formu ...
clouds under very high atmospheric pressure. The rover can move in any direction, regardless of wind direction. ''Zephyr'' would sail up to 15 minutes per day to reach its next target, where it would park using a combination of brakes and feathering the wingsail while it performs its science activities. The rover would carry a science payload of , including a robotic arm. The overall mission architecture aims to achieve telerobotic capability, with a 4-minute delay in radio communication. The Principal Investigator is
Geoffrey Landis Geoffrey Alan Landis (; born May 28, 1955) is an American aerospace engineer and author, working for the National Aeronautics and Space Administration (NASA) on planetary exploration, interstellar propulsion, solar power and photovoltaics. He ...
of NASA's
Glenn Research Center NASA John H. Glenn Research Center at Lewis Field is a NASA center within the cities of Brook Park and Cleveland between Cleveland Hopkins International Airport and the Rocky River Reservation of Cleveland Metroparks, with a subsidiary facilit ...
in Cleveland, Ohio.NASA's Plan To Put a Landsail Rover on Venus.
Jon M. Chang, ''ABC News.'' 26 August 2013. When the most critical hardware becomes available and is tested, Landis intends to propose the mission to NASA's Discovery program to compete for funding and a launch intended for 2039.
rover Rover may refer to: People * Constance Rover (1910–2005), English historian * Jolanda de Rover (born 1963), Dutch swimmer * Rover Thomas (c. 1920–1998), Indigenous Australian artist Places * Rover, Arkansas, US * Rover, Missouri, US * ...
propelled by a rigid
wingsail A wingsail, twin-skin sail or double skin sail is a variable-camber aerodynamic structure that is fitted to a marine vessel in place of conventional sails. Wingsails are analogous to airplane wings, except that they are designed to provide lif ...
, inspired on the
landsailing Land sailing, also known as sand yachting, land yachting or dirtboating, is the act of moving across land in a wheeled vehicle powered by wind through the use of a sail. The term comes from analogy with (water) sailing. Historically, land sail ...
vehicles. The vehicle has only two moving parts: the sail, and the steering front wheel. The mission concept is named Venus Landsailing Rover, and the rover is called ''Zephyr'', after the Greek god of the west wind,
Zephyrus In ancient Greek religion and myth, the Anemoi (Greek: , 'Winds') were wind gods who were each ascribed a cardinal direction from which their respective winds came (see Classical compass winds), and were each associated with various seasons and ...
. For simplicity, the rover's wingsail is actually rigid, like a vertical wing with solar cells on its surface. Although some technology development is needed to bring the high-temperature electronics to operational readiness, the study showed that such a mobility approach is feasible, and no major difficulties are seen. The aimed rover's design lifetime is 50 days. Given the extreme environmental conditions at the surface of Venus, all previous landers and atmospheric probes operated for a few hours at most, so the Glenn Research Center team plans to use materials and electronics developed to withstand not just the extreme pressure, corrosive atmosphere and heat, but also operate with minimum solar power and without a cooling system, which reduces the landing mass significantly. The temperature at the surface is 740  K (467 °C, 872 °F), and the pressure is 93 
bar Bar or BAR may refer to: Food and drink * Bar (establishment), selling alcoholic beverages * Candy bar * Chocolate bar Science and technology * Bar (river morphology), a deposit of sediment * Bar (tropical cyclone), a layer of cloud * Bar (u ...
(9.3 
MPa MPA or mPa may refer to: Academia Academic degrees * Master of Performing Arts * Master of Professional Accountancy * Master of Public Administration * Master of Public Affairs Schools * Mesa Preparatory Academy * Morgan Park Academy * Mound ...
), roughly the pressure found underwater on Earth. For the purposes of propulsion, surface wind velocities of at least and up to are assumed. ''Zephyr'' would sail up to 15 minutes per day to reach its next target. From the images acquired by the Russian
Venera The Venera (, , which means "Venus" in Russian) program was the name given to a series of space probes developed by the Soviet Union between 1961 and 1984 to gather information about the planet Venus. Ten probes successfully landed on the s ...
probes, the surface of Venus can be seen to have landscapes of flat, even terrain stretching to the horizon, with rocks at only centimeter scale at their locations, making it possible for
landsailing Land sailing, also known as sand yachting, land yachting or dirtboating, is the act of moving across land in a wheeled vehicle powered by wind through the use of a sail. The term comes from analogy with (water) sailing. Historically, land sail ...
. The largest expected surface irregularities are about in height. The vehicle uses three metallic wheels with cleats, each with a diameter of and wide. Funding from the
NASA Innovative Advanced Concepts The NASA Institute for Advanced Concepts (NIAC) is a NASA program for development of far reaching, long term advanced concepts by "creating breakthroughs, radically better or entirely new aerospace concepts". The program operated under the name N ...
(NIAC) program, is allowing research into developing the needed "Venus-hardened" systems. NASA may also provide some of this equipment to the future Russian
Venera-D Venera-D (russian: Венера-Д, ) is a proposed Russian space mission to Venus that would include an orbiter and a lander to be launched in 2029. The orbiter's prime objective is to perform observations with the use of a radar. The lander, ba ...
mission to Venus by providing a long-lived (24 hours) experimental surface station fit on the Russian lander. In 2017, Landis's work was the subject of the book ''Land-Sailing Venus Rover With NASA Inventor Geoffrey Landis'', published by
World Book The ''World Book Encyclopedia'' is an American encyclopedia. The encyclopedia is designed to cover major areas of knowledge uniformly, but it shows particular strength in scientific, technical, historical and medical subjects. ''World Book'' wa ...
publishing.Heilman, Richard
"Book spotlights scientist's work on Venus rover"
''Berea News Sun'', Nov. 17 2017. Retrieved Dec, 7, 2017.


Electric power

Previous Venus landers have relied on batteries for electric power, which limits operation to a few hours at most, relying on thermal mass to delay the death of the system due to overheating. The power system for this mission uses sodium–sulfur batteries (NaS) that are re-charged by solar arrays and can function under Venus surface conditions without the need for heavy cooling systems.Landis, G. A. and Harrison, R. (2008) "Batteries for Venus Surface Operation," ''Journal of Propulsion and Power'', Vol. 26, Number 4, 649-654, July/Aug 2010; originally presented as paper AIAA-2008-5796, 6th AIAA International Energy Conversion Engineering Conf., Cleveland OH, July 28–30, 2008. The wingsail and upper deck would be covered with solar panels made of
indium gallium phosphide Indium gallium phosphide (InGaP), also called gallium indium phosphide (GaInP), is a semiconductor composed of indium, gallium and phosphorus. It is used in high-power and high-frequency electronics because of its superior electron velocity with ...
(InGaP, also called GaInP2) because it has been well characterized for use in solar cells, it has a wide enough
band gap In solid-state physics, a band gap, also called an energy gap, is an energy range in a solid where no electronic states can exist. In graphs of the electronic band structure of solids, the band gap generally refers to the energy difference (in ...
that it can work at Venus temperature, and responds to light in the band of about 360 to 660 nm. Although the thick cloud layer limits sunlight reaching the surface, there is enough light to use
solar panels A solar cell panel, solar electric panel, photo-voltaic (PV) module, PV panel or solar panel is an assembly of photovoltaic solar cells mounted in a (usually rectangular) frame, and a neatly organised collection of PV panels is called a phot ...
for low-power demand systems.


Wind force

While the wind speed at the surface of Venus is , at Venus pressure and density (65 kg/m3), even low wind speeds develop significant force.


Wingsail

The propulsion concept is a rigid
wingsail A wingsail, twin-skin sail or double skin sail is a variable-camber aerodynamic structure that is fitted to a marine vessel in place of conventional sails. Wingsails are analogous to airplane wings, except that they are designed to provide lif ...
, mounted perpendicular to the base that can rotate via an electric motor about its mean aerodynamic center to produce a lift (thrust) vector at any orientation, depending on the direction of the wind. The wing also provides a more stable surface on which to mount the solar cells used to power instruments on the rover. A symmetric flat airfoil is much easier to control at the sacrifice of a small amount of lift. Construction of the wing is standard spar, rib, and skin, using materials appropriate for the corrosive high temperature environment. At wide, the rover is stable on the surface, and the NASA GRC Team estimates that in order to prevent a roll-over caused by wind gusts, the system will incorporate sensors so that a sustained wind gust of or more will be recognized by its meteorology suite, and would give enough time to slack the sail by rotating it to a zero-lift position parallel to the wind. The diameter of the
aeroshell An aeroshell is a rigid heat-shielded shell that helps decelerate and protects a spacecraft vehicle from pressure, heat, and possible debris created by drag during atmospheric entry (see blunt body theory). Its main components consist of a heat ...
sets the length of the wingsail to , its area at and a height of above the ground. For launch, the wingsail is folded into three sections for storage in the
aeroshell An aeroshell is a rigid heat-shielded shell that helps decelerate and protects a spacecraft vehicle from pressure, heat, and possible debris created by drag during atmospheric entry (see blunt body theory). Its main components consist of a heat ...
, and it is deployed after the parachute descent and landing on its three wheels.


Science payload

The eyes of the rover would be a mechanically-scanned camera similar to the one used by the
Venera 9 Venera 9 (russian: Венера-9, lit=Venus-9), manufacturer's designation: 4V-1 No. 660, was a Soviet uncrewed space mission to Venus. It consisted of an orbiter and a lander. It was launched on June 8, 1975, at 02:38:00  UTC and had a m ...
lander, that would operate without cooling at Venus temperature, , and under Venus illumination conditions and spectrum. The design would use a linear
photodiode A photodiode is a light-sensitive semiconductor diode. It produces current when it absorbs photons. The package of a photodiode allows light (or infrared or ultraviolet radiation, or X-rays) to reach the sensitive part of the device. The packag ...
array as the light-sensing element, and except for the
focal plane In Gaussian optics, the cardinal points consist of three pairs of points located on the optical axis of a rotationally symmetric, focal, optical system. These are the '' focal points'', the principal points, and the nodal points. For ''ideal'' ...
photodiode array, the camera is fabricated with
silicon carbide Silicon carbide (SiC), also known as carborundum (), is a hard chemical compound containing silicon and carbon. A semiconductor, it occurs in nature as the extremely rare mineral moissanite, but has been mass-produced as a powder and crystal sin ...
electronics. Beside the imaging cameras, the rover would carry approximately of science instruments, including a robotic arm based on the Mars ''Phoenix'' robotic arm, but simplified to a two-joint arm to minimize complexity. This arm would hold several science instruments. The notional science payload includes: *The atmospheric science package: an
anemometer In meteorology, an anemometer () is a device that measures wind speed and direction. It is a common instrument used in weather stations. The earliest known description of an anemometer was by Italian architect and author Leon Battista Alberti ( ...
(wind speed and direction), a
thermometer A thermometer is a device that temperature measurement, measures temperature or a temperature gradient (the degree of hotness or coldness of an object). A thermometer has two important elements: (1) a temperature sensor (e.g. the bulb of a merc ...
, and a
barometer A barometer is a scientific instrument that is used to measure air pressure in a certain environment. Pressure tendency can forecast short term changes in the weather. Many measurements of air pressure are used within surface weather analysis ...
(pressure sensor). *In-situ mineralogy: These instruments would be fitted to the end of the robotic arm to make contact with the rocks and regolith and determine composition and mineralogy. These instruments include a rock abrasion grinder,
alpha particle X-ray spectrometer :''APXS is also an abbreviation for APache eXtenSion tool, an extension for Apache web servers.'' An alpha particle X-ray spectrometer (APXS) is a spectrometer that analyses the chemical element composition of a sample from scattered alpha part ...
(APXS) or an Energy-dispersive X-ray spectroscope (EDAX) for composition, and
X-ray diffraction X-ray crystallography is the experimental science determining the atomic and molecular structure of a crystal, in which the crystalline structure causes a beam of incident X-rays to diffract into many specific directions. By measuring the angles ...
for mineralogy. In addition to the surface science instruments, the mission may also have science packages that operate during descent, and may also deploy stationary science instruments, such as a
seismometer A seismometer is an instrument that responds to ground noises and shaking such as caused by earthquakes, volcanic eruptions, and explosions. They are usually combined with a timing device and a recording device to form a seismograph. The outpu ...
, that are not carried on the rover. All data would be transmitted to the orbiter with a high-temperature radio, so that the whole system has no cooled parts.


Orbiter

Because of the thick Venus atmosphere, radio signals from the rover would lack the power and reach, so a relay orbiter needs to be incorporated in the mission architecture. After ''Zephyr'' separation, the orbiter would propulsively brake into a highly eccentric orbit around the planet. This orbit would have a 24 hr period, permitting communication with ''Zephyr'' for 12 to 18 hr during each orbit. When Venus is at its closest to Earth, the communications time-lag from Venus and Earth is approximately four minutes, which is too long to control from Earth in real time, so the rover would be parked most of the time performing observations with the sail slack, while the ground controllers examine the terrain and decide the next target. If selected for funding, the relay orbiter could also host some science instruments.


References

{{Venus spacecraft Missions to Venus Proposed NASA space probes Three-wheeled robots Wind-powered vehicles