Huygens probe
The probe Huygens, manufactured by the European Space Agency (ESA) and named after the 17th century Dutch astronomer Christiaan Huygens, (discoverer of the moon Titan of the planet Saturn), is an entry probe into Titan's atmosphere carried as part of the Cassini-Huygens mission. The Cassini-Huygens spacecraft was launched from Earth on October 15, 1997. Huygens separated from the Cassini orbiter on December 25, 2004, and landed on Titan on January 14, 2005 near the Xanadu region.
Description
The Huygens probe was designed to explore the clouds, atmosphere, and surface of Titan, Saturn's largest moon, penetrating Titan's atmosphere and bringing a robotic laboratory to the surface. When the mission was planned, the type of surface Titan could have was unknown. In the months prior to the landing of the probe, it was hoped that the analysis of Cassini data would help answer this question. The biggest initial uncertainty was whether the probe would land on solid ground or on the surface of a hydrocarbon lake or sea.
Based on images taken by Cassini, about 1,200 km away from Titan, the landing site appeared to be a coastline. Assuming that the landing site would not be solid, the Huygens probe was designed to survive several minutes of impact with the liquid surface and return information about the conditions encountered. It was expected to be the first time a human probe had landed in a non-terrestrial ocean. The probe had only about three hours of power in its batteries, most of which would be spent during the descent. Engineers expected to get at most 30 minutes of data from the surface.
The Huygens probe consists of the probe itself, which descended on Titan, and the 'Probe Support Team' (PSE), which remains attached to the orbiting probe (Cassini). The PSE includes the electronics necessary to track the probe, retrieve the data acquired during the descent, and process and send the data to the orbiter, from where it was transmitted to the ground.
The probe remained dormant during the 6.7-year interplanetary journey, except for biannual checkups whose results were transmitted back to Earth for analysis by ESA payload and systems experts.
Prior to separation of the probe from the orbiter, a final 'health' check was performed on December 25, 2004. A timer was loaded with the period necessary to turn on the probe's systems (15 minutes before its encounter with Titan's atmosphere), and then the probe undocked from the orbiter and sailed through space to Titan for 22 days, with the systems off except the 'wake up' timer.
The main phase of the mission consisted of parachuting through Titan's atmosphere. Batteries and all resources were sized for an estimated duration of 153 minutes, corresponding to a maximum descent time of 2.5 hours plus an additional 3 minutes (possibly half an hour or more) on Titan's surface. The radio link with the probe was activated at the beginning of the descent phase, and the orbiter listened to the probe for the next 3 hours. Shortly after the end of this 3-hour communication window, Cassini's High Gain Antenna (HGA) was reoriented from Titan toward Earth.
Large telescopes on Earth were also listening to Huygens's 10-watt transmission using a technique of 'very broad-based interferometry' and synthesis opening mode. At 11:25 CET on January 14, the Robert C. Byrd Green Bank Telescope (GBT) in Virginia detected the carrier signal from the probe. The GBT continued to detect the signal long after Cassini stopped listening. In addition to the GBT, eight of the ten other VLBA telescopes were also listening for the Huygens signal.
The strength of the Huygens signal received on Earth was comparable to that of the Galileo probe as received by the Very Large Array network.
It was hoped that Doppler shift analysis of the signal as it descended in Titan's atmosphere would allow the wind strength and direction to be calculated with some precision. Through interferometry, the position of the landing spot was accurately determined (On Titan 1 km by 1 km measures 1.3' latitude and longitude at the equator) from Doppler data, at a distance of the Earth of about 1,200 million kilometers. This is an angular resolution of approximately 170 arcseconds. The probe landed on the surface at 10.573°S, 192.335°W. A similar technique was used to determine the landing point of the rovers on Mars by analyzing their telemetry.
Research
The landing site of the Huygens probe, named Hubert Curien Memorial Station in memory of Hubert Curien (first president of the European Space Agency), [1] it was in a region known as Adiri—visible from the Cassini probe as a dark area. Preliminary analysis suggested that this place was a liquid ocean, although today it is known that the probe landed in that dark area and that it is actually solid, there being no such ocean.
Instruments revealed "dense cloud or thick fog approximately 18-20 kilometers from the surface," which is probably the background of methane above the surface. The photographs have revealed a spongy terrain.
Huygens has also been recording sounds for more than two and a half hours on the satellite.
Conclusions of Huygens' discoveries after landing on Titan:
- Titan contains oceans, lakes and rivers of liquid methane and these are fed by rain, also from liquid methane and organic fragments.
- These methane rains and evaporations cover the celestial body of a faint fog. These methane surfaces include islands and depth areas. The methane erodes the landscape as on Earth and then filters.
- The solid surface of Titan is orange, spongy, very cold and with some rocks scattered over it. It has been said that it should be imagined as a desert similar to Arizona. The surface itself seems to consist of a clay material; scientists compared it with yogurt.
- There could be something similar to volcanic activity in the past, only that instead of lava the eruptions would have been of ice and ammonia.
- In the celestial body you can detect winds that go in the direction in which the satellite rotates, being on the surface between 60 and 100 km/h of speed.
- The satellite is at a temperature of -180Co.
- In Titan there is internal geological activity.
- Ice stews can be found on the satellite.
Instrumentation
The Huygens probe has six complex instruments on board that took a wide range of scientific data after the probe descended into Titan's atmosphere. The six instruments are:
Huygens Atmospheric Structure Instrument (HASI)
This instrument contains a suite of sensors that will measure the electrical and physical properties of Titan's atmosphere. Accelerometers will measure the forces experienced in all three axes during the descent through the atmosphere. Since the aerodynamic properties of the probe are known, it will be possible to determine the density of Titan's atmosphere and detect air currents. If it lands on a liquid surface, the motion of the probe due to waves could also be measured. Pressure and temperature sensors will measure the thermal properties of the atmosphere. The Permittivity component and Wave Analysis Component will measure the conductivity of the atmosphere and look for electromagnetic wave activity. On Titan's surface, conductivity and permittivity will also be measured. The HASI subsystem also contains a microphone that will record sounds during descent and landing. If the Huygens mission is successful, it will be the second time in history (a Venera 13 spacecraft was the first) that sounds from another planet have been recorded.
Doppler Wind Experiment (DWE)
This experiment uses an ultra-stable oscillator to improve communication with the probe by giving a very stable frequency to the carrier. Probe drift due to winds in Titan's atmosphere will produce a measurable Doppler shift of the carrier signal. Unfortunately, the researchers did not receive the data from this instrument due to a programming error that resulted in the loss of one of the data channels. This failure also resulted in the loss of half the descent images. However, analysis of the 10-watt signals received on the ground by a worldwide network of radio telescopes should allow us to deduce most of the information that the DWE would have provided. The measurements began 150 kilometers above Titan's surface, where Huygens was blown eastward at more than 400 kilometers per hour, according to the first measurements of 200-kilometer-altitude winds made in recent years with telescopes.. Between 60 and 80 kilometers, Huygens was buffeted by rapidly fluctuating winds, believed to be vertical wind shear. At ground level, Earth's Doppler-based and VLBI-based measurements show light winds of a few meters per second, almost in line with expectations.
Descent Imager/Spectral Radiometer (DISR)
This instrument will make spectral observations using various sensors. By measuring the flux of radiation up and down, the radiation balance (or imbalance) of Titan's thick atmosphere will be measured. Solar sensors will measure the intensity of light around the Sun due to scattering by aerosols in the atmosphere. This will allow calculation of the size and density of the suspended particles. Two cameras (one visible, one infrared), will observe the surface during the last phases of the descent, and since the probe will rotate slowly, they will build a mosaic of photographs around the landing site. Lateral images will also be taken to obtain a horizontal view of the horizon and the underside of the cloud cover. For spectral measurements from the surface, a lamp that will be turned on briefly before landing will augment the weak sunlight.
Gas Chromatograph Mass Spectrometer (GC/MS)
This instrument is a versatile chemical gas analyzer designed to identify and measure chemical compounds in Titan's atmosphere. It is equipped with samplers that will be filled at a high altitude for analysis. The mass spectrometer will build a model of the molecular masses of each gas, and a more powerful separation of molecular species will be achieved with the gas chromatograph. During the descent, the GCMS will also analyze pyrolysis products (ie samples altered by heating) collected by the Aerosol Collector Pyrolyser. Finally, the GCMS will measure the composition of Titan's surface if a safe landing is made. This investigation is possible by heating the GCMS just before impact to vaporize surface material after impact. The GC/MS was developed by the Goddard Space Flight Center and the University of Michigan Space Physics Research Laboratory.
Aerosol Collector and Pyrolyser (ACP)
This experiment will pass aerosol particles from the atmosphere through filters, which are then heated in ovens (the pyrolysis process to vaporize volatile components and break down complex organic materials. The products are then sent through a pipeline to the GCMS for analysis Two filters are available to collect samples at different altitudes The ACP was developed by a (French) ESA team at the Laboratoire Inter-Universitaire des Systèmes Atmosphériques (LISA).
Surface-Science Package (SSP)
The SSP contains a number of sensors designed to determine the physical properties of Titan's surface at the point of impact, whether the surface is liquid or solid. An acoustic sonar, activated during the last 100 m of the descent, will continuously measure the distance to the surface, measuring the rate of descent and the roughness of the surface (eg due to waves). If the surface is liquid, the sonar will measure the speed of sound in the "ocean" and possibly the structure below the surface (depth). During descent, measurements of the speed of sound will provide information on the composition and temperature of the atmosphere, and an accelerometer will accurately measure the deceleration profile during impact, indicating the hardness and structure of the surface. Another sensor will measure any pendulum movement during descent and indicate the orientation of the probe after landing and show any movement due to waves. If the surface is indeed liquid, other sensors will measure its density, temperature, and reflection of light, thermal conductivity, heat capacity, and electrical permittivity. A penetrometer instrument, which protruded 55 mm beyond the bottom of the descent module of the Huygens probe, the penetrometer was used to create a plot when Huygens landed on the surface by measuring the force exerted on the instrument by the surface, as the instrument broke off the surface and was pushed down on the planet by the force of the lander itself. The footprint shows this force as a function of time over a period of about 400 ms. The trace has an initial spike that suggests the instrument struck one of the ice pebbles on the surface imaged by the DISR camera.
The SSP Huygens was developed by the Department of Space Sciences at the University of Kent and the Rutherford Appleton Laboratory's Department of Space Sciences, under the direction of Professor John Zarnecki. The SSP research and responsibility transferred to the Open University when John Zarnecki transferred in 2000.
Ship design
Huygens was built under prime contractor Aérospatiale at its Space Center in Cannes Mandelieu, France, now part of Thales Alenia Space. The heat shield system was built under the responsibility of Aérospatiale, near Bordeaux, now part of EADS SPACE Transportation.
Parachute
Martin-Baker Space Systems was responsible for the Huygens parachute and the structural components, mechanisms, and pyrotechnics that control the probe's descent into Titan. IRVIN-GQ was responsible for defining the structure of the Huygens parachutes.
Lander Design
Huygens is made up of two parts: the probe and the probe support team (PSE). The probe is made up of two elements as well: the aeroshell, which protects the instruments during high-speed entry into Titan's atmosphere, and the descent module, which contains the scientific instrumentation. The descent module is enclosed in the aerodeck. These elements are attached to each other at three points.
The aeroshell is made up of two parts: a front shield and a rear cover. The frontal shield is 79 kg, 2.75 m in diameter, 60 degree half-coni angle spherical surface. Tiles of "AQ60" Ablative material (a phenolic resin felt reinforced by silica fibers) provides protection against heat from entering Titan's atmosphere. The support structure is a carbon fiber reinforced honeycomb, also designed to protect the descent module from heat generated during entry. The tiles were attached to the support structure using an adhesive. A suspension of the silica spheres in a hollow silicone elastomer (Prosial) was sprayed directly onto the aluminum frame of the rear surface of the shield to further insulate the surface. The rear cover, which experiences heating at least during reentry into the atmosphere, carries several layers of insulation to protect the probe during the cruise phase to Saturn and during the shore phase. A hole in the deck to allow depressurization during launch and allows repressurization during entry. It is a 11.4 kg with hardened aluminum casing protected by a 5 kg layer of Prosial.
The descent module consists of a forward dome and a cone afterward that surround the experiment platform. A complete upper platform of the enclosure. The forward cupola and upper deck contain a variety of ports to allow access to sensors to test the atmosphere and to provide a means for parachute deployment.
The PSE, although a part of the Huygens system, remains attached to the Cassini spacecraft. Its purpose is to support research and provide power to the probe before separation and to provide communications between the probe and the orbiter, both before and after separation. Likewise, it establishes the rotation given to the probe during the separation process.
Power of the Huygens probe after separation has five LiSO2 batteries capable of storing 1600 Wh of energy and can provide about 250 W of power for the expected three hours of operation of the probe. For thermal control, the probe uses multiple layers of insulation and around 35 W radioisotope heaters. A Power Distribution Conditioning Unit (PCDU) handles the distribution and conversion of orbital power and probe battery power for all experiments and probe subsystems. It also provides weaponry and firing functions for the Pyro lines. Before separation, all of the probe's power is provided by the Cassini orbiter.
Probe events are controlled through software and hard-wired sequences, including a triple-watch up redundant timer and a G-switch to detect the deceleration of the probe through Titan's atmosphere. Redundant 20 km downward altitude measuring radar altimeters, each transmitting 60 mW of power at 15.4 or 15. GHz via a 125 x 162 mm antenna flat groove.
A critical design flaw
Long after launch, tenacious engineers discovered that Cassini's communications equipment had a critical design flaw, which would have caused the loss of all data transmitted by the probe >Huygens.
Since Huygens is too small to transmit directly to Earth, it is designed to radio back to Cassini the telemetry obtained during descent, which in turn it relays it back to Earth using its 4-meter-diameter main antenna. Some engineers, including ESA Darmstadt employees Claudio Sollazzo and Boris Smeds, were uneasy about the fact that, in their opinion, this feature had not been tested before launch under realistic conditions. Smeds managed, with some difficulty, to convince his superiors to run additional tests while Cassini was in flight. In the early 2000s, he sent simulated telemetry data at various degrees of power and Doppler shift from Earth to Cassini . It happened that Cassini was unable to retransmit the data correctly.
The reason: when Huygens descends on Titan, it accelerates relative to Cassini, causing its signal to shift due to the Doppler effect. Thus, Cassini hardware was designed to receive in an offset frequency range. However, the firmware was not designed taking into account that the Doppler effect not only changes the carrier frequency, but also the timing of the bits, encoded at 8192 bits per second, and this was not taken into account by the module's programming.
Reprogramming the firmware was impossible and as a solution the path had to be changed. Huygens separated a month later (December 2004 instead of November) and approached Titan on a course such that its transmissions travel perpendicular to its direction of motion relative to Cassini', greatly reducing the Doppler shift.
The trajectory change undid the design flaw and the transmission was successful.
Contenido relacionado
Hafnium
Right ascension
Edgar Frank Codd