Wednesday, October 19, 2016

ExoMars Mission Arrives at the Red Planet After a Seven-Month Journey

Artist’s rendition of Schiaparelli separating from Trace Gas Orbiter. Image Credit: ESA / D. Ducros

Europe’s ExoMars 2016 mission has finally arrived at the Red Planet on Oct. 19, completing a lengthy interplanetary trip. The Trace Gas Orbiter (TGO) has been inserted into Martian orbit and the Schiaparelli module descended to the planet’s surface. However, the fate of the lander is currently unknown as ESA still awaits for the confirmation of the touchdown.

The joint ESA-Roscosmos ExoMars (Exobiology on Mars) mission, was launched by a Proton-M rocket from the Baikonur Cosmodrome in Kazakhstan, on Mar. 14, 2016. The mission, tasked with searching for biosignatures of life on Mars, consists of two spacecraft: the TGO orbiter, and the Entry, Descent and Landing Demonstrator Module (EDM) called “Schiaparelli”.

Cruising to Mars

Nearly 11 hours after liftoff, the stack comprising of TGO and Schiaparelli, was sent on a journey to Mars with an initial velocity of some 20,500 mph (33,000 km/h). Shortly after, when the ExoMars spacecraft reached a stable orientation, it deployed its X-band high gain antenna and two power-generating solar arrays. The first signals from the spacecraft were received about 12 hours after launch by the Italian Space Agency’s (ASI) Malindi ground station in Kenya and then relayed to the European Space Operations Centre (ESOC), ESA’s mission control in Darmstadt, Germany.

It took the spacecraft three days to perform its initial set of checkouts and reconfigurations. After that, the mission it entered its commissioning phase lasting until Apr. 24, during which the controllers carried out detailed checks of the orbiter and the lander. They also conducted a trajectory correction maneuver on Mar. 21, to remove launch vehicle insertion errors and set up the proper trajectory for the deep space cruise phase of the flight.

In late April, the spacecraft started the cruise phase, when all of its systems and instruments were checked out and verified. Until the end of June, the mission was kept in a quiet cruise mode, during which only three communications sessions per week were carried out.

Critical hour

After completing about 60 percent of its journey, the ExoMars spacecraft was ready for its most crucial maneuver of the cruise phase – the firing of its powerful 424 N bi-propellant main engine. This operation was performed on July 28, when the engine was fired for 52 minutes.

This deep space maneuver was the biggest and the most important burn out of the four such operations performed during the cruise. Planned well in advance, the firing was necessary to put the spacecraft into a trajectory allowing it to intercept Mars and precisely deliver the Schiaparelli lander onto a target area.

“The engine provides about the same force as that needed to lift a 45-kilogram (100-lbs.) weight in a fitness studio, and it ran for about 52 minutes, so that’s quite a significant push,” Silvia Sangiorgi, deputy spacecraft operations manager at ESA, said in July.

This critical maneuver was carried out with the assistance of an ultra-precise navigation technique that allows to pinpoint the spacecraft’s position to within 0.6 miles (1 kilometer) at a distance of 93 million miles (150 million kilometers) from Earth.

Are we there yet?

With the biggest burn completed, the a busy period for mission controllers started, as their work became more intense. Since the beginning of August ESA’s deep-space tracking stations at Malargüe, Argentina, and New Norcia, Australia, began to provide daily telecommanding passes. The contact with mission was even more intensified about 10 days ahead of arrival at Mars, allowing the team to receive data 24 hours a day. This enabled engineers to carefully monitor the spacecraft and plan its complex orbit-entry activities.

From August to October, the spacecraft has completed three trajectory correction maneuvers: on Aug. 11, in mid-September and on Oct. 14. The last correction was achieved by firing TGO’s thrusters for a minute to get a change in speed and direction of just 1.4 centimeter per second (0.55 inch per second). Although a very tiny overperformance from the thrusters was reported by ESA, the burn was overall very good and lined up the spacecraft perfectly on the right orbit to deliver Schiaparelli onto the desired area.

On Oct. 16, at 10:42 a.m. EDT (14:42 GMT), the Schiaparelli module has been successfully separated from TGO. However, during the release of the lander, a small glitch was encountered, as the orbiter did not return telemetry, sending only its carrier signal that indicated it is operational. Fortunately, the full telemetry link with the mission has been restored about two hours later, via the Malargüe station.

One day after separation, at 2:42 GMT (10:42 p.m. EDT on Oct. 16), an orbit raising maneuver of TGO was conducted. The firing lasted approximately one minute and 46 seconds and raised the probe’s orbit by several hundred miles above the Martian surface, to avoid collision with the planet.

Grand finale

With both spacecraft separated and TGO put into higher orbit, the mission was all set for Oct. 19 - the most important day of the ExoMars’ journey to the Red Planet. This is the day of TGO’s Mars Orbit Insertion (MOI) and Schiaparelli’s landing in Meridiani Planum - a plain containing an ancient layer of hematite, an iron oxide, that almost always forms in an environment containing liquid water.

ExoMars 2016 Schiaparelli descent sequence. Image Credit: ESA/ATG medialab
ExoMars 2016 Schiaparelli descent sequence. Image Credit: ESA/ATG medialab

The last day before arrival at Mars was quiet for both spacecraft. Schiaparelli has been ‘asleep’ and continuing its coast towards landing. All commands for its entry, descent, landing and science mission were previously uploaded by the engineers. Meanwhile, the final command sequence was uploaded to the TGO. It managed the spacecraft autonomously during its critical orbit entry maneuver.

With the Giant Metrewave Radio Telescope (GMRT) in India and a fleet of NASA and ESA spacecraft orbiting Mars, and final commands uploaded, the teams were ready to listen for the first signals of Schiaparelli’s landing. As for the TGO, the controllers successfully ignited the orbiter at 9:05 a.m. EDT (13:05 GMT) on Oct. 19, burning its engine for about two hours and 19 minutes in order to slow it down and inject it into the Martian orbit.

Meanwhile, the Schiaparelli lander ‘woke up’ at 9:27 a.m. EDT (13:27 GMT), slightly more than one hour before its planned landing. It was confirmed by a very faint signal received by GMRT.

The lander was activated at an altitude of about 76 miles (122.5 kilometers). Schiaparelli was designed to make use of its aerodynamic heat shield during the atmospheric entry and to deploy its parachute when approximately 7 miles (11 kilometers) above the surface. 

The lander’s liquid propulsion system should be activated to reduce the speed to less than 4.35 mph (7 km/h) when it is about 6.5 feet (2 meters) above the ground. The engines were expected to be switched off and the module was planned to be dropped to the ground.

Darmstadt, we have a problem

The landing was expected to take place at 10:48 a.m. EDT (14:48 GMT), however, although initial signals provided by GMRT confirmed that Schiaparelli descended to the surface of Mars, so far no signal indicated the touchdown. Moreover, no confirmation of the landing came from ESA’s Mars Express spacecraft and NASA’s Mars Reconnaissance Orbiter (MRO) that are currently orbiting the planet.

“A series of windows have been programmed to listen for signals coming from the lander via ESA’S Mars Express and NASA’s Mars Reconnaissance Orbiter (MRO) and Mars Atmosphere & Volatile Evolution (MAVEN) probes. The Giant Metrewave Radio Telescope (GMRT) also has listening slots. If Schiaparelli reached the surface safely, its batteries should be able to support operations for three to ten days, offering multiple opportunities to re-establish a communication link,” ESA said in a press release.

While the situation of Schiaparelli is still under assessment, the TGO status has been confirmed to be in good health after successfully completing its MOI maneuver at 11:24 a.m. EDT (15:24 GMT).

“TGO’s Mars orbit Insertion burn lasted from 13:05 to 15:24 GMT on Oct. 19, reducing the spacecraft’s speed and direction by more than 1.5 km/s (3,350 mph). The TGO is now on its planned orbit around Mars. European Space Agency teams at the European Space Operations Centre (ESOC) in Darmstadt, Germany, continue to monitor the good health of their second orbiter around Mars, which joins the 13-year old Mars Express,” ESA said.

Signal received from ExoMars Trace Gas Orbiter. Photo Credit: ESA
Signal received from ExoMars Trace Gas Orbiter. Photo Credit: ESA

Tracing trace gases

The TGO, built by Thales Alenia Space, will monitor seasonal changes in the atmosphere’s composition and temperature in order to create and refine detailed atmospheric models. Its instruments will also map the subsurface hydrogen, with improved spatial resolution compared with previous measurements. The TGO is able to detect a wide range of atmospheric trace gases such as methane, water vapor, nitrogen oxides, and acetylene.

The orbiter’s dimensions are 11.5 × 6.5 × 6.5 feet (3.5 × 2 × 2 meters) with solar wings spanning 57.4 feet (17.5 meters) and providing up to 2,000 W of power. It has a mass of approximately 4.3 metric tons.

The TGO is equipped with four scientific instruments for the detection of trace gases: Nadir and Occultation for MArs Discovery (NOMAD), Atmospheric Chemistry Suite (ACS), Colour and Stereo Surface Imaging System (CaSSIS), and Fine Resolution Epithermal Neutron Detector (FREND).

NOMAD combines three spectrometers, two infrared and one ultraviolet, to perform high-sensitivity orbital identification of atmospheric components, including methane and many other species, via both solar occultation and direct reflected-light nadir observations.

ACS will help scientists to investigate the chemistry and structure of the Martian atmosphere. It will complement NOMAD by extending the coverage to infrared wavelengths, and by taking images of the Sun to analyze better the solar occultation data.

CaSSIS is a high-resolution camera capable of obtaining color and stereo images over a wide swathe. It will provide the geological and dynamical context for sources or sinks of trace gases detected by NOMAD and ACS.

FREND is a neutron detector that will map hydrogen on the surface, revealing deposits of water-ice near the surface.

The TGO will enter a highly elliptical orbit that takes four Martian days to complete one revolution. Aerobraking maneuvers between January and November 2017 will bring the orbiter into a circular orbit at 250 miles (400 kilometers) above the surface. Science operations will begin in December 2017 and will continue for two years.

Europe’s second Mars landing

Schiaparelli is expected to demonstrate the capability of ESA to perform a controlled landing on Mars. It will also deliver a science package that will operate on the surface of the Red Planet for a short duration after landing, planned to last approximately from two to four Martian days.

The landing of Schiaparelli is the second European attempt to land on Mars after the Beagle 2 spacecraft failed to do it on Dec. 25, 2003. No contact was received at the expected time of landing on Mars, and ESA declared the mission lost in February 2004.

The Schiaparelli lander, built by Thales Alenia Space, is about 5.4 feet (1.65 meters) in diameter and 5.9 feet (1.8 meters) high and has a mass of 1,322 lbs. (600 kg). It is designed to be capable of landing on a terrain with rocks as high as 1.3 feet (0.4 meters) and slopes as steep as 12.5 degrees. It is expected to be operational for up to eight Martian days after landing.

Schiaparelli is fitted with a series of sensors that will monitor the behavior of all key technologies during the mission. These technologies include a special material for thermal protection, a parachute system, a radar Doppler altimeter system, and a braking system controlled by liquid propulsion.

Artist impression of the Schiaparelli module on the surface of Mars. Image Credit: ESA/ATG medialab
Artist impression of the Schiaparelli module on the surface of Mars. Image Credit: ESA/ATG medialab

Schiaparelli’s surface payload, the DREAMS (Dust Characterisation, Risk Assessment, and Environment Analyser on the Martian Surface) package, consists of a suite of sensors to measure the wind speed and direction (MetWind), humidity (DREAMS-H), pressure (DREAMS-P), atmospheric temperature close to the surface (MarsTem), the transparency of the atmosphere (Solar Irradiance Sensor, SIS), and atmospheric electrification (Atmospheric Radiation and Electricity Sensor; MicroARES).

In addition to the surface payload, a camera called DECA (Entry and Descent Module Descent Camera) on the EDM will operate during the descent. It will deliver additional scientific data and exact location data in the form of images. It will be used to image the Martian surface as it approaches the landing site, to determine the transparency of the Martian atmosphere, and to support the generation of a 3-D topography model of the surface of the landing region.

The lander will carry out a program known as AMELIA (Atmospheric Mars Entry and Landing Investigation and Analysis) to study Schiaparelli’s engineering data for reconstructing its trajectory and attitude to determine atmospheric conditions, such as density and wind, from a high altitude to the surface.

Schiaparelli carries the Combined Aerothermal and Radiometer Sensors Instrument Package, called COMARS+, which is installed on the back cover of Schiaparelli will gather the data to study this. COMARS+ consists of three small (22-mm-diameter) combined sensors (COMARS) spaced equally across the rear cover of Schiaparelli, one broadband radiometer, and an electronic box.

The lander is also equipped in INRRI – a Cube Corner laser Retroreflector (CCR) located on the zenith-facing surface of Schiaparelli, the ExoMars entry, descent, and landing demonstrator. It will enable Schiaparelli to be located from Mars orbiters by laser ranging, both during Schiaparelli’s mission lifetime and, as it is passive and maintenance free, afterward.

Background

ExoMars project began to materialize in July–August 2009 when ESA signed contracts with NASA and Roscosmos to develop the mission. However, due to budgetary cuts in 2012, NASA terminated its participation in the project. One year later, Roscosmos became the main partner for ESA when the agencies signed a deal obligating the Russian side to deliver launch services, scientific instruments for TGO and landing systems, together with rover instruments, for the second mission initially scheduled for 2018.

The second part of the ExoMars mission, now delayed to 2020, will include an ESA carrier module as well as a Russian lander that will deploy a rover to Mars’ surface. The stack will be launched atop a Russian Proton-M booster from the Baikonur Cosmodrome located in Kazakhstan.

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