Editing Mars Express (section)

== Orbiter and subsystems ==

=== Structure ===
The ''Mars Express'' orbiter is a cube-shaped spacecraft with two [[Photovoltaic module|solar panel]] wings extending from opposite sides. The launch mass of 1223&nbsp;kg includes a main bus with 113&nbsp;kg of payload, the 60&nbsp;kg lander, and 457&nbsp;kg of propellant. The main body is 1.5 m × 1.8 m × 1.4 m in size, with an aluminium honeycomb structure covered by an aluminium skin. The solar panels measure about 12 m tip-to-tip. Two 20 m long wire [[dipole antenna]]s extend from opposite side faces perpendicular to the solar panels as part of the radar sounder.<ref name="ref1">{{cite web |url=http://www.esa.int/Our_Activities/Space_Science/Mars_Express/The_spacecraft |title=The spacecraft / Mars Express |publisher=[[ESA]] |date=October 10, 2005 |access-date=March 29, 2016 }}</ref>

=== Propulsion ===
The Soyuz/Fregat launcher provided most of the thrust ''Mars Express'' needed to reach Mars. The final stage of the Soyuz, Fregat was jettisoned once the probe was safely on a course for Mars. The spacecraft's on-board means of propulsion was used to slow the probe for Mars orbit insertion and subsequently for orbit corrections.<ref name="ref1" />

The body is built around the main propulsion system, which consists of a [[Bipropellant rocket|bipropellant]] 400 [[Newton (unit)|N]] main engine. The two 267-liter propellant tanks have a total capacity of 595&nbsp;kg. Approximately 370&nbsp;kg are needed for the nominal mission. Pressurized helium from a 35-liter tank is used to force fuel into the engine. Trajectory corrections will be made using a set of eight 10 N thrusters, one attached to each corner of the spacecraft bus. The spacecraft configuration is optimized for a Soyuz/Fregat, and was fully compatible with a [[Delta II]] launch vehicle.

=== Power ===
Spacecraft power is provided by the solar panels which contain 11.42 square meters of silicon cells. The originally planned power was to be 660{{nbsp}}[[Watt|W]] at 1.5{{nbsp}}[[astronomical unit|AU]] but a faulty connection has reduced the amount of power available by 30%, to about 460{{nbsp}}W. This loss of power does not significantly affect the science return of the mission. Power is stored in three [[lithium ion battery|lithium-ion batteries]] with a total capacity of 64.8{{nbsp}}Ah for use during eclipses. The power is fully regulated at 28{{nbsp}}[[Volt|V]], and the [[Terma A/S|Terma]] power module (also used in ''[[Rosetta (spacecraft)|Rosetta]]'') is redundant.<ref>{{cite news |url=http://ing.dk/artikel/terma-elektronik-vaekker-rumsonde-fra-aarelang-dvale-165600 |title=Terma-elektronik vækker rumsonde fra årelang dvale|newspaper=[[Ingeniøren]] |first=Mie |last=Stage |date=January 19, 2014 |access-date=March 29, 2016 }}</ref><ref>{{Cite journal |title=Power Conditioning Unit for Rosetta/Mars Express |journal = Space Power |volume=502 |page=249 |publisher=[[Astrophysics Data System]] |last1=Jensen |first1=H. |last2=Laursen |first2=J. |bibcode=2002ESASP.502..249J |date=2002 }}</ref> During routine phase, the spacecraft's power consumption is in the range of 450–550{{nbsp}}W.<ref>{{cite web |url=http://www.asi-proc.it/missions/mex |title=MEX — ASI-PROC|publisher=Planetary Radar Operational Center |date=March 29, 2016 |access-date=March 29, 2016 |archive-url=https://web.archive.org/web/20160413141724/http://www.asi-proc.it/missions/mex |archive-date=April 13, 2016 }}</ref>

=== Attitude control - avionics ===
Attitude control (3-axis stabilization) is achieved using two 3-axis inertial measurement units, a set of two [[star camera]]s and two [[Sun sensor]]s, [[gyroscope]]s, [[accelerometer]]s, and four 12&nbsp;N·m·s [[reaction wheel]]s. Pointing accuracy is 0.04 degree with respect to the inertial reference frame and 0.8 degree with respect to the Mars orbital frame. Three on-board systems help ''Mars Express'' maintain a very precise pointing accuracy, which is essential to allow the spacecraft to use some of the science instruments.

=== Communications ===
The communications subsystem is composed of three antennas: A 1.6&nbsp;m diameter parabolic dish [[high-gain antenna]] and two omnidirectional antennas. The first one provide links (telecommands uplink and telemetry downlink) in both [[X-band]] (8.4&nbsp;GHz) and [[S-band]] (2.1&nbsp;GHz) and is used during nominal science phase around Mars. The low gain antennas are used during launch and early operations to Mars and for eventual contingencies once in orbit. Two Mars lander relay UHF antennas are mounted on the top face for communication with the ''Beagle 2'' or other landers, using a Melacom transceiver.<ref name="melacom">{{cite web |url=http://apps.qinetiq.com/perspectives/micro_news_article7.asp |title=QinetiQ to put Mars in the picture |archive-url=https://web.archive.org/web/20060831063330/http://apps.qinetiq.com/perspectives/micro_news_article7.asp |archive-date=August 31, 2006 |quote=Consisting of a lightweight bespoke transponder and transceiver weighing less than 650 grams, the system will provide the 10,000-kilometre UHF radio communications link between the ''Mars Express'' orbiter and Beagle-2 lander. |publisher=[[Qinetiq]] |access-date=March 29, 2016 }}</ref>

==== Earth stations ====
Although communications with Earth were originally scheduled to take place with the ESA 35-meter wide Ground Station in New Norcia (Australia) [[New Norcia Station]], the mission profile of progressive enhancement and science return flexibility have triggered the use of the ESA [[ESTRACK]] Ground Stations in [[Cebreros Station]], [[Madrid]], Spain and [[Malargüe Station]], [[Argentina]].

In addition, further agreements with NASA [[Deep Space Network]] have made possible the use of American stations for nominal mission planning, thus increasing complexity but with a clear positive impact in scientific returns.

This inter-agency cooperation has proven effective, flexible and enriching for both sides. On the technical side, it has been made possible (among other reasons) thanks to the adoption of both Agencies of the Standards for Space Communications defined in [[CCSDS]].

=== Thermal ===
Thermal control is maintained through the use of radiators, [[multi-layer insulation]], and actively controlled heaters. The spacecraft must provide a benign environment for the instruments and on-board equipment. Two instruments, PFS and OMEGA, have infrared detectors that need to be kept at very low temperatures (about −180&nbsp;°C). The sensors on the camera (HRSC) also need to be kept cool. But the rest of the instruments and on-board equipment function best at room temperatures (10–20&nbsp;°C).

The spacecraft is covered in gold-plated aluminium-tin alloy thermal blankets to maintain a temperature of 10–20&nbsp;°C inside the spacecraft. The instruments that operate at low temperatures to be kept cold are thermally insulated from this relatively high internal temperature, and emit excess heat into space using attached radiators.<ref name="ref1" />

=== Control unit and data storage ===
The spacecraft is run by two Control and Data management Units with 12 gigabits<ref name="ref1" /> of solid state mass memory for storage of data and housekeeping information for transmission. The on-board computers control all aspects of the spacecraft functioning including switching instruments on and off, assessing the spacecraft orientation in space and issuing commands to change it.

Another key aspect of the ''Mars Express'' mission is its [[artificial intelligence]] tool (MEXAR2).<ref name="ESA1">{{cite web |title=Artificial Intelligence Boosts Science from Mars |url=http://www.esa.int/Our_Activities/Operations/Artificial_intelligence_boosts_science_from_Mars |publisher=ESA |date=April 29, 2008 |access-date=March 29, 2016 }}</ref> The primary purpose of the AI tool is the scheduling of when to download various parts of the collected scientific data back to Earth, a process which used to take ground controllers a significant amount of time. The new AI tool saves operator time, optimizes [[Bandwidth (signal processing)|bandwidth]] use on the [[Deep Space Network|DSN]], prevents data loss, and allows better use of the DSN for other space operations as well. The AI decides how to manage the spacecraft's 12 gigabits of storage memory, when the DSN will be available and not be in use by another mission, how to make the best use of the DSN bandwidth allocated to it, and when the spacecraft will be oriented properly to transmit back to Earth.<ref name="ESA1" /><ref>{{cite journal |doi=10.1109/MIS.2007.75 |url=http://mexar.istc.cnr.it/mexar2/publications/mexar2-ieee-intsys.pdf |title=Mexar2: AI Solves Mission Planner Problems |journal=IEEE Intelligent Systems |volume=22 |issue=4 |pages=12–19 |first=Amedeo |last=Cesta |date=2007 |s2cid=14477705 |access-date=December 7, 2011 |archive-date=March 5, 2012 |archive-url=https://web.archive.org/web/20120305230348/http://mexar.istc.cnr.it/mexar2/publications/mexar2-ieee-intsys.pdf }}</ref>