Saturday, November 13, 2010

ESA Hones Design For Mars Orbiter/Lander

ESA Hones Design For Mars Orbiter/Lander

Nov 11, 2010

By Michael A. Taverna

Engineers are moving into the last phase of detailed design for ExoMars, a twin lander/orbiter mission planned by the European Space Agency and NASA to pave the way for a sample return from the red planet.

ExoMars was conceived as an all-ESA endeavor with a single launch. However, rising costs and technology risks forced planners last year to morph the undertaking into a twin-launch scenario, with NASA as partner, and to redefine system requirements. This was completed in March. Thales Alenia Space (TAS) was retained as prime contractor.

Vincenzo Giorgio, who heads the optical observation and science business line of TAS’s Italian unit, says he expects to deliver a final proposal for Phase C/D full-scale development for the twin missions in January. Lower-level PDRs are due to be finished by March. The official development kick off is set for April, and systems are to be delivered in June 2015—a schedule that Giorgio admits is “very aggressive.”

To meet it, a protoflight model verification approach has been adopted, obviating the need for qualification or structural-thermal models, except for critical subassemblies. The flight modules will be mated at the very end of the integration and test phase, allowing their development and test schedules to be decoupled. Giorgio says 70% of procurement is complete and there are no critical fair-return issues—always a concern on ESA missions.

The first ExoMars mission, set for January 2016, will be led by ESA, which will supply the entry, descent and lander (EDL) module and orbiter. NASA will provide an orbiter communications and science package. The communications system will serve the two 2016 and 2018 missions as well as other international Martian assets.

The second mission, slated for 2018, will be NASA-run and include twin rovers, one each from the two agencies, and be carried on NASA’s Skycrane EDL. The European rover will be fully autonomous and will include a drill capable of boring down 2 meters to capture samples of the Martian subsurface—a major innovation over previous missions. The U.S. rover is still being defined.

Both will be launched by a U.S. Atlas V rocket using 4-meter-dia. fairings.

The 2016 mission is set to launch between Jan. 7-27, 2016, and perform a deep-space maneuver May 20-29. The EDL will separate from the orbiter on Oct. 16 and land on Oct. 19, touching down in the middle of the dust season—another Martian first—at a landing site in the Meridiani area, between 5 deg. S. Lat. and 35 deg. N.

The orbiter will enter its initial Martian orbit on the same day. It will employ aerobraking to reach final orbit beginning on Nov. 8 and ending on June 25, when the science phase is set to start. The 2018 rovers are due to arrive on Mars on Jan. 15, 2019.

The modified mission scenario led engineers to downsize the EDL for the 2016 flight from 1,200 kg. to 600 kg. (1,322 lb.) landing mass, reducing the size of the surface science package and emphasizing the technology demonstration. The design trade-off also led engineers to replace the vented air bag with a lighter crushable system and choose a hyperbolic entry trajectory. A material characterization test for the crushable design is to be completed by next spring and full-scale drop/impact tests are to begin in mid-2011.

TAS executives say the EDL design can be scaled up and could be employed for the 2018 mission, using the vented airbag design, in the event of a problem with the Skycrane on NASA’s 2011 Mars Science Laboratory mission.

The EDL will be powered by a battery sized to handle entry, descent and landing functions and support science operations for one sol (24 hr. 40 min. on Earth). Science will focus on atmospheric surface measurements and surface physical-chemical processes. A package of engineering instruments, including a camera, will monitor the 244-sec. descent phase and build a soft vision basis for a later Mars Sample Return landing system.

The module will feature a 2.4-meter-dia. heat shield with a MER-like aerodynamic profile and a single disk-gap-band Huygens-type parachute. The heat shield is composed of a 20-mm. honeycomb aluminum core/carbon skin frontshield and 24.2-mm. ablative norcoat liege thermal tiles, based on heritage from ESA’s Atmospheric Reentry Demonstrator and other missions. The guidance, navigation and control system, intended to control both lander orientation and touchdown velocity, will include a cluster of 400-newton hydrazine pulse-modulated thrusters designed to shut off 1.5 meters before landing, along with a radar Doppler altimeter and inertial measurement units.

The orbiter will carry five instruments—three radiometers/spectrometers and two imagers—to monitor atmospheric trace gases, in particular methane, characterize their spatial and temporal variation and localize the sources. The science mission will last one Martian year and 30 days.

NASA last month tapped Ball Aerospace for hardware for two of the instruments, a high-resolution stereo color imager and the Mars Atmosphere Trace Molecule Occultation Spectrometer.

ESA’s 2018 rover will weigh 300 kg. and be designed for a nominal mission of 180 sols (about 185 Earth days). It will be capable of traveling to a target 70 meters away within one sol.

Photo: NASA

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