Phoenix Mars Lander

Description

Phoenix landed successfully on Mars at 23:53:44 UT (7:53:44 p.m. EDT) on Sunday, 25 May.

The Phoenix Mars Lander is designed to study the surface and near-surface environment of a landing site in the high northern area of Mars. The primary science objectives for Phoenix are to: determine polar climate and weather, interaction with the surface, and composition of the lower atmosphere around 70 degrees north for at least 90 sols; determine the atmospheric characteristics during descent through the atmosphere; characterize the geomorphology and active processes shaping the northern plains and the physical properties of the near-surface regolith focusing on the role of water; determine the aqueous mineralogy and chemistry as well as the adsorbed gases and organic content of the regolith; characterize the history of water, ice, and the polar climate and determine the past and present biological potential of the surface and subsurface environments.

Spacecraft and Subsystems

The spacecraft comprises an octagonal base supported on three landing legs. Two octagonal solar panel wings extend from the base to provide power. Communication will be primarity through UHF relay via the Mars 2001 Odyssey orbiter, but Mars Reconnaissance Orbiter and Mars Express can also be used as relays, and Phoenix has a steerable medium gain X-band antenna to provide communications directly with Earth.

The science experiments and a robotic arm are mounted on the base. The experiments are: the Microscopy, Electrochemistry, and Conductivity Analyzer (MECA), the Robotic Arm Camera (RAC), the Surface Stereo Imager (SSI), the Thermal and Evolved Gas Analyzer (TEGA), and the meteorological station (MET). Total science payload mass is 55 kg.

Mission Profile

Phoenix launched on 4 August 2007 at 9:26:34 UT (5:26 a.m. EDT) on a Delta II 7925 from Cape Canaveral Air Force Station. The 681 million km heliocentric cruise to Mars took approximately 10 months, with landing on Mars on 25 May 2008. Fourteen minutes before touchdown, and about 7 minutes before atmospheric entry (defined as reaching an altitude of 125 km) the cruise stage was jettisoned. The spacecraft entered the atmosphere and the heat shield initially slowed the craft. After about 3 minutes the parachute deployed, followed by ejection of the heat shield 15 seconds later, deployment of landing legs 10 seconds after that, and radar activation 50 seconds later. At 1 km altitude the parachute was released and a powered descent and soft-landing was achieved using a pulsed propulsion system with 8 thrusters, which turned off when footpad sensors detected touchdown.

Touchdown occurred at 23:53:44 UT (7:53:44 p.m. EDT) on 25 May. The landing site is in the north polar region between 65 and 72 degrees N, nominally at 68.15 N, 125.9 W, a relatively boulder-free area with a high (30-60%) ratio of ice to rock. Surface temperatures in this region range between about 190 and 260 K and the landing altitude is about 3.5 km below the planetary reference. Mars was 275 million km from Earth at the time of touchdown, a light travel time of about 15 minutes. Communications were maintained through the relays on the orbiting Mars spacecraft Mars Reconnaissance Orbiter and Mars Express throughout the descent and for about 1 minute after touchdown, after which there was no communications with Phoenix for about an hour and a half.

The solar panels were deployed after allowing 15 minutes for the dust to settle. Phoenix then took its first images of itself and its surroundings. When communications resume the first images, along with spacecraft health telemetry, were relayed back to Earth. Landing occured just before the northern summer solstice, at 68 degree latitude the Sun will be in the sky full time and will not dip below the horizon until August.

All instruments will be deployed in the first two days after landing, but there will be an 8 to 10 day "characterization phase" to check out all systems. After this, the first soil sample will be delivered to the TEGA experiment. Surface samples will be analyzed by TEGA and MECA for the next 10 to 15 days and then deeper layers will be explored in 2 to 3 cm increments. Ice is expected to be 2 to 5 cm deep. As the summer ends the mission will have less solar energy to operate and will end when its power is depleted. Cost of the mission is estimated at $417 million.