Program Overview
The mission has two goals. One is to study the geologic history of water, the key to unlocking the story of past climate change. The second is to search for evidence of a habitable zone that may exist in the ice-soil boundary, the "biological paydirt." Phoenix's instruments are suitable for uncovering information on the geological and possibly biological history of the Martian Arctic. Phoenix will be the first mission to return data from either of the poles, and will contribute to NASA's main strategy for Mars exploration, "Follow the water."
The primary mission is anticipated to last 90 sols (Martian days) – just over 92 Earth days. Researchers are hoping that the lander will survive into the Martian winter so that it can witness polar ice developing at the spacecraft's exploration area. As much as three feet of solid carbon dioxide ice could appear in the area. Even if it does survive part way into the winter, it is very unlikely that the lander will function throughout the entire winter due to the intense cold.[2] The mission was chosen to be a fixed lander rather than a rover because:[3]
1. costs were reduced through reuse of earlier equipment; 2. the area of Mars where Phoenix is landing is thought to be relatively uniform and thus traveling is of less value; and 3. the equipment weight that would be required to allow Phoenix to travel can instead be dedicated to more and better scientific instruments.
History of the Program
In August 2003 NASA selected the University of Arizona "Phoenix" mission for launch in 2007 as what was hoped would be the first in a new line of smaller, low-cost, Scout missions in the agency's exploration of Mars program.[4] The selection was the result of an intense two-year competition with proposals from other institutions. The $325 million NASA award is more than six times larger than any other single research grant in University of Arizona history.
Peter H. Smith of the University of Arizona Lunar and Planetary Laboratory, as Principal Investigator, along with 24 Co-Investigators, were selected to lead the mission. The mission was named after the Phoenix, a mythological bird that is repeatedly reborn from its own ashes. The Phoenix spacecraft contains several previously built components. The lander used for the 2007-08 mission is the modified Mars Surveyor 2001 Lander (canceled in 2000), along with several of the instruments from both that and the previous unsuccessful Mars Polar Lander mission. Lockheed Martin, which built the lander, had kept the nearly complete lander in an environmentally controlled clean room from 2001 until the mission was funded by the NASA Scout Program.[5]
Phoenix is a partnership of universities, NASA centers, and the aerospace industry. The science instruments and operations will be a University of Arizona responsibility. NASA's Jet Propulsion Laboratory in Pasadena, California, will manage the project and provide mission design and control. Lockheed Martin Space Systems, Denver, Colorado, built and tested the spacecraft. The Canadian Space Agency will provide a meteorological station, including an innovative Laser-based atmospheric sensor. The co-investigator institutions include Malin Space Science Systems (California), Max Planck Institute for Solar System Research (Germany), NASA Ames Research Center (California), NASA Johnson Space Center (Texas), De La Salle University (Philippines),Mababang Paaralan ng Maynila (Philippines), Jeepney-Tech, Optech Incorporated, SETI Institute, Texas A&M University, Tufts University, University of Colorado, University of Copenhagen (Denmark), University of Michigan, University of Neuchâtel (Switzerland), University of Texas at Dallas, University of Washington, Washington University in St. Louis, and York University (Canada). Scientists from Imperial College London and Bristol University have provided hardware for the mission and will be part of the team operating the microscope station.[6]
On June 2, 2005, following a critical review of the project's planning progress and preliminary design, NASA approved the mission to proceed as planned.[7] The purpose of the review was to confirm NASA's confidence in the mission.
Launch
Phoenix was launched on 4 August 2007, at 5:26:34 am EDT (09:26:34 UTC) on a Delta 7925 launch vehicle from Pad 17-A of the Cape Canaveral Air Force Station. The launch was nominal with no significant anomalies. The Phoenix lander was placed on a trajectory of such precision that its first trajectory course correction burn, performed on 10 August 2007 at 7:30 a.m. EDT (11:30 UTC), was only 18 m/s. The launch took place during a launch window extending from 3 August 2007 to 24 August 2007. Due to the small launch window the rescheduled launch of the Dawn mission (originally planned for 7 July) had to stand down and was launched after Phoenix in September. The Delta 7925 was chosen due to its successful launch history, which includes launches of the Spirit and Opportunity Mars Exploration Rovers in 2003 and Mars Pathfinder in 1996.[8]
A noctilucent cloud[9] was created by the exhaust gas from the Delta II 7925 rocket used to launch Phoenix. The cloud took on not only the appearance of the mythical phoenix bird, but also the red and blue colors of the Phoenix Mars Lander logo. The colors in the cloud formed from the prism-like effect of the ice particles present in the exhaust trail.[10]
Landing
The Jet Propulsion Laboratory made adjustments to the orbits of three satellites around Mars to be in the right place on May 25, 2008 to observe Phoenix as it entered the atmosphere and to monitor it up to one minute after landing. This information will allow for better design for future landers.[11] The projected landing area was an ellipse 100 km by 20 km covering terrain which has been informally named "Green Valley"[12] and contains the largest concentration of water ice outside of the poles.
Phoenix entered the Martian atmosphere at nearly 21,000 km (13,000 miles) per hour, and within 7 minutes had to be able to decrease its speed to 8 km (5 miles) per hour before touching down on the surface. Confirmation of atmospheric entry was received at 4:46 p.m. PDT (23:46 UTC). Radio signals received at 4:53:44 p.m. PDT confirmed that Phoenix had survived its difficult descent and landed 15 minutes earlier, thus completing a 680 million km (422 million mile) flight from Earth.[13]
Parachute deployment was about 7 seconds later than expected, leading to a landing position some 25–28 km long (east), near the edge of the predicted 99% landing ellipse. The reason for this delay is not yet publicly known.
Mars Reconnaissance Orbiter's High Resolution Imaging Science Experiment (HiRISE) camera photographed Phoenix suspended from its parachute during its descent through the Martian atmosphere. This marks the first time ever one spacecraft has photographed another in the act of landing on a planet[13][14] (the Moon not being a planet, but a satellite). The same camera also imaged Phoenix on the surface with enough resolution to distinguish the lander and its two solar cell arrays. Ground controllers used Doppler tracking data from Odyssey and Mars Reconnaissance Orbiter to determine the lander's precise location as 68.218830°N 234.250778°E.[15] The landing site is here on the Google Mars web-based map and here on the NASA World Wind planetary viewer (free installation required; "MOLA Color (ASU)" is the Google image).
Phoenix landed in the Green Valley of Vastitas Borealis on May 25, 2008,[16] in the late Martian northern hemisphere spring (Ls = 76.73), where the Sun will shine on its solar panels the whole Martian day.[17] By the Martian northern Summer solstice (2008-06-25), the Sun will appear at its maximum elevation of 47.0 degrees. Phoenix will experience its first sunset at the start of September 2008.[17]
The landing was made on a flat surface, with the lander reporting only 0.3 degrees of tilt. Just before landing, the craft used its thrusters to orient its solar panels along an east-west axis to maximize power generation. The lander waited 15 minutes before opening its solar panels, to allow dust to settle. The first images from the lander became available around 7:00 p.m. PDT (2008-05-26 02:00 UTC).[18] The images show a surface strewn with pebbles and incised with small troughs into polygons about 5 m across and 10 cm high, with the expected absence of large rocks and hills.
Like the 1970s era Viking spacecraft, Phoenix used rocket motors for its final descent.[19] Experiments conducted by Nilton Renno, mission co-investigator from the University of Michigan, and his students have investigated how much surface dust would be kicked up on landing.[20] Researchers at Tufts University, led by co-investigator Sam Kounaves, will be conducting additional in depth experiments to identify the extent of the ammonia contamination from the hydrazine propellent and its possible effects on the chemistry experiments. In 2007, a report to the American Astronomical Society by Washington State University professor Dirk Schulze-Makuch, suggested that Mars might harbor peroxide-based life forms which the Viking landers failed to detect because of the unexpected chemistry.[21] The hypothesis was proposed long after any modifications to Phoenix could be made. One of the Phoenix mission investigators, NASA astrobiologist Chris McKay, stated that the report "piqued his interest" and that ways to test the hypothesis with Phoenix's instruments would be sought.
