The Phoenix Lander lowers itself onto Mars using a set of powerful thrusters. No airbags for this tricky touch down on the red planet. Image
Credit: JPL/Corby Waste
DENVER, Colorado - The next Mars lander is undergoing assembly and testing, being readied for departure next year to explore the martian arctic. This probe is equipped to dig deep, quite literally, into an ongoing mystery--the history of water on Mars and the planet's potential as an extraterrestrial address for life.
NASA's Phoenix Mars mission is the first in the space agency's Scout series, a class of spacecraft designed to be inventive but relatively low-cost in furthering Mars exploration.
Phoenix is headed for liftoff in August 2007, cruise across the vacuum void for 10 months and set itself down on the red planet in late May 2008. This time there's no bouncing to full-stop on air bags. It will come to a soft touchdown using controlled thrusters.
The Mars-bound spacecraft and related parts--a heatshield and protective backshell--sit within a cleanroom here at Lockheed Martin Space Systems--the firm that has designed, built, integrated, and is testing the Phoenix for its journey.
Gigantic, below-the-floor filters keep the airflow around Phoenix in clean and dust-free condition.
"We do have planetary protection requirements for the mission. We don't want to contaminate Mars," said Peter Doukas, engineering manager for the Phoenix Mars Scout program at Lockheed Martin Space Systems. "So every step of the way we're performing what we call bio-assays...to literally take spore counts of things so we're not contaminating Mars when we get there," he told SPACE.com.
Doukas reiterated a phrase that has been attached to Phoenix.
"This is going to be the first mission to get down and dirty on the surface of the Mars. With all due respect to the Spirit and Opportunity Mars rovers...we're going to get muddy. They got dusty," Doukas noted.
Living up to its namesake
Still to arrive are the various instruments that are to be mounted on the "deck" of the three-legged Phoenix. They will fit alongside the craft's robotic arm. Icy, muddy samples of the martian soil are to be scooped up via the mechanical appendage, with those specimens deposited into instruments for detailed chemical and geological analysis.
"It's not like we're going to incubate bacteria on Mars. But we are going to study the soil for its ability to harbor life," Doukas explained.
The Phoenix mission has lived up to its namesake as it "raises from the ashes" a spacecraft and science gear from two previous unsuccessful attempts to explore Mars: the Mars Polar Lander failure of 1999, as well as a Mars Surveyor 2001 lander that was well along in development, but mothballed in the wake of back-to-back failures at Mars.
That 2001 lander was overhauled to improve the spacecrafts robustness. Also, the revamped probe includes "here's what I'm doing" ways to advise Earth controllers of critical events as Phoenix plunges toward Mars for a landing.
"It has been a tough job to put a new mission into an existing box,", Doukas noted.
Throttle up to get down
To get down and dirty on Mars, Phoenix must first ease itself down on the planet. For the first time since NASA's Viking missions of the 1970's, the intent is for the spacecraft to achieve a successful and safe self-powered landing onto Mars utilizing onboard engines.
Punching through the martian atmosphere, Phoenix will slow down to Mach 1.7 (that's 1.7 times the speed of sound). At that moment a parachute is deployed. Shortly after the parachute blossoms, the vehicle's protective heat shield is jettisoned. Then the probe's landing radar is turned on and its legs extended.
Even under parachute, Phoenix speeds through the martian atmosphere until it comes within .6 miles (1 kilometer) of Mars' landscape. At this point, the lander frees itself from the parachute. It then throttles up a set of landing thrusters fed by ultra-pure hydrazine and decelerates.
When Phoenix is either at an altitude of 39 feet (12 meters) or traveling at 7.9 feet per second (2.4 meters per second) the spacecraft starts traveling at a constant velocity. On touchdown, the landing engines are turned off, controlled by footpad-mounted sensors that detect contact with the surface.
Once down, Phoenix is a fixed lander--a firm-footed, stay-put probe ready for research in the northern polar plains of Mars.
At a special hot fire test facility here, the Phoenix propulsion system design has undergone extensive shakeout. These were very successful, Doukas said, with thruster firing tests wrapped up first of the year.
Between early this month and mid-May of next year, Doukas said, Phoenix goes through Assembly, Test, and Launch Operations, or ATLO for short. Completing ATLO, the Mars lander will be transported to Florida for launch atop a Boeing Delta 2 booster. The sojourn to Mars will start sometime within a 22 day launch window in August 2007.
While engineers are busy prepping Phoenix for its sendoff, scientists are on track in plotting out their own high-expectations for mission success.
At the 37th Lunar and Planetary Science Conference (LPSC), held March 13-17 in Houston, Texas, Phoenix team members presented both excitement and nervousness about the Phoenix Mars endeavor--specifically, addressing the dangers lurking at the spacecraft's landing zone.
During the summer season, the Phoenix robotic arm will dig a trench and provide samples to instruments on the deck of the spacecraft, reported Peter Smith of the University of Arizona's Lunar and Planetary Laboratory in Tucson. He heads the Phoenix Mission.
A set of experiments is planned to help researchers understand the chemistry and mineralogy of the surface materials down to a layer where ice is stable, Smith said. Because the landing site is selected with the expectation of finding water ice near the surface, the Phoenix mission may provide the first on-the-spot examination of water on Mars, he explained.
The search for evidence of a habitable zone and assess the biologic potential of the ice-soil boundary is high on the scientific agenda for Phoenix.
Microbial colonies can survive in a dormant state for extremely long periods of time, Smith reported at LPSC. He highlighted recent work showing that as water ice melts onto soil crystals at temperatures as cold as - 20 C, microbes are activated and are able to search for food. As temperatures increase, growth and reproduction begin.
The question is, Smith asked: Can this cycle take place on Mars?
"It is unlikely that a single trench in the vast northern plains will find evidence for biological communities even if they exist there," Smith noted in a research paper issued at LPSC. "Our goal is to determine whether conditions favor their preservation."
Phoenix is to drop itself down on the high northern latitudes of Mars. But what awaits the lander in terms of dangerous geography is still being thrashed out.
No egregious landforms
Mars scientist, Ray Arvidson of Washington University in St. Louis, Missouri, said the region under review where Phoenix is to touch down does not have "egregious landforms" in terms of safety.
That belief, Arvidson added, will be strengthened by imagery from the just arrived Mars Reconnaissance Orbiter (MRO), as well as Mars Global Surveyor, Mars Odyssey and the European Space Agency's Mars Express--orbiters all.
Still, there's a host of engineering issues that must be addressed to get Phoenix safely down on Mars, said Joe Guinn, mission system manager for Phoenix at the Jet Propulsion Laboratory (JPL) in Pasadena, California.
Guinn said the spacecraft is quite robust as it enters the martian atmosphere and descends to Mars. "But it is pretty risky," he added. "If we lose an engine, the other engines are guaranteed to get us to the scene."
Additional uncertainties include air density, winds, lander attitude control...and just how well Phoenix will deal with slopes and rocks, Guinn explained. Fortunately, the northern plains of Mars are very flat and low.
Belly up to Mars
"As far as we can tell from all available data...slopes look relatively benign," added Matt Golombek, a JPL planetary geologist and Mars landing site specialist.
However, rock distribution remains the least understood safety hazard for Phoenix.
Golombek pointed out at the LPSC that the Phoenix lander has about 14 inches (35 centimeters) of clearance above the surface, depending on the force taken by the lander's legs.
"If there is a pointy rock that you come down on, the belly pan [of the lander] could hit that rock...and that would be of serious concern," Golombek said. "So there is concern here. We will be looking at the MRO data with great interest," he concluded.