May 23, 2008

The World Watches Phoenix on its Final Approach to Mars; Interview with Phoenix Mission Public Affairs Manager, Sara Hammond

The Entry, Descent and Landing (EDL) - "Seven Minutes of Terror" for Phoenix

At 16:53 PST on Sunday afternoon (19:53 EST Sunday evening, or 00:53 GMT Monday morning) the world will be quiet, waiting for a signal from the Phoenix lander.

Shortly before this time, the robotic explorer will have sped toward the Martian atmosphere at a velocity of 12,750 miles per hour (20,500 kilometres per hour). Using only the upper atmosphere of the Red Planet, Phoenix will begin to aerobrake, slowing rapidly as it re-enters. A parachute will deploy once the lander's heat shield has done its job, slowing the craft from 900 miles per hour (1,450 kilometres per hour) to 250 miles per hour (400 kilometres per hour) in a nerve-racking 15 seconds. Should the parachute be deployed too early, the high velocities may rip the tough canopy to shreds; open the parachute too late, Phoenix may not have time to slow sufficiently for landing. This is only the start of Phoenix's "Seven Minutes of Terror" (chronicled by this superb, and inspiring NASA video).

When sufficiently slowed, the descending craft will jettison its heat shield so it can continue to drop through the atmosphere. This will be the first time the Phoenix lander will be exposed to the Mars air. Shortly after the heat shield has been removed, Phoenix will lower its legs in preparation for landing with its radar systems, tracking how far it is from the ground.

When the time is right, when Phoenix is about 3,200 ft (that's about a kilometre) from the ground, the onboard systems will decide on the point at which the lander will separate from the "back shell" and parachute. It will detach from the parachute at a velocity of 125 miles per hour (200 kilometres per hour) and then freefall from a height equivalent to two Empire State Buildings stacked on top of one another... this will be the most frightening point of the Entry Descent and Landing (EDL) phase.

The onboard systems will have to make sure the craft is falling at the correct orientation, being careful to ensure a safe (and upright) landing. Then the most critical part; Phoenix will light up all its thrusters to slow it sufficiently to land gently on the Martian regolith. Once the EDL is complete, a signal will be sent back to Earth, which we will receive eight minutes later at 16:53 PST.

All the operations carried out during the entry, descent and landing are fully automated. This intense seven minutes will be controlled solely by Phoenix, there is no human intervention.

Exclusive interview with Public Affairs Manager, Sara Hammond

Last year, the Mars Foundation selected the Phoenix Mars Lander as our "Featured Mars Mission" as we realized the huge potential the lander had for aiding the future of manned settlement plans. The MarsHome.org story "The Phoenix Mars Mission", investigates how Phoenix will further our understanding about water held in the Martian polar regions and how the "Scout Class" lander will be the first step toward establishing a human presence on the Red Planet. But how was the Phoenix landing site chosen in the first place? Which Mars missions aided the search for the location? We were very lucky to get some answers to our questions from the Phoenix science team's Public Affairs Manager, Sara Hammond.

Sara was kind enough to provide some very interesting details to how and why the Mars polar region was chosen for the Phoenix landing, what the lander will be looking for when it carries out science operations and which previous Mars missions have helped pave the way for Phoenix.

1) Which Mars missions helped with the selection of a landing location on the Martian surface?

Sara: In a way, data/imagery from all previous successful missions has helped in determining an appropriate landing site. Current missions that have helped extensively with this and are currently involved are Mars Reconnaissance Orbiter, Mars Odyssey, and Mars Express. Mars Orbiter Camera (MOC) images from the Mars Global Surveyor mission were widely used in locating potential landing sites before HiRISE images became available.

2) Was the location primarily selected due to the possibility of finding life? Or was it to aid the understanding of surface composition for future manned missions?

Sara: The landing site was not chosen with the intent of finding life. The landing site was chosen because of the nature of the surface and the lack of hazards to landing (i.e. large expanses with little variation on the surface, low abundance of large boulders, low surface slopes, relatively smooth surface texture) and evidence for ground ice near the surface. The payload of instruments is particularly appropriate for examining an environment of ice and soil and for gaining a better understanding of surface or near surface composition to determine if the Martian arctic soil could have in the past, or currently, support life. While the science payload of Phoenix is not designed for life detection, this mission is an important stepping stone in the search for whether Mars has life.

3) Do you expect to find surface ice near the landing site? How much information can be found out about possible permafrost water ice?

Sara: Yes. NASA's Mars Odyssey orbiter found evidence in early 2002 that this region shelters high concentrations of water ice mixed with the soil just beneath the surface. Isotopic ratios in the ice will be measured with the mass spectrometer. Differences between the isotopic ratios in the subsurface ice and in atmospheric water could indicate whether or not the ice is ancient. Simply finding ground ice will provide ground-truth for the measurements made by orbiting spacecraft and will refine models of ice depth and of atmospheric-ice interactions in widespread areas of Mars that contain subsurface ice.

The Mars Foundation really appreciates Sara taking the time to respond to our questions, especially during this very busy time!

So how can you keep up with Phoenix events? Firstly, check out the Phoenix mission site (http://phoenix.lpl.arizona.edu/index.php) and the regularly updated blogs by the mission control scientists (http://www.nasa.gov/mission_pages/phoenix/blogs/index.html)

Secondly, check out your local TV news listings for coverage of the event...

We look forward with anticipation for the message from Mars on Sunday, we will update MarsHome.org with news as we get it...

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