When Phoenix Lands.. Options

[tedstryk]

I have been wondering about something....given the performance of the MERs, if one or both survive this winter, is it not conceivable that they could be operational when Phoenix lands? It would, I believe, be the first landing on anything but the moon with other landers (other than parts of the same mission) still operational.

[Stu]

For those people who haven't yet taken a look (shame on you! ) at Rui's excellent Q&A from yesterday with Peter Smith over on the spacEurope blog, here are some snippets... some real gold nuggets of info in here...

The robotic arm is 2.35 m long and powerful enough to scrape into hard
materials. It is true that if the spacecraft footpad perches on a rock or is
otherwise unstable, then the RA has the strength to move the lander. We often
joke that landing on ice in low gravity will allow us to pull ourselves along
the surface using the RA from rock to rock. If the ice is exceptionally hard
we will not dig through it, but instead, will use our RASP to scrape up
samples to be delivered to instruments on our deck.

The MARDI instrument was found to interfere with the guidance system under
rare circumstances forcing the difficult decision to turn it off during the
descent. The microphone does work and may be used later in the mission to hear
the sounds of the RA scraping on the Martian ice.

Discovering Martian life is beyond the goal of this mission. We are looking
first to see if the Martian arctic is habitable: periodic liquid water,
organic material (it could be from meteors), and energy sources available for
power an organism.

On May 25, the lander "feels" the Martian gravity and begins to accelerate
toward the planet. Its speed increases from 6000 to 12,500 mph. Fifteen
minutes before entry, the lander separates from the cruise stage that have
been its life support system for the last 10 months since launch. Seven
minutes before landing, we enter the upper atmosphere and the aeroshell
experiences the heat of friction with the thin atmosphere. We must enter
within a degree of our proper angle or else we can skip off into space or heat
too rapidly and overwhelm our protection systems.

After the aeroshell has slowed us to 900 mph, the parachute is deployed and we
start a leisurely descent to about 1 km above the surface. At a speed of 150
mph, the spacecraft is released from the backshell and drops toward the
surface. Twelve thruster ignite and using radar for guidance bring us to our
landing site at a speed of 5 mph. the specially designed landing legs take up
the shock of landing. Fifteen minutes later the solar arrays deploy and the
camera starts taking images. Our mission begins.

The first week of the mission consists of taking images and preparing for
gathering samples. At the end of the first week we expect to have delivered a
surface sample to our TEGA instrument. The summer is our prime science
opportunity and we expect to meet all our mission goals by September. As you
might expect, the mission will continue longer than this up until solar
conjunction in mid-November. Recovering operations after that in late December
will be very difficult as the Sun is setting in this high arctic region. By
February we expect that carbon dioxide ice is forming a thick layer around the
lander and without heat Phoenix will not survive. No 4 year mission for us.

The landing site has been well imaged from space by the HiRISE camera, a 0.5 m
telescope with resolution of rocks 1 - 1.5 m or greater. We have found a safe
site with few boulders to insure a safe landing. However, it will not be free
of cobbles and smaller pebbles. I am curious to see how these stones have
weathered over time and whether they are aligned with the polygonal
boundaries.

There are few slopes in the neighborhood and the horizon should look extremely
flat, no hills. However, the site is far from boring. We are near a 10 km
crater and should be on the ejecta blanket containing material brought to the
surface from depth. We are also on the slope of a large volcano, Alba Patera
and may encounter ash blown from the interior. Finally, the site is a shallow
valley and has undergone erosion which may leave signatures.

We land just before summer solstice and the first few months of the mission
have plenty of sunlight altho our power generation depends on the tilt of the
lander which we cannot control. Our science team has many arguments about how
ice might react when the overburden of soil is removed. We will try to force
some of the ice to melt by putting it in the warmest place we can find--the
lander deck, then imaging it as solar heating tries to melt it. The question
is will it sublimate before melting?

We are flying an atomic force microscope built in Switzerland by Urs Staufer
for the first time ever. This is a difficult instrument to fly because it is
sensitive to vibration even the tiny vibes caused by temperature change and
wind. It has worked well in the lab and during environmental tests giving a
resolution of an amazing 100 nm per pixel.

Our TEGA instrument which has 8 ovens is used to determine the minerals in the
soil and to drive off vapors which are measured in a mass spectrometer. The
ovens can only be used once so we must allocate them intelligently. Our basic
goal is a surface measurement, an ice sample, and a sample half way between.
Then will try to verify that what we have seen is real if the signal are near
the noise level.

Our thruster use hydrazine as fuel, its formula is N2H4 and our ultra-pure
mixture has no detectable organics. The combustion products are ammonia and
water. The more difficult question is what about the 1% that doesn't combust,
it is highly reactive and may alter the chemistry of the surface layers that
it contacts. We are vigilant and will try to avoid contaminated areas.

Another major part of our science is the study of polar climate. Not only is
Phoenix a traditional weather station, but we use LIDAR, built by our Canadian
partners, to measure cloud properties and heights. The camera has special
lenses for determining dust opacity and we do look for atmospheric phenomena
like dust devils and solar haloes.

The end of the mission has not been carefully studied and there are no
guarantees after we complete our primary mission. As much as anything, the
NASA budget limits our longevity. We will do everything in our power to last
until the last rays of sunlight energize the spacecraft.

All good things come to an end and we will leave important questions for
future mission to unravel--Phoenix is a stepping stone on the path to
discovering the Truth about Mars.

Good bye all and thank you for your interest!