|
Can Mars Support Life?
(Design News Via Acquire Media NewsEdge) Fifty years ago, Orson Welles terrified millions of Americans with a pre-Halloween radio broadcast pretending to announce a Martian invasion (http://rbi.ims.ca/5711-537
). In the next few months, we may find out if, in fact, Mars could ever support life as we know it. On May 25, a scientific lab is scheduled to land on Mars and will begin the first in-depth exploration for the possible existence of life forms on the Red Planet.
The Phoenix Mars Mission (http://rbi.ims.ca/5711-538
) is operated by the University of Arizona on a NASA contract, under the leadership of Principal Scientist Peter Smith, who has worked on several NASA projects through his role at the University's Lunar and Planetary Lab.
The purpose of the mission is to follow up on the discovery by Mars orbiter Odyssey of the ice on the northern pole of Mars (http://rbi.ims.ca/5711-539). In fact, there's a lot of ice ? enough to fill Lake Michigan twice over based on readings from an onboard neutron spectrometer.
?If you get to a place where there is ice, you wonder if over time, the climate could have changed to the point where that ice melted,? says Smith. ?Now if you have liquid water, soil and sunlight, then you have a lot of the ingredients, but not all, that can lead to a place where life can take a foothold.?
The key tasks of the Phoenix Mars Missions are to answer these questions:
Can the Martian arctic support life?
What is the history of water at the landing site?
How is the Martian climate affected by polar dynamics?
The Lander uses a robotic shovel to dig into the Martian earth. Camera images from the end of the shovel are sent back to scientists on earth who determine where to strike.
?We feel very confident we can get through even very hard-packed soils,? says Smith. ?The robot arm is very strong. If you were to brace your legs and hold on to that arm and try and stop it from moving, it would drag you.? Mission engineers feel the shovel can even handle ice that could have the consistency of granite. ?We've put a power tool on the end of the arm that actually acts as a rasp and it spins and it throws pieces of ice chips inside of the back of our scoop, and we can deliver those to our instruments. So we are sure that we'll get a sample of even the hardest materials,? says Smith. ?Putting the spacecraft down on one of the colder parts of Mars is really something that has stressed our engineering team and so we've had to come up with a well-insulated container to hold our electronics, which only work down to certain temperatures, and then we put in heaters to keep those electronics above that temperature at all times.?
Temperatures in the polar zone of Mars, equivalent to northern Alaska, range from -140 to -60C in an atmosphere that is extremely dry. Special testing is required to determine materials' fitness for those conditions. On the plus side, tests only had to determine fitness for a few uses, not thousands and thousands of cycles.
At the heart of the mission are the scientific experiments that will be conducted.
The Thermal and Evolved Gas Analyzer, or TEGA (http://rbi.ims.ca/5711-540
), is a combination of eight tiny high-temperature ovens coupled with a mass spectrometer. Contents will be analyzed after they're baked. The ovens are about the size of an ink cartridge in a ballpoint pen. Scanning calorimetry shows transitions from solid to liquid to gas of captured Martian earth. Scientists can measure how much water vapor and carbon dioxide gases are given off and how much water-ice is present. And most intriguingly, what if, as Smith surmises, there may have been a warmer and wetter past? What minerals may have been formed at that time? And if organic volatiles are released, they will be measured.
TEGA was built by the University of Arizona and University of Texas at Dallas. One of the exotic materials used on TEGA is a proprietary titanium sheet from ATI Wah Chang, an Allegheny Technologies company. ?ATI 425 titanium sheet was selected for major structural elements in the Phoenix Project Thermal Analyzer due to its good cold formability,? says Mike Williams, lead mechanical engineer for the TEGA team.
Studying Dissolved SaltsLike much of the equipment on the Phoenix Mars Mission, the Microscopy, Electrochemistry and Conductivity Analyzer (http://rbi.ims.ca/5711-541
) was originally conceived for a cancelled 2001 mission. Four wet chemistry labs will mix soil with water in a container loaded with 20 electrochemical sensors. They're looking for pH, dissolved oxygen and amounts of salts and minerals. MECA is being built by a team at the Jet Propulsion Lab., headed by Michael Hecht. Sam Kounaves, a chemistry professor at Tufts University, is a Phoenix co-investigator and the project leader for MECA's four wet chemistry labs project. ?The solution in the beaker will dissolve salt in the soil,? says Jason Kapit, a mechanical undergraduate engineering student at Tufts University who worked on the project. ?The dissolved salts in the soil will teach us about the history of water on Mars.?
The upper assembly of MECA consists of a sealed, fluoropolymer-coated, titanium leaching solution reservoir. Cast epoxy is used as a reaction vessel. Reaction chambers for future experiments will use Ultem polyetherimide (http://rbi.ims.ca/5711-542
).
One of the MECA instruments is a thermal and electrical conductivity probe consisting of three small spikes that will measure temperature and thermal properties of the soil. The spikes will also analyze the electrical conductivity to indicate any transient wetness that might result from the excavation. Unfrozen water on Mars could exist in the form of thin, briny films on the surface of particles. The electrical conductivity measurement could confirm their presence. The probe was developed by Decagon Devices of Pullman, WA.
Also on board will be a Meteorological Station, or MET, which will track weather on the ice cap until it is rendered useless by the onset of winter on Mars in November. It includes LIDAR, or Laser Imaging Detection and Ranging, which will count dust particles in the atmosphere. The team working on LIDAR includes the Canadian Space Agency, York University, the University of Alberta, Dalhousie University, the Finnish Meteorological Institute, Optech and the Geological Survey of Canada. It was built by MacDonald Dettwiler and Assoc. Ltd. of Richmond, B.C.
The other two major partners in the Phoenix Scout project are the Jet Propulsion Lab. (JPL), which is the project manager, and Lockheed Martin Space Systems (LMSS), which is the flight system manager.
One of the JPL functions is to provide interface to the Deep Space Network, sending command sequences and receiving data during the 10-month cruise to Mars. Lockheed Martin built the spacecraft in a project headed by Ed Sedlivery, who was also the chief engineer on the 2001 Mars Surveyor Lander, the mission that was canceled.
?The basic structure and most of the avionics are identical to the 2001 lander,? says Tim Gasparrini, deputy program manager at Lockheed Martin in charge of entry, descent and landing of the Phoenix Mission lander. ?We made changes in some of the components and changed out some of the thermal protection systems and we made a number of changes to the flight software and some of the algorithms we use to fly the spacecraft.?
The lander weighs 772 lb and is about 7 ft tall and 18 ft long with the solar panels deployed. The science deck is about 5 ft in diameter. The lander uses a mono-propellant hydrazine system that is designed to decompose exothermically into hydrogen, nitrogen and ammonia. The test equipment takes into account the ammonia deposited on the surface by the lander. Use of airbags was never considered for this lander.
Powered by SunlightSolar power is used extensively to supply power to the lander. ?During the cruise stage, there are about three meters of solar arrays that generate anywhere from a thousand watts down to 360 watts,? says Gasparrini. ?When we get to Mars, a second set of solar arrays deploys. They are about four square meters and they generate about 300 watts on the surface of Mars.? On earth, those some solar arrays would yield far more power ? about 1,450W.
The fundamental spacecraft structure is made of graphite-reinforced polycyanate composites (http://rbi.ims.ca/5711-543
). Two of the benefits of polycyanate matrices over materials such as epoxy are improved moisture absorption and outgassing properties. The result is fewer dimensional changes due to dry-out during orbit. Polycyanates are more resistant to micorcracking during thermal cycling, as well.
Aluminum and titanium are used for various fittings on the spacecraft. The primary adhesives used are based on epoxy and acrylic. ?We use acrylic adhesives mainly for the multilayer insulation blankets on the outside of the spacecraft,? says Neal Tice, the chief mechanical engineer for the lander. ?Blankets are also used on the ground. Acrylics are a very good adhesive for space-forming applications. It has a very broad temperature range.? External temperatures in space approach minus 220F. On the sun side, temperatures approach 250F. ?That's in a vacuum environment, so there is no convection,? adds Tice. Ablation temperatures on re-entry approach 3,000F.
A proprietary thermal protective system developed by Lockheed Martin is made of room-temperature-vulcanizing (RTV) silicone rubber and other materials. The shield ablates during re-entry. The ablative shield burns away so heat can be carried away from the spacecraft.
There are two unique metal constructions used to absorb impact when the lander touches down on the granite-like ice permafrost surface. ?In the legs of the lander, we use a cylindrical honeycomb crusher (made from aluminum) to absorb energy on landing,? says Gasparrini. ?We also have annealed stainless-steel load limiters attached to the legs. I have one on my desk and it's all bent over.? The parts were evaluated on special testing equipment developed by Lockheed Martin.
?Going to Mars is a hard thing,? says Gasparrini. ?There are a number of difficult engineering challenges. Entry, descent and landing itself is a difficult task to perform because we basically take this aircraft that is in a cruise configuration. In the space of seven minutes we transform from cruising to when we land gracefully on Mars. So when we enter we are coming in at 5,000 meters per second and we touch down at a meter per second. We take velocity out of the system with ablation where we use the atmosphere to slow us down. We then deploy a parachute and then we have to get the lander out of the aeroshell and then have the engines touch down. It's a complex set of operations that takes place in six or seven minutes.?
So, here it is 50 years after the Orson Welles radiocast and it's not the Martians coming here looking for life; it's us going to Mars.
Values for Polycyanate Versus Epoxy at 175C Cure Neat Properties
Polycyanates
Epoxies
Design parameters
Moisture absorption (%)
0.6 to 2.5
4 to 7
Moisture stability and contamination
Out gassing, TML (%)
0.1 to 0.3
0.3 to 1.5
Contamination
Coefficient of thermal expansion, CTE (ppm/C)
40
60
Dimensional stability
Go to www.designnews.com
and click on podcasts to hear interviews with Peter Smith and Tim Gasparrini.
Copyright ? 2008 Reed Business Information. All Rights Reserved.
[ Back To TMCnet.com's Homepage ]
|
INDUSTRIES
Activate Email 
Find Solutions for Enterprises, SMBs & Service Providers at the INTERNET TELEPHONY Conference and EXPO East, January 20-22, 2010. Miami, FL.
