DENVER, Colorado —Getting the Phoenix Mars Lander down and dirty on the red planet is anengineering saga stretching out over a decade. Its mission "raises fromthe ashes" a spacecraft and instruments from two prior tries to reach thered planet: the Mars Polar Lander that failed to phone home in 1999and a 2001 lander that was mothballed and shelved by NASA.
The builders of those twoearlier spacecraft here at Lockheed Martin Space Systems have taken lessonslearned to send Phoenix on its way.
Fingers are crossed forsure, but confidence is high that, indeed, the flight of the Phoenix will openup a new chapter in Mars exploration.
Shimmy and shake, digdeeper
In putting togetherNASA's next Mars lander, special attention was placed on the spacecraft's gangof a dozen pulse-firing descent thrusters that use rapidly opening and closingvalves. The vibration they create was found to shimmy and shake throughout thespacecraft structure. A similar system was utilized on the failed Mars Polar Lander.
"That was a hugerisk item to get retired very early," said Ed Sedivy, the company's Phoenix program manager. He led the Lockheed Martin engineering team in designing,constructing, and testing the Phoenix spacecraft.
Other problems that were spotlightedin a failure investigation board looking into the loss of the Mars Polar Lander— as well as those identified by company experts — were tackled by testing,testing and more testing.
"If you look back atthe Mars Polar Lander experience, that mission did not have every opportunityto be successful," Sedivy told SPACE.com.
Having another chance towork out those problems was key, said Timothy Priser, the Phoenix entry, decentand landing phase lead at Lockheed Martin Space Systems. "We were given anopportunity to do it again. And engineers when they are given that opportunityare going to dig deeper and they are going to make it better," he added.
Not on the radar screen
An early problem Phoenix designers also wrestled with was the prospect that the lander's radar might lockonto the spacecraft's own discarded heat shield — and not on the rapidlyapproaching Martian landscape.
That issue was not on theradar screen, quite literally, for the Mars Polar Lander mission nor the MarsSurveyor 2001 program, Priser said. Radar behavior improvements through the useof an algorithm in the computer brains of the Phoenix lander have solved thisconcern, he added.
Additionally, in thelanding profile for Phoenix, there is a 70 second delay between heat shieldjettison and the time the space probe starts to use its radar to gauge distanceto ground, speed of descent and horizontal velocity.
"It turned out to bea pretty simple fix ... and the delay in the timeline is what will mitigateit," Priser said.
Big wild card
One of the unknowns thatthe 772 pound (350 kilogram) Phoenix will encounter happens as the craft setsits three legs onto the arctic terrain. The ground texture shows polygonalcracking — a fractured surface.
"The reconnaissanceof the landing sites has been like nothing we've ever been the beneficiary ofin the past," Sedivy said. He points to the super-powerful camera gearaboard NASA's Mars Reconnaissance Orbiter (MRO), adding: "It is visualimagery with resolution far better than we've had in the past."
Still, what truly awaits Phoenix in terms of arctic surface geology and cold temperatures is a puzzle.
"It's the thingthat's the big wild card for us. We're going to a place that nobody has everput an asset before," Sedivy explained. "It could be thermally morehostile than we were expecting ... or it could be more benign. We just don'tknow."
With descent thrustersfiring, Phoenix will be speeding at about 5.4 miles per hour (2.4 meters persecond) in vertical velocity just before touchdown. But the horizontal velocitycould be up to 1.4 meters per second, advised Tim Gasparrini, deputy programmanager for the Phoenix entry, descent and landing at Lockheed Martin SpaceSystems.
What will truly greet thelander in terms of slopes, polygons, and rocks is not known. "It'ssomewhat of a complicated analysis to do in terms of touchdown," Gasparrinisaid. "But we've got a reasonably high probability of landing success evengiven all factors."
Phoenix fan dance
Nevertheless, Sedivy saidhe's nervous when trying to second-guess the depth of those polygonal fracturesand what may await Phoenix in terms of any crevasses.
"If they are narrow,the lander won't care. If they are not so narrow, the lander might care,"Sedivy noted.
Phoenix is about exploration, Gasparrini said, "andthis is one of the risks of that exploration." All the MRO imagery anddata gathered about the landing site has been phenomenal, he said, "butit's not the same as being there ... and Phoenix is going to be there."
Once the Phoenix footpads detect contact with the ground, the lander's thrusters will shut down. Theblast effect from those thrusters — from soil liquefaction and gas-soilbursting — is expected to toss light soil and dust up into the air.
Indeed, before thelander's solar arrays are unfurled, there's a 20 minute wait, a period of timethought long enough for churned up dust and dirt to settle.
Then the Phoenix fan dance begins: two nearly circular decagons of energy-generating solar cellsextend from opposite sides of the lander, unfolded in Chinese fan-like fashion.
"It's reallyimportant to get the solar arrays open, to get ourselves power-positive,"Sedivy said. "You don't begin to breathe again until you see your solar arraysdeployed."
That crucial opening daydeployment of solar arrays comes down to a wax job.
Electrical power isapplied to a paraffin actuator that, when that wax melts, allows the arrays tospread outward. That process should take some two to five minutes, with thevariability due to temperature in the landing area and how long it takes forthe wax to melt, Sedivy explained.
In the event that onearray fails to fold out, Gasparrini responded: "We can run a mission.It'll be a little different and may not get everything quite done that you wantdone. But you would be able to run a mission ... one that is tailored to meet yourpower constraints."
Sedivy added: "Onpaper, we've got a pretty respectable mission with one solar array."
But the bad news comes ifboth solar arrays are a no-show. Phoenix will be alive on batteries for about31 hours. That trickling down of energy and a ticking countdown clock wouldmean taking risks. A fast-paced, priority-setting scenario would have to bescripted in order to maximize scientific output from the dying lander.
"It's not the sortof activity you'd like to see after spending the last four years designing thevehicle," Sedivy said. "So being diligent engineers, there arecontingency procedures in place. To be ill-prepared for surprises is not inanybody's best interest," he pointed out.
The first photos from Phoenix are meant to provide engineering data. That is, a footpad picture will conveytechnical information about the surface upon which the lander is resting.Imagery is also to be taken of pie-shaped sections of the solar arrays. Thatshould reveal if they are under full-tension and latched in place or a problemhas occurred during deployment.
The cost of the Phoenixmission breaks out into a U.S. investment of $420 million, includingdevelopment, science instruments, launch and operations; plus the CanadianSpace Agency's investment of $37 million for the weather station carriedby the Mars lander.
In coming to full-stop onMars, the spacecraft will have traveled about 422 million miles (679 million km).
As landing day for Phoenix approaches, the designers, builders and operators of the spacecraft feel thatthey've treated concerns flagged by the Mars Polar Lander loss and learned fromthe shelved Mars Surveyor 2001 mission.
Confidence-building onthe Phoenix project via extensive testing was done. A laundry list of issueshas been addressed that might crop up to hinder the lander from safely reachingthe red planet and operating successfully at the Martian polar north.
Yet, fingers are stillcrossed. Getting to Mars is a balance of risk, hard work and a good dose ofluck.
"I think we've doneeverything that we could have done," Sedivy concluded.
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