Postcards from Mars
Spirit has landed on Mars. After a journey of nearly half a million kilometers (about 300 million miles), NASA’s Spirit rover last night reported back to engineers waiting anxiously back on Earth that it had arrived on the red planet. And then, before going to sleep for the night, it sent home a few picture postcards.
During what was described as a textbook entry, descent and landing (EDL) sequence, NASA engineers could do nothing but sit back and wait as Spirit, under the control of onboard software, hurtled down through the martian atmosphere.
|Due to good positioning, the image team was able to capture 60-80 images the first night. The predicted best case was for a transfer rate of 16 megabits per second, but instead the rover exceeded this data rate by 150%, or 24 megabits per second–as shown here in montage on a single view screen in Pasadena.|
Sean O’Keefe, NASA Administrator, said: ‘We couldn’t have expected as much, as soon, and in such volume. Ladies and gentlemen, Mars!’
NASA Associate Administrator for Science, Dr. Ed Weiler, said: ‘I would have been happy to go to the hotel tonight if I had heard a single tone. A middle-C, one musical note from Mars. Instead, you heard the symphony’.
Because it takes radio signals about 11 minutes to travel between Earth and Mars, engineers would not have been able to react quickly enough to control the EDL process accurately. "Entry, descent and landing is something we cannot control from Earth. We let the software onboard control all these actions very precisely, in real time," said Rob Manning, who was in charge of the EDL procedure.
Spirit did its job well, sending back one signal after another during the EDL sequence indicating that it was performing exactly as planned.
At about 7:00 PM PST, in preparation for entering the Martian atmosphere, Spirit began turning itself around so that its heat shield faced forward. About an hour later, the spacecraft ejected its cruise stage, which contained the thrusters used during its journey from Earth to ensure that it stayed on-course. Shortly after 8:30, Spirit’s parachute deployed, on-schedule, and a few minutes later, at 8:36 PM, the Spirit control room at NASA’s Jet Propulsion Laboratory (JPL), received the first indication that Spirit had reached the surface. Final confirmation of the landing came at 8:52 PM.
Going into the EDL sequence, engineers were pleased with the accuracy achieved by Spirit’s navigation team during its journey from Earth to Mars. So pleased, in fact, that after a course-correction maneuver last Friday, the fourth such scheduled adjustment, they decided to skip the fifth and sixth corrections entirely.
"It’s kind of like playing a par 5 hole in golf, where you tee off in Paris and the hole is in Tokyo, with a little water hazard in the end. The Nav[igation] team managed to get a birdie on this hole; it only took 4 maneuvers," said MER Navigation Team Chief Lou D’Amario. Spirit is believed to have come to rest within a few kilometers of its target.
There was one anxious moment after Spirit sent back the first signal that it had reached the surface. Immediately after the signal was received, it disappeared. The delay "caused us some pause," said Manning. "It was nerve wracking." It wasn’t until 10 minutes later that the signal reappeared, confirming that Spirit was, indeed, on Mars and functioning as expected.
But that was only the first good news of the night. The mission team soon learned that the rover landed right side up. During its journey, the rover was enclosed by a set of four "petals." It had a one-in-four chance of landing right side up, on its base petal. Because it did, Spirit avoided having to go through a complicated sequence of maneuvers to right itself. Consequently, it was able to retract its airbags and deploy its solar panels, a process referred to as "critical deployment," relatively quickly.
|‘For the first time in human history’, said NASA Associate Administrator for Science, Ed Weiler,’we have an interplanetary communication channel over another planet. Data moved from Spirit [on the surface] to Odyssey [in orbit] to the Deep Space Network [on Earth, positioned in Canberra, Australia, Goldstone, California and Madrid, Spain]. [In the panoramas], there’s not too many big rocks, it looks like an interstate highway. Or what a dry lake bed should look like. We want to drive!’|
This, in turn, enabled Spirit, to get some additional work done before the sun went down and rover went to sleep. Using its Navcam (navigational camera) in low-resolution mode, Spirit took a stunning series of images of the landing site. These are the first close-up images ever seen of Gusev Crater. Spirit transmitted the images to the Mars Odyssey orbiter, which flew over Spirit shortly after it landed. Mars Odyssey then beamed them back to Earth.
By 11:30, imaging specialists had assembled a 360-degree panorama of the rover’s surroundings. In the panorama is one large rock, just to the right off the front of the lander, a likely target for further investigation.
Gusev Crater is believed to be the site of an ancient and long-gone martian lake, fed by a massive river valley, Ma’adim Vallis. Scientists are hopeful that by studying the rocks in the area, they will be able to learn about the history of water in the region and, thus, about its potential as a habitat for life.
It will be at least another nine days, though, before Spirit rolls off its platform and begins to explore Gusev. During that time, engineers will conduct a comprehensive assessment of its health. Spirit will also take a series of images, using its Pancam (panoramic camera) to produce a high-resolution, full-color stereo panorama of the site, and its Mini-TES (Mini-Thermal Emission Spectrometer) to produce a matching set of infrared images that will be used to analyze the mineral composition of the rocks at the site. These images, which may begin arriving as early as Sunday, will also help scientists determine more precisely where Spirit is located and plan what targets the rover will investigate once it rolls off its platform.
Already, though, the science team is thrilled with the potential of the landing site. "We have hit the sweet spot [within the landing ellipse] from a scientist’s perspective," said Steve Squyres, principal investigator for the MER missions. "It’s a place that looks like it was tailor-made for our vehicle. We see rocks, but not so many that they will get in our way. So we’re looking forward to some great driving in the months ahead."