Express, Hope, Spirit, Opportunity
a The pioneering science quartet is now en route to Mars.
|Rocket-camera, July 7th Delta launch rocket for MER mission, as imaged during Monday's successful take-off. Opportunity could have launched as late as July 15th, with a 24 hour turnaround to troubleshoot any problems with its Delta rocket. But after the fifteenth, a stand-down of four years would have been needed for the same mission profile to reach Mars as efficiently. In a nail-biting series of finishing fixes, five launch delays pushed the take-off to late Monday night, when its spectacular take-off finally illuminated the Florida Space Coast.
The latest Mars rover, Opportunity, launched July 7th, and its sister rover, Spirit, which was launched on June 10th, have begun challenging trips to act as robotic geologists. The twin launches begin journeys leading to an eventual three months of exploration on the martian surface. To help scientists determine whether there was ever enough water on Mars to sustain life, the motorized explorers will send back images of sediment and mineral deposits.
Monday night's launch of the six-wheeled Opportunity rover-- about the size of a large riding lawn mower-- provides a vehicle loaded with equipment to analyze the Martian surface. Ten times bigger than the highly successful 1997 Sojourner rover, these twin vehicles are equipped to traverse the planet's surface over a daily distance of about a football field. With 6,000 miles separating the two landing locations on Mars, both surface missions will begin in January, 2004 and continue for three months through April, 2004.
Monday's take-off of Opportunity also successfully marked a remarkable joining of scientific cohorts to study the Red Planet. "It's one of the most intensive explorations of another planet in history," said Ed Weiler, associate administrator for NASA's Office of Space Science. The first launch of Spirit has so far performed its initial calibration maneuvers. It is currently more than 17 million miles from Earth.
Those twin rovers are following two other probes already on their way to Mars. Japan's trouble-plagued Nozomi is scheduled to arrive in late December or early January. Nozomi, first launched five years ago, is Japan's first attempt to explore the Red Planet. After gaining insufficient velocity on its first sling-shot pass by Earth, it maneuvered for a second pass that will take it towards its scheduled end-of-year encounter.
Scheduled to arrive at about the same time is the European Space Agency's Mars Express orbiter and its British-built Beagle 2 lander.
Sending back images to Earth now, NASA's Mars Global Surveyor and Mars Odyssey are already circling the planet and awaiting the rovers' arrival in six to seven months.
Weiler said, "Literally, the world is going to Mars."
Successful launches, complex orbital manuevers, landings and remotely-controlled operations millions of miles away--those are just a short-list of challenges that await mission planners. Out of nine previous attempts to land on Mars, only three have succeeded because of the difficulty of traveling more than 300 million miles and landing on the windy, dust-covered planet. The cost of sending the two rovers to Mars is $800 million. "One for three is a good batting average in baseball," Weiler said. "But when these things cost so much it's not that great for space."
"Everytime I see the descent and landing video, I get nervous," said Weiler. "There are too many moving parts. Too many things that can go wrong. We can do absolutely everything right...after the failure of Mars 99, but if we get a gust of wind that exceeds the limits [on descent in January], we can lose the lander."
"There was a huge boulder next to Viking," noted Weiler, as he described the 1976 rocket-powered Viking spacecrafts' descent onto Mars. "All it takes is a boulder of the wrong size in the wrong place. Three [successes] out of 9 [attempts] aren't good odds."
But in addition to multiple landers increasing the chances for success, the primary reason for the summer flurry of missions is a unique close approach between Earth and Mars. Mars is approaching Earth in what will soon be the closest the planets have been in 73,000 years--a confluence set officially for 5:46 AM, Wednesday, August 27, 2003. That night, the Red Planet will be the brightest object in the sky as it reaches its closest Earth encounter, or opposition, at 34,646,418 miles.
|Mars Opposition, Summer 2003. While Mars and Earth will be closest at the end of August, the complex orbital paths required to land on the Red Planet make early summer launches optimal.
At opposition Mars will be as close as it has been since September 12, 57,537 B.C. or one-third closer than the average opposition. The next approach this close is August 28, 2287 A.D at 34,620,000 miles.
The planet's bright magnitude should begin August 20 and continue through September 2 but fades rapidly thereafter as Earth pulls ahead of it and the Moon begins to grow full.
Cornell University Professor Steve Squyres, lead principal investigator of the science packages called Athena, noted one advantage of this orbital closeness is faster communication: "At closest approach, the one-way transmission time is around 11 minutes." [In contrast, Viking in 1976-77 took around 19 minutes for one-way transmission].
The NASA rovers are nearly sisters, but not exactly so in an engineering or hardware sense. Comparing the twin rovers, Squyres indicated how the first and second surface missions differ: "The one intentional difference is they transmit on different frequencies. So we don't get confused which one we are talking to. The differences are very minor. One of the things we found, the actuator that moves the mirror on Opportunity is a little stiffer when it gets cold. So we have to be sure to warm up Opportunity slightly more than Spirit."
Compared to the twin NASA rovers, the European lander is smaller, less mobile, and more biologically-oriented in its testing protocols. "This is the first time Europe has gone to Mars," continued Weiler, noting that the European Space Agency, ESA, launched its own probe June 2nd, called the Mars Express, with a lander, named after the famous voyage, Beagle, that carried Englishman Charles Darwin on his world tour in search of how life evolved on Earth. "I sent an email after the successful Mars Express, wishing ESA luck," said NASA's Weiler. "After the [first Mars Exploration Rover] MER-A launch, ESA sent me a congratulatory email."
"Beagle is a softlander," said Weiler. "It would be great to have multiple landers on Mars. The last time we had multiple landers on Mars was 1976."
With a landed mass of less than 30 kg, Beagle 2 represents the most ambitious science payload-to-systems mass ratio ever attempted. Almost a third of the payload will carry out various types of analysis or be used to manipulate and collect samples for study on the surface of Mars. One of its main tasks will be the step-wise heating of martian soil in a kind of oven, to determine the elemental composition of any volatiles including organic compounds.
|Mars Express spacecraft.
Since its June 2nd launch from the Russian Cosmodrome, mission control for the European Space Agency has issued two status reports, noting the power-up and communication tests with their probe are proceeding.
On June 24th, mission engineers summarized their status: "All operations planned for the Launch and Early Operations Phase (LEOP) have been completed and the near-Earth verification phase has commenced as planned. All operations are now being conducted via the high gain antenna, which is the nominal configuration. The performance of the ESA and [Deep Space Network] DSN ground stations supporting the mission is excellent throughout the communications passes. Spacecraft platform subsystems (power, thermal, attitude and orbit control, on-board data handling) behave in a nominal manner. Payload and platform commissioning continue in parallel. Just 3 weeks after the launch of Mars Express, initial checkouts reveal that the overall status of the Mars Express orbiter payload is nominal and very satisfying. One of the major upcoming activities will be the Beagle-2 lander checkout, planned for 4 and 5 July."
Following their initially planned lander checkout, on July 8th, engineers continued to view the progress favorably: "Spacecraft platform subsystems (thermal, power, attitude and orbit control, on-board data handling) behave in a nominal manner. Spacecraft commissioning will continue into the end of July. Payload commissioning, including the Beagle-2 lander checkout, will be completed by mid-July. All orbiter payload instruments are in good health. The initial checkouts and calibrations have revealed very satisfying results. The Beagle-2 lander has been successfully switched on for the first time in flight on 4 and 5 July and has been communicating with the orbiter. On the 2nd of July, the Mars Express Science Working Team decided to modify the baselined reference orbit, adopting a G3u-type orbit [tuned for optimal low-altitude day and night-side viewing] starting with a pericenter at the equator. This new reference orbit is taking into account the post-launch delta-V[elocity] budget, and allows for an optimization of the science return from the Mars Express mission."
|Nozomi, Japanese probe Hope, joins NASA's Spirit and Opportunity.
Nozomi, a Japanese (ISAS) Mars probe, has also completed its final Earth swingby operation on June 19 (JST), and is on its way to Mars. Nozomi, which means Hope, passed within 18,000 km of the Earth in a manuever designed to use the planet's gravity to slingshot the probe toward Mars.
Nozomi, launched in July 1998, is Japan's first attempt to explore Mars. Its mission is to orbit Mars and gather data on the Martian atmosphere and its interaction with solar wind for up to two years. It was originally scheduled to reach its destination in October 1998, but an earlier Earth swingby failed to give it sufficient speed, forcing a drastic rescheduling of its flight plan. In April last year, a burst of solar flares damaged Nozomi's heating system and cut off most communication link between the probe and tracking stations on Earth.
The computer control systems on the probe were intact, however, allowing engineers on Earth to repair the spacecraft. ISAS will begin trying to repair the electrical damage from July through November. If successful, it will arrive in late December, and will be thrown into orbit around Mars.
Each of the quartet has its own challenges and rewards. Beagle is smaller and will perform some of the first biology detection experiments since the 1976 Vikings first injected microbial nutrients in hopes of seeing evolved gases and byproducts of martian metabolism. Beagle will be less mobile, relying on a mole-like digging tool to burrow for its soil samples just below the dusty top-layers. The Mars Exploration Rovers, Opportunity and Spirit, will have panoramic cameras and much greater mobility to travel beyond where they initially come to rest. Late this year and early next will give focus to the international science effort to explore whether the 'wetter and warmer' Mars can be viewed up close.
In looking back on the success of the 1997 Mars rover, Pathfinder project scientist, Dr. Matthew Golombek, of the Jet Propulsion Laboratory, reflected that: "Power for a solar spacecraft must be managed very carefully. Managing the lag in knowledge from one day to the next is also important. Better autonomy placing instruments against rocks and targets and more autonomous roving could help look at more materials on the surface and visit more sites. For deep space missions, all it takes is one mistake for the mission to fail. Every launch has a 5 times out of 100 chance of blowing up. Part of exploration is confronting the unknown and risk can never be removed completely. In cases like Pathfinder taking a little risk can result in an enormous payoff."
Orbital projections of where Mars Express and the Mars Exploration Rovers are right now, can be continuously monitored over their half-year journeys.
JPL, a division of the California Institute of Technology, manages the Mars Exploration Rover project for NASA's Office of Space Science, Washington, D.C. Additional information about the project is available from JPL and from Cornell University, Ithaca, N.Y.