MRO: Delicate Dips into the Martian Atmosphere
Putting on the brakes! Mars Reconnaissance Orbiter is now dipping into the martian atmosphere to adjust its orbit. The controlled use of atmospheric friction is a process called “aerobraking”, a technique that changes the initial, very elongated orbit of the orbiter into a rounder shape optimal for science operations at Mars. Image
Credit: JPL/Corby Waste

NASA's newest mission to the red planet--the Mars Reconnaissance Orbiter (MRO)--is working well as it shaves off altitude in order to swing into active science-gathering duties later this year.

The initial capture by Mars' gravity put the spacecraft into a very elongated, 35-hour orbit.

Now underway is the delicate art of "aerobraking"--using hundreds of cautiously calculated dips into the upper atmosphere of Mars. The process uses brief burns from MRO's thrusters. Those dips have to be deep enough to slow the spacecraft by atmospheric drag ... but not deep enough to overheat or damage the orbiter.

At aerobraking's end, MRO's orbit around Mars will be approximately two hours. At that point, from the spacecraft's nearly circular orbit, the mission's science observations are to begin in earnest.

The multi-tasking Mars Reconnaissance Orbiter will study the history of water on the red planet. In addition, it will become the first link in a communications bridge back to Earth--an "interplanetary Internet" that can be used by spacecraft in coming years.

Furthermore, MRO's ultra-powerful camera system can guide future spacecraft missions--such as NASA's Phoenix lander and the Mars Science Laboratory--to precise and safe landings on that faraway world. Data gleaned by MRO can also help plot the touch down zones for human explorers too.

Half-empty, half-full

Making aerobraking all the more risky is that Mars' atmosphere can swell rapidly. It must be monitored closely to keep MRO at an altitude that is effective but safe. In this regard, other orbiters at Mars are providing a daily watch of atmospheric conditions at Mars.

Jim Graf, project manager for MRO at the Jet Propulsion Laboratory (JPL) in Pasadena, California has likened aerobraking to "a high-wire act in open air".

Right now, for MRO, "the glass is either half full or half empty depending on how you want to look at it," Graf said. "The spacecraft is presently well on its way through its aerobraking phase having completed approximately five out of 24 weeks of activity--or around 20 percent--relative to the calendar," he told SPACE.com.

The orbit duration of MRO has decreased from the original 35 hours to 25 hours, Graf said. MRO's apoapsis--the point in its orbit which is farthest from that Mars--has decreased from 27,340 miles (44,000 kilometers) down to 21,748 (35,000 kilometers).

"That sounds like a lot of progress...and it is," Graf added. "The team has worked very hard to get MRO to this point. But looking at the glass half empty, he continued, "we have completed only 26 of the planned 547 orbits...so we have a long way to go."

Mars milestone

MRO handlers here on Earth expect to reach the 24-hour orbit around Mars milestone on May 14.

As MRO's orbit period gets smaller, the rate of reduction is increased and the process is more demanding. In August, the period should be down to about 4 hours and the team will be very busy monitoring the individual drag passes, Graf explained.

"The spacecraft is performing superbly with no anomalies being worked at this time," Graf said, and temperature readings on the MRO during the drag passes are matching computer model results.

Performing the dainty maneuvers is a combined team located both in Denver at a Lockheed Martin control center and at JPL in Pasadena.

"Periodically, they perform small maneuvers to push the spacecraft lower into the atmosphere to keep the proper level of drag per pass through the atmosphere," Graf said.

For example, MRO's thrusters were fired again May 10 lowering the spacecraft's periapsis altitude--the point in an orbit when MRO and Mars are closest together--down to roughly 65 miles (104 kilometers), Graf said.

Instrument deployments

Another step toward full-commission of MRO is set for September.

The team is preparing for this transition phase--the final MRO instrument deployments.

The Shallow Subsurface Radar (SHARAD) and the Compact Reconnaissance Imaging Spectrometers for Mars (CRISM) will be operated for the first time in their science modes, Graf said.

SHARAD will seek liquid or frozen water in the first few hundreds of feet (up to one kilometer) of Mars' crust. The radar wave return, which is captured by the radar's antenna, is sensitive to changes in the electrical reflection characteristics of the rock, sand, and any water present in the surface and subsurface. SHARAD is an instrument supplied by the Italian Space Agency (ASI).

CRISM will search for the residue of minerals that form in the presence of water and might have been left by hot springs, thermal vents, lakes, or ponds on Mars far back in its history when water may have been present on the surface. CRISM will read the hundreds of "colors" in reflected sunlight to detect patterns that indicate certain minerals on the surface, including the signature traces of past water. This device has been provided by the Applied Physics Laboratory at Johns Hopkins University.

Eagle-eye vision,

Last March, MRO's powerful High Resolution Imaging Experiment (HiRISE), the Context Camera (CTX), a Mars Color Imager (MARCI), and a Mars Climate Sounder (MCS) received their first checkouts.

Thanks to MRO's eagle-eye vision, the orbiter can hone in on objects just a few feet across. With that capability, the most promising locales for scientific study can be spotted. In addition, the spacecraft's zoom lens gear can help pick future sites for expeditionary crews to boot across.

MRO was launched on August 1, 2005 from Cape Canaveral Air Force Station, Florida, slipping across the interplanetary void to arrive at Mars on March 10 of this year.

The $720 million MRO mission is managed by JPL, a division of the California Institute of Technology, Pasadena, for the NASA Science Mission Directorate in Washington, D.C. Lockheed Martin Space Systems, Denver, is the prime contractor for the project and built the spacecraft.

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