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MRO: Delicate Dips into the Martian Atmosphere

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
(Image: © JPL/Corby Waste)

NASA'snewest mission to the red planet--the Mars Reconnaissance Orbiter (MRO)--isworking well as it shaves off altitude in order to swing into activescience-gathering duties later this year.

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

Nowunderway is the delicate art of "aerobraking"--using hundreds of cautiouslycalculated dips into the upper atmosphere of Mars. The process usesbrief burns from MRO's thrusters. Those dips have to be deep enough to slowthe spacecraft by atmospheric drag ... but not deep enough to overheat or damage theorbiter.

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

Themulti-tasking Mars Reconnaissance Orbiter will study the history of wateron the red planet. In addition, it will become the first link in acommunications bridge back to Earth--an "interplanetary Internet" that can beused by spacecraft in coming years.

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

Half-empty, half-full

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

Jim Graf, projectmanager 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 onhow you want to look at it," Graf said. "The spacecraft is presently well onits way through its aerobraking phase having completed approximately five outof 24 weeks of activity--or around 20 percent--relative to the calendar," he toldSPACE.com.

Theorbit 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--hasdecreased from 27,340 miles (44,000 kilometers) down to 21,748 (35,000kilometers).

"Thatsounds like a lot of progress...and it is," Graf added. "The team has worked veryhard 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 togo."

Mars milestone

MROhandlers here on Earth expect to reach the 24-hour orbit around Mars milestoneon May 14.

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

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

Performingthe dainty maneuvers is a combined team located both in Denver at a LockheedMartin control center and at JPL in Pasadena.

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

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

Instrument deployments

Anotherstep toward full-commission of MRO is set for September.

Theteam is preparing for this transition phase--the final MRO instrumentdeployments.

TheShallow Subsurface Radar (SHARAD) and the Compact Reconnaissance ImagingSpectrometers for Mars (CRISM) will be operated for the first time in theirscience modes, Graf said.

SHARAD will seek liquid orfrozen 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, issensitive to changes in the electrical reflection characteristics of the rock,sand, and any water present in the surface and subsurface. SHARAD is aninstrument supplied by the Italian Space Agency (ASI).

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

Eagle-eye vision,

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

Thanks to MRO's eagle-eyevision, the orbiter can hone in on objects just a few feet across. With thatcapability, the most promising locales for scientific study can be spotted. Inaddition, the spacecraft's zoom lens gear can help pick future sites forexpeditionary crews to boot across.

MRO was launched on August1, 2005 from Cape Canaveral Air Force Station, Florida, slipping across the interplanetaryvoid to arrive at Mars on March 10 of this year.

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

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