Mars Odyssey, Mars Reconnaissance Orbiter and the Mars Atmosphere and Volatile Evolution (MAVEN) orbiter all are part of a campaign to study comet C/2013 A1 Siding Spring and possible effects on the Martian atmosphere from gases and dust released by the comet.
The comet sped past Mars much closer than any other known comet flyby of a planet, NASA said.
NASA's newest orbiter at Mars, MAVEN, took precautions to avoid harm from a dust-spewing comet that flew near Mars and is studying the flyby's effects on the Red Planet's atmosphere.
The MAVEN spacecraft reported back to Earth in good health after about three hours of precautions against a possible collision with high-velocity dust particles released by the comet.
"We're glad the spacecraft came through, we're excited to complete our observations of how the comet affects Mars, and we're eager to get to our primary science phase," said MAVEN Principal Investigator Bruce Jakosky of the University of Colorado, Boulder.
The opportunity to study this rare near-miss of a planet by a comet comes during the project's commissioning phase.
A few weeks of instrument calibration and orbit fine-tuning remain before the start of the primary science phase. The mission will study the upper atmosphere of Mars and its interaction with the solar wind.
Comet Siding Spring hurtled past Mars at about 56 kilometres per second, coming within about 139,500 kilometres of the planet.
That is equivalent to about one-third of the distance between Earth and the Moon.
MAVEN kept in a defencive posture to reduce its profile relative to the direction from which the comet's high-velocity dust particles would come.
In that "hunkered down" orientation, its main antenna was not facing the right way for transmitting to Earth, so communications were maintained at low data rate via a secondary antenna.
The mission performed a manoeuvre on October 2 that set its orbit timing so that the spacecraft was behind Mars, relative to the possible dust flow.