A new view of Olympus Mons

After 100,000 orbits and nearly 23 years on Mars, NASA’s Mars Odyssey orbiter has seen a lot. The spacecraft was sent to map the ice and study its geology, but along the way, it has captured more than 1.4 million images of the planet.

A recent image captured the Solar System’s tallest mountain and volcano, Olympus Mons.

This image won’t win any photo contests, but that’s not the point. Scientists are experts at extracting information, and images like this contain information that is part of the overall puzzle of Mars.

In this image, Odyssey is taking a horizontal look at Mars. The spacecraft usually points down at the surface and captures images in long strips, which is why the image has such an unusual shape. But this horizontal view is part of an effort to use Odyssey and its Thermal Emission Imaging (THEMIS) camera to capture high-altitude images of the Martian horizon.

“Normally, we see Olympus Mons in narrow strips from above, but by turning the spacecraft toward the horizon, we can see in a single image just how big it looks over the landscape,” said Odyssey project scientist Jeffrey Plaut. of NASA’s Jet Propulsion Laboratory. in Southern California, which manages the mission. “Not only is the image spectacular, but it also provides us with unique scientific data.”

Odyssey captured its first image of the horizontal horizon in late 2023, and it took engineers three months to get the operation right. THEMIS is fixed in position and points straight down. For these images, the entire spacecraft had to tilt 90 degrees. But it also had to maintain a position where the Sun could hit its solar panels. To accomplish this, Mars Odyssey used its thrusters to orient itself so that its antennae pointed away from Earth. As a result, the spacecraft could not communicate with Earth for the duration of the maneuver.

Orbiters such as Odyssey, MRO and Mars Express have imaged the Martian surface in great detail and provided us with an extensive image archive. But these images are different. They give scientists a different view of the Martian sky, its clouds and dust.

THEMIS is an infrared camera designed to sense temperature changes on the Martian surface. It can distinguish between sand, rock, ice and dust. By pointing to the sky, THEMIS can measure the presence of ice and dust in the Martian atmosphere.

Odyssey personnel first realized that they could steer the spacecraft over the horizon when other missions were landing on the surface of Mars. When Curiosity landed in 2012, Odyssey played a key role by relaying information about the landing on Earth. To do this, it had to be oriented differently, pointing its antenna at the rover’s landing ellipse. While positioning the antenna for that job, the scientists realized that THEMIS was pointing at the horizon.

“We just decided to turn on the camera and see what it looked like,” said Odyssey mission spacecraft engineer Steve Sanders of Lockheed Martin. Lockheed Martin built Odyssey and helps run day-to-day operations alongside mission managers at JPL. “Based on those experiments, we designed a sequence that keeps THEMIS’ field of view centered on the horizon as we orbit the planet.”

The Odyssey was a definite success by any measure and is still going strong. In fact, it is the longest continuously active mission around another planet. But this achievement requires careful planning and operation.

“Physics does a lot of the hard work for us,” Sanders said. “But it’s the subtleties that we have to manage again and again.” The spacecraft is solar-powered and is out of direct sunlight for a few minutes in each orbit, but the instruments must be kept within a certain range to stay operational, which means meeting the power demands.

The Odyssey also has a limited amount of hydrazine fuel for its thrusters. Without a fuel gauge, engineers must recalculate the amount remaining after each maneuver. One way to do this is by applying heat to the two propellant tanks to see how long it takes them to warm up. In March 2023, NASA said the spacecraft has enough fuel to last until at least the end of 2025.

“It takes careful monitoring to sustain a mission this long while maintaining a historic timeline of scientific planning and execution — and innovative engineering practices,” said Odyssey project manager Joseph Hunt of JPL. “We look forward to collecting more great science in the years to come.”

Odyssey can change its orbit, so there is no way to calculate exactly how many orbits it has left. But he has completed over 100,000 in almost 23 years, and will likely complete several hundred more before his hydrazine runs out.