Orientation is more important than most people thing when it comes to sensing. A common example would be when the lasers of a garage door are mis-aligned, forcing the door to remain open until they are brought back in line. But when it comes to scientific sensors, orientation is even more important. So it was with great fanfare that NASA announced a new way to orient sensors on one of the most venerable of its spacecraft - the Mars Reconnaissance Orbiter (MRO) - and the resultant scientific discoveries it enabled.
The results of three “Very Large Rolls” (VLRs) made by MRO over the past two years are reported in a recent paper in the Planetary Science Journal. Each of these VLRs required the spacecraft to turn 120 degrees compared to its typical orientation. And they were completed to benefit one particular instrument on MRO - the Shallow Radar (or SHARAD) instrument.
First, it’s worth understanding they layout of MRO’s sub-components. It has five different science instruments, each with their own requirements in terms of orientation and signal strength. The craft also has a set of solar panels that are its primary source of power, and also a high-gain antenna that is intended to send high-speed data back to Earth. The orientation of each of these components is critical to the craft’s overall operation. For example, if the solar panels aren’t orientated to the Sun, the craft’s overall power drops precipitously. Or if the high-gain antenna isn’t directly pointed towards Earth, the speed of data down and uploads slows dramatically.
Brief video explaining MRO and SHARAD.Credit - Planetary Science Institute YouTube Channel
All of these considerations have gone into planning the orientation for MRO throughout its 18 year lifetime. As a result, SHARAD, one of the five scientific instruments, kind of got stuck with the short stick in that it was placed on the far side of the craft, essentially facing away from the planet. This allowed other instruments, like HiRISE, which is responsible for some of the most fantastical images of Mars ever collected, a freer view of the Red Planet.
Unfortunately, that meant that SHARAD, which is designed as a sounding radar, had to deal with the noise and interference caused by having to pass its 10W signal through the body of MRO itself in order to send and receive signals that bounced off the Martian surface. Even with those signal to noise constraints, SHARAD still did an admirable job of collecting data about the Martian subsurface about 1-2 km underground. But its science team members knew it could do better.
After what was surely a lot of constructive discussion and debate, the SHARAD team got its chance. They convinced the mission controller at NASA’s Jet Propulsion Laboratory to turn the spacecraft 120 degrees, a third of the way to a full circle, in order to point SHARAD directly at the ground. The scientific results they got from that were nothing short of impressive.
Fraser discusses how water ice could be hiding under the surface on Mars.Over the course of three different VLRs between 2023 and 2024, SHARAD had an increase in signal strength of 9, 11, and 14 decibels, which, since dB exponentially scales, means that on average the instrument had a ten-fold increase in signal strength. Those three VLRs allowed SHARAD to peer at the Medusae Fossae Formation, Ultimi Scopuli at the south pole, and Amazonis Planitia. At each location it found something interesting.
At Medusae Fossae, it managed to image a basalt layer underground down around 800m, and it measured around 1500m of ice at Ultimi Scopuli. But perhaps the most interesting discovery was one that might have only taken place a few weeks ago. Back in 2018, scientists reported on data from the Mars Advanced Radar for Subsurface and Ionosphere Sounding (MARSIS) aboard Mars Express that appeared to show liquid water under some of the glaciers at the planet’s South Pole. With this newfound signal strength increase, SHARAD should now be able to confirm those findings, and the first opportunity to collect that data would have been this past May, though the results (if there are any) have not yet been published.
While confirmation of that finding would be a great boon to planetary scientists, there remain some challenges regarding the physical implementation of the VLRs. While SHARAD is pointed at the ground, both the solar panels and the high-gain communications antenna are not in their ideal positions, so careful planning about how to maneuver the spacecraft is critical for future rolls. Any abrupt change could destabilize the entire spacecraft, putting an end to what has long been one of NASA’s most prolific missions.
Sometimes old orbiters, even those old enough to have graduated high school, can be taught new tricks. With this one trick that MRO’s operators have told it, it seems there’s a decent chance of unlocking plenty of new scientific discoveries, including one that could significantly impact future scientific efforts on the Red Planet. We’ll just have to wait a little bit longer to see if its operators are up to the challenge of collecting the necessary data, and whether the little orbiter that could still has some major discoveries left in it.
Learn More:
NASA - NASA Mars Orbiter Learns New Moves After Nearly 20 Years in Space
N Putzig et al - SHARAD Illuminates Deeper Martian Subsurface Structures with a Boost from Very Large Rolls of the MRO Spacecraft
UT - Martian Probe Rolls Over to See Subsurface Ice and Rock
UT - New layers of water ice have been found beneath Mars' North Pole
