Can You Hear Me Now?
By Henry Bortman
NASA’s Phoenix mission encountered its first significant glitch on Tuesday, May 27, when the Mars Reconnaissance Orbiter (MRO) failed to communicate with the lander. The problem was with the UHF radio on MRO that the orbiter uses to send commands to and receive data from Phoenix.
|These images of the Phoenix lander, parachute and heat shield were captured by the HiRISE camera on the Mars Reconnaissance Orbiter. Click image for larger view.|
Credit:NASA/JPL-Caltech/University of Arizona.
When it came time for MRO to send back to engineers on Earth a confirmation that it was ready for its Tuesday morning communication with Phoenix, the orbiter instead reported that its UHF radio had encountered a “transient event,” and that MRO had shut the radio down, said F u k Li, manager of the Mars Exploration Program at the Jet Propulsion Laboratory in Pasadena, California.
“Transient event” is a generic term that means, simply, something went wrong. The cause of the problem is not yet known, and engineers are working feverishly to analyze and correct it. The radio may have been struck by a cosmic ray, Li said, but he hastened to add, “I’m speculating. Overspeculating.”
The fault occurred when MRO attempted to send Phoenix its marching orders for sol 2. Martian days, which are 40 minutes longer than Earth days, are referred to as “sols.” Sol 2 is the second full day of Phoenix’s operation on the martian surface.
Each morning the Phoenix team uplinks a sequence of commands for Phoenix to perform over the course of the day. The command sequence is sent to either MRO or Mars Odyssey, another spacecraft orbiting Mars. The orbiter then relays those commands to Phoenix via a UHF communications link.
Each evening, Phoenix sends images and other data back to one of the orbiters, which then relay the information back to Earth. MRO’s UHF radio had been working as expected Monday evening, when it sent back data and images from sol 1. But 12 hours later, when engineers performed a set of diagnostic tests prior to instructing MRO to talk to Phoenix, the spacecraft reported that the UHF radio had encountered a problem.
MRO did receive the sol 2 sequence from Earth – the communications link between Earth and MRO continues to operate normally. But subsequently MRO reported that there had been a “problem with the handshake between MRO and Phoenix,” Li said. A handshake is the set of signals the radios on the two spacecraft send each other to establish a data-communications link.
As a result, Phoenix didn’t receive instructions for sol 2 activities. That doesn’t mean it will be twiddling its thumbs until sol 3. Stored onboard it has what is known as a “runout sequence,” a set of commands that tells it what to do if it doesn’t receive any new commands.
Unfortunately, the sol 2 commands included instructions to complete the panoramic imaging of the “digging area,” the terrain immediately surrounding the lander, where the robotic arm will scoop up samples of soil and ice for analysis. It also included commands to unstow the robotic arm, which has not yet been deployed. As a result, science activities – deciding where to dig, and actually digging – will be delayed by at least a day.
Meanwhile, although MRO is having trouble talking to Phoenix, it continues to send back spectacular images of Phoenix, captured by its HiRISE camera. The HiRISE team Tuesday released a more comprehensive view of the image, released Monday, that it took of Phoenix during its descent. The new image shows a 10-kilometer-wide (6-mile-wide) crater, unofficially named “Heimdall” crater, in the background, as Phoenix, some 20 kilometers (12 miles) closer to the camera, drops through the martian atmosphere toward its landing site.
The HiRISE team also released images of Phoenix, its heat shield and its parachute, taken from orbit. The images have enabled the Phoenix science team to pinpoint the lander’s position more precisely.
UPDATE:NASA’s Mars Reconnaissance Orbiter successfully received information from the Phoenix Mars Lander Tuesday evening and relayed the information to Earth. The relayed transmission included images and other data collected by Phoenix during the mission’s second day after landing on Mars. NASA’s Mars Odyssey orbiter is scheduled for relaying commands to the lander on Wednesday morning.