By Steven Siceloff,
NASA's Kennedy Space Center
It's not easy to simulate millions of miles electronically, but that's what engineers did recently as they tested the all-important communications system the MAVEN spacecraft will use to relay its study results from Mars orbit to Earth-bound researchers.
Working from their consoles at NASA's Kennedy Space Center, a team of test engineers from the Jet Propulsion Laboratory in California, better known as JPL, conducted more than a week of evaluations on the antennas and circuitry aboard the spacecraft.
They beamed signals to the low-gain and high-gain antennas on MAVEN and basically treated the machine as though it really were flying on a 10-month journey from Earth to Mars and then studying the upper atmosphere of the Red Planet.
Such work is critical, mission managers said, because there is no way to fix a spacecraft's communications system once it leaves Earth.
"It doesn't matter what we do out there if we can't get the data back to Earth," said Jeff Coyne, Lockheed Martin's Assembly Test and Launch Operations manager for the project.
MAVEN is short for Mars Atmosphere and Volatile Evolution. It is scheduled to launch in November aboard a United Launch Alliance Atlas V.
"I say this is one of the most important things, because if we can't talk to it . . . ," said Sheryl Bergstrom, manager of JPL's Cape Operations Office at Kennedy.
The testing was standard stuff for the engineers, but nonetheless mind-bending considering that the spacecraft will operate millions of miles from Earth and rely on commands from operators at Goddard Space Flight Center in Maryland.
To mimic the distances between the spacecraft and Earth, the electronic signals sent between the two during testing are run through a cabling system that quickly ramps down the power by going through various wiring networks.
"We'll try to squeeze the signal down to its lowest possible point," said Chris Green, an engineer with Exelis who supervised the testing. "It's a machine and we test its actual flight performance -- every scenario of flight configuration it would be in is what we go through in testing."
"We allow the project to get online and do what they would do on a normal day so they can perform all the tasks through us just as if MAVEN was actually in space," said Lorenzo Morgan, one of the engineers operating and evaluating the procedures.
Although every spacecraft goes through intense communications testing, the work is not considered routine because every spacecraft has unique requirements.
"Every mission is different, every mission has its own peculiarities," said Albert Ibarra, also a test engineer for the communications system. "You have to know the details on every spacecraft design and so you become familiar with it as soon as they start putting the spacecraft together."
NASA has an intricate system of antennas in California, Spain and Australia to pick up and transmit signals to its fleet of spacecraft that now reaches out beyond the solar system in the form of Voyager 1.
Called the Deep Space Network and referred to by its acronym, DSN, the system uses antennas almost as big as a football field to communicate with the spacecraft that are using their own much smaller antennas and more limited power sources.
It's the system NASA uses to communicate with all of its interplanetary probes and some of the spacecraft studying Earth, as well. In addition to Voyager 1, whose signal is incredibly weak because of the vast distance it is from Earth, the network is picking up signals from newer spacecraft such as New Horizons, which is speeding toward Pluto. Cassini in orbit around Saturn, Juno on its way to Jupiter and the Curiosity rover operating on Mars all relay their data to Earth on the DSN and get their commands from ground operators through the same network.
Kennedy's portion of the DSN structure is a testing facility called MIL-71, a reference to the time when the space center was known as the Merritt Island Launch Annex. Every time a spacecraft comes to Kennedy for launch preparations, a team of engineers sets up racks of equipment and computer servers before beginning several days of 12-hour shifts to make sure the mission's communications system and interface with the Deep Space Network will work.
With the spacecraft checked out, the team takes its gear back to California and gets ready for launch day, knowing very well that it won't hear anything from the spacecraft until well after liftoff. In the case of MAVEN, the engineers and scientists won't find out if the testing really was successful until 54 minutes after launch from Cape Canaveral when MAVEN makes its initial contact with the DSN.
"When the signal is acquired," said Bergstrom, a veteran of long wait-times for good missions and bad, "that's when we get to breathe."