Earlier this year, the pulse of planetary science skipped a beat.
In January, the NASA Cassini spacecraft was climbing from an orbit around Saturn's equator to a polar orbit, which would allow the spacecraft to cap its 13-year exploration of the planet with gauntlet runs through its rings and a final dive into the atmosphere. Cassini's thrusters would burn for less than a minute to torque it into a new orbit, but fuel was scarce and every second mattered. When the moment came for an uplink, the radio signal connecting the spacecraft to Earth went haywire. By the time a fix came, Cassini had missed its mark.
A day later, managers did get the spacecraft moving toward polar orbit. There had been no problem with Cassini. The problem was on Earth.
The Cassini incident was one of several recent glitches in the Deep Space Network (DSN), NASA's complex of large radio antennas in California, Spain, and Australia. For more than 50 years, the DSN has been the lifeline for nearly every spacecraft beyond Earth's orbit, relaying commands from mission control and receiving data from distant probes. On 30 September, in a meeting at NASA headquarters, officials will brief planetary scientists on the network's status. Many are worried, based on anecdotal reports, that budget cuts and age have taken a toll that could endanger the complex maneuvers that Cassini and Juno, a spacecraft now at Jupiter, will require over the next year.
"Everyone is concerned that there is a problem," says Larry Nittler, a planetary scientist at the Carnegie Institution for Science in Washington, D.C. NASA's science advisory committee is also likely to take the issue up, adds its chair, Brad Peterson, an astronomer at the Space Telescope Science Institute in Baltimore, Maryland. As NASA launches increasingly complex and data-hungry missions, Peterson says, "the need for DSN is only going to increase."
It's worked so well for so many years that people do take it for granted. Are proper investments being made so we can continue to?
For most of its life, the network, run by the Jet Propulsion Laboratory (JPL) in Pasadena, California, has been metronomic in its reliability. Its three sites, spaced 120° apart around the globe, all have a 70-meter dish built in the 1960s or '70s, and several newer, 34-meter dishes, which can be arrayed together to match the larger dishes' downlink performance. The network allows continuous contact with spacecraft anywhere in the solar system—or beyond it, as in the case of Voyager 1, which officially entered interstellar space in 2013. Currently, 35 missions rely on the DSN.
Ironically, the glitches this past December and January largely stemmed from problems with the network's newest 34-meter antenna, DSS-35, in Canberra, which began operating in 2014, NASA says. Rain and dust compromised an instrument that helps aim it, several other pointing components overheated, and contaminants leaked into a cryogenic refrigerator used to cool an amplifier. NASA says these problems have mostly been fixed, and the Canberra station's reliability will increase when its next 34-meter antenna, DSS-36, begins operating on 1 October.
Staffing issues have also compounded the hardware problems. In January, the Magnetospheric Multiscale mission, which measures the boundary between Earth's magnetic field and the solar wind, was, like Cassini, having trouble connecting to DSS-35. Communications could have shifted to another Canberra antenna. But on 22 January, a snowstorm shut down the Goddard Space Flight Center in Greenbelt, Maryland. No one was there to reconfigure the spacecraft, and so the retrieval of a day's worth of data was delayed.
Pete Vrotsos, a deputy program manager at NASA's Space Communications and Navigation office in Washington, D.C., which oversees the network, says that in January, the network still delivered 95% of both outbound and incoming signals, its minimum goal. Since then, he says, it has nearly returned to its typical 99% reliability. Still, many scientists worry about the network's future.
It's no secret that, like many parts of the federal government, it has been asked to do more with less. In 2009, network managers began a plan to find $227 million in efficiencies to help pay for upgrades, like the construction of the new 34-meter dishes. But in 2013, as these plans were underway, NASA asked the DSN to cut its budget by $100 million over 7 years. In late 2015, the DSN was asked to find further cuts. "If you look at NASA's budget for the DSN it tends to go down in time, rather than up," said Leslie Deutsch, deputy director of JPL's interplanetary network directorate, in an August presentation to a NASA working group.
These cuts do not hit day-to-day operations, Vrotsos says. "Our first, second, and third job is to return all the science data possible." But they have delayed the start of new antennas and transmitters in Madrid and California, and they could complicate repairs to cracking, degraded concrete in the pedestals of two Madrid dishes. Last year, a report from NASA's Office of Inspector General warned that these postponements could jeopardize the network's reliability, especially for older missions, like Voyager 1 and 2, that depend on congested radio bands only supported by some of the network's older dishes.
If there's hope for further investment in deep-space communication, it might be international: In 2013, the European Space Agency (ESA) finished its own 120° network of 35-meter antennas in Spain, Australia, and Argentina, which now communicates with ESA missions like Rosetta, Gaia, and Mars Express, and also backs up the NASA network. India and Japan have individual antennas to communicate with their missions, and NASA has been in talks with South Korea and the United Arab Emirates as potential DSN partners.
Further on, JPL plans to save money by operating the antennas remotely rather than staffing each location continuously. It also plans to move to an internet-inspired scheme for transmitting data packets that is more tolerant of faults.
Meanwhile, NASA has begun testing laser-based systems as possible successors to radio transmissions. Optical signals, with wavelengths 10,000 times shorter than radio waves, allow far higher rates of data transmission and aren't subject to interference from Earth's cacophonous radio bands. As a result, the transmitters can be small, light, and energy efficient. (However, clouds can easily block the signals, which means that low-Earth-orbit relay satellites may be needed for an "interplanetary internet.")
For now, scientists want to be certain the DSN has the support it needs to stay in the background, says Clive Neal, a lunar scientist at the University of Notre Dame in Indiana. "It's worked so well for so many years that people do take it for granted," he says. "Are proper investments being made so we can continue to?"
*Correction, 30 September 2016, 10:36 a.m.: A previous caption incorrectly suggested that a picture showing a 34-meter dish was a 70-meter dish at the same NASA complex.