Less than 10 days and a mere 7.2 million miles (11.6 million km) from its quarry—the dwarf world Pluto, its binary companion Charon, and a system of four tiny moons—NASA’s New Horizons spacecraft encountered an anomaly yesterday (Saturday), when communications with Earth were briefly lost. Although contact was re-established after about 80 minutes, via the worldwide antennas of the Deep Space Network (DSN), the spacecraft correctly responded to the situation by placing itself into “safe mode,” thereby allowing engineers to determine the cause of the problem. New Horizons’ extreme distance from Earth, and the resultant nine-hour round-trip communications time lag, will require between “one and several days” for normal operations to be restored. Although the New Horizons’ team expressed confidence on Twitter that the problem was being worked through, the incident adds further anxiety and nail-biting anticipation as humanity prepares for its first-time, close-range reconnaissance of the last of the Solar System’s “traditional” nine planets.
According to NASA, New Horizons’ mission operations center at the Johns Hopkins University Applied Physics Laboratory (APL) in Laurel, Md., lost contact with the baby-grand-piano-sized spacecraft at 1:54 p.m. EDT and regained its signal a little more than an hour later, at 3:15 p.m., via the DSN, which is equipped with multiple communications and deep-space tracking assets in semi-mountainous regions of Goldstone, Calif., together with Canberra, Australia, and Madrid, Spain. “During that time, the autonomous autopilot on-board the spacecraft recognized a problem and—as it’s programmed to do in such a situation—switched from the main to the backup computer,” it was noted. “The autopilot placed the spacecraft in ‘safe mode’ and commanded the backup computer to reinitiate communication with Earth. New Horizons then began to transmit telemetry to help engineers diagnose the problem.”
New Horizons carries two computers: the Command and Data Handling system and the Guidance and Control processor, each of which is duplicated for redundancy, producing a total of four units, powered by a 12 MHz radiation-hardened Mongoose-V processor. In addition to distributing operating commands to subsystems and collecting and processing scientific data, the computers run advanced “autonomy” algorithms with the capability to check system statuses, correct problems, switch to backup systems, or contact Earth for assistance.
In the immediate aftermath of the incident, a New Horizons Anomaly Review Board (ARB) was convened at 4 p.m. EDT Saturday to gather more data on the problem and initiate a recovery plan, with the goal of returning the spacecraft to normal operations, as it closes in on its long-awaited Closest Approach with the Pluto-Charon system on 14 July. Launched 9.5 years ago, in January 2006, New Horizons is well into the homestretch of its journey to conduct humanity’s first-time reconnaissance of the last of the Solar System’s “traditional” nine planets. Already, as described in recent days by the AmericaSpace team, the spacecraft successfully executed its final pre-encounter course-correction maneuver, lasting 23 seconds, on 29 June, as Pluto and Charon grew steadily larger in the viewfinder. Last week, as the Command Load Flight Plan for the historic flyby was uploaded to New Horizons, intriguing surface features on the dwarf world were resolved, including an enigmatic “chain” of dark equatorial “spots.” At the same time, joint measurements were conducted from Earth’s skies of a stellar occultation of Pluto, observed by NASA’s aircraft-borne Stratospheric Observatory for Infrared Astronomy (SOFIA).
Of course, the sheer distance of Pluto from Earth—close to three billion miles (4.9 billion km)—means that the round-trip communications time of nine hours is a painfully lengthy one for anomalies such as this to develop. “Full recovery is expected to take from one to several days,” NASA explained. “New Horizons will be temporarily unable to collect scientific data during that time.” The 1,040-pound (470-kg) spacecraft is powered by a plutonium-fed General Purpose Heat Source (GPHS) Radioisotope Thermoelectric Generator (RTG)—the latest in a family of nuclear power sources which have sustained numerous deep-space missions, including the Pioneers, the Voyagers, the Jupiter-bound Galileo, and the Saturn-orbiting Cassini—and a system of hydrazine thrusters for stabilization and control.
From an instrumentation and science-gathering standpoint, yesterday’s anomaly poses a hiccup during New Horizons’ final days, as it approaches the once-in-a-lifetime opportunity to view the Pluto-Charon system, up close and personal, for the first time. Already, since January 2015, the spacecraft’s Long-Range Reconnaissance Imager (LORRI) has returned many tantalizing monochromatic images of the dwarf world, whilst the Multispectral Visible Imaging Camera (MVIC) and the near-infrared Linear Etalon Imaging Spectral Array (LEISA) of the on-board Ralph telescope have begun to reveal Pluto’s reddish-brown surface hue and the much darker Charon.
According to The Planetary Society’s Emily Lakdawalla, observations planned over the next several days were expected to acquire a series of critical optical navigation images of the dwarf world and its entourage. These would resolve the surfaces of both Pluto and Charon at steadily increasing resolutions of between 34.4 miles (55.4 km) per pixel on Sunday, 5 July, to just 16.8 miles (27 km) per pixel by Thursday, 9 July. Additionally, images of two of Pluto’s tiny moons—Nix and Hydra, first discovered in Hubble Space Telescope (HST) observations in 2005—would have been captured from a distance of between 6.9 million miles (11.2 million km) and 3.4 million miles (5.4 million km), yielding surface resolutions as fine as 16.8 miles (27 km) per pixel.
The responses on Twitter from the New Horizons team carried the kind of calm, “working the problem,” aura for which NASA and its associates are famous. “New Horizons in safe mode,” the spacecraft team tweeted late Saturday. “We’re working it folks.” Others, including former NASA engineer and Rocket Boys bestselling author Homer Hickam, called upon higher authority to assist. “I absolutely believe that prayer can affect outcomes,” Hickam told his 5,715 followers. “Please pray for @NewHorizons2015, the bravest little spacecraft out there tonight.” Elsewhere, Planetary Science Institute astrobiologist Dr. David Grinspoon—who served as Interdisciplinary Scientist for Europe’s recently concluded Venus Express mission—added: “Yikes! Temporary loss of contact w @NewHorizons2015 as rapidly closes on Pluto!”
However, with all of its course correction maneuvers successfully concluded, and the spacecraft approved to pursue its “Best Flight Path” through the Pluto system on 14 July, New Horizons’ current trajectory is the optimum one for maximum scientific data return. As described recently by AmericaSpace’s Mike Killian, fears of potential impacts with rings, as-yet-unseen moons, or tiny dust particles—which might have been lethal, bearing in mind New Horizons’ blistering 30,000 mph (50,000 km/h) flyby velocity—proved ultimately unfounded and the spacecraft was kept on track to conduct its originally baselined science plan. Had a slightly revised approach become necessary, backup planning encompassed a range of Safe Haven By Other Trajectory (SHBOT) profiles. Although the New Horizons team remains confident that their hardy little spacecraft will be in fighting form for its date with Pluto, it is clear that the final days before our species concludes its initial reconnaissance and inspection of the last of the Solar System’s nine “traditional” planets will be as nail-biting and filled with anxious expectation as the long-awaited encounter itself.
Stay with AmericaSpace for regular updates and LIVE COVERAGE of New Horizons’ approach and flyby of the Pluto system.
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