Rosetta and Philae

Nation	European Space Agency (ESA)
Objective(s):	Comet Orbit and Landing
Spacecraft	Rosetta Orbiter / Philae Lander
Spacecraft Mass	6,614 pounds (includes 221 pound lander) / 3,000 kilograms (includes 100 kilogram lander)
Mission Design and Management	ESA
Launch Vehicle	Ariane 5G+ (V158) (no. 518G)
Launch Date and Time	March 2, 2004 / 07:17:44 UT
End of Mission	Sept. 30, 2016 / 11:19:37 UT
Launch Site	(CSG / ELA-3)
Scientific Instruments	Rosetta Orbiter 1. Ultraviolet Imaging Spectrometer (ALICE) 2. Comet Nucleus Sounding Experiment by Radiowave Transmission (CONSERT) 3. Cometary Secondary Ion Mass Analyzer (COSIMA) 4. Grain Impact Analyzer and Dust Accumulator (GIADA) 5. Micro-Imaging Dust Analysis System (MIDAS) 6. Microwave Instrument for the Rosetta Orbiter (MIRO) 7. Optical, Spectroscopic and Infrared Remote Imaging System (OSIRIS) 8. Rosetta Orbiter Spectrometer for Ion and Neutral Analysis (ROSINA) 9. Rosetta Plasma Consortium (RPC) 10. Radio Science Investigation (RSI) 11. Visible and Infrared Thermal Imaging Spectrometer (VIRTIS) Philae 1. Alpha Proton X-ray Spectrometer (APXS) 2. Cometary Sampling and Composition Instrument (COSAC) 3. Ptolemy Evolved Gas Analyzer 4. Comet Nucleus Infrared and Visible Analyzer (CIVA) 5. Rosetta Lander Imaging System (ROLIS) 6. Comet Nucleus Sounding Experiment by Radiowave Transmission (CONSERT) 7. Multi-purpose Sensors for Surface and Sub-surface Science (MUPUS) 8. Rosetta Lander Magnetometer and Plasma Monitor (ROMAP) 9. Surface Electric Sounding and Acoustic Monitoring Experiments (SESAME) 10. Sample and Distribution Device (SD2)

Firsts

• Sept. 10, 2014: First spacecraft to orbit a cometary nucleus (Rosetta)

• Nov. 12, 2014: First spacecraft to land on a comet (Philae)

In Depth: Rosetta and Philae

Rosetta was a European deep space probe launched on what was originally projected to be an 11.5-year mission to rendezvous, orbit, study and to land on the comet 67P/Churyumov-Gerasimenko.

Part of ESA’s Horizon 2000 cornerstone missions, which includes SOHO (launched 1995), XMM-Newton (1999), Cluster II (2000), and INTEGRAL (2002), Rosetta consisted of two parts—an orbiter called Rosetta and a lander called Philae. Each was equipped with a variety of scientific instruments.

Originally, the mission was to target comet 46P/Wirtanen but when the launch was delayed due to problems with the Ariane 5 launch vehicle, the mission was redirected to Churyumov-Gerasimenko.

Rosetta was launched into an escape trajectory with a 17-minute burn of Ariane’s EPS second stage, putting the spacecraft on a trajectory that culminated in a 0.885 × 1.094 AU heliocentric orbit inclined at 0.4 degrees to the ecliptic.

Its voyage to its target comet was punctuated by a series of gravity-assist maneuvers, the first of which occurred at 22:09 UT March 4, 2005, when Rosetta flew by Earth (over the Pacific, west of Mexico) at a distance of about 1,215 miles (1,954.7 kilometers).

A risky flyby of Mars followed on Feb. 25, 2007, when Rosetta came within 155 miles (250 kilometers) of the Red Planet, experiencing a brief and critical period out of contact with Earth and in Mars’ shadow.

The flybys produced spectacular photographs of Earth and Mars.

The Mars assist sent the spacecraft toward Earth for a second time, flying past our planet at a range of 3,290 miles (5,295 kilometers) on Nov. 13, 2007.

Before the final Earth flyby Nov. 12, 2009, Rosetta performed a close flyby (about 500 miles or 800 kilometers) of asteroid 2867 Steins in the main asteroid belt at 18:58 UT Sept. 5, 2008, collecting a large amount of information.

A second asteroid flyby—this time asteroid 21 Lutetia at 16:10 UT July 10, 2010, at a range of 1,965 miles (3,162 kilometers)—produced spectacular images (using the OSIRIS instrument) of a battered minor planet riddled with craters. Resolution was as high as 200 feet (60 meters) in a body whose longest side is about 81 miles (130 kilometers).

In June 2011, Rosetta was placed in hibernation as it made its way beyond the orbit of Jupiter where there was no solar energy to power the vehicle.

On Jan. 20, 2014, its internal clock awakened the spacecraft and sent a signal back to Earth that all was well. Now about 5.6 million miles (9 million kilometers) from its primary target, Rosetta began its final race to comet 67P/C-G.

On Aug. 6, 2014, at a distance of about 252 million miles (405 million kilometers) from Earth (about halfway between the orbits of Mars and Jupiter), Rosetta finally rendezvoused with the comet as it completed the last of 10 maneuvers (that began in May 2014) to adjust velocity and direction.

During close operations near the comet on Sept. 15, scientists identified a landing site for the spacecraft, “Site J” (later named “Agilkia”), located near the smaller of the comet’s two lobes.

By this time (Sept. 10, 2014), the spacecraft was in a roughly 18-mile (29-kilometer) orbit around 67P/C-G, becoming the first spacecraft to orbit a cometary nucleus.

Just before the planned landing Nov. 12, controllers identified a problem in Philae’s active descent system thruster which was to provide thrust to prevent the spacecraft from bouncing. It was decided to move forward with the landing and to rely only on harpoons instead of the thruster to keep the spacecraft moored.

At 08:35 UT Nov. 12, the two spacecraft separated, initiating Philae’s seven-hour descent to the comet at a relative velocity of about 3 feet per second (1 meter per second).

A signal confirming the touchdown arrived at Earth at 16:03 UT (about 28 minutes, 20 seconds after the actual event). It was later determined that Philae had actually landed three times on the comet (at 15:34:04, 17:25:26, and 17:31:17 UT comet time) because the two harpoons did not fire as intended.

Later analysis showed that all three of the methods meant to secure Philae to the comet had faced problems: the ice screws, which were designed for soft materials, did not penetrate the hard surface of the Agilkia region; the thruster failed to fire due to a problem with a seal; and the harpoons didn’t fire due to an electrical problem. As a result, Philae bounced several times before settling down about half a mile (1 kilometer) away from its intended landing site in an area known as Abydos.

All of Philae’s instruments were activated for data collection, but for a short period, ESA controllers did not know the disposition of the lander because it went into hibernation.

On Nov. 14, 2014, contact was re-established with Philae, after which its data was transferred to the mothership. Philae’s primary battery drained and contact was lost at 00:36 UT Nov. 15. By this time, it had operated independently for 64 hours including 57 hours on the surface.

Philae had completed 80 percent of its planned first science sequence, returning spectacular images of its surroundings, showing a cometary surface covered by dust and debris ranging in size from inches to a yard (millimeters to a meter).

Philae also found complex molecules that could be the key building blocks of life, monitored the daily rise and fall of temperature, and assessed the surface properties and internal structure of the comet.

ESA controllers hoped that the lander could be revived in August 2015 when sunlight fell on its solar panels, but they assumed that Philae’s mission was essentially over in November 2014.

Then, Philae awakened after seven months of hibernation. At 20:28 UT June 13, 2015, controllers at ESA’s European Space Operations Center in Darmstadt received signals (about 663 kilobits of data over 85 seconds) from the lander, suggesting at least initially that Philae was “doing very well” and “ready for operations,” according to DLR Philae Project Manager Stephan Ulamec.

A second smaller burst was received at 21:26 UT June 14 followed by six more bursts July 9, 2015, after which time Rosetta was no longer in range to receive data from Philae.

A year after landing, in November 2015, mission teams still remained hopeful that there would be renewed contact with the lander, especially as the Rosetta orbiter began to approach the lander again. But in February 2016, ESA announced that it was unlikely that Rosetta would ever pick up any more signals from Philae again, partly due to failures in a transmitter and a receiver on board.

On Sept. 5, 2016, ESA announced that they had conclusively identified the landing site of Philae in images taken by Rosetta’s OSIRIS narrow-angle camera when the orbiter approached to just 1.7 miles (2.7 kilometers) of the surface.

Rosetta, meanwhile, had continued its primary mission orbiting Comet 67P/Churyumov-Gerasimenko as the comet itself arced closer to the Sun.

In November 2014, the orbiter adjusted its orbit several times to position it about 19 miles (30 kilometers) above the comet, interrupted by a brief dip down to about 12 miles (20 kilometers) for about 10 days in early December.

On Feb. 4, 2015, Rosetta began moving into a new path for an encounter, timed for 12:41 UT Feb. 14, at a range of about 4 miles (6 kilometers). The flyby took the spacecraft over the most active regions of the comet, allowing scientists to seek zones where gas and dust accelerates from the surface.

In June 2015, ESA extended Rosetta’s mission to at least September 2016 (an extension of nine months from its original mission). During this extension, Rosetta accompanied comet 67P/C-G on its closest approach to the Sun, a distance of 116 million miles (186 million kilometers), on Aug. 13, 2015.

At the perihelion, gases and dust particles around the comet reached peak intensity, clearly visible in the many spectacular images sent back by the orbiter.

Finally, at 20:50 UT Sept. 30, 2016, Rosetta carried out a final maneuver sending it on a collision course with the comet from a height of about 12 miles (19 kilometers).

During the descent, Rosetta studied the comet’s gas, dust, and plasma environment very close to the surface and took numerous high-resolution images.

The decision to end the mission was predicated on the fact that the comet was heading out beyond the orbit of Jupiter again, and there would be little power to operate the spacecraft.

Confirmation of Rosetta’s final impact arrived at Darmstadt at 11:19:37 UT Sept. 30, 2016, thus ending one of ESA’s most successful planetary missions.

Besides collecting a vast amount of data on the properties of the comet, including its interior, surface and surrounding gas, dust, and plasma, Rosetta’s key findings included the discovery of water vapor in comet 67P/G-C (vapor that is significantly different from that found on Earth), the detection of both molecular nitrogen and molecular oxygen for the first time at a comet, the existence of exposed water ice on the comet’s surface, and the discovery of amino acid glycine (commonly found in proteins) and phosphorus (a component of DNA and cell membranes) in the comet.

Key Source

Siddiqi, Asif A. Beyond Earth: A Chronicle of Deep Space Exploration, 1958-2016. NASA History Program Office, 2018.