How Esa scientists believe Philae has landed on the comet – on its side. Photograph: European Space Agency/Reuters |
Excerpt from
theguardian.com
The robotic lander that touched down on a comet on Wednesday came to rest on its side in the shadow of a cliff, according to the first data beamed home from the probe.
Pictures from cameras on board the European Space Agency’s Philae lander show the machine with one foot in the sky and lodged against a high cliff face that is blocking sunlight to its solar panels.
The precarious resting place means mission controllers are faced with some tough decisions over whether to try and nudge the spacecraft into a sunnier spot. If successful, that would allow Philae to fully recharge its batteries and do more science on the comet, but any sudden move could risk toppling the lander over, or worse, knock it off the comet completely.
The washing machine-sized lander was released by its Rosetta mother ship at 0835am GMT on Wednesday morning and touched down at a perfect spot on the comet’s surface. But when anchoring harpoons failed to fire, the probe bounced back off into space. So weak is the gravitational pull of the comet that Philae soared 1km into the sky and did not come down again until two hours later. “We made quite a leap,” said Stephan Ulamec, the Philae lander manager.
In the time it took the probe to land for the second time, the comet had rotated, bringing more treacherous terrain underneath. The spacecraft bounced a second time and finally came to a standstill on its side at what may be the rim of an enormous crater.
“We bounced twice and stopped in a place we’ve not entirely located,” said Jean-Pierre Bibring, Philae’s lead scientist. Teams of scientists are now trying to work out where the probe is. What mission controllers do know is that they are not where they hoped to be. “We are exactly below a cliff, so we are in a shadow permanently,” Bibring added.
With most of Philae in the dark, the lander will receive only a fraction of the solar energy that Esa had hoped for. The spacecraft needs six or seven hours of sunlight a day but is expected to receive just one and a half. Though it can operate for 60 hours on primary batteries, the probe must then switch to its main batteries which need to be recharged through its solar arrays. If Philae’s batteries run out it will go into a hibernation mode until they have more power.
The spacecraft was designed with landing gear that could hop the probe around, but from its awkward position on its side the option is considered too risky.
Though caught in a tight spot, the Philae lander’s systems appear to be working well. The Rosetta spacecraft picked up the lander’s signal on Thursday morning and received the first images and more instrument data from the surface of the comet.
One of Philae’s major scientific goals is to analyse the comet for organic molecules. To do that, the lander must get samples from the comet into several different instruments, named Ptolemy, Cosac and Civa. There are two ways to do this: sniffing and drilling. Sniffing involves opening the instruments to allow molecules from the surface to drift inside. The instruments are already doing this and returning data.
Drilling is much riskier because it could make the lander topple over... Pushing down into the surface will push the lander off again. “We don’t want to start drilling and end the mission,” said Bibring.
But the team has decided to operate another moving instrument, named Mupus, on Thursday evening. This could cause Philae to shift, but calculations show that it would be in a direction that could improve the amount of sunlight falling on the probe. A change in angle of only a few degrees could help. A new panoramic image will be taken after the Mupus deployment to see if there has been any movement.
Meanwhile, the Rosetta orbiter team will continue to try to pinpoint Philae’s position.
Crashed spaceship pilot unaware co-pilot unlocked brake
Pilot Peter Siebold told the National Transportation Safety Board that he was not aware co-pilot Mike Alsbury had pulled a brake-unlocking lever before the rocket designed one day to fly tourists to the edge of space was done accelerating. Seconds later, SpaceShipTwo began to disintegrate over Southern California.
Protocol for the flight was to announce the unlocking, an agency spokesman said.
It is not clear if Siebold didn’t hear Alsbury or the co-pilot never indicated he was taking the action. The safety board plans to analyze flight audio next week, spokesman Eric Weiss said.
Virgin Galactic and said it could not comment on the investigation and referred questions to the NTSB. Siebold has not spoken publicly.
Pilots and co-pilots typically agree in advance before making important decisions, said Michael Lopez-Alegria, a former space shuttle astronaut who now consults on commercial space flight. One method is a “challenge and response” system in which one voices an intended action and the other confirms it before the action is taken.
Lopez-Alegria said he did not know whether the unlocking of SpaceShipTwo’s brakes was considered critical enough to require agreement, but “you would never take that action on your own.” He noted that in the cockpit of a commercial airliner, the pilot and co-pilot call out and confirm an action as routine as raising the wheels after takeoff.
The Oct. 31 crash about 120 miles north of downtown Los Angeles killed Alsbury, injured Siebold and cast a shadow over the immediate future of space tourism. It could take a year for the NTSB to determine the cause, though Virgin Galactic CEO George Whitesides said last week the company wants to resume test flights as early as next summer with a replacement craft.
The eventual goal is to launch spaceships carrying six passengers from a spaceport in New Mexico. For their $250,000 ticket, passengers would get a fleeting feeling of weightlessness and a spectacular view of Earth from about 62 miles up.
Pilot Siebold was hospitalized after the crash, but when he spoke to investigators Friday he had been discharged.
He told them that he was flung from the vehicle when it disintegrated. He said he unbuckled from his seat at some point during his fall that began miles above Earth, and his parachute deployed automatically.
Investigators have not revealed the exact altitude of the breakup, but previous SpaceShipTwo test flights peaked at about 10 miles, much lower than the height expected for commercial flights.
Co-pilot Alsbury could be seen on inflight video unlocking the system before the vehicle had reached Mach 1.0, Hart has said. The feathers aren’t supposed to be unlocked until the craft reaches Mach 1.4, or more than 1,000 mph. At that point, it would have reached an altitude where the thinner air would not have provided so much violent resistance.
Even after Alsbury unlocked them, the feathers were not supposed to move. For that to happen, the crew would pull a second lever. The crew didn’t take the second step, but the system engaged anyway. Two or three seconds later, the craft began to break apart.
The NTSB has said the feathers could have deployed because of aerodynamic forces on the craft. The agency said Wednesday that it is looking at those forces and reviewing safety documentation and the feather system’s design.
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Associated Press writers Brian Melley and John Antczak contributed to this report. View Article Here Read More