Thursday, February 11th saw the announcement of the first direct detection of gravitational waves (not to be confused with “gravity waves”, as some in the media initially took to calling them, but which are something else entirely*), which are ripples in the fabric of space-time whose existence was first proposed by Albert Einstein, in 1916.
The detection came about partly as happenstance, in that the Large Interferometer Gravitational Wave Observatory (LIGO), a world-wide operation established in 1992 and involving 900 scientists from 80 institutions in 15 countries. However, the detectors in use up until recently had failed to provide direct evidence of gravitational waves.
Enter the National Science Foundation in the United States. Over the last five years, they have funded the development and construction of two “Advanced LIGO” detectors, themselves massive feats of technology and engineering, located 3,000 km apart in the United States. One resides Livingston, Louisiana, and the other in Hanford, Washington State.
These detectors started running in February2015, in what was called an “engineering mode”. However, in September 2015 work started on running them up to full operational status when, and completely unexpectedly and within milliseconds of one another, both appeared to detect gravitational passing through them.
The odds of such an event occurring almost precisely at the time when the detectors were starting to do the work for which they have been designed would seem to be – and no pun intended – astronomical. As a result the LIGO investigators wanted to be sure of what had just happened and verify what they had apparently detected; hence why the news was only released on February 11th, 2016, several months after the actual detection had been made.
Since the initial detection, the LIGO teams have deduced the gravitational waves were created by two black holes, each barely 150km across, but each travelling at around half the speed of light and massing around 30 times as much as our on Sun, spinning around one another and merging together some 1.3 billion light years away. As such, the detection marked two things: the first direct proof of gravitational waves and the conformation of a another theory: that black holes can meet and coalesce to create much larger black holes.
But what are “gravitational waves”, and why are they important?
Predicted over a century ago by Einstein in his theory of general relativity, gravitational waves are at their most basic, ripples in spacetime, generated by the acceleration or deceleration of massive objects in the cosmos. So, for example, if a star goes supernova or two black holes collide or if two super-massive neutron stars orbit closely about one another, they will distort spacetime, creating ripples which propagate outwards from their source, like ripples across the surface of a pond. The problem has been that these ripples are incredibly hard to detect, although the proof that they may well exist has been available since 1974.
It was in that year, two decades after Einstein’s passing, that astronomers at the Arecibo Radio Observatory in Puerto Rico discovered a binary pulsar (two rapidly rotating neutron stars orbiting one another). Over the ensuing years, astronomers measured how the period of the stars’ orbits changed over time. By 1982 it had been determined the stars were getting closer to each other at exactly the rate Einstein’s of general theory relativity predicted would be required for the generation of gravitational waves. In the 40 years since its discovery, the system has continued to fit so precisely with the theory, and astronomers have had little doubt it is emitting gravitational waves.
The LIGO detection however, provides the first direct evidence of gravitational waves, and with it comes the ability to see the universe in a totally new way.
“It’s like Galileo pointing the telescope for the first time at the sky,” LIGO team member Vassiliki Kalogera, a professor of physics and astronomy at Northwestern University in Illinois, said. “You’re opening your eyes — in this case, our ears — to a new set of signals from the universe that our previous technologies did not allow us to receive, study and learn from.”
Just as we’re able to study the universe in various wavelengths of light, using them to reveal things we otherwise would not be able to see, so gravitational waves will allow us to see the more of the dynamics in cosmic events which have so far remained hidden from us. We would in theory be able to see precisely what is happening in the heart of a supernova for example, and be able to detect the collisions and mergers of black holes, and more. So gravitational waves offer us a further means to increase our understanding of the cosmos.
(*In case you were wondering, gravity waves are physical perturbations driven by the restoring force of gravity in a planetary environment; that is, they are specific to planetary atmospheres and bodies of water, not cosmological events.)
Philae Hunt Ends
The European Space Agency is giving up on trying to contact the lost Philae, the little lander vehicle carried to comet 67P/Churyumov-Gerasimenko by ESA’s Rosetta vehicle, and which attempted to make a safe touchdown on the comet on Wednesday, November 12th, 2014.
Designed to “harpoon” itself onto the comet’s surface – the gravity on 67P/C-G is so negligible there was a real risk the lander would bounce right back off it and be lost in space if it did not anchor itself on arrival – the little craft performed a perfect descent to the comet, only for its anchoring system to malfunction.
The result was that despite touching down at 15:33 UT – precisely on schedule and on target, Philae did indeed bounce, rising possibly by as much as a kilometre above the comet over the course of an hour, before dropping slowly back down once more, touching the surface again a further hour later – and then bouncing again, at 17:26 UT, albeit with far less force, and finally coming to rest on the comet at 17:33 UT.
The bounces, while they did not overly harm the lander, did result in two things. The first was that because the direction in which the little craft bounced was unknown, coupled with the comet’s tumble through space, meant that no-one actually knew where it eventually finished up. The second was that when telemetry and images were relayed to Earth via Rosetta, it became apparent Philae was lying partially in the shadow of nearby cliffs and unable to receive the required sunlight needed to re-charge its battery systems.
Even so, over the course of the 60-hour life span of the battery system, Philae was able to carry out the majority of its science mission. It just wasn’t able to transmit all the data back to Earth before power levels became critical. Rather than exhaust the battery system totally, the science team opted to order the lander into a hibernation mode, in the hope that as 67P/C-G travelled closer to the Sun, Philae would enter into a period of increased sunlight and thus be able to recharge the batteries.
That’s precisely what happened, and on Sunday, June 14th, 2015, ESA confirmed Philae had ‘phoned home – and had been attempting to do so since around mid-April; June 14th was the first time its call had been heard by the comet-orbiting Rosetta.
This started a frantic attempt to maintain contact with the lander, ascertain it’s precise location and retrieve the remaining data – estimated to be around 8,000 packets, with 300 returned during the 85-second long communications link on June 14th. Unfortunately, however, it appeared that Philae hadn’t come through its period of hibernation unscathed; communications over the course of the next month were sporadic, but sufficient data was received to suggest the primary communications system was malfunctioning. The last contact with the lander came on July 9th, 2015.
Since then efforts to re-establish communications with the lander have continued as Rosetta and 67P/C-G have passed around the Sun and headed back out towards the orbit of Jupiter. But with both now passing beyond the orbit of Mars, it is once again likely that Philae sits largely in shadow, unable to recharge its batteries. so it was that on Friday, February 12th, 2016, ESA officially announced the Philae mission was effectively at an end.
“The chances for Philae to contact our team at our lander control centre are unfortunately getting close to zero,” says Stephan Ulamec, Philae project manager at the German Aerospace Center, DLR. “We are not sending commands any more and it would be very surprising if we were to receive a signal again.”
Even so, the seven periods of contact which took place between June 14th and July 9th, 2015, meant a fair amount of the remaining data gathered by the Lander could be returned to Earth. However, the communications periods were too short to successfully re-start Philae’s data gathering operations.
Rosetta has also gathered a plethora of data about the comet, allowing scientists greater understanding about the formation of the solar system, the nature of comets and more. The orbiter vehicle will continue to study 67P/C-G through until about September 2016, when it will be commanded to make a gentle crash landing on the comet, having insufficient power or fuel to maintain further operations. But for Philae, the February 12th announcement means that a long, eternal sleep has officially begun.
Adam Steltzner Honoured
Adam Steltzner, the JPL engineer who helped pioneer the breakthrough technique for landing the one-tonne Curiosity rover on Mars, is to be inducted into the US National Academy of Engineering one of the highest professional distinctions an engineer in the USA can receive.
Admission to the Academy is awarded to those who have made outstanding contributions to “engineering research, practice, or education, including, where appropriate, significant contributions to the engineering literature” and to “the pioneering of new and developing fields of technology, making major advancements in traditional fields of engineering, or developing/implementing innovative approaches to engineering education.”
A flamboyant character, referred to as the “rock-and-roll engineer” during the lead-up to the Mars Science Laboratory’s arrival at the Red Planet on account of his Elvis hairstyle and hip approach to the media, Steltzner has worked on multiple NASA flight projects over the years, including the Shuttle–Mir Programme, Galileo, Cassini, Mars Pathfinder, and the Mars Exploration Rover (MER) missions. However, he is being recognised for conceiving and leading the development team behind the unique and daring Entry Descent and Landing (EDL) system used in the MSL mission.
Up until the Curiosity mission, landers and rovers had arrived on Mars in one of two ways. In the first, the craft would drop towards Mars beneath one or more parachutes, which would be released while the vehicle was still a few dozen metres altitude in order to avoid them fouling the craft after landing, and retro-rockets used to cushion the final drop to touch down.
In the second, as used by Mars Pathfinder and the MER missions, parachutes would again be used and released a few dozen metres above the ground, the vehicle having been cocooned in an air bag system which would protect it as it dropped the final few metres before bouncing and rolling to a standstill, after which the air bags would be deflated freeing the vehicle inside.
At a tonne in mass and almost the side of a small car, Curiosity was simply too big for either system. Instead, Steltzner and his team worked for 10 years developing an entirely new aeroshell, parachute system and the now famous “sky crane” system for landing the rover on Mars, the last element of which actually hovered around 7 metres from the Martian surface (making it the first vehicle to achieve powered flight over Mars rather than just powered descent), and winched the rover down to the ground, before flying up and away from the rover, to crash-land a safe distance away.
Steltzner referred to the EDL phase of the mission, which was entirely under the management of his team, as the “seven minutes of terror”, and for two reasons. Not only did it mark the length of time in which Curiosity would enter the Martian atmosphere at 20,800 kilometres per hour (13,000 mph) and slow down to a hover just 8 metres above ground; the time delay for Mars-Earth transmissions at the time of the landing was 14 minutes. This meant that by the time the data concerning the success or failure of the landing had been received, Curiosity would either have been resting on its wheels on Mars for seven minutes, unfolding its various communications and camera arrays, or it had been a new, and probably slightly smoking hole on the surface of Mars.
Of course, it was a remarkable success, and since that time, Steltzner spent time working on the kind of EDL systems which will be required for human landings on the surface of Mars, a challenge of an altogether greater order of magnitude, requiring as it does gently setting down craft with a mass of around 40 tonnes. Most recently, however, he’s been leading the team developing the EDL / sky crane system which will be employed for the Mars 2020 rover mission.