Another trip: to Leiden and Noordwijk, the Netherlands. In Noordwijk, a seaside town, there is the headquarters of ESTEC, the European Space Research and Technology Centre. This is the European Space Agency’s technology centre.
In the excellent cafeteria, one can see things like this:
Each winter we make a trip to L’Observatoire de Haute-Provence (or, OHP). I wrote about it before On this blog. It is always a challenge to find something new to photograph!
This year I spent a lot of time photographing heavy machinery inside the domes. Very old heavy machinery because this stuff was made in the 1950s. Here are the ventilation fans inside the dome of the largest telescope, the 193cm (this is the first telescope in the world that detected a planet around another star). Much later, other instruments like the Canada-France-Hawaii Telescope would also adopt similar strategies to improve atmospheric conditions inside the domes. The fans are an attempt to make air flow freely over the telescope and remove turbulence, which is the effect which make stars twinkle. Great for poets, not so great for astronomers.
At OHP, as far as I can tell, they are not used any more, and it’s not clear if they made a big difference. The “intrinsic seeing” of site is quite bad.
Breaking out of low-earth orbit: realising the promise of Falcon Heavy
So it seems, maybe, that the “high frontier” of human space exploration may not be closed after all. The successful test flight of SpaceX’s Falcon Heavy Lift vehicle was also the first time a private company, rather than a government, sent anything beyond low earth orbit. In a master-stroke of publicity and whimsy, SpaceX’s founder Elon Musk decided to attach his red electric car, manufactured by SpaceX’s sister company Tesla, to the front of the second stage booster. Sitting inside, one hand on the draped nonchalantly over the windowsill and the other posed coolly on the steering wheel, a mannequin modelled SpaceX’s appropriately futuristic but actually fully functional space suit. By the time this unusual cargo reached orbit, there was enough propellant left over to inject both the booster and the attached car into an elliptical orbit around the sun reaching to the asteroid belt. Out there, it will probably be undisturbed for millennia.
The livestream of the launch was carefully choreographed, with cheering SpaceX employees heard in the background behind the engineer-presenters, together with blasts of pop music at the appropriate moments. It was much more exciting than any rocket launch had been for a long time, partly because (it seemed) no-one was entirely sure what would happen. But what happened, in the end, matched almost exactly what had appeared in a simulation video only days before. Does this mean, perhaps, that prospects for manned space exploration might be improving soon too?
Recall, for an instant, what manned space “exploration” has been like for the last fifty years: a series of uninspiring endurance tests in an orbiting space station, the ISS. In fact, the space station itself seems to have been created to give a safe destination for manned rocket launches and to assure the future of heavily subsidised American aerospace industry. It’s not clear at all how we can dig ourselves out of this particular hole of sending people into orbit to (mostly) take pictures of the Earth through fancy windows.
Pessimistic SF writers had imagined that the frontier had closed, so the reasoning went, because all the engineering talent was now going to writing software for internet start-ups, most of whom were just interested in finding new ways to distract people in order to sell them more advertising. Worse, fingertip access to the world’s store of knowledge (or at least Wikipedia) meant that it has become discouragingly easy to find out just how impossible it was to do something that had never been done before. But the truth turned out to be more complicated and interesting than that.
On the one hand, those internet start-ups created a new class of geek-entrepreneur who love rockets and spaceships, and advanced software engineering turned out to be very useful for lowering launch costs by enabling boosters to return to the landing sites. The most impressive aspect of the Falcon Heavy launch is how perfectly the highly complex system followed the simulations made before launch, validating SpaceX’s impressive engineering capabilities. However, all this still takes place within the systems which have paralysed the human exploration of space over the last half-century.
Elon Musk has decided that no resources will be devoted to making Falcon Heavy meet NASA’s stringent requirements for manned launches. Instead SpaceX are focussing on near-term launches to the ISS with the smaller Falcon 9, because that’s where the money is. Meanwhile, NASA themselves are locked into a vast multi-year spending program for their new rocket, the Space Launch System (or more unkindly, the Senate Launch System), a billion dollar disposable rocket with no clearly defined destination. In an unfortunate commentary on the state of innovation in rocket technology for the SLS contractors, the spacecraft actually makes use of spare parts left lying around after the end of the shuttle programme.
Meanwhile, in low earth orbit, the ISS is supposed to be decommissioned at the end of the next decade. Needless to say, not everyone is in favour of this, especially those whose livelihood depends on it. In an attempt to find some use for the fantastically expensive SLS, it has been proposed to create a new space station — but this time, groan, in orbit around the moon. Reaction to the Falcon Heavy launch has been mostly positive, although one ill-informed killjoy commentator did insist that we should “think about the environmental impact”. Yes indeed. Today, Musk is about the only player in this game with a clearly defined vision extending beyond low Earth orbit. Let’s hope he makes enough money from his satellite launches to realise it.
Making discoveries: planning the Euclid space mission
Let’s start with some philosophy. Where does new knowledge come from? Well, from doing experiments, and comparing the results of those experiments with ideas — hypotheses — concerning physical laws. This works: technology created from knowledge gained this way has transformed the world.
However, as our knowledge of the Universe increases, so each new experiment becomes more complicated, harder to do and more expensive. They have to because each new hypothesis must also explain all the previous experiments. In astronomy, technology enables new voyages to some unknown part of “parameter space”, which in turn lead to ever more stringent tests of our hypotheses concerning how the world works. These experiments allows us to take a good long look at something fainter, faster, further away. Something which was undetectable before but detectable now.
Space missions are really different from traditional science experiments. For one, the margin of error is minuscule and generally errors are catastrophic although there can be a few happy counter-examples. What this means is that a careful web of “requirements” must be written before launch. The influence of every aspect of the mission on the final scientific goal is estimated together with the likely margin of error.
So here’s the paradox: how do you build a vastly complicated experiment which is supposed to find out something new and be certain that it will work? How to make sure that you covered all the bases, that you thought of all things and still leave open the possibility for discovery? Even harder, how do you persuade someone to give you a big chunk of change to do it? The answer is a kind of weird mixture of psychology of and book-keeping. So first the (conceptually) straightforward bit: the book-keeping, which comes from trying to carefully chart all the tiny effects which will perturb your final measurement. This is actually notoriously difficult.
There are many celebrated examples of this kind of thing which didn’t quite work out from the annals of astronomy missions. After the launch of the Gaia satellite, astronomers were dismayed to find that there was an unknown source of background light. It turned out that this came from sunlight scattering off fibres sticking out from the sun-shield, which nobody had thought about before. Some changes to the instrument configuration and processing have helped mitigate this problem.
An even more epic example is Gravity Probe B experiment, designed to make a stringent test of General Relativity. This experiment featured the smoothest metal balls ever produced. Planning, launching and analysing data from this satellite took almost a half-century (work started in 1963 and the satellite survived multiple threatened cancellations). The objective was to measure how relativistic effects changed the rotation of these two metal balls. After an enormous amount of work analyzing data from the satellite featuring very smart people indeed, a result was announced, confirming General Relativity — but with errors around an order of magnitude larger than expected (Cliff Will has an excellent write-up here. Despite decades of work, three sources of error were missed, the most important of which being stray patches of static electricity on the balls’ surface, which exploded the final error budget. In the case of both Gaia and Gravity Probe B the missions were successful overall, but unknown sources of error were not entirely accounted for in mission planning.
Part of the Euclid challenge is to make the most accurate measurement of galaxy shapes of all time. Light rays passing through the Universe are very slightly perturbed by the presence of dark matter. If two rays pass next to the same bit of dark matter, they are perturbed in the same way. Euclid aims to measure this signal on the “cosmic wallpaper” of very faint distant background galaxies. These galaxies are effectively a big sheet of cosmic graph paper: by measuring how this correlated alignment depends on distance between the galaxies you can find out about the underlying cosmology of the Universe.
So how do you do this? The problem is that on an individual galaxy the effect is undetectable. Millions of sources must be measured and combined, and instrumental effects can completely submerge the very weak cosmological signal. We need to know what these effects are, and to correct for them. Some are conceptually straightforward: the path of light inside the telescope will also deform the galaxies. Or maybe as the camera is read out electric charge falls into holes in the detector silicon (drilled by passing charged particles) and gets trailed out. This, annoyingly, also changes galaxy shapes. Even worse: imagine that galaxies are not really randomly orientated on the sky, but line up because that’s how they were made back in the mists of cosmic time. You need to find some way to measure that signal and subtract it from the one coming from dark matter. In general, the smaller the effect you want to measure, the more care you need to take. This is all the more important today, where in general the limiting factor is not how many things you have to measure (as it was before) but how well you can measure them. In the end, your only hope is to try to list each effect and leave enough margin so that if anything goes wrong, if you miss anything, the mission is not compromised.
After accountancy, psychology, or more particularly cognitive biases. For example “strong gravitational lensing”– where background galaxies are visibly deformed by dark matter present in massive objects like galaxy clusters– had already been seen on photographic plates well before it was “discovered” in electronic images in the 1980s. Before that, people were not expecting it, and in any case those distorted galaxies on photographic plates looked too much like defects and were ignored.
So how do you plan an experiment to derive cosmological parameters without including some cosmological parameters in your analysis? After dodging all the bullets of unknown systematic errors, how to do you make sure you haven’t included an unknown bias which comes from people just having some preconceived ideas about how the universe should be? The answer must come from trying to design an analysis with as few unwarranted assumptions as possible, and if there are any to be made, hide them from the researchers doing the sums.
The recent story of the discovery of gravitational waves provides a fine example. Most scientists didn’t know until very late on that the signal they were dealing with was real and not a simulation. Such simulations had been routinely injected into the computers by colleagues wanting to make sure everything was working (this was how they had been testing everything). For Euclid, that would be the “Matrix” solution: most astronomers wouldn’t know if data under analysis was real or a simulation after some secret sleight-of-hand early on. But making a realistic simulation of whole Universe as seen by the satellite might be, to say the least, very challenging. More realistically this test might happen later on, with catalogues of objects being shuffled around so that only a few people would know which one corresponded to the real Universe. Like drug trials, but with galaxies.
In the end, you can’t plan for the unexpected because, well, it’s unexpected. But you can at least try to prepare for it. You have to, if you want your results to stand up to the scrutiny of peer-review and make that new discovery about how the universe really works.