EXCLUSIVE – Behind the Mission with a Rosetta Engineer!

From University to retirement, Mike Batchelor has always been involved with space-flight.

Since our first meeting, Mike and I have struck up a keen friendship based upon a shared interest of space and astronomy.

Mike worked on Rosetta, even before it was named so, and kindly agreed to share some insights with me for my blog.

JC. What was your involvement with Rosetta?

MB. My very first involvement was over 26 years ago, before the project was called Rosetta. ESA already had an extremely bold but expensive plan to collect and bring a frozen sample from a comet back to Earth, but to share costs, they had commissioned a study see how this could be combined with a proposed NASA comet rendezvous spacecraft. I was excited to be part of an industry team studying the technical side of this. My own involvement was investigating the comet lander part, which meant working out how to arrange its many functional requirements and special hardware into an actual design and somehow combine this with the NASA part.

Many years later, the Rosetta mission, in its current form was announced and I was very excited to be involved in one of the industry bids to produce the Rosetta spacecraft, working on the “configuration” design, which is the overall mechanical layout of the spacecraft. The lander (yet to be christened Philae) was to be provided by DLR, the German space agency. I was even more excited when my company DSS (now part of Airbus DS) won the bid. Having already established the spacecraft layout during the bid and now entering into contracts with subcontractors, the role as the “configuration” engineer evolved into producing drawings and finding solutions for of all the normal development issues which crop up, without generating a cascade of undesired technical or contractual side-effects. The most commonest  issues were increases the mass, size or power requirement or additional field of view or positioning restrictions. As there was a strict maximum mass set by Ariane 5’s interplanetary launch capability, and drastic power limitations when the spacecraft was at its furthest from the Sun, keeping up to date mass and power budgets was critical.

JC. Did it seem like an ambitious project? Did you think it would work?

MB. It didn’t take long to appreciate that, not only was the project ambitious, but it also pushed many technical aspects of the spacecraft design to their limits.

A nuclear power generator (RTG) was not an option for ESA, however solar power had never been used so far from the Sun before. At that time, nobody had orbited an asteroid or a comet (let alone an active comet). Simultaneous pointing of the science instruments at the comet, solar panels to the Sun and High Gain Antenna at the Earth was a technical challenge. Designing a landing system for the lander was very difficult, as nobody knew what surface characteristics to expect. If you add to that, three Earth flybys, two asteroid flybys, a Mars flyby, and a large propulsion manoeuvre required at the end of a journey time of nearly 10 years, it was hard not to think about the things that could go wrong.

To answer the second part of the question, though, I think that when enough people spend enough time thinking about and around their tasks, and keep asking themselves what could possibly go wrong, there’s actually a reasonable chance things will go all right. I’m pleased to see this seems to have been the case.

JC. Were there any major engineering issues that had to be resolved for the mission?

MB. For the spacecraft designers there was actually a small cascade of engineering issues. These started with the strict limitation on launch mass and the need to rely on solar panels at distances from the Sun where they would generate less than 1/25th of their output at Earth. ESA had prepared for this in advance by supporting a research program to develop special solar cells which could perform well both at low temperature and in low intensity sunlight. Such cells were, therefore, available for the mission. Despite this however, the panel area needed to run spacecraft and heaters in the most basic mode at the most distant point from the Sun, was still greater than could be carried within the mass limit. This forced two further technical developments. The first was that, to reduce heater power, special techniques had to be developed to improve Rosetta’s thermal insulation of the spacecraft. The second was the radical idea to deliberately switch off almost all of the electronics and place the spacecraft in a “hibernation mode”. Without sensors and computer to control the spacecraft attitude however, it was necessary to set Rosetta into a controlled spin with a rotation axis aligned to keep its solar panels pointing at the distant Sun, and rely on a simple timer to wake Rosetta up as its orbit brought it back closer to the Sun. This, in turn, required sophisticated autonomy to enable Rosetta to deal with any problems in restarting, and returning itself to 3-axis control so it could point its High Gain Antenna back to the Earth again.

For the mission controllers, other major challenges were how to manage the orbital trajectory around the comet. The comet’s low gravity meant even small errors performing a manoeuvre have a large effect on this. Orbit prediction is much more complex than around planets because of the comet’s large unknown variations in local gravity. One doesn’t have to look at many images to recognise the comet is not a uniform a body like the Earth. Although these variations are now becoming better characterised with time, it will become more difficult to predict orbital perturbations caused by gas and dust emissions from the comet as the comet activity increases. Philae had no propulsion system of its own so, to set it off on the right trajectory, Rosetta needed to be in the right position at the right time pointing in the right direction, and the eject mechanism had to eject at exactly the right speed. These activities were made all the more difficult, given typical two-way communication delays of the order of an hour.

JC. Did you watch the live footage of Philae landing?

MB. Yes, I’ve been addicted to the Rosetta website for months, and had to be unglued from the computer screen the evening after Philae’s landing. I watched with confusion at the controllers’ initial smiles at what seemed to be the landing, followed by their bemused expressions (which we now realise must have been them watching an enormous bounce) and was having an e-mail exchange with a space enthusiast friend in Finland discussing this odd behaviour.

The other thing I enjoyed about the live coverage was the emphasis placed on the fact that Rosetta was a European-led, multi-national, decades-long, collaborative project. I hope that everybody watching took away a feeling that amazing things can be achieved when people put sustained effort into working together.

JC. What is your interpretation of the scientific information that has been released?

MB. I think the most exciting surprise was to find that the comet looked like two comets stuck together. Although there has been a growing awareness that it’s not unusual for minor bodies to be accompanied by another body, I don’t think anybody was expecting 67P Churyumov-Gerasimenko to look like a ‘contact binary’. Whether this is actually the case, or whether dust and gas escaping from the neck have just eroded this region to give this appearance, will probably be determined conclusively as the mission progresses. I also noted another preliminary result, which was that, contrary to expectations, there didn’t appear to be any water ice visible on the comet’s surface. The outer surface is dustier than expected and appears to surround a less dense core. This surface also appears to be extremely hard. This particular information would have actually been very useful about 17 years ago when the landing system was being designed! This hard surface probably contributed to Philae rebounding with more energy than had been expected.

For the more detailed results, it takes time for raw data to be calibrated, checked and turned into understandable information, and longer still to fit this into a bigger picture about what is happening on 67P CG. In another year, when Rosetta has followed the comet activity through closest approach to the Sun and back out again, I hope we will start to hear about the significant new insights gained by the scientific community. P67 CG was chosen for Rosetta because (astronomically speaking) it is a relative newcomer to the inner solar system and has not had time to become significantly altered by its passages closer to the Sun. The comet’s construction, composition and the process occurring should ultimately provide important information relating to lofty questions such as the initial conditions at the formation of the solar system, whether the Earth’s oceans came from comets, whether life on Earth could have been seeded by comets, and may even give us a better idea of whether there is anybody else out there.

JC. Are there any other ‘small body’ missions you are looking forward to?

MB. Absolutely!  In July 2015 NASA’s ‘New Horizons’ will be the first ever spacecraft to fly by the dwarf planet Pluto and its moons. This should dramatically improve our understanding of the outermost parts of the solar system. The flyby will then use Pluto’s gravity to retarget it to fly past a Kuiper Belt Object (KBO) about 4 years later. KBOs are mysterious comet-like bodies beyond Pluto which, like 67P CG, are believed to be sources of the material which formed the planets. The target KBO is about 10 times bigger that 67P CG and it will be very exciting  for us to find out how this compares.

Currently NASA’s ‘Dawn’ is headed for an April 2015 arrival at the asteroid Ceres, having already orbited and investigated the rocky asteroid Vesta for 14 months en-route.  Ceres was the first and largest asteroid to be discovered and is also unique, in that it seems to be somewhat like a comet in containing large amounts of ice. This was first verified this year by ESA’s Infra-Red Observatory satellite Herschel.

Japanese Hayabusa-2 should be launched in just a few days on a 6 year mission to return a sample from an asteroid, with an arrival at 1999-JU3 in 2018, and NASA’s ‘Osiris-Rex’ should launch in 2016 on a similar 7 year mission to return a sample from asteroid 101955, also arriving in 2018. Hayabusa-2 is a more sophisticated version of an earlier mission which succeeded in returning more than 1000 microscopic particles from asteroid Itokawa.

For the planned future, Rosetta’s mission to orbit and land on a comet is unmatched, even given this was a scaled down version of the original plan to return a frozen comet nucleus sample to Earth. I enjoyed the ESA short film “Ambition” because it portrays a future where there were bigger missions later, but Rosetta was the first to actually ‘catch a comet’.

JC. What was your career path, and what advice could you give to students at school thinking about an engineering/science/maths career?

MB. I was interested in spaceflight and astronomy from quite a young age and, at school, I liked maths and science, especially because these subjects were useful and allied to my interests. After A-levels I studied astronomy at university, which involved a fair share of physics & maths. I discovered, though that I enjoyed the practical side, using the telescopes and getting a result out of the data, much more than the maths used to come up with the theories. After I graduated I worked making telescope optics for a while, before I got my first permanent job with British Aerospace Space Division (an engineering company building satellites). They offered me a job even though I didn’t have any ‘proper’ engineering qualification or demonstrable experience. I suspect both my enthusiasm for space and the fact that mechanical engineering is based very much on maths and science, helped a lot in being offered this job. Since then, I have worked for other space companies in the UK and in Germany.

My career advice to students would be, as a first guide, follow your interests. If you are interested in something, you will be enthusiastic and more motivated to put in whatever effort is needed to make you a useful person in the field. If your interests and strengths are related to the STEM subjects, so much the better, because the STEM skills are not only useful in themselves, but also transferrable into a wide range of satisfying careers. Even if your actual career diverges from your interests, you can still have the best of both.

Mike B

Mike with a spacecraft “selfie”.

Probably before the word “selfie” was even invented!

I cannot thank Mike enough for his input to this article. I found it a fascinating and inspiring read, and I hope you do too.


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