Subject: Robot due to Land on Space Duck
From: Alex Kemp
Date: Monday, 15 September 2014 21:31:47 +0100
To: Micaela Kemp, Liisa Kemp, Davin Kemp

One of my better headlines, although I think that the comet has a ‘head’ that looks more like a dinosaur or a dog than a rubber duck (the original NAVCAM photo is available via the ESA Blog):-

Comet 67P/C-G; Rosetta navigation camera (NAVCAM) image taken on 9 August 2014 at about 99 km from the comet

In November 1993 the European Space Agency (ESA) agreed on a mission to send an orbiter + lander to rendezvous with & investigate a comet. ESA decided to call this €billion Euro mission “Rosetta” (named after the unique Rosetta Stone, which--together with a bilingual obelisk found on the island of Philae within the River Nile--was the key to unlocking the meanings of the Ancient Egyptian hieroglyphs). I find it a touch difficult to link the Rosetta Mission with the Rosetta Stone/Philae Obelisk, but then ESA is based in France, so let’s give them a little leeway.

This 20-year mission had some rocky moments. The initial launch was planned for 12 January 2003, to intercept comet 46P/Wirtanen in November 2011. Then, on 12 December 2002, the latest model of the Ariane series of space-rockets (the Ariane 5-ECA) had it’s maiden flight (Flight 157) from Kourou spaceport in French Guiana, South America. It blew up shortly after launch, causing the complete loss of 2 on-board satellites worth €600m Euro. By 7 January 2003 the Ariane 5 series of rockets--which had almost completely taken over from the older, but utterly reliable Ariane 4--had flown 14 times:- twice it had failed, and twice it had put satellites into the wrong orbit. On Tuesday, 31 December, 2002 ESA had postponed the Rosetta mission until an inquiry into Flight 157 was completed. The irony here was that Rosetta was due to be lifted into orbit by the standard model of the Ariane 5 rather than this newer (and more powerful) variant. Nevertheless, after 10 years of development & a billion Euros the postponement was hardly surprising. The problem was that the mission to reach Wirtanen had a 19 day window starting on 12 January. The flight plan was immensely complex, using a deep-space ‘swing-by’ Mars (once) & Earth (twice) to increase speed sufficiently so that Rosetta could intercept the comet on the far side of Jupiter. If they could not launch within that window, then they would have to either cancel or find another target.

The commission of inquiry reported on 6 January 2003 that “what went wrong on Flight 157 was down to new components in the ECA”. In spite of that all Ariane 5 rockets were grounded and, by Friday, 7 March, 2003, Rosetta had a fresh target:- 67P/Churyumov-Gerasimenko. It was the same orbiter + lander, a similar flight-plan & the same mission to land on a comet, so everyone was happy. There were some differences, mostly due to size (Wirtanen is just 0.6-km diameter, whilst 67P is almost 2 km), which meant that the gravity would be different and, as just one example, the lander’s legs needed to be stiffened. Changes like this cost the Agency another €70m (do you think that they may be being overcharged?).

The launch would now be in 2004 with a 7 billion kilometre journey until rendezvous with 67P in 2014. Meanwhile, in a clever marketing wheeze to maintain interest, a competition was launched to give a name to the lander (Philae). That was won by Serena Olga Vismara (aged 15 in 2004) from Arluno near Milan, Italy. Finally, on Tuesday, 2 March, 2004, after yet another last-minute delay, Rosetta made a successful launch from the Kourou spaceport.

The 10 year journey before rendezvous probably appears to be utterly crazy from outside, but it is the only way to achieve the velocities necessary to escape from the sun’s gravity & reach outside the orbit of Jupiter. It makes use of the Earth & Mars as a ‘slingshot’ (or perhaps Basque pelota) where, if the entry vector is correct, the exit speed can be magnified over that of entry. For 67P/Churyumov-Gerasimenko this this meant orbiting Mars once (25 February 2007), the Earth three times (4 March 2005, 13 November 2007 & 2009) and into the asteroid belt twice (2008 + 2010). The final Earth pass-by on Friday, 13 November 2009 added another 4 km/sec to it’s speed, and it was making 13 km/sec at closest approach (and 15 km/sec at exit).

Rosetta had already flown close to (and broadcast pictures of) asteroids, but surely Wednesday 8 June 2011 must have been one of the most nervous days for it’s operators. The reason? It was sent a signal at 12:58 GMT to go into a state of hibernation until 10:00 GMT on 20 January 2014. It was now so far from the sun (660 million km) that very little light energy was reaching the solar panels. Therefore, most systems were shutdown in the preceding months and, finally, Rosetta was turned so that it’s solar panels faced the sun & it was placed into a slow spin (for centrifugal stability). Finally, all on-board systems were shut down except for two:

  1. A pair of heaters, to make sure that Rosetta does not freeze solid.
  2. A clock, to ensure that it wakes up again.

You can perhaps imagine the state of the people in the room in Germany as the controllers waited for the signal from Rosetta that said “I’m awake again”! As Gerhard Schwehm, mission manager for Rosetta, said: “After 31 months in hibernation, what is 45 minutes to wait?” It finally arrived at 18:17 GMT on 20 January 2014, as planned.

At it’s then distance from earth (800 million km), signals took 45 minutes to travel between the 2 points, and Rosetta was 9 million km distant from the comet. By 9 August it had managed, across the previous 2 months, to slow itself sufficiently--from a relative 2,880 km/hour to about 3 km/hour--to go into orbit around the comet just 100 km away & 400 million km from earth. If you think about it, that previous sentence is an utterly awesome achievement. The stats are also a touch awesome. At that date Rosetta & the comet were each travelling at 55,000km per hour (34,2000mph) towards the sun (and getting faster as each hour passes). Comet 67P is actually approximately 4km (2.5mi) wide:-

How big is 67P? (bigger than you think)

The plan is that Rosetta & 67P will spend a year together, whilst the comet passes around the sun and begins again to head out into the void.

Now a little more awesomeness...
Here is a selfie that Rosetta took on 7 September from a distance of about 50km from the comet (seen at the top of the picture):-

Rosetta Selfie, taken with CIVA camera (~50km from 67P; 7 September 2014)

The photo above was actually taken with the CIVA camera situated on Rosetta’s landing craft (now known as Philae). Rosetta has 2 of those 14m-long solar wings and, to put the photo into perspective, here is another picture of those wings taken on earth when they were being constructed:-

The 14m Solar Wings unfurled during testing after construction; Noordwijk, June 2002

There is an awful lot more that could be said, but I do not want this email to get so big that you have too much difficulty downloading it.