We are working on flight control and science operations for Rosetta, now orbiting comet 67P, and Philae, which landed on the comet surface last week. Ask us Anything! AMA!

Which is harder: landing on a comet in real life or landing on a comet in Kerbal Space Program?

(TF) I've tried in Kerbal and failed miserably... Poor Jebediah...

One of us! One of us!

[TF] There are actually lots of us here in ESA ;)

I for one have some poor Kerbals stranded on the surface of Duna :(

Now when someone gives me crap about a stranded Kerbal, I'm pointing them to this!

Also, super cool to see that you enjoy what you do for work so much as to use part of your personal time to run a simulation of what you do for work.

[TF] Kerbal is real fun. Normally I try to see what crazy contraptions I can put in orbit and try not to focus on realism. Nothing like strapping a poor Kerbal to 10 solid rocket boosters to see how far he can fly :)

I do have some colleagues here that are really good at it!

Well for once, the time delay with Rosetta is about 28 minutes at the moment. So if you are in the wrong path it will take you 28 minutes to realize, then you need to think what you do about it and then, the reaction would occur 28 minutes later!! RP

Welcome to our AMA! We have a team ready to answer and we are really looking forward to this event... Will now ask the ESA & DLR participants to begin answering

Thank you all for doing this in late evening! CONGRATULATIONS to you all!!!!! I have been so excited watching this mission, watching the progress of the landing operation, and everything else! Please take me/us all along until the end of the mission! I'm sure your are enjoying, too!! Let's have fun today! Masanori

Thank you very much, Masanori. I can confirm to you that many people at ESA & DLR are just amazed (and delighted!) by the unexpected level of public support, engagement and media endorsement - it makes working on all our missions and communicating to you guys a real joy! [DS]

How likely is it to pinpoint Philae location on 67P/Churymov-Gerasimenko? How come the harpoon did not work as planned?

The Narrow Angle Camera from the OSIRIS is the instrument that is more likely to find Philae. In December we will orbit in 20km circular orbits where the pixel size corresponds to ~40 cm. Additionally, the Sun will lit more and more the lower lattitudes of 67P in the comming months. RP

On what kind of orbit is Rosetta now? Even if OSIRIS' resolution isn't enough to directly see Philae now, would it be possible to see sun reflect from its solar panels? Kind of how one can see sun reflect from cars, windows and ditches while flying at 10km, or how it's possible to see satellites moving across the nightsky, brightening rapidly just for a moment when all the sunlight reflects from the solar panels.

It's at a distance of about 30km now. As we know when the lander received its sunlight on the single panel which gave it power, then we can plan (and are planning) our OSIRIS images to do a scan in that area at a similar time in the comet day. So yes, you are completely correct. This is certainly one way we will use to identify the lander - the solar panels have a much higher albedo than the background comet. [LOR]

How would you suggest a citizen living in one of the contributing countries to the ESA go about pushing increased budget to your organisation? Is it our MEPs or local governments we contact?

What fact about your organisation would you yourself highlight to the elected to win over more support?

MEP

Join local science/space groups/astronomy groups, follow your national agency - what they do, what they announce to the media, events they sponsor - and raise questions to your local mp/govt - it's the member states who fix the ESA budget, and that can only be influenced by becoming an engaged citizen [DS]

If you were to launch Rosetta and Philae today, what would be different given technological advances that happened between the launch and now?

TF + ME: In our opinion (from Orbiter perspective) that thing is pretty awesome as it is. It stayed 10 years in space and still works like a charm with tech from the 90s!

However, we think the most progress could be achieved by having faster processors and more storage space. Especially with components getting lighter we could add more instruments.

I know it's kind of a stupid question, but I'd like to have a model of Rosetta and Philae, and additionally the ESA could be supported, is anything planned? Like Revell models, LEGO or something else?

LEGO

Wow! Not stupid at all! Many of us LOVE LEGO...! I know the ESA PR/Comm team haven't had time to set up anything formally with Lego, but there are some really nice informal directions; here are some links:

• https://www.youtube.com/watch?v=1oEaGjgOB0M
• http://www.esa.int/Our_Activities/Space_Science/Rosetta/ESA_s_Rosetta_comet-chaser_goes_LEGO_R
• http://blogs.esa.int/rosetta/2013/11/08/using-lego-to-simulate-esas-touchdown-on-a-comet/

So it's super badass and awesome that we landed a spacecraft on a comet, but can you tell us a little more about what we've learned / hope to learn from the mission?

(Hopefully a little more specific than the "learn about our solar system's origins" that everyone keeps repeating)

Thanks for your comment. This is a mission to study a comet in its orbit around the sun. We're going to watch it wake up and fall asleep again and be there up, close & personal during the full ride. There is a lot to learn from being so close to a comet, primarily because our knowledge of comets comes from observations from the ground and very fast flybys by other spacecraft. We get to see how its structure/surface changes over time, what (and how much) gases are produced & when, how solid is the surface, how much dust is released on a daily basis, why is it shaped like it is, will it look different after it goes through perihelion and much more. All these questions we are now getting answers for. Of course you have to add about our solar system's origins but indeed the mission is much more than that. [LOR]

from LOR

It has been really amazing to follow Rosetta mission through the last months and years. And last week, living with the descent of Philae and all the struggle and success that followed it.. Nerve wrecking and joyful at the same time! Big congratulations to ESA!

So, the questions.

How many pictures was Philae able take on the surface of the comet? Any plans on releasing more than the initial ÇIVA panorama? Any ROLIS images from the surface?

Also, does anyone have information on how the ÇIVA cameras are positioned on the lander? I made a 360 panorama of the images released last week, but not knowing how the cameras are angled on the lander makes it hard to get the projection precise. http://www.360cities.net/image/philae-lander-on-comet-67p-churyumov-gerasimenko-1

It depends on how you count the pictures! The CIVA panorama includes 2 stereo pictures off the balcony, and 4 pictures from cameras located on solar array panel 1, 2, 4 and 5 (those would be the two big panels - 1 and 5 - and the two diagonal small panels - 2 and 4). I can't give you the exact angles off hand, but the cameras aren't plane to the solar panels. Those on 1 and 5 point a bit towards the back and those on 2 and 4 complete the circle. Back to the number of images, we also got 5 ROLIS images during descent and 2 ROLIS images after the final landing: pre- and post-rotation. All of the images have been released/leaked. - VLL

Dear redditors, Tiago Francisco here! This was a blast! Had lots of fun answering your questions and I'm happy to see such interest! If I could, I would stay here all night chatting with all of you.

I hope we can do one another AMA some time in the future, because you deserve it :D

Until next time!

If I dropped a brick from 5 feet off the surface, how long would it take to hit the surface?

Hi digiwinne

gravity field indeed varies with the location on the comet, but just computing the time to get down for the average g on the comet is about 3 minutes !

( gravity acceleration is about 1/100000 that on Earth, i.e. Philae is |100 kg but weighs on the comet only | 1 gram )

FC

As the comet gets more active, the plan is for Rosetta to watch from further out, beyond the Hill radius within which orbits are possible. What are the tradeoffs there? What are the implications and risks of being blown off-course by the emissions from the comet? How fast does stuff come out of the comet, how big is it, and could it damage Rosetta? What do you miss by being further out?

[LOR] Lots of good questions. There is no doubt that there are a lot of tradeoffs between ensuring spacecraft safety versus getting the best science from the mission. The way we do it is to plan two trajectories. One which is the Preferred which we will always fly, the second is the high activity trajectory. The high activity trajectory we move to if we cannot continue to fly on the preferred because of activity. Our desire is always to stay on the preferred and so in general stay closer to the comet. The fact that the activity hits a certain level means that we will no longer be able to orbit meaning we then do flybys (close flybys up to 8.5 km, reasonably close up to 15km and far flybys from 100-50km) all linked to the distance to the sun. As for stuff coming fast off the comet - you have to realize that we are flying at a relative speed to the comet of about 1m/sec in general so the stuff coming our way has not reached a significant velocity to cause damage. Otherwise, we would have not survived up to now.

Thank your for this AMA, I apologize if I use the wrong terminology.

How do Rosetta and Philae handle packet loss and data corruption? Are there any specific protocols used in spacecrafts that are found in mainstream programming?

(ME) From our perspective there are two occasions where packet loss/corruption can happen - either downlink (TM) or uplink (TC):

For uplink there are indeed high level protocols that insure every packet is sent in the correct order and arriving consecutively.

However both up-link and down-link are ensuring error correction by encoding protocols like reed-solomon.

Hey there, glad you're doing an AMA.

I have two questions, one technical and one more political:

1. Given that Philae landed in a relatively hidden area where there isn't much light, do you think it will be possible for it to survive the comet's sun approach?

2. ESA and the EU have been collaborating in a lot of programs (e.g. Galileo) and the majority of ESA's funding comes from the EU. Do you reckon the ESA will keep being an independent, seperate entity in regards to the European Union or do you see it being "annexed" in the future, ar at least being the de facto EU space agency?

For No. 1: We're in the process of finding the answer to that question right now ourselves! From an energy perspective, it's not unlikely that we will get the energy to boot at some point. The question is more what the temperatures will be like and whether we will have enough to get the battery to 0° so it can be charged with the little energy we have. Also, we'd need a pretty well-timed link if we can't charge the battery. We're also not sure all instruments will survive the low temperatures we have until sun approach. - VLL

ESA and the EU have been colaborating in a lot of programs (e.g. Galileo) and the majority of ESA's funding comes from the EU. Do you reckon the ESA will keep being an independent, seperate entity in regards to the European Union or do you see it being "anexed" in the future, ar at least being the de facto EU space agency?

None of us can really answer the question about ESA/EU in the future. It's certainly talked about a lot in the media and we hear some discussion every so often, but it's really up to the sr managers and the member states to figure this out. Those of us here working on the missions are a tad too busy to be to focussed on this now :-) [DS]

PS+++ Note that ESA funding comes directly from Member States' national budgets, and not "from the EU"

From what I can tell Philae used RTX2010 CPUs. Were those used only for science instruments or were they also used for the actual landing. Were they coded in Forth?

Correct, RTX2010RH CPUs. The CDMS is equipped with 2 DPUs running in parallel (hot redundant) and they were/are used to control the Lander including all subsystems. The processor is used by most science instruments as well. In total Philae is equipped with 9 RTX2010 running at 4-5MHz. They were coded in Forth, except for 1 science instrument where 'C' was used instead. (OKm)

How does one gets to work in ESA? (Assuming they are from Europe)

(TF) There are several ways to start a career in ESA.

Either by applying to open positions, or joining ESA via a trainee program!

ESA has an internal program, the so called Young Graduate Trainee (http://www.esa.int/About_Us/Careers_at_ESA/Young_Graduate_Trainees) and some countries run their own programs. In my case, Portugal had a similar program for which I applied.

Have a look here:http://www.esa.int/About_Us/Careers_at_ESA

But what if you wanna work in ESA but you're nor young neither graduate?

[TF] Good question MajjorTom

There are many positions, and some of them might not require a degree in engineering for instance.

There are several websites were you can apply for the so called Contractor Positions, in which some cases you don't need an engineering degree.

We planned this AMA for an hour, ending at 20:00 CET; it's now just after, but most of us are keen to stay until 20:15 CET or so; even so, we'll check back tomorrow AM to see if there are any new questions - everyone's DELIGHTED at the response to tonight's AMA! ;-) [DS]

Can you imagine landing softly Rosetta on the comet when the mission comes to an end ?

PM: That would be really cool. Currently Rosetta mission goes up to end of 2015, but it is possible to get a mission extension. The mission managers will decide how the end of mission will be.

Anyway this would be a very interesting way to end the mission, slowly reduce the distance to the comet, so that we can take pictures and other scientific observations with extremely high resolution. It would be even cooler to reunite Rosetta and Philae at the end.

Do you have any regrets, or something you would have done differently in retrospect?

Personally, I would go for a different solar array design. We currently have two solar array strings per panel oriented vertically on the sides. I would go for more strings and orient then differently to minimize the effects of shadowing. - VLL

I would probably say, no regrets on the side of Flight Dynamics ! ;)

The targeting accuracy of the (original) landing site was even a bit beyond our expectations, thanks to a lot (!!) of work in the past 3 months to understand how to navigate around the comet, and a good last-minute calibration of the accelerometers cutting the thrusters during the pre-delivery manoeuvre... and of course, thanks to Rosetta which behaved perfectly =)

FC

From the orbiter point of view, I think we can say we regret nothing. Rosetta is performing absolutely brilliantly. The spacecraft is 10 years old, that's the age where most of them retire! Ours just starts her life... and apart from a couple of problems that we could work around, it all goes tremendously well.

AH

Why and how did the harpoon malfunction and what was the reaction in the control room when it happened?

Well... after having lost already the ADS (Thruster) system we were a bit anxious to see that the 'Rip cords' were still closed in the first TM around touchdown. The reason for the malfunction is still TBD. (OKm)

How did you feel when you learned that phillae bounced and that it has to go into hibernation?

Also if you could do anything differently what would you do?

Also what organic molecules were discovered and what is their significance?

[IT] Hi there,

• On the bounce: I was looking at the TM screens and my hearth just sank. Everybody in the back row (FD, OD, big cheeses, etc) were jubilant, but I realized that we were not out of the woods yet. I actually went through this sort of thing several times during that week...

• On the changes: A better RCS for ROS would be nice. We had to skip the second pressurisation, which was always a big risk.

• The significance of the finding of organic molecules is still to be clarified by the scientists, but it could potentially be huge.

Could you (or any other astrophysicists in the thread) clarify the acronyms RCS and ROS?

I believe rcs stands for reaction control system it is like small thrusters used for tiny delta v changes. I only know this due to kerbal space program.

But I have no idea what ros is.

ROS = Rosetta

Hi. Does Rosettas mass measurably influence the comets trajectory, and if yes, how? Thank you.

PM: The comet's mass is so many times bigger than Rosetta's that the effect in it's trajectory is tiny, totally negligible. There are other effects that have a small but measurable influence on comet trajectory such as the outgassing.

I'm just watching a documentary about the mission and they're talking about Osiris and its terran duplicate. Does every instrument on Rosetta and Philae have a "spare" copy on earth for diagnostic purposes?

AH: almost all instrument teams have copies at their institutes that they use for tests and validation. At ESOC, we have a copy of Rosetta, which we use to test anything we want to perform with the spacecraft. It a priceless tool, that allows us to investigate problems on ground, as well as rehearse specific activities before we do them on the spacecraft. Finally, we have a simulator that is used for the big simulation campaigns, like the one we had in October.

And when the "doubles" are not needed anymore, that sometimes get to fly on a real spacecraft after ;)

CF: for Philae, we have a quite good copy of the Lander in our Control center in Cologne. It is made of spare copies of each instrument and subsystems, and we extensively use it to prepare and fine tune the separation, landing and on comet sequences, and to investigate problemy and anomalies.

Whats the bit rate for transmission to earth? ie: How long would a picture take to send (Depending on the size of course.) Also, you guys ROCK!

I can't find the source right now as I'm on my phone but I read it was 28kb from Rosetta to Earth.

I can't find the source right now as I'm on my phone but I read it was 28kb from Rosetta to E

TF + ME: Dependent on the distance and the antenna we are using on ground we can get up to 91kbps. During the Lander delivery we used 28kbps as you correctly stated. Of course some (small) percentage of the data rate is used for internal Telemetry (health status etc.). Pictures can be compressed and dependent on the size it takes a few seconds to get all the data.

Note though, you still have to wait at least a bit till the image comes down because we are 28 min away and other instruments want to dump their data too :)

Hi everybody, since we still have some celebrating to do, we're leaving for today ;) But it was fun to chat with so many interested people ! We'll try to give a look again tomorrow... Francesco & Ramon & Pablo for the Flight Dynamics team

Did you have any initial idea of the quite special shape/form of the comet 67P before Rosetta arrived? If not, what were your first feelings/thoughts/ideas when you received the first images of the comet?

There was a very rough idea of the shape comming from light curves observations from telescopes on Earth and Hubble. It is known that celestial bodies tend to be more irregular the smaller they are. However it was a big surprise to see the rubber duck shape! RP

AH: We had an idea, because some observations had been done using Hubble during 67P's last perihelion 6 years ago (you can find these pictures easily). But when we actually started to resolve the shape of the comet in our cameras, it had nothing to do with it! Our first feelings were a mix of excitation as we realised the opportunity it was for science, and head scratching to find how to navigate around it.

What's our best knowledge about the attitude - esp. the tilt relative to horizontal - of Philae at the time it shut down? Did the movements of the MUPUS penetrator and drill cause late changes? How stable is the lander now, with how many feet on the ground? How far away from the "wall" is it - and how high (degree-wise) is the horizon in other directions?

We're still playing around and bouncing ideas about on this question. First, they said we'd landed on our right side, then on our feet, then on our left side. I've been a firm proponent of the Philae-is-a-cat faction all along. I work with the solar array and can say we have illuminaiton on the lid (facing "up") so we're at least not on our head! According to last info, we may be tilted towards solar array 1. We definatley saw no change due to APXS deployment, MUPUS deployment or SD2 drilling because the 4 day profiles we have data from (the last being well after SD2 drilling) are ridiculously identical. I can see shadows on the panels that are within minutes of eachother each day (and our sampling rate is just over 2 minutes!). We have panel 2 completey free and see nothing in the CIVA picture, but there are shadows cast on it. On all other sides we see rock faces except underneath where there seems to be a very deep hole! So we were really lucky despite all the bad luck! The calibration on the CIVA cameras isn't exact so I can't give you exact numbers, but the walls look pretty close and they are definately all higher than the Lander! - VLL

Oh, and we're probably facing NWish with panel 2 since we see the sunset (the sun rises in the East, sets in the West goes over North at noon). - VLL

The cartoon that was made of Philae and Rosetta was super cute. Are there any plans for more little cartoon films, or even stickers or toys?

Now that Philae has landed the series is complete, but there are T-shirts .. [DS]

Does the comet rotate, and , judging by it's projected path, what are the odds that you'll eventually have the photovoltaic panel pointed at the sun?

Many thanks, for taking this mission as far as it has gone!

Yes, the come rotates. One day is about 12.4043 hours and one illumination period is about 4.5 hours where we landed. :( Panel two seems to be looking pretty directly at a nice comet afternoon and sunset, but we're surounded by rocks/cliffs that are casting some nasty shadows. As we approach the sun (right now we're at about 3 AU or 3x the distance between the Earth and the sun) the intensity of the light reaching our solar array will increase meaning that it will provide us with more energy than it is now. We haven't found the Lander yet, but we seem to be pretty close to the equator, so we're not expecting a ton of change on the direction of the sunlight or number of panels illuminated. Perhaps we'll be lucky though the shadows will fall less fatally across the array! - VLL

1. Flight Dynamics Team are doing a marvellous job steering Rosetta so precisely so far away from Earth. Are they going to share their knowledge and experience with future mission controllers? If so, how?

2. NASA issued extensive reports after completing their space programs - Mercury, Gemini or Apollo. Is there a report planned about Rosetta and Philae? Maybe containing Rosetta blog entries?

3. A few years into the mission Rosetta suffered a serious propellant leak and flywheels failure. How did it affect manouvering the orbiter? How much longer would the mission last if Rosetta had its tanks full at arrival at the comet?

Ok, I can answer to 1) and 3) on FD's side!

Within Flight Dynamics we transmit our knowledge and experience throughout the years through a mixture of training to the newcomers, and internal technical notes & documentation. There's also quite a lot of publicly available papers presented at various conferences, journals, etc. !

For the propellant leak & reaction wheel issues, I would say they had some impact but they did not affect critically the operations of Rosetta. The leak simply meant that we could not operate the thrusters in "pressurized" but only in "blow-down" mode (i.e. the pressure decreases as the propellant is depleted, it is not continuously pressurized by the Helium), which means the thrusters are a bit less efficient. But the propellant margin on Rosetta was luckily more than sufficient for the braking manoeuvres in May-August and to fly it around the comet until the end of mission =)

About the reaction wheels, they actually still all work fine. We have seen both before and after hibernation higher friction levels in two of four wheels, when we were operating them at very low speed or even when crossing zero (i.e. to stop rotating on one side and start spinning in the other direction). This resulted in some concern on our side, so there was a lot of testing both on ground with the engineering model we have at ESOC and on the spacecraft itself. As a precaution, it was actually decided to avoid in most of the cases using the wheels at low speeds. This reduces a bit the manoeuvrability of the spacecraft in slews (rotations) but we can still do everything we need for our operations !

FC

First of all, congrats on landing on Chury! You guys made Europe really proud, thanks guys. Two questions:

How/why was Churyumov-Gerasimenko selected? Is the comet different from others or did it just happen to be the most convenient option?

And after the Rosetta mission, what will be the next big project? Mars?

ME: 67P/Churyumov–Gerasimenko was the "second" choice as the launch of Rosetta was delayed. (First choice was 46P/Wirtanen). Both targets have in common that their orbit is reachable - i.e. you can get there with your fuel and gravity assist maneuvers.

Now to your second question: We are already right now at Mars with the Mars Express probe! And two projects to Mars are in the pipeline (ExoMars). Also ESA has currently a fantastic mission around Venus (Venus Express). Check it out http://www.esa.int/Our_Activities/Space_Science/Venus_Express

Thaks Bakee! 67P was not even the original target. After a delay on the launch date the mission had to be re-optimised and 67P was the winner. There are not so many reachable periodic comets. RP

What do you plan to work on after the expiration of this project, what's next?

So, for us in Flight Dynamics for science missions, we'll of course continue supporting Rosetta, there's lots of more exciting operations to come in the next couple of years ! Besides that, we support as well routine operations of Mars Express, Venus Express and Gaia... But really "new" for the next few years there will be Lisa Pathfinder in 2015, Exomars Part 1 and Bepi Colombo in 2016, Solar Orbiter in 2017 and Exomars Part 2 in 2018...

So, plenty of new & interesting coming up ! =) FC

Hi there [IT],

In the interplanetary division of ESA, we have currently three missions in preparation: * BepiColombo will tranfer to Mercury using solar electric propulsion and orbit very close to the surface to study the planet, releasing a japanese probe before it reaches its final orbit. Launch date is 2017. * Exomars is a double mission, first with an orbiter in 2016 to serve as a relay and then a lander in 2018 to carry out exploration of the surface and in-situ experiments. * Solar Orbiter (my next mission) will launch in 2017 and will orbit the Sun with a perihelion at 0.28 AU to study how the Sun controls the heliosphere.

Besides these, which we're preparing now, we also are working on JUICE, a Jovian Icy Moon explorer, which will do a tour of the Jovian moons and finally orbit Ganymede. The mission has yet to be approved (hopefully before the end of this year) and launch in 2023.

Did you guys ever get to the bottom of the Rosetta Earth Swingby Anomaly?

[PM] Not really, this still an open riddle. There have been other missions in the past that suffered the same anomaly. Last year Juno NASA mission to Jupiter did an Earth swing-by and NASA and ESA ground stations were tracking the spacecraft around the clock to gather the data of the trajectory. No anomaly was detected. But it is a really interesting problem which would be great to solve.

What do you think the chances are of charging the batterys again on Philae? and what other experiments would you like to do if you did?

Once we get a bit of sunlight on our panels, we first have to heat the battery in order to charge it. Once that is done, we would like to actually start our LTS (Long Term Science) program which we already had prepared but couldn't really run. (OKm)

Is there any chance of Philae "waking up" given enough cumulative sunlight over a certain period?

Two factors play in favour of waking Philae up: 1-. The Sun will gradually lit the lower lattitudes of 67P in the incomming months. 2-. The Sun will be closer and its intensity will grow up to a factor of 8

If I was standing on 67P and jumped, how high would I fly?

PM: Be carefull if you jump with moderate velocity you would escape from the comet's gravity field, and never come back. The escape velocity on the comet surface is about half a metre per second.

Did you enjoy the live coverage XKCD did ?

[TF] I had a change to look at it after my Lander delivery shift was over... It was great!!! I loved it :)

Hopefully you don't mind a whole lot of questions at once from one person. I've split them up into what I see as Rosetta respectivly Philae questions.

Rosetta questions:

1. How much fuel does Rosetta still have? The nominal mission end is in 2015, but will fuel be an issue if you get an extension into 2016?

2. Is there any chance of Rosetta surviving a second hibernation, following the comet out to aphelion and back for a second go at observing the comet? It would take it even further out from the sun than it was in the first hibernation, so I suppose the power available would be an even greater problem than before.

3. If you think 2. is a possiblity, would it even be worthwhile to attempt it? Would alternative ends be more rewarding (e.g. attempting to land Rosetta on the comet)?

4. If you attempt to (soft)land Rosetta on the comet, how exactly will the power situation work out, and how well could it even communicate with earth?

5. Has the enviornment around the comet posed any problems at all to the operations of Rosetta so far? If we ignore what must be quite a lumpy gravitiational field.

6. What has been the most unexpected/exciting thing that Rosetta has told you about the comet so far?

7. The scientific phase of Rosetta begins now, it is said. But surely all the instruments have gotten a chance to do their thing during the Philae landing site mapping/delivery phase too. I can understand how OSIRIS might have been forced to prioritize Philae quite a bit and that the specific orbits used might have had Philae in mind to ease mapping, but how does this new phase really differ from before?

8. Will Rosetta ever go for a specific close approach to attempt to pinpoint Philae, or will it only do so for purely scientific investigations?

9. Did any other Rosetta instrument attempt to image Philae when it was first released, such as say, VIRTIS? I'm a bit unsure of their capabilities in this respect, could they even have seen it when Philae was still relatively close? Would this just have been way too superfluous?

10. Building upon 9. Did any experiments have any "use" for Philae as an physical object with known properties.

11. Which experiments other than CONSERT has the most to gain from looking at the data provided by Philae, to better understand and improve upon their own results.

12. Do you know the reason behind the "hiccups" during the hibernation period (that is the reboot in 2012 and the need for a second bootup during its wakeup)?

13. Any new issues with Rosetta, is the flywheels doing okay?

Philae questions:

1. Both the harpoons and, correct me if I am wrong, the lander itself had accelerometers. The lander accelerometers were turned off during descent to prevent them from triggering the touchdown sequence, were they never turned on again? Were the accelerometers in the harpoons not on either?

2. Related to 1. During the initial landing confusion, wouldn't the MUPUS sensors within the harpoons have indicated that they did not fire? Was it simply a matter of this data comming in later due to priorities on what to send from Philae/Rosetta to earth?

3. The ice screws on the feet are passive system, but does that mean there isn't any sensor at all to even to see if they have moved?

4. The latest ESA Rosetta blog post seems to indicate that of the SESAME experiments both CASSE and PP worked. Does this mean you have an idea of which feet were on the ground at the final landing position now?

5. The CONSERT experiment relies quite a bit on a good landing site to get full advantage of it. Posts indicate that you know its position to 100m, is the position suitable for CONSERT?

6. To build upon 5. When did CONSERT run? I was under the impression it would only be run when Rosetta was on the other side of the comet, but as you didn't know where Philae is...

7. CIVA took three rounds of panoramas from my understanding: at first touchdown and twice at the final landing site. Is the first set so garbled that you can't even get anything useful out of it (not necessarily in the sense of pretty pictures for publishing)? The second has been shown. Was the third panorma a complete failure as well due to the light conditions?

8. The ROLIS images have not been released, but are they good in the sense of focus/exposure?

9. Is the ROMAP team very happy about the bounce? :)

10. Would you be willing to speculate on how long until every Philae experiment can say whetever they got useful information from Philae? That is to say not clear results, but just that they have something to study to begin with. Thinking about an experiment like APXS, which might have gotten some result even though they had lens cap issue, if any dust got there. Or SESAME DIM, that I haven't heard anything about at all.

11. Would you speculate on whetever a landing on 46P/Wirtanen would have lead to a very different result. The descent speed would have been quite a bit lower at least, so maybe the damping might have been more effective?

12. If you, through the power of magicical foresight, would have known Philae would bounce as it did, what would you have attempted to do differently with its delivery to the comet and/or had Philae do differently after first touchdown.

Thank you for an exciting mission and an exciting landing, hope you get the most out it with a phoenix rising up again next year with signals from the surface. Good luck with your future operations!

(As an aside, perhaps the ESA web team could put out a compiled version of this AMA on the Rosetta blog later?)

Philae Question 1:

Both the harpoons and, correct me if I am wrong, the lander itself had accelerometers. Yes, inside the Landing Gear unit. The lander accelerometers were turned off during descent to prevent them from triggering the touchdown sequence The small one was disabled, the large one was on and it triggered at touchdown. Were the accelerometers in the harpoons not on either? The accelerometers in the harpoons belong to MUPUS and as the harpoons didn't fire, MUPUS was unable to measure anything. (OKm)

I thought you guys were thinking about doing a hop but then I didn't see anything about a hop. Did you guys decide against trying to hop Philae?

Hi there, thanks for your question. Besides the fact that doing a hop was difficult e.g. one idea would be to retry the thruster that failed before separation, there remained a high possibility that you placed poor Philae in a worse off situation with it lying on its head where the communication antenna are located. You have to remember we had contact with it and although the power was not good, we at least could keep that contact. The safest & most secure way to ensure we could at least try to have Philae wakeup in the future was to rotate such that one of the bigger solar panels was facing the sun. It means of course that we have to wait until 67P & Philae get closer to the sun, but at least we know that we are power limited at this point, rather than having hopped and lost the signal close to battery end and not knowing whether it was the battery or a failed hop. When it comes to operations, it's important to take the approach which guarantees a known clear result rather than possibly creating a worse situation. Hope this helps explain a little. [LOR]

Firstly well done and thank you all!

This achievement and the attention around it will doubtless inspire many to get into and take up sciences. My question is what inspired some of you personally to join this profession, and is there anything you think should be done (by governments or others) to inspire young people to take up this subject?

Star Trek! :) Thank you, William Shatner for the twitter message, btw! Personally, I wanted to be an astronaut but I have terrible eyes, so I had to go for astronautical engineering instead. ;) In all seriousness though, I think that the type of public interest we are getting for Philae and Rosetta is exactly the thing needed to get more young people into the field, don't you? So a huge thanks to all of you! - VLL

[LOR] Personally, I always had an interest in space but never believed I would enter the space field. I entered ESA via the Young Graduate Programme and this for me is one of the best ways to enter when you have graduated. The chance to join ESA even if it is for only one year is really great and indeed opens doors for you. Having experience in space, even if it is for one year, makes it much much easier to stay in the space field with a lot of companies providing chances afterwards. There are other possibilities of course - stagiarre, Spanish trainee, space masters, etc. I honestly believe the best way to inspire is to have more missions such as Rosetta which show young people that dreams can become a reality. I also believe that how the mission is publicized has a lot to do with it - grabbing the imagination is difficult, with Rosetta I think it has been achieved. [LOR]

What is the inertial navigation accuracy you achieve with Rosetta? I am amazed you could land Philae that precisely!

What is the inertial navigation accuracy you achieve with Rosetta? I am amazed you could land Philae that precisely!

[PM] Relative to the comet we have an accuracy of few metres in orbit reconstruction (that is knowing where Rosetta was in the past). In predicting Rosetta position in the future we have an accuracy of about 100 m in a few days. But this depends on which orbit we are flying, for example in the 10 km orbit we had bigger errors.

The Philae landing point was 100 m away from the landing target. This was indeed very good accuracy considering that the landing ellipse was of 500 m radius.

With respect to the Earth we can only know Rosetta position with an accuracy of about 5 km (this is because Rosetta is about 500 million km from the Earth).

How long were you hoping to have Philae up and running on the surface? Are you disappointed that it only lasted for 57 hours or are you satisfied with the amount of data you've gained from it?

In our simulations, the planned 'first science sequence' was lasting about 50 hours, so we are quite happy with the operations we have performed - despite we had to deviate a bit from the originally planned program. (CF)

Hi there,

First things first - thanks a ton for doing this AmA! The Rosetta mission was huge success - very exciting stuff. I cant wait to see what you'll find, once the data is thoroughly analyzed!

Now, to my Question(s) - it's more about the people behind the mission, than the mission itself:

How did you manage to end up in such an exciting job? What field did you guys study? I imagine you're mostly (astro-)physicists, mechanical- or aerospace engineers?

I'm asking since i'd really like to get into spaceflight some day, and maybe participate in a mission as exciting as this. Trouble is, i dont even know what to study to have the best chances in getting there. I'm actually living very close to Darmstadt, and i'm thinking about studying mechanical engineering at the TU Darmstadt (Or HS Mannheim) next year - i'm just not sure if thats the right field of study.
I'd greatly appreciate any advice you could give me on that!

Secondly: How do i have to imagine your worklife "in between events" - You built and launched rosetta, and then had to wait around 10 years for it to reach 67P. What did you do in those 10 years? Work on other ESA projects? Work in the industry?

Big Thanks!

Hi there [IT]:

Most of the engineers in Operations have some kind of engineering degree. I graduated on Aerospace and then got a Masters on Space Systems. Once you get into Spacecraft operations, you'll realize that it's a very small world, and you can end up working in Darmstadt either for ESA or for EUMETSAT. Any degree from a good university with a strong background on Math/Physics plus computer science/programming should do the trick.

For the second question: I did move to other projects after the launch of ROS (first VEX, then Bepi, then SOL), but others remained in the team. The Cruise phase was actually quite active, apart from the hibernation phase.

How did you control the rotation of Philae on the descent from Rosetta to 67P and after the bounses? It could vers easily tilt, I think?

AH: The Lander had a Flywheel that was providing a momentum to stabilise it during descent. After touchdown, the flywheel was automatically stopped, but since Philae was in the air again when it stopped, the momentum got transferred to Philae itself, and it started rotating, which kept a relative stability.

Seems debris/particles have been already ejected from the comet. Some of them look like big enough to be imaged in the pictures Rosetta took. Did some of them hit Rosetta?? If they did and you already know that, how do you know that?? And how do you know it's seriously damaged or ignorable?

Hi there [IT],

The particles being ejected by the comet so far do not seem to be damaging Rosetta in any noticeable way. Remember that the relative velocities between the S/C and the comet are very low (below 1 m/s), and that any collision with the comet 'dust' will be very low energy. We worry about long-term effects, though, like deposits in the Solar Arrays that will reduce power production or covering up of the Star Tracker/Navigation Camera lenses. This we will be able to see only after we spend longer around CG.

Hi guys, I might add that we try to protect the navcam lenses: we have 3 different covers that we can use to take pictures, one of these was used only during approach to image the comet when it was still very faint with a star background... well, now we use it as "dust collector" to protect the cover which we actually need to use when taking pictures of the comet ! FC

Do you have a theme song for the mission?

Do you have a theme song for the mission?

I can answer from the ESA PR team that we don't really; of course each of the engineering teams and even the scientists might; they are spread out all over Europe, so there's unlikely to be 'one' theme song... The sonification of the PRC-MAG EM data seems to have become some sort of popular hit, thought... 5 million + listens in SC https://soundcloud.com/esaops/a-singing-comet --> NO ONE expected that :-) [DS]

[deleted]

The scientific measurements were prioritised by the Philae science community. The operations team scheduled the measurements according to the priority assigned to the observations. Not all 'must be' observations could be scheduled in the first science sequence, due to primary battery limitation, but it has been possible to add some shorter and less power consuming observaton in parallel to the main measurements. We have tools to suppor the operations scheduling, but the experience of the team played a major role in fie tuning the plan! (CF)

What do the MUPUS hardness results tell us about the composition of 67P?

Go, power mode 4 ;-)

'One does not simply use Mode 4 on a comet!' :) (OKm)

Will you attempt to fire the harpoons in case Philae wakes up again?

CF: we are still discussing this possibility. No decision taken yet!

Why was the lander not equipped with a secondary power source likely to a (RTG) Radioisotope Thermoelectric generator ? maybe a small one? as a contingency. Thank-you

That is a European policy thing, unfortunately. Also, the launch was 10 years ago and RTG safety has increased since then. - VLL

How much data Philae sends to the HQ and what's the link speed?

Link speed between Philae and Rosetta: 16kBit/s We have 7MBytes to store data in during non-visibility slots.

What is the speed of Rosetta relative to the comet?

What is the speed of Rosetta relative to the comet?

PM: Right now Rosetta is in a 30 km circular orbit around the comet with a (really slow) relative velocity of 0.15 m/s (0.54 km/h).

• Why does this comet seem to fire it jets from middle creating such an odd shape?

• Is this high activity in middle region the cause of smooth 'bridge' between two lobes?

• Was APXS instrument unable to reach out to take proper reading or was there some other issue?

Amazing technical achievement and great outreach campaign by ESA :)

CF: the APXS team is still investigating the sensor head down movement, to figure out what happened. The analysis of ROLIS camera images may help.

Question: What kind of orbit will Rosetta be in once the coma is at it's maximum? I mean, how is Rosetta going to protect itself?

What kind of orbit will Rosetta be in once the coma is at it's maximum? I mean, how is Rosetta going to protect itself?

[PM] We will have to increase the distance to the comet and keep Rosetta close to the terminator plane (plane separating day and night side of the comet). There the coma activity is expected to be lower and also the solar panels (that are always pointing to the Sun) are edge-on to the incoming gas, so that the drag force is reduced and the less amount of dust particles hit the solar arrays.

But still we want to observe the comet activity from close distances. To do so, the plan is that Rosetta will perform several comet fly-bys with miss distances in the range 8-50 km.

Hi. You knew the thruster on top of Philae wasn't functional since the first Go/NoGo decisions in the evening of 11th November.

Which was the reason for you decided to go ahead (Paolo Ferri said you would have had another landing opportunity in a couple of weeks)? Perhaps you thought it was just a false alarm? Or maybe you realised it was a failure it wasn't possible to fix anyway?

Thank you and congratulations for your historical achievement.

Hi there [IT],

I was present in the discussions following the failure to prime the ADS system, and the decision to GO was taken as follows: First we posed the question 'Is there anything else that can be done to re-attempt a priming?'. The answer was 'No', since the primary priming procedure already took all possible steps (multiple commanding of both priming lines). Therefore it was clear that the ADS was out, and having a NO GO would not help clear the situation. After this we asked 'Can the landing be attempted without the ADS?'. The answer to this was 'Yes, but with higher risk.' This risk could not be mitigated, but there was not alternative, so we decided to cross fingers and release the lander.

Hi, will Philae be in danger as the comet gets closer to the Sun? Under assumption that everything will be ok with the lander by than

There's certainly dangers with being on the comet but these very much link to its location. What we've seen is that the comet is most active in the neck region but we would expect other regions to come more active as they become visible to the sun and as we get closer. The fact that Philae is in a location far from the active neck region which receives less sunlight than others and it is in lodged against a wall and shadowed would suggest that there are high possibilities that it might not be in too much danger. But this we would only confirm when the final location is known - then we will know the implication on its location versus how the sun will illuminate it. [LOR]

Question: From the 1.5 hours of periodic sunlight currently available to Philae and going to the heaters, what temperature extremes do you predict will be seen by the electronics and battery over the next few months, and do these temperatures allow a good chance of surviving until the sunlight time increases? Thanks!

We're still working on that at the moment. Even when we had 5-6 hours of illumination in simulations, the battery was going so low that we spent most of the solar energy heating it up before it could be charged. At a good spot with 7ish hours we still needed about 8 comet days to charge the battery (about 100 Wh) at 3AU because we had to heat it so long every morning. The system is qualified to -60°C and the comet surface might be about -170° C at night (based on anchor temperatures) but it should stay warmer in the compartment if we get some sun to the absorbers. So, short answer: we're definately not going to overheat, which was our initial fear! We'll see about the cooling. - VLL

If escape velocity is about half a meter per second on 67P, I guess a person walking at normal speed (roughly 5 km/h) would fly direcly out of orbit ?

Also, why didn't you equipped Philae with an EU flag to plan in the comet ? (But perhaps seeing how the harpoons didn't worked it wouldn't either). ;)

Hi Remicas: Read Prof Rhett Allain's calculations here; he nailed it pretty well! his calculated Vescape is a tad high, but he concludes (correctly) that an astronaut could easily jump off and away:

• http://www.wired.com/2014/08/comet-walk/

[DS]

In terms of 80's computer, such as Motorola 6800, or Vax 11 780's, what roughly is the computing power on Rosetta? on Philae?

Comparable to the once you've listed, but running on 5MHz. Weeeee! :) (OKm)

How long do you think Rosetta will be actively monitoring 67P CG? What happens in the unfortunate case where 67P CG disintegrates on way to Perihelion? Does Rosetta have enough fuel to reroute to a new target?

[LOR] The nominal mission was planned to finish end 2015 but the reality is that we would expect to continue following the comet until Aug/Sept 2016. If 67P disintegrates then we will have one major ringside seat to watch it - it would be incredible but certainly present dangers to the satellite which we'd have to take care of first before doing the science. Rosetta does not have enough fuel to reroute to a new target. Honestly, we're delighted with the one we have :-)

Question: What happens to Rosetta after the end of the mission?

Hi there [IT],

Good question! Once ROS fuel runs out, the mission is over. We will patch the software to passivate it and switch it off for good. It will lose control and spin off into nothingness, possibly accompanying the comet until some gravitational perturbance send it away. Of course we may choose to land it somewhere on the surface (big TBC), in which case it would come to rest there essentially as long as there is a CG-67P.

Have you been on the project the entire time? If not, how hard is it to come in and adapt to an undertaking of this scale?

The planning of this mission started almost 20 years ago, I was on high school. Some of us were lucky enough to participate on the development effort of the last years before arriving to 67P. RP

Instead of starting Philae's "first science sequence" and draining the batteries, could you have used the batteries' energy to move the lander to a location with more sunlight? At such a brighter location, could you have charged the batteries enough to then commence the science sequence?

CF: in the hours after landing we had some ideas of what could be done to 'move' the lander from the place it ended up with: re-activating the flywheel, fire the harpoons, use COSAC gas tanks.. But (apart from rotating the larger panel towards the sun) none of the ideas sounded convincing enough, so the decision was to do as much science measurements as possible until energy was available.

As a systems admin, I'm always interested in the computing behind these probes. What kind of OS runs that little guy? Is it custom written from the ground up? Or built from a mainstream OS? (for the love of god, please tell me it's not windows. You'll never hear from it again ;) What kind of hardware supports it all? I'm not digging for national secrets, but any info would be appreciated! Thanks for all your hard work!

Hard realtime OS, specifically designed for this processor and it's not windows :D No HD, 128kRAM, 128kEEPROM, 64k Code size (OKm)

what do you think about this reconstruction of Philae bounce, made on unmannedspaceflight.com forum?

https://www.youtube.com/watch?v=WF3anN_A1mw

does it contradict your estimates of Philae landing site?

It is clear there is quite some work behind this reconstruction, but it does contradict our current best estimates. In particular, Philae cannot be on the night side of the comet for several reasons, among which we know that it was illuminated for at least some time during the day from the solar panel data. So, it is probably somewhere still on the head of the comet, in the vicinity of the big crater. FC

Is it possible to make career at ESA or DLR as a computer scientist (with ambitions towards robotics) without doing a PhD?

BTW, yoyoyomama1, take a look at:

• http://www.esa.int/About_Us/Careers_at_ESA/What_you_need_to_know_about_the_Network_Partnering_Initiative

This is a list of universities that ESA will work with to co-fund your Phd, if that's what you later wish to do... [DS]

In general terms, yes; many jobs call for only a Master's degree (i.e. 2nd degree). Note, in fact, the current call for Graduate Trainees contains several openings for CS/CE/EE majors:

• http://www.esa.int/About_Us/Careers_at_ESA/Young_Graduate_Trainee_Opportunities

You don't need a Phd for these; regular staff positions do some up fairly often and there's a lot of robotics work being done -- esp with ExoMars and the METERON Project. Also lost of stuff here:

• http://www.esa-telerobotics.net/

But, having said all that, getting a Phd is always beneficial in the long run. [DS]

Do you received any measurement results from APXS (Alpha Proton X-ray Spectrometer) so far?

CF: not yet: the APXS team is currently investigating the behaviour of the instrument during deployment.

Due to the speed of light being the speed of communication between earth and for example, Philae's lander, how is it possible to control it to a safe landing, without crashing, if your vision is ~1000 seconds behind real time?

Everything is preprogrammed. The SW needs to react to certain events, e.g. the detection of Touchdown which would then trigger firing of the harpoons. (OKm)

How does one get lucky enough to get involved in such amazing projects? What must I do to become like you? I'm currently studying aerospace engineering at Auburn, and I love reading about and studying these major breakthroughs. You are all inspirations!

[TF] Hi Tsar!

Good to know we're inspiring people :)

You're already on the path! Keep it up and have a look at the various trainee programs that the Space Agencies from the world offer!

Good luck with your studies!

• Which is the "moving power" of the landing gear? Any technical document available? (I can only find them for alternative landing gear) Could it even allow "hopping", or it can just raise the lander body?

• Was the flywheel causing lander rotation on its Z axis while landing?

• Why was the flywheel turned off immediately after landing? What's the issue with a running flywheel in an anchored lander?

• Was the flywheel stopped by means of a brake or just by its own friction?

The landing gear can do several things that each require a different amount of power. It can rotate, raise and lower the Lander and tilt the Lander. The amount of energy required also depends on the size/duration of the movement. We tried to "hop" by raising the Lander right before switch-off, but the ROLIS picture taken afterwards doesn't show any movement. :( Yes, the flywheel was rotating the Lander about the Z-axis at a very stable rate. We weren't expecting to hop so that's why we turned off the flywheel. It did spin down for about 40 minutes after, in which time the Lander was quite stable. Afterwards, you can see the solar array on the top wobbling about at a pretty regular interval (it was recieving constant sunlight up to then). The flywheel doesn't have a brake, but spins down. - VLL

Since hopping around on a comet worked (...with a little luck ;), would you consider building bouncy bots for future missions to comets, or even heavier bodies like moons in the future?

Hi there [IT],

In my opinion, the experience of Philae shows that bouncing around a small body will create uncertainties in your final position, and make operations more difficult. I'd rather go for a passive, non-bouncy lander (like the old soviet Venera probes), which are likelier to stay put where they land, and with less complexity. I cannot say much on the science value, but as an ops engineer, simpler is better.

Have you considered renaming the comet Rosetta Stone?

AH: No for 2 reasons: 1- it would be very ungracious and unfair to Mrs Gerasimemko and Mr Churyumov. 2- Celestial bodies names are chosen by the International Astronomical Union, not by us !

First of all - Congratulations! Job well done!

Secondly - what will happen with Rosetta? Is it intended to survive past the loop around the sun and head back out with Philae? How long is it expected to keep sending back info?

Thank you for doing such worthwhile work.

Hi there [IT],

Thanks. This is fun!

We will keep ROS orbiting the comet as long as the fuel onboard lasts. We have good chances of surviving the perihelion passage (closest point to the Sun) in August 2015, and beyond that. End of mission will occur before the next hibernation arc - the point at which the panels will not produce enough power for the on-board systems - since we cannot hibernate ROS again (not enough fuel for that!). This will happen around mid-2016.

What was/(will be hopefully:)) the local link data rate from Philae to Rosetta?

16000Bits/s TC, 16384Bits/s TM, QPSK (OKm)