
Philae status, a day later - ilyagr
http://elakdawalla.tumblr.com/post/102544296955/philae-status-a-day-later
======
Osmium
These are the original photos from which 67P/Churyumov-Gerasimenko was
discovered back in 1969:

[https://www.flickr.com/photos/europeanspaceagency/1539815083...](https://www.flickr.com/photos/europeanspaceagency/15398150830/in/set-72157638315605535)

I find it amazing how we've gone from a dim blur on a photographic plate
(which was found by accident when trying to photograph a different comet
entirely) to what we see now.

I also find it fascinating to think how close we were to landing on an
entirely different comet if the original launch window had been hit. There's
just so much out there. What was on that other comet (46P/Wirtanen) that we
might never get to see?

------
Osmium
Looks like COSAC data is coming in!
[https://twitter.com/esaoperations/status/533387528376942592](https://twitter.com/esaoperations/status/533387528376942592)

This is an instrument that does analysis on whatever samples the drill picks
up. We know the drill successfully deployed earlier, so hopefully that means
it picked up _something_ and we now have the data from that!

Looks like that's pretty much it for the battery though, unless last minute
manoeuvrings result in the potential for a recharge in the future:

[https://twitter.com/Philae2014/status/533403430489178112](https://twitter.com/Philae2014/status/533403430489178112)

Edit: CONSERT data now coming in! CONSERT is an instrument to detect a radar
pulse sent out by Rosetta that travels _through_ the centre of the comet to
tell us something about its internal structure. Also another ROLIS image
(panorama) has been taken, though it's not clear to me if it's been
transmitted yet. Very low battery now.

[http://en.wikipedia.org/wiki/CONSERT](http://en.wikipedia.org/wiki/CONSERT)

Edit: I missed this before, but it looks like Ptolemy data has been received
too! This is another instrument that's supplied with samples from the drill.

[http://sci.esa.int/rosetta/31445-instruments/?fbodylongid=89...](http://sci.esa.int/rosetta/31445-instruments/?fbodylongid=896)

~~~
ajuc
Times are in funny format:

2014.318.14.09.20.272 - 2014.318.22.31.05.464

It seems to be YYYY.dayOfYear.hh24.mi.ss.miliseconds

~~~
kijin
I guess months don't mean much without the moon.

~~~
erispoe
What about years without the Earth?

~~~
lostlogin
When I think about this it gets progressively more amusing. Year 2014 is a
time point when Jesus was between 4 and 6. That level of imprecision contrasts
starkly with the time stamps being discussed. That Jesus even comes into it is
fascinating. Maybe 2014 CE is less controversial, although somewhat dishonest
as it uses the same time point as reference.
[http://en.m.wikipedia.org/wiki/Anno_Domini](http://en.m.wikipedia.org/wiki/Anno_Domini)

[http://en.m.wikipedia.org/wiki/Nativity_of_Jesus#Date_of_bir...](http://en.m.wikipedia.org/wiki/Nativity_of_Jesus#Date_of_birth)

~~~
kijin
The beginning of the Holocene around 11700 BP might serve as a good objective
reference point. Nearly every interesting thing that happened in the history
of human civilization took place in the Holocene. No more negative years to
worry about!

"Present" in "before present" (BP) usually means 1950 AD [1], so this year
would be Year 11764 of the Holocene epoch. Brb, gotta find some COBOL
programmers to fix that Y10K problem.

But then, the starting date of 11700 BP is also kinda arbitrary. No single
short-term event defines the boundary between Pleistocene and Holocene, so
we're still left with a sizable margin of error, probably even larger than the
error in Jesus' date of birth.

[1]
[https://en.wikipedia.org/wiki/Before_Present](https://en.wikipedia.org/wiki/Before_Present)

------
akavel
Some twitter streams painting good coverage together:

[https://twitter.com/ESA_Rosetta](https://twitter.com/ESA_Rosetta)

[https://twitter.com/Philae2014](https://twitter.com/Philae2014)

[https://twitter.com/elakdawalla](https://twitter.com/elakdawalla)

[https://twitter.com/chrislintott](https://twitter.com/chrislintott)

[https://twitter.com/FrancescoTop](https://twitter.com/FrancescoTop)

Also each Philae experiment seems to have a "personal" twitter account set up
too, and with a short description, worth a quick reading when they link to
them.

Some specially noteworthy recent updates from accounts above:

@elakdawalla: _The sun will rise on Philae around 6:00 am UTC. It is
theoretically possible it could wake up then. Next comm pass would be at
around 11:00_

@chrislintott: _Current comms mode is 1 packet every a few minutes - but no
science data left on @philae2014 - it all got uploaded! Wonderful!
#cometlanding_

@FrancescoTop: _Consert PI is confident that using tonight 's data w/ previous
one we can triangulate and find where #Philae is on the comet._

@elakdawalla: _Even if the solar panel is in a better position, it 's quite
possible it won't wake up tomorrow, but could recharge over days, wake later_

~~~
acqq
It was immense luck all the time. Since harpoons failed, there was serious
chance for lander not to remain on the comet at all, or to get seriously
destroyed or disabled earlier than now. Now it seems that most (all?) of the
experiments were performed. Wow.

But in order to get lucky, we have to first dare to try and then invest in
work. Congratulations!

~~~
ajuc
Bad luck earlier with the thruster and harpoons, and the need to hibernate the
Rosetta. Good luck later with the bouncing.

~~~
acqq
Yes, the harpoons definitely weren't the only problem in the mission. We can
always imagine even better outcomes (like, bouncing but ending on a place with
a lot of sunlight) but it appears it was very good even so: until recently we
weren't sure if any movement would launch the lander back into space. Or if
the battery would last long enough for more experiments to be done. Or the
results to be sent.

------
kartikkumar
So the latest news from Darmstadt is that telemetry is coming in! Philae is
alive! :) That's fantastic news, because there was a real concern that it
would have died off due to the limited solar irradiance. The most important
thing to figure out is whether the drill that was extended 200mm actually
grabbed hold of anything. Also, it's possible that Philae got displaced in the
meantime.

Getting live updates from mission control at the moment ... exciting! They're
in the midst of performing a "lift and turn" maneuver to try to get Philae
into a better position.

~~~
publicfig
I believe that regardless of whether or not they have solar power, Philae
should run for ~60 hours without power if I remember what I had heard
correctly.

~~~
codeulike
Yep, and those 60 hours could run out anytime from now

edit: voltages dropping right now
[https://twitter.com/FrancescoTop/status/533401941163114496](https://twitter.com/FrancescoTop/status/533401941163114496)

edit: looks like its going dark right now.
[https://twitter.com/elakdawalla/status/533403569660379136](https://twitter.com/elakdawalla/status/533403569660379136)

edit: link still up but expecting to lose it any time. Getting science data in
[https://twitter.com/esaoperations/status/533406632278261760](https://twitter.com/esaoperations/status/533406632278261760)

edit: there's a chance the shift in position about 20 mins ago might help with
solar recharge. Also there is chance of better solar around Christmas when the
comet orientation towards the sun is different.

~~~
sliverstorm
Wait, so Philae could possibly reboot months from now when it gets more
sunlight? It sounded like charging could only be initiated if the computer was
already operational and the batteries were already heated to 0C.

~~~
ajuc
If it will get enough sun when hibernated it will heat battery up and start
charging. When there's enough charge (possibly after many periods of charging
and hibernation) it can start working again.

But it's probable that the dust will acumulate on the solar cells before comet
is close enough to sun for this to work.

~~~
sliverstorm
Is there much dust circulation on the surface of a comet? Mars has its dust
storms, but I didn't know it was an issue on comets

~~~
codeulike
Comet has very low gravity and - think of classic 'comet tails' \- stuff gets
stripped off by solar winds etc near sun. So yes I think it can be a bit dusty

------
sigmar
Philae has been successfully rotated (post on twitter 6 minutes ago here:
[https://twitter.com/Philae2014/status/533393729156308992](https://twitter.com/Philae2014/status/533393729156308992))

I hope the adjustment will mean more power

------
r721
Next post is also worth reading:
[http://elakdawalla.tumblr.com/post/102615327170/philae-
updat...](http://elakdawalla.tumblr.com/post/102615327170/philae-update-my-
last-day-in-darmstadt-possibly)

------
jessriedel
Does anyone know whether there was a good engineering reason to give Philae
only solar-charged battery power rather than a nuclear generator? Or was is
just regulatory/cost?

And what is the major power draw that leads to such a short battery life? The
heater to keep the electronics warm?

~~~
danielweber
I didn't know this until a few years ago, but solar panels beat RTG on a
power/mass ratio for most missions that are in space (as opposed to on a
planetary body) out to the orbit of Jupiter or Saturn. It would have added
mass to the mission to supply the same power.

There were a dozen ways that Philae could have gone wrong, and using an RTG
would have only helped with one failure mode.

I'm sure they aways hoped it would live for weeks, but apparently most of the
experiments have already run in the first day. That was the important part. I
don't know the precise engineering trade-offs, but I suspect "get it to land
and live for 24 hours" was the first goal, and anything that made that goal
riskier was dismissed.

~~~
jessriedel
Good points I'll grant, but it naively seems to me that this issue with
batteries running low is a perennial problem with spacecraft.

Unless the RTG/solar mass ration is very high, your points about having most
of the experiments already ran in the first day, or about RTGs not helping
with other failure modes, don't matter too much. Either way when you include a
power source (RTG or solar) you are doing so for the purpose of getting data
after the first day.

Besides avoiding the shading problem, I believe RTGs are also more robust to
unfurling issues and to impact damage.

~~~
3am
You have a better physics background than me, but it seems like the Philae
mission would be particularly concerned with weight because of the velocity it
had to achieve. Considering it took 10 years to reach its destination, maybe
the shielding required for an RTG would be prohibitively heavy.

Maybe the overhead in increased costs due to limited availability of PU238 and
additional launch preparations/safety were better spent elsewhere.

I figure the ESA made the best decision for the mission, though, and were well
aware of the tradeoffs involved, don't you?

~~~
maaku
What shielding? There's nothing live on it.

~~~
mikeash
Electronics aren't particularly fond of radiation either.

~~~
beefman
All space-faring electronics need to be rad-hardened, and not because of an
RTG source that emits only alpha particles.

------
wozniacki
Latest from Ms.Lakdawalla on the location of Philae [1][2][3] :

    
    
      So after a tip from Gerald at  
      http://www.unmannedspaceflight.com/index.php?
      showtopic=7896&view=findpost&p=215245 … I wonder if 
      bright spot is Philae and dark spot its shadow????? 
    

[1]
[https://twitter.com/elakdawalla/status/533385159564095488](https://twitter.com/elakdawalla/status/533385159564095488)

[2]
[http://www.unmannedspaceflight.com/index.php?act=attach&type...](http://www.unmannedspaceflight.com/index.php?act=attach&type=post&id=34303)

[3]
[http://www.unmannedspaceflight.com/index.php?s=af65642091d8b...](http://www.unmannedspaceflight.com/index.php?s=af65642091d8b10a57b3b3c889463ac4&showtopic=7896&st=525&p=215245&#entry215245)

~~~
maaku
A shadow would imply its in the sun. It's not.

~~~
jessaustin
My apologies if this is a stupid question, but in that case, how can we see it
at all?

~~~
serf
my guess would be reflection. Space is filled with _stuff_ , i'd imagine light
would bounce around all of it pretty haphazardly.

------
larrydag
Rosetta blog: Philae still talking
[http://blogs.esa.int/rosetta/2014/11/15/philae-still-
talking...](http://blogs.esa.int/rosetta/2014/11/15/philae-still-talking/)
First hour of lander communication
[http://blogs.esa.int/rosetta/2014/11/15/first-hour-of-
lander...](http://blogs.esa.int/rosetta/2014/11/15/first-hour-of-lander-
communication/)

------
dang
Also
[https://news.ycombinator.com/item?id=8609302](https://news.ycombinator.com/item?id=8609302).

------
macrael
I'm confused, if after the first contact the lander expected to be stationary
but was actually moving 20cm/s away from the comet, how is the lander still on
the comet? 20cm/s seems like it would take it off into space pretty quickly.
How does a lander "bounce" on a comet without an appreciable gravity, wouldn't
it only bounce once?

~~~
acqq
[http://blogs.esa.int/rosetta/2014/11/14/three-touchdowns-
for...](http://blogs.esa.int/rosetta/2014/11/14/three-touchdowns-for-
rosettas_lander/)

"But then the lander lifted from the surface again – for 1 hour 50 minutes.
During that time, it travelled about 1 km at a speed of 38 cm/s. It then made
a smaller second hop, travelling at about 3 cm/s, and landing in its final
resting place seven minutes later."

It's not that its direction was directly away from the comet. It's that it's
estimated that it slowly moved during almost 2 hours. The sensors detected
landing once then almost 2 hours later again. The speed is an estimate, but
it's reasonable. Also note the shape of the comet, it isn't spherical.

------
ChuckMcM
This is has been a great story. Many great space missions have had a major
component failure and still provided data that changed our view on things. I
find it especially interesting to see if the lander gets 'spit out' when the
comet starts outgassing, we might get still more data out of it if it returns
to a spot with good solar coverage. Given the lander's mass and the lack of
harpoons, if it is in a position to get pushed out I expect there is a very
good chance it will.

------
StavrosK
Aren't these space missions sort of like firing a pebble off a gun and hitting
a 1 cm target half way around the earth? It always amazes me how low the
failure rate seems to be.

~~~
Osmium
That comparison is a bit disingenuous. There's plenty of opportunity to
correct the trajectory as and when you need to, which is something you can't
do with a bullet. Still a _huge_ achievement though.

What I find particularly impressive is that they managed to get in a fly-by of
two different asteroids as well! So that the orbit was optimised to hit not
one but three targets (though presumably they had a lot of asteroids to chose
from).

~~~
StavrosK
Aren't the adjustments minute, though? Although I guess that even minute
adjustments of the angle will result in huge changes in the final trajectory,
over thousands of kilometers.

~~~
greenhorn
You are correct that the adjustments are minute.

But you're also ignoring the fact that unlike a bullet, there isn't any
atmosphere or unpredictible factors in your way. You can do the math and be
sure about it. You can also use your math to course-correct after the fact.

That's not _at all_ like pointing your gun and pulling the trigger.

------
danielweber
I think it's amazing how they thought it had landed and it was still moving.
This is a very very tough thing they are trying to do.

Couldn't Rosetta have told them that Philae had bounced? I might have the
wrong scale in my head of just what Rosetta could see.

In any case this is all still wondrous.

~~~
jessriedel
I can't for the life of me understand why Rosetta doesn't have equipment to
determine Philae's relative position to cm resolution, except perhaps in the
case where the comet is between them.

~~~
joshvm
Because positioning doesn't work like that.

It's possible that Rosetta could have carried a detector that could get the
time of flight of Philae and so get a rough sphere where it could be. However,
over the distances that we're talking about, you'd probably need a powerful
laser with a very low divergence in order to get any signal there/back. LIDAR
will break a power budget easily.

If you're thinking why couldn't we use some kind of GPS type positioning,
remember that you need four satellites minimum for that (plus ground stations
to correct things). There was some discussion about using multiple flybys of
Rosetta, but it's not clear whether there'll be enough time to do this before
the batteries die.

We can locate things on Mars because we have excellent cartography of the
planet and the landers were the right way up. We're able to figure out where
things are based on the images they send back. Once we know where a lander is
the first time, it's easier to figure out where it is afterwards based on this
imagery.

~~~
13
Why are four satellites needed for positioning, wouldn't three do the trick?

~~~
joshvm
The first satellite gives you a sphere (a shell really)

The second satellite gives you a circle of intersection between the spheres.

The third satellite gives you two points where three spheres intersect. One of
these is usually in space so it's discarded.

The fourth one lets you correct for timing errors in the reciever. A
microsecond uncertainty corresponds to around 300m (i.e. c * 1µs).

You could get coarse information with three satellites, for instance if you
already know your altitude, but four+ is preferable.

------
grecy
No talk on why the harpoons didn't hold it down when it initially "landed" ?

Also, if the batteries die, can't they just wait a few days until the
~1.5hrs/day of sunlight charges them enough to do something useful again?

~~~
codeulike
Harpoons didn't fire. They kept identical harpoons in vacuum here on earth,
and after 10 years, they didn't work. I guess that component just didn't
survive the journey.

re: batteries: I gather the 1.5hrs a day would never be sufficient to get
enough for a wake-up. Some hope that shift in position earlier today may help.
Also some hope that comets orientation to sun will change (likely around
Christmas)

~~~
noselasd
They mentioned at the google hangout yesterday that it wasn't out of the
question they could wake it later again(weeks/months) when the comet is closer
to the sun and receives more light and has charged up the lander.

------
chrishare
For mine, scientific endeavors such as these are worth much more than the
experiments they entail; they help inspire the next generation of scientists,
engineers, mathematicians and so on.

------
usaphp
How long does it take for a signal from Earth to reach Philae?

~~~
barrybob
I could be wrong, but I think I saw somewhere it's ~20 minutes

