Subject: Rosetta Mission: Where’s Philae? :: Redux
From: Alex Kemp
Date: Monday, 24 November 2014 08:17:17 +0000
To: Oliver Kemp, Micaela Kemp, Liisa Kemp, Davin Kemp

I've got some perfectly astonishing Orbiter movies + the latest best-guess from ESA using info derived from CONSERT. The problem is that this latest ESA info contradicts earlier info.

First, the before & after pictures taken from ROLIS / OSIRIS:

ROLIS before touchdown
OSIRIS after touchdown (+ Boulders)
Philae first touchdown?

(I've added the middle `Boulders' to show the location of some boulders that, possibly, caused the Philae first touchdown to fail)

The 3 photos above are from a gif animation created by Emily Lakdawalla.
'ROLIS' is the downward-facing camera on Philae
' OSIRIS' is a hi-res camera on Rosetta.

From the comet's point of view, the lander was descending vertically, then bounced east. From Rosetta's point of view, Philae was tracking north-west, then sharply east.

The point here is that, after the first touchdown, Philae rose approx 1 mile vertically; it was almost 2 hours before the second touchdown. The second bounce was very much shorter in duration.
Incoming velocity 1 m/s
First bounce velocity 0.38 m/s (Vb)

First touchdown 15:34:06 (T+0)
Post touchdown picture with dust 15:35:32, 27m (T + 86 sec)
Osiris picture 15:43:51, 196m (T + 585 sec)
Distance to rim 882m
Second touchdown 17:25 (T + 6654 sec, 1h 50m 54'')
Third touchdown 17:32

Last sighting was 196m away at 15:43 (196m in 585 sec, 0.34 m/s).
2 hour flight suggests 2.2 km horizontal movement (which takes the 2nd touchdown right off the top of the smaller lobe & across to the larger lobe).
50.8° vertical trajectory [arctan (38/31)]
(11m 24s YouTube showing this, but boring:

Philae 1st Touchdown Visualization:
(this shows the Rosetta path around 67p + release of Philae + first touchdown)
(YouTube 2m 50s)

Philae 2nd Touchdown Simulation:
(this suggests a touchdown just over the horizon - excellent)
(YouTube 1m 30s)

CONSERT Estimation of Landing Area

CONSERT = Comet Nucleus Sounding Experiment by Radio wave Transmission

Essentially, it is Tomography for the comet, allowing various properties (such as density) of the internal structure to be deduced from transmission times between Rosetta & Philae. However, they also need to know exactly where Philae is (and also Rosetta, of course) to be able to derive the values. So, they have been working in the other direction to decide where Philae may be.

Just one problem:- this proposed landing area is NOT a 2.2 km horizontal flight away from the original touchdown site (in fact, barely 1 km). Oops.

Alex Kemp