All eyes on #Rosetta part 4: #CONSERT

Note: In this – hopefully – daily series of postings I’ll highlight one of the many instruments on board of the Rosetta spacecraft and the Philae lander.

Hello Space Geeks, welcome to the fourth posting of this series about the scientific instruments on board of Rosetta and Philae! It’s Monday and only four more days to go until the DLR will host it’s big recommissioning-event in Cologne, and boy, am I excited.

Today I’d like to present you CONSERT, the “Comet Nucleus Sounding Experiment by Radio wave Transmission”-experiment. This experiment consists of two parts, first a transmitter on board of Rosetta, and a transponder installed on the lander Philae. CONSERT was built in cooperation of the Max-Planck-Institute for Solar System Research and the l’Institut de Planétologie et d’Astrophysique de Grenoble.

CONSERT (Comet Nucleus Sounding Experiment by Radiowave Transmission) probes the internal structure of the nucleus. Radio waves from the CONSERT experiment on the orbiter travel through the nucleus and are returned by a transponder on the lander.

Principal Investigator: Wlodek Kofman, Institut de Planétologie et d’Astrophysique de Grenoble, Grenoble, France.


Basically CONSERT works as follows: After Philae landed on 67P, Rosetta will fly around the comet until it’s facing the opposing site. Now, CONSERT’s trasmitter will send a 90 MHz Radar-signal right at the comet and Philae’s transponder – sitting on the other side of the comet – will try to pick up the signal, modify the signal by some data (that’s what a transponder does) – and send it right back, through the comet again, to Rosetta.

Transponder Operation Principle

Transponder Operation Principle; Waveform 11 shows what Rosetta initially sends out, Waveform 12 shows the data Philae want’s to encode (time of receive, signal strength, phase-, frequencies-shifts if any), Waveform 13 shows the modulated transponder signal Philae sends to Rosetta; From US Patent “Radar transponder operation with compensation for distortion due to amplitude modulation”; Source

Rosetta then will pick up the modified (“modulated”) signal and record all the data:

  • How long did it take from Rosetta to Philae? (Philae encoded this in the signal)
  • How long did it take from Philae back to Rosetta? (Rosetta compares the time of receiving the transponder signal with the encoded timestamp)
  • How faint was the signal, when Philae received it? (means: How large is the attenuation of the comet)
  • Did the polarization change?
  • Was the signal somehow otherwise modified? (e.g. phase-shift)

Rosetta and Philae will conduct multiple, many many thousand send-receive experiments and at the same time record their position. From all the data then ESA will be able to calculate the inner structure of the comet:

  • How many layers are there and how thick are these?
  • From which material is the comet made of?
  • What’s the density?
  • Are there regions in the comet more or less dense?
  • If yes, how do these look like?
Seismic Tomography

Seismic Tomography; this is an example of using earthquakes to determine the inner structure of earth; CONSERT will apply the same principle, the earthquakes are here the Radar-sender, the receiver an antenna instead of an seismometer. The Department of Earth & Atmospheric Sciences , Cornell University; Source:

CONSERT won’t be useful before Philae landed, but it’s a rather interesting instrument. Until now we can only guess about the internal composition of a comet. We made educated guesses, but you never now until you had a real look at it.


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