Information on Rosetta's Earth Fly-By 2
Someone was asking for information on the Rosetta fly-by of Earth in November 2007. I asked the Rosetta science ops people for some info.
The closest approach (CA) will take place on November 13 (DOY317). At the moment of closest approach, the altitude of Rosetta will be 5330 km above the Earth surface, at sub-surface position: 63°46' S, 74°35' W (local time 16:17). A glance at Google Earth shows the closest approach is above the Magellen Strait, between South America and Antarctica. Not the spot I would have picked, but that's why I don't work in Flight Dynamics.
The Earth solar elongation around closest approach shows a very unfavorable configuration for observing the Earth during the ESB2 event. The solar angle from +Z, towards +X, must not exceed 140 degrees for thermal reasons. We assume a minimum observing angle of 10° and a maximum angle of 140°. For solar elongation angles between 20 and 95 degrees, the duration of the attitude is not constrained; for larger angles (but smaller than the hard upper limit 140 degrees at 1 AU) the maximum attitude period is 4 hours. Attitudes with SEA smaller than 20 degrees would violate several instrument constraints.
Power and data rate are not expected to present any constraints, since we are at 1 AU.
Some of the ideas being explored for instrument operations are shown below.
ALICE (AL): UV spectrometer observations:
• decontamination) and dark exposures)
• 1 Earth pointing spectral calibration and flatfield using Earth Airglow)
• 3 Moon pointing observatoins with absolute flux calibration and flatfield using Moon’s limb, slit in N-S direction)
• 1 stellar pointing for calibrations with preferentially Vega
MIRO (MR): Microwave Instrument for the Rosetta Orbiter Observations:
• 2 Earth pointings to stare at Earth during approach and recession for detector linearity calibrations.
• 2 Moon pointings to stare at Moon during approach and recession for detector linearity calibrations.
• 1 Asteroid Mode sequence test run at closest approach
OSIRIS (SR): Science camera SR Observations:
• 3 Moon pointings for science – spectrophotometry of lunar disk), Moon Na/OH tail, also straylight calibration)
• 2 Stellar pointings for calibrations on Vega and 16 Cyg
• 1 Earth pointing for calibration and imaging, Spectroscopy and straylight
• 3 imaging observations
VIRTIS (VR): Visible and Infrared Mapping Spectrometer Observations:
• 1 stare to Earth terminator, repeated several times before CA
• 2 scans from Earth limb to terminator, repeated several times before CA
• 1 raster mosaic
PHILAE (LZ): Rosetta Lander Observations:
• continuous RoLand Magnetometer and Plasma Monitor (ROMAP) measurements 6 days before and 1 day after CA
• 1 imaging of different CIVA images during CA
Magnetometer (RP) Observation: continuous magnetometer science observation 7 days around the CA
Radio Science (RS) Observation: one ground station configuration for radio science anomalous acceleration measurement
SREM (SE): Radiation Monitor Observations: continuous science observation with increased sampling of 24 hours around CA
So to summarize what I take away from this, the trajectory is not great for observations due to observation constraints. We come in on the dark side, close to the terminator, which means we have the highest relative speeds with the worst observing conditions when we are closest. Still, the early planning has a lot going on. They'll try to catch more images with the Lander camera, like they did at Mars, but they are not certain what the orientation will be so it isn't at all certain yet. During the long cruise phase, the teams are not in place to do experiments. So the fly-by and the time around it will be used for a number of calibrations, which are important if not overlly exciting. Should be able to get some decent images as we sail away on the light side.
The ESA page on the Rosetta mission is at: http://www.esa.int/SPECIALS/Rosetta/index.html
Rosetta Science page: http://www.esa.int/esaSC/120389_index_0_m.html
Hope that helps.