Log: (05-14-2009 - 05-17-2009)

16-17 May 2009 (L+2-L+3, DOY 136-137)

Today I had occasion to record in the HSCOM log:

HSC essentially nominal. Quietest day for almost a year, as we wait for spacecraft checks to give way to more instrument activities. 2 Spacecraft (Herschel & Planck) crossing Lunar orbit. In the past 24 hours our Spitzer colleagues reported the exhaustion of their cryogen and we congratulated them on the end of their so-successful cold mission. Quite a special day!

[L. Metcalfe from HSC ESAC, posted 17 May 2009]

15-16 May 2009 (L+1-L+2, DOY 135-136)

Herschel operations are essentially nominal and the spacecraft continues to perform well. The first trajectory course correction was successfully carried out as planned about a day after liftoff on 15 May, injecting 8.7 m/s being within 1-2% of the planned magnitude, a small delta will be performed in a few days. On 16 May the spacecraft attitude control mode was successfully changed from thruster controlled mode to reaction wheel controlled mode.

The cooldown of the spacecraft follows the predictions. In particular this has been verified for the telescope which will be heated to stabilise its temperature at 170 K for an extended period (the heating will start on 18 May), and the cryostat which will reach maximum superfluid helium temperature of just under 2 K on 18 May and maximum mass flow of just under 15 mg/s on 19 May.

[G. Pilbratt from CSG Kourou, posted 17 May 2009]

14 May 2009 (Launch date, DOY 134)

Herschel was launched together with Planck on flight V188 on an Ariane 5 ECA on 14 May 2009 from CSG Kourou, the liftoff took place at 13:12:02 UT, at the very beginning of the launch window. The launch itself was flawless, and Herschel separated from the launcher at 13:37:55 UT, just under 26 mins after lift-off.

The spacecraft was acquired by the New Norcia ground station at 13:49 UT, and good telemetry was received shortly afterwards. The spacecraft was confirmed to have acquired nominal attitude and overall status was confirmed nominal. The uplink was established and the first command was executed at 14:10 UT.

Already before even separating from the launcher, a major milestone had been achieved. The helium subsystem is working according to the book, both the large and small nozzles are open, and there is positive confirmation that the phase separator is working nominally. Together with a helium temperature at launch of only 1.81 K, this is good news regarding the cryo subsystem.

The launcher performance was very good, and the preliminary assessment of the orbit is: perigee 270.0 km (intended 270.0 ± 4.5), apogee 1,197,080 km (intended 1,193,622 ± 151,800), inclination 5.99 deg (intended 6.00 ± 0.06); or in plain english: spot on.