Wednesday, September 16, 2009

Log: (06-19-2009 - 09-11-2009)

11 September 2009 (L+120, DOY 254)

Update on the HIFI anomaly investigation

On Monday this week, the team established by ESA to investigate into the HIFI anomaly together with SRON met with instrument experts in Groningen for an extended question and answer session. Over the coming weeks the ESA team will help HIFI in trying to piece together what appears to be a complex puzzle of events which includes, but seems to be more complex than, failure of a DC/DC converter. By correctly understanding the failure scenario we hope to be able to minimise the risk when we switch HIFI back on, possibly using its redundant signal chain.

[J. Riedinger, Mission Manager and co-chair of the ESA investigation team]

4 September 2009 (L+113, DOY 247)

An update regarding the ongoing HIFI LCU malfunction investigation activities has today been posted on the ESA Corporate website.

The bottom line is that the investigation effort underway in SRON since the problem occurred is being augmented by an ESA team. The common objective is to determine the chain of events leading to the malfunction, and to decide when and under what conditions it can be considered safe to continue HIFI operations using the redundant set of warm electronics units.

[G. Pilbratt from ESTEC, posted 4 September 2009]

14 August 2009 (L+92, DOY 226)

Statement regarding HIFI LCU malfunction

On 3 August 2009 it was discovered by HIFI that on the day before the local oscillator control unit (LCU) had developed an anomaly leading to HIFI shutting down. Since then the HIFI consortium has been intensely investigating the nature of the problem; today the HIFI Principal Investigator Frank Helmich has provided the following statement:

"During normal check-out observations HIFI was shut down due to an unknown event in the analog voltage supply unit of the control electronics of the HIFI Local Oscillator. Engineers and scientists from the HIFI Instrument Control Centre and the hardware institutes are working to determine the cause and resume HIFI observations. An ongoing analysis suggests that there was either an upset in the power supply unit itself, or a voltage drop of the central unit supplying power to it. The power supply unit is needed for the instrument to obtain science observations. HIFI does have a duplicate, or redundant, set of electronics that will be used and which provides full functionality. The engineering and science team is working to understand the cause of the anomaly before switching to the duplicate set of electronics."

[G. Pilbratt from IAU GA in Rio de Janeiro, posted 14 August 2009]

10 July 2009 (L+57, DOY 191)

Herschel 'First Light' observations

You can now have a look at the 'first-light' observations released today, including SPIRE imaging of the nearby galaxies M66 and M74, HIFI spectroscopy of the star-forming region DR21, and PACS imaging spectroscopy of the planetary nebula NGC 6543.

The beauty and quality of these very first test observations is encouraging and demonstrates that a lot of new discoveries and exciting science is ahead of us! Follow Herschel progress also on the 'Latest News' page.

[P. Garcia-Lario, HSC ESAC, posted 10 July 2009]

7 July 2009 (L+54, DOY 188)

'First Light' web release this friday

A collection of 'First Light' images and spectra taken by the three instruments onboard Herschel during the days following the cryo-cover opening will be publicly made available this Friday 10 July. Watch out for the accompanying set of coordinated web releases by ESA and the different ICC consortia!

[P. Garcia-Lario, HSC ESAC, posted 7 July 2009]

3 July 2009 (L+50, DOY 184)

The coldest place in the outer space is no longer Herschel

Last night, the detectors of Planck's HFI (High Frequency Instrument) reached a temperature of 100 mK, making them the coldest thing in space, surpassing the record established by SPIRE detectors, which are operating at a warmer temperature of only 280 mK. After a successful orbit insertion maneouvre started at 13:15 CEST yesterday, Planck has now entered its final orbit around L2. Congratulations to our Planck colleagues!

[P. Garcia-Lario, HSC ESAC, posted 6 July 2009]

2 July 2009 (L+49, DOY 183)

50 days in space

Today is the 50th day of Herschel in space. As of yesterday, 80% of the planned commissioning phase activities have been executed. The initial check-out comprises a large number of tests, including switching-on of all instruments, basic functional tests, controlled cooling of the telescope, local oscillator stability measurements by HIFI, determination of the cooler recycling hold times by PACS and SPIRE, cryo-cover opening and initial determination of the focal plane geometry following 'sneak previews' of the infrared sky by all instruments, among many other checking activities. After a (so far) flawless period of almost 2 months of Commissioning Phase, with Herschel functioning nominally, we are now looking forward to starting the Performance Verification phase activities formally, something currently expected to occur on 16 July.

[P. Garcia-Lario, HSC ESAC, posted 6 July 2009]

29 June 2009 (L+46, DOY 180)

The Uplink validation chain

Before any observations can be uplinked to Herschel they must go through a series of rigorous tests. The HSC is the "meat in the sandwich" between ICC and MOC when carrying out uplink validation. The aim is to ensure that Herschel is protected from receiving any commands that could, potentially, be harmful and that nothing that has not been fully validated gets even as far as MOC, let alone to the spacecraft.

The Instrument Control Centres (ICCs) usually have to prepare their observation requests under great stress and time pressure, so it is essential to ensure that everything that has been delivered is correct and self-consistent and using the latest version of the uplink software, orbit file, etc. Under pressure, it is easy to make a mistake and deliver a wrong file in the middle of dozens of correct ones. Similarly, there is information that a particular ICC does not and cannot know when it is preparing its own observations, especially when a particular day is shared between two or more instruments: how much time is needed to slew from the end position of the first instrument's observations to the start position of the other's? Is the slew pattern acceptable to Flight Dynamics? Do all the observations from the different instruments fit in to the time available when combined?

If an inconsistency is found in validation, it must be understood and, almost invariably, the delivery is rejected and must be re-delivered. Only when the uplink information has been fully validated does it then go to the HSC Mission Planners who put together the final observing schedule and apply the last layer of checks, comparing between the schedule that is expected from the ICC input and the one that is actually obtained when that input is processed at the HSC. If a discrepancy is found, however trivial, it must be queried and if a change has had to be made to the sequence of observations, approval for the change must be sought from the ICC. Only when the "i"s are dotted, the "t"s crossed and everything is shipshape and Bristol fashion will the planning files be passed to the Project Scientist for his approval of the schedule and then on to MOC for transmission to the spacecraft.

The HSC Uplink Validation Team:
Delivery validators - Larry O'Rourke and Mark Kidger
Mission Planning - Charo Lorente and the Mission Planning Gang (Álvaro Llorente, Fernando Rodríguez and Mar Sierra)

[M. Kidger, HSC ESAC posted 6 July 2009]

25 June 2009 (L+42, DOY 176)

Can Herschel see Planck?

Some people may think that Herschel and Planck are quite close together in their orbits around the Second Lagrange Point of the Sun-Earth system and that a hypothetical observer on Herschel would be able to see Planck and vice-versa. How true is this?

At launch, of course, Herschel and Planck were very close together, but they separated quite quickly. At midnight on launch day the two were just 44 km apart and to a hypothetical stowaway on Herschel, Planck would have been about magnitude -3, but this distance between them increased quickly and, as a result, Planck would have faded rapidly from sight. By early on the morning of 17 May it would have been lost to the naked eye. On 29 May the separation between the two passed 50 000 km and on 7 June it passed 100 000 km. At the same time, the relative velocity between Herschel and Planck has increased considerably from the initial 1.3 m/s at 00UT on 15 May, to a maximum velocity of recession of 130 m/s on 18 June. In contrast, on 22 August, Planck will be approaching Herschel at no less than 119 m/s.

The distance and relative velocity between Herschel and Planck follow an approximately 3 month cycle. However, they are never separated by less than 0.5 Lunar Distances (LD) and the separation reaches a maximum value of 1.225 LD (471 000 km). Over the course of 2009, the closest approaches are on 5 September (207 000 km) and 4 December (159 000 km), with maximum separations on 26 July (471 000km) and 16 October (458 000km). Seen from Herschel, Planck is never brighter than V=14.9 and gets as faint as V=17.2

A Herschel or Planck ephemeris can be generated for any observing site on Earth or in space using JPL's Horizons system.

[M. Kidger, HSC ESAC, posted 6 July 2009]