The Herschel Space Observatory (HSO)  was an European Space Agency (ESA) space mission that operated between 2009 and 2013. Belgium had a strong involvement in this mission and in return had a significant amount of "guaranteed time" to conduct several science programs.

The satellite had three instruments on board:

• HIFI, the Heterodyne Instrument for the Far Infrared, a high-resolution spectrograph that operated in the range of 480 to 1250 GHz in five bands and 1410 to 1910 GHz in two additional bands.
• PACS, the Photodetector Array Camera and Spectrometer, a bolometer array photometer and a photoconductor array imaging spectrometer that operated at a wavelenght range between 60 and 210 µm. 
• SPIRE, the Spectral and Photometric Imaging Receiver, consisting of a 3-band imaging photometer and a Imaging Fourier Transform Spectrometer that operates at wavelengths between 200 and 670 µm. 

Belgium was involved in the HSO through a partnership at the co-PI level (Prof. Christoffel Waelkens, KUL) for a 20% share in the Photodetector Array Camera and Spectrometer (PACS). Belgium was involved in building of parts of the hardware (at the Centre Spatial de Liege, involving various companies as subcontractors, and at the Interuniversity MicroElectronics Center) and in the ground segment (the Instrument Control Center) at the Instituut voor Sterrenkunde, K.U. Leuven. 

The Belgian contribution to PACS implied that Belgium disposed of about 400 hours of "guaranteed time" observations.

The largest time investment was in the "key program" MESS (Mass Loss of Evolved Stars), led by Martin Groenewegen from the ROB.
It also involved other scientist from ROB, as well as scientists from K.U. Leuven, ULg, and ULB. 
Guaranteed time was also provided by partners in Austria (Univ. of Vienna), Germany (Heidelberg), the SPIRE consortium (mainly UC London), the Herschel Science Center, and a Mission Scientist.

MESS and other Belgian Herschel proposals were supported by the Federal Government PRODEX program "Herschel-PACS Guaranteed Time and Open Time Programs: Science Exploitation".

The MESS program has led to a large number of publications, and in fact the exploitation of the data is still ongoing.

Some of the publications with main involvement by ROB scientists are:

• van Hoof P.A.M., Van de Steene G.C., Barlow M.J., et al.   2010, A&A 518, L137   Herschel images of NGC 6720: H2 formation on dust grains
• Ladjal D., Barlow M.J., Groenewegen M.A.T., et al.  2010, A&A 518, L141  Herschel PACS and SPIRE imaging of CW Leo
• Groenewegen M.A.T., Waelkens, C., Barlow M.J., et al. 2011, A&A 526, A162  "MESS (Mass-loss of Evolved StarS), a Herschel Key Program"
• van Hoof P.A.M., Van de Steene G.C., Exter K.M., et al.  2013, A&A 560, A7  "A Herschel study of NGC 650"
• Etxaluze M., Cernicharo J., Goicoechea J.R., van Hoof P.A.M., et al. 2014, A&A 566, A78 "Herschel spectral-mapping of the Helix Nebula (NGC 7293): Extended CO photodissociation and OH+ emission"
• van de Steene G.C., van Hoof P.A.M., Exter K.M., et al.    2015, A&A 574, A134  "Herschel imaging of the dust in the Helix Nebula (NGC 7293)"