Operations and performance of the PACS instrument ³He sorption cooler on board of the Herschel space observatory

A ³He sorption cooler produced the operational temperature of 285 mK for the bolometer arrays of the Photodetector Array Camera and Spectrometer (PACS) instrument of the Herschel Space Observatory. This cooler provided a stable hold time between 60 and 73 h, depending on the operational conditions of the instrument. The respective hold time could be determined by a simple functional relation established early on in the mission and reliably applied by the scientific mission planning for the entire mission. After exhaustion of the liquid ³He due to the heat input by the detector arrays, the cooler was recycled for the next operational period following a well established automatic procedure. We give an overview of the cooler operations and performance over the entire mission and distinguishing in-betweenthe start conditions for the cooler recycling and the two main modes of PACS photometer operations. As a spin-off, the cooler recycling temperature effects on the Herschel cryostat ⁴He bath were utilized as an alternative method to dedicated Direct Liquid Helium Content Measurements in determining the lifetime of the liquid Helium coolant.

1. The earlier increase of the evaporator temperature triggered an autonomy function and put PACS into safe mode leading to the failure of OBSIDs 1342270750 & 1342270751 planned to observe asteroid (2000) Herschel.

PACS has been developed by a consortium of institutes led by MPE (Germany) and including UVIE (Austria); KUL Leuven, CSL, IMEC (Belgium); CEA, LAM (France); MPIA (Germany); INAF-IFSI/OAA/OAP/OAT, LENS, SISSA (Italy); IAC (Spain). This development and the operation of the PACS Instrument Control Centre, planning the calibration observations, analyzing and documenting the measurements and supporting the mission planning stray-light protection has been supported by the funding agencies BMVIT (Austria), ESA-PRODEX (Belgium), CEA/CNES (France), DLR (Germany), ASI/INAF (Italy), and CICYT/MCYT (Spain).

Authors and Affiliations

1. Commissariat à l’Energie Atomique, IRFU, Orme des Merisiers, Bât. 709, 91191, Gif/Yvette, France

   M. Sauvage & K. Okumura

2. Max-Planck-Institut für Astronomie, Königstuhl 17, 69117, Heidelberg, Germany

   U. Klaas

3. Max-Planck-Institut für extraterrestrische Physik, Giessenbachstraße, 85748, Garching, Germany

   Th. Müller, A. Poglitsch & H. Feuchtgruber

4. Konkoly Observatory, MTA CSFK, Konkoly Thege Miklós, út 15-17, 1121, Budapest, Hungary

   A. Moór

5. Commissariat à l’Energie Atomique, INAC, Service des Basses Températures, 17, rue des Martyrs, 38054, Grenoble, France

   L. Duband

Corresponding author

Correspondence to M. Sauvage.

Herschel is an ESA space observatory with science instruments provided by European-led Principal Investigator consortia and with important participation from NASA.

Appendix A: Common uplink system (CUS) command script for PACS cooler recycling

• // Missionphase :

• //

• // Purpose : Perform the cooler recycling

• //

• // TCL author : TM

• // TCL file : tm_phot_cooler_recycling.tcl

• // CUS author : DAC

• // Script file : BOLO_cool_recycle.txt

• //

• // Input arguments

• // type name description

• // N/A

• //

• // Return values

• // Type Description

• // int [] Several duration times

• //

• // Description : see PhFPU UM, chapter 4

• //

• // Dependencies :

• //

• // Preconditions :

• //

• // Comments : Based on the PhFPU UM Draft 6.0 and

• abundant e-mail

• // exchanges with SAp

• //

• // Version : 2.0

• //

• int[] block BOLO_cool_recycle PACS 203 {

• }{

• // disable AF 14 (to check for TEMP_EV < 0.3 K)

• Pacs_DPU_SET_FUNCT(”EVENT_BOL_T_FPU”,”DISABLE”);

• // disable AF 21 disable AF 14 (to check for TEMP_EV < 0.3 K)

• Pacs_DPU_SET_FUNCT(”EVENT_BOL_I_SP1”,”DISABLE”);

• // enable AF 18 (to check if the current of the sorption

• pump heater is below 30mA)

• Pacs_DPU_SET_FUNCT(”EVENT_BOL_I_SP2”,”ENABLE”);

• //

• // Obtain and set Block ID

• WriteBBID($BBID);

• // Define variables to communicate various durations

• to HSPOT.

• // NOTE: all time variables in units of number of ramps

• (SPEC) or

• // number of readouts (BOLO). The calling program

• must convert this

• // count into actual duration in true time units

• seconds .

• // SRC, REF, CAL, OVR stand for time spent on SRC,

• REF (on sky),

• // CAL source, and overheads (wait for something).

• Total

• // duration is given by duree_num. If no error,

• this duration

• // must be equal to the sum of all others

• // NOTE: here all durations are given in [sec]

• int duree_num = 0;

• int duree_SRC = 0;

• int duree_REF = 0;

• int duree_CAL = 0;

• int duree_OVR = 0;

• // Set HK to PHOT

• Pacs_DPU_SET_HK_LIST(”PHOT”,”BOTH Array”);

• // content of ”Preparation_au_recyclage.txt”

• // Set SP heater current to to 0.00000000 amperes (0)

• // # P 07 01 0000

• int operand = 0x7010000;

• Pacs_DMC_SEND_COMMAND_BOLC(operand);

• int t_wait = 1;

• delay(t_wait);

• duree_num = t_wait;

• duree_OVR = t_wait;

• // Set HSP heater current to to 0.00000000 amperes (0)

• // # P 07 02 0000

• operand = 0x7020000;

• Pacs_DMC_SEND_COMMAND_BOLC(operand);

• t_wait = 1;

• delay(t_wait);

• duree_num = duree_num + t_wait;

• duree_OVR = duree_OVR + t_wait;

• // Set HSE heater current to to 0.00140000 amperes (3572)

• // # P 07 03 0DF4

• // Attendre 300000 ms

• // # S 01 0493E0

• operand = 0x7030df4;

• Pacs_DMC_SEND_COMMAND_BOLC(operand);

• t_wait = 300;

• delay(t_wait);

• duree_num = duree_num + t_wait;

• duree_OVR = duree_OVR + t_wait;

• // Set HSE heater current to to 0.00118000 amperes (3011)

• // # P 07 03 0BC3

• // Attendre 900000 ms

• // # S 01 0DBBA0

• operand = 0x7030bc3;

• Pacs_DMC_SEND_COMMAND_BOLC(operand);

• t_wait = 900;

• delay(t_wait);

• duree_num = duree_num + t_wait;

• duree_OVR = duree_OVR + t_wait;

• //********************************************************

• //** **

• //** Automatic Cooling reclycling **

• //** (”Recyclage_Auto_Time.txt”) **

• //** **

• //********************************************************

• //

• // - 23/01/06 Procedure of reclycling in Saclay cryostat

• with Phfpu MV

• // - note : this is timing version without temperature test

• //

• // Initialisation of BOLC

• //

• // Set temp probe on/off FF hexa

• // # P 07 00 00 FF

• //

• // Initialisation of LTU

• //

• // Inhiber enregistrement TM

• // # S 08

• // Valider enregistrement TM

• // # S 09

• //

• // Initial conditions

• // TEMP_SP < 10K

• // TEMP_EV < 2K

• //

• // Set SP heater current to to 0.02730000 amperes (2231)

• // # P 07 01 08B7

• //

• // Attendre 2100000 ms

• // # S 01 200B20

• operand = 0x70108b7;

• Pacs_DMC_SEND_COMMAND_BOLC(operand);

• t_wait = 2100;

• delay(t_wait);

• duree_num = duree_num + t_wait;

• duree_OVR = duree_OVR + t_wait;

• //

• // Set SP heater current to to 0.00700000 amperes (580)

• // # P 07 01 0244

• //

• // Attendre 2820000 ms

• // # S 01 2B07A0

• operand = 0x7010244;

• Pacs_DMC_SEND_COMMAND_BOLC(operand);

• t_wait = 2820;

• delay(t_wait);

• duree_num = duree_num + t_wait;

• duree_OVR = duree_OVR + t_wait;

• //

• // Set HSE heater current to to 0.00000000 amperes (0)

• // # P 07 03 0000

• //

• // Attendre 720000 ms

• // # S 01 0AFC80

• operand = 0x7030000;

• Pacs_DMC_SEND_COMMAND_BOLC(operand);

• t_wait = 720;

• delay(t_wait);

• duree_num = duree_num + t_wait;

• duree_OVR = duree_OVR + t_wait;

• //

• // Set SP heater current to to 0.00000000 amperes (0)

• // # P 07 01 0000

• operand = 0x7010000;

• Pacs_DMC_SEND_COMMAND_BOLC(operand);

• t_wait = 1;

• delay(t_wait);

• duree_num = duree_num + t_wait;

• duree_OVR = duree_OVR + t_wait;

• //

• // Set HSP heater current to to 0.00140000 amperes (3569)

• // # P 07 02 0DF1

• //

• // Attendre 480000 ms

• // # S 01 075300

• operand = 0x7020df1;

• Pacs_DMC_SEND_COMMAND_BOLC(operand);

• t_wait = 480;

• delay(t_wait);

• duree_num = duree_num + t_wait;

• duree_OVR = duree_OVR + t_wait;

• //

• // Set HSP heater current to to 0.00118000 amperes (3010)

• // # P 07 02 0BC2

• operand = 0x7020bc2;

• Pacs_DMC_SEND_COMMAND_BOLC(operand);

• t_wait = 1;

• delay(t_wait);

• duree_num = duree_num + t_wait;

• duree_OVR = duree_OVR + t_wait;

• //

• // ************************

• // ** **

• // ** end recycling **

• // ** **

• // ************************

• // Last message

• debug_print(”Recycling completed, in about 20 min,

• TEMP_EV < 0.3 K”);

• t_wait = 1200;

• duree_num = duree_num + t_wait;

• duree_OVR = duree_OVR + t_wait;

• delay(t_wait);

• //

• // AF settings

• //

• // disable AF 18 (to check if the current of the sorption

• pump heater is below 30mA)

• Pacs_DPU_SET_FUNCT(”EVENT_BOL_I_SP2”,”DISABLE”);

• // enable AF 21 (to check if the absolute value of the HSP

• current is below 2*10ˆ(-5)A)

• Pacs_DPU_SET_FUNCT(”EVENT_BOL_I_SP1”,”ENABLE”);

• //

• // Set HK to NO PRIME (to have the clean SAFE settings again)

• Pacs_DPU_SET_HK_LIST(”NO_PRIME”,”BOTH Array”);

• // Return the array of times

• int[] time_array = [duree_num,duree_SRC,duree_REF,

• duree_CAL,duree_OVR];

• return time_array;

• }

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