ISO

 1995-062A

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ESA's Infrared Space Observatory was launched by Ariane 44P (V80) with the 02 fairing. The spacecraft, built by Aerospatiale, is 3.56 x 2.77 m across ( with a 2.3m diameter dewar section) and 5.3m long. Launch mass of ISO is 2498 kg; BOL mass is 2418 kg; dry mass is 1515 kg. The initial orbit is to be 530 x 71620 km x 5.3 deg; the hydrazine thrusters will raise this to a geosynchronous 1000 x 70568 km in two burns at T+2d (Perigee) and T+6d (apogee adjust). The inclination slowly decreased to 2 degrees during the mission. Control from Villafranca center will begin at T+5 days. A cryo cover was released after a fortnight.

On 1996 May 30 the spacecraft accidentally observed the Earth for a period of about 2 minutes, while out of contact with the ground during perigee passage. Temperatures increased significantly with the baffle at 42K and the support structure at 10K; the spacecraft entered safemode. Only a small amount of helium seems to have been lost, and the spacecraft cooled down and resumed observations two days later. The cryogen finally ran out in Apr 1998. Observations with SWS in the post-cryo phase included 2-4 micron spectra of stars.

ISO
Date	Time	Event	Orbit
1995 Nov 17	0120	Launch by Ariane 44P (V80)	CSG ELA2
	0123	Stage 2 burn
	0125	Stage 3 burn
	0138	Stage 3 cutoff
	0140	Stage 3 separation	1448.8 570 x 71498 x 5.2
			1475.25 534 x 72564 x 5.4
1995 Nov 19	1310	Perigee raise, 1h 51m burn	1030 x 71606 x 5.2
1995 Nov 24	0245	Apogee lower, 39m	1437.16 1036 x 70578 x 5.2
1995 Nov 27	1027	Cryo cover ejected
1995 Nov 28		ISOCAM first light image (M51)
1996 May 30		Accidental earth view
1996 May 18			1436.38 1047 x 70536 x 3.8 GEO 172.1W+0.1W
1996 Sep 6			1435.60 1074 x 70479 x 2.6 GEO 132.5W0.1E
1996 Sep		Orbit trim
1996 Sep 14			1437.41 1082 x 70542 x 2.5 GEO 132.0W+0.3W
1996 Oct 11			1437.25 1087 x 70530 x 2.2
1997 May 14	0030	Orbit trim no. 2
1997 Dec 11		Orbit trim no. 3
1998 Apr 8	0700	LHe depleted, warmup
	2307	Observing complete, 4K
1998 Apr 9		Engineering tests
1998 Apr		SWS stellar spectra survey
1998 May 4			1436.3 1331 x 70251 x 2.2
1998 May 11		Orbit lower
1998 May 16			1418.4 684 x 70196 x 2.2
1998 May 18		end of ops
1999 Oct 14			1417.71 463 x 70388 x 5.7

Payload:

• IR telescope, 0.6m

• Helium dewar, 2140 l. at 1.8K

• CAM ISOCAM camera (3-17 mu)

• PHT ISOPHOT multiband photometer (3-200 mu)

• LWS Long wavelength spectrometer (45-180 mu)

• SWS Short wavelength spectrometer (3-45 mu)

• PLM Payload module

• SVM Service module

• Hydrazine Propulsion system (Matra Marconi Space)