1. Introduction NICMOS (Near-Infrared Camera and Multi-Object Spectroscopy) was installed on the Hubble Space Telescope during SM2 in 1997 and has been the observatory’s only near–infrared instrument. It was initially cooled by solid nitrogen. The nitrogen was consumed prematurely in early 1999 due to a thermal short in the dewar. In January 1999 NICMOS warmed up and remained inactive until the installation of a mechanical cooling system in March 2002. With the NICMOS Cooling System (NCS) the NICMOS detectors have continued to operate at a stable temperature of 77.15K. NICMOS will continue to be one of the HST instruments after Servicing Mission 4 (SM4). A full functional verification, instrument re-characterization, and initial re-calibration will be carried out in SMOV4. It is expected that NICMOS will maintain all of its current observing modes in the coming cycles. It will no longer be the only instrument capable of NIR observations, but will be joined by the IR–channel in WFC3. The two NIR instruments, NICMOS and WFC3, will complement each other and together they will provide observers with a powerful and versatile near-infrared observing tool. NICMOS Post–SM4 U nique C apabilities T. Wiklind 1, E. Barker 2, E. Bergeron 2, I. Dachevsky 2, T. Dahlén 1, R. de Jong 2, H. McLaughlin 2, A.Koekemoer 2, N. Pirzkal 1, G. Schneider 3, B. Shaw 2, D. Thatte 2, A. Viana 2, T. Wheeler 2 Unique NICMOS Capabilities The NIR capabilities of the new WFC3 and NICMOS will compliment each other. The WFC3 IR channel will provide an efficient wide–area coverage, with imaging and grism capability, for ≤1.7  m. The NICMOS cameras have smaller field of views but provide diffraction limited imaging, coronagraphic and polarimetric capabilities, as well as access to wavelengths longer than 1.7  m for imaging, grism and polarimetric observations. Below we list six areas where NICMOS will provide unique capabilities for NIR observers after SM4:  Observations at wavelengths longer than 1.7  m NICMOS will be the only instrument capable of observing at >1.7  m. This capability is available for all three NICMOS cameras in imaging mode. In addition, observations at >1.7  m are also available for polarimetry, grism spectroscopy and coronagraphy (see below).  Coronagraphy NICMOS is the only instrument providing coronagraphic capability at NIR wavelengths. Coronagrapy is provided with the NIC2 camera.  Polarimetry NICMOS is the only instrument with polarimetric capabilities at NIR wavelengths, providing polarimetric imaging with high spatial resolution and high sensitivity to linearly polarized light from 0.8 to 2.1  m. The polarimetric capability is available for NIC1 and NIC2, with wavelength coverage 0.8–1.3  m for NIC1 and 1.9–2.1  m for NIC2.  Grism observations at >1.7  m NICMOS provides grism imaging spectroscopy in the spectral range between 0.8 and 2.5  m through three different grisms. The long wavelength grism extends from 1.4 to 2.5  m with a resolution of 200 per pixel.  High spatial resolution imaging NIC1 and NIC2 will provide diffraction limited imaging at wavelengths longer than 1.1  m and 1.75  m, respectively. NIC1 has a pixel scale of 0.043 arcsec/pixel, and NIC2 has 0.075 arcsec/pixel.  Unique and complimentary NIR filters NICMOS provides unique narrow and medium band filters. These include [SIII] 0.95  m, HeI  1.08  m, Pa  1.87  m, [SVI] 1.96  m, H 2 2.12  m, Br  2.16  m and the CO band at 2.4  m. NICMOS and SMOV4 Following the installation of the NICMOS Cooling System (NCS) in March 2002, the NICMOS detectors and filters have been actively maintained at a stable temperature of 77.15K. During SM4 the NCS will be turned off, and NICMOS will warm up. This thermal cycling makes a complete verification of NICMOS functionality and performance as well as photometric and astrometric re–calibrations necessary. Once the HST is released from the space shuttle, the NCS will be started and NICMOS is expected to cool down to its nominal operating temperature, with the detectors at 77.15K. At this point the NICMOS SMOV4 activities will commence. During SMOV4, the mechanical functionality of the filter wheel mechanisms, the Field Offset Mirror (FOM) and the Pupil Alignment Mirror (PAM) will be tested. The optical alignment and geometrical stability as well as the focus and optical aberrations will be checked and corrected if necessary. In addition, a measurement of the biases and detector response will be performed. Particular attention is given to those capabilities which will be NICMOS unique in the post– SM4 era, such as coronagraphic observations and a characterization of the long wavelength thermal background. Following shortly after SMOV4, a complete photometric and grism calibration will be performed. CameraFoVPixel scale coverage Capabilites NIC111”x11”0.043” up to 1.9  m Polarimetry Diffraction limited for >1.1  m NIC219”x19”0.075” up to 2.4  m Polarimetry Coronagraphy Diffraction limited for >1.75  m NIC351”x51”0.2” up to 2.4  m Polarimetry Grisms Basic NICMOS Parameters 1 European Space Agency/Space Telescope Science Institute 2 Space Telescope Science Institute 3 Steward Observatory