Status Report

NASA Hubble Space Telescope Daily Report #3987

By SpaceRef Editor
November 14, 2005
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NASA Hubble Space Telescope Daily Report #3987

HUBBLE SPACE TELESCOPE – Continuing to collect World Class Science


PERIOD COVERED: UT November 11, 12, 13, 2005 (DOY 315, 316, 317)



NICMOS Post-SAA calibration – CR Persistence Part 1.

A new procedure proposed to alleviate the CR-persistence problem of NICMOS. Dark frames will be obtained immediately upon exiting the SAA contour 23, and every time a NICMOS exposure is scheduled within 50 minutes of coming out of the SAA. The darks will be obtained in parallel in all three NICMOS Cameras. The POST-SAA darks will be non-standard reference files available to users with a USEAFTER date/time mark.

ACS/WFC 10740

Absolute Photometric & Spectrophometric Calibration

This program has several goals: 1.}Verify repeatability of the ACS instrumentation on a single bright star to +/-0.2%. 2.}Determine any shift in the filter bandpasses since the preflight lab measurements. 3.}Determine the relative magnitude of the 3 primary WD calibrators to 0.1%. 4.}Refine the sensitivity calibration of the CCD prism and grisms at field center and determine the repeatability accuracy of this calibration. 5.}Determine the level of variability of the three HST red standard stars: VB-8 {M7}, 2M0038+18 {L3.5} and 2M0559-14 {T5}, and also measure their short wavelength {<7000A} fluxes. 6.}Cross calibrate with a faint STIS and NICMOS standard WD and solar analog star.


ACS CCDs daily monitor

This program consists of a set of basic tests to monitor, the read noise, the development of hot pixels and test for any source of noise in ACS CCD detectors. The files, biases and dark will be used to create reference files for science calibration. This programme will be for the entire lifetime of ACS. Changes from cycle 13:- The default gain for WFC is 2 e-/DN. As before bias frames will be collected for both gain 1 and gain 2. Dark frames are acquired using the default gain {2}. This program cover the period Oct, 2 2005- May, 29-2006. The second half of the program has a different proposal number: 10758.

NIC1/NIC3 10726

NICMOS non-linearity tests

This program incorporates a number of tests to analyse the count rate dependent non-linearity seen in NICMOS spectro-photometric observations. In visit 1 we will observe a few fields with stars of a range in luminosity in NGC1850 with NICMOS in NIC1 in F090M, F110W and F160W and NIC2 F110W, F160W, and F180W. We will repeat the observations with flatfield lamp on, creating artificially high count-rates, allowing tests of NICMOS linearity as function of count rate. To access the effect of charge trapping and persistence, we first take darks {so there is not too much charge already trapped}, than take exposures with the lamp off, exposures with the lamp on, and repeat at the end with lamp off. Finally, we continue with taking darks during occultation. In visit 2 we will observe spectro-photometric standard P041C using the G096 and G141 grisms in NIC3, and repeat the lamp off/on/off test to artificially create a high background. In visits 3&4 we repeat photometry measurements of faint standard stars SNAP-2 and WD1657+343, on which the NICMOS non-linearity was originally discovered using grism observations. These measurements are repeated, because previous photometry was obtained with too short exposure times, hence substantially affected by charge trapping non-linearity. Measurements will be made with NIC1: Visit 5 forms the persistence test of the program. The bright star GL-390 {used in a previous persistence test} will iluminate the 3 NICMOS detectors in turn for a fixed time, saturating the center many times, after which a series of darks will be taken to measure the persistence {i.e. trapped electrons and the decay time of the traps}. To determine the wavelength dependence of the trap chance, exposures of the bright star in different filters will be taken, as well as one in the G096 grism with NIC3. Most exposures will be 128s long, but two exposures in the 3rd orbit will be 3x longer, to seperate the effects of count rate versus total counts of the trap probability {in one exposure, we get the full PSF worth of count rates, but we need a longer exposure to separate the effect of rate versus total couts}. Filters used: NIC1 F090M, F110W, F170M and F160W; NIC2 F110W, F160W, F205W, F187W; NIC3 G096, F110W, F160W; 3x longer exposures: NIC1 and NIC2 F110W.

NIC2 10717

Quasar Bolometri Luminosity and Spectral Energy Distributions from Radio to X-ray

We propose to build the best SED data set spanning from radio to X-ray wavelengths for 35 quasars. We will use new and archival mid-to-far IR data from Spitzer as well as other existing multi-wavelength data. We have unique quasi-simultaneous FUV/UV-optical spectra for our sample, greatly reducing the uncertainty due to quasar intrinsic time variability in the UV bump. We will derive accurate bolometric luminosities for the sample and seek to establish a more reliable and accurate way to obtain the bolometric luminosity of quasars from their partial SEDs and/or spectral properties. We will also apply multivariate analysis to the SEDs, study the quasar multi-wavelength spectral properties and their dependence on the overall SEDs, and thus better understand the physical processes quasars employ emitting across the entire electromagnetic spectrum. HST NICMOS observations will be used to remove host galaxy contamination from the quasar SEDs. This is a joint Spitzer-HST project.

FGS 10610

Astrometric Masses of Extrasolar Planets and Brown Dwarfs

We propose observations with HST/FGS to estimate the astrometric elements {perturbation orbit semi-major axis and inclination} of extra-solar planets orbiting six stars. These companions were originally detected by radial velocity techniques. We have demonstrated that FGS astrometry of even a short segment of reflex motion, when combined with extensive radial velocity information, can yield useful inclination information {McArthur et al. 2004}, allowing us to determine companion masses. Extrasolar planet masses assist in two ongoing research frontiers. First, they provide useful boundary conditions for models of planetary formation and evolution of planetary systems. Second, knowing that a star in fact has a plantary mass companion, increases the value of that system to future extrasolar planet observation missions such as SIM PlanetQuest, TPF, and GAIA.

ACS/WFC 10586

The Rosetta Stone without a Distance: Hunting for Cepheids in the Primordial Galaxy I Zw 18

The Blue Compact Dwarf galaxy I Zw 18 is one of the most intriguing objects in the Local Universe. It has the lowest nebular metallicity of all known galaxies {Z=1/32 solar}. It has long been regarded as a possible example of a galaxy undergoing its first burst of star formation. However, its real evolutionary state continues to be controversial. The WFPC2 and NICMOS detection of AGB stars by our group and others suggested the presence of an underlying older population. However, deeper ACS observations by Izotov & Thuan {2004} recently failed to detect the signature of RGB stars. This was interpreted as confirmation that I Zw 18 is in fact a galaxy “in formation”, a local analog of primordial galaxies in the distant Universe. This result was widely reported in the international news media. However, an alternative possibility is that I Zw 18 is somewhat further away than previously believed, so that Red Giant Branch stars were too faint to detect. Quoted distances in the literature have ranged from 10 to 20 Mpc. We intend to resolve this controversy by direct determination of the distance to 1 Mpc accuracy using Cepheids. For this we request 12 visits of two orbits each, to execute at carefully planned intervals. We will obtain V and I band ACS/WFC photometry in each visit. The new data will be combined with archival data, but we show that the archival data by themselves are insufficient to achieve our science goals. The distance will allow us to place I Zw 18 into its proper place in the evolutionary sequence of galaxy formation.


NGC 4449: a Testbed for Starbursts in the Low- and High-Redshift Universe

We will obtain deep ACS/WFC broad-band imaging in F435W, F555W, and F814W of the Magellanic irregular galaxy NGC 4449 in order to infer the properties of the resolved {young and old} stellar population, compare the current strong star-formation activity to that at earlier epochs, trace the major episodes of star formation over cosmic time, and relate them to the past history of interaction/merging of this galaxy. NGC 4449 is one of the closest {< 5 Mpc} global starbursts with a widespread star-formation activity that could have been triggered by interaction or accretion. It is, therefore, the perfect laboratory where to address issues related to star formation in extreme environments and investigate processes connected to the formation and evolution of galaxies in the early universe. At a distance of 4.2 Mpc, the stellar content in NGC 4449 can easily be resolved with HST. Yet, up to date no comprehensive dataset has been collected that is suited to infer a global star-formation history of the galaxy and to better understand its evolution. ACS/WFC provides the angular resolution and sensitivity to easily reach magnitude limits necessary for the detection of individual stars at the tip of the red giant branch {i.e., with ages from 1 Gyr up to 12 Gyr} with the required accuracy. A mosaic of 2 pointings along the major axis will give a good coverage of the galaxy and will allow us to infer a star- formation history unbiased by local properties of peculiar regions. Narrow-band imaging in F658N {Halpha} will provide a map of the ionized gas. Finally, WFPC2 parallel observations in F555W and F814W will allow to search deep in the HI halo of NGC 4449 for evidence of stars belonging to tidal streams. Our investigation of NGC 4449 will benefit from the wealth of observations already available over almost the whole electromagnetic spectrum and will be crucial in better understanding how starbursts can be influenced by merging phenonema in both the low- and high-redshift universe.

ACS/WFC 10576

An ACS Imaging Survey of the Galaxies Hosting Strong Mg II Absorption

Strong MgII absorbers {with rest-frame absorption equivalent width W_MgII > 0.3 A} at redshift z < 1 are known to arise in extended gaseous halos around luminous galaxies. Detailed absorption line studies based on high-solution spectra of background quasars yield tight constraints on the metallicity, ionization state, and kinematics of the gaseous clouds. But whether they originate in gas accreted from surrounding satellite galaxies or outflows associated with active starburst in the host galaxies remains unclear. We have recently completed a search of the Sloan Digital Sky Survey data archive for strong MgII absorbers and identified over 1000 new systems that are previously unknown. A subset of these MgII absorbers with W_MgII > 1.8 A exhibit extreme kinematics with velocity widths {exceeding 200 km/s} in our follow-up echelle spectra. Their dynamics are consistent with various scenarios that include gas accretion {with speeds exceeding the virial velocity} and starburst outflows {possibly driven by recent merger events}. Independent of their exact nature, it is clear that strong MgII systems serve as signposts to galactic halos with extreme gas dynamics. Here we propose to conduct a snapshot survey of galaxies in the fields toward high-redshift quasars with known, strong MgII absorbers at 0.5 < z < 2. We plan to obtain high spatial-resolution ACS/WFC images of 60 fields to uncover galaxies fainter than L* at the redshifts of these absorbers and study their morphology. We will complement the HST observations with follow-up spectroscopic observations and IR images acquired at the Keck and Magellan Observatories to for redshift identifications and for measuring broad-band colors. We will investigate the correlation between absorption line kinematics and galaxy morphology. In particular, we will address whether on-going mergers is responsible for the extreme dynamics observed in MgII absorption based on their rest-frame ultraviolet morphology.


Lyman alpha morphology of local starburst galaxies

Our pilot imaging study of 6 local galaxies using ACS/SBC in the cosmologically important Lyman- alpha line has begun to reveal intriguing results. Here we propse ACS/HRC imaging of this sample, the approval of the which will allow for a significant increase in the impact of the original study and extend the limits of current understanding of Lyman-alpha escape. With this data we can accurately calibrate our Lyman-alpha line-only images and explore for the first time Lyman- alpha fluxes and equivalent widths in spatially resolved systems. These data would also allow us to test the current models of Lyman-alpha escape mechanisms and investigate possible correlations between Lyman-alpha emission and other local parameters such as age and internal reddening. The addition of high-resolution H-alpha data allows us to quantitatively study the decoupling of Lyman-alpha from non-resonant radiation and spatially explore the destruction and attenuation of Lyman-alpha. The study will go a long way towards resolving the outstanding issues complicating the interpretation of high redshift studies and the use of Lyman-alpha to quantitatively study the distant universe.

ACS/HRC 10556

Neutral Gas at Redshift z=0.5

Damped Lyman-alpha systems {DLAs} are used to track the bulk of the neutral hydrogen gas in the Universe. Prior to HST UV spectroscopy, they could only be studied from the ground at redshifts z>1.65. However, HST has now permitted us to discover 41 DLAs at z<1.65 in our previous surveys. Followup studies of these systems are providing a wealth of information about the evolution of the neutral gas phase component of the Universe. But one problem is that these 41 low-redshift systems are spread over a wide range of redshifts spanning nearly 70% of the age of the Universe. Consequently, past surveys for low-redshift DLAs have not been able to offer very good precision in any small redshift regime. Here we propose an ACS-HRC- PR200L spectroscopic survey in the redshift interval z=[0.37, 0.7] which we estimate will permit us to discover another 41 DLAs. This will not only allow us to double the number of low-redshift DLAs, but it will also provide a relatively high-precision regime in the low-redshift Universe that can be used to anchor evolutionary studies. Fortunately DLAs have high absorption equivalent width, so ACS-HRC-PR200L has high-enough resoultion to perform this proposed MgII-selected DLA survey.

ACS/WFC 10550

The Nature of LSB galaxies revealed by their Globular Clusters

Low Surface Brightness {LSB} galaxies encompass many of the extremes in galaxy properties. Their understanding is essential to complete our picture of galaxy formation and evolution. Due to their historical under-representation on galaxy surveys, their importance to many areas of astronomy has only recently began to be realized. Globular clusters are superb tracers of the formation histories of galaxies and have been extensively used as such in high surface brightness galaxies. We propose to investigate the nature of massive LSB galaxies by studying their globular cluster systems. No globular cluster study has been reported for LSB galaxies to date. Yet, both the presence or absence of globular clusters set very strong constraints on the conditions prevailing during LSB galaxy formation and evolution. Both in dwarf and giant high surface brightness {HSB} galaxies, globular clusters are known to form as a constant fraction of baryonic mass. Their presence/absence immediately indicates similarities or discrepancies in the formation and evolution conditions of LSB and HSB galaxies. In particular, the presence/absence of metal-poor halo globular clusters infers similarities/differences in the halo formation and assembly processes of LSB vs. HSB galaxies, while the presence/absence of metal-rich globular clusters can be used to derive the occurrence and frequency of violent events {such as mergers} in the LSB galaxy assembly history. Two band imaging with ACS will allow us to identify the globular clusters {just resolved at the selected distance} and to determine their metallicity {potentially their rough age}. The composition of the systems will be compared to the extensive census built up on HSB galaxies. Our representative sample of six LSB galaxies {cz < 2700 km/s} are selected such, that a large system of globular clusters is expected. Globular clusters will constrain phases of LSB galaxy formation and evolution that can currently not be probed by other means. HST/ACS imaging is the only facility capable of studying the globular cluster systems of LSB galaxies given their distance and relative scarcity.

ACS/HRC 10545

Icy planetoids of the outer solar system

Early HST studies of satellites of Kuiper belt object focussed on the 50-200 km objects that were the largest known at the time. In the past 3 years we have discovered a population of much more rare and much larger {500-2000+ km} icy planetoids in the Kuiper belt. These objects are the largest and brightest known in the Kuiper belt and, in the era when we now know of more than 1000 Kuiper belt objects, these few planetoids are likely to be the focus of much of the research on physical properties of the outer solar system for years to come. We are currently engaged in an intensive program involving Spitzer, Keck, and other telescopes to study the physical and dynamical properties of this new population. HST is uniquely capable of addressing one parameter fundamental to completing the physical picture of these planetoids: the existence and size of any satellites. The detection and characterization of satellites to these large planetoids would allow us to address unique issues critical to the formation and evolution of the outer solar system, including the measurement of densities, internal properties, sizes and shapes of these objects, the study of binary formation as a function of primary size, and the context of the Pluto-Charon binary. For these bright objects, a satellite search takes less than a full orbit, allowing the opportunity for a new project on UV spectroscopy of the planetoids to piggyback at no added time cost. This poorly explored spectral range has the potential to show unique signatures of trapped gasses, cosmochemically important ices, and complex organic materials.

NIC2 10519

Testing the Stellar Coalescence and Accretion Disk Theories of Massive Star Formation with NICMOS

The importance of massive stars cannot be underestimated – they produce most of the heavy elements in the universe and dominate the evolution of the interstellar medium in their vicinity. In spite of their significance, our understanding of their formation is meager. Both accretion through disks, analogous to the process of low-mass star formation, and coalescence of low-mass stars through collisions in the dense cores of stellar clusters have been suggested. Possibly both mechanisms occur. High spatial resolution polarization measurements of the closest massive young stellar objects {YSOs} will enable us to search for evidence of disk accretion or coalescence in the form of patterns indicative of light scattered off a coherent disk or off a disk disrupted by an infalling star, respectively. Here we propose to use 2 micron polarimetry with NICMOS to identify the presence of accretion disks around massive YSOs or to characterize their environments as possibly disrupted from a close stellar encounter. There are only a few sources that meet the stringent selection criteria for this investigation {even with HST}, which we will examine here. High spatial resolution is required, but even more important, the point spread function {PSF} must be stable with time. Furthermore, the PSF must put minimal flux into large spatial scales, something that cannot be achieved with adaptive optics. This combination of high Strehl ratio and stable PSF can only be achieved from space.


Kuiper Belt Binaries: Probes of Early Solar System Evolution

Binaries in the Kuiper Belt are a scientific windfall: in them we have relatively fragile test particles which can be used as tracers of the early dynamical evolution of the outer Solar System. We propose a Snapshot program using the ACS/HRC that has a potential discovery efficiency an order of magnitude higher than the HST observations that have already discovered the majority of known transneptunian binaries. By more than doubling the number of observed objects in dynamically hot and cold subpopulations we will be able to answer, with statistical significance, the question of whether these groups differ in the abundance of binaries as a result of their particular dynamical paths into the Kuiper Belt. Today’s Kuiper Belt bears the imprints of the final stages of giant-planet building and migration; binaries may offer some of the best preserved evidence of that long-ago era.

WFPC2 10501

Extending the Heritage: Clusters, Dust, and Star Formation in M51

Strongly interacting systems in the Local Universe offer the opportunity to investigate the modality of star formation under dynamical conditions more typical of the intermediate redshift Universe {z~0.5-1}, at an exquisite resolution unmatched by distant galaxies. M51 is one such system. Most recently, the Hubble Heritage program dedicated 24 HST orbits to obtain a 3X2 ACS mosaic of M51 in BVI, and Halpha. While this is designed to produce a lovely multi-color image of this photogenic target, its scientific return will be limited for star formation studies. Hence we propose to augment these observations by obtaining WFPC2 U band and NICMOS H band primary imaging {with NICMOS Paschen alpha in parallel} of selected pointings of this interacting galaxy system. At the modest cost of 14 additional orbits, we will: {1} accurately determine the ages of the young star cluster population; {2} secure the identification of 60-70 old globular clusters; {3} search for heavily dust enshrouded stellar clusters; {4} investigate the distribution of the cluster populations as a function of location {galactocentric, arms, interarms, etc.}; and {5} both remove the effects of dust and determine its properties. In addition to our specific science goals, these observations lend themselves, on their own or in synergy with data from GALEX and Spitzer, to a host of other investigations, including those on evolved diffuse stellar populations, galactic structure, and dust radiative transfer. We will thus release these data early to the community, by relinquishing part of the proprietary period.

ACS/WFC 10497

Cepheid Calibrations of the Luminosity of Two Reliable Type Ia Supernovae and a Re- determination of the Hubble Constant

We propose to determine the luminosity of two type Ia supernovae {SNe Ia}, 1995al in NGC 3021 and SN 2002fk in NGC 1309, by observing Cepheids in their spiral hosts. Modern CCD photometry yields an extremely tight Hubble diagram for SNe Ia with a precisely determined intercept {i.e., Delta H_0/H_0}. Yet, the measurement of the true Hubble constant via SNe Ia is limited by the calibration derived from problematic and unreliable SN data. Most of the SNe Ia calibrated by HST to date are significantly compromised by the systematics of photographic photometry, high reddening and SN peculiarity, and by the photometric anomolies associated with WFPC2. The extended reach of ACS now provides opportunities to more reliably calibrate SNe Ia and H_0. Our Cepheid calibration of a reliable SN Ia dataset, SN 1994ae, using ACS in Cycle 11 resulted in a 15% increase in H_0 from the value derived by the HST SN Ia Calibration Program. Yet, there remains a terribly small sample of reliable SN Ia data sets on which to base such a crucial cosmological result. SN 1995al and SN 2002fk are two of the best observed SNe Ia both with little reddening. They provide two opportunities to use ACS for placing the calibration of H_0 via SN Ia on firmer footing and potentially improve its precision.

ACS/WFC 10494

Imaging the mass structure of distant lens galaxies

The surface brightness distribution of extended gravitationally lensed arcs and Einstein rings contains super-resolved information about the lensed object, and, more excitingly, about the smooth and clumpy mass distribution of the lens galaxies. The source and lens information can non-parametrically be separated, resulting in a direct “gravitational-mass image” of the inner mass-distribution of cosmologically-distant galaxies {Koopmans 2005}. With this goal in mind, we propose deep HST ACS-F555W/F814W and NICMOS-F160W imaging of 15 gravitational-lens systems with spatially resolved lensed sources, selected from the 17 new lens systems discovered by the Sloan Lens ACS Survey {Bolton et al. 2004}. Each system has been selected from the SDSS and confirmed in a time-efficient HST-ACS snapshot program {cycle-13}; they show highly-magnified arcs or Einstein rings, lensed by a massive early-type lens galaxy. High- fidelity multi-color HST images are required {not delivered by the 420-sec snapshot images} to isolate these lensed images {properly cleaned, dithered and extinction-corrected} from the lens galaxy surface brightness distribution, and apply our “gravitational-mass imaging” technique. The sample of galaxy mass distributions – determined through this method from the arcs and Einstein ring HST images – will be studied to: {i} measure the smooth mass distribution of the lens galaxies {Dark and luminous mass are separated using the HST images and the stellar M/L values derived from a joint stellar-dynamical analysis of each system}; {ii} quantify statistically and individually the incidence of mass-substructure {with or without obvious luminous counter- parts such as dwarf galaxies}. Since dark-matter substructure should be considerably more prevalent at higher redshift, both results provide a direct test of this prediction of the CDM hierarchical structure-formation model.

ACS/WFC 10491

A Snapshot Survey of the most massive clusters of galaxies

We propose a snapshot survey of a sample of 124 high X-ray luminosity clusters in the redshift range 0.3-0.7. Similarly luminous clusters at these redshifts frequently exhibit strong gravitational lensing. The proposed observations will provide important constraints on the nature of the cluster mass distributions and a set of optically bright, lensed galaxies for further 8-10m spectroscopy. We acknowledge the broad community interest in this sample and waive our data rights for these observations.

ACS/WFC 10483

HH110: Collision between a Jet and a Cloud

We propose to study the shortlived event when a high-velocity protostellar outflow collides with a dense molecular cloud core. It has recently been realized that Herbig-Haro flows can attain gigantic proportions, with flow lobes stretching over many parsecs. This greatly increases the probability that an outflow rams into an obstacle such as a molecular cloud core as it plows through the interstellar medium. The HH 110 flow represents the rare case of an outflow that has suffered a grazing collision with a cloud core. Fortunately, the resulting shock is so bright that only a few orbits are required for analysis. ACS imaging in Halpha in Cycles 12 and 14 will permit the study of detailed structure and kinematics of the flow as it passes through the region of impact. This study has consequences for our general understanding of the energy cycle and chemical processing of the interstellar medium, turbulence in molecular clouds, and the role of sequential star formation among low mass stars.


The Formation and Evolution of Spirals: An ACS and WFPC2 Imaging Survey of Nearby Galaxies

Over 50% of galaxies in the local universe are spirals. Yet the star formation histories and evolution of this crucial population remain poorly understood. We propose to combine archival data with new ACS/WFC and WFPC2 observations of 11 galaxies, to tackle a comprehensive investigation of nearby spirals covering the entire spiral sequence. The new observations will fill a serious deficiency in HST’s legacy, and maximize the scientific return of existing HST data. The filter combination of UBVI, and Halpha is ideal for studying stellar populations, dust properties, and the ISM. Our immediate scientific objectives are: {i} to use the resolved cluster populations, both young massive clusters and ancient globular clusters as a chronometer, to understand how spirals assembled as a function of time; {ii} study the rapid disruption properties of young clusters; and {iii} understand dust distributions in spirals from pc to kpc scales. Each of these goals provides an important step towards charting the evolution of galaxies, and an essential baseline for interpreting the galaxy populations being surveyed in both the early and present universe. The resolution of our survey, which exploits the excellent imaging capabilities of HST’s two optical cameras, will enable us to understand the record of star cluster, and galaxy formation in a level of detail which is not possible for more distant systems. Finally, the proposed observations will provide a key to interpret an extensive, multiwavelength archive of space- and ground- based data at lower spatial resolution {SPITZER, CHANDRA, GALEX, NICMOS P alpha and H band imaging} for local spirals.


Significant Spacecraft Anomalies: (The following are preliminary reports of potential non-nominal performance that will be investigated.)


10014 – Loss of Lock while guiding under two FGSs @ 315/10:29:01z At 315/10:29:01, while guiding under two FGSs, a loss of lock occured, and HST transitioned from F2GFnLSc to T2GAttHd. Subsequent REACQ(2,1,2) at 315/11:07:15 was successful.

10015 – GSACQ(2,1,2) failed, search radius limit exceeded @ 315/18:43:51z OBAD at 18:43:51 had attitude correction of -42158 arc seconds on V3 and resulted in 486 ESB flag 1902, indicating “OBAD failed ID”. GSACQ(2,1,2) occurred while HST was LOS, at AOS the vehicle was in M2G control with search radius limit flag on FGS 2. Map at 18:56:25 showed error of 102.80 arcseconds in V2, outside of search radius.

10016 – GSAcq(2,1,2) results in finelock backup (2,0,2) using FGS2 @ 318/07:45:52z The GSAcq(2,1,2) scheduled at 318/07:45:52 – 07:53:56 resulted to finelock backup (2,0,2) using FGS2 after multiple attempts during acquisition walkdown.

Prior OBAD at 318/07:41:22, correction was successful (RSS) value ~9.00 arcsec. Followed by 486 ESB 1806 (T2G Open Loop Timer Expired) at 318/07:43:26.



                            SCHEDULED      SUCCESSFUL      FAILURE TIMES
FGS GSacq                  37                     36                 Hstar 
# 10015
FGS REacq                  22                      22
OBAD with Maneuver   110                     110

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