EPOXI
Two intriguing investigations -- One flight-proven spacecraft
Mission Status Reports
Mission Status Reports
| DATE WHO |
REPORT |
| 2013.09.23 A'Hearn |
On Monday, 16 Sept, after considerable effort transmitting low-level hardware commands, we determined that there were no other plausible scenarios under which we could recover command and control of the spacecraft. We recommended that NASA declare the mission lost. That declaration was announced by NASA on Thursday, 19 Sept. |
| 2013.09.03 A'Hearn |
We have not received any of our expected observations of comet ISON due to a spacecraft problem. Communication with the spacecraft was lost some time between August 11 and August 14 (we only talk to the spacecraft about once per week). The last communication was on August 8. After considerable effort, the team on August 30 determined the cause of the problem. The team is now trying to determine how best to try to recover communication. |
| 2013.01.23 A'Hearn |
With a small amount of money from NASA, the Deep Impact Flyby spacecraft continues to study comets after the official end of the EPOXI mission. After the Hartley 2 flyby there was not sufficient fuel remaining to go to any other comets. The only target reachable with our remaining fuel is the Near Earth Asteroid 2002 GT, which we would not reach until 2020. This asteroid is considered a Potentially Hazardous Object, i.e., it passes within 0.05 AU (7.5 million km) of Earth's orbit. NASA authorized us to make a maneuver for that encounter and it was done in two steps over the last year.
Meanwhile, we use the spacecraft as a remote observatory for studying comets. We made a series of observations of comet Garradd (C/2009 P1) in February-April of 2012 and we have now just begun observations of the new sungrazing comet ISON (C/2012 S1). For comet Garradd we were able to study the rotation rate, the relative abundances of gases in the coma, and show that CO/H2O ratio was higher post-perihelion than pre-perihelion. For comet ISON, we began taking data on 17 Jan and we have shown that the brightness varies on a timescale of hours. With more data we will determine a rotation period. For now we are obtaining only visible-wavelength images but in mid-February we will begin to obtain IR spectra. Since the spacecraft is generally on the opposite side of the sun from Earth, observing windows from the DI Flyby are very different from observing windows from Earth. The present observing window ends on 8 March. We have an additional window from early July to early September. There are also two windows after the comet passes perihelion and if the comet survives perihelion passage we can observe it early March to early May 2014 and most of September-November 2014. |
| 2012.07.12 A'Hearn |
Over the last year, the Deep Impact eXtended Investigation (DIXI) science team has been working primarily on the calibration and interpretation of the Hartley 2 data collected back in November 2010. Many research papers have been written and we anticipate publication of a special issue of the journal Icarus later this year with many of those papers. These papers include studies of: the thermal properties of the nucleus of Hartley 2, the shape and mass-loss of the nucleus of Hartley 2, the excited rotational state of Hartley 2 and how it could be influenced by the mass loss, the physical properties of the large, and the icy grains discovered around Hartley 2's nucleus. The special issue will also contain a few papers from Stardust-NExT that had its flyby of Tempel 1 in Feb 2011 to include the interpretation of the impact location made by Deep Impact (as observed by Stardust-NExT a full orbital period later), and so on. We have also written a broader paper on the volatiles in comets, triggered by our own observations of CO2, and how this implies a different formation scenario for comets. Details of a few of these papers will be provided in a later update.
We have also spent time this year using the DI Flyby spacecraft as an observatory. Among other things, we observed comet 2009 P1 Garradd from a distance of 1.4 AU. 1 AU is ~150,000,000 km, so our observations of Garradd were much farther away than our ~700 km flyby distance of Hartley 2 (we don't have enough fuel to go to any more comets, unless of course one is discovered that will come very close to us). Even at that distance, we determined that Garradd's outgassing varies with a period of 10.4 hours, presumably due to rotation of its nucleus. We also obtained the only measurements of its dry ice content, roughly 10% of its water ice content by number of molecules. The spacecraft has been in an unusual state during the past year, without an official mission, while waiting for NASA's Senior Review of most of the planetary missions requesting extended operations. That review took place at the end of June and we hope to hear in the next month or two whether we will be allowed to continue operating as an observatory, both observing selected comets as we did with Garradd and also carrying out other observational programs on Mars, Jupiter, and exoplanets producing micro-lensing events by passing in front of a star. |
| 2011.11.01 A'Hearn |
As we approach the anniversary of the EPOXI flyby of Hartley 2, it is time to look at what we have learned about comets from this mission. In the first week of October, a special session of the annual DPS meeting, jointly held with the European Planetary Science Congress, highlighted recent mission results in an all-day session. Key results from EPOXI included:
The results for the abundances of carbon monoxide (CO) and carbon dioxide (CO2) relative to water mesh nicely with results from the Akari satellite on these abundances in other comets and the results on deuterium in Hartley 2 suggest that the origin of comets needs to be rethought.
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| 2010.10.20 A'Hearn |
The spacecraft went through a cool-down period at the end of September to optimize the capabilities of the near-IR spectrometer and to carry out a Trajectory Correction Maneuver (TCM). This maneuver changed our target point based on our improved knowledge of the position of the comet relative to the spacecraft. We think that the new target point will be within 100-200 km of the desired flyby point (which is 700 km from the nucleus). We expect our next and final TCM to be on October 27. We have a contingency plan for a TCM on November 2 in case the previous TCM does not perform as expected.
We have been receiving Hartley 2 data from a variety of other spacecraft and collaborators. The WISE mission released data acquired in May. Those data will be useful in understanding the onset of activity by the comet as it approaches the sun in its orbit. Weaver et al. released Hubble Space Telescope images acquired on September 25. The HST images are particularly valuable because they allowed us to confirm that the cometary nucleus is separable from the coma. Eventually, we will be able to separate the nucleus from the coma within our own data. For now, HST has a huge advantage over our own cameras in this respect due to the much larger aperture of HST coupled with the fact that Earth and HST were much closer to the comet than was our spacecraft. These data are consistent with earlier determinations of the size of the nucleus. We have also been receiving widespread reports of jets in the coma of the comet. The first such report was from Matthew Knight and colleagues at Lowell Observatory who found jets in the gas (the unstable radical CN) but not in the dust during an August observing run . Since then, we have had more recent reports of jets from both professional and amateur observers. Since the Deep Impact spacecraft has its cameras dedicated to monitoring Hartley 2 during this phase of the mission, we now have an advantage over other observatories and telescopes because we have nearly continuous coverage (16 out of every 24 hours). We too see fluctuations and jet-like structures in our data that are presumed to be due to variations in the release of dust and gas as the nucleus rotates. More excitingly, we have discovered a new cometary phenomenon! In September, outgassing from CN, as detected by the MRI, increased slowly by a factor of 5 and then slowly decreased while the dust showed no dramatic change. This activity took place over the course of 16 days. We are unaware of any other instances of this type of activity in any other comets and it is very different from the dust outbursts observed with the same instrument at Tempel 1. (Reported in CBET 2512, which requires a subscription to view.) |
| 2010.09.14 A'Hearn |
We have now been observing the comet for about a week (we began on Sunday, 5 September). After the first day it was clear that portions of the spacecraft were getting hotter than we had predicted. The previously agreed procedure was executed to turn off the HRI, which generates a moderate amount of heat in the parts of the spacecraft near the telecommunications system. As we approach the comet, the geometry changes enough to make the instruments and the other parts of the spacecraft fit better into the shadow behind the solar panels so things will cool off and we can turn the HRI back on. Although we had planned on taking HRI images during this period, we had not scheduled any spectroscopy until the end of September and we expect to have the instrument turned back on by then.
We have begun preliminary analyses of the images from the MRI and we can already see variations in the brightness that appear to be correlated with the rotational period that has been previously announced by ground-based observers (Knight et al., IAU Circular 9163), namely 16.6 hours. At this time we only take observations every 6 hours because of the heating of the spacecraft, so we do not yet have enough temporal resolution to separate how much of the variation is due to the varying cross-section of the nucleus and how much is due to activity, but it seems clear that there is some variation in activity, possibly including at least one short-duration outburst. In our images, the coma is seen to extend several tens of thousands of km (Image 1 released 8 Sep; Image 2 released 14 Sept). As a point of comparison, at the time of the previously released image (5 Sept), the comet was 0.40 AU from the spacecraft but only 0.36 AU from Earth. We will be looking for any structure in the images and whether that structure varies with rotation. |
| 2010.08.20 A'Hearn |
The EPOXI mission is now in the home stretch, almost ready to start our encounter campaign. We have completed all our course corrections to put us close enough to the comet that our on-board cameras can be used on close approach to refine the targeting at about 700 km from the nucleus. We are not trying to control the time of closest approach and this will change depending on the details of future targeting maneuvers. We currently expect closet approach to be roughly between 13:50 and 14:00 UTC on 4 November. We will know that much more accurately in the day or so before encounter.
On 24 September we will undergo our Critical Events Readiness Review, which is meant to allow management at JPL and NASA to evaluate whether we are ready for the encounter. Over the last few weeks we have been in an attitude that heats the upper deck of the spacecraft so we have temporarily turned off one of our instruments to minimize the temperature on that deck. That instrument will be restarted on 23 Aug. Our encounter operations begin with carrying out a special calibration of the Point Spread Function of HRI in the first week of September and then we begin regular observations of comet Hartley 2 on Sept 5. We will periodically post images on the web site to show the changes in the comet as we approach it. Initially, because of the long range to the comet, this is likely to be once a week but it should ramp up to daily as we get closer. |
| 2010.06.28 A'Hearn |
This past weekend, our spacecraft flew past Earth. Closest approach was at approximately 22:04 UTC on 27 Jun at a geocentric distance of 0.000246 AU or approximately 36,860 km. The purpose of this flyby was to retarget the spacecraft onto its final trajectory to comet 103P/Hartley 2. Data are expected beginning later today that will be analyzed to determine how accurately we achieved our goal but our general experience is that nearly all the maneuvers with this spacecraft, both simple thruster maneuvers in deep space and gravity assists, have all gone with high precision. The new orbit, which will change slightly but not much due to subsequent maneuvers to optimize the flyby, has an orbital period of about 14 months, with perihelia near Earth's orbit. The details of the flyby of comet Hartley 2 will be set up in subsequent maneuvers, but the nominal distance of closest approach is 700 km at several minutes before 14:00 UTC on 4 November.
Meanwhile, the science team and the operations team are busy studying the planned observations at encounter to ensure that everything will execute properly and return the scientific results that we are aiming for. Observations of the comet will begin on 5 September, 2 months prior to closest approach, and continue through 25 November, 3 weeks after closest approach. A routine recalibration of the instruments after the flyby will be the last scientific activity on this mission. Since all of the observations are pre-programmed, with simple commands from the ground to start long sequences, everything must be thoroughly tested on simulators on the ground (we have such testbeds both at JPL and at Ball Aerospace) to wring out all the little things that can go wrong. The science team is also working very hard to obtain the best possible calibration of the instruments, which will enable us to obtain higher quality data at Hartley 2 than we were able to obtain at comet Tempel 1 and also to recalibrate the data from comet Tempel 1. |
| 2010.03.03 A'Hearn |
As the EPOCh team moves from processing data to writing papers about their results, the DIXI team is ramping up its activities in preparation for the encounter with comet Hartley 2 on November 4.
The majority of the data from EPOCh have been made public both at the Small Bodies Node of NASA's Planetary Data System (PDS-SBN) and at the Multi-Mission Archive at Space Telescope (MAST). A few datasets taken in 2009 and some derived data (such as the final light curves of transiting planets) still remain to be delivered. There were two significant activities for DIXI in February. On February 16 we carried out the first of several cruise calibrations that are planned. The others will be in the summer, a few weeks prior to encounter, and a few weeks after encounter. These data ensure that we understand the operation of the instruments and can readily provide calibrated data after the encounter. The second significant activity in February was a face-to-face meeting of the science team with key members of the operations team to lay out the detailed sequence of observations to be made during the encounter (much like the Sequence Symphony from Deep Impact). These observations will include observations on approach starting 60 days prior to closest approach and observations on departure for 21 days. The details of these plans must be decided well in advance because it is necessary to test them extensively on simulators in order to be sure that everything operates as planned. Deep space flyby encounters such as this one do not allow any opportunity to redo any observations if something goes wrong and last minute changes are very risky. Thus these encounters are dealt with much more rigorously than are observations, e.g., with telescopes in orbit around Earth. For those observatories, it is essential to ensure the safety of the spacecraft and instruments but if the observation fails it can be repeated. We have no chance to repeat the observations. We will continue to change some details to the observing sequence over the next few months but the basic approach is completely determined at this time. |
| 2009.07.31 A'Hearn |
IR spectrometer calibration The calibration team has been analyzing the best set of IR spectrometer calibration measurements from the Moon that have been acquired to date. Key to good calibration data is to have the IR spectrometer operating at cold temperatures to reduce noise in the data. The team is quite pleased with the results and are confident that the calibrations of the past year will result in improvements in the discrimination of signal from the noise and they hope to have improved spectroscopic data for scientific interpretation soon. A team of calibrators has also been at work characterizing components of the system in the laboratory at the Jet Propulsion Lab. Stay tuned for results of these analyses and resulting scientific interpretations. |
| 2009.06.05 A'Hearn |
Characterizing Comet Hartley 2 Although the EPOXI mission's spacecraft is in a period of relative inactivity, the team is still actively working on a variety of questions. One of the key areas of investigation is the characterization of the next target, comet Hartley 2. Several investigations have been carried out to characterize the nuclear size and albedo, the large dust, and the rotation of the nucleus. These investigations have been aimed for the period before the nucleus begins outgassing significantly as it approaches the sun. Observation were taken with the Spitzer Space Telescope in August 2008. The analysis of those data yields a nuclear effective radius of 0.6 km, slightly smaller than, but still comparable to, the size deduced using the European Infrared Space Observatory at the previous apparition. These observations also show that there is a trail of large dust particles released much earlier and still orbiting the sun close to the nucleus. This is a common phenomenon among comets. The next step was an effort to determine the rotational period in order to design the observing sequence for the approach to the comet. A series of observations with the Hubble Space Telescope (HST) in late April were somewhat puzzling. Subsequent observations with a variety of ground-based telescopes, particularly with Gemini-South and Gemini-North on the same night, have suggested a rotational period near 2/3 day, but with narrow minima that were not caught in the HST observations. |
| 2009.01.01 A'Hearn |
2008 Flyby On December 29, our spacecraft flew past Earth, getting a gravity assist that reoriented the orbit to optimize the encounter with comet Hartley 2 in November 2010. There will be 3 more flybys of Earth before the encounter with the comet. As usual, the navigation team did a great job and the spacecraft had flawlessly performed its last maneuver in mid-December to set up this encounter. All indications from a quick analysis are that the flyby went exactly as planned. The spacecraft was tracked for range and Doppler shift by the Deep Space Network, and it was also observed optically as a 17th magnitude object at closest approach. Rob McNaught, of the Siding Spring Survey (University of Uppsala & Australian National University), provided an animation showing the motion during two minutes somewhat prior to closest approach. |
| 2008.12.12 A'Hearn |
Interplanetary Internet From mid-October to mid-November 2008, the Deep Impact spacecraft carried out a series of experiments for the interplanetary Internet. The terrestrial Internet with which most people are familiar routes messages as a series of small partial messages that travel different routes. These different routes are chosen depending on other Internet traffic and on where roadblocks (computers that are down or are very busy) occur. The pieces are automatically reassembled at the receiving end into the complete message so that the user does not have to worry about how the pieces travel. For an interplanetary network, say from Mars via several different spacecraft (in Martian orbit, in a terrestrial orbit, en route to some other destination in the solar system), the time delays between different routes may be measured in tens of minutes to many hours rather than in milliseconds to a few seconds as is the case for the terrestrial Internet. This requires different software and the present project called DTN, or Delay Tolerant Networking. The test with the Deep Impact spacecraft was called DINET (Deep Impact DTN experiment). Computers on the ground at JPL were used to simulate stations on Earth, on Mars, and on the Martian moon Phobos. Images were sent among these computers with some information being routed entirely on the ground and other information being routed via the Deep Impact spacecraft. The entire experiment was successful, including transmitting all the data without corruption as various faults and breakdowns in the system were simulated. Although the Deep Impact spacecraft's role was just to provide a mechanism for the DINET team to test their software, we were closely involved because we had to load new software onto our spacecraft to make it act like a router for data. We are pleased to have been able to support this activity that will ultimately lead to much better communications across the solar system. |
| 2008.10.04 Deming |
End of EPOCh Observations EPOCh observations concluded on August 31, with observations of the strongly irradiated giant planet HAT-P-7. During the January - August period of EPOCh observations, we collected over 180,000 photometric quality images. The transiting planet systems we observed include: HAT-P-4, TrES-2, TrES-3, XO-2, GJ436, WASP-3, and HAT-P-7. Each system was observed for 5 to 6 transits, as well as secondary eclipses. We observed the Gliese 436 system for over 20 days, and this time period corresponds to orbits in the habitable zone of this M-dwarf star. The EPOXI data processing computers are still busily calibrating the images, and the science team is deep into the process of extracting precision photometry from the images. Already we have seen that our photometric precision averages down as the inverse square root of the number of images, so our space-based data are free of the "red noise" that often plagues ground-based observations. In addition to transiting planet observations, EPOCh observed the Earth-as-a-planet. The Earth observations comprised narrow-band visible filter images, and 2- to 5-micron infrared spectroscopy, over a full Earth rotation, at three well-separated dates. The EPOCh science team will present preliminary results at the October 10-15 meeting of the AAS Division for Planetary Sciences, at Cornell University. EPOCh presentations at the DPS meeting include:
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| 2008.06.25 Deming |
Contingency Observations EPOCh observations will resume on June 27, and continue until August 31. This period of "contingency" observations will replace the science lost during the safe mode entry and telecom problems experienced in the spring. The targets for the contingent observations are TrES-2, HAT-P-4 (revisit), WASP-3, and HAT-P-7. The EPOCh photometry team has made great progress in analyzing the stellar data obtained thus far, and we are now achieving close to photon-limited signal-to-noise ratios, and the noise is averaging down as the inverse square root of time, as it should. The EPOCh Earth observations are now complete and the team is deep into the data analysis. |
| 2008.06.19 Agle |
EPOXI Burns for Comet Flyby The EPOXI flight team fired their spacecraft's engine today to refine its trajectory. This trajectory sets the stage for an encounter with comet Hartley 2 on Nov. 4, 2010. |
| 2008.05.23 Deming |
EPOCh Observations EPOCh observations resumed on May 4, as the spacecraft telecom anomaly has disappeared at greater Sun range. EPOCH is now observing transits of the Neptune-sized planet orbiting the nearby (d=10 pc) red dwarf star GJ436. The orbit of this planet is known to have a significant eccentricity (e=0.15), and this eccentricity is believed to be forced by the gravitational perturbations from a second planet. The second planet may have a mass comparable to Earth, and the EPOCh team believes it has an orbital period in the range from 20 to 30 days. Because this star is small and much less luminous than the Sun, the second planet may be close to or within the habitable zone. So searching for this "exo-Earth" is a high priority for EPOCh. EPOCh has two ways to find it. First, it may lie in the same orbital plane as the Neptune-sized planet, and may therefore transit the star while EPOCh is watching. In that case EPOCh can measure its radius, and we will be sensitive to planets nearly as small as our own Earth! A second method EPOCH is using involves looking for changes in the transit characteristics of the Neptune-sized planet, produced by the gravitational perturbations of the exo-Earth. In this case too, EPOCh has excellent sensitivity. So this is an exciting time for EPOCh, as we search for an exo-Earth orbiting a stellar neighbor of our Sun! On May 29 and June 5, EPOCh will again turn the EPOXI telescope toward our own Earth, and observe it in the visible and infrared for a full rotation. These data will be used to characterize the "Earth as an exoplanet," essentially to calibrate the properties of possible "pale blue dots" that may eventually be imaged by advanced missions such as the Terrestrial Planet Finder. The May 29 observations will be especially interesting because the Moon will "transit" the Earth while EPOCh is watching, and this is a view of the Earth-Moon system that has seldom if ever been seen before. |
| 2008.04.28 A'Hearn |
Cooling Down The spacecraft's signal strength has returned to expected performance after losing about 8dB during perihelion (closest point to the sun). At the end of last week, as the spacecraft cooled (a combination of moving further from the sun and all instruments being turned off), telemetry strength returned. Observations for EPOCh are scheduled to be resumed at the end of this week. |
| 2008.04.02 Deming |
EPOCh Observes X0-2 On March 28, EPOCh downlinked over 5000 photometric CCD frames of the metal-rich transiting planet system XO-2. The was the largest volume of data in a single downlink for EPOXI to date. Following this downlink, EPOCh observations have been paused, to investigate the cause of a weaker-than-normal downlink signal, and some slightly elevated temperatures on the spacecraft. |
| 2008.03.26 Deming |
EPOCh Observes TrES-3 EPOCh has recently completed observations of the massive hot Jupiter exoplanet, TrES-3 (pronounced "trace three"). After recovering from safe mode on March 6, EPOXI promptly observed 5 transits, and 6 secondary eclipses of TrES-3. On March 18, EPOXI observed the Earth for a full 24-hour rotational cycle, obtaining narrow-band visible images and infrared (1.5-4.5 micron) spectroscopy. The EPOCh science team will use the Earth data to define the properties of the "Earth-as-an-exoplanet," i.e. the rotational light curve of Earth's integrated light. This light curve should exhibit signatures due to cloud patterns and vegetation on the land masses, and similar signatures may eventually be observable for Earth-like exoplanets. On March 20, EPOXI turned to observe transits of the metal-rich giant planet system XO-2. |
| 2008.03.03 Duxbury |
Back to Normal Ops EPOXI exited safemode Friday (29 Feb) and is currently downlinking the EPOCh images taken before safemode entry. New EPOCh imaging will begin on Thursday (6 Mar). EPOXI is now back to normal operations. |
| 2008.02.25 A'Hearn |
Safe Mode Update The Deep Impact spacecraft continues to be in "safe mode" with that mode's very slow communication links to Earth. Although the hiatus interrupted EPOCh observations, the scientific output will not be compromised because additional observations can be carried out after the previously scheduled end of operations for EPOCh. Therefore, there has been no rush to bring the spacecraft out of safe mode, since the spacecraft is healthy and safe in that mode. Enough of the engineering data has now been brought down to Earth to give us confidence that we can bring the spacecraft out of safe mode without triggering new problems. Assuming that all goes as planned we anticipate resuming observations for EPOCh next week, beginning with downlinking the several days' worth of data that were stored on board prior to entering safe mode. |
| 2008.02.19 Duxbury |
Spacecraft in Safe Mode NASA's Deep Impact spacecraft has temporarily halted EPOCh (Extrasolar Planet Observation and Characterization) observations starting this past Sunday, Feb. 17. The pause was generated when the spacecraft entered safe mode - a condition where all but essential systems are turned off until the spacecraft receives new commands from mission control. Safe mode was entered while the spacecraft was turning to an optimal attitude to transmit data to Earth. The spacecraft is currently communicating with Earth, and EPOXI mission controllers at NASA's Jet Propulsion Laboratory in Pasadena, Calif. anticipate no major challenges to returning the spacecraft to the planned EPOCh observations. They believe the safe mode was triggered when one of the reaction wheels, which helps maintain spacecraft attitude, experienced slightly higher temperatures than what the on-board fault protection software would allow. |
| 2008.02.04 Deming |
EPOCh Observes HAT-P-4 EPOCh observations of the giant transiting planet HAT-P-4 began on January 22. The initial observations showed a pointing discrepancy that caused the star to move out of our field of view about 20% of the time. The EPOCh team was able to make some technical adjustments to the spacecraft that improved the pointing, thanks to the collaborative efforts of the flight team at JPL, the spacecraft engineers at Ball Aerospace, and the EPOCh science team. These efforts have led (as of Feb 2) to the successful collection of tens of thousands of observations of HAT-P-4, and the EPOCh science team has confirmed that the giant planet transits are seen in these data. Ongoing efforts to improve the calibration of the data will allow sensitivity to small planets that we hope to discover in our target systems. |
| 2008.01.21 A'Hearn |
PI miscellaneous thoughts On 9 January we carried out the first of our standard cruise calibrations. These observations include observations of several standard stars, both solar analogs and hot stars with few absorption lines in their spectra, both for absolute calibration of all instruments, a cluster for checking geometric distortion in the cameras, and a planetary nebula (NGC 7027) for checking the wavelength calibration of the spectrometer. This sequence, with few if any changes, will be rerun after completion of the EPOCh observations and then again just before and just after the observing program for comet Hartley 2. Due to a minor error in the lunar calibration sequence, a series of IR dark frames was not recorded but that sequence was rerun on 16 Jan and all data are now at the science data center. |
| 2007.12.31 A'Hearn |
Lunar Calibration and Flyby Today, 31 December, the Deep Impact flyby spacecraft, executed its flyby of Earth to set it on course for its EPOXI activities - observations of extrasolar planets for EPOCh and an encounter with comet Hartley 2 for DIXI. The encounter went just as expected. Analysis of tracking data over the next week or two will allow us to determine how accurately we are on track and whether a "cleanup" maneuver is needed just before we begin the EPOCh observations. Since launch, the spacecraft has executed maneuvers flawlessly and we have skipped many of our scheduled "cleanup" maneuvers, including skipping the one in late November to take out errors in the maneuver of 1 Nov. Two days ago, 29 December, we took numerous observations of the moon to calibrate our scientific instruments. The most crucial of these calibrations was a set of sweeps across the moon with the spectrometer in order to determine the "flat field" characteristics of the IR detector in the spectrometer. This is needed to carefully remove the pixel-to-pixel variations in the response of the instrument. We were unable to do this effectively on the prime mission because we passed the moon so soon after launch and this particular piece of the calibration requires a large, bright source. All of the data have been received on the ground and we are beginning our analysis of the calibration data. The spacecraft did everything we asked it to do and in general the data look very good. It will be several weeks to a couple of months before we have all these data folded into our calibration pipeline for processing the data of more direct scientific interest. |
| 2007.12.17 A'Hearn |
Scattered Light Calibration Today, 17 December, EPOXI carried out a calibration for scattered light using Earth's moon. The spacecraft is on course to get a gravity assist from Earth on 31 December and to do a primary calibration on the moon on 29 December. Many of today's 66 images were obtained with the moon outside but near the field of view of the cameras. The images were brought to the ground via the DSN to JPL and then sent to the Science Data Center. They are now available to the science team for analyzing the amount of light that is scattered into the field of view from bright objects just outside or within the field of view. |
| 2007.12.03 A'Hearn |
EPOCh has data! The EPOCh team is excited to learn that EPOXI is now a fully approved mission, and we congratulate Dr. A'Hearn and the DIXI team on their impressive plans for the Hartley 2 encounter. On November 5, EPOXI's spacecraft observed a bright (V=9) visual binary star for 12 continuous hours, as a test of pointing and photometric stability. The observations were taken using the 256 x 256 subarray mode of the HRI's CCD. The spacecraft successfully captured the star images and held them on the subarray for the full duration of the test. We were initially puzzled because they appeared to be offset from the central 128 x 128 subarray that we will use for the EPOCh observations. This is due to stellar aberration, which was not included for stellar observations during the Deep Impact mission. After correcting for aberration, the spacecraft pointing was within specifications. We are now examining Deep Impact stellar data taken since the release of the impactor. These data will refine our knowledge of the boresight between the star tracker and the HRI. Factoring in corrections for aberration, we anticipate excellent pointing precision for the EPOCh targets. Examination of the photometric time series from the test shows that, after applying flat-field calibrations, intensity is correlated with position on the CCD, so the EPOCh photometry team plans to refine the flat-fielding corrections. The photometry is already at the milli-magnitude level of precision, and even greater precision will result from more refined flat-fielding. The first EPOCh transit observations will occur on January 23, as we target a transit and eclipse of the giant, massive exoplanet HAT-P-2! |
| 2007.12.02 A'Hearn |
Hartley 2 Approved Following the surprising realization in mid-October that, despite tremendous efforts by many observatories and observers, we could not recover comet Boethin in time to plan our flyby of Earth, we recommended to NASA that we be allowed to fly to our backup target, comet Hartley 2. As indicated in previous messages, NASA allowed us to target the Earth flyby (which will happen on New Year's eve) to go to Hartley 2 and the relevant maneuver was executed on 1 Nov. Meanwhile, the team assessed the many issues associated with Hartley 2: - can we confidently deliver as much science as we promised? - does the spacecraft have enough fuel to get there reliably? - are there parts that will wear out because of the extra two years in space? - how much more will it cost just to fly the spacecraft an extra two years? On Friday, 30 Nov, we presented our plans and assessments to the NASA Science Mission Directorate. They agreed that our science was intact at comet Hartley 2 and that the margin on all mission related engineering was adequate, i.e. that the risks were low. They therefore approved our mission to comet Hartley 2. The EPOCh program of characterizing extra-solar planetary systems will be carried out, as originally planned in the first half of calendar 2008. The spacecraft will then go into hibernation for approximately two years, unless NASA approves another program with separate funding to use the spacecraft during those two years, and will be reawakened in summer 2010 for an encounter with Hartley 2 that is currently planned for 11 October 2010. |
| 2007.11.12 A'Hearn |
EPOXI's First Observations EPOXI made its first targeted (pointed at a specific target) observations during the past week. The High Resolution Instrument (HRI) was used to take repeated, white-light images of a pair of 9th magnitude stars in the constellation Ursa Major. The observations consisted of more than 1500 30-second exposures and continued for over 12 hours. The data were transmitted from the spacecraft to the ground on Thursday (8 Nov). The purpose of these observations was to test the stability of the instrument because the EPOCh program requires far higher precision in its photometry than was required for Deep Impact. Members of the EPOCh team are now working to study the details of the photometric stability in these data. Clarification: The photometric test observations for EPOCh were actually obtained on Nov 5. Due to a downlink problem in the first attempt right after the data were taken, they were not downlinked from the spacecraft to JPL's Deep Space Network until Nov 8. They were then transferred from the JPL flight operations computer to the science team's data center early on the morning (EST) of Nov 9. |
| 2007.11.05 A'Hearn |
New Target In the first half of October, Karen Meech organized an heroic effort to recover comet Boethin in time to plan the spacecraft's flyby of Earth, which would put it on target to go to the comet. The orbit is very uncertain due to the comet having been observed at only two apparitions, with no observations since 1986, and the uncertainty is so large that we would not have enough fuel on board to compensate for the uncertainty in the orbit after the flyby of Earth. This effort was not successful. As a result, I recommended to NASA that we switch to our backup target, comet 103P/Hartley 2, which has a very well defined orbit but which requires two extra years for the mission and thus additional funding from NASA. The encounter for the backup plan is on 11 October 2010. NASA authorized us to plan and execute the Earth flyby as though we were going to comet Hartley 2, while they consider whether they can afford to pay for the longer mission. The maneuver to set up the flyby of Earth was executed on 1 November and appears to have been flawless. The flyby of Earth will occur on New Year's Eve, 31 December 2007. |
| 2007.10.04 A'Hearn |
Instrument Check Today the scientific instruments on the spacecraft were turned on for the first time in more than two years. We confirmed operation of mechanical components (shutters, filter wheels) and detector readouts. The "observations" have been transmitted to Earth and everything seems normal. The images, of a random point in the sky, show stars and both the optical and the infrared detectors show nominal behavior of the background levels and the optical detectors show nominal response to an internal lamp. Detailed analysis over the next few days will determine whether anything has drifted in the two years. Observations of specific targets will start in early November. |
| 2007.09.26 A'Hearn |
DI Wakeup On Mon-Tue, 24-25 Sept 2007, we woke up the DI flyby spacecraft. During this wakeup we checked only the basic health and safety of the spacecraft and everything seems to be as expected. Since July of 2005, the spacecraft has been awakened roughly once every 6 months to check its health and safety and then put back to sleep. Now we are keeping it awake. We will obtain several days of tracking data to ensure that we know the orbit accurately. The next on-board activity is scheduled for Thur, 4 Oct, when we will turn on the scientific instruments and check out their basic functionality. The instruments have not been turned on since July 2005, but we fully expect them to be as healthy as the spacecraft. |
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