LCROSS Frequently Asked Questions

 

This is a strictly unofficial page of questions and answers related to amateur observations of the LCROSS impact. Although some answers supplied by LCROSS scientists in response to specific questions have been paraphrased, most of the questions are both posed and answered by Group members, so the answers may not be correct. For more authoritative information, and for information about LCROSS in general, consult the official LCROSS FAQ.     Related messages: 1

 

 

1. What is LCROSS?

 

LCROSS is a NASA-funded space mission whose goal is to impact (and observe the impact of) a large rocket booster onto the shadowed floor of a crater near one of the Moon's poles.

 

 

2. Who is responsible for this website?

 

The LCROSS Observing Google Group was created by Brian Day, an amateur astronomer from the Silicon Valley area, and LCROSS Education and Public Outreach Lead.  The group is managed by Rick Baldridge , another Silicon Valley amateur, and Paul Mortfield.   

 

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3. When will the LCROSS impact occur?

 

The spacecraft carrying LCROSS launched from Cape Canaveral on June 18, 2009 at 5:32 p.m. EDT; and a south polar impact is currently projected for 11:31:30 UT on October 9, 2009 (as listed under the launch photo on the LCROSS/NASA Ames homepage).  According to a presentation by Galal (2008; slide 11) the spacecraft takes about 5 days to reach the Moon, at which point it can be targeted to swing over the intended pole, impacting there a total of approximately 86 or 114 days after launch; or it can be targeted to swing over the opposite pole, impacting at the intended pole 100 days after launch. A 72 day plan (swinging over the opposite pole from the intended one) is also possible. The presentation also indicates that the exact timing of the impact can be adjusted, during the flight, by as much as +/-12 hours. That capability appears to have been lost as result of a spacecraft pointing problem on August 22nd which consumed about half the fuel budget. The appearance of the Moon and the areas of the Earth from which it could be observed on the impact date are illustrated here . The impact area is more officially illustrated in the Principal Investigator's PowerPoint presentation (7.2 MB, also available as a smaller PDF file).

Update:  The LCROSS impact is now history.  See Question 25 for more details of what happened and what was learned.

 

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4. Where will the impact occur?

 

The LCROSS spacecraft is being directed towards an impact point in the crater Cabeus (see Sept. 28, 2009 announcement).    The short list of south polar sites that were considered included the following possible targets:

 

SP_A (Faustini)    87.2°S/89°E
SP_B (Shoemaker)    88.5°S/50°E
SP_C (Cabeus)    85.6°S/308.9°E
SP_CB (Cabeus B)    81.9°S/305.3°E
SP_CC (no IAU name)    83.9°S/338.9°E
SP_D (Haworth)    87.4°S/355°S
SP_F (no IAU name)    82.3°S/12°E
SP_G (no IAU name)    84.3°S/1°E

In addition to the targets listed above, the graphic includes "SP_E" which is indicated as a point inside Shackleton.  An impact in Cabeus A was also considered.

 

See the Finders page for more information about the location of these potential impact points.  A webpage illustrating the observing circumstances on the impact date is also available.

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5. Have any other details of the impact sites been announced?

 

The LCROSS science team has repeatedly mentioned that they are focusing attention on certain "sweet spots" inside the announced target craters, and the impact will presumably be directed towards one of these.  At one point, the "sweet spot" was described as being in crater Cabeus A, presumably the purple area depicted in the zoomed graphic from the crater selection press release, which is actually not part of Cabeus A, but rather a separate 19-km diameter crater partially overlaying its rim.  It has been informally named "Cabeus A1".  Some of the reasons for selecting Cabeus A1 are explained in a PDF file on the LCROSS website. However, the decision to target "Cabeus A1" was not final, and has been changed to site in the neighboring crater, Cabeus (lunar craters are named by proximity, and despite the similarity of names, there is no necessary geologic relation between the sites).  The location within Cabeus has not been finalized.

 

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6. What role will amateurs play in the preparations for the impact?

 

The main role that has been announced for amateur astronomers is the assembly of a photographic atlas of the Moon's poles, showing their appearance with a variety of lightings and librations. Such an atlas would assist professional Earth-based astronomers in pointing their telescopes at recognizable targets, especially if the photos are taken under conditions similar to those that will obtain in the hours before impact. Many photos of the Moon's poles were undoubtedly taken from professional observatories during the heyday of Earth-based lunar photography in the 1960's, but aside from a handful that were published in printed atlases from that era, they do not seem to be readily accessible to the LCROSS team.

 

 

7. Does the LCROSS team have other resources to assist in Earth-based targeting?

 

Yes.  The LCROSS science team are reportedly able to simulate the lighting and geometry expected from Earth using digital elevation maps generated with data returned by Earth-based radar and Moon-orbiting spacecraft such as Kaguya.  However, the results to date have not been as satisfactory as might be hoped and none of the results have been made publicly available (Heldmann, 2009). Amateur observations may help by supplying missing information on the relative albedos (reflectances) of the features as seen from Earth. The LCROSS scientists are reportedly also reviewing new data being returned by the LRO spacecraft (with which it was launched).

 

 

8. Who is coordinating the amateur observing effort?

 

According to recent LCROSS presentations, Dr. Jennifer Heldmann is the Observation Coordinator. Her job includes coordinating not only amateur programs, but also those being planned at professional observatories.

 

 

9. What are training sessions?

 

Training sessions are times that have been set aside at professional observatories for practicing pointing at and photographing targets at the Moon's poles. Amateur photos are sometimes solicited in connection with these exercises.

 

 

10. What professional observatories will be making observations of the LCROSS impact from Earth?

 

A list of NASA-approved proposals for using specific Earth-based observatories has been announced. The impact was originally planned to be timed in such a way as to make possible simultaneous nighttime observations from Hawaii and South America,  but the current plan seems to be to observe from Hawaii and the western continental United States.  A current list of sites expected to participate in the program can be found on the Ground and Space Based Observations page. The list now includes professional observatories in South Korea, and South Africa that could presumably monitor the impact site in the hours after the event.  In addition to the Earth-based observatories, space-based facilities are one the "confirmed" list.  These include  the Hubble Space Telescope, LRO, Odin.

 

11. When is the next training session?

 

No future training sessions have been announced.

 

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12. Will amateurs be able to see the impact?

 

Amateurs in those parts of the world where the sky is dark and Moon above the horizon at the moment of impact may be able to catch glimpses of the dust plume spreading out from the impact site for a minute or two after impact. Particles in the dust cloud will rise into the sunlight above the shadowed crater, where they can be seen by reflected light. However, unless the dust is extremely fine, the particles will likely fill only a small fraction of the available space, so the intensity of the reflection will be low, and it will probably be difficult to discern except against a dark background. The particles may also be concentrated at the edges of the curtain, making reflected light visible mostly in two thin sections at the extremes of an expanding wave. The instantaneous flash from the impact itself will likely be hidden from view, either by intervening terrain or by the transient crater that forms as part of the impact. The permanent crater left by the impact is never expected to be observable by amateurs: it will be too small (~10-20 m in diameter) and in permanent shadow.

Recent estimates by LCROSS scientists assign to the densest concentrations of  sunlit ejecta grains a surface brightness as seen from Earth (at visible wavelengths) equivalent to as much as 4 magnitudes per square arc-sec (about the same as the surface of Mars), if the grains at 70 microns in diameter, or even brighter if the grains are more finally divided.  This would make those parts of the plume about as bright as the solid sunlit lunar surface.  Given other descriptions of the plume at such altitudes being very tenuous, there is reason to doubt the accuracy of these brightness estimates. Peak surface brightnesses from the plume as low as 11 mpsas are not impossible. Two-dimensional graphics of the possible appearance of the cloud of ejecta grains as seen in projection from Earth (though not specific to the Cabeus A1 impact) are available in articles by Goldstein and Summy, as well as in a poster on the official ground-based Observations page.

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13. How large will the ejecta plume be?

 

Estimates seem to range up to about 20 km wide by 5 km high, but the suspended particles responsible for the reflected light observable from Earth will be concentrated near the bottom, and will drain rapidly out of the cloud after a minute or two.  According to Bart (2008, p. 14), maximum visibilty is expected during the period from 10 to 60 sec after impact, during which interval the diameter of the cloud will expand from about 2 to 20 km, and the amount of material more than 2 km above the surface (and therefore in sunlight) will be greatest.  The cloud will continue to expand horizontally, reaching a diameter of roughly 150 km after 5 minutes, but it will be much fainter then since most of the material will have drained out. As described in the previous answer, the horizontal distribution of brightness will most likely be highly non-uniform, with the reflecting particles probably concentrated at the edges of the expanding wave .

 

 

14. What will the geometry be like at the moment of impact?

 

The October 9th impact will occur with the Moon's south pole tilted sightly towards Earth, and the target crater well onto the visible disk.  Presumably as dust rises and spreads outward from the impact point, the first parts of the ejecta plume will become visible over the shadowed interior of the target crater.  The upper parts of the plume will then spread over the sunlit far inner wall of that crater, and the sunlit terrain beyond.  It is unclear if the plume will add or subtract to the brightness in the sunlit areas.  See this page for typical viewing geometries.

 

 

15. What will the lighting conditions be like at the moment of impact?

 

Many considerations regarding lighting conditions, not all of which can be simultaneously achieved, go into the choice of the most favorable impact date.  The dust cloud following the impact will be visible primarily by reflected sunlight and to maximize the chance of seeing its lowest and densest parts (especially with the instruments on the shepherding spacecraft) it is desirable to choose a geometry in which sunlight is available at the minimum possible height above the shadowed impact site.  To accomplish this, the date was chosen to make the sun angle over the impact crater  as large as possible (for an impact at the center of a 20 km diameter crater, if the sun's rays are horizontal the first available rays of sunlight will be above the impact site by the height of the shadowing crater rim; each 1 deg increase in sun angle lowers that height by about 175 m). 

In the early mission planning, somewhat arbitrary additional constraints were also imposed to "optimize" viewing conditions from Earth, but these may not maximize the brightness or contrast of the plume relative to background features.  Among these constraints are the desires to have the Moon at least 45 degrees above the horizon and the Sun 30 degrees below the horizon ("two hours before/after sunrise/sunset") from at least some Earth-based observatories, and to be "30 degrees away" from Full Moon.  In normal astronomical terminology these requirements can be roughly translated into saying that the elongation of the Moon from the Sun is wished to be at least 75 degrees, but no more than 150 degrees.  This translates into an illumination at the time of impact of roughly 37 to 93%.  At 11:30 UT on 2009 Oct 09, the Moon as a whole, as viewed from most locations on Earth, will be 71% illuminated.

 

16. Are there any more detailed predictions of what the impact will look like from Earth?

 

According to Heldmann (2009), the LCROSS science team has detailed best-guess predictions showing the expected two-dimensional distribution of brightness contours in the ejecta plume as seen in projection from Earth at various times after impact. These charts have not yet been made public. Of course, since a dust cloud on the Moon has never before been successfully imaged from Earth, there is considerable uncertainty in all such predictions.

 

 

17. How do I submit images?

 

The procedure for submitting images to the present group is described here. Images of the actual impact, and ones of assistance in planning for observations of the impact, should be submitted to the official NASA site that has been established for this purpose.

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18. Are past observations of the Moon's poles wanted?

 

Yes. The present group welcomes all photos of the Moon's poles, provided the date, time and location (on Earth) from which they were taken is known. The NASA sites seeks only images of the south polar impact region.  Some photos taken on key dates in the past are actually more likely to match the combination of lighting and libration that will occur on impact night than will any that can be taken between now and then.

 

 

19. How do I know if my image shows one of the target regions?

 

Group member Kurt Fisher has assembled a page with a few images pointing out the locations of the currently announced possible targets in relation to more readily observable features with a few different lightings and librations.  The actual target locations are never visible (because they are permanently shadowed), but the rims or the craters in which they are located are often lit by sunlight. 

 

 

20. Are amateur photos of the actual impact desired?

 

Yes. The LCROSS science team is seeking as many observations with as many kinds of instruments as possible. They should be submitted to the NASA site.

 

 

21. What will be the best way for amateurs to observe the impact?

 

That, of course, depends on the details of what the impact will look like. Rick Baldridge and Derek Breit are recommending a low-light video system of the sort used for documenting stars grazing by the Moon's polar peaks. NASA itself predicts that apertures of 10-12 inches will be required to observe the impact.  Additional advice can be found on the NASA amateur image collection website.

 

22. What other observations would be useful?

 

As Kurt Fisher has pointed out, there appears to be little data available on the brightness of sunlit features in the polar regions, against which background the sunlit ejecta cloud will likely be seen. Modern CCD cameras make it relatively easy for amateurs to record the intensities of such features compared to better documented ones closer to the Moon's center at a variety of phases. Such data would improve our understanding of how the anticipated cloud will look.

 

23. What are the best sites for finding official news of the NASA LCROSS mission?

 

Internet search engines will return links to two websites associated the NASA and LCROSS: the current NASA LCROSS News and Features Stories Site (2/2009) on the main NASA public website and an outdated LCROSS News site at NASA Ames Research Center (7/2008). NASA LCROSS also maintains a NASA LCROSS Twitter page and a NASA LCROSS Facebook page which are useful in that announcements and LCROSS-related news stories in non-NASA publications may only be noticed or may be noticed first on the Twitter or Facebook pages and not on the News and Feature Stories site. LCROSS Flight Director Paul D. Tompkins maintains a blog. Northrop Grumman Corp., the contractor who built the LCROSS satellite, also has a Northrop Grumman LCROSS site, although separate searches of News and Media-Press Kits section should be done to find current information.  The NASA Launch Schedule website maintains the current launch schedule.  Related materials may also be found on the NASA LRO site. For a summary of sites with LCROSS news, see the links page.

 

24. What other amateur observing campaigns are active?

• South America: Valmir Martins de Morais - valmirmmorais@yahoo.com.br  

  Coordenador da LCROSS Lunar Impact - SL/REA Campaign

  
  

25. What happened?

The impact of the Centaur rocket stage happened as scheduled, on October 9, 2009, apparently at around 11:31 UT, followed by that of the Shepherding Spacecraft about 4 minutes later.  A timeline of the morning's events can be found at SpaceWeather.com.

A good summary of preliminary results and observations can be found in Alan MacRobert's report on the Sky and Telescope website, including links to spectacular adaptive optics images of the impact region taken with the 200-inch Hale Telescope on Mount Palomar.  Unfortunately even these show no obvious evidence of a sunlit ejecta plume (although the frames posted on the internet, taken 10 and 15 seconds after impact, may have been taken too early and not deeply enough exposed to show effects).  The Palomar observations (at 2.1 microns) make it seem unlikely that amateurs will have been able to detect anything at visible wavelengths.  A faint impact flash was reportedly observed in the infrared by LCROSS's own instruments on the Shepherding Spacecraft; and evidence of an ejecta plume has been reported by two instruments on the companion LRO spacecraft.  Dr. Diane Wooden, observing from the Keck II telescope in Hawaii, is also hopeful of having seen something in the infrared from Earth, but her results have not been analyzed yet.  The Shepherding Spacecraft did not at first appear to see any obvious evidence of an ejecta plume at visible wavelengths, but one was later detected in enhanced images. 

A news story from Nature magazine shows an image of what is purportedly a 20 m diameter wide crater observed by the Shepherding Spacecraft in the infrared.  The impact crater could presumably not have been imaged at visible wavelengths since the impact occurred in a permanently shadowed region, which would have remained in darkness after the impact.  Despite the absence of a spectacular impact, the Nature story is hopeful that good scientific results will appear after there has been time to analyze the combined results from the instruments on LCROSS and LRO.

There do not seem to be any reports regarding whether the OH cloud that was predicted to be observable from Earth for many hours after impact was looked for, or seen.

Sky and Telescope added a second blog page with somewhat more recent results.  The LCROSS multimedia page has images in addition to those featured on their news page.

The first scientific results were made available through a NASA press release and news conference on November 13, 2009.    Portions of the news conference are available from CNN and YouTube.  As usual, Sky and Telescope's description of those results is clearer and more concise than NASA's. Additional results will reportedly be presented at the LEAG 2009 conference, November 16-19, 2009, but none of the LCROSS-related presentations currently appear to be on-line.