{"id":518,"date":"2009-12-16T23:22:27","date_gmt":"2009-12-16T23:22:27","guid":{"rendered":"http:\/\/192.168.10.99\/KES\/?p=518"},"modified":"2016-09-26T15:48:30","modified_gmt":"2016-09-26T15:48:30","slug":"518","status":"publish","type":"post","link":"https:\/\/www.kandrsmith.org\/KES\/index.php\/2009\/12\/16\/518\/","title":{"rendered":"What Happened on Impact Night?"},"content":{"rendered":"

From the LCROSS Flight Director (Paul Tompkins) Blog. Reposted from\u00a0https:\/\/blogs.nasa.gov\/lcrossfdblog\/2009\/12\/16\/post_1260990722929\/<\/a><\/p>\n

Kimberly Ennico Note: I contributed the information in Mark Shirley\u2019s addition to this entry in Paul Tompkins (Mission Operations Manager) LCROSS blog series about what was happening on the LCROSS payload during impact night. Mark was sitting in the MOCR\/Mission Operations Control Room while I was in the SOC.\/Science Operations Control across the hallway.<\/em><\/p>\n

The LCROSS mission was ultimately focused on the final four minutes of flight, starting at the time of the Centaur impact, and ending with the impact of the Shepherding Spacecraft.\u00a0 During that time, the Payload Engineer and the Science Team took operational center stage.\u00a0 Once the science payload was powered on, the team\u2019s job was to confirm the full functionality of the instruments, and then to adjust instrument settings to make sure the data we received was the best it could possibly be.\u00a0 For Impact, there were no second chances \u2013 the Shepherding Spacecraft was to be destroyed as a forgone outcome of its observation of the Centaur lunar collision.<\/p>\n

In this post, I\u2019ve invited Payload Engineer Mark Shirley to provide his perspective of impact night.\u00a0 Mark was the Payload Software Lead, in charge of the design and implementation of onboard instrument command sequences and other onboard software components, as well as a large fraction of the science-related data processing software used on the ground.\u00a0 During flight, Mark sat in the Mission Operations Control Room (MOCR) with the rest of the Flight Operations team.\u00a0 On the final day, his job was to assess and maintain the engineering functionality of the science payload in those minutes before impact.<\/p>\n

In the impact video sequence, from the public\u2019s perspective, there were a lot of things that happened operationally that were probably difficult to understand. \u00a0Mark will explain the plan for gathering data from the impact and also describe what actually happened in flight.\u00a0 On a lighter note, Mark was one half of our now famous (or notorious) \u201chigh-five malfunction\u201d that created such a buzz on the social media circuit after impact.\u00a0 He\u2019ll explain that as well. I\u2019ll let Mark take it from here.\u00a0 Enjoy!<\/p>\n

I\u2019d like to describe our plan for collecting data about the Centaur impact from the shepherding spacecraft (S-S\/C), how actual events differed from the plan, and what that says about the process of developing and flying spacecraft.\u00a0 In particular, I\u2019ll cover why some of the pictures were fuzzy and some were white and why we were sending commands during the last minutes.\u00a0 I won\u2019t touch on the scientific interpretation of the data, only the process of gathering it.\u00a0 This story contains some hard work, a few mistakes, a little nail biting tension, and finally, success.<\/p>\n

Central to the story is the type of mission LCROSS was: a cost-capped, fixed-schedule mission.\u00a0 That meant if LCROSS had been late, LRO would have flown with a dead or inactive LCROSS.\u00a0 If the project had run out of money, whatever hadn\u2019t been done wouldn\u2019t have gotten done.\u00a0 Within the LCROSS project, the instruments were in a similar position.\u00a0 The original idea was to observe the Centaur impact from Earth only.\u00a0 Onboard instruments were soon added to the design but with a total instrument budget of approximately $2 million.\u00a0 That\u2019s much less than single instruments on many other missions.<\/p>\n

Two things made success possible.\u00a0 First, project managers kept a tight focus on using the barest minimum hardware and testing required to perform the science, and went beyond that, only as the budget allowed, to increase the likelihood of success.\u00a0 Second, everyone stayed on budget. The payload team had no choice, but if any other part of the project had overrun by a lot, the payload might have been eliminated or flown only partially ready.<\/p>\n

The LCROSS Instruments<\/strong><\/p>\n

LCROSS carried nine instruments.\u00a0 Five were cameras to take pictures over a large range of wavelengths, that is, colors. One was for visible light that our eyes can see.\u00a0 Two near-infrared cameras captured mineralogy and water signatures, and two mid-infrared cameras captured thermal signatures from -60C to +500C).\u00a0 LCROSS carried three spectrometers to measure color very precisely.\u00a0 One covered ultra-violet and visible wavelengths and two covered near-infrared wavelengths.\u00a0 The latter spectrometers were the best at searching for water, and one looked down toward the Centaur impact the vapor cloud it kicked up and the other looked to the side as LCROSS passed through that cloud.\u00a0 Finally, LCROSS carried a high-speed photometer to measure the brightness of the impact flash.<\/p>\n

The instruments are described in detail here<\/a>.\u00a0 Data from all nine instruments had to share LCROSS\u2019 one Mbps (one megabit or million bits per second) radio link to the ground.\u00a0 At that rate, it takes 2 seconds to transmit a typical cell phone picture.\u00a0 This was the maximum data rate available for the LCROSS mission and used only twice: lunar swingby on June 22nd<\/sup> and impact on October 9th<\/sup>. All other instrument activities that took place during the 112 day mission used speeds less than 256 kbps (kilobits or thousand bits per second), which was sufficient for collecting data to calibrate the instruments.<\/p>\n

Link to LCROSS Instruments<\/a><\/p>\n

The Observation Plan<\/strong><\/p>\n

The two components of the LCROSS mission, the Centaur and the Shepherding Spacecraft (S-S\/C), separated about 10 hours before they reached the moon.\u00a0 At the moment the Centaur impacted, the S-S\/C was still 600 kilometers above the surface.\u00a0 Falling at 2.5 kilometers per second, the S-S\/C reached the surface 4 minutes later.\u00a0 Observations of the Centaur impact event made during those 4 minutes were the purpose of the mission.\u00a0 Unlike orbital missions that can usually try multiple times to collect data, we had just one shot.<\/p>\n

The diagram below shows the plan for observing from the S-S\/C, starting one minute before Centaur impact, at the beginning of what we called \u201cSequence 2\u201d in the NASA TV video.\u00a0 The diagram plots our intended schedule of instrument observations against time: each row represents one of the instruments (instrument abbreviations appear below each row of data), and each tick mark along a row represents one observation, either an image or a spectrum.\u00a0 Over some intervals, the observations are spaced so closely that the plot looks like a solid bar.<\/p>\n

\"1009194main_shirleyblog_observationplancropped\"<\/a><\/p>\n

Figure 1 The LCROSS impact observation plan: These timelines indicate when each image and spectra was planned to occur during the final four minutes of the mission.\u00a0 The horizontal axis represents time.\u00a0 Each row represents an instrument, and each tick mark represents the timing of a sample (an image or spectrum) from that instrument.<\/p>\n

The last four minutes were divided into three periods, called FLASH, CURTAIN and CRATER.\u00a0 Each period focused on a different aspect of the expected impact event and emphasized data collection from different instruments.<\/p>\n

FLASH started one minute before the Centaur impact and focused on the very short burst of light generated by the Centaur impact itself.\u00a0 Starting from the top of the diagram, the plan was to stop both the Visible Light Camera (VIS) and the Near-Infrared Camera #2 (NIR2).\u00a0 This would allow us to focus on NIR1 images which we felt had the best chance of catching the location of the impact flash which we expected to be visible for less than one second.\u00a0 These three cameras shared a common input to our payload computer, called the Data Handling Unit (DHU), and could not be used simultaneously. By stopping VIS and NIR2, we could run NIR1 at a faster rate (see the segment labeled \u2018A\u2019), increasing the odds it would image the flash.\u00a0 The planned sequence also increased the NIR1 exposure time to capture the flash signature even if it was very faint.\u00a0 We knew this would produce a badly overexposed image of the illuminated lunar surface, but our goal was to locate the impact.\u00a0 We\u2019d have plenty of other pictures of the surface.\u00a0 This sort of shifting attention between cameras accounts for the periods where one camera image would stop updating for a while.<\/p>\n

We also designed the FLASH strategy for the spectrometers around our expectation of a dim, short duration flash event.\u00a0 Near Infrared Spectrometer #1 (NSP1), the main water-detection instrument, was put into a high-speed, low resolution mode (represented by the yellow bar).\u00a0 The Visible and Ultraviolet light Spectrometer (VSP) was commanded to take long exposures, and Total Luminescence Photometer (TLP) was powered early enough to reach equilibrium and be at its most sensitive for the flash event.<\/p>\n

The second phase, CURTAIN, started just after the Centaur impact and ran for three minutes.\u00a0 Its purpose was to take spectra and images of the expanding vapor and dust clouds thrown up by the impact.\u00a0 CURTAIN was the most important period and also the simplest.\u00a0 All instruments ran in their default modes, as follows.\u00a0 The DHU shifted between the three analog cameras in a stuttering pattern \u2013 VIS, VIS, NIR1, NIR2 \u2013 repeating.\u00a0 Both thermal cameras monitored the plume shape and temperature. The two downward-facing spectrometers (NSP1 and VSP) looked for water and other chemicals.\u00a0 The side-looking spectrometer (NSP2) also looked for water and other compounds, but from sunlight scattered or absorbed by the dust and vapor cloud.\u00a0 The TLP continued to take data during this period, but it\u2019s primarily function was during FLASH.<\/p>\n

The goal of CRATER, the final period, was to image the crater made by the Centaur impact to get its precise location and, more importantly, its size.\u00a0 From its size and their detailed models of crater formation, the LCROSS Science Team can potentially tell us how the crater evolved over the few seconds of its formation and how much material was excavated.\u00a0 The primary instruments in this period were the two thermal cameras, MIR1 and MIR2.\u00a0 Their sample rates were increased relative to those for CURTAIN.\u00a0 To image the crater in a second frequency band, NIR2, the more sensitive near infrared camera, was commanded to its most sensitive setting.\u00a0 NIR1 and VIS would not be used during this period because neither was sensitive enough to see anything in the permanently shadowed area.\u00a0 All spectrometers would continue running to look for light reflected off of any plume or vapor cloud.\u00a0 At the end of this phase, the S-S\/C would fall below the rim of Cabeus Crater, cutting off radio transmission to Earth, and then impact the surface a couple of seconds later.<\/p>\n

There were three keys to making this plan work:<\/p>\n