 |
 |
||
 |
|
||
 |
 |
 |
 |
 |
 |
 |
 |
 |
 |
||||||||
 |
The Planetary Society BlogBy Emily LakdawallaLRO & LCROSS Up Close Tour: Part 2, Hunting for Lunar WaterJun. 5, 2009 | 22:06 PDT | Jun. 6 05:06 UTC
by Ken Kremer
Herein I'll report further on LCROSS and then on my subsequent tour of the Atlas V launch pad and operations facilities in a later report. LCROSS purpose in life is to definitively confirm the presence or absence of water in a permanently shadowed crater near one on the moons poles. Finding water as a naturally existing resource on the moon would be a major finding with crucial implications for future human settlers. The existence of minable quantities of ice and other precious materials would enable visitors to ‘live off the land' so to speak and expedite lunar exploration and habitation. It's tremendously expensive to transport all water and other supplies up from the Earth's gravity well and back down to the moon's surface. Theoretically the ice could be used as drinking water or be converted to breathable oxygen and rocket fuel. The water could also be used as a radiation barrier. The presence of previously unknown water at the moon's poles in permanently shadowed lunar polar craters has been inferred based on the discovery of concentrated signatures of hydrogen and other science data by the Lunar Prospector and Clementine missions. The water may have been deposited by comet bombardments billions of years ago. Since the crater floors have likely never seen sunlight they act as ‘cold traps' to capture volatile materials such as water at temperatures roughly just 60 °C (110 °F) or so above absolute zero. LCROSS is in fact a grand experiment designed to unmask the hoped for water as one of the moons' most tantalizing secrets. The two main components of LCROSS are the Shepherding Spacecraft (S-S/C) and the Centaur upper stage rocket. The sheparding spacecraft sits below LRO on the combination stack.
About an hour after launch, LRO separates from LCROSS and the Centaur upper stage. LCROSS first of its kind mission is to utilize the spent Centaur as a high velocity kamikaze impactor and guide it to a spectacular man made smash-up inside a lunar crater. Neither the Centaur nor the attach ring for the LCROSS payload has ever been used in this manner before. "Post launch, LCROSS will fly-by the moon and enter into a looping orbit around the Earth. It will drag the Centaur upper stage through space for about 4 months in order to empty it of the rocket fuel which would otherwise contaminate the impact scene with the very hydrogen and oxygen for which we are searching. Residual propellants will be vented", said Kimberly Ennico at a LRO/LCROSS press briefing at the Kennedy Space Center during the STS-125 Hubble repair mission. Ennico is a payload scientist at NASA Ames in California which led the development of LCROSS.
"Mathematical calculations and Physics will be used to determine when the Centaur tank is empty. There are no measuring devices", states Ennico. "The impact will occur near the lunar South Pole around October 7 to 11 depending on the launch date". "The looping earth orbit will also allow the team to set up the right trajectory to optimize the impact angle. During this time period, LRO will be taking high resolution images of the south polar region to help select the target crater", Ennico told me in an interview. The goal is to kick up an ejecta plume of lunar debris "rising to about 10 km high and excavate perhaps 350 metric tons". Hopefully enough water ice will be ejected in the plume and for a long enough period of time that it can be detected and studied in precise and immense detail. After 4 minutes or so the debris cloud will inexorably fall back down to the moons surface and a new impact crater should be visible. "Extensive computer modeling and projectile gun studies have been conducted" to optimize and understand the impact scenario, say Ennico and LRO Project Manager Craig Tooley from NASA Goddard Spaceflight Center. "Much" was gleaned from the Deep Impact (DI) comet smashing mission. "Several DI team members are LCROSS co-investigators". "About 9 hours 40 minutes before final impact, LCROSS will itself separate from the Centaur" said Ennico. The 2200 kg Centaur will crash at over 5600 MPH (9600 km/h). "It is expected to create a debris plume 1 to 10 km wide. A flash should be visible from Earth for perhaps 1 to 2 minutes as the dust is illuminated by sunlight". 4 minutes later, LCROSS will fly directly into the ejecta plume while relaying data, spectra and photos before crashing itself to create a 2nd debris spray and a 2nd chance to measure lunar water a few miles (km) distant from the first impact but still inside the targeted crater.
LRO will closely monitor the impact from orbit with its science suite. "All but one of the LRO science instruments will be targeted", Tooley said to me. Simultaneously, a carefully coordinated armada of orbiting telescopes including Hubble precisely targets the spectacular fireworks to make as many scientific measurements as possible to maximize the data return. "The impact event will be observable from the ground by amateur astronomers with an 8 inch to 10 inch telescope", informed Ennico. "We have organized a coordinated ground based telescope campaign as well. The Deep Impact team has been a great help to us", based on their prior experience a few years back. "We need to decide on an impact point at T minus 30 days to figure out the burns and steering", according to Ennico. "We have 6 or 7 different possible crater regions in the south pole we are targeting. The targeting accuracy is 2.4 km. We could target a crater as small as 3.5 km in diameter. But the selection is also critically dependent on achieving a proper sun angle to illuminate the ejecta". "To obtain the best data signature the deepest crater desired is about 1 to 2 km. We want to maximize the ejecta and collect the data within about 4 minutes of the impact". Craig Tooley, LRO Project manager, told me that LRO could detect "as little as 0.5% water by weight in the soil". The team aims to excavate the few meters or so of lunar soil to maximize the water content. As the cloud of ejecta rises above the targets crater rim and is exposed to sunlight, any water ice or organics will vaporize and break down into their basic components. Cameras and spectrometers will measure and relay back to earth the characteristics, composition and behavior of the debris plume. LCROSS is an innovative low cost mission which uses all commercial-off-the-shelf and flight proven parts to reduce development cost, time and risk. "The spacecraft was developed and constructed on a very tight cost capped budget and fast paced schedule of just 26 months" said Ennico. The LCROSS team was offered no choice but to be ready in time for the LRO launch or they would be left behind, no excuses. LRO would not wait. "If we were not ready in time for launch we would be cancelled. It was build to launch in 2 years. I liked that challenge. LCROSS was a great mission to work on and a great learning experience because it was a new way of doing business at NASA", Ennico told me. The science payload comprises of 1 visible camera, 2 near infrared and 2 mid-infrared cameras, 1 visible light and 2 near-infrared spectrometers and one photometer. They will be powered on at one hour prior to impact and will return data until impact of the S-S/C.
"We look forward to engaging a wide cross section of the public in LCROSS' spectacular arrival at the moon and search for water ice," said LCROSS Project Manager Dan Andrews of NASA's Ames Research Center at Moffett Field, Calif. "It's possible we'll learn the answer to what is increasingly one of planetary science's most intriguing questions." As I write this, Kimberly Ennico tells me that the LCROSS team has just completed their mission ops rehearsal exercises simulating the entire intense schedule of mission events for the critical first 6 days after launch. With 2 spacecraft launching simultaneously to the same point in the sky, a lot of stress will be placed on the already taxed Deep Space Network (DSN) system as the LRO and LCROSS teams work together to share resources for a successful outcome. In part 3, I'll report on more of my LCROSS conversation with Kimberly Ennico. And in part 4, I'll describe the next exciting leg of my journey taking me from Astrotech for a special visit directly into Launch Complex 41 and the powerful Atlas V/Centaur rocket that will blast the LRO/LCROSS duo into space on one million pounds of thrust. Please look here for Part 1 of my LRO/LCROSS reports. In the meantime, check out my visit to Launch Complex 17 and the Delta II rocket during the Dawn launch here. I'd like to thank NASA, Astrotech and United Launch Alliance for truly wonderful experiences with more to come. It's now only T- minus 2 weeks to launch, currently scheduled for June 17 at 3:41 PM EDT. Planetary Society volunteer Ken Kremer is reporting for us from the Kennedy Space Center, where he is covering the upcoming launch of NASA's Lunar Reconnaissance Orbiter. Kremer is a research scientist and freelance journalist who spends his spare time giving public outreach presentations on behalf of The Planetary Society as a volunteer and NASA's Jet Propulsion Laboratory as a Solar System Ambassador. He also enjoys creating Mars mosaics. Thanks Ken! |
||||||||||
 |
 |
||||||||||
Copyright © 1993 – 2009 The Planetary Society. All rights reserved.
Privacy Policy | Contact Us | Society Updates
[ what is this? ]
[ what is this? ]