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GRAIL

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This is an old revision of this page, as edited by 69.7.77.20 (talk) at 18:24, 18 December 2012 (→‎Transit phase: Corrected Lagrange point designation per http://solarsystem.nasa.gov/grail/missiondesign.cfm - Sun-Earth not Earth-Moon). The present address (URL) is a permanent link to this revision, which may differ significantly from the current revision.

For other uses, see Grail (disambiguation).

Template:Infobox spacecraft

The Gravity Recovery and Interior Laboratory (GRAIL) was an American lunar science mission in NASA's Discovery Program which used high-quality gravitational field mapping of the Moon to determine its interior structure. The two small spacecraft GRAIL A (Ebb) and GRAIL B (Flow)[1] were launched on 10 September 2011 aboard a single launch vehicle: the most-powerful configuration of a Delta II, the 7920H-10.[2][3][4] GRAIL A separated from the rocket about nine minutes after launch, GRAIL B followed about eight minutes later. They arrived at their orbits around the Moon 24 hours apart.[5] The first probe entered orbit on 31 December 2011 and the second followed on 1 January 2012.[6] The two spacecraft impacted the Lunar surface on December 17, 2012.[7]

Overview

Fourth grade students at Emily Dickinson Elementary School in Bozeman, Montana who suggested names Ebb and Flow.[1]

Maria Zuber of the Massachusetts Institute of Technology is GRAIL's principal investigator. NASA's Jet Propulsion Laboratory manages the project. As of August 5, 2011, the program has cost US$496 million.[8] Upon launch the spacecraft were named GRAIL A and GRAIL B and a contest was opened to school children to select names. Nearly 900 classrooms from 45 states, Puerto Rico and the District of Columbia, participated in the contest. The winning names, Ebb and Flow, were suggested by 4th grade students at Emily Dickinson Elementary School in Bozeman, Montana.[1]

Each spacecraft transmits and receives telemetry from the other spacecraft and Earth-based facilities. By measuring the change in distance between the two spacecraft, the gravity field and geological structure of the Moon can be obtained. The two spacecraft are able to detect very small changes in the distance between one another. Changes in distance as small as one tenth of a micron—or half the diameter of a human hair—are detectable and measurable.[9] The gravitational field of the Moon will be mapped in unprecedented detail.[10]

Objectives

  • Map the structure of the lunar crust and lithosphere
  • Understand the asymmetric thermal evolution of the Moon
  • Determine the subsurface structure of impact basins and the origin of lunar mascons
  • Ascertain the temporal evolution of crustal brecciation and magmatism
  • Constrain the deep interior structure of the Moon
  • Place limits on the size of the Moon's inner core

The data collection phase of the mission will last 90 days, and will be followed by 12 months of data analysis.[10] Results will begin to become available about 30 days after the collection begins.[11] The knowledge acquired will aid understanding of the evolutionary history of the terrestrial planets and computations of lunar orbits.[11]

Spacecraft

Instruments

Gravity map of the moon by GRAIL
  • Ka band Lunar Gravity Ranging System (LGRS), derived from the Gravity Recovery and Climate Experiment instrument.[12] 90% of the GRACE software was reused for GRAIL.[13]
  • Radio science beacon (RSB)
  • Moon Knowledge Acquired by Middle school students (MoonKAM).[14] Each MoonKAM system (one per spacecraft) consists of a digital video controller and four camera heads.[15] Click here for a MoonKAM photo from lunar orbit.

Propulsion

Thrusters aboard each spacecraft are capable of producing 22 newtons (4.9 lbf).[12] Each spacecraft was fueled with 103.5 kilograms (228 lb) of hydrazine to be used by the thrusters and main engine to enable the spacecraft to enter lunar orbit and transition to the science phase of its mission. The propulsion subsystem consists of a main fuel tank and a He-repressurization system which will be activated shortly after lunar orbit insertion.[16]

Mission profile

Launch attempts

All times are in EDT (UTC-4).

Attempt Planned Result Turnaround Reason Decision point Weather go (%) Notes
1 8 Sep 2011, 8:37:06 am scrubbed[17] — high level winds 8 Sep 2011, 8:30 am 40% A weather balloon was released minutes before the decision point to take the latest readings of upper level winds and Air Force weather reconnaissance aircraft were aloft beginning at 7 am.
2 8 Sep 2011, 9:16:12 am scrubbed[17] 0 days, 0 hours, 39 minutes high level winds 8 Sep 2011, 9:07 am 40% [18] Range was reconfigured for omni antennae instead of tracked ones to support 99 degree azimuth.
3 9 Sep 2011, 8:33:25 am abandoned[17] 0 days, 23 hours, 17 minutes rocket propulsion 40% An issue with the rocket's propulsion system was detected while the Delta 2 rocket was drained of fuel.
4 10 Sep 2011, 8:29:45 am scrubbed[17] 0 days, 23 hours, 56 minutes high level winds 10 Sep 2011, 8:21 am 60%
5 10 Sep 2011, 9:08:52 am Success[17] 0 days, 0 hours, 39 minutes

Transit phase

GRAIL-transit-Earth-Moon

Unlike the Apollo program missions, which took three days to reach the Moon, GRAIL made use of a three- to four-month low-energy trans-lunar cruise well outside the Moon's orbit and passing near the Sun-Earth Lagrange point L1 before looping back to rendez-vous with the Moon. This extended and circuitous trajectory enabled the mission to reduce fuel requirements, protect instruments and reduce the velocity of the two spacecraft at lunar arrival to help achieve the extremely low 50 km (31 mi) orbits with separation between the spacecraft (arriving 24 hours apart) of 175 to 225 km (109 to 140 mi).[11][19] The very tight tolerances in the flight plan left little room for error correction leading to a launch window lasting one second and providing only two launch opportunities per day.[18]

Science phase

The science phase of GRAIL lasted for 90 days. Following the science phase (or extended mission phase), a five-day decommissioning period is planned, after which the spacecraft will impact the lunar surface in about 3 days.[20] The gravity mapping technique is similar to that used by Gravity Recovery and Climate Experiment (GRACE), and the spacecraft design is based on XSS-11.[21]

The orbital insertion dates were December 31, 2011 (2011-12-31) (for GRAIL-A) and January 1, 2012 (2012-01-01) (for GRAIL-B).[17]

The spacecraft will be operated over a 90 day mission, with possibility for extension. That mission is divided into three 27.3 day long nadir-pointed mapping cycles including of two daily 8-hour passes in view of the Deep Space Network for transmission of science and "E/PO MoonKam" data.[22]

Terminal phase

Ebb and Flow's Final Moments
GRAIL's Final Resting Spot

At the end of the science phase and a mission extensions, the spacecraft was powered down and decommissioned over a five-day period. The spacecraft impacted the lunar surface on December 17, 2012.[22][23] [24][25][26][27] Both spacecraft impacted an unnamed lunar mountain between Philolaus and Mouchez at 75°37′N 26°38′W / 75.62°N 26.63°W / 75.62; -26.63. Ebb, the lead spacecraft in formation, impacted first. Flow impacted moments later. Each spacecraft was traveling at 3,760 miles per hour (6,050 km/h). A final experiment was conducted during the final days of the mission. Main engines aboard the spacecraft were fired, depleting remaining fuel. Data from that effort will be used by mission planners to validate fuel consumption computer models to improve predictions of fuel needs for future missions.[28] NASA has announced that the crash site will be named after GRAIL collaborator and first American woman in space, Sally Ride.[29]

References

  1. ^ a b c Agle, DC. "Montana Students Submit Winning Names for NASA Lunar Spacecraft". NASA JPL.
  2. ^ Cite error: The named reference ula was invoked but never defined (see the help page).
  3. ^ "Delta II: The Industry Workhorse" (PDF). United Launch Alliance. 2010. Retrieved 2 August 2011. {{cite journal}}: Cite journal requires |journal= (help)
  4. ^ Grey Hautaluoma (10 December 2007). "New NASA Mission to Reveal Moon's Internal Structure and Evolution". NASA. Retrieved 31 August 2011.
  5. ^ Moon-bound twin GRAIL spacecraft launch success
  6. ^ "First of NASA's GRAIL Spacecraft Enters Moon Orbit". NASA. Retrieved 1 January 2012.
  7. ^ GRAIL Twins crash into the Moon to complete highly successful Mission
  8. ^ Marcia Dunn, AP Aerospace Writer (Friday, 5 August 2011). "NASA Spacecraft Begins 5-Year Trip to Jupiter". Yahoo News. Retrieved 7 September 2011. {{cite news}}: Check date values in: |date= (help)
  9. ^ Washington Post December 17, 2012
  10. ^ a b "About GRAIL". Massachusetts Institute of Technology. Retrieved 2011-03-12.
  11. ^ a b c "GRAIL: Mission Overview". MIT. Retrieved 10 September 2011.
  12. ^ a b "Spacecraft and Payload". MIT.
  13. ^ "GRAIL: Mission Operations & Data Processing". MIT. Retrieved 2012-12-14.
  14. ^ "About GRAIL MoonKAM". Sally Ride Science. 2010. Retrieved 2010-04-15.
  15. ^ "GRAIL Launch Press Kit" (PDF). NASA. Retrieved 31 August 2011.
  16. ^ GRAIL (Gravity Recovery and Interior Laboratory)
  17. ^ a b c d e f Harwood, William. "NASA launches GRAIL lunar probes". CBS News. Retrieved 11 September 2011.
  18. ^ a b Justin Ray (17 August 2011). "GRAIL Launch Window Chart". SpaceFlight Now. Retrieved 9 September 2011.
  19. ^ "Mission Design". NASA. Retrieved 10 September 2011.
  20. ^ "GRAIL: Mission Design". Massachusetts Institute of Technology. Retrieved 13 April 2011.
  21. ^ Taylor Dinerman (Monday, 31 December 2007). "Is XSS-11 the answer to America's quest for Operationally Responsive Space?". The Space Review. Retrieved 31 August 2011. {{cite news}}: Check date values in: |date= (help)
  22. ^ a b "GRAIL: Mission Design". MIT.
  23. ^ "NASA GRAIL Twins Complete Their Moon Impact". NASA. 2012-12-17. Retrieved 2012-12-17.
  24. ^ Wall, Mike. "Twin GRAIL probes readied for crash into Moon". MSNBC. Retrieved 2012-12-13.
  25. ^ Wall, Mike (2012-12-11). "Twin NASA Probes to Crash into Moon Next Week". Space.com. Retrieved 2012-12-13.
  26. ^ "Twin NASA spacecraft prepare to crash into moon". Phys.Org. 2012-12-13. Retrieved 2012-12-13.
  27. ^ Knapp, Alex (2012-12-14). "NASA Prepares To Crash Its Probes Into The Moon". Forbes. Retrieved 2012-12-13.
  28. ^ http://www.jpl.nasa.gov/news/news.php?release=2012-396&cid=release_2012-396
  29. ^ http://www.space.com/18944-nasa-grail-moon-crash-sally-ride.html
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