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GRAIL

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For other uses, see Grail (disambiguation).

Template:Infobox spacecraft

The Gravity Recovery and Interior Laboratory (GRAIL) is an American lunar science mission in NASA's Discovery Program, which will use high-quality gravitational field mapping of the Moon to determine its interior structure. The two small spacecraft GRAIL A and GRAIL B were launched on 10 September 2011 aboard a single launch vehicle: the most-powerful configuration of a Delta II, the 7920H-10.[1][2][3] 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.[4] The first probe entered orbit on 31 December 2011 and the second followed on 1 January 2012.[5]

Overview

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 via the Sun-Earth Lagrange point L1 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).[6][7] 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.[8]

The science phase of GRAIL will last 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 40 days.[9] 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.[10]

The orbital insertion dates were December 31, 2011 (2011-12-31) (for GRAIL-A) and January 1, 2012 (2012-01-01) (for GRAIL-B).[11]

Maria Zuber of the Massachusetts Institute of Technology is GRAIL's principal investigator. The mission's team of expert scientists and engineers also includes former NASA astronaut Sally Ride, who will lead the mission's public outreach efforts. NASA's Jet Propulsion Laboratory manages the project. As of August 5, 2011, the program has cost US$496 million.[12]

Objectives

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 gravitational field of the Moon will be mapped in unprecedented detail.[13]

Primary 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.[13] Results will begin to become available about 30 days after the collection begins.[6] The knowledge acquired will aid understanding of the evolutionary history of the terrestrial planets.[6]

Instruments

  • Ka band Lunar Gravity Ranging System (LGRS), derived from the Gravity Recovery and Climate Experiment instrument.[14] 90% of the GRACE software was reused for GRAIL.[15]
  • Radio science beacon (RSB)
  • Moon Knowledge Acquired by Middle school students (MoonKam).[16] Each MoonKAM system (one per spacecraft) consists of a digital video controller and four camera heads.[17]

Propulsion

Thrusters aboard each spacecraft are capable of producing 22 newtons (4.9 lbf).[14] 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.[18]

Science Phase

The spacecraft will be operated over a 90 day mission, with possibility for extension. That mission is divided into 3 27.3 day long nadir-pointed mapping cycles including of 2 daily 8-hour passes in view of the Deep Space Network for transmission of science and "E/PO MoonKam" data. [19]

At the end of the science phase and any mission extensions, the spacecraft will be powered down and decomissioned over a 5 day period. Each will impact the lunar surface after approximately 40 days.[19]

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[11] — 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[11] 0 days, 0 hours, 39 minutes high level winds 8 Sep 2011, 9:07 am 40% [8] Range was reconfigured for omni antennae instead of tracked ones to support 99 degree azimuth.
3 9 Sep 2011, 8:33:25 am abandoned[11] 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[11] 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[11] 0 days, 0 hours, 39 minutes

References

  1. ^ Cite error: The named reference ula was invoked but never defined (see the help page).
  2. ^ "Delta II: The Industry Workhorse" (PDF). United Launch Alliance. 2010. Retrieved 2 August 2011. {{cite journal}}: Cite journal requires |journal= (help)
  3. ^ Grey Hautaluoma (10 December 2007). "New NASA Mission to Reveal Moon's Internal Structure and Evolution". NASA. Retrieved 31 August 2011.
  4. ^ Moon-bound twin GRAIL spacecraft launch success
  5. ^ "First of NASA's GRAIL Spacecraft Enters Moon Orbit". NASA. Retrieved 1 January 2012.
  6. ^ a b c "Mission Overview". MIT. Retrieved 10 September 2011.
  7. ^ "Mission Design". NASA. Retrieved 10 September 2011.
  8. ^ a b Justin Ray (17 August 2011). "GRAIL Launch Window Chart". SpaceFlight Now. Retrieved 9 September 2011.
  9. ^ GRAIL web page. "Mission Design". MIT. Retrieved 13 April 2011.
  10. ^ 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)
  11. ^ a b c d e f Harwood, William. "NASA launches GRAIL lunar probes". CBS News. Retrieved 11 September 2011.
  12. ^ Marcia Dunn, AP Aerospace Writer (Friday, 5 August 2011). "NASA Spacecraft Begins 5-Year Trip to Jupiter". Yahoo News. Retrieved 07 September 2011. {{cite news}}: Check date values in: |accessdate= and |date= (help)
  13. ^ a b "About GRAIL". MIT. Retrieved 2011-03-12.
  14. ^ a b "Spacecraft and Payload". MIT.
  15. ^ "Operations". MIT.
  16. ^ "About GRAIL MoonKAM". Sally Ride Science. 2010. Retrieved 2010-04-15.
  17. ^ "GRAIL Launch Press Kit" (PDF). NASA. Retrieved 31 August 2011.
  18. ^ GRAIL (Gravity Recovery and Interior Laboratory)
  19. ^ a b "Mission Design". MIT.

External links

Wikimedia Commons has media related to Gravity Recovery and Interior Laboratory.
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