Operator | NASA / JPL [1] [2] |
---|---|
COSPAR ID | 2011-046 (A, B) |
SATCAT no. | 37801, 37802 |
Website | moon |
Mission duration | 1 year, 3 months, 7 days, 9 hours |
Spacecraft properties | |
Manufacturer | Massachusetts Institute of Technology, LMSS |
Launch mass | 202.4 kg (each) [3] |
Dry mass | 132.6 kg (292 lb) |
Power | (Solar array / Li-ion battery) |
Start of mission | |
Launch date | September 10, 2011, 13:08:52.775 UTC |
Rocket | Delta II 7920H-10 D-356 |
Launch site | Cape Canaveral SLC-17B |
Entered service | December 31, 2011 (Ebb) January 1, 2012 (Flow) |
Orbital parameters | |
Reference system | Selenocentric |
Regime | Polar orbit [4] |
Semi-major axis | 1,788.0 kilometres (1,111.0 mi) |
Periselene altitude | 25 kilometres (16 mi) |
Aposelene altitude | 86 kilometres (53 mi) |
Period | 113 minutes |
Lunar impactor | |
Impact date | GRAIL A: December 17, 2012, 22:28:51 UTC |
Impact site | 75°36′30″N33°24′15″E / 75.6083°N 33.4043°E |
Lunar impactor | |
Impact date | GRAIL B:December 17,2012,22:29:21 UTC |
Impact site | 75°39′01″N33°09′51″E / 75.6504°N 33.1643°E |
|
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) [5] [6] were launched on 10 September 2011 aboard a single launch vehicle:the most-powerful configuration of a Delta II,the 7920H-10. [1] [7] [8] 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 25 hours apart. [9] [10] The first probe entered orbit on 31 December 2011 and the second followed on 1 January 2012. [11] The two spacecraft impacted the Lunar surface on December 17,2012. [12]
Maria Zuber of the Massachusetts Institute of Technology was GRAIL's principal investigator. NASA's Jet Propulsion Laboratory managed the project. NASA budgeted US$496 million for the program to include spacecraft and instrument development,launch,mission operations,and science support. [13] 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. [6]
Each spacecraft transmitted and received 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 was obtained. The two spacecraft were able to detect very small changes in the distance between one another. Changes in distance as small as one micrometre were detectable and measurable. [14] [15] The gravitational field of the Moon was mapped in unprecedented detail. [4] [16] [17] [18] [19]
The data collection phase of the mission lasted from 7 March 2012 to 29 May 2012,for a total of 88 days. A second phase,at a lower altitude,of data collection began 31 August 2012, [20] and was followed by 12 months of data analysis. [4] On 5 December 2012 NASA released a gravity map of the Moon made from GRAIL data. [21] The knowledge acquired will aid understanding of the evolutionary history of the terrestrial planets and computations of lunar orbits. [22]
Thrusters aboard each spacecraft were capable of producing 22 newtons (4.9 lbf). [23] 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 consisted of a main fuel tank and a Re-repressurization system which were activated shortly after lunar orbit insertion. [27]
Attempt | Planned | Result | Turnaround | Reason | Decision point | Weather go (%) | Notes |
---|---|---|---|---|---|---|---|
1 | 8 Sep 2011,8:37:06 am | scrubbed [28] | — | 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 [28] | 0 days,0 hours,39 minutes | high level winds | 8 Sep 2011,9:07 am | 40% [29] | Range was reconfigured for omni antennae instead of tracked ones to support 99 degree azimuth. |
3 | 9 Sep 2011,8:33:25 am | abandoned [28] | 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 [28] | 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 [28] | 0 days,0 hours,39 minutes |
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 rendezvous 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 25 hours apart) of 175 to 225 km (109 to 140 mi). [22] [30] 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. [29]
The primary science phase of GRAIL lasted for 88 days, from 7 March 2012 to 29 May 2012. It was followed by a second science phase that ran from 8 Aug 2012 into early Dec 2012.
The gravity mapping technique was similar to that used by Gravity Recovery and Climate Experiment (GRACE), and the spacecraft design was based on XSS-11. [31]
The orbital insertion dates were December 31, 2011 (for GRAIL-A) and January 1, 2012 (for GRAIL-B). [28] The initial lunar orbits were highly elliptical near-polar, and were later lowered to near-circular at about 25-86 km altitude with a period of about 114 minutes. [32]
The spacecraft were operated over the 88-day acquisition phase, divided into three 27.3 day long nadir-pointed mapping cycles. Twice each day there was an 8-hour pass in view of the Deep Space Network for transmission of science and "E/PO MoonKam" data. [33]
The first student-requested MoonKam images were taken by Ebb from 2012 March 15-17 and downlinked to Earth March 20. More than 2,700 schools spanning 52 countries were using the MoonKAM cameras. [34]
Flow's MoonKam camera captured LRO as it flew by at a distance of about 12 miles (20 km) on May 3. It's the first footage of a moon-orbiting robotic spacecraft taken by another one. [35]
At the end of the science phase and a mission extension, the spacecraft were powered down and decommissioned over a five-day period. The spacecraft impacted the lunar surface on December 17, 2012. [33] [36] [37] [38] [39] [40] Both spacecraft impacted an unnamed lunar mountain between Philolaus and Mouchez at 75°37′N26°38′W / 75.62°N 26.63°W . Ebb, the lead spacecraft in formation, impacted first. Flow impacted moments later. Each spacecraft was traveling at 3,760 miles per hour (1.68 km/s). 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. [41] NASA has announced that the crash site will be named after GRAIL collaborator and first American woman in space, Sally Ride. [42]
Gravity passes through matter. In addition to surface mass, a high-resolution gravity field gives a blurred, but useful, look below the surface. Analyses of the GRAIL data have produced a series of scientific results for the Moon.
Mare Orientale is a lunar mare. It is located on the western border of the near side and far side of the Moon, and is difficult to see from an Earthbound perspective. Images from spacecraft have revealed it to be one of the most striking large scale lunar features, resembling a target ring bullseye.
Mare Moscoviense is a lunar mare that sits in the Moscoviense basin. It is one of the very few maria on the far side of the Moon. Like Mare Marginis, this mare appears to be fairly thin. However, it is clearly centered within a large impact basin. It is also much lower than either the outer basin floor or the farside highlands.
In lunar astronomy, libration is the cyclic variation in the apparent position of the Moon perceived by Earth-bound observers and caused by changes between the orbital and rotational planes of the moon. It causes an observer to see slightly different hemispheres of the surface at different times. It is similar in both cause and effect to the changes in the Moon's apparent size due to changes in distance. It is caused by three mechanisms detailed below, two of which cause a relatively tiny physical libration via tidal forces exerted by the Earth. Such true librations are known as well for other moons with locked rotation.
The Discovery Program is a series of Solar System exploration missions funded by the U.S. National Aeronautics and Space Administration (NASA) through its Planetary Missions Program Office. The cost of each mission is capped at a lower level than missions from NASA's New Frontiers or Flagship Programs. As a result, Discovery missions tend to be more focused on a specific scientific goal rather than serving a general purpose.
In astronomy, astrophysics and geophysics, a mass concentration is a region of a planet's or moon's crust that contains a large positive gravity anomaly. In general, the word "mascon" can be used as a noun to refer to an excess distribution of mass on or beneath the surface of an astronomical body, such as is found around Hawaii on Earth. However, this term is most often used to describe a geologic structure that has a positive gravitational anomaly associated with a feature that might otherwise have been expected to have a negative anomaly, such as the "mascon basins" on the Moon.
Lunar Prospector was the third mission selected by NASA for full development and construction as part of the Discovery Program. At a cost of $62.8 million, the 19-month mission was designed for a low polar orbit investigation of the Moon, including mapping of surface composition including Lunar hydrogen deposits, measurements of magnetic and gravity fields, and study of lunar outgassing events. The mission ended July 31, 1999, when the orbiter was deliberately crashed into a crater near the lunar south pole, after the presence of hydrogen was successfully detected.
Hertzsprung is an enormous lunar impact crater, or impact basin, that is located on the far side of the Moon, beyond the western limb. In dimension, this formation is larger than several of the lunar mare areas on the near side. It lies in the northwestern fringe of the blast radius of the Mare Orientale impact basin. Nearby craters of note include Michelson across the northeast rim, Vavilov across the western rim, and Lucretius to the southeast.
The near side of the Moon is the lunar hemisphere that always faces towards Earth, opposite to the far side. Only one side of the Moon is visible from Earth because the Moon rotates on its axis at the same rate that the Moon orbits the Earth—a situation known as tidal locking.
In astronomy, lunar orbit is the orbit of an object around the Moon.
Maria T. Zuber is an American geophysicist who is the vice president for research at the Massachusetts Institute of Technology, where she also holds the position of the E. A. Griswold Professor of Geophysics in the Department of Earth, Atmospheric and Planetary Sciences. Zuber has been involved in more than half a dozen NASA planetary missions aimed at mapping the Moon, Mars, Mercury, and several asteroids. She was the principal investigator for the Gravity Recovery and Interior Laboratory (GRAIL) Mission, which was managed by NASA's Jet Propulsion Laboratory.
The acceleration due to gravity on the surface of the Moon is approximately 1.625 m/s2, about 16.6% that on Earth's surface or 0.166 ɡ. Over the entire surface, the variation in gravitational acceleration is about 0.0253 m/s2. Because weight is directly dependent upon gravitational acceleration, things on the Moon will weigh only 16.6% of what they weigh on the Earth.
A permanently shadowed crater is a depression on a body in the Solar System within which lies a point that is always in darkness.
Universal Space Network, Inc., or USN is an American company specializing in tracking, telemetry, and control of spacecraft. It is a subsidiary of Swedish Space Corporation, with four main sites and cooperative agreements with many others. USN has been used by commercial satellite operations such as Sirius XM Radio and scientific missions both in low Earth orbit and in orbit around the Moon. USN has offered a 50% discount for their services for competitors for the Google Lunar X Prize.
GRAIL MoonKAM (Moon Knowledge Acquired by Middle school students) was part of NASA’s GRAIL satellite mission to map the Moon’s gravity.
The Freundlich-Sharonov Basin is a Pre-Nectarian impact basin on the far side of the Moon. It is named after the younger craters Freundlich near the northwest margin and Sharonov near the southwest margin. It lies east of Mare Moscoviense basin and northwest of Korolev basin.
The Schiller-Zucchius Basin is a Pre-Nectarian impact basin on the near side of the Moon. It is named after the elongated crater Schiller at the northeast margin and fresh crater Zucchius near the southwest margin. This basin has received the unofficial designation 'Schiller Annular Plain' among lunar observers.
The Mendel-Ryberg Basin is a Nectarian impact basin on the southwestern limb of the moon. It is named after the crater Mendel on the west margin and the smaller crater Rydberg north of the center of the basin. The basin is due south of the larger, younger Orientale basin, and ejecta and other geomorphological effects from the younger basin have overprinted the older one.
The Coulomb-Sarton Basin is a Pre-Nectarian impact basin on the far side of the Moon. It is named after the crater Coulomb northeast of the center of the basin and the smaller crater Sarton just south of the center. The basin is not obvious on the lunar surface. There are only small fragments of inner rings and a rim, and the most indicative topographic feature is a smooth, low plain at the center.
The Dirichlet–Jackson Basin is a pre-Nectarian impact basin on the far side of the Moon. It is named after the craters Dirichlet and Jackson. It lies to the north of the similar-sized basin Korolev.
The gravity of Mars is a natural phenomenon, due to the law of gravity, or gravitation, by which all things with mass around the planet Mars are brought towards it. It is weaker than Earth's gravity due to the planet's smaller mass. The average gravitational acceleration on Mars is 3.72076 ms−2 and it varies.