LINEAR
History of LINEAR
Introduction
Lincoln Laboratory has a long history of developing electro-optical space surveillance technology for resident space-object search, detection, orbit determination, and catalog maintenance of objects in the Earth's orbit. Advances in large-format, highly sensitive charge-coupled devices (CCDs) have made possible the application of these technologies to the detection and cataloging of asteroids, including near-Earth objects (NEOs). When equipped with the Lincoln Laboratory focal plane, camera, and signal processing technology, the modest sized (1 m class) Air Force Ground-based Electro-Optical Deep Space Surveillance (GEODSS) telescopes have considerable capability to conduct sensitive, large coverage searches for Earth-crossing and main belt asteroids. Field measurements have indicated that CCD-equipped GEODSS telescopes are capable of achieving a limiting magnitude of 22, over a 2-square degree field of view, with less than 100 seconds of integration. This is comparable to the sensitivity of considerably larger telescopes equipped with commercial CCD cameras. In addition to its high sensitivity, the Lincoln Laboratory CCD employs frame transfer technology that is well suited to high-coverage, high-rate asteroid search operations since each frame can be read out while the next frame is integrating. Technology development for asteroid search operations has been conducted at the Lincoln Laboratory Experimental Test Site in Socorro, New Mexico, over the past decade.
Late 1990s
Initial results, reported during the Fifth International Conference on Space '96 meeting held in Albuquerque, New Mexico, on June 1–6, 1996, indicated that the search system, known as LINEAR (Lincoln Near-Earth Asteroid Research), had considerable promise. By using the new large-format 2560 x 1960 pixel frame transfer CCD camera mounted in a GEODSS telescope, 49 new asteroids were discovered over a period of several months, including one NEO (designated 1996MQ). In addition, observations on 79 known objects were collected and sent to the Minor Planet Center.
After those initial attempts, LINEAR search operations were considerably improved and automated. Data acquisition was streamlined, detection algorithms were updated, and the signal processing of the resulting data was closely integrated with the data acquisition process. Field tests resumed in January of 1997, with the objective of quantifying the capability of the system to conduct large-area searches, detect new asteroids, and provide quality metric measurements to the Minor Planet Center. Since the large 2560 x 1960 pixel CCD camera was unavailable during this time, an older 1024 x 1024 pixel CCD camera was used. The smaller-format camera has the same sensitivity as the larger camera but fills only about 1/5th of the field of view of the GEODSS telescope. The large-format CCD fills the field of view of the GEODSS telescope. Observations were conducted over the dark of the moon periods during the months of March, April, and May. Each search area was covered three times over a period of three to seven days to generate discovery observations of each new object that could be linked from day to day. The Minor Planet Center requires that newly discovered objects be observed over at least two nights before granting the object a designation.
Search productivity was quite high during each of the observing runs, in spite of the fact that a small-format camera was employed. The main search strategy employed was to search near solar opposition and near the ecliptic. A wide-area search pattern for detecting NEOs was also briefly tested with promising results. Using the opposition search strategy, the LINEAR system was capable of repeatedly covering an area extending 15 degrees by 10 degrees over a period of a few days, to a limiting visual magnitude of approximately 19.5 magnitude.
In the late 1990s, the large format 1960 x 2560 CCD camera became available for use by LINEAR. Initial operations tests were conducted during the dark of the moon period spanning late October and early November 1997. Use of the new CCD resulted in nearly an order of magnitude improvement in asteroid detection rates, with 52,575 observations gathered over 10 nights of observing. A total of 11 potential NEOs were detected, 9 of which were successfully confirmed, and new designations issued by the Minor Planet Center. Availability issues with the large format slowed observing during the dark periods in late November 1997 through January 1998.
In March 1998, LINEAR began operations with the large-format CCD. In the first month, over 151,000 observations were sent to the Minor Planet Center, with 13 NEOs confirmed with new designations issued by the Minor Planet Center. These statistics are summarized in the table below.
Dark Periods |
CCD Used |
Obs Generated |
Obs/Month |
New NEOs |
|---|---|---|---|---|
| 3/97–7/97 | 1024 x 1024 | 24,103 |
6,014 |
4 |
| 10/97 | 1960 x 2560 | 52,575 |
52,575 |
9 |
| 11/97–1/98 | Mix of both | 31,203 |
10,401 |
5 |
| 3/98 | 1960 x 2560 | 151,035 |
151,035 |
13 |
These series of observations validated that the large-format 2560 x 1960 Lincoln Laboratory CCD technology, originally developed for the Air Force GEODSS upgrade, is also quite effective when applied to the problem of discovering asteroids.
2000s
The LINEAR program has been running since 1998 with operational funding from NASA. The LINEAR system has proven to be a reliable supplier of discoveries of NEOs, comets, unusual asteroids, and main-belt asteroids. LINEAR has also been a key contributor to the discoveries of large NEOs. LINEAR has discovered more than 2400 NEOs and is responsible for more than 35% of all observations in the Minor Planet Center's database. LINEAR has discovered nearly 30% of all known NEOs to date, more than 40% of large NEOs, and more than 35% of all known potentially hazardous asteroids. LINEAR has achieved this success by aggressively scheduling the telescopes for as many nights as possible each lunar month and by covering the entire available sky at least once each month, weather permitting.
The following table summarizes LINEAR's productivity over the last 14 years. The data are complete to September 15, 2011.
Year |
Observations Accepted by Minor Planet Center |
NEO Discoveries |
Comet Discoveries |
All Discoveries |
2011 |
951,960 |
48 |
6 |
189 |
2010 |
2,183,622 |
104 |
12 |
990 |
2009 |
1,851,759 |
108 |
16 |
1006 |
2008 |
2,483,714 |
141 |
8 |
2313 |
2007 |
2,473,077 |
112 |
13 |
3677 |
2006 |
2,227,581 |
96 |
11 |
1859 |
2005 |
2,051,694 |
137 |
12 |
4755 |
2004 |
3,211,745 |
304 |
25 |
17,741 |
2003 |
2,996,173 |
235 |
27 |
15,854 |
2002 |
3,069,126 |
286 |
34 |
31,827 |
2001 |
3,089,881 |
279 |
33 |
48,383 |
2000 |
2,088,982 |
258 |
29 |
52,779 |
1999 |
1,104,520 |
161 |
36 |
29,278 |
1998 |
583,253 |
136 |
17 |
18,288 |
Pre-1998 |
79,603 |
18 |
0 |
2143 |
Total |
30,446,690 |
2423 |
279 |
231,082 |
LINEAR has contributed to the scientific characterization of the NEO population through an analysis of the number, orbital properties, albedo properties, sizes, and impact hazards of the NEO population. The extensive archive of all LINEAR image data acquired between December 2002 and March 2008 (amounting to more than 6 million images) has been made accessible for a number of astronomical investigations.
The success of NASA's efforts to discover and track NEOs means that the remaining undiscovered NEOs are smaller and dimmer than those previously discovered. Therefore, Lincoln Laboratory's recent and future efforts are geared toward developing technology to enable more sensitive detection and searches deeper into space, thereby providing a more comprehensive picture of the NEO environment.
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