Beyond_Earth-_A_Chronicle_of_Deep_Space_Exploration_1958-2016.pdf

Results: Chang'e 1 was the first deep space mission launched by China, part of the first phase of the so-called Chinese Lunar Exploration Program, divided into three phases of "circling around the Moon," "landing on the Moon," and "returning from the Moon" that would be accomplished between 2007 and 2020. The goal of this first mission, besides proving basic technologies and testing out several engineering systems, was to create a three-dimensional map of the lunar surface, analyze the distribution of certain chemicals on the lunar surface, survey the thickness of the lunar soil, estimate Helium-3 resources, and explore the space environment (solar wind, etc.) in near-lunar space. The spacecraft itself was based on the design of the reliable DFH-3 satellite bus. After launch, the spacecraft entered a 205 × 50,900-kilometer orbit for a day before firing its 50 kgf thrust main engine at 09:55 UT on 25 October to raise perigee to 593 kilometers. Subsequent burns (this time near perigee) were performed on 26 October (at 09:33 UT), 29 October (at 09:49 UT), and 31 October (at 09:15 UT) increasing apogee to 71,600, 119,800, and finally 400,000 kilometers, respectively. On its way to the Moon, Chang'e 1 (or CE-1, as it was often named in the Chinese English-language press) made one midcourse correction before entering lunar orbit with a 22-minute burn that began at 02:15 UT on 5 November 2007, thus becoming the first Chinese spacecraft to orbit the Moon. Initial orbital parameters were 210 × 860 kilometers. Two maneuvers on 6 and 7 November lowered perigee to 1,716 and 200 kilometers, respectively. Its final working orbit—a 200-kilometer polar orbit with a period of 127 minutes—was reached soon after on the same day. On 20 November, CE-1 returned the first raw image of the lunar surface, and by 28 November, all its scientific instruments were fully operational. A composite of 19 strips of raw images was issued by the Chinese media on 26 November at a ceremony attended by Chinese Premier Wen Jiabao. There was some controversy regarding this image which some believed was a fake or a copy of an image returned by Clementine but this proved not to be so: the high-quality image was indeed quite real. Through December 2007, CE-1 continued to photograph the Moon (including in stereo), and began imaging the polar regions in January 2008. The spacecraft successfully fulfilled its 1-year mission after which it continued extended operations. On 12 November 2008, Chinese space authorities issued a full-Moon image map produced using CE-1 images taken over 589 orbits covering 100% of the lunar surface with a resolution of 120 meters. In December 2008, over a period of two weeks, the spacecraft's perigee was progressively lowered to 15 kilometers to test operations for future orbiter and lander spacecraft. Finally, on 1 March 2009, CE-1 was commanded to impact on to the lunar surface, making contact at 08:13:10 UT at 52.27° E and 1.66° S, thus becoming the first Chinese object to make contact with the Moon. Its most significant achievement was to produce the most accurate and highest resolution 3D map of the lunar surface.

217

Chandrayaan-1 and MIP

Nation: India (1)

Objective(s): lunar orbit, lunar impact

Spacecraft: Chandrayaan-1 / MIP

Spacecraft Mass: 1,380 kg

Mission Design and Management: ISRO

Launch Vehicle: PSLV-XL (no. C11)

Launch Date and Time: 22 October 2008 / 00:52:11 UT

Launch Site: Sriharikota / SLP

Scientific Instruments:

Main Satellite:

• 1. terrain mapping camera (TMC)
• 2. hyper spectral imager (HySI)
• 3. lunar laser ranging instrument (LLRI)
• 4. high energy x-ray spectrometer (HEX)
• 5. Moon impact probe (MIP)
• 6. Chandrayaan-1 x-ray spectrometer (CIXS)
• 7. near infrared spectrometer (SIR-2)
• 8. Sub keV atom reflecting analyzer (SARA)
• 9. miniature synthetic aperture radar (Mini SAR)
• 10. Moon mineralogy mapper (M3)
• 11. radiation dose monitor (RADOM)

MIP:

• 1. radar altimeter
• 2. video imaging system
• 3. Chandra's altitudinal composition explorer (mass spectrometer) (CHASE)

Results: Chandrayaan-1, the first Indian deep space mission, was launched to orbit the Moon and dispatch an impactor to the surface. Scientific goals included the study of the chemical, mineralogical, and "photo-geologic" mapping of the Moon. Besides five Indian instruments, the spacecraft carried scientific equipment from the United States, the U.K., Germany, Sweden, and Bulgaria.

<!-- image -->

Chandrayaan-1 was launched into an initial geostationary transfer orbit of 225 × 22,817 kilometers at 17.9° inclination. Over a period of 13 days, the apogee of the orbit was increased by five burns of its 44.9 kgf Liquid Engine that successively raised orbit on 23 October (to 37,900 kilometers), 25 October (to 74,715 kilometers), 26 October (to 164,600 kilometers), 29 October (to 267,000 kilometers), and 4 November (to 380,000 kilometers). Finally, the probe successfully entered lunar orbit after a burn that began at 11:21 UT on 8 November and lasted about 13.5 minutes. Initial lunar orbital parameters were 7,502 × 504 kilometers. Between lunar orbit insertion on 8 November and 12 November, Chandrayaan-1's orbit was reduced gradually so that it ended up finally in its operational polar orbit at about 100 kilometers above the lunar surface. Two days later, at 14:36 UT, Chandrayaan released its 29-kilogram Moon Impact Probe (MIP) which fired a small deorbit motor and went into freefall, sending back readings from its three instruments until it crashed onto to the lunar surface at 15:01 UT near the Shackleton crater at the lunar south pole. Indian scientists reported that data from the CHASE instrument, which took readings every 4 seconds during its descent, suggested the existence of water in the lunar atmosphere, although the data remains inconclusive absent further verification. Chandrayaan-1 experienced abnormally high temperatures beginning late November 2008, and for a time, it could only run one scientific instrument at a time. In May 2009, the spacecraft was delivered to a higher 200-kilometer orbit, apparently in an attempt to keep the temperatures aboard the satellite to tolerable levels. Chandrayaan-1 also suffered a star sensor failure after nine months of operation in lunar orbit. A backup sensor also failed soon after, rendering inoperable the spacecraft's primary attitude control system. Instead controllers used a mechanical gyroscope system to maintain proper attitude. Last contact with the spacecraft was at 20:00 UT on 28 August 2009, thus falling short of its planned two-year lifetime, although ISRO noted that at least 95% of its mission objectives had been accomplished by then. The most likely cause of the end of the mission was failure of the power supply due to overheating. Perhaps Chandrayaan-1's most important finding was related to the question of water on the Moon. In September 2009, scientists published results of data collected by the American M3 instrument which had detected absorption features on the polar regions of the surface of the Moon usually linked to hydroxyl- and/or water-bearing molecules. This finding was followed later, in August 2013, by a further announcement of evidence of water molecules locked in mineral grains on the surface of the Moon, i.e., "magmatic water," or water that originates from deep in the Moon's interior. Magmatic water had been found in samples returned by Apollo astronauts but not from lunar orbit until the operation of the M3 instrument, although Cassini, during its flyby of the Moon in August 1999, had detected (using its VIMS instrument) water molecules and hydroxyl. Later, NASA's Deep Impact-EPOXI mission, which flew by the Moon in June 2009 also returned the same type of data.

218

Kepler

Nation: USA (92)

Objective(s): solar orbit

Spacecraft: Kepler

Spacecraft Mass: 1,039 kg

Mission Design and Management: NASA / ARC / JPL

Launch Vehicle: Delta 7925-10L (no. D339)

Launch Date and Time: 7 March 2009 / 03:49:57 UT

Launch Site: Cape Canaveral Air Force Station / SLC-17B

Scientific Instruments:

• 1. photometer (Schmidt telescope)

Results: Kepler, the tenth in the series of low-cost, low-development-time, and highly-focused Discovery class science missions, is designed to discover Earth-like planets orbiting other stars in our region of the Milky Way. More specifically, Kepler has been equipped to look for planets whose size spans from one-half to twice the size of Earth ("terrestrial planets") in the habitable zone of their stars where liquid water might exist in the natural state on the surface of the planet. Its scientific goals include determining the abundance of these planets and the distribution of sizes and shapes of their orbits, estimating the number of planets in multiple-star systems, and determining the properties of stars that have planetary systems. Kepler detects planets by observing transits, tiny dips in the brightness of a star when a planet crosses in front of it. The spacecraft is basically a single instrument—in this case, a specially designed 0.95-meter diameter aperture telescope and image sensor array—with a spacecraft built around it. (The diameter of the telescope's mirror is 1.4 meters, one of the largest mirrors beyond Earth orbit).

<!-- image -->

As originally planned, it was designed to monitor about 100,000 main-sequence stars over a period of three-and-a-half years. Kepler was initially launched into Earth orbit at 185 × 185 kilometers at 28.5° inclination. Subsequently, after another first stage burn, the second stage fired to set Kepler on an escape trajectory into solar orbit. It passed lunar orbit at 04:20 UT on 9 March, eventually entering heliocentric orbit at 0.97 × 1.041 AU at 0.5° inclination to the solar ecliptic. In order to improve resolution, on 23 April 2009, mission planners optimized the focus of the telescope by moving the primary mirror 40 micrometers toward the focal plane and tilting it by 0.0072°. Less than a month later, on 13 May, Kepler finished its commissioning and began its operational mission. Already during its first six weeks of operation, Kepler discovered five exoplanets (which were named Kepler 4b, 5b, 6b, 7b, and 8b), which NASA announced in January 2010. Later, in April 2010, mission scientists published results that showed that Kepler had discovered the first confirmed planetary system with more than one planet transiting the same star, Kepler-9. That discovery was the result of surveying more than 156,000 stars over a period of seven months. The planetary system orbiting Kepler-11, a yellow dwarf star about 2,000 light years from Earth, included six planets. NASA announced in February 2011 that these planets were larger than Earth, with the largest ones comparable in size to Uranus and Neptune. In 2011, Kepler suffered at least two "safe mode" events, when the spacecraft essentially shut down science operations as a result of a suspected anomaly. In both cases, in February and March, the Kepler project team were able to revive the vehicle relatively quickly, within two to three days. In September, mission scientists announced the discovery of a planet (Kepler-16b) orbiting two stars, where we might expect a double sunset, much like the fictional planet Tatooine depicted in the film Star Wars. (A subsequent double-star system was announced in January 2012 and multiple planets orbiting multiple stars—the Kepler-47 system—was announced in August 2012). Finally, in December 2011, NASA announced that Kepler had found its first planet (Kepler-22b) in the "habitable zone" of a star where liquid water could exist on the planet's surface. In April 2012, the mission, closing in on its three-and-a-half-year lifetime, was formally extended through fiscal year 2016 after a review of its operations, with the extended mission beginning on 15 November 2012. By that time, Kepler had identified more than 2,300 planet candidates and confirmed more than 100 planets. Based on data collected by Kepler, scientists were able to announce in January 2013 that about 17% of stars (about one-sixth) have an Earth-sized planet in an orbit closer than Mercury is to our Sun. Given that the Milky Way has about 100 billion stars, this would suggest at least 17 billion Earth-sized worlds in our galaxy. (In November 2013, this number was revised up to 40 billion). Following two brief lapses into "safe mode" in May, one of the spacecraft's four reaction wheels (no. 4) was found to have failed. Given that an earlier one failed in July 2012 and that at least three such wheels were needed to accurately aim the telescope, there was anxiety that the mission might be jeopardized. Subsequent to that point, and after another safe mode event in late May, Kepler operated in Point Rest State (PRS) mode—where the spacecraft used thrusters and solar pressure to control pointing—while controllers devised a way to reactivate the wheels necessary for accurate pointing of the spacecraft. After several months of activity, on 15 August 2013, NASA officially announced that it would be ending efforts to fully recover Kepler. NASA solicited proposals from the public on how to reformulate a new mission for Kepler given its obvious limitations. During this period, in October 2013, Kepler mission scientists announced that they had conclusively identified the first Earth-sized rocky planet, Kepler-78b, which circles its host star every eight-and-a-half years, making it a very hot planet. A further announcement in April 2014 confirmed the discovery of the first Earth-sized planet (Kepler-186f) in the "habitable zone" of a star. At the end of the year, the Kepler team proposed a new mission, known as K2 ("Second Light"), using the two remaining reaction wheels to investigate smaller and dimmer red dwarf stars. Mission definition of the K2 proposal continued into 2014, with the mission finally approved by NASA in May 2014 and data collection beginning on 30 May. Observations continued through the year with several "campaigns" of data collection. As of January 2015, Kepler had found 1,004 confirmed exoplanets in about 400 star systems. By November 2016, Kepler, now in its K2 mission (which included "relaxed fault or sensitivity limits") was in its eleventh "campaign" of scientific observation, which began on 24 September. There was some concern on the eve of Campaign 9, slated to begin on 8 April, when controllers found the spacecraft in a "fuel-intensive coma," a kind of emergency mode much more serious than a "safe mode" and closer to complete systems failure. Fortunately, controllers were slowly able to fully revive the spacecraft by 22 April. On 9 June 2016, NASA announced that Kepler would continue science operations through to the end of Fiscal Year 2019 by which time, on-board propellant would probably be depleted. The spacecraft was named after the famed German astronomer Johannes Kepler (1571–1630).