Beyond_Earth-_A_Chronicle_of_Deep_Space_Exploration_1958-2016.pdf

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Herschel

Nation: European Space Agency (6)

Objective(s): Sun–Earth L2 Lagrange Point

Spacecraft: Herschel

Spacecraft Mass: 3,400 kg

Mission Design and Management: ESA

Launch Vehicle: Ariane 5ECA (no. V188)

Launch Date and Time: 14 May 2009 / 13:12 UT

Launch Site: Kourou / ELA 3

Scientific Instruments:

• 1. infrared telescope
• 2. heterodyne instrument for the far infrared (HIFI)
• 3. photoconductor array camera and spectrometer (PACS)
• 4. spectral and photometric imaging receiver (SPIRE)

Results: Both Herschel and Planck were launched by the same Ariane launch vehicle and were both ESA missions (with significant NASA contributions) but they had different science missions. Herschel, the largest infrared telescope ever launched into space (3.5-meter mirror), was designed to study the origin and evolution of stars and galaxies, the chemical composition of atmospheres and surfaces of solar system bodies, and molecular chemistry across the universe, to help understand the evolution of the universe. Herschel's mirror, one-and-a-half times bigger than the one on Hubble, was made almost entirely of silicon carbide, 12 such segments being brazed together. Following launch, Ariane's ESC-A stage sent both Herschel and Planck into a highly elliptical transfer orbit of 270 × 1,197,080 kilometers at 6° inclination to enable the spacecraft to reach the Sun–Earth L2 Lagrange Point, the local gravitationally stable point that is fixed in the Sun–Earth System, about 1.5 million kilometers directly "behind" Earth as viewed from the Sun. Herschel did not have a dedicated engine for major course changes but used its own small thrusters for minor corrections. Herschel's operating lifetime was expected to be about three-and-a-half years, determined by the amount of coolant available for its instruments. In mid-July 2009, about two months after launch, Herschel entered a Lissajous orbit of 800,000 kilometers (average) radius around L2 and soon, on 21 July, began active operations. (Herschel's distance from Earth varied, depending on its orbital position, between 1.2 and 1.8 million kilometers). The observatory's operations were organized in 24-hour cycles where it communicated with ground control for 3 hours every day with the remainder of the time dedicated to scientific observations. Less than a year later, at a symposium to discuss the first results of Herschel, scientists reported a number of major findings: Herschel had found high-mass protostars around two ionized regions in the Milky Way, showing an early phase in the evolution of stars; the HIFI instrument (which had actually been inoperable due to a glitch between August 2009 and February 2010) had investigated the trail of water in the universe over a wide range of scales, from the solar system to extragalactic sources; and Herschel found a previously unresolved population of galaxies in the GOODS (Great Observatories Origins Deep Survey) fields identified by the Hubble, Spitzer, and Chandra spacecraft. In August 2011, Herschel mission scientists reported that they had identified molecular oxygen in the Orion molecular cloud complex, previously reported by the Swedish Odin satellite. Herschel data also suggested that much of Earth's water could have come from comets, results suggested by observations of Comet Hartley 2—although this notion has been dispelled since. Observations by Herschel, in fact, confirmed that Comet Shoemaker-Levy's impact into Jupiter in 1994 had actually delivered water to the gas giant. One of the oldest objects in the universe was located in 2013; scientists published results in April that showed the existence of a starburst galaxy which had produced over 2,000 solar masses of stars a year, originating only 880 million years after the Big Bang. On 29 April 2013, Herschel finally ran out of the liquid helium coolant required to maintain the operational temperature of the instrument detectors. On 13–14 May the spacecraft conducted a maneuver with its thrusters to boost it out of orbit around L2 and into its final resting place in heliocentric orbit. (A possible end on the lunar surface was also contemplated but not chosen because of cost). Following a last maneuver to deplete the propellant on board, at 12:25 UT on 17 June 2013, the final command to terminate communications was sent to Herschel, rendering the spacecraft dead. After a highly successful mission, the inert spacecraft will remain in heliocentric orbit. Scientists continued analyzing the vast amount of data returned from the observatory. For example, in January 2014, scientists announced that data from Herschel indicated the definitive detection of water vapor on the dwarf planet Ceres, a discovery which came prior to the arrival of NASA's Dawn mission at Ceres. This research was part of the so-called Measurements of 11 Asteroids and Comets Using Herschel (MACH-11) program. The observatory is named after British astronomers William Herschel (1738–1822) and his sister Caroline Herschel (1750–1848).

220

Planck

Nation: European Space Agency (7)

Objective(s): Sun–Earth L2 Lagrange Point

Spacecraft: Planck

Spacecraft Mass: 1,950 kg

Mission Design and Management: ESA

Launch Vehicle: Ariane 5ECA (no. V188)

Launch Date and Time: 14 May 2009 / 13:12 UT

Launch Site: Kourou / ELA-3

Scientific Instruments:

• 1. low frequency instrument (LFI)
• 2. high frequency instrument (HFI)
• 3. telescope

Results: Both Herschel and Planck were launched by the same Ariane launch vehicle as ESA missions (although Herschel, especially, had significant NASA contributions) but they had different science objectives. Planck, named after German physicist Max Planck (1858–1947) was the first European space observatory whose primary objective was to study the Cosmic Microwave Background (CMB). The spacecraft used sensitive radio receivers operating at very low temperatures to determine the black body equivalent temperature of the background radiation. Such measurements were then used to produce detailed maps of directional (anisotropic) temperature differences in the CMB radiation field, improving upon observations made by NASA's Wilkinson Microwave Anisotropy Probe (WMAP)—Planck had a higher resolution and sensitivity than WMAP. Besides mapping CMB anisotropies, Planck would also provide data to test inflationary models of the early universe, measure the amplitude of structures in the CMB, and perform measurements of the Sunyaev-Zeldovich effect (the distortion of CMB by high energy electrons through inverse Compton scattering). The Planck spacecraft was made up of two primary components, the payload and service modules. The former contained a telescope with primary and secondary mirrors that collected microwave radiation and directed it into the focal plane units. The octagonal service module (SVM) was common to both Herschel and Planck, both being cornerstone missions in ESA's science program (along with Rosetta and Gaia). Like Herschel, Planck was put into an elliptical orbit that eventually led to Sun–Earth L2 where it entered a Lissajous orbit with a 400,000-kilometer radius on 3 July 2009. ESA announced that Planck's High Frequency Instrument reached their low temperatures of –273.05°C, making them the "coolest" known objects in space. (This temperature is only 0.1°C above absolute zero, the coldest temperature theoretically possible in our universe.) Such low temperatures are necessary to study CMB, the "first light" released by the universe only 380,000 years after the Big Bang. This visible light gradually faded and moved to the microwave wavelengths due to the expansion of the universe. By studying, with Planck's two instruments, patterns imprinted in that light today, scientists sought to understand the Big Bang and the very early universe. The spacecraft began its first "all-sky" survey on 13 August working for two continuous weeks, generating excellent preliminary results within a month. On 15 January 2010, ESA extended the mission by 12 months (from its original end point of late 2011). In July 2010, ESA reported that Planck had returned its first all-sky image, "the moment that Planck was conceived for," as ESA Director of Science and Robotic Exploration David Southwood (1945– ) noted. The image spanned the closest portions of the Milky Way to the "furthest reaches of space and time." As expected, the High Frequency Instrument's sensor ran out of coolant on 14 January 2012, concluding its ability to detect this faint energy, but not before fully completing its survey of the early universe, i.e., the remnant of light from soon after the Big Bang itself. Based on data from Planck collected over its initial work spanning 15.5 months, in March 2013, ESA released the most detailed map ever created of the CMB. The map suggested that the universe is slightly older than earlier thought; the data points to an age of 13.798±0.037 billion years. In August 2013, having completed its mission, Planck was "nudged" away from its L2 orbit towards a more stable orbit around the Sun. Through September and October, mission controllers prepared the spacecraft for shutdown by using up its remaining fuel. Finally, at 12:10:27 UT, on 23 October 2013, ESA sent the final command to shut down Planck, ending a highly successful mission.

221

Lunar Reconnaissance Orbiter (LRO)

Nation: USA (93)

Objective(s): lunar orbit

Spacecraft: LRO

Spacecraft Mass: 1,850 kg

Mission Design and Management: NASA / GSFC

Launch Vehicle: Atlas V 401 (no. AV-020)

Launch Date and Time: 18 June 2009 / 21:32:00 UT

Launch Site: Cape Canaveral Air Force Station / SLC-41

Scientific Instruments:

• 1. cosmic ray telescope for the effects of radiation (CRaTER)
• 2. diviner lunar radiometer experiment (DLRE)
• 3. Lyman-Alpha mapping project (LAMP)
• 4. lunar exploration neutron detector (LEND)
• 5. lunar orbiter laser altimeter (LOLA)
• 6. lunar reconnaissance orbiter camera (LROC)
• 7. Mini-RF miniature radio frequency radar

NASA's Lunar Reconnaissance Orbiter (LRO) captured this oblique view of the Moon, looking east-to-west over the Apennine Mountains towards Hadley Rille (upper left). Mount Hadley, at center right, casts a long shadow. The crew of Apollo 15 landed between the Apennines and Hadley Rile in 1971. Credit: NASA/Arizona State University

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Results: The Lunar Reconnaissance Orbiter (LRO) was part of NASA's now-cancelled Lunar Precursor Robotic Program (which also included LCROSS) and was the first U.S. mission to the Moon in over 10 years. LRO's primary goal was to make a 3D map of the Moon's surface from lunar polar orbit as part of a high-resolution mapping program to identify landing sites and potential resources, investigate the radiation environment, and prove new technologies in anticipation of future automated and human missions to the surface of the Moon. LRO was launched together with LCROSS; the Centaur upper stage boosted them both into high apogee orbits soon after launch. At 11:27 UT on 23 June 2009, LRO successfully entered orbit around the Moon, having fired its rocket motor on the far side of the Moon. Initial orbital parameters were roughly 30 × 216 kilometers. A series of four engine firings over the next four days left LRO in its optimal orbit—roughly circular at 50 kilometers—allowing the satellite to begin its primary mission on 25 September 2009, expected to last one year and overseen by NASA's Exploration Systems Mission Directorate (ESMD). During this period, LRO gathered information on day-night temperature maps, contributed data for a global geodetic grid, and conducted high-resolution imaging. The spacecraft paid particular emphasis to the polar regions, where constant solar illumination might be possible and where there is the possibility of water in the permanently shadowed regions. In September 2010, LRO operations were handed over to NASA's Science Mission Directorate (SMD) to continue the science phase of the mission (rather than activities purely related to exploration and future missions) for another five years. Among LRO's achievements was to take extremely high-resolution photographs of landing sites of several older lunar landers and impact vehicles, such as landing sites from all the Apollo landing missions (plus Surveyor III near the Apollo 12 site) and the Apollo 13, 14, 15, and 17 Saturn IVB upper stages. Other targets included the later Ranger impact probes (VI, VII, VIII, and IX), and the Soviet Luna 16, 17, 20, 23, and 24 soft-landers, and the Chinese Chang'e 3 lander/rover. In November 2011, NASA released the highest resolution near-topographical map of the Moon ever created, showing surface features over nearly the entire moon. An interactive mosaic of the lunar north pole was published in March 2014. LRO also carried out the first demonstration of laser communication with a lunar satellite when, in January 2013, NASA scientists beamed an image of the Mona Lisa from the Next Generation Satellite Laser Ranging (NGSLR) station at NASA's Goddard Space Flight Center in Greenbelt, Maryland to the LOLA instrument on board LRO. One of the LRO instruments, the Mini-RF partially failed in January 2011, although fortunately, it had already completed its primary science objectives by that time. On 4 May 2015, controllers at Goddard Space Flight Center sent commands to LRO to fire its engines twice to change its orbit, taking it closer to the Moon than before—a polar orbit of about 20 × 165 kilometers. Perilune was close to the lunar South Pole. The new orbit allowed LRO's LOLA instrument to produce better return signals and also allow it to better measure specific regions near the South Pole that have unique illumination conditions. One of the more interesting finds of the orbiter was its identification, in December 2015, of the hitherto unknown impact site of Apollo 16's S-IVB upper stage that was deliberately impacted on the lunar surface in 1972. In early 2017, LRO was still in excellent shape with propellant use limited to a few kilograms per year. Total remaining in early 2017 was about 30 kilograms. It is not unlikely that the spacecraft will remain operational in its low elliptical orbit—which was about 30 × 150 kilometers in late 2016—for several more years.