Beyond_Earth-_A_Chronicle_of_Deep_Space_Exploration_1958-2016.pdf

222

Lunar Crater Observation and Sensing Satellite (LCROSS)

Nation: USA (94)

Objective(s): lunar orbit

Spacecraft: S-S/C

Spacecraft Mass: 621 kg

Mission Design and Management: NASA / ARC

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. visible camera
• 2. 2 near infrared cameras
• 3. 2 mid-infrared cameras
• 4. visible spectrometer
• 5. 2 near infrared spectrometers
• 6. total luminescence photometer (TLP)

Results: The mission of Lunar Crater Observation and Sensing Satellite (LCROSS), like LRO, part of NASA's now-cancelled Lunar Precursor Robotic Program, was to confirm the presence of water ice in a permanently shadowed crater at the Moon's south pole. Notably, both missions were originally funded as part of NASA's human spaceflight Constellation program to return humans to the Moon. Ancillary goals for LCROSS included the testing of new modular subsystems for potential use in future mission architectures. Its mission profile involved impacting a Centaur upper stage on the surface of the Moon and then flying LCROSS through the debris plume about four minutes later to collect data on the soil, and then itself impact a little later. LCROSS was launched along with the Lunar Reconnaissance Orbiter (LRO) and traveled to the Moon as a "co-manifested" payload aboard the launch vehicle. The Centaur upper stage entered a 180 × 208-kilometer parking orbit before firing again at 22:15 UT on 18 June to reach a 194 × 353,700-kilometer orbit at 28.2° inclination. At that point, LRO separated from the Centaur-LCROSS combination, and the Centaur then vented some remaining propellant, which slightly altered its orbit to 133 × 348,640-kilometer orbit at 28.0° inclination, ensuring a lunar flyby. The combined Centaur-LCROSS then passed the Moon at a distance of 3,270 kilometers at 10:29 UT on 23 June and entered into an Earth polar orbit at approximately 357,000 × 582,000 kilometers at 45° inclination with an orbital period of 37 days. The combined stack reached apogees near the Moon on 10 July, 16 August, and 22 September until its trajectory intersected with that of the Moon on 9 October. A serious problem was discovered earlier, on 22 August, when mission controllers found that a sensor problem had caused the spacecraft burning through 140 kilograms of propellant, more than half of the amount remaining at the time. The loss meant that the original mission could still be accomplished but with very little margin. At 01:50 UT on 9 October, Centaur and LCROSS separated. The former then crashed onto the surface of the Moon at 11:31 UT in the Cabeus crater at the lunar South Pole. The impact excavated roughly 350 (metric) tons of lunar material and created a crater estimated to be about 20 meters in diameter. Four minutes later, LCROSS flew through the resulting debris plume that rose above the lunar surface, collecting data before it itself struck the Moon at 11:36 UT at a velocity of 9,000 kilometers/hour. The LRO's Diviner instrument obtained infrared observations of the LCROSS impact point as it flew by about 90 seconds after the impact at a range of about 80 kilometers. On 13 November 2009, NASA formally announced that data from LCROSS "indicates that the mission successfully uncovered water … near the Moon's south pole." Nearly a year later, on 21 October 2010, mission scientists announced new data, including evidence that the lunar soil within Cabeus was rich in useful materials (mercury, magnesium, calcium, silver, sodium) and that the Moon is chemically active and has a water cycle. They also confirmed that in some places the water on the south pole is in the form of pure ice crystals.

223

Venus Climate Orbiter (VCO) / Akatsuki

Nation: Japan (7)

Objective(s): Venus orbit

Spacecraft: PLANET-C

Spacecraft Mass: 517.6 kg

Mission Design and Management: JAXA

Launch Vehicle: H-IIA 202 (no. 17)

Launch Date and Time: 20 May 2010 / 21:58:22 UT

Launch Site: Tanegashima / Area Y1

Scientific Instruments:

• 1. 1-micron camera (IR1)
• 2. 2-micron camera (IR2)
• 3. ultraviolet imager (UVI)
• 4. longwave infrared camera (LIR)
• 5. lightning and airglow camera (LAC)
• 6. ultra-stable oscillator (USO)
• 7. radio science experiment (RS)

Artist’s impression of Japan’s Venus Climate Orbiter. Credit: JAXA/Akihiro Ikeshita

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Results: This was Japan's first interplanetary mission after Nozomi (launched in 1998), that spacecraft having failed to enter orbit around Mars. The goal of Venus Climate Orbiter, or Akatsuki ("dawn") as it was known after launch, was to investigate atmospheric circulation in Venus by globally mapping clouds and minor constituents with four cameras at ultraviolet and infrared wavelengths, detect lightning, and observe the vertical structure of the atmosphere. A nominal mission would last two or more years in an elliptical orbit around Venus at 300 × 80,000 kilometers. The scientific goals of VCO were closely related to those of ESA's Venus Express launched in 2005. VCO was launched with a fleet of satellites, including three Japanese cubesats (KSAT, Negai*, and Waseda-Sat 2). The H-IIA rocket's second stage restarted in Earth orbit to accelerate three other spacecraft to escape velocity: Akatsuki, UNITEC 1, and IKAROS. On 21 May 2010, Akatsuki conducted a mid-course correction to sharpen its trajectory to Venus orbit. This was the first time that a ceramic thruster (with 51 kgf thrust), made of silicon nitride, was used in space conditions. The spacecraft was supposed to enter Venus orbit by firing its orbital maneuvering engines at 23:40 UT on 6 December 2010. Although the engine fired on time, it apparently cut off early. When communications were reestablished with Akatsuki (after a planned blackout due to occultation), the spacecraft was found to be in "safe mode" and spin-stabilized, slowly rotating once every 10 minutes. A later investigation (whose results were issued on 30 June 2011) showed that the engine had fired for less than 3 minutes (instead of 12 minutes), thus providing insufficient delta-V to enter Venusian orbit. Apparently, salt deposits jammed a valve that delivered fuel to the combustion chamber, making the combustion oxidizer-rich. The thruster nozzle was probably damaged in the firing. Soon, JAXA scientists began devising a backup plan to enter Venusian orbit in November 2015, which would be possible if subsequent tests of thruster were successful. On 7 and 14 September 2011, test firings were carried out of the beleaguered engine which showed that the thrust was about one-ninth of normal (about 4.1 kg). As a result, a new plan was formulated to discard all the unused oxidizer (65 kilograms), lightening the spacecraft, and using the smaller reaction control system (RCS) thrusters to attempt Venus orbital insertion on 22 November 2015. Three firings of the RCS system (587.5, 544, and 342 seconds in length) in November 2011 were successful in altering the trajectory of VCO for rendezvous with Venus in either 2015 (preferable in terms of spacecraft lifetime) or 2016 (preferable in terms of the original science mission). The main problem at this time was VCO's exposure to incredibly high temperatures as it sped through perihelion—six times by April 2014—conditions it was not designed to survive, described by JAXA as "three times hotter than that of Earth." Yet telemetry showed that the spacecraft was still functioning. In January 2015, the planned Venus orbit insertion was shifted to early December 2015 with a possible apogee of 300,000 to 400,000 kilometers. As per the new plan, Akatsuki successfully entered orbit around Venus on 7 December 2015 by using its attitude control thrusters for 20 minutes, following earlier spacecraft from the former Soviet Union, the United States, and the European Space Agency. Initial orbital parameters were approximately 440,000 × 400 kilometers at 3° inclination and an orbital period of 13 days 14 hours, fortuitously much lower than mission planners had hoped to achieve in original pre-launch planning. (Originally, the plan was to have an apoapsis of 79,000 kilometers and an orbital period of 30 hours, partly to match the flow of Venusian winds for part of the spacecraft's orbit.) The new orbit had one drawback—it meant that Akatsuki would be in Venus' shadow for part of each day, longer than the 90-minute limit set for the spacecraft. Remarkably, despite the stress from overheating, three of the five cameras on Akatsuki remained in perfect condition and sent back impressive imagery of the planet. On 26 March 2015, the vehicle lowered the high point of its orbit to about 330,000 kilometers, shortening its orbital period to about nine days. After several months of checkout, on 28 April 2016, the spacecraft finally began its standard science mission. In March 2017, JAXA announced that two of the cameras, the 1-µm and 2-µm cameras) on Akatsuki had "pause[d] scientific observations" as of 9 December 2016 due to an electrical problem. Perhaps the most significant discovery of Akatsuki was the detection, in December 2015, of a bow-shaped feature in the Venusian atmosphere stretching about 9,600 kilometers from almost pole to pole, a feature which some have called a "sideways smile." In a paper published in January 2017 in Nature Geoscience, scientists suggested the "smile" was the result of a gravity wave, a kind of disturbance in Venusian winds that propagates upwards as a result of the topography on the surface. In September 2017, Japanese scientists announced, based on Akatsuki data, the discovery of an equatorial jet in the Venusian atmosphere. Like a number of other deep space vehicles, Akatsuki carried the names of people (260,214 names) printed in fine letters on an aluminum plate.

224

Shin’en

Nation: Japan (8)

Objective(s): Venus flyby

Spacecraft: UNITEC 1

Spacecraft Mass: 20 kg

Mission Design and Management: UNISEC

Launch Vehicle: H-IIA 202 (no. 17)

Launch Date and Time: 20 May 2010 / 21:58:22 UT

Launch Site: Tanegashima / Area Y1

Scientific Instruments:

• 1. radiation counter
• 2. camera

Results: The UNISEC Technology Experiment Carrier 1 (UNITEC 1) was a Japanese student-built spacecraft designed for a flyby of Venus to study the effects of deep space travel on computers. Intended to be the first student spacecraft to operate beyond geocentric orbit, it was built and operated by UNISEC (University Space Engineering Consortium), a collaborative program involving 20 Japanese universities developing nano-satellites. Known as Shin'en ("abyss") after launch, the satellite carried six computers, a camera, a radiation counter, a low-power communications system, and solar cells for power. The launch and transplanetary injection occurred without incident (see Venus Climate Orbiter). Shin'en was the last spacecraft to separate from the multi-satellite stack and enter heliocentric orbit. The plan was for it to fly past Venus in December 2010. Although signals from the spacecraft were received on the first day after launch, there was no further communication after 15:43 UT on 21 May 2010 when Shin'en was 320,000 kilometers from Earth. A beacon was tracked until 31 May when it also stopped. The inert spacecraft flew past Venus sometime in December 2010.

225

IKAROS

Nation: Japan (9)

Objective(s): Venus flyby

Spacecraft: IKAROS

Spacecraft Mass: 310 kg

Mission Design and Management: JAXA

Launch Vehicle: H-IIA 202 (no. 17)

Launch Date and Time: 20 May 2010 / 21:58:22 UT

Launch Site: Tanegashima / Area Y1

Scientific Instruments:

• 1. instrument to measure variation in dust density (ALADDIN)
• 2. gamma-ray burst polarimeter (GAP)

Results: One of the most unique and innovative missions in the history of deep space exploration, IKAROS (Interplanetary Kite-craft Accelerated by Radiation of the Sun) was the world's first spacecraft to use solar sailing as the main propulsion. The mission was designed to demonstrate the deployment of a large (20 m diameter), square-shaped, and thin (7.5 micron) solar sail membrane, which had integrated into it thin-film solar cells to generate power for the main payload. It had instruments to measure the acceleration generated by radiation pressure. While radiation pressure constituted the main form of propulsion, the spacecraft used variable reflectance LCD panels (80 of them) for smaller attitude control movements. The sail also carried the ALLADIN (Arrayed Large-Area Dust Detectors in Interplanetary Space) instrument, which was a network of eight "channels" or separate (polyvinylidene difluoride) PVDF sensors attached to the sail. Collectively they had a detection area of 0.54 m2, making it, according to JAXA, "the world's largest dust detector" ever sent into space. ALLADIN's goal was to count and time hypervelocity impacts by micrometeoroids larger than a micron in size during its 6-month voyage to the vicinity of Venus. Launched along with the Venus Climate Orbiter, IKAROS was sent on a trajectory to Venus with its co-payloads, VCO and Shin'en. After separation from the launch vehicle, IKAROS, shaped like a drum, was spun up to 5 rpms, then spun down to 2 rpm to deploy four "tip mass" objects that uncoiled from the drum. At this point, on 3 June 2010, the "quasi-static" stage of the sail deployment began. The spacecraft spun up to 25 rpm and the membrane gradually unfurled through centrifugal force, slowing the central drum down to about 5–6 rpm once the four booms had reached to 15-meter-diameter lengths by 8 June. The second stage, the "dynamic" phase of the deployment began at that point when a stopper was dislodged at the center, releasing in 5 seconds the entire membrane (which after deployment, took about 100 seconds to stop vibrating). By 10 June, the full membrane was deployed with the spacecraft spinning at 1–2 rpms. At this point, IKAROS was 7.7 million kilometers from Earth and actively generating power from its thin-film solar cells. Two small separation cameras (DCAM2 and DCAM1) were deployed on 15 and 19 June, respectively, to take pictures of the solar sail. On 9 July, JAXA announced that IKAROS was, indeed, being accelerated by the solar sail (at a value 0.114 grams). On 13 July, the spacecraft successfully implemented attitude control using the LCDs on its solar panel, another first in the history of space exploration. IKAROS flew by Venus on 8 December 2010 at a range of 80,800 kilometers, essentially completing its originally planned mission, which JAXA extended into the indefinite future. Slowly, attitude control degraded on IKAROS, making it more difficult to communicate with. In March 2013, the IKAROS project team was disbanded but the project was reactivated three months later, on 20 June 2013 and telemetry was received from that point until 12 September 2013. There was intermittent detection of transmissions in 2014, punctuated by long periods of hibernation. In mid-March 2015, IKAROS appeared to wake up from hibernation. On 23 April 2015, ground controllers found the spacecraft about 120 million kilometers from Earth. However, after last data reception on 21 May 2015, IKAROS entered hibernation mode again, for the fifth time, when the spacecraft was about 110 million kilometers from Earth.