Now (Jan. 23), IKAROS's data rate is only 13 byte/Day (not 13 byte/sec)
Ошизеть. Нанонизм в чистом виде.
Может быть, это из-за влияния помех от близкого Солнца на линии передачи? Как-то сомнительно, чтобы аппарат делали на такую смешную мощность. Тем более, вряд ли он смог бы передать вышеприведенный снимок.
IKAROS is a spin-stabilized spacecraft. Its unique feature is a huge solar sail of an ultra-flexible structure, 14m x 14m in size and 7.5µm in thickness (Fig. 1). Before and after the success of full deployment of the sail on June 9, 2010, public attention was concentrated on the sail itself and its deployment system. However, the role of the attitude-control system is critical to allow IKAROS to perform "solar sailing" using its deployed sail without problems. At the same time, we were under pressure to implement the IKAROS mission at low cost. Under the circumstances, we tried a new inconspicuous yet highly capable attitude system. Let me introduce four examples here (Fig. 2).
Figure 1. IKAROS flying in deep space, photographed by deployable camera (DCAM)
Figure 2. IKAROS under final check-up in Tanegashima Instruments in boxes highlighted in red are those related to the attitude and orbital control system.
The first example is the "gas-liquid equilibrium thruster," a new type of propulsion system onboard IKAROS for attitude control. A nontoxic alternative to the chlorofluorocarbon is used as propellant of the thruster. Since the propellant can be stored as a liquid and fired as a gas, it allows us to build a propulsion system of low pressure and small volume storage tank. Thus, the propulsion system of IKAROS, which was launched as a piggyback payload, was very easy to handle in terms of both launch-site operation and simplification of rocket interface.
The second is an attitude-detection system. Usually, for a spin-stabilized satellite, spin-axis direction in outer space is determined uniquely by earth sensor, or by a combination of sun sensor and star sensor. IKAROS uses a sun sensor and a low-gain antenna (LGA) for communication to determine its attitude. This is adopted to lower the cost of the spacecraft itself. When radiowaves transmitted from the LGA are received on the ground, the frequency is Doppler-shifted due not only to orbital movement but also its spin. The Doppler shift level is determined by the relation of the earth to IKAROS's spin axis. Accordingly, by measuring the amount of Doppler-shift and then calculating back, we can know the "earth angle." This technique evolved from one used in HAYABUSA in an emergency. Since IKAROS does not carry a high-gain antenna, we are forced to operate it through very thin line. This method that references the carrier waves without decoding the telemetry allowed us to estimate IKAROS's attitude to some degree. It proved very handy for us in actual operation of IKAROS. The third is a variable-reflectivity element (liquid-crystal device). This is a kind of electric frosted glass sometimes seen in executive offices, etc. The reflectivity of the device developed by us for IKAROS varies in response to power ON and OFF. The devices were enclosed in thin polyimide film, the same material as the sail, and mounted in line around the edges of the sail. As they turn ON and OFF repeatedly in synchronization with the spin rate, solar-light pressure becomes unbalanced, eventually generating torque that affects the entire spacecraft to tilt its spin axis. With this method using light pressure, we can control IKAROS's attitude without use of fuel. As reported in our press release, this mechanism has functioned very well.
The fourth example is attitude-control logic. Since IKAROS flies hoisting a huge, ultra-flexible film at all times, we needed to satisfy contradictory requirements. Specifically, since the solar sail is orbitally controlled by changes in the sail direction, we have to maintain stably the shape of the huge, ultra-flexible structure and, at the same time, to perform quick attitude control. The traditional control law called "rhumb-line control" is usually adopted for attitude control of spin-satellites. For IKAROS we introduced a control law called "flex rhumb-line control," which added some measures needed for a flexible structure to the conventional law. However, our attempt failed. Unfortunately or fortunately, as the structural attenuation of IKAROS's sail is strong enough, the new control law did not work fully. As a control specialist, this is regrettable. But I accepted this fact positively because the new approach was introduced following the principle of space development "better safe than sorry."
Verified acceleration caused by solar-light pressure
On June 9, 2010, IKAROS successfully deployed its sail fully. The deployment status was confirmed promptly by information from gyro, then the Doppler. As IKAROS does not perform active attitude control while the sail is deployed, its spin rate is governed by the principle of conservation of angular momentum. This means that, by monitoring any decrease of spin rate by gyro data, we can see to what degree the sail deploys. Our staff in charge of IKAROS's attitude was monitoring the data.
On the other hand, staff in charge of IKAROS's orbit was monitoring the Doppler. By filtering and removing spin modulation of the Doppler appearing in the communication waves mentioned above, we were able to determine the speed at which IKAROS left the earth or the velocity in the direction-of-sight line. The data clearly indicated that IKAROS started accelerating just after sail deployment with an acceleration amount of 3.6 x 10-6m/s. This value is just that we predicted as solar-light pressure acceleration. It was this very moment that we confirmed start of cruising by solar-sail in deep space for the first time in the world.
Attitude operation strategy for IKAROS
The solar-light pressure applied to the sail also acts as a torque disturbing IKAROS's attitude in addition to translational force (i.e., light-pressure acceleration). For a solar sail requiring much light-pressure acceleration, torque disturbance by light pressure is an unavoidable issue. From the planning stage before the launch, we intended to perform attitude control positively using this light-pressure torque disturbance.
Although IKAROS is a spin-stabilized spacecraft, its spin axis fluctuates opposite to the principle of conservation of angular momentum because its sail receives huge solar-light pressure. We can forecast the fluctuation accurately if we know the shape and optical characteristics of the sail exactly. Actually, however, since, at the development stage, we were unable to estimate accurately the sail's wrinkles after deployment and temporal changes of optical characteristics, we were required to make model identification using flight data.
With IKAROS, we realized our plan to perform model identification and, then, make use of the tendency of the fluctuation reversely so as to orient IKAROS to the desired direction while saving the propellant as much as possible. In fact, almost no propellant was consumed to keep the sail's surface direction to the Sun. The amount of change of the spin axis to inertial space was 180 degree over six months, which means that the sail was tuned just to the opposite direction without use of fuel (Fig. 3). IKAROS used its fuel mainly to change the sail direction promptly or maintain the spin rate.
Figure 3. IKAROS's flight route and attitude The figure is expressed in the inertial coordinate system centered on the Sun. Black arrows show direction of spin-axis vector at respective times
Manipulating IKAROS's orbit
Now let me move to the main topic - navigation and guidance of the solar sail. IKAROS's navigation and guidance task is roughly divided into two parts ? orbit determination and orbit control.
One problem in orbit determination for the solar sail is that it has to be implemented under constant minute perturbations caused by light pressure. Even with HAYABUSA, orbit determination during minute thrust conditions was difficult. We needed to implement the task as a routine operation with IKAROS. If we were able to estimate the perturbation accurately, however, we could evaluate the sail condition in orbit, i.e., "the solar-sail performance." A research group was launched within the IKAROS team to conduct the evaluation. With the participation of many postdoctoral fellows and students as well as JAXA staff and external companies, we were able to complete the analysis using flight data. With this orbit-determination technology, a thin beam from the 64m antenna at Usuda has been able to track IKAROS constantly. Currently, we are trying to draw out more detailed information on sail performance by estimating optical parameters, which are higher order than the usual orbit determination.
Orbital control for the solar sail means attitude control stated above. Specifically, the task is to control the sail direction to the Sun daily so that IKAROS may fly along the given target orbit. IKAROS is a mission that has no predetermined destination. The orbit was designed to optimize the AKATSUKI mission, which was co-launched with IKAROS. For this reason, we set up a tentative target on the collision cross-section (technically known as the B-plane) including Venus and have evaluated the guidance performance by guiding IKAROS to the target (Fig. 4). In other words, we set a provisional point situated at the same distance as Venus and flew IKAROS towards that point. Thus, we were able to fly IKAROS, which was initially inserted to about the same orbit as AKATSUKI by the H-IIA rocket, to pass the opposite side of AKATSUKI across Venus (i.e., the night side of Venus). We are still evaluating the guidance and navigation performance in detail. Nevertheless, the IKAROS team is confident that it has obtained the solar-sailing technology.
Figure 4. Result of Venus relative guidance Lower right is conceptual illustration of Venus B-Plane (collision cross-section including Venus) relative guidance. Upper left shows actual result. Projected point of ballistic flight does not move over time and is expressed as a dot on the B-Plane. Since IKAROS performed non-ballistic flight with the solar sail, its trajectory is described as non-dot one on the B-Plane.
IKAROS acquired acceleration of 100m/s from the solar-light pressure over six months until it passed Venus. This value is equal to propellant amount consumed for orbital adjustment of deep-space exploration missions of usual ballistic flight. Moreover, the advantage is simply proportional to flight duration. Our next technical target is a sail area 10 times that of IKAROS and mission duration over five years. This translates to an acceleration capability of several km/s, which is virtually the same as obtaining rocket acceleration capability without fuel. Furthermore, by using the large sail as a generator, we plan to drive an electric propulsion system with high-specific impulse and high power, eventually add more freedom to mission planning. I hope that you see how solar-power sail technology can drastically change deep-space exploration in the future.
Japanese Researchers Controlled Solar Sail[/size:8ba9a2a4c5]
Jun 2, 2011
By Frank Morring, Jr.
Japanese researchers are working on a solar-sail spacecraft with 10 times the surface area of the Ikaros testbed launched toward Venus last year, after achieving all of their technical objectives with the testbed.
This spacecraft will launch on a five-year mission instead of the six-month span allotted to Ikaros. Lofted as a piggyback payload with the Venus Climate Orbiter Akasuki on May 21, 2010, Ikaros passed Venus on Dec. 8.
Researchers hoped to demonstrate automatic sail deployment, power generation with thin-film solar cells on the sail surface, verification that the pressure of photons from the Sun caused the sail to accelerate, and guidance and navigation with the sail. The sail met its intended acceleration of 100 meters per second and veered off the ballistic trajectory it would have followed without the Sun’s pressure, says Yuichi Tsuda, an assistant professor in the Japan Aerospace Exploration Agency (JAXA) Space Exploration Center, in an English-language report on the experiment’s outcome.
The deployment and power generation were demonstrated early on. To control the 14 x 14-meter (46 x 46-ft.) spin-stabilized sail, the Ikaros team used a non-toxic “gas-liquid equilibrium thruster” for attitude control, and an attitude-detection system that combined a Sun sensor and Doppler measurements from the low-gain antenna.
To tilt the spin axis of the spacecraft, the team powered a liquid-crystal variable-reflectivity element mounted as a thin polyimide film around the edges of the sail off and on to throw the spinning sail off balance and tilt it as it spun. As it happened, the spacecraft required almost no fuel to keep its sail facing the Sun, even though it turned a full 180 deg. over the six months, according to Tsuda.
Drawing on experience navigating the solar-electric-powered Hayabusa asteroid sample-return mission with only one of its thrusters working, the JAXA team determined the Ikaros orbit using flight data obtained by tracking it with the 64-meter antenna at the Usuda Deep Space Center. Using that data and the control system, the team was able to fly Ikaros to the night side of the planet while the Akasuki probe flew to the opposite side, the only difference in trajectory being the sunlight pressure on the sail.
“We are still evaluating the guidance and navigation performance in detail,” Tsuda says. “Nevertheless, the Ikaros team is confident that it has obtained the solar-sailing technology.”
October 18, 2011 Updated Result of IKAROS 'reverse spin operation'[/size:55812668b1]
On Oct. 18, 2011 (Japan Standard Time), JAXA performed a "reverse spin operation" of the IKAROS. As a result of the jet thrust to shift IKAROS's spin direction to the reverse way for about 20 minutes from 7:20 a.m. on the 18th, the membrane successfully spun in the reverse course without being entangled. The IKAROS is in good shape after reversing its spin, and its spin rate at the time of completing this operation was -0.24rpm. We are currently evaluating if we will continue the mission. For assessing it more in detail, the following information must be acquired. 1) Attitude related date from the data recorder that accumulated information during the reverse spin. 2) Data necessary for predicting future attitude change. We will announce the detailed evaluation results as soon as we complete data acquisition and analysis.[/size:55812668b1]
JAXA's solar sail mission IKAROS is still hibernating, and there's no way of knowing if the spacecraft will reawaken or not. They try to raise contact with the spacecraft once a month, with the last attempt being made on March 10; we can only wait to see if they'll succeed. What better time to release a theme song for the mission? IKAROS has always been even more full of personality even than other JAXA missions (which is saying a lot).
Sing it, IKAROS! IKAROS performs his theme song! Credit: JAXA
By the way, I'm not sure why, but this flash player is not showing any kind of control that allows you to stop it once it starts. Until I figure out how to do that, all you need to do if you want to stop the song is to refresh the page.
Of course, it's in Japanese; all I managed to catch on a first listen was an "arigato" (thank you) to DCAM1 and DCAM2, the little deployable cameras, long gone now, that photographed IKAROS spinning in space. But they posted a PDF with the lyrics (which also included that adorable cartoon), and with a little help from Twitter I have a translation. The translation was by Nathaniel Guy (@NattyBumpps), who also commented, "If this were the theme song to an anime, I would totally watch it!" Me too!
(Spoken) All right! Hop on the yacht and let's travel through the solar system!
(1st) The sun sparkles in the sea of space Spinning around, the world's first space yacht IKAROS No matter what happens, it's a challenge! You'll keep on going! Believing in distant, great dreams Dreams infinitely far off, out into space Come on, take off! Recharge your courage! Spread your sails with all your might Let's set forth into the future, catching the light of hope!
(2nd) Your polished membrane makes electricity with solar cells Your flashing crystals Your sails are thin, but they're tough polyimide Vast, vast space... what could be up ahead? Believe in the path you take An epic voyage through the sea of far space So journey on, pushed on by light Steer as you will A silver sparkle blooming like a flower in the dark
(Spoken) "DCAM1, DCAM2, thank you for taking photos out in space! No matter how far we go, the three of us will always be together. Forever and forever!" I'll grow larger, and go on adventures, farther and farther! Next is Jupiter, my dream and the dream of big brother Hayabusa!
(3rd) These passions I shut up within my heart for so long It's time to open them up, right now! Passing through the darkness of outer space Come on, let's work together Full of dreams, I spread my sails wide Into the unlimited future, catching the light of hope!
September 11, 2012 Updated IKAROS to wake up from hibernation
The IKAROS was confirmed to have shifted itself into hibernation mode (or shutting down its onboard equipment due to low power generation) sometime before Jan. 6, 2012. After moving into hibernation mode, the IKAROS team has been searching for the IKAROS twice a month. On Sept. 6 (Thu.), 2012, a radio wave that appeared to be emitted from the IKAROS was detected. On the 8th (Sat.) it was confirmed to be from the IKAROS, and we made sure that the IKAROS came out from hibernation mode (or recovered.) We are now checking the satellite's status.
Гамма-всплески — довольно редкие события, связываемые с коллапсом вещества обычной массивной звезды в нейтронную звезду или чёрную дыру. Энергия их необычайно велика — к примеру, равна энергии, излучаемой Солнцем за 10 млрд лет, то есть за всю жизнь светила, включая ту, что только предстоит. Поляризация, которую удалось с беспрецедентной точность измерить японцам, знакома любому посетителю так называемого 3D-кинотеатра. Там при помощи поляризованных очков вы видите наложение двух изображений, содержащих сходную «картинку» с разной поляризацией.
Благодаря огромному удалению источников гамма-всплесков от Земли мы можем, проанализировав их фотоны, сделать вывод об их поляризации на протяжении тех миллиардов лет, которые ушли у гамма-фотонов всплеска на преодоление пути до земного наблюдателя. В результате проведённых измерений удалось установить, что, несмотря на огромное время путешествия этих гамма-фотонов, их поляризация не вращалась.
Отсутствие такого вращения накладывает серьёзные ограничения на нарушение CPT-инвариантности — фундаментальной симметрии физических законов при преобразованиях, включающих одновременную инверсию заряда, чётности и времени. Именно CPT-инвариантность, предполагающая, что между частицами и античастицами есть строгое равенство массы и магнитного момента, считается фундаментальным качеством физических законов. И именно её теория суперструн считает неверной на очень малых расстояниях, где такая симметрия свойств частиц и античастиц должна нарушаться, как уверяют нас сторонники этой гипотезы.
«Полученный результат накладывает фундаментальные ограничения на квантовую гравитацию — теорию-мечту, объединяющую эйнштейновскую теорию гравитации и квантовую теорию», — полагает Кенджи Тома. Отметим, что не только теория суперструн, но и петлевая квантовая гравитация принципиально зависят от существования предсказываемого ими, но пока не обнаруженного экспериментально нарушения CPT-инвариантности.
Новые данные, свидетельствующие о линейной поляризации фотонов гамма-всплесков, накладывают на нарушение СРТ-инвариантности ограничения в 1015 на миллион. Хотя ряд предыдущих наземных экспериментов уже накладывал такого рода ограничения, они были на восемь порядков менее строгими, что давало не много в смысле доказательности: отсутствие нарушения было показано только для величин, очень далёких от планковской длины, а именно на её масштабах, как считается, должны проявляться как струны, так и нарушение СРТ-инвариантности. Новый же результат, по всей видимости, заставит пересмотреть параметры струнных теорий в целом.