A new mission for Akatsuki, and status updates for Hayabusa2 and Chang'e
Posted by Emily Lakdawalla
09-02-2015 18:32 CST
Here are brief updates on four ongoing missions: JAXA's Akatsuki and Hayabusa2, and China's Chang'e 3 and Chang'e 5 test vehicle.
Japan's Akatsuki Venus orbiter will re-attempt Venus orbit insertion on December 7, 2015. Even if its orbit insertion is successful, Akatsuki won't be the same mission it was intended to be. JAXA described the new shape of the mission in a press release late last week.
Originally, Akatsuki's orbit was to have a periapsis of 300 kilometers and an apoapsis of 79000 kilometers, with a period of 30 hours. The shape of this orbit was chosen so that Akatsuki's orbital motion would be roughly synchronized with the flow of Venus' upper-level winds for a period of 20 hours of every orbit. Here's how they would have used that orbit, according to project scientist Takeshi Imamura:
Global images of the atmosphere and the ground surface will be obtained every 2 hours successively and continuously from such a ‘quasi-synchronized’ orbit...The systematic imaging sequence of Venus Climate Orbiter is advantageous for detecting meteorological phenomena with various temporal and spatial scales. The quasi-synchronized orbit is suitable for obtaining cloud-tracked wind vectors, especially the small deviation of local wind vectors from the background super-rotation. With such wind vectors the characterizations of the meridional circulation, mid-latitude jets and various wave activities are anticipated. Close-up images of meso-scale features and limb images will also be obtained near the periapsis. The shadow region along the orbit is utilized for observing faint light such as lightning and airglow. Radio occultation experiment will also be performed when the spacecraft is hidden by Venus as viewed from the ground station.
The new orbit will have a different shape. It will be much more distant, reaching between 300,000 and 400,000 kilometers from the surface at apoapsis, and with a period of 8 to 9 days, depending upon the engines' performance at orbit insertion.
Will they still be able to perform the planned science? Last week, JAXA announced a new set of science goals for the modified mission:
- When flying further away from Venus, or about 10 times the radius of Venus from the planet, the Akatsuki will continuously observe Venus as a whole to understand its clouds, deep atmosphere, and surface conditions.
- When flying closer to Venus, or less than 10 times the radius of Venus, the orbiter will conduct close-up observations to clarify cloud convection, the distribution of minute undulatory motions and their changes.
- When Akatsuki comes closest to Venus, it will observe the layer structure of clouds and the atmosphere from a lateral direction.
- When the orbiter is in the shade of the Sun, it will monitor lightning and airglow (night glow).
- Akatsuki will also observe to capture the atmospheric layer structure and its changes by emitting radio waves that penetrate the atmosphere of Venus and receiving them on the ground.
On the face of it, these goals sound pretty similar to the original goals; it's good that they'll be able to salvage some of the planned-for science from this meeting. The differences come down to the frequency of distant and close-up observations. The nature of elliptical orbits is that the spacecraft spends much more of its time very far from Venus than it will spend close up. Almost all of Akatsuki's activity is described in item 1: continuous observations of the clouds. Of course, since the spacecraft will reach distances 5 times farther than originally planned, Venus will appear much smaller and lower-resolution for most of this period than planned. The rest of the goals, items 2-5, will only be addressed for the short periods near periapsis, once every 8 or 9 days, rather than once every 30 hours.
Meanwhile, a brief Hayabusa2 status update from JAXA tells us that the "initial functional confirmation" period is going well. They have tested each of the four ion engines one at a time, generating thrust of 7 to 10 millinewtons. Later, they tested long-duration thrusting, running two or three engines simultaneously for periods longer than 24 hours, with a maximum thrust of 28 millinewtons. They successfully tested the Ka-band radio system, a first for JAXA. Ka-band is higher-frequency than the more commonly used X- and S-band radio; NASA, too, is shifting toward the use of Ka-band, having tested it for the first time in deep space on Mars Reconnaissance Orbiter. Next up for Hayabusa2 is instrument commissioning; the mission should transition into routine cruise operations in March. It is headed toward a July 2018 rendezvous with asteroid (162173) 1999 JU3.
It's been a while since I wrote about the status of the Chang'e program. On the lunar surface, amazingly enough, it appears that the Yutu rover is still alive and communicating with Earth. Amateur radio operators have detected its signal:
Signal from Chinese YUTU rover ! http://t.co/BVqC1w66ju - I am utterly amazed this thing is still transmitting! Checking EME uplink next— UHF Satcom (@uhf_satcom) February 2, 2015
Another FFT of Yutu downlink, slight Doppler noted, but consistent strong signal with no modulation. http://t.co/uEdI8Vxrco on air now ;-)— UHF Satcom (@uhf_satcom) February 3, 2015
Finally, the Chang'e 5 test vehicle service module has traveled via the Earth-Moon L2 point into a tight circular lunar orbit. According to a Chinese defense ministry press release, it entered into a 200-kilometer, 127-minute orbit, inclined 43.7 degrees to the equator, on January 13. Since then, they have conducted a series of successful tests with the service module that were designed to simulate some challenging elements of the future Chang'e 5 sample return mission. They will have to perform an on-orbit rendezvous between an orbiter and a presumably less maneuverable sample return capsule launched from the lunar surface. The tests involved adjusting the orbit's height and speed to deliver the orbiter to the right position with the right velocity at the right time to rendezvous with the capsule.