A question from here: "Why would Kepler rotate towards Earth instead of having an antenna always directed to Earth"?
这里有一个问题：“为什么开普勒会向地球旋转，而不是让天线始终指向地球”？
2 个解决方案
#1
25
Kepler has a parabolic dish antenna fixed to its body.
开普勒的抛物面天线固定在其身体上。
There are many possible designs of transmitting devices. For spacecraft, parabolic dish antennas are preferred, because they have the least attenuation for radio waves with distance. But dish antennas must be pointed to the receiver.
传输设备有许多可能的设计。对于航天器，抛物面天线是优选的，因为它们对具有距离的无线电波具有最小的衰减。但碟形天线必须指向接收器。
The Kepler telescope was over-budget for a Discovery-class mission, so some compromises were accepted. One of them was to use a fixed dish instead of a dish on a steerable arm.
开普勒望远镜对发现级任务的预算过高，因此接受了一些妥协。其中一个是在可操纵的手臂上使用固定的碟子而不是碟子。
Instead of this:
而不是这个：
it turned to this:
它转向了这个：
You can see the fixed dish at the lower part of the spacecraft.
您可以在航天器的下部看到固定的碟子。
From the NASA FAQ about Kepler:
关于开普勒的美国宇航局常见问题解答：
D6. Why is the high-gain antenna fixed on the spacecraft rather than on a gimbaled arm?
D6。为什么高增益天线固定在航天器而不是万向节臂上？
Early in the spacecraft design phase, a decision was made to mount the antenna directly on the spacecraft. There were two reasons: it reduced the mission design and construction cost, and it reduced risk of failure of the arm to extend the antenna after launch.
在航天器设计阶段的早期，决定将天线直接安装在航天器上。有两个原因：它减少了任务设计和建造成本，并降低了发射后手臂伸出天线失败的风险。
Because of this, Kepler needs to interrupt its observations for transmission of collected data. It turns the whole body to point the fixed dish antenna towards Earth.
因此，开普勒需要中断其观察以传输收集的数据。它将整个身体转向指向固定碟形天线朝向地球。
To address the comment:
要发表评论：
why is Kepler not design in a way that it always points to Earth with the communication device simultaneously being able to collect data
为什么开普勒的设计方式总是指向地球，同时通信设备能够收集数据
Kepler is on an Earth-trailing orbit with a period of 371 days. You can see it in this picture:
开普勒位于地球尾随轨道上，时间为371天。你可以在这张图片中看到它：
Kepler's distance to Earth is changing with time as well as direction. Kepler was designed to stare at a fixed area in the sky for at least three years. Remember also that both Kepler and Earth are moving around the Sun, but stars do not. As a result, the angle between two lines (Kepler-Earth and Kepler-area of interest) is always changing. So it's impossible to set a fixed dish to always point towards Earth.
开普勒与地球的距离随时间和方向而变化。开普勒的目的是盯着天空中的固定区域至少三年。还要记住，开普勒和地球都在绕着太阳运动，但是恒星却没有。结果，两条线（开普勒 - 地球和开普勒 - 感兴趣区域）之间的角度总是在变化。因此，不可能将固定的碟子设置为始终指向地球。
The same is for the K2 mission where Kepler stares at a fixed area in the sky for about 80 days and then switches to another area. (The areas should be close to the ecliptic because of solar light pressure balance requirements). These pictures show K2 areas as well as the initial (primary mission) area:
同样是K2任务，开普勒盯着天空中的固定区域大约80天，然后切换到另一个区域。 （由于太阳光压力平衡要求，这些区域应靠近黄道）。这些图片显示了K2区域以及初始（主要任务）区域：
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#2
7
Why would Kepler rotate towards Earth instead having an antenna always directed to Earth?
为什么开普勒会向地球旋转而不是将天线始终指向地球？
There was no need to always have an antenna pointed directly at the Earth because communication with the Earth was infrequent, less than eight hours per month.
没有必要总是直接指向地球的天线，因为与地球的通信很少，每月不到8小时。
There are a lot more deep space assets than there are receivers to communicate with those assets. The solution is to have intermittent communications, with the space assets recording data for subsequent high speed playback during their short communication time slots with the Deep Space Network.
深度空间资产比接收者与这些资产进行通信的要多得多。解决方案是进行间歇性通信，空间资产记录数据，以便在与深空网络的短通信时隙期间进行后续高速回放。
Time on the Deep Space Network is rather expensive, ranging from about \$1000 (US) to \$5000 per hour, plus an extra hour each of setup and teardown time. Because the Earth rotates, a full time, 24/7/365 contact would require switching between ground stations, requiring over 30 hours of DSN contact time per day, including setup and teardown time. A full-time, 24/7/365 contact would have made Kepler's DSN costs alone be well in excess of ten million dollars per year. It would also have required that Kepler have a significantly more expensive antenna than it did have.
深空网络上的时间非常昂贵，从每小时1000美元到每小时5000美元不等，每个设置和拆卸时间都需要额外增加一小时。由于地球旋转，全天24/7/365接触需要在地面站之间切换，每天需要超过30小时的DSN接触时间，包括设置和拆除时间。全天候24/7/365联系将使开普勒的DSN成本每年超过一千万美元。它还要求开普勒拥有比它更昂贵的天线。
Kepler was intended from the start to be a low cost mission. Instead of full-time contact, Kepler had once a month contacts with the DSN. For the vast majority of the month, Kepler was out of contact and was instead collecting data.
开普勒从一开始就打算成为一项低成本的任务。开普勒没有与全职联系，而是每月与DSN联系一次。在本月的绝大部分时间里，开普勒没有接触，而是收集数据。
#1
25
Kepler has a parabolic dish antenna fixed to its body.
开普勒的抛物面天线固定在其身体上。
There are many possible designs of transmitting devices. For spacecraft, parabolic dish antennas are preferred, because they have the least attenuation for radio waves with distance. But dish antennas must be pointed to the receiver.
传输设备有许多可能的设计。对于航天器，抛物面天线是优选的，因为它们对具有距离的无线电波具有最小的衰减。但碟形天线必须指向接收器。
The Kepler telescope was over-budget for a Discovery-class mission, so some compromises were accepted. One of them was to use a fixed dish instead of a dish on a steerable arm.
开普勒望远镜对发现级任务的预算过高，因此接受了一些妥协。其中一个是在可操纵的手臂上使用固定的碟子而不是碟子。
Instead of this:
而不是这个：
it turned to this:
它转向了这个：
You can see the fixed dish at the lower part of the spacecraft.
您可以在航天器的下部看到固定的碟子。
From the NASA FAQ about Kepler:
关于开普勒的美国宇航局常见问题解答：
D6. Why is the high-gain antenna fixed on the spacecraft rather than on a gimbaled arm?
D6。为什么高增益天线固定在航天器而不是万向节臂上？
Early in the spacecraft design phase, a decision was made to mount the antenna directly on the spacecraft. There were two reasons: it reduced the mission design and construction cost, and it reduced risk of failure of the arm to extend the antenna after launch.
在航天器设计阶段的早期，决定将天线直接安装在航天器上。有两个原因：它减少了任务设计和建造成本，并降低了发射后手臂伸出天线失败的风险。
Because of this, Kepler needs to interrupt its observations for transmission of collected data. It turns the whole body to point the fixed dish antenna towards Earth.
因此，开普勒需要中断其观察以传输收集的数据。它将整个身体转向指向固定碟形天线朝向地球。
To address the comment:
要发表评论：
why is Kepler not design in a way that it always points to Earth with the communication device simultaneously being able to collect data
为什么开普勒的设计方式总是指向地球，同时通信设备能够收集数据
Kepler is on an Earth-trailing orbit with a period of 371 days. You can see it in this picture:
开普勒位于地球尾随轨道上，时间为371天。你可以在这张图片中看到它：
Kepler's distance to Earth is changing with time as well as direction. Kepler was designed to stare at a fixed area in the sky for at least three years. Remember also that both Kepler and Earth are moving around the Sun, but stars do not. As a result, the angle between two lines (Kepler-Earth and Kepler-area of interest) is always changing. So it's impossible to set a fixed dish to always point towards Earth.
开普勒与地球的距离随时间和方向而变化。开普勒的目的是盯着天空中的固定区域至少三年。还要记住，开普勒和地球都在绕着太阳运动，但是恒星却没有。结果，两条线（开普勒 - 地球和开普勒 - 感兴趣区域）之间的角度总是在变化。因此，不可能将固定的碟子设置为始终指向地球。
The same is for the K2 mission where Kepler stares at a fixed area in the sky for about 80 days and then switches to another area. (The areas should be close to the ecliptic because of solar light pressure balance requirements). These pictures show K2 areas as well as the initial (primary mission) area:
同样是K2任务，开普勒盯着天空中的固定区域大约80天，然后切换到另一个区域。 （由于太阳光压力平衡要求，这些区域应靠近黄道）。这些图片显示了K2区域以及初始（主要任务）区域：
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资源
#2
7
Why would Kepler rotate towards Earth instead having an antenna always directed to Earth?
为什么开普勒会向地球旋转而不是将天线始终指向地球？
There was no need to always have an antenna pointed directly at the Earth because communication with the Earth was infrequent, less than eight hours per month.
没有必要总是直接指向地球的天线，因为与地球的通信很少，每月不到8小时。
There are a lot more deep space assets than there are receivers to communicate with those assets. The solution is to have intermittent communications, with the space assets recording data for subsequent high speed playback during their short communication time slots with the Deep Space Network.
深度空间资产比接收者与这些资产进行通信的要多得多。解决方案是进行间歇性通信，空间资产记录数据，以便在与深空网络的短通信时隙期间进行后续高速回放。
Time on the Deep Space Network is rather expensive, ranging from about \$1000 (US) to \$5000 per hour, plus an extra hour each of setup and teardown time. Because the Earth rotates, a full time, 24/7/365 contact would require switching between ground stations, requiring over 30 hours of DSN contact time per day, including setup and teardown time. A full-time, 24/7/365 contact would have made Kepler's DSN costs alone be well in excess of ten million dollars per year. It would also have required that Kepler have a significantly more expensive antenna than it did have.
深空网络上的时间非常昂贵，从每小时1000美元到每小时5000美元不等，每个设置和拆卸时间都需要额外增加一小时。由于地球旋转，全天24/7/365接触需要在地面站之间切换，每天需要超过30小时的DSN接触时间，包括设置和拆除时间。全天候24/7/365联系将使开普勒的DSN成本每年超过一千万美元。它还要求开普勒拥有比它更昂贵的天线。
Kepler was intended from the start to be a low cost mission. Instead of full-time contact, Kepler had once a month contacts with the DSN. For the vast majority of the month, Kepler was out of contact and was instead collecting data.
开普勒从一开始就打算成为一项低成本的任务。开普勒没有与全职联系，而是每月与DSN联系一次。在本月的绝大部分时间里，开普勒没有接触，而是收集数据。