Cassini CIRS post launch operations support

驾驶卡西尼号飞船。2004年7月，卡西尼号飞船抵达土星，开始对这颗行星进行为期四年的详细研究，其壮观的光环和广泛的卫星系统。牛津大学的大气、海洋和行星物理系帮助建造了卡西尼号上安装的一种仪器，即复合红外光谱仪（CIRS）。CIRS以红外光谱的形式记录物体发出的特征热信号。利用这些数据，我们能够确定土星及其巨大卫星泰坦（太阳系中唯一已知的具有大量大气层的卫星）的大气层的组成和温度，以及环和其他卫星（主要是岩石和冰的混合物）的表面特性。我们实际上是如何进行这些测量的？如何在14亿公里的距离上控制航天器？首先，你必须得到命令的航天器（'上行'），然后你必须得到你的测量结果以及有关航天器的信息返回地球（'下行'）。自使命开始以来，牛津大学的小组一直参与上行链路和下行链路的工作。上行链路过程开始于将科学界设计的观测结果转换为用于使卡西尼号指向目标的命令。例如，一个典型的观测请求可能会说“将CIRS指向泰坦并上下扫描”。卡西尼号上有12台仪器，因此这些观测是与所有其他仪器团队协调进行的。为了帮助这个过程，卡西尼号的轨道之旅被分成几个部分，每个仪器都分配了一段时间，根据观测要求，如果土卫六隐藏在土星后面，那么就没有必要分配时间来观察土卫六！位于帕萨迪纳的美国宇航局喷气推进实验室（JPL）负责规划过程的这一部分，因为他们全面负责卡西尼号的使命。然后，仪器团队必须利用分配的时间进行最佳观测。观测设计被提交给航天器指令，并使用喷气推进实验室提供的软件工具进行测试。这模拟了卡西尼号进行测量，以检查它不会做可能伤害航天器的事情。这包括转动太快或将敏感部件（例如冷却CIRS的散热器）指向太阳等热物体。一旦设计完成并通过这些检查，它将被发送到JPL进行进一步测试。最后，它被发送到卡西尼使用美国宇航局的深空网络（DSN）。DSN是一个由西班牙、美国和澳大利亚的三个地面跟踪站点组成的网络。正如你所料，要与卡西尼号这样遥远的航天器通信，需要一个比数字电视迷你天线大得多的天线，例如美国的主天线直径为70米！我们在牛津大学的工作一直是与CIRS（位于美国宇航局戈达德航天中心）的仪器操作团队合作，主要为泰坦提供设计。所以我们实际上驾驶卡西尼一点！随着观测设计变成真实的航天器命令并加载到卡西尼号上，我们现在需要将数据返回（下行）到地球。卡西尼号在一端安装了一个大型圆盘，将数据发送回地球。然而，由于涉及非常大的距离，它需要DSN的非常敏感的碟形天线才能接收传输。一旦数据被DSN收集，它就会被JPL分发给每个仪器科学团队进行解包和分析。牛津大学的研究小组提供了一种软件，可以获取DSN接收到的原始信息，然后将其格式化，以便戈达德的研究小组可以对其进行校准（原始数据转化为有意义的光谱）。然后，CIRS团队的其他成员和更广泛的科学界将对数据进行分析。

Driving the Cassini Spacecraft. In July 2004 the Cassini spacecraft arrived at Saturn and began a four year detailed study of the planet, its spectacular rings and extensive system of moons. The sub-department of Atmospheric, Oceanic and Planetary Physics at the University of Oxford helped to build one of the instruments mounted on Cassini, the Composite Infrared Spectrometer (CIRS). CIRS records the characteristic heat signature emitted by objects in the form of an infrared spectrum. Using this data, we are able to determine the composition and temperature of the atmospheres of Saturn and its giant moon Titan (the only known moon in the Solar system to have a substantial atmosphere) and the surface properties of the rings and other satellites (which are mainly mixtures of rock and ice). How do we actually make these measurements? How do you control a spacecraft from a typical distance of 1.4 billion kilometres? Firstly, you have to get commands to the spacecraft ('Uplink') and then you have to get the results of your measurements as well as information about the spacecraft back to Earth ('Downlink'). Since the beginning of the mission, the group at Oxford have been involved in both uplink and downlink. The uplink process starts with turning observations designed by the science community in to commands that are used to turn Cassini to point at a target. For example, a typical observation request may say 'Point CIRS at Titan and scan up and down'. There are twelve instruments on Cassini, so these observations are made in co-ordination with all the other instrument teams. To help with this process, Cassini's orbital tour is divided into sections with each instrument allocated a block of time, based on the observations requirements, there is no point being allocated time to look at Titan if it is hidden behind Saturn! NASA's Jet Propulsion Laboratory (JPL) in Pasadena handles this part of the planning process, as they have overall responsibility for the Cassini mission. The instrument teams then have to use their allocated time to make the best possible observations. Observation designs are turned in to spacecraft commands and tested using a software tool provided by JPL. This simulates Cassini making the measurement to check that it does not do things that may harm the spacecraft. This includes such things as turning too quickly or pointing sensitive parts (e.g. the radiator to cool down CIRS) at hot objects such as the Sun. Once the design has been completed and passed these checks, it is sent to JPL for further testing. Finally, it is sent to Cassini using NASA's Deep Space Network (DSN). The DSN is a network of three ground-tracking sites in Spain, America and Australia. As you might expect, to communicate with a spacecraft as far away as Cassini requires a dish quite a bit bigger than a digital TV mini-dish / for example the main dish at the site in America is 70m in diameter! Our role at Oxford has been working with the instrument operations team for CIRS (based at NASA's Goddard Spaceflight Center) to provide designs mainly for Titan. So we actually drive Cassini a bit! With the observation design turned into real spacecraft commands and loaded on to Cassini, we now need to get the data returned (downlinked) to Earth. Cassini has a large dish mounted on one end to send the data back to Earth. However, because of the very large distances involved it needs the very sensitive dishes of the DSN to be able to receive the transmissions. Once the data is picked up by the DSN it is then distributed by JPL to each of the instrument science teams to be unpacked and then analysed. The group at Oxford provide software that takes the raw information received by the DSN and then formats it so that it can be calibrated (the raw numbers turned in to meaningful spectra) by the team at Goddard. The data is then ready to be analysed by the rest of the CIRS team, and the wider scientific community.