Cassini CIRS post launch operations support

驾驶卡西尼号宇宙飞船。2004年7月，卡西尼号宇宙飞船抵达土星，开始对这颗行星、其壮观的光环和广泛的卫星系统进行为期四年的详细研究。牛津大学大气、海洋和行星物理学分部帮助建造了安装在卡西尼号上的仪器之一--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特征。利用这些数据，我们能够确定土星及其巨星卫星土卫六(太阳系中唯一已知的拥有大量大气的卫星)的大气成分和温度，以及土星环和其他卫星(主要是岩石和冰的混合物)的表面属性。我们实际上是如何进行这些测量的？你如何在14亿公里的典型距离上控制航天器？首先，你必须得到航天器的命令(‘上行链路’)，然后你必须得到你的测量结果以及航天器返回地球的信息(‘下行链路’)。自任务开始以来，牛津大学的团队一直在参与上行和下行链路。上行链路过程始于将科学界设计的观测转化为用于将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‘指向泰坦，向上和向下扫描’。卡西尼号上有12台仪器，所以这些观测是在所有其他仪器团队的协调下进行的。为了帮助这一过程，卡西尼号的轨道旅行被分成几个部分，每个仪器都分配了一段时间，根据观测要求，如果泰坦隐藏在土星后面，那么分配时间去看它是没有意义的！NASA位于帕萨迪纳的喷气推进实验室(JPL)负责这一部分的规划过程，因为他们对卡西尼任务负有全面责任。然后，仪器团队必须使用他们分配的时间来进行尽可能好的观测。观测设计被提交给航天器命令，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，以检查它没有做可能损害航天器的事情。这包括转得太快或将敏感部件(例如，用于冷却CIRS的散热器)对准太阳等高温物体。一旦设计完成并通过这些检查，它就会被送到喷气推进实验室进行进一步测试。最后，使用NASA的深空网络(DSN)将其发送到卡西尼号。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。正如你可能预料的那样，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碟子大得多的碟子/例如，美国现场的主碟子直径为70米！我们在牛津的角色一直是与CIRS(总部设在NASA戈达德航天中心)的仪器运营团队合作，主要为土卫六提供设计。所以我们实际上开了卡西尼号一段路！随着观测设计变成真正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。卡西尼号的一端安装了一个大碟子，用于将数据发送回地球。然而，由于涉及的距离非常远，它需要DSN的非常敏感的碟子才能接收传输。一旦数据被DSN获取，然后由喷气推进实验室将其分发给每个仪器科学团队进行拆包，然后进行分析。牛津大学的团队提供软件，获取DSN接收的原始信息，然后对其进行格式化，以便戈达德的团队可以对其进行校准(将原始数据转化为有意义的光谱)。然后，数据就可以由CIRS团队的其他成员和更广泛的科学界进行分析了。

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.