NASA's Mission to Pluto and the Kuiper Belt
Pluto and the Kuiper Belt hold many secrets that scientists are anxious to uncover, so the science team works hard to figure out what questions to ask and what data (including images) to collect to reveal those secrets. In addition to choosing the right observations, the scientists must be able to study the data once it comes back to Earth.
The Tombaugh Science Operations Center at the Southwest Research Institute, Boulder, Colorado.
The New Horizons spacecraft, just like Earth-bound computers, speaks in a stream of cryptic-looking 1's and 0's (in this case traversing space via radio waves). How do we make sense of this? How do we command the spacecraft to do what we want it to do? The New Horizons Science Operations Center answers these questions.
The Science Operations Center (or "SOC") is both a computer facility in Boulder, Colorado, and an experienced and synergistic team of people who have to stay a step ahead of the spacecraft during its journey. The SOC has three main responsibilities:
The New Horizons spacecraft listens to Earth, waiting to be told what to do next. It hears radio waves, and riding on those waves are commands composed of patterns of "bits" (1's and 0's). The commands themselves are sent to the spacecraft by the Mission Operations Center (or "MOC") at the Johns Hopkins Applied Physics Lab in Maryland, which is where all direct communication with New Horizons happens. But if those commands involve collecting science data, the SOC uplink team has to first work with the scientists to interpret and translate their objectives into the spacecraft's language. The plan might be to collect data that will tell us something we never knew before, or just to take some really cool pictures--and there are plenty of those to be taken!
The act of translating scientists' objectives into spacecraft commands is called "sequencing," and it is a very specialized skill. It requires both an understanding of the science and an intimate familiarity with the spacecraft's capabilities. These experts have to know a LOT about New Horizons and how it works in very fine detail. Also, sequencing is a great responsibility. Those commands have to be right! There is a way, however, to try out the commands before they ever are sent for real, and that is to use a ground-based simulator. Simulating the behavior of the spacecraft to the commands ahead of time goes a long way toward making sure there are no mistakes in the sequences, reducing risk.
The 3D nature of space makes planning observations extremely tricky. Software tools are used to help with visualizing the fields of view for the instruments (like the view you see when you look through your camera, for example), making sure that the instrument takes a snapshot of just the region the scientists want to observe.
These tools can also calculate important parameters for spacecraft and instrument safety, such as the angle between the spacecraft and the Sun. To point an instrument for an observation, often the spacecraft has to rotate around through, say, 90 degrees, but there are a few instruments onboard that would be harmed if they looked straight at the Sun during one of these turns. So sequences are designed to rotate the spacecraft in a specific way to avoid looking at the Sun.
Even moving at the speed of light, radio waves can take hours to reach the spacecraft - so many of the commands sent to the spacecraft are programmed to execute at a specific time in order to capture images and data at just the right moment (like "closest approach," when we can get the most detailed images). Thus, uplink is a little like choreographing an intricate dance between New Horizons, Pluto, its moons, and other Kuiper Belt objects like Ultima Thule. The result is the data that are sent back to Earth, where the downlink processing happens.
From Pluto, radio waves take 4½ hours to reach Earth. Also, at that distance, the signal is very weak, so large antenna dishes on Earth, part of NASA's Deep Space Network, are needed to receive the faint radio waves. A ground-based network gets the raw data to the MOC for processing, where the data is cleaned up (bad data is removed) and put into large "daily archive" files. At this point, the data is intact, but it is in a very raw form that would not make much sense to anyone who would need to look at or use it. It is the SOC's job to sort this out and produce usable science data.
View images from the Science Operations Center (SOC) >
The SOC computers fetch the large archive files from the MOC each day over the Internet and put them through an automated system called the Science Data Pipeline. The data in the archives is in the form of packets of bits, and these packets need to be decoded and pieced together to make each data set or image. As illustrated below, an image can contain thousands of packets with millions of bits.
Packets can arrive out of order, and they can even be missing (having undergone damage during their long voyage). Also, science data is mixed in with "housekeeping" information like temperatures and voltages from the spacecraft and the various instruments. So in order to find the observations within this "soup" of data, the pipeline must sort and group the packets, ultimately producing science data files. In the case of New Horizons, all of the files produced by the pipeline are in a format called FITS (Flexible Image Transport System), which has been used for years in astronomy. This process is depicted below (click on the diagram for a larger version):
But what if data is late in arriving or never makes it back? The pipeline will actually detect these cases and go on to produce the data file, leaving the missing area blank. If the missing data does finally come in, the pipeline will then generate a new version of that file.
As you can imagine, it is not cheap to send data over such vast expanses of space. Also, New Horizons is going so far from Earth that the transmission speed will eventually slow to less than that of an old-fashioned telephone modem! In fact, data from the Pluto encounter took many months to download. Because of this slow data rate, much of the data sent back is compressed. The same is true for the Ultima Thule encounter.
There are two kinds of compression used: lossless and lossy. Lossless data, as the name implies, preserves every bit when reconstruced. It is a little like a "zip" file on a PC: you can expect to recover the original data exactly. But even more compression can be achieved by using using lossy compression, which is like the method most digital cameras and web pages use to save memory space. Lossy images lose some information, but they still look great, and because they take less time to receive, they will likely be the first images to hit the Web and newspapers. Lossless versions of those same images (well, at least the good ones) will be downloaded later for precise scientific use.
And it does not stop there. There is one more important step that the pipeline performs automatically. For data to be truly scientifically useful, it needs to be correct. Measurements were taken both before and after launch that establish exactly how the instruments perform, and still more are planned. This information is used to correct for the fact that the instruments are real-world devices. The space environment, and even the launch itself, can affect how the instruments perform. So after the data sets are made, they are calibrated, giving them scientifically useful accuracy and making the results meaningful.
You might be wondering what kind of computers are used for all of this. Well, high-end servers are now in use, and they were considered fast machines at the time of purchase. But no matter how fast computers are today, they will seem pretty sluggish in 5 or 10 years, and this mission is at least 13 years long! For this reason, the hardware will be upgraded at least once during the mission. Also, almost all software used is "open source" (include the operating system, which is Linux), meaning the source code is available in case it is ever needed — which is a good thing for a long mission like this.
The SOC also is the place mission scientists go to get their data. It hosts its own archive and an interactive Web-based database that can be searched to find specific data. However, there is another kind of archive that is important for future generations of scientists. To ensure that mission data is available for years to come, NASA maintains the Planetary Data System (PDS) archive, and after each major phase of the New Horizons mission, the SOC will send data to the PDS where it will be safely stored long-term.
As you can see a lot of exciting things are happening every day at the Science Operations Center. In fact, the SOC is the place to be if you want to be the first to see the official data!