When NASA first formed, getting to space was extremely dangerous and no one really knew how to do it. Therefore, there was an acceptance of a large amount of risk. Part of the reason for this is that the amount of money invested in NASA was enormous – at one point in the late 1960s, NASA’s budget was 6% of the total federal budget. This allowed NASA to rapidly solve problems by trying new and innovative things and iterate on the design over and over until it worked. For example, the Atmospheric Explorer satellites, built in the 1970s, had four versions that each lasted only a few months until AE-E lasted for many years. The IMP series of satellites measured characteristics of space between the Earth and the Sun. There were seven satellites that lasted only a few months until IMP-8 lasted 30+ years. The reason that NASA could do this is because the ratio between the cost of a satellite to the total budget of the agency was quite small. Therefore, failing on a few satellites didn’t matter very much.
NASA today is quite different. The budget is 0.5% of the total federal budget and dropping every year. The total number of satellites launched is significantly smaller, and each one needs to succeed, since they cost so much compared to NASA’s total budget. While failure still happens at NASA, it is not something that is taken as a lesson; it is taken as a failure. Therefore, there are a plethora of lessons learned, sets of rules that need to be followed, and significant numbers of reviews that must be held to move the project to the next phase. While this helps to ensure success, and it is a natural outcome of a system with limited budgets, it stifles innovation and greatly increases the cost of each satellite.
When a satellite is launched, the rocket (or launch vehicle) has a certain capability. For example, a given rocket may be able to launch a satellite with a mass of 1000 kg to a 700 km altitude. If the satellite that is being designed is 950 kg, the rocket then has excess capacity and, in order to get the satellite to the exact desired orbit, 50 kg of ballast needs to be added to the rocket. Sometimes, this ballast can be another satellite.
The idea of a CubeSat was created when Bob Twiggs suggested that there could be a standardized deployer for very small satellites that could be used as ballast on almost any launch vehicle. The deployer could be very strong and could ensure that if anything went wrong with the little satellite inside it, the primary payload (i.e., large satellite) would not be affected. The P-POD deployer was invented to allow cheap access to space for extremely small satellites as secondary payloads. It created a standard for a tiny satellite, dubbed a “CubeSat”, that could fit into the P-POD deployer and be launched into space wherever a P-POD could be used. A P-POD accepts a satellite that is roughly 4 inches by 4 inches by 12 inches, or 3 satellites that are roughly 4 inches on a side (hence the name “CubeSat”).
The invention of the P-POD deployer has revolutionized space, since is allows cheap access to space for anyone who can build a satellite that can fit within its extremely limited confines. At first, it was considered too small to be of any use for any real science to be conducted. This has since changed, though. The National Science Foundation has embraced CubeSats as both an educational tool and a science tool. They have funded over 10 CubeSats that have been used to conduct science ranging from lighting detection to radiation belt monitoring.
CubeSats have been successful because that have placed the community into a place where the satellites are once again quite cheap compared to the total budget of the institution. This has allowed innovation and rapid technology development to reenter the satellite industry. Because of this, a large number of companies have been created to support such an industry, creating smaller and smaller supporting hardware for tiny satellites. For example, small, high-speed radios have recently been introduced that can be used to downlink massive amount of data. Without such radios, it would be extremely expensive to get all of the data from the satellite to the ground.
With the emergence of small-satellite hardware, agencies such as NASA and the Department of Defense could start to look at creating missions that are designed in a radically different way – instead of launching a single satellite that was quite expensive, they could explore how to get the same science return with two or more smaller, cheaper, satellites.
Another technology that has led to the creation of missions such as CYGNSS, a satellite constellation mission that I am involved with, is the Global Navigation Satellite System (GNSS), which is the general name for constellations such as GPS. These satellites were designed to provide precise position and time information for military systems, but their use has become significantly more general. GPS is ubiquitous, with everyone having a receiver in their phone, which has done two things – pushed GPS receivers to smaller and smaller sizes and lowered the price for those receivers.
In space, a GPS receiver can be used to do many different things. One of the most common is to use the delay between when the GPS satellite sent the signal and when the monitoring satellite received the signal to tell something about the atmosphere. This can be done because electromagnetic waves travel at different speeds in different medium. So, for example, if the waves travel through the ionosphere, they slow down a bit and take longer to reach the satellite. This difference can be measured and the amount of ionosphere between the two satellites can be determined. Just like the ionosphere, the waves slow down when they travel through water vapor, so, when the waves have to travel through the atmosphere, the amount of water between the satellites can be determined. This is the primary use of GPS on satellites today – radio occultation to determine atmospheric characteristics. Because of the inexpensive nature of GPS receivers, constellations can be launched that take advantage of this. The COSMIC satellites are an example.
The CYGNSS satellite mission uses GPS signals, but in a very different way than other satellites – it measures how much of the signal is reflected off of the ocean’s surface, which says something about the roughness of the ocean. The amount of scattered signal is dependent upon the surface roughness, which itself is dependent upon the winds over the water. Therefore, the scattered GPS signal strength that is measured by a satellite such as CYGNSS depends on the wind speed over the ocean. CYGNSS takes advantage of there being the GPS satellites in orbit around the Earth continuously sending signals towards the Earth.
Past satellites that have measured the wind speed over the ocean have had to both transmit a radio wave and receive the wave back. In order to measure the signal, the transmitter had to be quite large and powerful. Since CYGNSS does not contain the transmitter, it can be significantly smaller.
In addition, CYGNSS takes advantage of a number of components that were designed for very small satellites (like CubeSats), such as the radio for communication with the ground station, the star trackers that provide information on the orientation of the satellite, the momentum wheels, which keep the CYGNSS satellites oriented in the proper direction, and the computer systems that run everything on the satellites. This has allowed NASA to launch eight very small satellites for cheaper than a normally priced large satellite, and it is all due to the shrinking of space technologies and the global availability of the GPS network.
By pushing the boundaries of what can be done with extremely small satellites, NASA has started to shift to considering constellation missions that can give us an idea of what is happening over a large portion of the globe instead of in a single place. It has allowed innovation and rapid development of cheap technologies to flourish. This will result in some amazing new science to take place in the next decade!