Last year, I got the chance to do some work experience at In-Space Missions, and I got to see what it really takes to launch a satellite- from design to orbit! It was such a valuable experience to hear from space professionals talk about their jobs and their journey into such an awesome industry, so I am grateful for that opportunity. And, I can now say that I’ve touched something that’s going to space, which is pretty awesome!
In-Space are part of the UK’s growing small satellite industry, specialising in CubeSats…
CubeSats are small satellites made out of standardised cube shaped units stacked together, and they’ve become more and more popular for both commercial and academic use in recent years for 2 main reasons:
- Sizes are standardised, meaning some parts can be bought ‘off-the-shelf’, so not everything has to be custom-built and tested from scratch every time, it’s possible to buy them in! This, and the fact they tend to be smaller than traditional satellites, makes them less expensive to build.
- But they are also less expensive to launch, as their small size and mass means they can often be launched on rideshare flights with multiple satellites, again reducing the economic (but also environmental) costs of launch- like catching the bus instead of taking the car!
CubeSats first came into use around the turn of the century, when they were used mainly in education as a low cost (ish) method for students to get hands-on experience with satellite engineering, and up until 2013, most launches were by academic institutions. But since then the industry has exploded, with many ‘NewSpace’ companies using the technology: Commercial CubeSats usually act as platforms for other companies or researchers to put payloads on. The payloads tend to take up 1U each (with some units left for the satellite manufacturer to use for payload integration (eg. a central computer), power and communication), and their purposes vary from remote sensing & earth observation (such as by Planet Labs) to communications and technology demonstrations (including astrobiology research and astrophysics research missions!)
So far, most CubeSats tend to be found in Low Earth Orbit- or more specifically, Sun Synchronous Orbits, particularly those used for the Earth Observation. The SSO orbit is near-polar, and the satellite will always pass over the same place at the same local time- an easy way to think about this is that for a satellite with an ascending node of 13:00, it will always pass over the equator going north at 1pm, no matter what longitude the satellite happens to be at. And in the time it takes for the satellite to go around the earth and back to the equator, the earth will have turned enough so that it is now 1pm in the new area the satellite is observing, so it is synchronised with the sun, hence the name SSO. This is a great orbit for earth observation satellites, as you can cover the whole earth in as short as a day (depending on the instrument field of view), and you have a consistent time of observation, making it easier to schedule communications with it, and to spot changes over time in the area of observation. In my opinion, this is what makes earth observation CubeSats so exciting- as with collaboration with local governments and other agencies, it could be used not only to track things like logging, forest fires and disasters, but also fight them, especially in remote areas, informed by frequent satellite observation!
SSO altitude is about 600km, which is about 200km higher than the ISS. Although the atmosphere is very thin up here (it would certainly feel like a vacuum if you tried to venture out without a spacesuit), it still exerts a drag force on the satellite, and combined with the pressure from the solar wind (the stream of particles emitted from the sun), it’s orbit will eventually decay until its low enough that it re-enters the thicker part of the atmosphere and burns up. This might seem like a bad thing, but this is actually one way we can keep space open to future generations and reduce space junk!
Before you send up a satellite into space, you must meet lots of different safety and sustainability requirements (you can read the guidelines here), including ensuring that it will safely be removed from its orbit. For LEO satellites, they are expected to de-orbit (atmospheric re-entry) within 30 years of end of life, and most small satellites have to rely on natural forces to cause de-orbit, as they have no propulsion system to push them further into the atmosphere. Although its good we have these guidelines in the first place, cubesats are still quite a big problem in terms of space junk, as many of them (particularly early ones, being built for school projects and technology demonstrations) didn’t have long active lifespans, and remain in orbit unable to be communicated with, making them, essentially, nothing more than space junk. However there are a few ways to overcome this problem.
First, we can build propulsion systems into satellites! But the limited space on CubeSats means that any propulsion system would have to be tiny- so chemical thrusters are out (too bulky and explosive, requiring large amounts of fuel and providing too much thrust for such a small satellite), but electrical ion thrusters are a possibility. They can take up less than 1U, so are definitely feasible in terms of space, at least for the larger cubesats, and providing thrust by accelerating xenon ions (xenon atoms stripped of some electrons) with an electromagnetic field, then ejecting them from the spacecraft after adding the electrons back. It works using electricity, which can be provided by the solar panels, and only a small amount of fuel. Propulsion systems also increase the satellite’s capabilities in general, allowing for formation flying of tight satellite constellations and increased manoeuvrability to avoid collisions with space debris, so it’s a win-win!
Satellite sustainability can also be increased by lengthening the satellite’s lifespan, by repurposing or reconfiguring the payload. This is known as a digital payload and consists of a standard payload which can be adapted to suit new customers by remotely adding new software, instead of being limited to a specific purpose by its hardware. OrbitFab are also working on an in-orbit refuelling station, further reducing satellite turnover.
Talking to the satellite
The small size of CubeSats comes in handy for keeping manufacturing and launch costs down, but it also makes it hard to communicate with your spacecraft! All the satellites on a rideshare launch are released in roughly the same area of space. Just the smallest bit of angular momentum can cause your spacecraft to tumble as it orbits, making communication not only difficult as the antennae may be spinning incredibly quickly and therefore not steadily pointing towards your ground station, but it’s also hard to tell which of the satellites is yours, especially in the early hours/days following separation from the launch vehicle.
To overcome this, satellites often have more than one antenna, facing in different directions, and the solar panels are angled such that they will be able to get some sun no matter the orientation.
The satellite can then be tracked using a Two Line Element set (TLE), given by NORAD (yep, the same people who track santa at christmas!), who oversee the tracking of objects in orbit. It describes the most up to date orbital parameters and can be inputted into a modelling software like STK to calculate where your satellite will be and when you can try to communicate with it!
When I was on my work experience, I got to update my STK model of In-Space’s satellite, Faraday, with the updated TLE, which I found really interesting, especially when playing around with different propagators. The propagator is the way the model interprets the data to plot out the orbit, and different propagators consider different factors (eg. gravity fluctuations, the oblateness (think of a squashed sphere) of the earth, the impact of the atmosphere etc.).
The Future: CubeSats beyond LEO
This communication issue is one of the reasons that CubeSats haven’t been used an awful lot beyond Low Earth Orbit, but that’s beginning to change. The first interplanetary CubeSats travelled to Mars with the Insight Lander in 2018, demonstrating new capabilities in communication and navigation, able to make their way to Mars independently, and relay communications during Insight’s descent phase. Like how many CubeSats catch a rideshare into space, the trend is also continuing beyond LEO, with Artemis 1 carrying 10 CubeSats to the moon, making the uncrewed missions leading up to the crewed return to the lunar surface not only important (and awesome) technology demonstrations, but will also directly contribute to widening our understanding of our closest neighbour and the surrounding space environment.
One way to overcome the communication challenges for missions for more distant planetary science missions is by launching the CubeSats with a larger spacecraft, as the main spacecraft could be used to relay communications to and from the CubeSats. Adding just a few CubeSats would give a totally new perspective, and as they are fairly inexpensive, they would be able to undertake more high risk manoeuvres that the main spacecraft couldn’t afford. When you’re already using incredibly powerful rockets to send billion dollar spacecraft out of earth’s gravity well, you might as well attach a few (relatively) light CubeSats (for only a few extra million) to get as much out of the launch and mission as possible! And as we saw with Cassini-Huygens, which orbited Saturn from 2004 to 2017 and released the Huygens probe to land on Titan, the composite missions can be hugely valuable.
With the opening of many new launch sites across the UK and beyond, access to space, particularly with small satellites, will become a whole lot easier. These new launch facilities won’t see the big rockets that launch out of Kennedy (Florida, NASA) or Kourou (French Guiana, ESA), at least for the foreseeable future, but instead are primed to become hubs for CubeSat launches. This is especially true for the UK, as its high latitude makes it perfect for launching into the polar/sun synchronous orbits popular with CubeSats!
More than 1600 CubeSats have been launched so far, and with the first launch out of Spaceport Cornwall in the next few weeks then its safe to say that if CubeSats are the future, then the future is already here!