Just recently, we completed a series of correction burns to match the semi-major axis of the orbit of both satellites to stop them drifting away from each other. In a few weeks/months we'll bring them back together and send a software update that will allow them to autonomously maintain formation flight.
Also, we will be doing live satellite operations at the Lange Nacht der Wissenschaften (22. June 2024) :)
It is and it does feel about as awesome as you can imagine. In our case we also had a tough integration and testing campaign where we were changing software and running into hardware issues, etc. so I was personally quite tense until we got first contact :) and since then, the satellites are surprising us every day with how well they work! (although we still have lots of things we want to improve)
I'm mentoring a group of high school students who were just selected by the CubeSat Launch Initiative to put a smallsat up.
It's not quite my first rodeo with this stuff, but it's still incredible to be a part of and see.
[It's incredible to be a part of, but it's also just a whole lot of attention to detail, paperwork, and paranoia]
People don't tend to let HS students do much, so it's pretty stirring when they get an email that said approximately "We appreciate your... dedication to furthering humanity’s presence in space and knowledge of the cosmos."
That is so cool! My biggest wide impact was creating the UI for first, or second, airline touchscreen check-in system ever deployed. The feeling of ownership/creation that I had knowing that my code was all around the West Coast was awesome.
I can only imagine how cool it must feel to be part of a project that has escaped the Earth's atmosphere, and zips by at orbital speeds. I would think that those high school kids will benefit from this project a lot. A truly mind-expanding experience.
Another application of satellites in formation is measure gravity fields:
> That brings us to GRACE—a backronym for gravity recovery and climate experiment—a pair of satellites that orbited the Earth at a fixed distance from each other. Or they would be fixed if the Earth’s gravity didn’t change in time and space. GRACE used a radar system to measure the distance between the two satellites to track those changes, providing information about the gravitational field it was traveling through.
I wonder how precisely they can control the relative separation of those interferometer spacecraft? (They advertise they can measure the separation to <0.01 nanometers—but that's not quite the same thing).
I think with those the idea is to make the arms so long that the precision of the relative separation matters less, especially since LISA is trying to listen for much longer wavelengths than LIGO. On top of that, they likely just need to get the unpredictable component of the relative acceleration to vary (unpredictable component of the relative jerk?) slower than the time taken for a gravitational wave to pass through.
Probably more a matter of precisely measuring the gravitational fields and accounting for those than of controlling their relative position extremely precisely (besides of course the precision needed to target the lasers across such a large distance).
I graduated from Purdue University Calumet Campus in northwest Indiana (PUCC.) At one point they considered renaming as the South Hammond Institute of Technology.
Lookup the World Taekwondo Federation, recently shortened to World Taekwondo. I pity the poor soul who had to explain the need to elders of the sport, many of which did not speak english.
> A backronym is an acronym formed from an already existing word by expanding its letters into the words of a phrase. Backronyms may be invented with either serious or humorous intent, or they may be a type of false etymology or folk etymology. The word is a portmanteau of back and acronym.[1]
> A normal acronym is a word derived from the initial letters of the words of a phrase,[2] such as radar from "radio detection and ranging".[3] By contrast, a backronym is "an acronym deliberately formed from a phrase whose initial letters spell out a particular word or words, either to create a memorable name or as a fanciful explanation of a word's origin."[1] Many fictional espionage organizations are backronyms, such as SPECTRE (special executive for counterintelligence, terrorism, revenge and extortion) from the James Bond franchise.
> For example, the Amber Alert missing-child program was named after Amber Hagerman, a nine-year-old girl who was abducted and murdered in 1996.[4] Officials later publicized the backronym "America's Missing: Broadcast Emergency Response".[5]
I understand that part of the objective is to demonstrate precise autonomous navigation and choreography, but for the "main" scientific objective re. observing the solar corona, why not just stick a big stick with a disk on the observing satellite?
That's what's been done so far [0], both on the ground and in space. As I understand it, the further your disk is from your telescope, the better. But your stick needs to be rigid enough to keep the disk exactly in its place. And a rigid stick has weight.
For Proba-3 the goal is to have the two satellites more than 100m apart. If you want to do that with a stick, your stick has to be longer than the ISS. That should tell you a thing or two about the complexity and cost of building and launching that stick.
I do have to admit I'm not exactly sure what the advantages are of having the disk further away from the telescope. I suspect it's to do with the interaction between the light and the edge of the disk, but I'm not sure.
The even more extreme version of this JPL has been working on with their Starshade program. Not specifically a cornograph, but same concept of blocking light from a star to look for something more dim, in this case its looking for exoplanets. But it is a much larger scale. A 25 m deployable shade in formation 100 km away with the same level of mm precision.
Edit: Just to be clear on status of this, Starshade is still in early technology demonstration phase that they can actually build the shade and do the formation maintenance. This is not in full build or slated to launch any time soon.
Huh, very interesting- and counterintuitive that distance matters. If anyone here knows why I’d love to learn more!!
EDIT: maybe not so counterintuitive after all: if you scale everything up, you get a higher fidelity sensor and more signal to noise. Same reason telescopes want to be big: to collect more light especially from dim signals. Distance of the occulter then reduces perspective distortion that would eclipse the inner parts of the sensor more than the outer ones. Just my speculation though.
I'm speculating past my understanding here, but wouldn't some sort of diffractive effect around the edge of the disk explain it? Like the further you are into the far field of that diffraction the better or such?
I worked on Proba-3 for a while. The original goal of the project was to demonstrate formation flying in preparation for another telescope (I forgot the name, but it was something like Xeus). That telescope would have a camera and lens on seperate spacecraft, and the idea was that by moving the lens backwards or forwards you'd be able to create a much bigger telescope than could be built with a single spacecraft. Unfortunately that telescope was cancelled, so although Proba-3 is still demonstrating a cool technology, it probably won't be applied elsewhere for a while.
I'm not familiar enough with the project to answer why specifically cold gas thrusters were chosen. What I can say : if old, proven technology will get the job done, there's a strong preference to use that.
When needed to achieve the mission, new technology will be developed - sometimes the whole point of a mission is specifically to develop new technology. In this case, one of the major goals of the mission is to develop formation flying technology. Learn what the pitfalls and the tricky bits are, and make the technology available for future missions.
But when the mission can be achieved with old technology - technology with a long record of being used in space, where the problems are known and understood, where we know what works and what causes problems - then the mission will use old technology.
If you use newer technology, there's always a risk that you'll hit a new issue, previously unknown. Maybe you can work around it, maybe you can't. But this isn't web development where you can refactor, switch to a new framework and continuous deploy your way out of it. For the hardware, you get one launch and that's it. Why run the risk if you can avoid it?
It'd be a shame if the mission can't achieve its primary objective (learning about formation flying) because it chose some new type of thruster, and encountered some new issue with it.
Cold gas thrusters are as reliable (because of simplicity - basically just container of pressurised gas and a valve [1]) and as precise in their thrust pulses execution as it can get. Better precision in thrust execution probably only ion engines have but just because of extremely low thrust levels in general (milli-newtons).
I saw a really good YT video a few months ago that explained this very well. Went over all the fuel types and tanks and propulsion designs.
Started with what you said - a simple gas pressurized and a single valve.
Slowly more and more was added until we get to current rocket designs with multiple stages or active pressurization / fuel transfer and all that entails.
They need the milli-newton level of thrust control and so need tiny thrusters. Generally the simplicity of the cold gas thrusters in a small package is easy. Yes it is not as efficient, but moving up in efficiency and complexity to catalyzed monopropellant (generally hydrazine) thrusters the thrust ranges are usually > 1N. Same story with any bi-prop thrusters. Certainly electric propulsion has the levels of thrust needed, but then you would need a lot of power for it. And since they are not doing large delta V maneuvers there is less concern about the actual amount of propellant that you need to take with you.
From what I can see on wikipedia [0] the first FEEP to be used in space was in 2018. Proba-3's implementation phase started in 2014 [1]. The choice of thruster technology was probably made well before that. They wouldn't use a technology that hasn't flown yet, unless it was crucial for the mission.
Everything has tradeoffs, and everything depends on use case.
The FEEP thrusters I've seen had a hefty power penalty to keep it on standby, and a long warmup time. Cold gas uses more propellant mass per unit impulse, but it can still come out ahead in total size/weight/power.
Yep, definitely power is an issue and a trade-off even with low levels of power. The other item is cost. Cold gas thrusters are super cheap and reliable. So the savings in amount of propellant in going to an electric propulsion system is not going to be worth it in the overall program. This is also because the total amount of maneuvering they are doing (in terms of deltaV) is probably not very large. Lots of little maneuvers. This is compared to something where you have large delta V for big maneuvers or continuously overcoming drag in low LEO orbits where the amount of propellant will become a huge design driver.
From the article, Proba-3 has 10 thrusters, so that would bring the total to 150 Watt.
I don't know the power budget for the satellite, but we can make an educated guess : the occulter is 1.4 meter diameter, or a surface area of 1.54 square meter. That's an upper bound for the surface area of the solar panels - there's nothing sticking out beyond the disk, that would interfere with observations.
Solar power at earth is about 1.3kW/sqm, solar panels are maybe 20% to 30% efficient. That puts you in the ballpark of 400 to 600W.
150W on standby would be a pretty big bite out of your power budget.
Speaking of razor-sharp formation flying satellites, reminder Interferometer Space Antenna (LISA) got the go ahead this year. Incredibly ambitious & cool attempt to build a much much much bigger space based version of the already 4km long Laser Interferometer Gravitational-Wave Observatory (LIGO). Requires absurdly stupensously precise formation of three satellites.
Yes. Super cool project. The free flying cores that get manipulated with magnets are crazy. Will allow gravitational wave observation in a totally different domain.
Many observations of the sun's corona just use a disk attached to the telescope, as you're suggesting [0]. However, for Proba-3 they want the disk to be over 100m away from the telescope, which isn't practical. Also, one of the goals of Proba-3 is to develop formation flying technology, because it will be useful for many other missions in the future.
No because it's exactly the opposite. Kessler syndrome results from satellites smashing into each other with high relative velocities. The entire point of formation flying is zeroing out relative velocity. That's how you stay in formation with something.
I was imagining them flying close-by, so any failure would have a higher chance of causing a cascade. I couldn’t find any info on how close they are, but I imagine it’s too far for this to be an issue.
The article says they're going to be 144 meters apart. A collision of things that are in basically the exact same orbit is also not going to be much of a risk, as the collision would be at a low relative velocity. Collisions between satellites are a kessler syndrome risk because due to differing orbits, the collision velocities can be in km/s, which can spread debris into a wide range of orbits, thus causing the heightened risk of cascading failures.
The goal is to have them a bit more than 100m apart. During observations they aim to maintain millimeter precision.
I'm pretty sure the risk of collision has been analysed to death. I would expect they've analysed what would happen if one or both devices suddenly stop listening to commands, and that even then there's essentially no risk.
It still doesn't matter according to physics. There's a reason why two NASCAR cars can be going 150+ miles an hour, and yet "rubbin's racin'," but a head-on collision at 60 miles an hour will kill you. The two race cars going 151 and 149 mph rub at ~2mph relative velocity, while the head-on collision with the drunk occurs at 120mph relative velocity.
And flying formation, be it in space or in the air, by definition involves getting as close to zero relative velocity as possible . . . or else you aren't in formation.
Just recently, we completed a series of correction burns to match the semi-major axis of the orbit of both satellites to stop them drifting away from each other. In a few weeks/months we'll bring them back together and send a software update that will allow them to autonomously maintain formation flight.
Also, we will be doing live satellite operations at the Lange Nacht der Wissenschaften (22. June 2024) :)