https://albedo.com/post/clarity-1-what-worked-and-where-we-g...
We got here after stacking quite a few capabilities we'd developed on top of one another and realizing we were beginning to see behavior we should be able to wrap up into a viable control strategy.
Traditional approaches to torque rod control rely on convergence over long time horizons spanning many orbits, but this artificially restricts the control objectives that can be accomplished. Our momentum control method reduced convergence time by incorporating both current and future magnetic field estimates into a special built Lyapunov-based control law we'd be perfecting for VLEO. By the time the issue popped up, we already had a lot of the ingredients needed and were able to get our algorithms to control within an orbit or two of initialization and then were able to stay coarsely stable for most inertial ECI attitudes albeit with wide pointing error bars as stated in the article. For what we needed though, it was perfect.
The main performance goal for us was NIIRS 7, and we decomposed GSD/MTF/SNR contributors optimized for affordability when we architected the system
Is the drag much better than a regular cubesat? It doesn't look tremendously aerodynamic. From the description I was kind of expecting a design that minimized frontal area.
>Additional surface treatments will improve drag coefficient further.
Is surface drag that much of a contributor at orbital velocity?
Yes it's a big contributor. The atmosphere in VLEO behaves as free molecular flow instead of a continuous fluid.
Stacks? Testing? Firmware Updates? Programming languages?
Thank you!
We wrote everything from low level drivers to the top level application and the corresponding ground software for commanding and planning as well. Going forward, we're writing everything top to bottom, just to simplify and have total ownership since we're basically there already.
For testing we hit it at multiple levels: unit test, hardware in the loop, a custom "flight software in test" we called "FIT" which executed a few different simulated mission scenarios, and we tried to hit as many fault cases as we could too. It was pretty stressful for the team tbh but they were super stoked to see how well it worked on orbit.
A big one for us in a super high resolution mission like this is the timing determinism (low latency/low jitter) of the guidance, navigation, and control (GNC) thread. Basically it needs execute on time, every cycle, for us to achieve the mission. Getting enough timing instrumentation was tough with the framework we had selected and we eventually got there, but making sure the "hot loop" didn't miss deadlines was more a function of working with that framework than any limitation of linux operating well enough in a RTOS fashion for us.
On orbit, we fixed it by pushing an FPGA update and adding software-level switching between the channels to prove the update applied and isolate the hardware path — which worked. Broader lesson, it is possible to design a sw stack capable of making updates to traditionally burned-in components.
Hah, this has bitten me often enough I check for it in test suites now - ok, you’ve proven the system works and the backup works, have you proven the primary works? Another in the long list of ways you don’t expect a system to bite you until it does…
Great write up!
Future systems we've got a few updates though based on learnings, and we'll be shooting for closer to 3-5 meter geolocation error without ground control points (GCPs)
I’d be interested to read a postmortem of the systems engineering approach there.
Alas.. the speed & resources of a startup. But we're learning.
To be honest, postmortems (especially from startups) toe a fine line of scaring off investors, and this write-up seems a bit too glaze-y. I'm very happy for you that so much worked so effortlessly post launch, but that's more a success story than a postmortem. I'd like to see more of the root cause analysis for the issue, both technically and programmatically.
You're correct on 1, we ended up hitting an edge case in their spec that they hadn't adequately tested to and the upper level management and engineering leadership were swift to accept the fault and implement fixes with us going forward.
From a SE perspective, as a "COTS" product, we had spec'd correctly to them, they accepted our requirements and then executed each unit's acceptance test plan (aka lower level than first unit quals or life tests where this should have been caught) on the ground without anything amiss. We ran through our nominal and off nominal cases at the higher level of assembly, but not for a duration that caught this on the ground. It wasn't until we were at extended operation on orbit the issues began.
Sadly like you state, space isn't like on the ground, you can't buy spares or replace things that fault, even for a true high volume COTS product that might slip through the acceptance testing.
> Next up was maneuvering from our LEO drop-off altitude down to VLEO, where it would be safe to eject the telescope contamination cover
Why would it be unsafe to do this earlier?
> We had been tracking intermittent memory issues in our TT&C radio throughout the mission, working around them as they appeared. Our best theory is that one of these issues escalated in a way that corrupted onboard memory and is preventing reboots. We've tried several recovery approaches. So far, none have worked, and the likelihood of recovery looks low at this point.
Seems to be a pretty big problem as well, I wonder what their ideas are to diagnose the root cause here.
It all sounds a bit overoptimistic, but that may just be my interpretation.
The radio came from a supplier who has been investigating the issue. We had concerns with their NAND and ECC implementation, and we weren’t able to fully root-cause it with them. Going forward, we’ll be building our own radios, which will make it easier to test, iterate, and resolve issues like this internally, or at least be able to trace possible latch ups or destructive failures and implement the right levels of redundancy.
Much good luck with this, those are hard problems to solve but you guys got so much right on the first try that you're probably ahead on your schedule now so you may have the time and the budget to get this right. I've visited the ESA open day a while ago and have seen the guts of what goes into satellite manufacture (not the most recent stuff, just what they had on display) and what struck me is that the degree of rigor that goes into designing stuff that is in the most literal sense out of reach for fixes or diagnostics requires simulating the environment the device will operate in to the best of their ability. This results in autoclaves that you can walk around in and various radiation sources to be able to test how the devices respond to space conditions.
Your manufacturer/supplier will probably come away from this effort with as much knowledge and improvement items as you do. Given the short time to failure I'm not so sure redundancy alone would have been a sufficient fix, but that's obviously bystander perspective, you know far more than I do. But it certainly is an amazing and interesting project.
The writing style sounds more like a tech bro describing some weekend conquest, and is wholly unappealing to most of the space industry (or at least the ones with decision making authority). Your CMGs were “locked in,” several times you “nailed it,” and so on.
You might have a business strategy that I’m not aware of but I’d expect that most of your market is controlled by aging men in suits, and they don’t talk like this. Most startups and tech bros aren’t spending money on space. It’s big established corporations that can fund this kind of stuff. Write like them. You can talk like a tech bro and get seed funding, but if you want to get to a sustainable business you have to talk corporate.
I would hate for your company to get passed over for lucrative opportunities because your public image seems immature. I looked at your website and you have a bunch of ex-government people on your senior advisory board. Get their opinion on your writing. It sounds silly, but you significantly lower your probability of winning contracts if people see you as a team of “bros.” People don’t want to spend millions on guys who are “locked in.” People want to spend millions on people who do professional engineering and risk reduction and clearly communicate how professional and competent they are.
I ranted way too long about your writing style. It’s pretty cool that you were able to design your own bus and most of it worked.
Why would I take a company seriously when they can't be bothered to write their own press statements and blog posts?
This is on the company blog. It ends with a call to action to either subscribe to their mailing list or explore their careers page.
It has the right tone for the goal. Tone policing isn’t helpful. The authors are even here answering questions which is very nice of them.