Everything we encounter in the solar system is moving, both on its path around the sun as well as on some sort of spin around one or more axis. That rotation rate is one of the bigger unknowns for any asteroid we target, in part because only a small portion of the total observed population (~10-15%) has that data available at all and in part because there is a fairly wide error band (from ~1% all the way up to 100%) around the observations we do have.
This rotation rate is crucial for mission design at 2 levels. Very tactically, every step up in rotation rate increases complexity and challenges for the portion of our mission where we interact with the asteroid in question. For a very fast rotator, we need to either try to match that rotational velocity before descending (ultra-high precision formation flying) or we need to approach at one of the poles. A slow rotator is simpler, cheaper (we need less fuel for that interaction) and safer.
There is a second, more strategic driver for our work on rotation rates that drives our mission design. We leverage a phenomenon called the '2.2 hour spin barrier' as one of the main drivers for our leaderboard and target selection. For our missions to return fuel/water, we want asteroids from the type called a rubble pile (slow rotators, beyond the 2.2 hour barrier) that are C-type (hydrated clays, containing water for us to extract).
An asteroid that spins faster than the spin barrier can't be one of these loosely consolidated 'rubble piles' as any unbound material is simply slung away by its spin force. Similarly, any larger asteroid that is spinning at these higher rotation rates would disintegrate due to the forces imposed on its body.
We are exploring a mission concept that focuses on these smaller fast rotators, where we can leverage this spin barrier knowledge to inform the designs of our grappling arms.
3I/ATLAS
Last year saw a very interesting object that ended up being called 3I/Atlas, the third (hence the 3I or third interstellar label) observed interstellar visitor after Oumuamua in 2017 and Borisov in 2019.
The discovery of Atlas kicked off a campaign of imaging across dozens of space-based and terrestrial observatories to get as much data as possible in the short time it spent in our solar system before heading back out into deep space.
Based on those, the comet is expected to be up to 7 billion years old (significantly more than the 4.5 billion years of our solar system) and measures somewhere between 300 m and 5.6 km (this wide range is at least in part due to its tail, which makes it hard to delineate the comet body).
At its closest approach to Earth, it would have taken ~7km/s of delta-v to rendezvous with the comet which is well within the capabilities of our High Frontier spacecraft.
We look forward to 4I/... as a possible mission target.
Space Gum, anyone?
Several new papers were published about the samples returned from asteroid Bennu. This ranged from a discovery by Yoshihiro Furukawa at Tohoku University in Japan of sugars that are possible building blocks for life to gum and stardust captured from distant supernovae.
Asteroids (and interstellar comets) are awesome!
High Frontier Mission Update
We're launching on a Transporter rideshare.
Our leaderboard of asteroid targets keeps expanding, with new asteroid discoveries up from 5-10 per week to 5-10 per day with the Rubin observatory now online and producing a massive amount of data every night.
Our mission design is anchored around flexibility to make sure that we leverage this expanding list of targets all the way up to launch. The visualization above shows the range of different targets we can reach for a specific launch date, with the color indicator showing the relative delta-v needed for rendezvous.
Spacecraft
Our spacecraft is coming together well with extensive testing happening at both component level and system level ahead of our full integration work.
Environmental/Qualification Testing
Shock & Vibe campaign for qualification of our primary structure
We are always balancing performance with mass in all of our work, which becomes especially important for our primary structure. These perforated honeycomb/carbon fiber panels are mounted on an aluminum base plate and carry/protect every other component of the spacecraft.
The main (really the only) design driver for structure is surviving the launch environment without issues. We use our vibe table to mimic that environment (including a lot of margin) to make sure everything survives without issues. If you look at the vibe video, you'll see the whole system shifting through higher and higher frequencies until the whole box seems to settle. At that point, we excede the frequency range at which the material resonates. Full marks for survivability!
Our deep space RF communications system (radio, power amplifier, diplexer, high and mid gain antennas) have gone through their full qualification tests, with flight models ready to go.
Testing of our hold-down-release mechanisms (HDRMs)
Our gimbals, excavator and solar arrays all use a deployable architecture that needs to survive launch in a packaged configuration before being deployed. To ensure that things deploy post-launch, we use pre-tensioned systems that want to naturally deploy but are held in place by specific tie-downs. These hold-down-release mechanisms are an essential part of the design to make sure that we can launch safely.
Avionics & Flight Software
Our vertically integrated approach extends beyond the spacecraft structure and mechanisms into the brains of the spacecraft, across avionics and flight software. We have developed our own flight computer, power control and distribution unit, motor controllers and navigation/payload computer.
A major part of the avionics design work deals with architectural redundancy, radiation performance and thermal efficiency. We run extensive high energy proton tests at the part level to make sure we have a good understanding of the probabilities involved for both our current mission profile as well as for future missions with stricter requirements.
Karman+ motor controller and flight software running first end-to-end test
Every board runs through multiple iterations and revisions, in which we use a tight coupling between hardware and flight software to test functionality and resilience.
Once all functionality is validated, we package the board in its enclosure and run it through the same environmental qualification test campaign as all of our other hardware, making sure it is ready for flight.
Excavation
Our Scoop design for excavation is ready for its flight build, with every component from the drive system and scoop elements to the regolith bag and deployment boom tested in isolation as well as fully integrated.
Regolith Age
To be able to scale from digging up 10s of kilograms to 10s of thousands of kilograms is mostly a linear scaling effort, but we are also looking at different approaches in parallel to ensure we keep pushing for the most optimal solution. One of the ideas we are working on is a flexible/controllable version of Scoop which would be able to navigate towards and through the surface of a rubble pile asteroid.
This kind of system increases resilience as it decouples any excavation motion from the spacecraft itself. It also scales very well for increased volume, which we will certainly need to return larger amounts of material over time.
Thanks for joining us on this adventure!
The Karman+ Team