¶What is SAR? Radar imaging penetrates clouds and is self-illuminating, allowing for consistent imaging night and day, regardless of weather. But, when compared to optical approaches, radar resolution is challenging, especially at orbital altitude due to the large physical antenna sizes necessary for handling electromagnetic waves 4,000x longer than visible light. To improve resolution, Synthetic Aperture Radar (SAR) combines data from multiple radar pulses as a platform moves past a target, creating images with resolutions comparable to an infeasibly large real aperture radar. (Another way to visualize SAR is that it works similarly to phased-array antennas, but multiplexes a single antenna in time relative to a stationary target vs multiple antennas in space relative to a moving target.) SAR, first developed in the ‘50s for military applications, has led to important scientific findings, such as the terrain imaging of Venus and the detection of liquid hydrocarbon lakes on Titan (paper). Today’s SAR systems have increased resolution and decreased cost, leading to a boom in smallsat SAR data from multiple new providers, including Ursa, Capella, ICEYE, iQPS, PredaSAR, Synspective, and Umbra (who just raised $32 million in additional funding). Capella Space is one of the industry leaders with resolutions of 50cm x 50cm from a 10-meter antenna deployed from a ~40kg smallsat (two of these were on Transporter-1, see below). According to Capella's lead SAR scientist, this resolution would require a real aperture radar of 49 km (yes, kilometers). SAR resolution along the orbital ground track (aka “azimuth” or “cross-range” resolution) is determined by radar pulse processing frequency—and therefore doesn't degrade with altitude, unlike optical and real aperture radar—, while the side looking "range" resolution is primarily determined by the radar's wavelength (many high-res SAR platforms use the ~3 cm 8–12 GHz X-band, including Capella). SAR's drawbacks include vertical height distortion (called layover and foreshortening) and shadowing due to its side-looking orientation in relation to the craft's ground track (SAR cannot look straight down). SAR is also unable to accurately observe moving targets and can produce significant amounts of “speckling” and noise due to reflectance from rough surfaces and corners (a good recent video overview of SAR). But, its side-looking orientation enables its high range (or “cross-track”) resolution, and when paired with elevation maps it can be used to reconstruct 3D models of the observation area—an intro to SAR course from NASA. Commercial applications of high-resolution SAR data have been speculated on (including your usual suspects of maritime tracking, crop monitoring, defense intelligence, and climate, with compelling all-weather natural disaster response added to the mix), but we don’t have many examples of real-world commercial use-cases just yet. Related: the Alaska Satellite Facility has a good repository of SAR data available if you’d like to experiment with some yourself.
A SAR image of a floating Chinese solar farm including panels, apparently laid out to resemble a fish.
¶All the missions on Transporter-1. So what was in the flotilla of 143 satellites launched on SpaceX’s Jan 24th Transporter-1 rideshare mission? Many were bundled through rideshare aggregators D-Orbit (20 on an ION SCV Laurentius vehicle), Exolaunch (30), Nanoracks (9), and Spaceflight (13 sats on their Sherpa space tug along with two hosted payloads, one of which was... the cremated remains of 104 people). Transporter-1’s diverse payloads provide an illustrative survey of how smallsats are used today and an indicator of the coming challenges for space situational awareness. These launches are (perhaps aspirationally) scheduled for every four months.
- IoT & Communication: 36 tiny Swarm SpaceBEE sats (sold through two different rideshare aggregators), 10 upgraded Starlink satellites equipped with laser inter-satellite links (which will be included on all Starlink satellites launched next year), 5 Astrocast SA 3U cubesats, 8 Kepler nanosats, and YUSAT (carrying an AIS and APRS receiver).
- Technology demonstrators: 3 ARCE-1 0.5U cubesats to test inter-satellite networking, the Turkish ASELSAT, Hiber Four’s green propellant demonstration, 3 V-R3x NASA cubesats to test communication and navigation tech, the PIXL-1 laser comm demonstrator, NASA’s 6U PTD-1 water-based propellant demo, and Prometheus-2 (a proof-of-concept for low-cost satellites from the Los Alamos National Laboratory).
- Science & Climate: IDEASSAT (ionospheric measurement), UVQS-SAT (measuring Earth’s Radiation Budget), GHGSat-C2 (greenhouse gas monitoring), and the student-built SOMP2b (measuring the pressure of the thermosphere).
- Optical imagery: 48 SuperDove cubesats from Planet (36 sold through SpaceX and 12 through rideshare aggregators), plus hosted payloads.
- Radio observation: 8 Spire Lemur-2 3U cubesats (weather, aircraft, and ship tracking), 3 HawkEye 360 sats (commercial SIGINT), and Aurora Insight’s Charlie to evaluate global radio spectrum usage and interference.
- SAR imagery: 3 ICEYE satellites, 2 Capella satellites, and 1 iQPS satellite.
- …and a Partridge in a Pear Tree 🎶 (seemingly the launch just had an off by one month error)
¶SN9 just couldn’t help but be a doppelganger. After a few days of Twitter hand wringing surrounding FAA licensing (licensing was held up due to a slightly murky violation of SpaceX’s previous license for the SN8 launch in December), Starship took flight for a second time from the coast of south Texas. Leading up to the launch, SN10 rolled out to the pad, treating us to views of dual Starships, and it is now ready for its own pressure testing and static fire. SN9’s flight, testing new helium-pressurized header tanks, performed well on the way up, including engine power-down and the belly flop maneuver. However, attempted relighting of a second engine during the final flip landing maneuver was unsuccessful (hardware from the bottom of Starship could be seen blowing off mid-landing). Final status: 💥 …just like SN8. And, the FAA will now investigate this explosion. Rinse and repeat. (Another double for SpaceX coming up: the company plans to launch two Starlink missions on Thursday.)
¶News in brief. The US Space Force officially ended their launch partnership with Blue Origin and Northrop Grumman, after spending over half a billion dollars to somewhat unclear benefit; SiriusXM’s $225 million SXM-7 satellite, launched last year, has encountered serious issues; Northrop Grumman successfully completed a static fire of the Vulcan Centaur’s GEM 63XL solid rocket motors; NASA is formally soliciting a commercial vehicle to launch Europa Clipper, although we know who will get it because only the Falcon Heavy is currently capable of the required Earth-Venus trajectory; Mikhail Kokorich, CEO of Momentus, is resigning to overcome US government concerns around export control; China launched three Yaogan military satellites (likely for naval observation) on a Long March 4C; NASA is going to repeat their SLS Green Run test, targeting at least 4 minutes of hot firing; Chinese carmaker Geely invested $637 million in a satellite internet project; iSpace suffered a failure with their second orbital launch attempt (iSpace was the first quasi-private Chinese launch company to achieve orbit with their Hyperbola-1 vehicle in July 2019); Astra will become the latest NewSpace startup to go public later this year via the Holicity SPAC (Special Purpose Acquisition Company), despite having yet to reach orbit; and, Jared Isaacman, CEO of Shift4 Payments, paid SpaceX to fly Inspiration4— the “first all-civilian mission to space”— and you can go along to orbit by donating to St. Jude Children’s Research Hospital or by… tweeting about Shift4Shop.
- Taikonautica, a great newsletter covering the latest in Chinese space developments, appears to be back after a short hiatus.
- Last week we talked about hypervelocity stars, but what about hypervelocity globular clusters (paper), where the entire star cluster encountered a supermassive black hole and is now moving at close to 1% the speed of light?
- Two more papers strongly call into question the detection of phosphine gas on Venus. One “analysed data from one of the telescopes used to make the phosphine claim — and could not detect the gas’s spectral signature,” while the other “concluded that what the original team thought was phosphine is actually sulfur dioxide (SO2), a gas that is common on Venus and is not a sign of possible life.”
- An incredible video of a single cell growing into a newt.🦎
- Recovering the lost Apollo 10 LM software (video). Apollo 10’s flight software has been lost to time—the only known copy is onboard Snoopy, the LEM of Apollo 10, somewhere in solar orbit. But, we know that it contained backports from a later version. When checksums were discovered for the two banks of missing backported software, they allowed Mike Stewart to reverse-engineer the missing changes from Apollo 11 software notes and develop a bit-for-bit reproduction of the original Apollo 10 software. Now on to launch!
- Now, this is how you blind an experiment.
The ‘Molten Ring’, GAL-CLUS-022058s, is one of the most complete Einstein rings ever discovered. Einstein Rings are caused by the gravity of an intervening galaxy focusing and distorting the light of distant galaxies beyond. Related: Machine learning algorithms were used to find 1200 new gravitational lens candidates in DESI data.