# The Orbital Index

Issue No. 105 | Feb 24, 2021

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 This week marks two years since we started writing The Orbital Index!   It’s been an exceptionally rewarding and educational experience. Here are a few favorites from our last 104 issues: Issue No. 1, our first issue ever! 🆕In Issue No. 48 we took a deep dive into climate change and how it relates to space. 🌍Andrew’s fav: Issue No. 42, about how you can get involved with space exploration and the CRS-19 launch (which he was thrilled to attend!) 🚀Ben’s pick: Issue No. 50, all about asteroids and them running into things ☄️And, Issue No. 21 about the Apollo 50th anniversary! 🧑‍🚀We’re now hoping to build on our foundation of nearly 5,000 subscribers (thank you!) to make the newsletter sustainable long term. With this in mind, we’d like to ask you a couple of questions:  Would you be up for sponsoring the newsletter as an individual or as a business? Would you share The Orbital Index with (at least) two friends or colleagues? (handy forward link is right there, but social media works too) 🙏☙✶❧
 ¶Percy has arrived. As you almost certainly already know, on Thursday, NASA’s 2.7-billion, 1,025 kg science laboratory-on-wheels landed successfully in Jezero Crater. There it will spend the next few years (and hopefully the next decade) looking for signs of ancient life in the 3.5 billion-year-old remains of a Lake Tahoe-sized lakebed, associated river delta system, and nearby terrain. Some of the region outside the crater is brecciated from massive impacts, while other parts have igneous lava flows to explore—here’s a bunch more about the geology of the region. Percy’s entirely autonomous descent involved 76 pyrotechnic devices, 16 rocket engines, 10Gs of deceleration at plasma blackout, the largest supersonic parachute ever, and a jeep-sized rover descending from a hovering skycrane on nylon cables. It went flawlessly, while those back home waited 11 minutes for light to crawl between the planets and let us know. (Meanwhile, Andrew can’t reliably get wifi from his office to his living room.) Percy will spend a little while getting its bearings, calibrating its instruments, aligning its high-gain direct-to-Earth antenna, and then start zapping, ranging, imaging, sampling, and listening to Mars. You absolutely have to watch the POV video of the landing.  It’s not every day that you see a photo of a car being lowered on cables from a rocket-powered skycrane on another planet. For Percy, that was Thursday. You’ve watched that video, right?  ¶Ingenuity. Tucked underneath Percy is Ingenuity, a 1.8 kg,80-million autonomous helicopter. Its counter-rotating carbon-fiber blades are tuned to move about as quickly as they can—their tips will be moving at around 70% the speed of sound in the Martian atmosphere (~240 m/s), which is about 1% the density of Earth’s. Ginny carries two cameras, a laser altimeter from SparkFun, and no scientific instruments—its singular mission is to demonstrate the first powered flight of an aircraft on another planet. Ingenuity runs Linux (for the first time on Mars) and uses the open-source F' software framework on a 2.26 GHz quad-core Snapdragon 801 processor. Radiation hardened processors aren’t fast enough for the real-time vision requirements of the experiment—but as an unprotected COTS processor, it will fail periodically due to radiation-induced bit flips, possibly as much as every few minutes. NASA’s solution is to use a radiation-tolerant FPGA ProASIC3 to keep an eye on the CPU (paper) and software that attempts to double-check operations as much as possible. “[I]f any difference is detected they simply reboot. Ingenuity will start to fall out of the sky, but it can go through a full reboot and come back online in a few hundred milliseconds to continue flying.” We talked about Ingenuity in more detail in Issue No. 64. The first flight may be in about 30 sols. Next stop: Titan.
 ¶Does a planet orbit Alpha Centauri A in its habitable zone? First, a quick primer on the confusing Alpha Centauri triple star system, our closest stellar neighbor at 4.37 light-years away. Alpha Centauri A and B are Sun-like stars that orbit each other with a period of 80 years, forming the binary system known as Alpha Centauri AB. Meanwhile, Alpha Centauri C (aka Proxima Centauri) is a faint red dwarf star that slowly orbits the AB duo 0.21 light-years away. We already know that Proxima Centauri has a planet in its habitable zone, but the planet is likely tidally locked and orbits a flare-prone star, so it’s probably not a great place to find life. Tantalizingly, there’s now early evidence that Alpha Centauri A might also have a ‘warm Neptune’ or super-Earth planet in its habitable zone (paper). If confirmed (it could just be dust or noise), this would be the first direct imaging of a planet in a habitable zone, made possible by the VISIR mid-infrared spectrometer on the 8.2-meter Very Large Telescope in Chile. The research project, called NEAR, looks for planets’ blackbody thermal emissions in a tight 10-micron infrared band while blotting out most of their stars’ light with a coronagraph. It was funded by Breakthrough Watch (which is part of the Yuri Milner-funded Breakthrough Initiatives that also hopes to laser-accelerate a probe to the Alpha Centauri system sometime ‘soon’). NEAR has the only coronagraph on Earth that could potentially image this planet today, but JWST, the Nancy Grace Roman Space Telescope, and a bunch of upcoming ground-based coronagraphs should usher in a new era of direct exoplanet imagery and atmosphere analysis. This is all very exciting because certain atmospheric compositions could be strong indicators of life—such as methane, or even pollution—although confirming any detection will be incredibly hard.
 ¶News in brief. SpaceX raised an additional $850 million, valuing the company at$74 billion, 60% more than last August's $46 billion valuation—Musk also shared that Starlink will require an investment of$10 billion, but could generate \$30 billion annually; SpaceX also hot fired Starship SN10—launch could happen in the next week if data looks good; NASA is planning to repeat their SLS hot fire test on the 25th, with less conservative test parameters (the test will require at least 250 seconds to pass requirements); the Russian Progress 77 and Northrop Grumman ‘S.S. Katherine Johnson’ Cygnus resupply ships both launched to the ISS, the latter carrying a record quantity of cargo, including an experimental brine processor to convert urine into drinking water, a commercial experiment to manufacture artificial retinas, and a bunch more; DART’s launch was delayed to November, but it won’t affect its arrival date at Didymos; ESA launched the Parastronaut Feasibility Project, a program enabling people with lower leg disabilities to become astronauts, and is also seeking more female astronauts; Russia is moving towards joining China’s proposed lunar base instead of joining the Artemis Accords and Lunar Gateway; and, the Inspiration4 mission named its first additional crew member, Hayley Arceneaux, a cancer survivor and physician assistant at St Jude hospital.
 ¶Etc.A recent SciAm article discussing JPL’s shrinking landing ellipses. The Viking missions had a target landing ellipse of 300 km x 100 km, Spirit and Opportunity brought that down to 150x20 km, Curiosity introduced active steering and a 20x7 km target, and now with Range Trigger and Terrain Relative Navigation (TRN), Perseverance’s landing ellipse was just 7.7x6.6 km. As you can see from NASA’s Where Is The Rover, it landed pretty darn close to the center, and TRN kept it 35+ m from the nearest orbitally-identifiable hazard. (Jatan, who wrote the article, also has an excellent lunar-focused newsletter called Moon Monday.)Scott Manley did a review of the SOHO spacecraft, now 25 years old, and how it was lost and recovered. NASA recently applied similar tricks to work around a failing Inertial Measurement Unit on their Lunar Reconnaissance Orbiter.This is why Perseverance isn’t solar powered: Mars InSight’s solar panels are covered in dust and are producing only 27% of their dust-free capacity. InSight recently completed its primary mission but received a mission extension to keep listening for Marsquakes. As Mars comes out of aphelion, and with passing dust devils hopefully providing some cleaning, there should be additional power for further science. (Shaking the panels didn’t seem to help much.) Raw images from Percy have started to flow. ‘Farfarout’ was recently confirmed as the most distant observable object in our solar system at 132 AU. Originally observed in 2018 by the team currently searching for the proposed Planet Nine, the ~400-km dwarf planet’s nickname comes from the fact that it is even farther out than the last record-breaking object the team found, ‘Farout’. Clever.Blue Origin recently released a video of its pathfinder Lunar descent stage.Relating to our SAR piece a couple of weeks back: this SAR tutorial (pdf) was recommended as an intro by the folks at Capella.  Ariel Waldman and Lisa Ballard have relaunched spaceprob.es, a lovingly designed site that displays information on the 36 active, non-Earth probes, all in one place.