Issue No. 20

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The Orbital Index

Issue No. 20 | Jul 9, 2019

🚀 🌍 🛰️

India is heading back to the moon. Chandrayaan-2, ISRO’s second moon mission, launches on an Indian-built GSLV-Mk III rocket next Monday, July 15th, with a lunar landing slated for September. The ambitious mission will look for water at the unexplored lunar south pole and includes an orbiter, lander, and rover. If successful, it will make India the 4th country to soft-land on the moon. (Chandrayaan-1’s impact probe carried Indian flags, but given that it arrived at the surface traveling 1.5 km/s, media claims in 2008 that an “Indian flag lands on [the] lunar surface” seem rosy. Solidly on-brand for humanity though.) Chandrayaan-2’s 1,471 kg lander, Vikram, carries multiple sensors and Pragyan, a 27 kg solar-powered rover which has two spectrographs, a range of around 500 m, and an expected lifetime of one lunar day (about 2 weeks). The Planetary Society’s Chandrayaan-2 overview dives into the mission with more detail.

An amateur astrophotographer caught an X-37B space plane overflight. After months of hunting, including tracking down an orbital maneuver with help from the amateur satellite observers-network, Ralf Vandebergh was able to image the secretive USAF Orbital Test Vehicle (OTV) as it passed over the Netherlands on July 2nd. The reusable X-37, built by Boeing, has been conducting classified operations in orbit for 670 days as part of its fifth orbital mission (and over 2,000 days combined). The autonomous “Space Shuttle Jr.” is a testbed for military satellite tech, and some think that it may also be searching for other countries’ classified spacecraft.

Tunguska-like events are rarer than we thought. On June 30, 1908, an explosion in a luckily uninhabited area of Eastern Siberia leveled 2,000 square km of forest, broke windows hundreds of kilometers away, and produced shockwaves detected globally. Rather than a comet, new research based on multiple independent simulations suggests that the Tunguska event was caused by a 50-80 m stony asteroid hitting the atmosphere at 15 km/s and exploding at 10-15 km altitude. This impact would have released the “energy of a 10 to 30 megaton explosion, equivalent to the blast energy of the 1980 Mount St. Helens eruption.” The simulations were also validated against the 2013 Chelyabinsk meteor burst (seriously, what’s space got against Russia?), suggesting that it too was a stony asteroid, this time “the size of a five-story building”, which exploded at 25 km with a 550 kiloton yield. Here’s a (loud) compilation video of the shockwave. (Friendly advice: if you ever see a very bright flash of light, please use the 3 s you get per km of distance from the blast to move away from, instead of towards, windows.) The good news is that these simulations, combined with recent asteroid population data, suggest that city destroying Tunguska-level events occur with a frequency on the order of millennia, not centuries, as was previously thought. Chelyabinsk-level events occur roughly every 50 years, though. (Related: NASA just announced that they’re delaying NEOCam, a space-based Near Earth Asteroid hunting telescope.)

Two new x-ray telescopes launch together on July 12th. The telescopes are mounted side-by-side on the Spektr-RG spacecraft and will produce high resolution x-ray maps of the entire sky, cataloging galactic nuclei/quasars, galaxy clusters, active black holes, supernova remnants, x-ray binaries, and neutron stars to better understand Dark Energy and other phenomena. Spektr-RG will take 3 months to reach the Sun-Earth L2 point, 1.5 million km away, after launching on a Proton-M with a Blok DM-03 upperstage from Baikonur Cosmodrome (its June 21 launch was scrubbed when a single-use battery was discharged due to an in-flight heater left on during testing—oops!). Spektr-RG continues in a lineage of space-based x-ray telescopes necessitated by our atmosphere’s propensity to absorb x-rays. It will orbit L2 for seven years (joining Gaia, and later JWST and others), imaging the full sky every 6 mos. The German 7-module Wolter-I eROSITA telescope follows the 90s-era German ROSAT and (failed) ABRIXAS telescopes and will observe the 0.2 - 12 keV band. Meanwhile, the Russian ART-XC (also a 7-module Wolter-I configuration) targets a smaller field of view in the “hard” 5 - 30 keV band (the telescopes’ bands are overlapped for calibration and mutual confirmation). Wolter telescopes work by reflecting x-rays—which are normally transmitted or absorbed by mirrors—at very small angles using two mirror surfaces oriented on complementary paraboloid and hyperboloid planes [a good description of similar optics from NuSTAR]. To increase the field of view, mirrors are built as concentric shells (eROSITA has 54 per module and ART-XC has 28).


News in brief. The DSCOVR NASA/NOAA mission that takes amazing Earth + Moon pictures from L1 entered safehold mode due to a positioning system failure (we hope that it’s recoverable and are disappointed that it didn’t catch last week’s eclipse, as it did in 2017); the Launch Abort System for NASA’s Orion human capsule was successfully tested July 2nd, pulling the boilerplate capsule away from a modified Peacekeeper missile launch stage that then plunged dramatically into the ocean at 400mph (related: a conversation about Orion’s manual abort button and its 12-15g’s of haptic feedback); a Soyuz-2.1b rocket delivered 33 satellites to orbit on July 5th, including a 2750 kg Russian weather satellite, 8 Spire cubesats, a water-based microwave electrothermal plasma thruster testbed, NSLComm’s tiny foldable communication satellite, and 20 other smallsats; SpaceX shared that 45 of its Starlink LEO satellites have reached their 550 km orbits—contact was lost with three others, and two more will be used to test propulsive deorbiting; and, we have the first atmospheric signature of an exoplanet with a size between Earth and Neptune—surprisingly, it looks like a hybrid between a rocky planet and a star, with a solid core buried under a thick H/He atmosphere that is largely free of heavier elements (unlike our solar system’s ice and gas giants).


Commanded by amateur radio operators, the 47 kg Chinese DSLWP-B lunar satellite took this image of the moon eclipsing the Earth. DSLWP-B’s onboard radio station allows amateurs to take and downlink images.

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