# The Orbital Index

Issue No. 61 | Apr 21, 2020

🚀 🌍 🛰
 ¶Happy 30th anniversary, Hubble! The Hubble Space Telescope was launched into LEO on April 24th, 1990 aboard Space Shuttle Discovery (STS-31 launch video). Featuring a 2.4 m mirror and optics that are smooth to 10 nanometers (but were in the wrong shape until corrected by the first of five servicing missions in 1993), Hubble takes images of the Universe with never-before-seen quality. The telescope may work into the 2040s, hopefully being joined by its more-advanced sibling, the JWST, next year. Take a moment to browse some of Hubble’s most stunning snapshots of the Universe, or check out an image that Hubble took on one of your birthdays.
 The Hubble Ultra Deep Field is the deepest visible-light image of the Universe ever taken. Containing almost 10,000 galaxies caught everywhere from having just formed 800 million years after the Big Bang (the smallest and most red-shifted) to mature galaxies whose light left them only a billion years ago (larger elliptical and spiral galaxies). This image was composited from 800 exposures taken over 400 orbits. Viewed from Earth, the portion of the sky in this photo appears almost empty of visible stars, and is just one-tenth the diameter of the Full Moon—it’s like “looking [at the sky] through a 2.5 metre-long soda straw.”
 ¶Proliferation in LEO (dubbed ‘pLEO’). Tomorrow, SpaceX will likely launch Starlink v1-6 (their 6th launch of v1.x operational Starlink hardware), bringing its total constellation to over 400 satellites—the largest single-purpose constellation in space (Planet has still launched more satellites—until this Starlink launch—but many of their satellites have since re-entered). A recent, very readable, policy paper from Aerospace Corp considers pLEO, its effect on astronomy, and avenues for impact mitigation. The paper (pdf) focuses on the impact of satellites at altitudes of 500 and 1,200 km, which maps closely to Starlink's current 550 km shell. (As of this week, SpaceX is no longer proposing a 1,200 km orbital shell, which should be good for optical astronomy.) Satellites impact astronomy most at dawn and dusk due to sunlight reflecting off them (video), reducing imaging time and limiting access to some celestial objects. (Here are some visualizations of Starlink’s potential effect on the night sky.) At the worst times, during the peak of summer, the safe field of view (FOV) of LSST in Chile could be reduced by up to 63% by the 500 km satellites (and 79% by the now-defunct 1,200 km satellites). Some of the potential FOV impact could be mitigated with high-precision tracking algorithms and improved scheduling of telescope time. Decreasing the albedo of the satellites through coatings (like darksat), conducting avoidance maneuvers, and modifying satellite orientation can all reduce a constellation’s impact on astronomical observations as well. Related: the Starlink train was photographed from the ISS. (Note: The paper is co-authored by Luc Riesbeck, who hails from Andrew & Ben's hometown in SE Ohio. 🎉)
 ¶NASA Innovative Advanced Concepts (NIAC) selects 23 concepts for early study. Included are 16 new concepts and 7 that have previously received NIAC awards. Most grants are small—Phase I is $125,000 for nine-months of study, Phase II is$500,000 for up to two years of study—except for the rare Phase III, which is $2 million and extends research another two years. Here are some of our favorites (we’ll cover a few more next week):A mission study from JPL that would use multiple small spacecraft delivered via solar sail to 548 AU (81 billion km from the Sun) where they could use the Sun as a gravitational lens for directly imaging Earth-like exoplanets (with 25 km-scale surface resolution at 30 parsecs 🤯). This is only the third study granted Phase III funding in the history of the program. (Here are the previous two.)Potentially supporting the previous mission is a study of metamaterials for solar sails. It explores materials that could withstand close proximity to the Sun. “Our technology enables reaching Jupiter in 5 months, Neptune in 10, surpassing Voyager 1 in 2.5 years and getting to the solar gravity lens location in just 8.5 years.” (Phase I)A JPL proposal for satellite-based “long-baseline atom-interferometer gravity gradiometers” to directly map the solar system’s gravitational field in order to look for the effects of Dark Energy. (Phase II) StarNAV, a navigation sensor that uses stellar aberration (relativistic perturbation of starlight) to calculate the motion of a spacecraft. (Phase I)The Lunar Polar Mining Outpost architecture which uses deployable solar arrays on towers to provide power to perpetually shaded lunar craters where ice has been detected. The power would be used to extract water through Radiant Gas Dynamic (RGD) mining, a process using multi-spectral radiation at the surface that “sublimates the ice and encourages a significant fraction of the volatiles to migrate upward out of the regolith into cryotraps where it can be stored in liquid form.” (Phase II)  TransAstra’s proposed Lunar Polar Mining Outpost.  ¶News in brief. Virgin Orbit performed a “captive carry” dress rehearsal for their first orbital launch—complete with an RP-1 fuelled and flight-ready LauncherOne—and won a$35 million US Space Force contract to launch 44 small test satellites; the US Space command announced that they are tracking a Russian ASAT test (meanwhile at least 14 pieces of debris from India’s ASAT test last year are still in ISS-crossing orbits); Intelsat-901 satellite, now with MEV-1 attached, resumes service; and, NASA set May 27th as the launch date for SpaceX’s crewed flight to the ISS—it could certainly slip, though.