Issue No. 23

The Orbital Index

Issue No. 23 | Jul 30, 2019

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So, you want to build a CubeSat? First, select an appropriate CubeSat form factor based on payload size, power requirements, and deployment mechanism. Consider power budget (especially for when the spacecraft is “in eclipse” on the dark side of the Earth), acceleration and vibration tolerance (the sound of launch alone can damage the spacecraft), and thermal management (your satellite is effectively sitting in a rather large vacuum thermos). Use Commercial Off-The-Shelf (COTS) parts with existing flight heritage wherever possible—see satsearch and CubeSatShop. Pick solar panels, batteries, and an Electrical Power System (EPS) to manage them. Include one or more antennas and radios to talk to a ground station or ground station network (or broadcast up to GlobalStar or Iridium instead). If you need to maintain orientation, include an Attitude Determination and Control Systems (ADCS) which will use some combination of Earth, Sun, and star trackers, gyroscopes, GPS receivers, and magnetometers to sense orientation, and rotate the spacecraft using magnetorquers and reaction wheels. Some CubeSats are even starting to have miniature thrusters for attitude control, desaturation, and orbit maintenance. Deployable components, such as antennas and solar panels, are usually stored under tension and released with electromagnets or redundant burn wires. Next, select an On-Board Computer (OBC) for Command & Data Handling (C&DH) and the software that will run on it, such as the open-source KubOS (made by a startup Andrew works for). Prior to assembly, perform “flatsat” testing with everything wired on a bench. This is also when you should test communicating with the spacecraft via its radios. Once assembled, put the CubeSat through vibration and thermal vacuum testing to ensure that it will survive the stresses of launch and the space environment. Finally, obtain the required certifications for earth observation, radio licenses, and an approved deorbit plan. NASA has a helpful guide for first time CubeSat developers with instructions and templates, and also a state of the art technology report. As always, see Awesome Space for more resources. (This overview is incomplete—please do not base your spacecraft design on an email newsletter.)

The Starhopper has hopped. Last week, SpaceX’s squat test version of its Starship spacecraft successfully made its first untethered hop, reaching 20 m and translating sideways. The videos are impressive (engine cam, drone cam, composite for different/better views), partly just for the immense amount of fire, dust, and exhaust produced—it’s difficult to imagine the scale of 35 Raptor engines doing this on the proposed Super Heavy booster. The hop happened after several delays, one when a test Raptor had its oxygen turbine stator “liberated” and purportedly damaged the engine mounted next to it. Just two days before the successful hop, an attempt was aborted immediately after ignition due to high chamber pressure (too much thrust is not a problem new rockets usually have). With the hop, Raptor became the first full-flow staged combustion engine to fly. Throughout testing, SpaceX has continued to refine the Raptor engine, fixing 600 Hz oscillation issues and increasing chamber pressure (now a record ~275 bar). The level of transparency compared to other rocket development programs is phenomenal and it’s entertaining that the majority of Starship/Super Heavy/Starhopper information has been disseminated via Twitter. Recent tweets suggest a hop to 200 m could happen within “a week or two”.

An explanation for Supermassive Black Holes. Most big galaxies (including ours) contain a Supermassive Black Hole (SMBH) at their center that anchors and shapes the host galaxy. SMBHs are black holes with masses of 100s of millions to billions of Suns, and their formation is difficult to explain. “Normal” black holes (with masses > ~2 Suns) form when stars overcome degeneracy pressure and collapse into gravitational singularities. (Black holes are especially cool because their formation is dictated by quantum mechanics.) Given time, a normal black hole can absorb enough matter to become an SMBH, but this mechanism can’t explain SMBHs that formed shortly after the Big Bang, such as 83 SMBHs identified in a recent study, or an 800 million Sun SMBH that formed just an estimated 690 million years after the Big Bang. Now, a new study (paper) attempts to explain early SMBHs mathematically through a process of “direct collapse” with no stars involved in which early-Universe matter collapsed very quickly over very short periods of time. Related: PhD Comics’ beautifully animated explanation of SMBHs.

News in briefLightSail 2, a 3U CubeSat, unfurled its 32 sq. m solar sail this week, growing its sun-facing area 2,500x; Toyota and JAXA are developing a pressurized lunar rover (video); iSpace launched from the Gobi Desert and became the first private Chinese company to reach orbit with their Hyperbola-1 3-stage solid-fuel launch vehicle; after weather delays, SpaceX CRS-18 launched cargo, the International Docking Adapter 3, and… “non-newtonian” Nickelodeon Slime, to the ISS and stuck the landing (see an excellent synchronized tracking shot, an annotated map of the landing area, and a photo of the booster as it passed through the sound barrier); Chris Kraft, NASA Flight Director, died at 95; and, Mars 2020’s MMRTG is receiving its nuclear fuel.

Papers. Peptides, key building blocks of life, can form directly from aminonitriles without involving amino acids in conditions likely to have been present on the primordial Earth (paper); a 2-3 cm-thick layer of silica aerogel could block UV, transmit visible light, and raise the temperature of the Martian surface above the melting point of water, allowing plants to grow (paper); the ML Word2Vec technique applied to science papers predicted new thermoelectric materials that researchers had missed (paper); and, data from a Moon-orbiting cosmic ray telescope indicates that, as the Sun entered the current Solar Minimum, its protective magnetic field weakened, allowing more cosmic rays to enter the solar system and potentially threaten astronauts (paper)—counterintuitively, the “Solar Minimum may actually be more dangerous than Solar Maximum”.


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