Issue No. 4

Welcome to issue four and our first whole month of writing The Orbital Index! Thanks for all the feedback, the content submissions, and for just opening up each issue and reading it. We’re taking the newsletter out of ‘beta’ for this issue, but that doesn’t mean it won’t keep evolving. So please keep sending us feedback and cool space content! And, as always, we’d really appreciate it if you forwarded this issue to a friend or two.

The Orbital Index

Issue No. 4 | Mar 19, 2019

🚀 🌍 🛰️

SABRE engine gets the green light. UK-based Reaction Engines’ air-breathing hybrid ramjet/rocket engine received investment from the ESA (€10m) and UKSA (£50m). The air-breathing phase of launch can take the proposed autonomous Skylon SSTO vehicle 22% of the way to orbital velocity, allowing the vehicle to carry 40% less oxidizer mass, thus increasing its relative payload capacity and making SSTO plausible. SABRE’s core technology is its insane pre-cooler which is rated at over 1 GW/m3 of heat transfer. It can cool super hot compressed intake air that is moving at up to Mach 5.4 by ~1000° K in a twentieth of a second, allowing the engine to be built out of the lighter weight alloys critical to attaining orbit. By using helium in the pre-cooler, and then running it through a heat exchanger with incoming cryogenic hydrogen propellant, the engine avoids challenges with hydrogen embrittlement that would compromise its 50 km (!!) of 30 micron-walled tubing. While recent coverage touts SABRE as ‘new’, Reaction Engines was established in 1989 to continue work on a canceled British Aerospace Horizontal Take-Off and Landing vehicle that was conceived of in 1982 as a cheaper alternative to the Space Shuttle. Testing SABRE’s pre-cooler was funded by DARPA in 2017. They’ll be conducting high-temperature airflow tests by shooting exhaust from an F-4’s turbojet engine into the pre-cooler at 1000° C. Look for this testing to begin in the next month or so.

Scientists used cosmic-ray induced muons to estimate the voltage differential of a thunderstorm to be a whopping 1.2GV, which is 10 times previous estimates. The study used the GRAPES-3 muon telescope in India to observe a decrease in muon flux as storms passed overhead. This decrease was due to the storm’s potential decelerating some of the muons. Storms were observed reaching potentials of 1.2GV in 6min, implying delivery of power >2GW. Storms with power levels of this magnitude could offer an explanation for a mysterious phenomenon: terrestrial gamma-ray flashes. These flashes of gamma-rays, typically observed via satellite, have been hypothesized to result from thunderstorms acting as electron accelerators, but until now storms had not been observed with enough power to explain the bursts. Related: cosmic ray muons have previously been used to passively “X-Ray” large objects, such as the insides of volcanoes and even secret chambers in the Great Pyramid. They may someday be used to image geology on Mars.

An enormous Solar Proton Event (SPE) struck the Earth 2600 years ago, according to a study of radionuclide Be-10 occurrence in two ice cores from Greenland, backed up by C-14 from tree rings. These radionuclides are formed through spallation when energetic solar particles strike atmospheric Nitrogen and Oxygen, and their rates of production rapidly increase during solar storms. This event was an order of magnitude stronger than any recorded with modern instruments and was comparable to the largest known SPE which occurred in AD 774. If such an event occurred now, it would be very dangerous to spacecraft and astronauts. While not directly the cause, SPEs also often occur along with geomagnetic storms, which can cause widespread disruption to electrical grids. So it’s good, then, that another recent study puts the likelihood of a catastrophic geomagnetic storm in the next decade between 0.46%-1.88%, much less than the previous estimate of around 12%. Related: here’s the current space weather.

No escape system heroics required this time as a Soyuz rocket successfully carried Nick Hague, Christina Koch, and Alexey Ovchinin to the ISS, months after Hague and Ovchinin’s MS-10 Soyuz launch in October automatically-aborted. That abort was the first since 1983, but the system worked perfectly, pulling the crew away from the failing rocket [video]. Launch escape systems are a key part of human spaceflight. Here’s a video about testing Apollo’s launch escape system, in which the test rocket itself accidentally blew up and the abort system performed admirably. Much more recently was SpaceX’s Crew Dragon pad abort test [video]. Later this year, SpaceX will perform an in-flight abort test (likely June), Boeing will perform a pad abort test of their CST-100 Starliner capsule (May), and NASA will conduct an in-flight abort test of the Orion capsule (June).

A 9% test rig of the SABRE air-breathing rocket engine’s pre-cooler and combustion chamber.
(9% as in 9% of the temperature drop, not 9% of the physical size.)

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