Issue No. 13

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The Orbital Index

Issue No. 13 | May 21, 2019

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NASA and ULA are developing an inflatable heat shield to be tested around 2022. NASA is interested in the technology for delivering heavy payloads to Mars, while ULA is interested in using it to recover the main BE-4 engines (which represent 65% of the booster’s cost) from their upcoming Vulcan rocket by catching them with a helicopter. We’ll be interested to see if and how they steer the heat shield during reentry. Here’s a video of an inflatable heat shield that was tested in 2009.

Planetary Defense. Earlier this month was the Planetary Defense Conference, which focuses on the threat to Earth posed by asteroids and comets, as well as their potential mitigations. Mitigations include nuclear weapons (for comets, since we won’t have much warning), kinetic impactors (being tested for the first time by the upcoming DART mission), and gravity tractors (which use a heavy spacecraft orbiting the asteroid while thrusting perpendicular to its orbit to slowly shift the combined gravitational system without any physical contact). Asteroid strikes are one of the few natural disasters that can potentially be prevented if we have early warning. One study presented at the conference, ADAM, found that the median required delta-v for redirection was 1.2 cm/s with 10 years warning, but only 0.55 cm/s with 20 years. (For comparison, DART will impart 0.2-0.3 cm/s.) Unfortunately, we have probably only identified one-third of the Near Earth Objects (NEOs) of 140m or larger. This is the size of an object that would cause regional, but not global, destruction. Projects currently active or on the horizon, including Pan-STARRS, the Catalina Sky Survey, ATLAS, and the LSST (which just received its primary mirror) should be able to catalog the majority of NEOs in this range. Identifying a significant percentage of smaller NEOs, still large enough to cause the Tunguska blast or create Meteor Crater in Arizona, will require new observatories. Resources: NASA’s Planetary Defense department, the International Asteroid Warning Network, and the B612 Foundation, started by Ed Lu, astronaut and co-inventor of the gravity tractor.

Solar Panels in Space. As small satellites tackle larger missions, they increasingly require more power and rely heavily on space-based solar PV tech (which is technically distinct from ground-based solar). Therefore, power system design dominates a growing portion of the overall design process—NASA's well-written State of the Art of Small Spacecraft Technology report includes a full chapter on power. Improvements in the past year in radiation hardened multi-junction photovoltaic cells, including growing them upside down on a germanium substrate, have brought cell output to an unprecedented 32% efficiency (note that these cells are early in production and were only rated at TRL 6 by NASA). However, more available power also brings with it additional mass requirement for battery capacity and hardware to radiate excess heat. Optimum system sizing has been the subject of several papers; a particularly approachable 2017 entry titled "Design an Optimum PV System for the Satellite Technology using High Efficiency Solar Cells" combines both economic and technical analysis.

News. NASA funded 11 companies to study lunar lander options and asked for $1.6 billion in additional funding for their 2024 Moon mission, now called Artemis, preliminarily consisting of 37 launches; SpaceX’s Starlink launch is now targeted for 5/23 after being delayed to update satellite software (it was also revealed that each satellite weighs about 227kg and will use Hall-effect thrusters with krypton instead of xenon—lower performance, but just 1/10th the cost—to raise their orbits to 550km).


The first photo taken of the Earth from space. Captured by the V-2 No. 13 rocket in Oct 1946.

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