Issue No. 225

The Orbital Index

Issue No. 225 | Jul 5, 2023

🚀 🌍 🛰

Gravitational wave background. We’ve previously written about NANOGrav and other pulsar timing array (PTA) efforts: decade-long efforts to correlate subtle shifts in timing signals from 80+ pulsars to detect very-low-frequency gravitational waves. Unlike the gravitational waves generated by colliding black holes and detectable by LIGO, Virgo, and KAGRA (in the 10 Hz to 1,000 Hz range), these are gravitational waves with periods measured in years generated by orbiting black hole binaries and other massive sources—the basic gravitational cacophony of the Universe. The NANOGrav effort previously had non-conclusive evidence (paper) of this “gravitational wave background” (akin to the cosmic microwave background). Now, along with international PTA efforts in Australia, China, Europe, and India, conclusive detection has been announced based on 15 years of data (paper). PTA expansion and further data analysis will let scientists look for nearby supermassive blackhole binaries and test hypotheses about the nature of gravitation. With more PTA efforts, the upcoming LIGO-India, the proposed Einstein Telescope, and the under development space-based LISA, gravitational wave astronomy is now truly coming into its own, opening up a whole new way to view the Universe.

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New Horizons might end up looking back at old horizons? Mostly undiscussed, NASA has been reevaluating New Horizons’ science agenda over the last few months. The original mission, validated by the National Research Council’s 2003 Planetary Science Decadal Survey, was to observe as many Kuiper Belt objects (KBOs) as possible after flying by Pluto. Its fly-by of Pluto revolutionized our understanding of the dwarf planet in 2015, with data that continues to yield new results 8+ years later. After Pluto, NH performed a fly-by of Arrokoth, a peanut-shaped contact binary, and humanity’s first close approach to a KBO. The science team is observing more distant KBOs to search for a final flyby target in the outer Kuiper belt (which the team now thinks is a belt of objects distinct from the main Kuiper Belt). However, in recent months NASA has suggested repurposing the mission to focus on heliophysics, replacing the planetary science team with a new one—the argument is that as NH flies farther out, possible additional fly-by targets are few and bogglingly far between, while it presents a unique vantage point on the Sun, solar wind, and potential microlensing events that could identify a wandering interstellar black hole (paper). (The $900M+ spacecraft is now sustained on a budget of merely ~$10M/year, so any change to the team will be unlikely to save the agency meaningful money and could even increase costs.) Some in the science community are frustrated by what they feel is a move toward early termination of the original mission, while the craft looks like it could be operational well into the 2030s, staying within the Kuiper belt until 2027 or 2028. Their reasoning is that NH is already producing some heliophysics data while performing ‘excellently’ in recent planetary science reviews—it is positioned to be much more impactful as an ongoing planetary science mission rather than a mediocre heliophysics one. NH is funded through 2024 for its current planetary science objectives but would switch to the proposed heliophysics mission in 2025 if NASA pulls the trigger on the change.

Starship is switching to hot staging. Taking to Twitter Spaces, as is his recently rate-limited fashion, Musk said that Starship’s upper stage will move to hot staging for separation (instead of the simple, but slow, rotational dynamics method we recently linked to). Hot staging involves lighting the upper stage engines just prior to stage separation to maintain consistent thrust and keep propellant settled without the need for ullage motors or other techniques. To minimize gravity losses, rockets also want to spend as little time as possible getting to orbit, and Starship’s previously proposed approach was slow. The downside of hot staging is the potential for damage to the booster by blasting it with (probably) three-raptor-engines-worth of hot exhaust—to minimize this, an interstage and venting ports are being added to the top of Super Heavy. The technique has never been used on a reusable vehicle, but Soviet/Russian rockets (and Chinese and Indian ones derived from them), as well as Titan II, have long used hot staging successfully.

A Soyuz rocket, mid-hot-staging, with its second-stage engine exhaust escaping through the rocket’s open strut-like interstage (video). Credit: ESA

Space funding.

  • Ramon.Space raised $26M for space-rated computing hardware.
  • French startup Look Up Space raised €14M for yet more space situational awareness.
  • Agile Space raised $13M for in-space chemical propulsion.
  • AIRMO raised a €5.2M pre-seed for a greenhouse gas emissions monitoring constellation.
  • AST SpaceMobile, maker of the massive BlueWalker 3 to talk to cell phones, raised $59.4M as a public offering, at a discount to its trading stock, which then dropped 30%. 😬

News in brief. ESA’s Euclid space telescope launched toward L2 on a Falcon 9 (c.f. Issue 224)Iranian-American Firouz Naderi, leader of five NASA Mars missions (with two landers), passed away at 77Vega C’s return-to-flight has been delayed after an unsuccessful static fire that lost pressure mid testRadio contact has been restored with Ingenuity—the helicopter lost contact with Perseverance on April 26th after its 52nd flight on Mars when hilly terrain blocked transmission Spire and OroraTech are collaborating on a wildfire monitoring constellation SpaceX will soon completely switch over to Starlink v2 Mini, with Starlink mission 5-15 as the last scheduled launch with a load of v1.5 satellites Three Italian Air Force and National Research Council personnel (plus payloads) flew to an altitude of 85 km on Virgin Galactic’s VSS Unity, the company’s first fully commercial SpaceShipTwo suborbital flight—incredibly, SpaceShipOne first flew in 2003.


VSS Unity gliding home after Virgin Galactic’s first commercial flight. Credit: SpaceNews/Jeff Foust


JWST captured a striking near-infrared image of the ringed planet on June 25th and three of its moons (Dione, Enceladus, and Tethys). The monochromatic image is mapped to orange in this presentation.

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