Space Sunday: equations and launch scrubs

Dr. Frank Drake and his equation

Anyone with a reasonable interest in astronomy will recognise the above image as containing the Drake Equation, sometimes referred to as “the second most famous equation after E=Mc2

It was first proposed in 1961 by American astronomer and astronomer and astrophysicist Dr. Frank Drake as a probabilistic argument to estimate the number of active, communicative extraterrestrial civilisations in the Milky Way Galaxy. Its values are defined as:

N = the number of civilisations in our galaxy with which communication might be possible (i.e. which are on our current past light cone);


R = the average rate of star formation in our Galaxy.

fp = the fraction of those stars that have planets.

ne = the average number of planets that can potentially support life per star that has planets.

fl = the fraction of planets that could support life that actually develop life at some point.

fi = the fraction of planets with life that actually go on to develop intelligent life (civilisations).

fc = the fraction of civilisations that develop a technology that releases detectable signs of their existence into space.

L = the length of time for which such civilizations release detectable signals into space.

In the decades since its initial publication, the Drake Equation has been widely critiqued by astronomers and mathematicians because the estimated values for several of its factors are highly conjectural  such being that the uncertainty associated with any of them so large, the equation cannot be used to draw firm conclusions.

However, these critiques actually miss the point behind Drake formulating the equation in the first place, because he was not attempting to quantify the number of extra-solar civilisations which might exist, but rather as a way to stimulate scientific dialogue about what had been very much looked upon as an outlier of research, and to help formulate constructive discussion on what is regarded on the first formalised discussion on the search for extra-terrestrial intelligence (SETI), as he noted in his memoirs:

As I planned the meeting, I realised a few day[s] ahead of time we needed an agenda. And so I wrote down all the things you needed to know to predict how hard it’s going to be to detect extra-terrestrial life. And looking at them it became pretty evident that if you multiplied all these together, you got a number, N, which is the number of detectable civilizations in our galaxy. This was aimed at the radio search, and not to search for primordial or primitive life forms.

– Frank Drake

Frank Drake not only hosted the first US meeting to discuss the potential for seeking signs of possible extra-terrestrial civilisations, he pioneered several of the earliest attempts to seek any such signals as demonstrating methods that might be used as a means to intentionally communicate our existence to other civilisations within the galaxy. As such, his work did much to put our speculative thinking about intelligences elsewhere in the galaxy on a solid foundation of scientific research, as will as being responsible for some for the foremost research in the field of modern radio astronomy.

This is his story.

Born in Chicago on May 28th, 1930, Frank Drake was drawn to the sciences and to electronics from an early age, and in order to further his education in both, he enlisted in the US Navy Reserve Officer Training Corps (ROTC).  This allowed him to obtain a scholarship at the prestigious Cornell University, ostensibly to obtain qualifications in electronics, but also study astronomy.

While at Cornell, Drake’s astronomy class were able to attend a lecture by astrophysicist Otto Struve. While his name may not be instantly recognised, Struve was one of the most distinguished astronomers of the mid-20th century, a member of a generational family of astronomers stretching by to the 18th century and Friedrich Georg Wilhelm von Struve. He was also one of the first astronomers to openly promote radio astronomy as a key to determining whether there might be other intelligences living in our galaxy – an idea his contemporaries tolerated, rather than embraced.

Struve’s presentation positively affected Drake, and following his required 1-year military service following graduation in 1951 (served as the Electronics Officer aboard the cruiser USS Albany), Drake enrolled at Harvard University, where gained his doctorate in astronomy, with a focus on radio astronomy.

Frank Drake in one of his official portraits at Green Bank observatory (1962). Credit: Green Bank

In 1956 Otto Struve was appointed as the first director of the National Radio Astronomy Observatory (NRAO)), and he started overseeing the establishment of a number of national radio astronomy centres across the United States. One of these was at Green Bank, Virginia, a facility Drake joined as a researcher in 1958. His initial work here started with the static arrays at Green Bank, carrying out the first ever mapping of the centre of the Milky Way galaxy, and the discovering that Jupiter has both an ionosphere and magnetosphere.

However, Struve was keen to enhance the facilities with steerable radio dishes, and to this end purchased an “off-the-shelf” 26 m dish and had engineer Edward Tatel (for whom it was later named) design a motorised mount for it so it could be pointed around the sky. This work was completed in 1959, and Struve turned to Drake to formulate the telescope’s first science mission.

At the time, Drake had just read an intriguing article in Nature magazine entitled Searching for Interstellar Communications. Within it, physicists Giuseppe Cocconi and Philip Morrison proposed using a large radio dish to monitor “incoming” radiation from stars along the 21-cm / 1,420.4 MHz wavelength – the radio frequency used by neutral hydrogen.  Given this is the most common element in the universe, Cocconi and Morrison speculated it would be logical landmark in the radio spectrum to manipulate as a message carrier.

Taking this idea, Drake developed Project Ozma, a three-month programme run at the start of 1960 to listen for any signals coming from the vicinity of either Tau Ceti or Epsilon Eridani. At the time, no-one knew if either star fielded planets (although both were found have at least one planet orbiting them almost 50 years after Drake’s experiment).

Frank Drake in front of the 85-1 (Tatel) Telescope. the first steerable telescope built at NRO Green Bank (and now one of 3 such telescopes, collectively referred to as the Green Bank Interferometer), used in Drake’s first SETI experiment, Project Ozma. Credit: NRAO Green Bank

Following Ozma, Drake was encouraged to formalise SETI research into a more co-ordinated effort (various programmes, such as Ohio State University’s work using the Big Ear telescope, were already in existence but without any real coordination). To this end, he helped put together the first small-scale meeting / conference on the subject in 1961 – the event at which he used his equation to  stimulate the discussion.

Among those attending were Otto Struve (now retired), Phillip Morrison, astronomers Carl Sagan and Su-Shu Huang, chemist Melvin Calvin, neuroscientist John C. Lilly, and inventor Barney Oliver. Together they called themselves The Order of the Dolphin (due to  Lilly’s work on dolphin communications), and together they laid the groundwork for a systematic approach to SETI research, which over the coming years would in turn give birth to numerous programmes, and more fully legitimise such research within scientific circles.

In the mid-1960s, and still based at Green Bank, Drake was nominated to spearhead converting the massive Arecibo Ionosphere Observatory  – originally built as a project to study the Earth’s ionosphere as a means of detecting nuclear warheads inbound towards the United States – into what would become more famously known as the Arecibo Observatory, for several decades the largest radio telescope in the world.

This work finished in 1969 when the National Science Foundation formally took over the Arecibo faculties, and two years later Drake was approached by Carl Sagan with another intriguing proposal. Sagan had himself been approached English journalist Eric Burgess – who at the time was writing about the upcoming NASA Pioneer 10 and Pioneer 11  missions – about the idea of sending a physical message out to the stars.

Sagan thought the idea fantastic, and set about lobbying NASA for such a message to be included with the Pioneer missions. NASA agreed – but gave him just 3 weeks to define the message; so he naturally turned to Frank Drake to collaborate on the idea, and they can up with the now-famous Pioneer Plaque, which in turn became the inspiration for the more complex Voyager Golden Records.

The Pioneer plaque designed by Carl Sagan and Frank Drake (with artwork by Sagan’s then wife, Linda Salzman Sagan). Top left: hyperfine transition of neutral hydrogen; Middle left: Relative position of the Sun to the centre of the Galaxy and 14 pulsars with their periods denoted. Right: a nude man and woman are shown in front of the spacecraft, indicating the builders of the vehicle. Bottom: The Solar System with the trajectory of the Pioneer spacecraft. Credit: NASA

In 1974, Drake more directly forayed into demonstrating how an intelligent civilisation might attempt to communicate with the cosmos at large with his Arecibo Message. For this, Drake again worked with Sagan to formulate the core data to be included in the message and then set out a simple pictogram of pixels designed to be read vertically when de-coded.

The entire message consisted of 1,679 binary digits comprising 7 image parts and totalling 210 bytes. It was transmitted at a frequency of 2,380 MHz with a frequency modulation of 10 Hz / 10 bits per second to differentiate between “ones” and “zeros”. It took three minutes to broadcast from the Arecibo observatory towards the globular cluster M13, home to a multitude of stars, some of which may have planets. It will arrive there in some 25,000 years.

The Arecibo Message formulated by Frank Drake and Carl Sagan. Note the colours are for illustrative purposes only and not part of the original message. Credit: Arne Nordmann

In 1984, Drake help to found the SETI Institute, and served as its President through until his retirement in 2010 at the age of 80 – although he still remained active within SETI-related research.

Sadly, Frank Drake passed away on September 2nd, 2022 of natural causes at his home in California. He is survived by his second wife, Amahl Shakhashiri, and his five children from his two marriages.  Right up until his passing, he was a man of extensive influence, inspiring many of today’s SETI practitioners who, as students, were informed by his efforts.

He almost single-handedly turned what was regarded as eccentric silliness whilst he was a student into a structured, well-regarded field of research before he turned 50, and while his equation – as noted – might be seen as “merely” a thought experiment, there is another way to look at it, as his daughter Nadia – herself an accomplished science journalist – stated:

If anything, the Drake Equation’s most enduring legacy is not a numerical solution, but a mirror: It asks us to think about Earth, and about humankind, from a cosmic perspective—to consider the fragility of our existence in this galactic sea.

Artemis 1: No launch Until October, Earliest

NASA’s Artemis 1 mission to cis-lunar space has suffered two further setbacks. As I reported in my previous Space Sunday update, it had been hoped the uncrewed mission – the first for NASA’s Space Launch System (SLS) rocket – would take place on August 29th, 2022, sending an Orion spacecraft on an extended 42-mission around and beyond the Moon before returning to Earth.

Everything was in order for the launch  until the final hours of the countdown. With propellant loading underway, one of the pre-flight requisites for the RS-25 engines which power the rocket’s core stage is to have a “bleed flow” through them. This is a procedure to allow a limited flow of super-cold liquid hydrogen through each of them to “thermally condition” it for the shock of tonnes of the super-cold liquid flowing through them every second during launch and ascent. However, an issue with the bleed feed line on engine #3 prevented the conditioning action from taking place.

The flight of Artemis 1 as depicted in the mission’s Press Pack. The mission phase durations are variable to account for the different possible launch dates / mission durations based on those dates at the time the pack was published. Credit: NASA (click for full size)

Several attempts were made to clear the problem, but they were hampered by a separate issue with an intertank vent value which refused to obey orders not to vent so that the bleed system could  be over-pressured in an attempt to clear any blockage. As a result, the decision was taken to scrub the launch and allow crews to inspect the bleed line directly.

Inspections showed the bleed issue could be addressed on the pad, but to give additional time for the work, NASA opted to push the second launch opportunity back from September 2nd to September 3rd,  shortening the mission from 42 days to 37, required a re-load of the flight software on both rocket and Orion.

However, this second attempt had to be aborted some three hours ahead of the planned launch – 15:18 UTC – this time due to a liquid hydrogen fuel leak, the result of an issue with the quick disconnect system located at the base of the rocket on the launch mount. It was this same system which caused issues during the Wet Dress Rehearsal (WDR) tests for the rocket mid-year.

Artemis 1 during propellant loading, September 3rd, 2022. Credit: NASA / Joel Kowsky

Multiple attempts were made to try to staunch the leak without success, and such was the outflow of hydrogen from the system, the launch had to be scrubbed. Given the severity of the issue, it almost means the remain opportunities to lunch during the current window – which closes on Tuesday, September 6th, have been abandoned.

The next launch window period opens on September 16th and runs through until October 4th. It’s not clear if any of these dates can be met, as it appears likely a gasket on the quick release system, which may require the vehicles being rolled back the Vehicle Assembly Building. Should this be the case, it is unlikely any launch will occur before the mid-October  opportunities, which commence on October 17th and runs to the end of that month.

Voyager 1 ‘Phones Home an “I’m OK!”

Earlier this year  I reported on NASA’s venerable Voyager  1  space probe, currently pushing its way through interstellar space, was having some communications issues, with the attitude articulation and control system (AACS) returning garbled information on the vehicle’s overall condition.

While this didn’t affect Voyager 1’s remaining science gathering capabilities,  it did mean the mission team on Earth faced  a couple of months in which they had no idea about the craft’s overall status which, given the mission is now 45 years old, was more than a little worrying.

Fortunately, the issue has now been resolved, and Voyager 1 is now correctly reporting status data to Earth. The problem turned out to be an onboard data comms issue. In short, for some reason, the AACS was gather the required information from the entire vehicle’s subsystems, but it was then routing it through the wrong computer, which was corrupting the data on its way to the main communications system.

An artist’s rendering of a Voyager craft looking back at the Sun from the outer reaches of the solar system Credit: NASA/JPL

Both Voyager vehicles have two identical computers for redundancy, and while operations can be switched back and forth between them, neither can be fully “turned off”.  This is to ensure that if a minor fault with one causes data handling to be switched to the other, which then suffers a major failure, data and commands can still be switched back to the faulty unit (and accounted for), rather than the entire mission being lost. Thus, while one of Voyager 1’s computers had developed a significant fault, it was still effectively running.

Exactly why the AACS suddenly decided to route its data to the faulty computer board. However, once this had been established as being the case (the result of engineers poring over current and past data), the solution was a “simple” matter of sending an order to Voyager 1 to switch AACS data routing back to the correct computer, and then requesting a full status update.

“Simple” in that with two-way communications now taking close to two days to complete due to the distance between Voyager 1 and Earth, so it took several days for the instruction to be sent, then AACS reply with a confirmation of the switch, followed by a further wait while AACS gathered updated information on the vehicle’s status  – and its own condition – and have that transmitted by to Earth.

It is hoped that the data on AACS may help determine why it switched to trying to use the faulty main computer. If this can be determined, it should help engineers circumvent any chances of the switch being made in the future.

2 thoughts on “Space Sunday: equations and launch scrubs

  1. The Artemis problems are as much systemic problems with NASA as they are individual issues with a particular rocket system.


    1. No disagreement there. NASA has a deep well of systemic issues at management level, in part coupled to matters of funding and to having to bow to political requirements (the latter has arguably had a significant impact on US lunar aspirations thanks to the Obama administration’s cancellation of Constellation / Ares, and then the Trump administration axing four years from the Artemis / SLS development cycle, setting up a certain level of unrealistic expectation for the programme in terms of time frames and achievements). In this, Artemis is currently following a path trod by both the early Saturn / Apollo development
      and flights and also STS development & flights (the latter of which were (rightly) additionally subject of an abundance of caution following STS-51L, an abundance that will doubtless (and again, potentially rightly) impact flight readiness thinking for Artemis, regardless of the physical issues which may occur on the pad).


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