The Equatorial Brain Worm
Unearned arrogance and the factoid that won't die.
Everybody likes feeling smart. People especially like feeling smarter than their political opponents, and the Internet has been very good at servicing this market. Your favourite partisan news source will “debunk” the ideas of those people you hate. You can readily find some talking head on YouTube DESTROYING your least favourite pundit with FACTS and LOGIC. Of course, that pundit’s fans can find the exact reverse. This is intellectual fast food, that makes you feel smarter while making you dumber - and, at the same time, more certain of the stupidity of everyone who disagrees with you. Unfortunately, the dynamic also exists in discussions of space.
Recently the Canadian government announced the passage of a Space Launch Act to facilitate launch from it’s territory. As a Brit I have little stake in Canadian politics, and I only found out about this when my X feed filled up with invective being fired at this act on the basis that it was either not possible, or extremely difficult, or commercially infeasible, to launch from anywhere in Canada due to it being too far north. As one commentator put it:
Does anyone in Ottawa understand basic physics?
It's significantly easier (ie, cheaper) to launch to space from near the equator.
That's why Europe's space port is in French Guiana.
Anyone launching from Canada is either an idiot or expecting massive government subsidies.
This may sound like a knock down argument to a non-expert. And indeed it received many appreciative responses who were happy to see through the physics-defying “scam” and feel smart. But it really is clinging on to one small factoid and drawing very wrong conclusions from it.
Getting to Orbit
To get to orbit a rocket needs to achieve a velocity horizontal to the ground of about 7.8 kilometres/second. Rockets launch vertically to get out of the thick part of the Earth’s atmosphere before gaining much speed, and to reach the target altitude - but horizontal velocity is the name of the game. Air resistance and gravity losses add to the cost of getting to orbit - so ultimately you need a bit over 9 km/s of Δv in total. But most of that is horizontal velocity.
If you are on the equator, you are moving eastwards at 465 metres/second already. At French Guiana, the closest space port to the equator at only 5 degrees north, the eastwards velocity is 463m/s. At Kennedy Space Centre, 28.5 degrees north, it is 410 m/s and at Baikonur, 46 degrees north, it is only 324m/s.
The argument goes that, while this is only a small fraction of the total speed required, the tyranny of the rocket equation kicks in and it means that the equatorial site has a huge advantage in putting material into orbit - so much so that only an idiot will build a northerly launch site.
But the truth is quite different.
It is rare for a rocket to launch due east. The only condition where you can do this is if the inclination of the target orbit is exactly equal to the latitude of the launch site. Once your launch azimuth deviates from due east, the already small advantage you get from rotational velocity is reduced. By the time you are flying due north, into a polar orbit, the boost is actually a penalty to your Δv because it needs to be cancelled out to reach your target orbit, which has zero eastward velocity. It is a small one, and not significant at all in practice, but it undermines the assertion that eastward velocity is always good. Beyond a 90 degree angle, when orbits become retrograde (such as a sun synchronous orbit, typically about 98 degrees inclined) the penalty imposed by eastward motion gets greater. So technically, it is easier to launch as far north as possible.
Nobody is clamoring for launch sites in the arctic circle though - the most northerly major spaceport is Plesetsk, near to Archangelsk in Russia. At 63 degrees north it is just sub-arctic. This is because the impact of eastward velocity is not really that great whereas the cost of operating in polar regions is.
But then why does it go the other way around? Why does ESA go to all the trouble of operating a near equatorial launch site far from it’s workforce and industrial base, with all the logistic headaches that brings?
Plane Changes
The key insight in how launch sites relate to orbits has nothing to do with the rotation of the Earth. It is all about inclination.
ArianeSpace carved out it’s commercial niche by launching satellites to geostationary orbit - a high altitude 0 degree inclination orbit. They also got costs down by pioneering dual manifesting of satellites. Prior to Falcon 9 taking the industry by storm, Ariane 5 was the market leader in the most lucrative part of the launch sector.
The near equatorial launch site was helpful to getting to this profitable equatorial orbit. To get to a geostationary orbit from Kennedy Space Centre would require about 400m/s extra Δv relative to Kourou, while getting there from Baikonur would require an extra 900m/s (although some clever Russia orbital dynamics can shave about 100m/s off that, but it is beyond the scope of this argument). However, the difference in eastward velocity only accounts for 50m/s and 140m/s respectively of the total difference. What causes the rest?
To get to a geostationary orbit (GEO) you start in a geostationary transfer orbit (GTO). This is an elliptical orbit with the perigee in LEO, or where your booster injected you into orbit, and the apogee at the altitude of GEO. Crucially, this transfer orbit is not equatorial - it is whatever plane is convenient to reach from your launch site. When you reach apogee, you perform a burn which simultaneously circularises your orbit and also changes it’s plane to 0 degrees. Almost the entire difference in difficulty getting to GEO is in this plane change.
This might seem like splitting hairs - because an equatorial site still comes out on top, even if it is for a very different reason than claimed. But in reality there are many other valuable orbits out there. GEO is not even commercially dominant any more - LEO constellations are the new thing, and they use significantly higher inclination orbits to get good coverage:
There is also a substantial market for sun-synchronous orbits, which are good for Earth observations and are also attractive for the proposed on-orbit data centres, due to being able to align them such that they almost never go into eclipse and thus have constant reliable solar power.
So the utility of a launch site for flying these commercial missions is not it’s latitude - it is whether or not the azimuth needed to reach the target orbit is available from that site. If the latitude is higher than the inclination a “dogleg” launch is required which does add Δv, but given there are profitable target orbits all the way up to sun-synchronous orbits at 98 degrees, there is no site that can be excluded on these grounds. Having a clear range in a set of useful azimuths is a lot more critical for site selection than mindlessly minimising latitude - as are many other factors, such as logistics and weather.
Why This Matters
I have been campaigning for some time for an indigenous launch capability in the UK, from the UK mainland. We do possess an overseas territory, Ascension Island, which lies almost exactly on the equator, but it is small, remote and operating there would impose significant costs. So I prefer launch from the British Isles. The government agrees, and has thus put money into Saxavord spaceport. This will host a launch by a German company RFA later this year, but I want to see British launch vehicles, and much larger vehicles, to pursue a more robust British space program.
When I raise this, I sometimes get asked a question about latitude, and if it is asked nicely I explain why it is not a problem as best as I can. Other times though, including one especially egregious opinion piece in one of our tabloid papers, I get called a “moron” for even suggesting it - by someone ignorant of all the actual physics I outlined above. Someone writing in a paper has a wider audience than my mere newsletter, and thus may be able to convince the public. There is a risk that public policy might be steered by people too stupid to understand how little they understand about spaceflight, to the detriment of the nation. Some quick snark about how only stupid people don’t understand the need for low latitude launch sites is a lot quicker to write than the explanations I offer above.
This has been summarised in Brandolini’s Law - “The amount of energy needed to refute bullshit is an order of magnitude bigger than that needed to produce it”. This unfortunate fact is a boon for cranks, hack journalists, self-described skeptics and con artists. All I can do is put in the work here, and hope that the truth can slowly make it’s way through the public consciousness and disarm the blowhards.