By the time you read this, we will know whether or not South Africa’s R26-million Sumbandila micro- satellite (SumbandilaSat) is safely in space, or not. At deadline, the rocket (with its payload of one major and six micro satellites) was about 60% of the way through a 24-hour hold, imposed because of bad weather and glitches in the telemetry system – telemetry is the data transmitted by the rocket (and spacecraft) to ground control, indicating how its systems are functioning and what is happening on board. The rocket concerned is a Russian Soyuz – a Soyuz-2 to be exact – which is the safest and most reliable satellite launch vehicle (SLV) there is.
Now, there is a saying, ‘It’s not rocket science’, meaning that something isn’t complicated.
Which is quite funny, because rocket science is, in its principles, actually very simple! The basis of rocket science is Isaac Newton’s Third Law of Motion: for every action there is an equal and opposite reaction. The combustion of rocket fuel creates action in one direction (the ejection of a stream of hot gases from the rear of the rocket); the equal and opposite reaction drives the rocket forward. This is what allows rockets to propel craft in the vacuum of space.
The actual combustion of the rocket fuel is itself also quite a straightforward concept. In liquid-fuelled rockets, you mix chemicals in the appropriate proportions to achieve combustion. One of the chemicals has to be an oxidiser, to provide the oxygen source necessary to achieve the reaction.
Liquid fuels are both more powerful and easier to control (not least, switching on and off) than solid fuels. Indeed, with what are called hypergolic propellants, the fuel and oxidiser react on contact, needing no ignition source. A typical hypergolic combination used by the US National Aeronautics and Space Administration (Nasa) is monomethyl hydrazine (the fuel) and nitrogen tetroxide (the oxidiser).
More efficient still, and often used on civilian space rockets, are cryogenic propellants, so-called because they have to be kept very cold indeed to remain in liquid form. Cryogenic propellants use liquid hydrogen as fuel and liquid oxygen as the oxidiser, and require an ignition source. Liquid hydrogen has to be kept at – 253˚ C or colder, and liquid oxygen at – 183˚ C or below. In the words of a Nasa information sheet, they have “a distressing tendency” to evaporate into gaseous form, making them difficult to store for long periods.
Another form of liquid fuel is a combination of highly refined kerosene (the fuel), desig- nated RP-1, and liquid oxygen. It is this combination that powers the Soyuz SLV, and is reli- able and more economical.
So the science is pretty straight- forward.
It is the rocket engineering that is fiendishly complicated. Reportedly, each of Nasa’s renowned Saturn V rockets, which launched the Apollo moon missions, contained six-million parts! The Saturn V is an extreme case – it has been called the most complex machine ever built. But SLVs contain a lot of parts, mechanical (pumps, valves, pipes), hydraulic and electronic, which have to be designed and built to the very highest standards. After all, the combustion of rocket propellants basically amounts to a big and barely controlled explosion.
Add the stresses imposed by gravity, and cross-winds, and everything in and on the rocket gets very shaken up indeed. Things fail. Sometimes the consequences are insignificant, and have no effect on the launch. At the other extreme, catastrophic failure results.
So launch control checks and rechecks everything. All systems must be go before the launch takes place. Indeed, this phrase – all systems go – comes from Nasa launch procedures. Each system on the rocket, particularly for crewed flights, was and is monitored by a different member of launch or mission control. As the countdown approached its climax, the Nasa Flight Director would (and still does) make a rollcall of the team, to find if all systems were (are) fully operational and thus ready for the rocket to go. Each team member would (and will) call out “Go!”, or “No go!”, depending on the data being displayed on his or her consol. Just one “No go!” would and will halt the countdown and put the launch on hold.
Although the terminology may differ, every space launching agency has the same basic launch procedures. Given that a rocket is a very complex piece of machinery, given that almost every component must be working almost perfectly before the Flight Director can proclaim: “All systems are go. We have a go!” (or an equivalent phrase), it is little wonder that launch holds are common. They are an accepted and unremarkable fact of life in the space community. Better a hold than suffer the loss of the rocket and its payload.
So, while it might have been frustrating for South Africans eager to see SumbandilaSat in orbit, the hold – or holds – on the launch were nothing to worry about. But holds are a reminder that, in a world where many people have become blasé about space launches, every single such launch remains a triumph of engineering and a testament to the incredibly high calibre of the planet’s rocket engineers.