Solar power in space: Vanguard 1

Today is an interesting anniversary: the sixtieth anniversary of solar power in space. On 17 March 1958, the American satellite Vanguard 1 entered orbit, becoming the fourth satellite ever to do so, and the first to use solar power. Vanguard 1 was small enough to be held by a person in one hand – 1.5 kg (3 lbs) in mass and 16 cm (6”) in diameter, or 76 cm (30”) wide including the antenna aerials. Altogether, Vanguard 1 had 6 silicon solar cells which generated about 1 watt in total. For comparison, the power produced by a typical rooftop solar PV system in 2018 is several thousand times greater.

Why did the first satellites use electrical power? Primarily, to send radio signals back to Earth. The first satellite ever to reach orbit, the Soviet satellite Sputnik 1, broadcast radio signals at 20 MHz and 40 MHz which could be detected on Earth, even by amateur radio users. The radio signals provided additional proof that the satellite was really in orbit around the Earth (it could also be seen with large telescopes), and allowed observers to measure its position and trajectory. The power to provide this radio signal came from batteries, which allowed it to broadcast radio signals for 21 days before the batteries went flat.

This radio communication was one-way only. Early satellites could not receive communications from Earth, and were essentially a battery, radio transmitter, and an antenna. The second and third satellites, the Soviet Sputnik 2 and US Explorer 1 also used batteries to power radio signals, which lasted somewhat longer (Explorer 1 had a lower power mode that lasted 105 days). Vanguard 1 had two radio transmitters. One transmitter (at 108 MHz) was powered by a battery, which lasted for 20 days. The second transmitter (at a slightly higher radio frequency, 108.3 MHz) was powered by the (as yet unproven in space) solar cells, and that broadcast for over six years, or over 23,000 orbits of the earth, before going silent.

Vanguard 1 schematic (Image credit: NASA)

Vanguard trajectory (Image credit: NASA)

Satellites and spaceflight were one the first uses of solar power in which – environmental reasons aside – it was clearly cheaper, more reliable, and more practical than other sources of electrical power. Generation of electricity on Earth, then and today, is most commonly done with a combustion engine. On Earth, oxygen is in the air everywhere and fuel can usually be found, whether it is wood, coal, natural gas, or some other fuel. Photovoltaic cells at that time were incredibly expensive, and their intermittent output was difficult to manage since rechargeable batteries were also very expensive.

In space, solar power had clear advantages. Combustion in space requires that both fuel and oxygen (or another oxidant) be brought up from the Earth in tanks. For example, the Saturn V rocket engines that sent humans to the moon had tanks of liquid hydrogen and liquid oxygen. (Those engines were obviously used to make the rocket move, not to generate electricity). Non-rechargeable batteries could not provide power for long without a lot of “chemical fuel”. In space, above the clouds, solar power was more or less constant the whole time that the panels were not behind the Earth. No fuel needed to be carried up. Satellites typically orbited the earth every few hours, so that when rechargeable batteries did start to be used with solar panels, they were small compared to those needed to last the entire long night on earth. What happened to Vanguard 1? Although its radio no longer transmits, Vanguard 1 continues to orbit the Earth today, at an altitude between 600 and 4,000 km, going around the Earth approximately every 2 hours. It is now the oldest object made by humans to still be in space. Sputnik 1 and Sputnik 2 reentered the atmosphere after around one year after launch, and Explorer 1 reentered in 1970. Vanguard 1 is in a very stable orbit, and is predicted by NASA to remain in orbit for another 180 years. Several websites track its location (Satflare, n2yo). You can see where Vanguard 1 is right now on this map provided by Satflare:

3D globe current position of Vanguard 1, by Satflare

As a final note, in researching this article I came across some amazing audio recordings of Vanguard 1 transmissions made by amateur radio enthusiast Roy Welch in 1958 and 59. (The signals have been modified to bring them into audible frequencies). Roy Welch wrote that he believed that the variations in frequency were due to the satellite spinning around, varying the light exposure to the solar cells. The one from 1959 I find quite eerie:

Vanguard 1 signal recorded by Roy Welch (link).

It is quite something to listen to the recording and imagine the tiny Vanguard satellite, moving high above the Earth, broadcasting its radio signal, and slowing turning around in the sunlight.

Update: this article is also published on Medium:

Herds Of Giant Wombats Grazing

When you walk through the doors of the museum here in Melbourne, there is a gigantic entrance hall which contains the entire skeleton of a blue whale. Walking throughout the Museum, there are dinosaurs and insects, there are gemstones of translucent purple, milky blue, and a thousand other colours. There is an entire native rainforest in a room, with actual plants and trees and a pond full of fish. There is an extraordinary kids play room, with rope ladders going up a series of tunnels to a succession of rooms which go over your head and then back down again to the ground. It takes 20 minutes for a child to crawl from one end to the other, so if you see your kids up there halfway through it, there is nothing to do but watch them and hope they don’t get stuck.

One of my favourite exhibits is the giant extinct wombat, diprotodon.

They were the size of a delivery van, and in life would have weighed over two tons. I like to think about herds of these giants, gently grazing over the western grasslands of Victoria. Imagine golden fields of grass at the end of summer, the long stems waving in the breeze, the sandstone hills of Arapiles in the background, and giant diprotodon thoughtfully chewing on the grass. Several artists have tried to draw what they might have looked like – which is basically a giant wombat, albeit with longer legs (in proportion) than modern day wombats. My favourite illustration is this one by Peter Trusler for the happy smile the artist gave the diprotodon. Trusler also made a beautiful illustration of a palorchestes, another extinct Australian mammal with a long,flexible nose. Here is a interesting video where he talks about the illustration at the Museum’s website here.

Discovery Of Helium Under the Earth

Another story from the discovery of helium is when it was discovered on Earth in large quantities. As I wrote in part 1, helium is so light that it will escape into space over time, and there is almost no helium in ordinary air less than (0.0006%). When helium was first discovered, it was trapped in tiny amounts in rock, where it had been created by nuclear reactions (for example, in uranium ore). These nuclear reactions tend to be slow, so the amount of helium obtained was very small. In 1900, it seemed that helium was so rare that it was unlikely to be useful for anything much.

Well that did change as you probably know and it is a nice story.

In 1905, a large natural gas well was drilled in Kansas, USA, which had huge amounts of gas coming out, a “howling gasser” as they said at the time. When it first discovered, it was estimated to be releasing 250,000 litres of gas per day (9 million cubic feet). (Methane has huge green house gas warming potential, so that is regrettable, but at the time of course they didn’t know about such things). The well had still not been capped – it was going to take some time for the equipment to arrive. So the townsfolk decided to have a huge celebration to celebrate their good fortune, and the impending wealth and industry that was likely to come to their town. The celebration would finish with lighting the escaping gas, which would burn non-stop until the well was capped. (I don’t actually know how they planned to extinguish such huge flame to cap the well, but I assume there is a way to do it).

The celebration had games, and music, and speeches. You can imagine a town party in rural America at the start of the 20th century. Colourful bunting flags. Distinguished old men in three piece suits with moustaches and muttonchops. Ladies in frilly dresses. The band with a tuba going omm-pah-pah.

At the end of the night, a burning bale of hay was pushed towards the gusher of escaping gas (with a long stick, one would hope). The band would have gone silent. Everyone is standing around (again, not too close), watching expectantly. The burning hay approached the hole and … Suddenly the flames went out. People say, “What? Huh.” The bale is retrieved, re-lighted, pushed back towards the hole. Again it goes out. They try a third time, and again it goes out. The crowd sighs. What is going on?

The celebration ends in an anti-climax. People go home wondering what happened, and what indeed is the gas coming out of the ground. Some people say it is a well of “hot air”, not natural gas. Sometime later, people come from the University of Kansas, and take a sample in a steel barrel. Analysis is done, and they find that gas does contain 15% methane (natural gas), but also 80% inert gases, most of which was nitrogen – too great a concentration for the bale of hay to burn. The gas also contained what they thought was an amazing 1.5% helium. Given the amount of gas coming out of that well, if even one percent of that was helium, that was millions of time more helium than had ever been discovered before. Helium was no longer rare, and was now able to be used in balloons, to make your voice funny, fly huge zeppelins, and also make MRI machines. Even today, all helium you use is mined from the ground in natural gas wells. Helium is even regulated by the US government as a “strategic reserve”. So the disapointed Kansan partygoers walking home that night actually had something to celebrate, they just didn’t know it.


Discovery of Helium in Natural Gas at the University of Kansas, American Chemical Society, 2000

Helium was discovered on the Sun before the Earth

As part of some barely work related research I have been doing, I read some new sources on the discovery of helium. I have always loved the fact that helium was discovered on the Sun before it was discovered on the Earth. It seems like an amazing thing – an entirely new element was discovered in the Sun, which no one had ever knew of before, and then only 13 years later it was discovered on the Earth. But no has ever been to the Sun to do testing, so how did they even know it was the same element they had previously found in the Sun?

Helium was discovered in the sun by taking sunlight, splitting it up into different colours, (such as in a glass prism, but they actually used a diffraction grating) and noticing that certain colours were much brighter than any other colours. Every kind of gas will emit (or absorb) very particular colours of light. At the time, they didn’t know why elements did this (quantum mechanics), but they did know that it was a unique, unchanging signature for each element. All hydrogen, for example, emits the same particular shade of red, light blue, dark blue, and purple, regardless of whether it is in France or India or Peru:

Because these particular shades are so specific (and the wavelength of each can be measured so precisely), that means that by the 1860s it was possible to determine that the Sun was mostly made of the same elements that were found on Earth. Which is already a pretty amazing discovery. The Sun could have been made of anything – completely different to anything on Earth. There was not much understanding of how the Sun worked, beyond a thousand year old notion that was somehow like fire. But nothing on Earth burned as long or as hot as the Sun (nuclear reactions weren’t known of yet.)

So in 1868, during a solar eclipse, Jules Janssen and Norman Lockyer (who later founded the journal Nature) each measured the spectrum of light from the sun, and found that it contained sets of colours (“spectral lines”) from many elements known on Earth, such as hydrogen, and some that they could not identify. The College of Chemistry in London tried to reproduce the lines from samples they had, but could not, suggesting that it was an element unknown at the time.

In 1881, Luigi Palmieri found similar colours in gases from an eruption on Mt Vesuvius, and in 1895 they were also seen in uranium ore by Sir William Ramsey, and not long after people realised that these were the same colours that had been seen in the Sun, and that it was the same element. The confidence in reasoning, the cleverness, to say that this thing we only previously found in the Sun, we have now found on Earth, I still find amazing. It is cool in the same way as anti-matter, or cosmic background radiation, which were predicted theoretically before they were discovered.

Incidentally, the reason helium had never been found before on Earth is that it weighs so little that, on its own, it will gradually drift out into space. Even in the cold upper atmosphere, the average kinetic energy of helium atoms is above the escape velocity. This is also true for hydrogen, but hydrogen is produced in many chemical reactions, so it was found much earlier. Helium is chemically unreactive, and all original surface helium left Earth billions of year ago, so. To be discovered, helium had to be found that had been trapped inside the Earth (like on Mt Vesuvius), and produced in a nuclear reaction inside rock (like the uranium ore). All the helium you have ever used in your life, all the helium balloons, every time you’ve even made your voice go high and funny, that helium was all mined from the Earth, as I write about more in part 2.