Launched in 1977, the Voyager 1 and 2 space probes have been operating non-stop for over 45 years, making their way from Earth to our solar system’s outer planets and beyond. Courtesy of the radioisotope thermoelectric generators (RTGs) which provided 470 W at launch, they are able to function in the darkness of Deep Space as well as they did within the confines of our Sun-lit solar system. Yet as nothing in the Universe is really infinite, so too do these RTGs wear out over time, both from natural decay of their radioactive source and from the degradation of the thermocouples.
Despite this gradual drop in power, NASA recently announced that Voyager 2 has a hitherto seemingly unknown source of reserve power that will postpone the shutdown of more science instruments for a few more years. The change essentially bypasses a voltage regulator circuit and associated backup power system, freeing up the power consumed by this for the scientific instruments which would otherwise have begun to shut down years sooner.
While this is good news in itself, it’s also noteworthy because the Voyager’s 45+ year old Multi-Hundred Watt (MHW) RTGs are the predecessor to the RTGs that are still powering the New Horizons probe after 17 years, and the Mars Science Laboratory (Curiosity) for over 10 years, showing the value of RTGs in long-term exploration missions.
Although the basic principle behind an RTG is quite simple, their design has changed significantly since the US put a SNAP-3 RTG on the Transit 4B satellite in 1961.
In The Martian we saw what kind of hacking was needed to stay alive for a relatively short while on Mars, but what if you were trying to live there permanently? Mars’ hostile environment would affect your house, your transportation, even how you communicate. So here’s a fun thought experiment about how you’d live on Mars as part of a larger community.
Not Your Normal House
Radiation on Mars comes from solar particle events (SPE) and galactic cosmic radiation (GCR). Mars One, the organization planning one-way trips to Mars talks about covering their habitats in several meters of regolith, a fancy word for the miscellaneous rocky material covering the bedrock. Five meters provides the same protection as the Earth’s atmosphere — around 1,000 g/cm2 of shielding. A paper from the NASA Langley Research Center says that the largest reduction comes from the top 15 to 20 cm of regolith. And so our Mars house will have an underlying structure but the radiation protection will come from somewhere between 20 cm to a few meters of regolith. Effectively, people will be living underground.
On Earth, producing water and air for your house is not something you think of doing, let alone disposing of exhaled CO2. But Mars houses will need systems for this and more.
It’s been 6 years since the hacker’s treat of a book, “The Martian” by Andy Weir, was self-published, and 2 years since the movie came out. We’ve talked about it briefly before, but enough time has passed that we can now write-up the book’s juicier hacks while being careful to not give away any plot spoilers. The book has more hacks than the movie so we’re using the book as the source.
For anyone unfamiliar with the story, Mark Watney is an astronaut who’s left for dead, by himself, on Mars. To survive, he has a habitat designed for six, called the Hab, two rovers, the Mars Descent Vehicle (MDV) they arrived in, and the bottom portion of the Mars Ascent Vehicle (MAV), the top portion of which was the rocket that his five crewmates departed in when they left him alone on the inhospitable desert planet. If you haven’t read it yet, it’s easy to finish over a long weekend. Do yourself a favor and pick it up after work today.
Watney’s major concern is food. They sent up some potatoes with the mission which will sprout roots from their eyes. To grow potatoes he needs water.
One component of the precious H2O molecule is of course the O, oxygen. The bottom portion of the MAV doesn’t produce oxygen, but it does collect CO2 from the Martian atmosphere and stores it in liquid form. It does this as one step in producing rocket fuel used later to blast off from the surface.