Humans to Mars: I’ve got the power!

In my previous post, I mentioned that the biggest technical challenge of human exploration of Mars – super heavy launcher – is on its way to be solved and promised to discuss the next key item: power.

Mars mission using modern or near-future rocket technology requires ISRU (In-Situ resource utilization). In simple terms, we need to produce fuel and oxidizer for the return trip from Mars to Earth – on Mars. Interplanetary travel in the foreseeable future will be done by using chemical rockets. They work by burning propellant (fuel+oxidizer) and throwing it out of the engine nozzles at high speed. It takes a lot of propellant to get anything to Mars. And it takes quite a bit to take stuff back from Mars to Earth. If we had to bring to Mars all the fuel needed to travel from Mars back to Earth, we’d need many flights of the most powerful rockets. And we’d need to somehow collect all that fuel in one place for the return flight – far from a trivial task. With current or near future technologies, such a mission to Mars would be flatly impossible.

This means we need to produce propellant on Mars. For that, we need power – quite a bit of it. Because oil has not been found on Mars, our best bet is to use CO2, which makes up 96% of Martian atmosphere. There are different ideas about possible chemical reactions and processes, but they all require some energy input. One estimate puts power requirements at 17 MWh per metric ton of propellant mix. Given that the mass of propellant needed to send a human mission  on a return trip from Mars to Earth is over 100 metric tons, we need to expend over 2,000 MWh of energy. We can’t count on more than a few year time to produce the propellant; realistically, it needs to be done in one two-year launch window period, which comes to 17,520 hours. This requires 100 kW power at near 100% availability.

Where will the power come from? Currently available technologies are solar and nuclear. Producing enough solar power would require shipping a large mass of solar panels and installing them. 

According to Tom Muller (CTO of Propulsion at SpaceX), the present plan is to power ISRU efforts with solar. He says “If you try to do it with solar; it’s extremely difficult, but doable. To get one ship back, you need about eight football fields worth of solar cells on Mars.”

Making this work is indeed very challenging. To start this effort, we need to install and deploy all those solar panels. Up to now, heavy duty industrial machinery has not been run in space. Several robotic rovers have travelled on Mars, but they have been very slow and lightweight rovers, traveling on average not more than 30 meters per day and moving no load other than themselves. To deploy 8 football fields of solar panels the rovers need to be able to transport those panels and also to travel faster than they’ve been doing. And faster and stronger rovers mean their own mass, plus the mass of propellant to move them.

Solar power has serious limitation – it can only be produced during the day. But running chemical plant 50% of the time means doubling the time needed to produce propellant. And this limitation becomes even more serious when we talk about power needs of the actual human expedition. An extended dust storm might exceed the storage capacity of the expedition and kill the crew. Add more batteries? But what if the storm arrives before those batteries are fully charged? And existing batteries are very heavy. Specific energy of the best lithium ion batteries (amount of energy per unit of mass) is roughly 50 times lower than that of typical rocket fuels such as methane and RP-1 (kerosene). This means that storing energy to keep Martian base working  for 1 day would require as much mass as fuel that would be enough for tens of days (even after accounting for less than 100% efficiency of fuel-burning process). Since we’ve already concluded that delivering fuel to Mars from Earth is prohibitively expensive, delivering enough batteries for energy storage is also a non-starter.

Nuclear power is a much better solution. Back in the 1950s people were optimistic about the nuclear-powered future, despite the fears of radiation. In the present, space nuclear power has 2 major shortcomings: it is politically difficult and it doesn’t exist (there are no space-rated nuclear reactors). The latter seems to be a major downer, but we have hope! NASA has designed and tested prototype of what is called “Kilo Power” – a series of nuclear reactor design for space applications with peak electric output range from below 1 kW to 10 kW. The design is amazing. Until started, the reactor is safe. This means that even in case of a launch failure, there will be no radioactive fallout. And reactor is designed to be self-regulating, automatically throttling down if little power is drawn from it. Of course, 10 kW is not enough to satisfy ISRU requirements of a human mission or a permanent base on Mars. For that, we’ll need something in the range from 100 kW to 1 MW, but that sounds like a manageable engineering problem once Kilo Power is proven.

With extra heavy lift launch vehicle and space-proven nuclear reactors, in the next decade we will have solved the 2 major problems standing in the way of human exploration of Mars. There are other things that require engineering work (space suits, proving ISRU and so on), but they are lesser challenges. On to Mars!

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Mars InSight mission and what’s next

InSight is a robotic mission to Mars that’s launched on May 5th, 2018. InSight lander is equipped with drilling equipment that will enable it to penetrate 15 feet into Mars, much deeper than was done before.

https://spaceflightnow.com/2018/05/05/foggy-departure-kicks-off-insights-journey-to-mars/

The mission will cost about 1 billion dollars. Is it money well spent?

Here’s the key quote:

“If you have an astronaut on the planet, you can do this in maybe 20 minutes or half an hour,” Banerdt said of the heat flow experiment. “But if you want to do it robotically, you have to get a little bit more clever.” Banerdt is InSight’s principal investigator from the Jet Propulsion Laboratory.

So the mission’s designer concedes that crewed mission would be much more productive. This means one thing: let’s focus our energy (and NASA’s budget) on preparing for a human mission to Mars! InSight gets a pass because it was planned about a decade ago and was almost ready to fly in 2018. But from now on, NASA should send robotic missions to Mars only with the goal to prepare a crewed mission. Any incremental science done by robots in the coming decade will be nothing compared to what a humans will be able to do. Continuing robotic exploration of Mars is wasteful.

This is not 1990s any more. Practical blueprint for a mission has been laid out by Dr. Zubrin more than 2 decades ago. We now understand what is required to make this mission a reality. The biggest technological challenge was believed to be a super heavy lift launcher. Now, not one but two firms are working on those (SpaceX’s BFR and US Government-funded SLS). SpaceX’s “aspirational goal” is to launch BFR to Mars in 2022 and crew in 2024. SLS is expected to fly in 2020. There will be the usual project delays, but it seems likely that within a decade, one or both will fly. This will solve problem #1. Next item: power. I’ll address it in the next post.