Astronomy
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Scaling Propellant Production on Mars is Hard
Putting humans on Mars has been one of NASA’s driving missions for years, but they are still in the early stages of deciding what exactly that mission architecture will look like. One major factor is where to get the propellant to send the astronauts back to Earth. Advocates of space exploration often suggest harvesting the necessary propellant from Mars itself – some materials can be used to create liquid oxygen and methane, two commonly used propellants. To support this effort, a group from NASA’s COMPASS team detailed several scenarios of the infrastructure and technologies it would take to make an in-situ resource utilization (ISRU) system that could provide enough propellant to get astronauts back to a Mars orbit where they could meet up with an Earth return vehicle. However, there are significant challenges to implementing such a system, and they must be addressed before the 8-9-year process of getting the system up and running can begin.
To understand these challenges, it’s first essential to understand some of the requirements the team was trying to meet. The goal was to provide 300 tons of liquid oxygen and liquid methane to a Mars Ascent and Landing Vehicle (MALV) being developed at other parts of NASA. That much propellant is necessary to get a crew of astronauts back into orbit, where they can be met by an orbiting Earth return vehicle.
Creating liquid oxygen and methane requires many ISRU systems, such as pumps, electrolyzers, dryers, scrubbers, and significant power systems, to run all these machines. Some raw materials, such as CO2, can be pulled from the Martian atmosphere. However, the system will also require 150 tons of water, which could be trucked in from Earth or harvested from Mars.
Fraser discusses how ISRU can provide resources to use for exploration.Designing the overall system architecture is the first step in determining the best method for getting enough propellant to get the astronauts back off of Mars. A paper from the group compares five different approaches to solving that problem and details three of them, focusing on three different methods of getting water to use in the creation of liquid propellants on the surface of Mars.
Let’s first look at the two options for extracting water locally on Mars. One architecture uses a borehole drill to melt subsurface ice and pump it back to the surface, which can be used in electrolysis. The other architecture uses surface harvesting techniques, where soil with a high frozen water content can be sorted, and the water itself melted to provide sufficient stockpiles for creating propellant.
Drilling a borehole deep enough to access subsurface ice has never been done before. It does have some advantages over other water collection methods, including taking less time and requiring one less MALV delivery of equipment (i.e., making it lower cost). However, it does require more power plants and some specialized equipment to be developed.
Fraser speculates on how a real Mars mission could play out.Collecting water from surface regolith utilizes some technologies already being developed at NASA – including the RAZZOR surface mining system that could be used on the Moon or Mars. However, it requires as much time and as many launches as shipping water from Earth, with many possible unknown failure points in the architecture.
By comparison, sending 150 tons of water directly from Earth, while it might be expensive in terms of launch costs, simplifies the overall architecture significantly. There would still technically be ISRU in this scenario, as the water would still be used to create propellant from local Martian resources. However, the added step of getting that water locally would be eliminated.
Even that is a more complicated process than the other two options the team considered, without as much detail in the paper as the actual ISRU setups. Mission designers could send either the methane or both the methane and oxygen from Earth directly, bypassing the need for any ISRU to happen. While these options require potentially more MALV landers, their overall risk is minimized, as the necessary chemicals would be available for use at any point the astronauts would need them. However, they would take longer to set up – especially the option of sending all of the propellants directly from Earth, which could take upwards of 10 years to get set up.
Fraser interviews Dr. Michael Hecht, an expert in ISRU on Mars.Other challenges abound for utilizing Martian resources to create propellants – including limited locations where the necessary water may be found. This geographical restriction might not overlap with where astronauts might be needed to do exciting science, so the architects would have to prioritize either scientific discovery or derisking the ISRU equipment – they likely couldn’t do both.
So, all things considered, if the purpose is to send people to Mars and back safely, it seems like the best, most reliable option is to send the total amount of propellant from Earth. However, in the long run, if humanity plans to make a sustainable presence on Mars, we will need to utilize local resources. The paper from the COMPASS team clearly defines a few strategies that could do that, and someday, it will become the better option – just maybe not quite yet.
Learn More:
Oleson et al – Kiloton Class ISRU Systems for LO2/LCH4 Propellant Production on the Mars Surface
UT – A Single Robot Could Provide a Mission To Mars With Enough Water and Oxygen
UT – Resources on Mars Could Support Human Explorers
UT – Mars Explorers are Going to Need air, and Lots of it. Here’s a Technology That Might Help Them Breath Easy
Lead Image:
Architecture Design of the water from Earth delivery option.
Credit – Oleson et al. / NASA
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Is an ‘Off-Year’ Leonid Outburst in the Cards For November?
There are good reasons to keep an eye on the Leonid meteors this year.
It’s still one of the coolest things I ever saw. I was in the U.S. Air Force in the 90s, and November 1998 saw me deployed to the dark skies of Kuwait. That trip provided an unexpected treat, as the Leonid meteors hit dramatic storm levels on the morning of the 17th. Meteor came fast and furious towards local sunrise, often lighting up the desert floor like celestial photoflashes in the sky.
Once every 33 years or so, the ‘lion roars,’ as Leonid meteors seem to rain down from the Sickle asterism of the constellation Leo. And while the last outbreak was centered around the years surrounding 1999, there’s some interesting discussion about possible encounters with past Leonid streams in 2024.
The Leonids in 2024To be sure, 2024 is otherwise slated to be an off year for the shower. The normal annual maximum for 2024 is expected to occur on Sunday, November 17th at around ~4:00 Universal Time (UT), with an expected Zenithal Hourly Rate (ZHR) of 15-20 meteors per hour seen under ideal conditions. This favors Europe in the early dawn hours.
The Leonid radiant, looking east at 2AM local. Credit: Stellarium. A Leonid Outburst in 2024?But there are also a few other streams that may arrive earlier this week and are worth watching for. Jérémie Vaubaillon of the Paris Observatory IMCCE notes that Earth may encounter three older streams from periodic comet 55P/Tempel-Tuttle. The comet is the source of the Leonids. On a 33.8 year orbit, a meteor shower occurs when the Earth plows headlong into the stream of dust and debris laid down by the comet.
The three suspect trails are:
-A trail laid down in 1633 (the source of the 2001 meteor storm). Earth is near this trail on November 14th at 16:37 UT, favoring northwestern North America in the early morning hours.
-A dust trail from 1733, peaking on November 19/20th at 23:53 to 00:54 UT, favoring north/central Asia.
-And finally, an encounter with a string of older (more than a millennium old) streams on November 14th at 16:37 UT, (the same time as the 1633 stream). It is worth noting that the 1733 stream was the suspected source of the 1866 Leonid meteor storm.
A bright green Leonid from 2023. Credit: Frankie Lucena.Watching this Thursday morning on the 14th could be a harbinger as to whether or not we’re in for a show. Unfortunately, the Moon is waxing gibbous and headed towards Full this week on November 15th, meaning that it with provide increasing illumination and cut down observed meteor rates.
The Leonids on past recent years have held steady at predicted rates of about or so 20 per hour. It’s worth noting that another encounter with the 1699 stream and possible outburst is predicted for next year, 2025.
Leonid TEFF (Total Effective observation time) rate versus meteors over the years. Credit: the International Meteor Organization (IMO). Meteor Shower… or Storm?Meteor storms occur when the zenithal hourly rate tops 500 or more per hour. Keep in mind, a ZHR of a thousand or higher means that you’re seeing a meteor every few seconds. The October Draconids and the December Andromedids are also prone to great outbursts, but the Leonids are the most notorious and well-known. The 1966 shower seen over the U.S. southwest topped an amazing ZHR of up to 150,000 per hour (!)
A depiction of the 1833 outburst over Niagara Falls. Credit: Mechanic’s Magazine/Popular Domain. Observing and Imaging the LeonidsEarly morning hours are best to see meteors, as you’re standing on the swath of the surface of the Earth that’s turned forward in to the stream. Pinpoint meteors will occur near the shower radiant, while long streaks will stand out out in stark profile about 45 to 90 degrees away on either side of the radiant. I like to aim my tripod-mounted DSLR at these regions, set the lens to the widest field of view possible, and simply let it run taking auto-exposures and see what turns up. An intervalometer is a great device to automate this process. This allows me to just sit back with a steaming hot cup of tea (a must for cold November mornings) and simply watch the show, as meteors slide by.
A Leonid pierces the night sky over southern Arizona. Credit: Eliot Herman.Perhaps, we’ll simply have to wait for 2030s to see strong activity from the Leonids again. But do you really want to risk missing a surprise show? To quote hockey player Wayne Gretzky: “You miss 100% of the shots you don’t take.” The same holds true for missing versus catching meteor storms: you just have to show up and watch.
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