The “Waiting Game” in Space Research

This week, PVL MSc student Grace Bischof considers the time required for space missions to come to fruition. For martian missions, this process can take a few years. But for those spacecraft headed to the outer planets, to get from proposal to science results can take the better part of a career.
(Image: https://pixabay.com/illustrations/calendar-date-mark-day-hand-4159913/ )

by Grace Bischof

When applying to grad school, I knew that space research was the only area of research I felt truly enthusiastic pursuing. So far, this research experience with PVL at York has been great. There are many wonderful parts of planetary science research – and astronomy as a whole – that I’ve learned over the past few months. However, I’ve also come to realize one its overwhelming downsides: How long it takes for anything to happen.

As a Mars researcher, it isn’t quite so bad. The Mars 2020 mission was first announced by NASA in 2012. The payload for the rover was determined only a couple of years later. Now, as of March 2021, Perseverance has been wandering through its home in Jezero Crater for over 30 sols. On average, an instrument sent from Earth will arrive at the red planet in 7 months. While the 8-year time period from proposal to landing might seem long initially, this is only the tip of the iceberg for the “waiting game” in planetary science and astronomy.

I recently listened to a talk given by Dr. Jason Barnes, who is a Deputy Principal Investigator on the Dragonfly mission. This mission involves sending a quad-copter to Titan – an icy moon of Saturn – to look for potential signs of life. First announced in 2019, Dragonfly is currently scheduled for a 2027 launch after being pushed back a year due to budget restrictions caused by the pandemic. By the time of launch, the Dragonfly mission will be the same age Mars 2020 was when it touched down on Mars’ surface. If that seems like a long wait, it gets even longer. Because Saturn is much further away than Mars, the Dragonfly will take another 6-10 years before it arrives at Titan, rounding off the mission life span to nearly 20 years before any primary science objectives have occurred.

Perhaps the most infamous long-wait in astronomy is the construction and launch of the James Webb telescope (JWST). The JWST is an incredibly powerful and complex infrared telescope, useful for its purpose of probing space to find the earliest formations of galaxies and planetary systems. Before the Hubble telescope had even launched, the JWST was proposed as a successor to Hubble in the 1990s. The JWST has seen many launch dates come and pass -- 2007, 2011, 2014, 2018 -- and was even in danger of being cancelled in 2011. The launch is now expected to occur on October 31st, 2021. After only a few months in space, the JWST will start its planned 5-year science mission.  There is a fun way I like to think about it: a baby born the day the JWST was proposed could be old enough to analyze the first data it returns in 2022.

Unfortunately, one of the biggest disadvantages to the long wait in space research is the advancements in technology that occur after the instrument has already been constructed but before the primary science occurs. The main objective of the New Horizons mission was to characterize Pluto by performing a flyby. After launching in 2006, the probe finally reached its target in 2015. Technology was 9-years advanced by the time New Horizons made it to Pluto. What else could we have learned if technology developed during that time was included in the mission? The vastness of space is both one of its most interesting characteristics and also one of the most frustrating aspects of studying it.

So far, I haven’t had to play this “waiting game” with my research. The data I work with primarily comes from the Phoenix mission, which completed its operations over 10 years ago. When campus opens back up (hopefully within the next few months), I will be testing a spectrometer under Mars-analog conditions. With these tests, we hope to use this instrument to measure methane on Mars in the future. Who knows where I’ll be if/when that time comes, but there is one thing I can be certain about: it will take a long time to happen.

How do you power a vehicle on Mars?

 

How is power generated for the vehicles that explore other worlds? This is a problem that PVL MSc student Justin Kerr is considering this term in his research. In the inner solar system, solar power tends to dominate, but once we move outward, electricity generated from the heat of nuclear decay in Plutonium is the only viable option. Even on Mars, however, the latter method can be attractive to guarantee a more stable source of power unperturbed by environmental factors such as the dust covering the Spirit Rover in the image above. (image by: NASA/JPL-Caltech/Cornell)

by Justin Kerr

With the recent landing of the Perseverance rover in Jezero crater, exploration of the Martian surface is now all over both the news and general scientific conversation. Perseverance is the latest in the ever-expanding list of vehicles successfully landed on Mars, and a large one at that. It weighs in at 1025kg and has dimensions of 3x2.7x2.2 meters, making it only a little smaller than the average car. But unlike a car, Perseverance obviously cannot just drive up to the local gas station for a refill. The amount of gasoline needed for a decently long mission would also be far too heavy and volatile to bring along for the launch from Earth and subsequent landing, so just how do we go about powering Perseverance and the vehicles before it while they explore the red planet?

Most past rovers and landers have utilized solar power to generate the electricity they needed to operate. Some recent examples of vehicles using solar power include the InSight lander alongside the Spirit and Opportunity rovers. While Mars is further from the Sun than Earth and thus receives less sunlight, solar panels on the surface can still produce enough energy to power a rover. They also have the huge benefit of never running out of fuel so long as the panels are still functioning, which allowed Opportunity to last for 14 Earth years, far longer than its expected lifespan. That being said, power outputs from the panels may themselves seem quite low compared to the usage of everyday devices on Earth. The panels on InSight are capable of an output of 600 Watts, and the Spirit and Opportunity rovers only 140W – a pittance compared to the 850W power supply in use on the computer on which I am currently typing this!  The Mars vehicles make up for this relatively low power generation rate by storing power in lithium-ion batteries much like those used in modern smartphones to use for larger expenditures or during the night – which brings us to some of the problems associated with solar panels.

The biggest problem with solar energy production is the inconsistent availability of sunlight with which to generate power. The most obvious source of this problem is nighttime, but there are others. Seasonal variations cause decreases in solar power output, with power generation being more difficult during winter. Solar power is most effective at the equator where the most sunlight is received, making it much more difficult to power vehicles closer to the Martian poles (you can actually expect a short paper related to this topic from me in the future!). Dust is a major problem on Mars, able to settle in a fine layer on top of vehicles we land there even during normal weather. Spirit had its solar panel efficiency drop to roughly 60% due to dust coverage in its first year – although the rover actually got lucky by having its panels cleaned off by a dust devil in early 2005. Of even larger concern are the global dust storms that can occur on Mars which put so much dust into the atmosphere that solar power generation becomes essentially impossible. You can see the extensive dust buildup on Spirit from one of these storms in 2007 at the top of this article. One such storm was famously responsible for the loss of Opportunity in 2018.   

While solar power may seem like the obvious solution for power on another planet and is indeed effective in many situations, it clearly isn’t perfect – so what else could we use? Perseverance, Curiosity, and the Viking landers of ages past instead utilized the radioactive decay of plutonium-238 for power generation. Specifically, the power is generated by a device known as a radioisotope thermoelectric generator (RTG). When the plutonium in the MMRTG (Multi-Mission RTG) decays into Uranium, it produces significant amounts of heat as the released radiation is absorbed by materials which can then be converted into electricity. In the Perseverance and Curiosity rovers, the excess heat lost in the conversion process can even be put to use keeping the delicate electrical components of the rover warm. This electricity production method gets around the issues of solar power not working at night, during winter, or when covered by dust – radioactive decay will occur regardless of the environmental conditions. 

 

A warm and glowing Pu-238 Pellet (image: US Dept. of Energy)

Nuclear power generation with MMRTGs still has some downsides compared to solar, such as the amount of power that can be generated by an appropriately sized RTG. Perseverance can currently only generate 110W of power, which is used to charge batteries in the same manner as the solar powered vehicles. This amount will also reduce over time as the amount of plutonium decreases as it decays. Plutonium-238 has a relatively short half-life of 87.7 years, meaning there will be a noticeable drop in the amount of available power by the end of the rover’s 14-year lifespan. There is also a concern with the amount of available plutonium-238 for future missions, as the United States only has enough left in their cold war era stockpiles for a few more missions. Thankfully there are plans to begin production of the isotope right here in Ontario at the Darlington nuclear power plant in the near future. In the end, neither RTGs nor solar power provide a perfect solution to the power requirements of the vehicles we send to Mars. We can expect to see a mix of these two methods in upcoming Mars missions, with the next two vehicles set to land (China’s Tianwen-1 and the ESA’s ExoMars) both utilizing solar power. Just like here on Earth, there seems to be no single best answer for power generation on Mars.