On October 19th, 2017, astronomers were astounded to learn that an interstellar object (named ‘Oumuamua) flew by Earth on its way out of the Solar System. Years later, astronomers are still debating what this object was – a comet fragment, a hydrogen iceberg, or an extraterrestrial solar sail? What’s more, the arrival of 2I/Borisov two years later showed how interstellar objects (ISOs) regularly enter our Solar System (some even stay!)
As expected, the mission concepts submitted to the 2020 Decadal Survey cover a wide range of scientific goals – from observing distant black holes and the early Universe to investigating exoplanets around nearby stars and studying the bodies of the Solar System. These ideas were thoroughly vetted by the scientific community, and four have been selected as being worthy of pursuit.
“This is game time for astrophysics. We want to build all these concepts, but we don’t have the budget to do all four at the same time. The point of these decadal studies is to give members of the astrophysics community the best possible information as they decide which science to do first.”
The four selected concepts include the Large Ultraviolet/Optical/Infrared Surveyor (LUVOIR), a giant space observatory developed in the tradition of the Hubble Space Telescope. As one of two concepts being investigated by NASA’s Goddard Space Flight Center, this mission concept calls for a space telescope with a massive segmented primary mirror that measures about 15 meters (49 feet) in diameter.
In comparison, the JWST‘s (currently the most advanced space telescope) primary mirror measures 6.5 m (21 ft 4 in) in diameter. Much like the JWST, LUVOIR’s mirror would be made up of adjustable segments that would unfold once it deployed to space. Actuators and motors would actively adjust and align these segments in order to achieve the perfect focus and capture light from faint and distant objects.
With these advanced tools, LUVOIR would be able to directly image Earth-sized planets and assess their atmospheres. As Study Scientist Aki Roberge explained:
“This mission is ambitious, but finding out if there is life outside the solar system is the prize. All the technology tall poles are driven by this goal… Physical stability, plus active control on the primary mirror and an internal coronagraph (a device for blocking starlight) will result in picometer accuracy. It’s all about control.”
There’ also the Origins Space Telescope (OST), another concept being pursued by the Goddard Space Flight Center. Much like the Spitzer Space Telescope and the Herschel Space Observatory, this far-infrared observatory would offer 10,000 times more sensitivity than any preceding far-infrared telescope. Its goals include observing the farthest reaches of the universe, tracing the path of water through star and planet formation, and searching for signs of life in the atmospheres of exoplanets.
Its primary mirror, which would measure about 9 m (30 ft) in diameter, would be the first actively cooled telescope, keeping its mirror at a temperature of about 4 K (-269 °C; -452 °F) and its detectors at a temperature of 0.05 K. To achieve this, the OST team will rely on flying layers of sunshields, four cryocoolers, and a multi-stage continuous adiabatic demagnetization refrigerator (CADR).
According to Dave Leisawitz, a Goddard scientist and OST study scientist, the OST is especially reliant on large arrays of superconducting detectors that measure in the millions of pixels. “When people ask about technology gaps in developing the Origins Space Telescope, I tell them the top three challenges are detectors, detectors, detectors,” he said. “It’s all about the detectors.”
Specifically, the OST would rely on two emerging types of detectors: Transition Edge Sensors (TESs) or Kinetic Inductance Detectors (KIDs). While still relatively new, TES detectors are quickly maturing and are currently being used in the HAWC+ instrument aboard NASA’s Stratospheric Observatory for Infrared Astronomy (SOFIA).
Then there’s the Habitable Exoplanet Imager (HabEx) which is being developed by NASA’s Jet Propulsion Laboratory. Like LUVOIR, this telescope would also directly image planetary systems to analyze the composition of planets’ atmospheres with a large segmented mirror. In addition, it would study the earliest epochs in the history of the Universe and the life cycle of the most massive stars, thus shedding light on how the elements that are necessary for life are formed.
Also like LUVOIR, HabEx would be able to conduct studies in the ultraviolet, optical and near-infrared wavelengths, and be able to block out a parent star’s brightness so that it could see light being reflected off of any planets orbiting it. As Neil Zimmerman, a NASA expert in the field of coronagraphy, explained:
“To directly image a planet orbiting a nearby star, we must overcome a tremendous barrier in dynamic range: the overwhelming brightness of the star against the dim reflection of starlight off the planet, with only a tiny angle separating the two. There is no off-the-shelf solution to this problem because it is so unlike any other challenge in observational astronomy.”
To address this challenge, the HabEx team is considering two approaches, which include external petal-shaped star shades that block light and internal coronagraphs that prevent starlight from reaching the detectors. Another possibility being investigated is to apply carbon nanotubes onto the coronagraphic masks to modify the patterns of any diffracted light that still gets through.
Last, but not least, is the X-ray Surveyor known as Lynx being developed by the Marshall Space Flight Center. Of the four space telescopes, Lynx is the only concept which will examine the Universe in X-rays. Using an X-ray microcalorimeter imaging spectrometer, this space telescope will detect X-rays coming from Supermassive Black Holes (SMBHs) at the center of the earliest galaxies in the Universe.
This technique consists of X-ray photos hitting a detector’s absorders and converting their energy to heat, which is measured by a thermometer. In this way, Lynx will help astronomers unlock how the earliest SMBHs formed. As Rob Petre, a Lynx study member at Goddard, described the mission:
“Supermassive black holes have been observed to exist much earlier in the universe than our current theories predict. We don’t understand how such massive objects formed so soon after the time when the first stars could have formed. We need an X-ray telescope to see the very first supermassive black holes, in order to provide the input for theories about how they might have formed.”
Regardless of which mission NASA ultimately selects, the agency and individual centers have begun investing in advanced tools to pursue such concepts in the future. The four teams submitted their interim reports back in March. By next year, they are expected to finish final reports for the National Research Council (NRC), which will be used to inform its recommendations to NASA in the coming years.
As Thai Pham, the technology development manager for NASA’s Astrophysics Program Office, indicated:
“I’m not saying it will be easy. It won’t be. These are ambitious missions, with significant technical challenges, many of which overlap and apply to all. The good news is that the groundwork is being laid now.”
With TESS now deployed and the JWST scheduled to launch by 2020, the lessons learned in the next few years will certainly be incorporated into these missions. At present, it is not clear which of the following concepts will be going to space by the 2030s. However, between their advanced instruments and the lessons learned from past missions, we can expect that they will make some profound discoveries about the Universe.
For decades, we could only imagine what the view of Pluto’s surface might be. Now, we have the real thing.
The images and data from the New Horizons’ mission flyby of Pluto in July 2015 showed us an unexpectedly stunning and geologically active world. Scientists have used words like ‘magical,’ ‘breathtaking’ and ‘scientific wonderland’ to describe the long-awaited close-up views of distant Pluto.
Even though scientists are still analyzing the data from New Horizons, ideas are starting to formulate about sending another spacecraft to Pluto, but with a long-term orbiter mission instead of a quick flyby.
“The next appropriate mission to Pluto is an orbiter, maybe equipped with a lander if we had enough funding to do both,” New Horizons’ principal investigator Alan Stern told Universe Today in March.
This week, Stern has shared on social media that the New Horizons’ science team is meeting. But, separately, another group is starting to talk about a possible next mission to Pluto.
Getting a spacecraft to the outer regions of our solar system as fast as possible provides challenges, particularly in being able to slow down enough to enable going into orbit around Pluto. For the speedy and lightweight New Horizons, an orbital mission was impossible.
What propulsion system might make a Pluto orbiter and/or lander mission possible?
A few ideas are being tossed around.
Space Launch System
One concept takes advantage of NASA’s big, new Space Launch System (SLS), currently under development to enable human missions to Mars. NASA describes the SLS as “designed to be flexible and evolvable and will open new possibilities for payloads, included robotic scientific missions.” Even the first Block 1 version can launch 70 metric tons (later versions might be able to lift up to 130 metric tons.) Block 1 will be powered by twin five-segment solid rocket boosters and four liquid propellant engines, with a proposed 15% more thrust at launch than the Saturn V rockets that sent astronauts to the Moon.
But an orbiter mission to Pluto might not be the best use of the SLS alone.
It takes a lot of fuel to accelerate a vehicle to fast enough speed to get to Pluto in a reasonable amount of time. For example, New Horizons was the fastest spacecraft ever launched, using a souped-up Atlas V rocket with extra boosters, it performed a big burn when New Horizons departed Earth orbit. The lightweight spacecraft sped away from the Earth at 36,000 miles per hour (about 58,000 km/ hour), then used a gravity assist from Jupiter to boost New Horizons’ speed to 52,000 mph (83,600 km/h), traveling nearly a million miles (1.5 million km) a day in its 3 billion mile (4.8 billion km) journey to Pluto. The flight took nine and a half years.
“To enter Pluto orbit, a vehicle [like SLS] would have to boost up to that same speed, then turn around and decelerate for half the trip to arrive at Pluto with a net velocity of zero relative to the planet,” explained Stephen Fleming, an investor in several alt-space startups including XCOR Aerospace, Planetary Resources and NanoRacks. “Unfortunately, due to the tyranny of the rocket equation, you would have to carry all the fuel/propellant to decelerate with you at launch … which means accelerating the orbiter AND all that fuel in the initial phase. That requires logarithmically more fuel for the initial burn, and it turns out to be a LOT of fuel.”
Fleming told Universe Today that using the multi-billion dollar SLS to launch a Pluto orbiter, you would wind up launching an entire payload full of propellant just to accelerate and decelerate a tiny Pluto orbiter.
“That’s an extraordinarily expensive mission,” he said.
A better option might be to use a propulsion system of combined technologies. Stern mentioned a NASA study that looked at using the SLS as the launch vehicle and to boost the spacecraft towards Pluto, but then using an RTG (Radioisotope Thermoelectric Generator) powered ion engine to later brake for an orbital arrival.
An RTG produces heat from the natural decay of non-weapons-grade plutonium-238, and the heat is converted into electricity. An RTG ion engine would be a more powerful ion propulsion system than the current solar electric ion engine on the Dawn spacecraft, now orbiting Ceres, in the asteroid belt, plus it would enable operation in the outer solar system, far from the Sun. This nuclear powered ion engine would enable a speeding spacecraft to slow down and go into orbit.
“The SLS would boost you to fly out to Pluto,” Stern said, “and it would actually take two years to do the braking with ion propulsion.”
Stern said the flight time for such a mission to Pluto would be seven and a half years, two years faster than New Horizons.
The proposal uses a Direct Fusion Drive (DFD) engine that has propulsion and power in one integrated device. DFD provides high thrust to allow for a flight time of about 4 years to Pluto, plus being able to send substantial mass to orbit, perhaps between 1000 to 8000 kg.
If this propulsion system works as planned, it could launch a Pluto orbiter and a lander (or possibly a rover), and provide enough power to maintain an orbiter and all its instruments, as well as beam a lot of power to a lander. That would enable the surface vehicle to beam back video to the orbiter because it would have so much power, according to Stephanie Thomas from Princeton Satellite Systems, Inc., who is leading the NIAC study.
“Our concept is generally received as, ‘wow, that sounds really cool! When can I get one?’” Thomas told Universe Today. She said her and her team chose a prototype Pluto orbiter and lander mission in their proposal because it’s a great example of what can be done with a fusion rocket.
Their fusion system uses a small linear array of solenoid coils, and their fuel of choice is deuterium helium 3, which has very low neutron production.
“It fits on a spacecraft, it fits on a launch vehicle,” Thomas explained in a NIAC symposium talk (her talk starts about 17:30 in the linked video). “There’s no lithium, or other dangerous materials, it produces very few damaging particles. It’s about the size of a minivan or small truck. Our system is cheaper and faster to develop than other fusion proposals.”
The Princeton team has been able to produce 300 millisecond pulses with their plasma heating experiment, orders of magnitude better than any other system.
“The biggest hurdle is the fusion itself,” she said. “We need to build a bigger experiment to finish proving the new heating method, which will require an order of magnitude more resources than the project has been receiving from the Department of Energy so far,” Thomas said via email. “However, it’s still small in the grand scheme of advanced technology projects, about $50 million.”
Thomas said that DARPA has spent much more on many technology initiatives that ended up canceled. And it’s also much less than other fusion technologies require for the same stage of research, since our machine is so small and has a simple coil configuration.” (Thomas said have a look at the budget for ITER, the international nuclear fusion research and engineering megaproject, currently running over $20 billion).
“To put it simply, we know our method heats electrons really well and can extrapolate to heating ions, but we need to build it and prove it,” she said.
Thomas and her team are currently working on the “balance of plant” technology – the subsystems that will be required to operate the engine in space, assuming the heating method works as currently predicted.
In terms of the Pluto mission itself, Thomas said there aren’t any particular hurdles on the orbiter itself, but it would involve scaling up a few technologies to take advantage of the very large amount of power available, such as the optical communications.
“We could dedicate tens or more kW of power to the communication laser, not 10 watts, [like current missions]” she said. “Another unique feature of our concept is being able to beam a lot of power to a lander. This would enable new classes of planetary science instruments like powerful drills. The technology to do this exists but the specific instruments need to be designed and built. Additional technology that will be needed that is under development in various industries are lightweight space radiators, next-generation superconducting wires, and long-term cryogenic storage for the deuterium fuel.”
Thomas said their NIAC research is going well.
“We were selected for the NIAC Phase II study, and are in contract negotiations now,” she said. “We are busy working on higher fidelity models of the engine’s thrust, designing components of the trajectory, and sizing the various subsystems, including the superconducting coils,” she said. “Our current estimates are that a single 1 to 10 MW engine will produce between 5 and 50 N thrust, at about 10,000 sec specific impulse.”
Laser Zapping to Pluto
Another futuristic propulsion possibility is the laser-based systems proposed by Yuri Milner for his Breakthrough Starshot proposal, where small cubesats could be zapped by lasers on Earth, basically “bug zapping” spacecraft to reach incredible speeds (possibly millions of miles/km per hour) to visit the outer solar system or beyond.
“It’s not really in the cards for us to use this kind of technology, because we’d have to wait decades just for this to be developed,” Stern said. “But if you could send lightweight, inexpensive spacecraft at speeds like one-10th the speed of light based on lasers from Earth. We could send these small spacecraft to hundreds or thousands of objects in the Kuiper Belts, and you’d be out there in a matter of two-and-a-half days. You could send a spacecraft past Pluto every day. That would be really game changing.”
The Realistic Future
But even if everyone agrees a Pluto orbiter should be done, the earliest possible date for such a mission is sometime between the early 2020s and the early 2030s. But it all depends on the recommendations put forth by the scientific community’s next decadal survey, which will suggest the most top-priority missions for NASA’s Planetary Science Division.
These Decadal Surveys are 10-year “roadmaps” that set science priorities and provide guidance on where NASA should send spacecraft and what types of missions they should be. The last Decadal Survey was published in 2011, and that set planetary science priorities through 2022. The next one, for 2023-2034, will likely be published in 2022.
The New Horizons mission was the result of the suggestions from the 2003 planetary science Decadal Survey, where scientists said visiting the Pluto system and worlds beyond was a top-priority destination.
So, if you’re dreaming of a Pluto orbiter, keep talking about it.
The planetary science community has released their “Decadal Survey” a set of recommendations and a wish list of future missions to explore the solar system. But, as panel chair Steve Squyres said in his presentation of the survey at the Lunar and Planetary Science Conference on late Monday afternoon, NASA’s current budget projections could mean the end of large, flagship missions.
“The budget we had to work with is a projection by OMB (Office of Management and Budget) of what the future of planetary exploration might look like,” Squyres said. “If implemented, it would mean the end of flagships programs in planetary science. But this is not set in stone by any means. This budget is the first step in the process from the executive branch of the government. There are many more steps involving the other branches, and Congress is answerable to its constituents, and that includes us. So those of us who care have an obligation to speak to our representatives and let them know what missions we would like to see.”
The Decadal Survey, a lengthy 400-page document supported by NASA, the National Research Council and the National Science Foundation, “transcends Congress and changes in administration and is our guiding light that moves us forward year after year, said Jim Green, NASA’s Planetary Science Chief.
Squyres said the Decadal Survey is “an extraordinary event where a governmental entity looks toward its constituency for input and actually listens to them.”
In total, the committee – made up of planetary scientists — identified 25 mission candidates for detailed studies.
Flagship missions were recommended in the report, but with the caveat that if they can’t stay under a certain budget, those missions will either be delayed or canceled. And if NASA doesn’t have enough money or cannot stay within budget, the space agency should focus on smaller, cheaper missions first. These recommendations appear to be a direct result of the money issues of the James Webb Space Telescope and the Mars Science Laboratory Rover.
Among the highest recommendations for the big flagship missions are a double rover mission to Mars working in cooperation with the European Space Agency, sending NASA’s Mars Astrobiology Explorer Cacher (MAX-C) rover, (which could be a sample return mission) and ESA’s ExoMars Rover to the Red Planet which could both help determine whether the planet ever supported life and could also help answer questions about its geologic and climatic history. NASA’s part of that joint mission should not exceed $2.5 billion, which is actually $1 billion less than the independent estimates provided to the committee. However, the panel suggested that both space agencies work to make the missions cheaper by reducing the scope of the mission (and they provided a checklist of how to do that).
The second highest recommendation for the flagship missions is to study Jupiter’s icy moon Europa and its subsurface ocean — one of the most promising environments in the solar system for supporting life. But again, NASA should fly the Jupiter Europa Orbiter (JEO) only if NASA’s budget for planetary science is increased, or if the JEO’s mission scope is made more affordable. The independent estimate put the price tag at $4.7 billion. The committee concluded that unless costs could be brought down, conducting JEO would preclude too many other important missions.
“De-scoping is a difficult thing,” Squyres said at the conclusion of his presentation. “It requires discipline, it requires leaving behind some of our most cherished hopes for what a mission might be.”
But Squyres reminded those in attendance of two famous de-scoped missions. One mission, originally called the Grand Tour ended up being cut because it was alltogether too large in scope and budget. It later became Voyager, and scientists later worked out a way to make the Grand Tour happen. The other mission was the VIRM mission to Venus, which was a radar and mapping mission to Venus, which was too expensive, and it was massively de-scoped to became the Magellan mission.
“Voyager and Magellan both revolutionized our understanding of five planets, so de-scoping — when done right — can lead to revolutionary missions,” Squyres said.
Other missions would be the first in-depth exploration of an ice giant plant – an orbiter to Uranus — and another to Saturn’s geyser-filled moon, Enceladus.
The Decadal Survey takes input from planetary scientists, and Squyres said the science community stressed the importance of smaller missions – known as New Frontier class missions — which would provide science quicker, cheaper and more frequently than the big flagship missions. Also, they said NASA should place high priority on research and development and technology funding.
Recommendations for New Frontiers missions for 2013-2022 include a Comet Surface Sample Return mission, and Io orbiter, a probe to deploy into Saturn’s atmosphere, a network of lunar landers and orbiters, and a Lunar South Pole-Aitken Basin Sample Return.
Squyres said the panel proceeded knowing their recommendations should be science-driven and but also that the missions would have to be maintainable within the projected budgetary resources. So, not just the science but the costs of the science.
“Science return per dollar — I understand science return is not highly definable in terms of cost,” Squyres said, which sometimes makes the projections difficult.
Other missions were recommend based on balance across the solar system and balance on mission size between the smaller and larger missions. Other criteria were the missions’ readiness of appropriate technologies, and availabilities of trajectories in the next 10 years — “You have to be able to get from here to there,” Squyres said.
They also recommended funding for current missions to continue or be extended including, MESSENGER, Dawn, Kepler, GRAIL, New Horizons, Juneo, Cassini, the current Mars missions, including the Mars Science Laboratory and MAVEN, and the LADEE lunar mission.