Discussing the state of space mission planning recently with Centauri Dreams contributor Ashley Baldwin, I mentioned my concerns about follow-up missions to the outer planets once New Horizons has done its job at Pluto/Charon. No one is as plugged into mission concepts as Dr. Baldwin, and as he discussed what’s coming up both in exoplanet research as well as future planetary missions, I realized we needed to pull it all together in a single place. What follows is Ashley’s look at what’s coming down the road in exoplanetary research as well as planetary investigation in our own Solar System, an overview I hope you’ll find as useful as I have. Dr. Baldwin is a consultant psychiatrist at the 5 Boroughs Partnership NHS Trust (Warrington, UK) and a former lecturer at Liverpool and Manchester Universities. He is also, as his latest essay makes clear, a man with a passion for what we can do in space.
by Ashley Baldwin
We’ve come a long way since the discovery of the first “conventional” exoplanets in 1995 ( of course, “pulsar” orbiting planets had been discovered several years earlier). Since then ground based RV and Transit surveys have discovered several hundreds of planets, supplemented by a thousand confirmed finds plus many more “candidates” by the miracle that is Kepler — the original and K2, aided and abetted ably by Corot and re modeled Hubble and Spitzer. Between these several dozen larger examples have been “characterised ” by a combination of RV,transit and transit spectroscopy. We are at a crossroads and stand at the edge of the beginning of a golden age, this despite the austere times in which we live. But as they say, necessity is the mother of invention, and the innovation arising from lack of funds has led to a versatility in hardware use unimaginable twenty years ago (along with 1800 plus exoplanets!).
So what next? Lots of things. Before talking about obvious things like space telescopes and spectroscopy I feel I must make space for asteroseismology. A new science and still little known, but without it hardly any of the recent exoplanet advances would have been possible. It is the process by which kinetic energy or pulsations inside stars is converted into vibrations. In effect sound waves. Originating in the Sun with helioseismology, asteroseismology is basically the same process by which seismic waves of earthquakes are used to inform us about the details of the Earth’s interior.
Vibrations from different parts of stellar interiors expand outwards to the star’s surface where their nature and origin can be determined with increasing accuracy. There are three types of these vibrations:
- Gravity or ‘g’ waves originate from stellar cores and have been implicated in the movement of stellar material into other areas as well as contributing to the uniform rotation of the core, linking thus with the outer convective zone of stellar-mass stars. These waves only reach the surface in special circumstances.
- Pressure or ‘p’ waves, arise from the outer convective zone and are the main source of information on this crucial area of a star’s interior as they reach the surface.
- Finally, “f” waves are surface “ripples”. These vibrations help astronomers accurately calculate the mass, age, diameter and temperature of a star, with age in particular being crucially determined to an accuracy of 10%. Why so important? Well, apart from determining the nature of stars themselves, they also underpin the description of orbiting exoplanets.
Understand the star and you understand the planet. The more stars that are subject to this analysis, the more precise it becomes. This is a little known but crucial element of Kepler (and CoRoT) and will also be central to PLATO (Planetary Transits and Oscillations of stars) in the 2020s. TESS (Transiting Exoplanet Survey Satellite), sadly, is too small and its pointing times per star too brief to add a lot to the process despite its huge capabilities for such a low budget. Kepler has a dedicated committee that oversees the correlation of all asteroseismological data as will PLATO, and the huge amounts of stellar information collected will provide precision detail on exoplanets by the end of the next decade (and indeed before).
Things start hotting up from next year with “first Light” on the revolutionary RV spectrograph ESPRESSO (Echelle SPectrograph for Rocky Exoplanets and Stable Spectroscopic Observations) at the VLT in Chile. This device is an order of magnitude more powerful than previous devices like HARPS, and in combination with the large telescopes of the VLT can discover planets the same size as Earth in the habitable zones of Sun-like stars. The first of its kind to do so. Apart from positioning such planets for potential direct imaging and spectroscopic characterisation, it will also provide mass estimates with varying degrees of accuracy.
Meanwhile, nearby ALMA (Atacama Large Millimeter/submillimeter Array) will provide unprecedented images and detail on the all-important protoplanetary disks from which planets form, and which inform the nature of our own system’s evolutionary history. The Square Kilometer Array (SKA), due to become operational next decade in South Africa and Australia, will also do this in longer, radio wavelengths, and its enormous collecting area (quite literally a square kilometer) with moveable unit telescopes (as with ALMA too) will create a synthetic “filled” aperture on a par with a solid telescope of similar dimensions and consequent exquisite resolution.
Image: ALMA antennae on the Chajnantor Plateau. Credit: ALMA (ESO/NAOJ/NRAO), O. Dessibourg.
Submillimetre astronomy is often referred to as molecular imaging, as the wavelengths used are perfect, given their low energy and related cool temperatures, for picking up chemical molecules in the interstellar medium, and have been instrumental in showing the ubiquity of many of the materials needed for life, like amino acids, the building blocks of proteins, and PAHs (poly aromatic hydrocarbons) which are key constituents of cell membranes as well as the long chain amines in the goo on Titan. ?ALMA has identified hydrogen cyanide and methyl cyanide , poisonous elements on Earth, but critical progenitor molecules for protein and life building amino acids. No one has discovered life off Earth to date, but the commonest elements created by stars, carbon, hydrogen,oxygen and nitrogen (CHON), are amongst the main constituents of life and in conjunction with molecules like amino acids and PAHs suggest that the key components of life are ubiquitous.
Even greater accuracy can be achieved by combining all the radio telescopes dotted across the Earth and even in space to create a “diluted ” aperture (not completely filled in but with equivalent width of its most remote elements) wider than the Earth itself. It isn’t difficult to guess the extent of such a device’s resolution! The SKA and ALMA, as with any new and sophisticated astronomical hardware, have a planned-out mission itinerary, but given their extreme capabilities have the added ability to make unexpected and exciting discoveries.
Returning to shorter wavelengths, ground based telescopes are being equipped with increasingly sophisticated adaptive optics (AO), in conjunction with high altitude sites, allowing them to image with increasing detail in wavelengths from optical to mid-infrared and bring to bear their large light gathering capacity without the huge expense of launch to and maintenance in space. This will culminate in the completion of the three extremely large telescopes (ELTs) between 2020 and 2024. Work is underway on 25-40 m apertures that will capture sufficient light in combination with AO to discover, image and characterise planets down even to Earth size.
In the shorter term, hot on the heels of ESPRESSO and reliant on its discoveries is TESS, a small satellite with multiple telescope/cameras and sensors, due for launch to a specially designed widely elliptical orbit to maximise imaging of exoplanet transits round “bright” nearby stars, largely M dwarfs. These small stars’ planets orbit close in and their transits eclipse a larger portion of the star, creating so- called “deep transits” on a regular basis (including in the habitable zones which are only 0.25 AU for even the largest M-class stars) that can be added together, or “binned”, to produce a potent signal.
Better still, TESS will work in concert with the James Webb Space Telescope following its launch a year later. JWST is largely an infrared telescope designed to look at extragalactic objects and cosmological concepts. Although, sadly, not an exoplanet imager, it has been optimised to spectroscopically analyse exoplanets, and with a 6.5m aperture it should do very well. It will image a transit and analyse the small amount of starlight passing through the outer atmosphere of the transiting planet in order to characterise it: A “transmission” spectrum. Alternatively, as the transit times can be calculated precisely, a spectrum of the combined planet and star light can be taken when they are next to each other and by subtracting the spectrum of the star alone whilst the planet is eclipsed behind it, a net planetary spectrum can be calculated.
Image: The principal goal of the TESS mission is to detect small planets with bright host stars in the solar neighborhood, so that detailed characterizations of the planets and their atmospheres can be performed. Credit: MIT.
It’s likely that given the huge workload of JWST, its exoplanetary characterisation work will be limited to premier targets. Smaller mission funding pools will be utilised to produce small but dedicated exoplanet transit spectroscopy telescopes to characterise larger exoplanets, as suggested in the previously unsuccessful ESA and NASA concepts EChO and FINESSE.
TESS itself will look at half a billion stars across the whole sky over a two year period and if it holds together, should get a much longer mission expansion. Parts of its field of imaging around the ecliptic poles are designed to overlap with the JWST’s area of operation to maximise their synergy. The longest periods of “staring” also occur there to allow analysis of planets with the longest orbital periods in the habitable zones of the largest possible (most Sun-like) stars. Ordinarily three proven transits are required for proof of discovery but given the nearby target stars any discoveries can be followed up by ESPRESSO for proof, reducing required transits to just two. There is growing optimism that with JWST, TESS might make the ultimate discovery!
Launched in a similar timeframe as TESS, the small ESA telescope CHEOPs will look for transits predicted by RV discoveries, allowing accurate mass and density calculations of up to 500 planets of gas giant to mini-Neptune size to add to the growing list of planets characterised this way, thus helping build up a picture of planetary nature and distribution. At present, planets in this category have been grouped by Marcy et al and the data suggests that Earth like planets (rocky with a thin atmosphere) exist up to about 1.6 R Earth or 5M Earth with larger objects more likely to have a thick atmosphere and be more akin to “mini Neptunes”. The larger the sample, the greater the accuracy, hence CHEOPs, TESS and ESPRESSO’s wider importance in characterisation, which will also,inform efficient future imaging searches.
Image: CHEOPS – CHaracterising ExOPlanet Satellite – is the first mission dedicated to searching for exoplanetary transits by performing ultra-high precision photometry on bright stars already known to host planets. Credit: ESA.
Into the Next Decade
Crunch time arrives in the 2020s. The beginning of the decade is the time of the routine Decadal survey that lays out NASA’s plans and priorities over the following ten years. It will determine the priority that exoplanets (and Solar System planets) are given. The JWST has left a huge hole in the budget that must be balanced and at a time when manned space flight, never cheap, is reappearing after its post Space Shuttle hiatus. There is room for plenty of optimism, though.
Unlike my dear old National Health Service here in Britain, year on year funding can be stored to be used at a later date. Any ATLAST (Advanced Technology Large Aperture Space Telescope), Terrestrial Planet Finder telescope or High Definition Space Telescope in the proportions necessary for detailed exoplanetary characterisation will cost upward of $15 billion. Huge, but not insurmountable, if funds are hoarded over 15 years ahead of a 2035 launch. Imagining a 16m monster like that! Quite a supposition.
Image: The Advanced Technology Large Aperture Space Telescope (ATLAST) is a NASA strategic mission concept study for the next generation of UVOIR [near-UV to far-infrared] space observatory. ATLAST will have a primary mirror diameter in the 8m to 16m range that will allow us to perform some of the most challenging observations to answer some of our most compelling astrophysical questions. Credit: Space Telescope Science Institute.
What is more definite is the Wide-field Infrared Survey telescope, WFIRST, due for launch circa 2024, maybe a bit earlier. Originally planned as a dark energy mission, it has grown enormously thanks to the NRO donation of a Hubble dimension, high-quality wide-field mirror. At the same time, Princeton’s David Spergel made a compelling and successful case for inclusion of an internal starlight occulter or coronagraph at about half a billion dollars extra (much of which was covered by partner space agencies). This would be a “technological demonstrator ” instrument. Large funds were released for advancing this largely theoretical technology to a useable level through experimental “Probe” concepts which also developed an external occulter technology.
The coronagraph has already massively exceeded all expectation of success and has at least 5 years more development time before the telescope development begins. That’s a lot of useful time. It’s aim is to allow direct imaging of Jupiter-Neptune mass planets about as far out from a star as Mars. The coronagraph blocks out the much brighter starlight that swamps the feeble planet light. Already the technology has improved to the point where a few Super Earths or even smaller planets might be visualised. Sadly, not quite in the habitable zone, but the wider orbits will allow more accurate categorisation of the planetary cohort thus telling us what to look for in the future. The final orbit of this telescope is yet to be decided and is crucial.
Given the long gap until ATLAST (envisioned as a flagship mission of the 2025 – 2035 period) and the finite life expectancy of Hubble and JWST, WFIRST is obviously intended to bridge the gap, and thus will need servicing like Hubble. To this effect it was felt necessary to keep it near to Earth (for convenience of data download too), but rapid advances in robotic servicing mean it could now be stationed as far afield as the ideal viewing spot, the Sun/Earth Lagrange point L2. It could possibly even be moved nearer to the moon for servicing. Thus locale would allow the addition of an external occulter if funding was available. This technology allows closer imaging to the star than the coronagraph, even into the habitable zone. Whether WFIRST ends up with both internal and external occulters remains to be seen and will likely to be decided by the 2020 Decadal study according to the political and financial climate of the day. Meantime, it’s great to know that such a useful planet hunter will be operational for a long time post 2024.
WFIRST does other useful exoplanetary work. It too will discover exoplanets by the transit method and also by the often forgotten microlensing principle. This involves a nearby star sitting in front of a further out star and effectively focusing its light via gravity, as described by Einstein in his relativity work. Exoplanets orbiting the nearer star stand out during this process and can have their radius and mass determined accurately. As this method works for further out planets, it provides a way of populating the full range of planetary orbits and characteristics, which we have seen is critical to establishing the nature of alien star system architecture. The downside of microlensing is that it is a one-off experience and can’t be revisited. Direct imaging, transiting, and microlensing makes WFIRST one potent exoplanet observatory. What more can it do? The answer is a lot.
Image: The Wide-Field Infrared Survey Telescope (WFIRST) is a NASA observatory designed to perform wide-field imaging and slitless spectroscopic surveys of the near infrared (NIR) sky for the community. The current Astrophysics Focused Telescope Assets (AFTA) design of the mission makes use of an existing 2.4m telescope to enhance sensitivity and imaging performance. Credit: NASA.
Consider astrometry. Like asteroseismology it is a little known science but rapidly expanding, and like asteroseismology is the shape of things to come. Astrometry measures sidewards movement of a star due to the gravitational effects of orbiting stars. A bit similar to the R.V method, but better in that it accurately determines mass of planets and also their location with pinpoint accuracy. Meanwhile, the ESA telescope Gaia (is currently in the process of staring for extended periods at over a billion Milky Way stars in order to determine their position to within 1% error. In the process, as with Kepler and PLATO, it will carry out detailed asteroseismology, which will advance this critical field even further. Know the star and you know the planet.
Astrometry will allow Gaia the added benefit of single-handedly accurately positioning several thousand gas giant planets. However, combining its results with WFIRST should allow accurate positioning and mass/radius of nearby planets down to Earth size, including planets in the habitable zone, helping develop an effective search strategy for the WFIRST direct imaging technology whether by internal or external occulter or both. Critically, astrometry helps discover and characterise planets around M-dwarfs which form the large part of the stellar neighbourhood. As the habitable zone for even the largest of these stars (and many of the next class up, K-class stars) is inside 0.4AU, it is unlikely that even an advanced internal or external occulting device would allow direct imaging so close to the star, so any orbiting planets could only be classified by astrometry and transit spectroscopy if they transit the star.
Image: Gaia is an ambitious mission to chart a three-dimensional map of our Galaxy, the Milky Way, in the process revealing the composition, formation and evolution of the Galaxy. Gaia will provide unprecedented positional and radial velocity measurements with the accuracies needed to produce a stereoscopic and kinematic census of about one billion stars in our Galaxy and throughout the Local Group. This amounts to about 1 per cent of the Galactic stellar population. Credit: ESA.
Generally, the closer a planet is to a star, the greater the likelihood of a transit, and the nature of planetary formation around M dwarfs also leads to protoplanetary disks that form in such a position as to create transiting planets. This, ironically, was the proposed for the now defunct TPF-I. If Gaia goes beyond its initial 5 year mission, WFIRST should be able to find and characterise up to 20,000 Jupiter or Neptune sized planets! All that for just $2.5 billion means that WFIRST will likely be one of the greatest observatories, anywhere, of all time.
PLATO is a cross between Kepler and TESS. Like Kepler, it is designed to find Earth-sized planets in the habitable zone of Sun-like stars, and as with TESS, these stars will be close enough to characterise and confirm from ground-based telescopes and spectroscopes. PLATO, too, will carry out extensive asteroseismology, which along with Kepler and Gaia will give unprecedented knowledge of most star types by 2030.
Image: PLAnetary Transits and Oscillations of stars (PLATO) is the third medium-class mission in ESA’s Cosmic Vision programme. Its objective is to find and study a large number of extrasolar planetary systems, with emphasis on the properties of terrestrial planets in the habitable zone around solar-like stars. PLATO has also been designed to investigate seismic activity in stars, enabling the precise characterisation of the planet host star, including its age. Credit: ESA.
Meanwhile, Hubble has been given a clean bill of health until at least 2020. The aim is for as much overlap with JWST as possible, bridging the gap to WFIRST. Spitzer will likely be phased out once JWST is up. WFIRST, if serviced and upgraded regularly like Hubble, could also last twenty years plus, certainly until the ATLAST telescope is operational and well after the Extremely Large Telescopes are fully functional on the ground. Given the huge cost of building, launching and maintaining space telescopes (not least $8.5 billion for JWST), NASA have now made it clear that future designs will be multi-purpose and modular for ease of service/upgrade.
Imaging an Exoplanet
In terms of resolving and imaging an exoplanet, we move into the realm of science fiction for now. To produce even a ten-pixel spatial image of a nearby planet would require a space telescope with an aperture equivalent to 200 miles. Clearly impossible for one telescope, but a thirty minute exposure employing 150 3m diameter mirrors with varying separations of up to 150 km, linked together as a “hyper telescope”, would be sufficient to act as an ‘Exo-Earth imager’ able to detect several pixel “green spots” similar to the Amazon basin on a planet within ten light years.The short exposure time is an added necessity for spatial imaging in order avoid blurring caused by clouds or planetary rotation. This is why it may be important to have an external occulter with WFIRST, not just for potent imaging but to allow the “formation flying ” necessary to link the two devices together. A small step but a necessary one to get to direct spatial imaging.
Meanwhile, everything we learn from direct imaging will be via increasingly sensitive spectroscopy of O2, O3, CH4, H20 (liquid in the habitable zone as determined by astrometry) and photosynthetic pigments like the chlorophyll “red edge” bio signatures from “point sources”. The bigger the telescope, the better the signal to noise ratio (SNR) and the better the spectroscopic resolution. WFIRST has a three dimensional “Integral field spectroscope” with a maximum resolution of 70. When you think that high resolution runs to the hundreds of thousands, it shows that we are only just scratching the surface. Apart from that and until spatial imaging (if ever), SETI, Infrared heat emission or spacecraft exhausts might be the only way to separate intelligent life from life per se.
That said, things are going to happen that would have been inconceivable even in 1995. Twenty thousand plus exoplanets by 2030, hundreds characterised. Exciting if crude and controversial spectroscopic findings, and just five years perhaps from launching a 16m segmented telescope into an orbit 1.5 million kms from Earth where it will be regularly serviced by astronauts and robots practising for Mars missions.
Missions and Their Development Paths
Closer to home, we have the ESA JUICE (Jupiter Icy Moons Explorer) mission to Jupiter with flybys of Europa and Callisto and a Ganymede orbiter. NASA will hopefully get its act together for a cost-effective Europa Clipper and we may yet find signs of life closer to home, though my money is on biosignatures first from an exoplanet, possibly as early as TESS but certainly from ATLAST. The key for me is that life (as we know it) is made from elements and molecules that are common.
This is why infrared astronomy is so important, for infrared light travels long distances and isn’t easily absorbed, and if it is, it soon gets re emitted. The missions to icy bodies in our system, like Rosetta, Dawn, OSIRIS-REX and New Horizons, are as critical to life discovery as TESS, WFIRST or even ATLAST, as they illustrate the ubiquity of all the necessary ingredients of life (including water) as well as the violent formation of our solar system. In the absence of “flagship missions”, the highest-funded NASA missions that were suspended after the JWST overspend, most planetary-style missions are now funded by smaller amounts, like Explorer (different cash levels up to $220 million plus a launch), Discovery ($500 million plus a launch) and New Frontiers ($1 billion plus a launch). NASA even has a list of prescribed launch vehicles and savings made, but fitting any mission into a smaller launcher can feed into the mission itself. Up to $16 million for a Discovery concept, for example. Applications are invited for missions according to how often they fly with the cheapest, Explorer, launching every three years.
Image: JUICE (JUpiter ICy moons Explorer) is the first large-class mission in ESA’s Cosmic Vision 2015-2025 programme. Planned for launch in 2022 and arrival at Jupiter in 2030, it will spend at least three years making detailed observations of the giant gaseous planet Jupiter and three of its largest moons, Ganymede, Callisto and Europa. Credit: ESA.
The limited funding has had the advantage, however, of inspiring great innovation and hugely successful mission concepts like TESS, just $200 million, Kepler at about $700 million, and Juno, a New Frontiers $1 billion mission currently en route to Jupiter. Without going into detail, the costs of missions are made up of numerous elements with hardware like telescopes and spacecraft contributing the biggest element, but they require constant engineering and operating support throughout their lifetime, which builds up and has to be factored into the initial budget.
Juno hasn’t reached Jupiter yet, but its science and engineering teams are all at work making sure it operates. So although budgets of hundreds of millions sound like a lot, they are in fact fairly small, especially if compared to “flagship” missions like Cassini, Galileo and the Voyagers, which in current funding would run into many billions of dollars. This contributes to a big hole in exploration, preventing follow up intermediate telescopes and interplanetary missions. The lack of any mission to Uranus or Neptune is a classic example, with no plan for even getting close since Voyager 2. The fact that even a heavily cut back Europa Clipper is still estimated at $2 billion for a 3.5 year multiple flyby mission (which is cheaper than an orbiter). The heavy contribution of running costs is bizarrely demonstrated by the fact that a Europa lander was considered over an orbiter because it would be cheaper simply because it wouldn’t last long due to the hostile environment! The next round of New Frontiers bids is just starting for a 2021 launch with just one outer Solar System concept involving a Saturn atmospheric probe and relay spacecraft. It is expected to transmit f0r 50 minutes after an 8 year journey and costs $1 billion.
All of this illustrates the problem mission planners face and the huge cost of such missions. Europa Clipper is actually a very good value mission and might just fly. In conjunction with the ESA JUICE mission, Europa Clipper will drive forward our knowledge of Jupiter’s inner moons, certainly confirming or disproving the idea of sub-surface oceans beyond all doubt and maybe finding some interesting things leaking out from the depths! The ESA face the same situation with JUICE, funded through their large or “L” programme scheme with a budget of just over a billion Euros, or about $1.5 billion. Their lesser funds have forced even greater innovation than NASA and the low cost of JUICE is due to innovative lightweight and cheap materials like silicon carbide for a mission concept very similar to Europa Clipper.
Returning to Uranus and Neptune, these planets always appear in both NASA and ESA discovery “road maps” but always with other things further ahead which, with limited funds, ultimately take precedent. There is constant pressure to have visible results, the success of which was obvious with the ESA Rosetta mission and, we can assume, with Dawn at Ceres as well. Out of necessity, such mission concepts tend to be favoured as opposed to a mission to Uranus that with conventional rockets would take as long as 13 years.
Remember that throughout that time the spacecraft needs looking after remotely from both an engineering and operations perspective, requiring the maintenance of near full time staff, all of which eats into a limited budget of $1 billion, the New Frontiers maximum unless alternative funding sources or partnerships are used. This is one of the reasons I welcome the Falcon Heavy launcher so much. It is much cheaper at about $100 million than any other comparable launcher and can lift bigger loads off Earth into orbit. What isn’t as well known is that it has the ability to send missions direct to their target rather than needing gravitational assists from Earth, Venus and Jupiter, as with previous outer Solar System missions since Voyager.
Falcon Heavy could lift about a 5 tonne payload to Uranus in well under ten years, and in reducing the mission length would of course lower its cost, allowing more “mission proper”, perhaps even fitting within a New Frontiers cost envelope. The ESA were certainly able to produce a stripped down “straw man” dual Uranus/ Neptune concept, ODINUS, within an L budget. New ion propulsion systems like NEXT (or its descendants) require far less propellant than conventional chemical rockets and could ultimately be used to slow a Uranus probe into orbit without taking up too much mass of the critical spacecraft and its instrument suite.
Image: Neptune, a compelling target but one without a current mission in the pipeline. Credit: NASA.
That just leaves one big obstacle: Power. So far out from the Sun, even huge versions of today’s efficient solar cells would be inadequate to power even basic spacecraft functions, never mind complex scientific equipment. Traditionally power comes from converting heat to electricity via radioactive decay of the isotope Plutonium 238 (not to be confused with its deadly bomb making cousin Plutonium 239) in a “Radioisotope Thermal Generator”. Cassini uses such a device, as does Voyager 2, that with an 80 year plus half life is ideally suited for such extended missions.
This isotope is a byproduct of nuclear bomb making, so post Cold War it is in increasingly poor supply and what is available is earmarked for other projects well in advance. This situation faces all missions mooted to go beyond Jupiter, like an Enceladus or Titan orbiter/lander, and is a real deal breaker that needs addressing. Uranus and Neptune in particular need to be explored in detail not least because the exoplanet categorisation described above illustrates that they, in varying sizes, are the most ubiquitous planet type in the galaxy and are on our doorstep.
It’s impossible to talk observational astronomy and not mention Mars. Undoubtedly, the most popular mission target given its proximity, with a solid surface on which to land and the possibility of life, slim but possible if not now then at some time in the distant past. The next tranche of missions starts in 2016 with an ESA orbiter and stationary lander and a NASA lander, Insight. Both landers are intended to last two Earth years and prepare the way for rovers.
The NASA mission was part of the Discovery programme and was chosen just ahead of the TiME concept, Titan Mare Explorer – a floating lander that would analyse the Titanian methane lakes whilst Earth was above the horizon so it could transmit direct to Earth without the need for an expensive orbiter. What a mission that would have been, and for just half a billion dollars. That chance is now gone for twenty years or so, and with it any hope of a near-term Saturn mission after Cassini, given the expense of a more complex mission profile to either Titan or Enceladus.
Meanwhile, Insight will dig some holes and do more analysis and help prepare the way for the Mars 2020 rover, a beefed up version of Curiosity which will have more sophisticated instruments, including drills, that will look specifically for life rather than just water, as with Curiosity. Crucially this will use one of the few remaining RTGs as opposed to solar panels like those on Opportunity (still going after running a marathon in ten years), thereby removing the possibility of using the device for outer Solar System exploration. Plutonium 238 production has begun again at Oak Ridge but yearly production is tiny, and it will take years to produce the kilogram masses necessary to power space missions. The ESA are also sending a rover to Mars, in 2018, funding and builders Roscosmos allowing. It will be solar powered and launched by a Russian Proton rocket, whose success rate isn’t the best.
For all the potential deficiencies in exploration, what has been achieved over the last twenty years is immense. What is planned over the next twenty years is not fully clear yet, but it is likely to culminate in a huge multi-purpose space telescope that will pull all previous work together, and in concert with other space and ground telescopes, and hopefully multiple interplanetary missions, will discover signs of life, if not at present, certainly in the past. I think ultimately we will find out that life is common, but much as I would like to disagree with Fermi and “Rare Earth”, I think finding intelligent life is going to be a whole lot harder. As the Hitchhikers Guide to the Galaxy says, “Space is a very big place “. Both in size and time.
Considering we are living in times of austerity, though, I think what we have done so far isn’t at all bad !
Given the problems of power in the outer solar system, and the limits of RTGs, it seems absurd to me that there is not a focussed effort on actual nuclear reactors. Reactors would make efficient and fast propulsion like VASIMR and related approaches practical, would allow a far larger power envelope for instruments, and the research might also prove useful for human habitation on the Moon and Mars. It seems silly that we are stuck with photovoltaic- and thermocouple-derived electricity for our probes.
One of the most comprehensive articles ever published on Centauri Dreams – thank you Ashley.
A couple of short comments on a large article “Critically, astrometry helps discover and characterise planets”. Indeed, this technique could come into its own with GAIA, after more than 50 years of false starts. AFAIK, only one real planet, VB 10b in 2009, has been discovered by astrometry. And this required the 5 metre Hale telescope. I dearly hope GAIA meets expectations.
Regarding hopes and dreams a couple of decades away, it is easy to extrapolate current technology that far forward. It is impossible to predict what kind of political/economic/environmental world will exist at that time.
The 71 year old Bretton Woods global financial system will not survive the current decade, maybe won’t even survive 2015. What comes after is a mystery, perhaps even beyond the control of the great and powerful. Neither the EU nor the USA are likely to exist in their current forms in 2035. If that prediction sounds extreme, recall that in 1990 no one thought that the early 21st century would feature international strife between Moscow and Kiev. Now in 2015 we have forces in Europe fighting under the nazi swastika banner again, and threats of nuclear war. The future is truly an unknown, undiscovered country. Whether it includes advanced scientific space missions is anyone’s guess.
TESS will look at all stars with magnitude, M, < 12. That's half a _million_ stars, not half a _billion_.
Great article as far as it goes (which was a long way) but one that misses what seems to me to be something of a tipping point, as private enterprise begins to take over from unwieldy national or supra-national space organizations. The likes of Space X and Planetary Resources, or their successors, are more likely to drive humanity’s expansion into the solar system (and beyond), and hence they will start to lead our understanding of it.
“[…] we may yet find signs of life closer to home, though my money is on biosignatures first from an exoplanet, possibly as early as TESS but *certainly* from ATLAST.”
“[…] and hopefully multiple interplanetary missions, will discover signs of life, if not at present, *certainly* in the past.”
I enjoyed the summary of upcoming missions, but extraterrestrial life and “certainly” don’t even belong in the same discussion. We have next to no data, so where could certainty about any position possibly come from? That’s a serious problem of epistemology, never-mind scientific tenability. Sure the elements of life are abundant, but their arrangement matters rather a lot with life being the most complex such arrangement we are aware of. “The elements are abundant” and “billions upon billions of stars” can hardly be called compelling arguments when we don’t know the conditions necessary for abiogenesis. I watched this SETI talk https://www.youtube.com/watch?v=nk_R55O24t4 that advances an impressively compelling case for a completely different origin scenario than the most widely accepted sea-floor vent story.
Now I’d like to give some thoughts on resolved exoplanet images. I think the best way to progress in that direction is to build up a space-based infrastructure for manufacturing. If you could launch the delicate, intricate and diverse instruments but fabricate the housing, sun-shield and mirror in space and perform final assembly there then you could leverage some huge engineering advantages.
A big fragile mirror is an unwieldy thing to launch. Space is a conducive environment for making much larger single mirrors than what is possible on Earth. You don’t have to worry about the mirror deforming under its own weight, you don’t have to build an extensive superstructure for support and you don’t have to make it deployable. If you could start fabricating big curved mirrors in space you could continue until the space cows come home, because they would prove a very useful product. For astronomy you could build larger and larger arrays or point them at separate targets (which only become more and more numerous as your resolving power increases). The business case comes from their use as space-based solar power concentrators. Lastly they could be harnessed for beamed propulsion.
“Now in 2015 we have forces in Europe fighting under the nazi swastika banner again …”
Forgive me, but what in the world are you talking about forces that are fighting under the swastika; what ‘swastika’ and its forces are you talking about ?
Alas Joy, even VB 10b proved to be a false alarm from memory. So we wait on Gaia…
Quick comment. This focuses mostly on Western projects. Thanks to recent growth of their economies, certain non-Western countries are now more and more present in space exploration.
Just out of memory China will complete its Five hundred meter Aperture Spherical Telescope(FAST) radio telescope in 2016(if all goes well of course)
You can read more on Chinese deep space and Mars program here(it is a brief overview)
They are thinking about doing couple of interesting missions, including Ceres sample return in 2020s-we will see what will come out of it.
I would assume India and Japan have some interesting proposals as well.
As to the rest of the article, I think that a mission to Enceladus should one of the priorities now. It would probably be better to re-purpose the Europa Clipper for that mission in light of recent findings suggesting Europa’s plums were impact based and likely a rare occurrence. Is it really impossible to fit a Saturn/Titan/Enceladus mission within the next two decades?
Btw, my other personal favorite is Triton, with its activity and water, but I am not getting any hopes up that I will see this mission anytime soon.
@Tulse April 10, 2015 at 13:49
Your suggestion about the use of nuclear reactors in space, by chance, coincides with the 50th anniversary of the first and only orbital test flight of an American reactor in space called “Snapshot”:
Given the checkered history of nuclear reactors in space, the dangers of flying fissile nuclear materials into orbit (both real and especially imagined) and the lack of funding for developing such technology, I don’t see any nuclear reactors flying again in my lifetime.
@William – the corrupt but lawfully elected government of Ukraine was violently overthrown in February 2014 by a junta of billionaire oligarchs backed by the guns of neo-Nazi street gangs. The Kiev junta immediately began talking of ethnically cleansing the eastern half of their country of Russian speakers. Within a month, former Ukrainian prime minister Yulia Tymoshenko was recorded saying that ‘nuclear weapons’ should be used to kill their ‘subhuman’ ethnic Russian population – fortunately, Ukraine does not yet have any.
In April 2014, the Kiev junta launched a civil war of extermination against their eastern population. So far 50,000 people have died and over a million have been made homeless. The elite shock troops of the Kiev regime march under the well known swastika or the wolfs angel – a similar nazi emblem. Google Azov or Aidar battalions for images. The elderly people who fought for Hitler in the 1940s have been declared ‘freedom fighters’ and awarded war pensions. Secretary of the NSDC of Ukraine, Oleksandr Turchynov has just called for Kiev to create a “dirty” atomic bomb to exterminate their unwanted eastern population. Ukraine’s Interpol-wanted leader of nazi extremist group Right Sector, Dmitry Yarosh, has been appointed as an adviser to the country’s Chief of General Staff.
So far this evil and tragic insanity, a miniature replay of WWII, has been confined to Ukraine, but the potential exists for the conflict spreading into a global conflagration. For obvious historical reasons, Russians do not like nazis, and are alarmed to see them back in action. Several Russian officials have dropped hints that nuclear weapons will be used if the nazis attack the Russian Federation. Such a development, and the inevitable global follow on consequences, could adversely impact the ability to launch advanced space missions in the decades to come. Is there intelligent life on Earth?
Thanks for the kind words. Your quite right. It is half a million not half a billion for TESE , a zero too many typo there. To be precise 2-5 hundred thousand according to who you believe. Hell of an achievement for an Explorer mission though. So well publicised and anticipated it’s easily forgotten . We hear a lot about ” mission creep”, increasing costs spiralling out of control as has happened to JWST , though if it operates for a time as with the Sydney Opera House it will be remembered for its achievements rather than costs. WFIRST to some extent has also undergone mission creep but in a totally positive way. It’s gone from a smallish dark energy mission to one of the potential truly great observatories and continues to get better all for $2.5 billion. Such are the foibles of time that it is likely to have a Hubble like lifespan wherever it ends up. Just one last fence to jump, the Presidential budget next year. Decadel will decide on whether it has a chance of a star shade which is dependent on orbit as much as anything and the politics at the time. Such is the progress David Spergel et Al have achieved with internal occulters we may not need the external type long term though short term the smaller IWA of even a 34m device would get into the HBZ. I fully expect the 1e10 contrast to have been achieved by then. The big reason I want an external occulter apart from the obvious eta Earth discovery potential within a decade is that it will require “formation flying” ( over big distances ) which is the requirement for interferometers ,not just for a distant future ” hyper scope” but for an optical NIR equivalent of ALMA and SKA. They are truly great and under recognised devices with fantastic potential .
In terms of VASIMR I agree re nuclear reactors , The Prometheus project was planned to provide for just that but scrapped on cost grounds. Sadly , giventhe political situation described above I fear a nuclear reactor in outer space would be a big no no. Not my decision just my opinion.
Enceladus , Titan , Triton – couldn’t agree more but can’t see how. TiME was only possible because there was a window at the time by which it could transmit to Earth direct . That time has now gone for twenty years and any linking spacecraft adds to the cost enormously. I’ve tried selling a Short lived Cassini carrier and “link” mission with a short lived Philae like lander but even Enceladus ‘ low gravity is too much and even with the time and cost lowering Falcon Heavy it couldn’t be done for less than the New Frontiers $1 billion plus launch budget. That’s the biggest fund after a “flagship” and at present Nasa can mange just one of them per decade with JWST for this and WFIRST the 2020s . The Decadel Survey Science Definition group for 2020 is recruiting this year. As a member of Exo-PAG ( exoplanetary Programme analysis group ) I have good idea of who it’s chairman will be . His plan , which will need ratifying of course ( and how far ahead can one plan accurately ?) is top slicing the annual budget over an extended period to build up $15 billion for the “High Definition Space Telescope , HDST or ATLAST , atlast ! A space bone fide ELT if you will . Lots of water under bridge before than though. The ESA plan to revamp EChO as ARIEL for a 2029 launch. Whether the U.S. Launch a transit spectroscopy telescope before then, to back up JWST and TESS, with the $230 million MIDEX bidding next year is a moot point . Watch that space. I’ve lobbied personally on that one as I have received several editing ideas and offers on that. Can’t say more . The most exciting thing I’ve seen in the New Frontiers pipeline is for round 5 ( the one after next ) with an Io Observer. Once the Falcon Heavy is up and running we may see more exciting missions planned given its big savings on running costs of missions and not just it’s cheaper cost per we. Savings on launchers can also be reinvested in the mission proper though which for Discovery amount too $16 million so presumably more for the double costing New Frontiers. Every little helps. The big area where Nasa loose out to ESA is on material science. They won’t use cheap , lightweight materials like silicon carbide despite its proven efficacy in missions like Herschel and Gaia . The low weight reduces running cost and launching requirements too. Despite being similar dimensions , Gaia with a bigger payload will weigh in at just a third of WFIRST . Politics plays a role with limitations on non US participation in missions to protect US firms who unfortunately haven’t developed silicon carbide to the same degree as European companies yet . That will change I’m sure . No harm lobbying though. Think New Frontiers- $ 1 billion plus launch and say $30 million savings top up, Discovery $500 million plus launch plus $16 million savings and Explorer $220 plus launch plus $10 million savings . That’s what Mars and Venus are so popular, nearby , long lasting and quick results . Insight is a classic example but Falcon Heavy brings .jupiter to within 2 years , solar cell technology negates need for RTG. June gets a year even going the long way round so perhaps if Saturn can be pulled to four or so years away maybe the exciting Enceladus data will get a New Frontiers mission mid next decade. If an international partner like the Japanese, India or Canada ( or all) are pulled in that might just get the funding up to the magical $1.5 billion dollar mark that should make for a decent but shortish lander mission .( orbiter too expensive to slow into orbit round moon ,so as with Huygens it will be as long as the carrier spacecraft stays in radio contact – couple of hours or so). I think we will see ,ore partnership arrangements as the cost of sos e missions is realised . There is a very close Cassini Enceladus pass ( 30 miles or so) next October so expect big publicity on that .
WFIRST has been the big bonus all in all and means what we have had and can expect though not what we all wanted , isn’t at all bad . I’ve been impressed by the innovation going into WFIRST, the astrometry with Gaia in particular is a stroke of true genius and increase TESS’ potency by accurately determining nearby small planets. The big disappointments for me are nothing to Uranus/ Neptune and no guaranteed transit spectroscopy telescope backup to overworked JWST on either side of the Atlantic. I think that thanks to Falcon Heavy and international collaboration we will see atleast something to Enceladus .
Joy-precisely for these reasons it is vitally important that we spread out in Solar System. On Earth there are too many feuds, too much bad blood, too much unresolved conflicts. We need fresh start.
To re-iterate, thanks for a most comprehensive summary of upcoming astronomical missions land and space based.. I’ve shared forwarded links to some of the SKA members and they are most appreciative and impressed with the content. The article actually explains that the ‘Square Kilometre’ refers to its effective filled aperture size, and projects the future potential of a SKA and ALMA with respect to a diluted aperture on the scale of the earth. I find these distinctions are often lost in press about SKA.
With regard to the political comments above, a friendly reminder that we need to stay on topic. Centauri Dreams is not a forum for political discussions, which often turn divisive and, more significantly, take the focus off deep space exploration. This is also stated explicitly in the comments policy, which is designed to keep the conversation on topic.
Thanks Project Studio. I mentioned this to Paul in a private conversation. It’s easy to get distracted by the perceived “popular science ” of JWST and Hubble etc , telescopes that look like telescopes , but forget the truly momentous achievement ALMA and SKA will be and the discoveries they will make. As I said , it would be nice to have a star shade with WFIRST for Eta Earths but it’s even more important long term to have the formation flying in place necessary for a space UVOIR interferometer as that’s the future . Not just bigger and bigger ELTs . An impracticality and impossibility. Interferometers are Versatile to with constant incremental upgrade . ALMAs discoveries of the ubiquity of life chemical precursors like the various cyanide derivatives , increasingly suggests to me that biosgnature are just around the corner and we will find that like itself is ubiquitous in some form or other . Then the race is on to find intelligence ! Admit to a slight conflict of interest of living near Jodrell Bank but it’s scary to know how close it and SKA cane to not happening and the battle those involved put up behind the scenes uncredited . E owe them big time !
BRS. I’m really that confident, slightly tongue in cheek. Bio signatures don’t necessarily mean life of course and there will be arguments over that with increasingly large telescopes producing increasingly large resolution and SNRs and even new signatures , if not chlorophyll’s ‘red edge’ then some other photosynthetic pigments- I’ve just sent Nancy Kiang at Goddard a paper to work up from a Chemist who has created a synthetic chlorophyll that works pretty much over the entire spectral band pass from extreme blue to NIR. My confidence comes from ALMA and other IR imaging that show increasingly the molecular building blocks of life are a common facet of the universe and the commonest readily available elements , Carbon, Hydrogen, Oxygen and Nitrogen are the commonest elements of the life we know ( reworded as to not sound like Captain Kirk) . Just seems a bit coincidental to me . Plenty of reason to disagree of course as any good scientist should -falsifiability and all that ,but that’s my thinking such as it is . MIT are so confident over TESS I think they have their media release already ! Good for them I say. The gauntlet is down…..
The nice thing about interferometer arrays is that the biggest separation between unit imagers gives you your “aperture ” equivalent which is or was certainly about 16 km . “Dilute ” because it isn’t one big solid mirror bit has the equivalent angular resolution though though not so the same light collecting ability or “sensitivity “. That’s what optical interferometer work best on small , bright targets like Active galactic nucleii or Betelgeuse , the first star to be imaged as more than a pint source , star spots and all. You can move the imagers about to different positions and of course as the Earth revolves they move position too, so called ” filling ” in the aperture -making it nearer to a solid telescope and increasing its sensitivity. The differences between points is a baseline with the largest being the “aperture ” and the smaller ones giving higher resolution. The more units , the more baselines ( especially if all different lengths or “non redundant ” . SKA and ALMA are the ultimate diluted apertures . Lots of unit imagers to pump up the sensitivity , lots of baselines and big ones too ( wider than the diameter of the Earth thanks to a Russian Space radio telescope ) to pump up angular resolution. The really clever bit is turning these individual baselines into a visible image. This is done by what’s called ” a reverse Fourier Transform”. You may have seen the name ( a real and brilliant mathematician to realise this- hardly ever heard of outside science circles yet one of the greatest theoretical discoveries of all time ) and wondered what it meant. Basically everything , you , me , ice cream -even Bob Hope , can be expressed as an equation . Complex but possible , each and everything a unique equation. Reverse that equation and you get a picture. Each baseline has an equation , if you put them altogether so their wavelength peaks coincide -constructive interference – and you can create the overall image . That’s how ALMA and the VLBA, very long baseline array and CHARA work. This last is interesting because it is optical rather than radio . The shorter the wavelength the harder it is to produce an image. Long radio waves are converted into “equivalent ” electrical fields and stored up for mixing at a later and convenient time. Their electric fields are weak so easy to manage but when you get down to visible light , nanometers instead of millimeters and the field strengths are enormous , too big for even the worlds most powerful computers to handle …yet. Meantime CHARA works ‘ real time’. Each of its units are connected by a tunnel with mirrors in them that connect each of the units light together – constructively of course- via “optical trains ” and a final “beam combiner” that’s pulls the lot together into a reverse Fourier Transform image. These mirrors pathways are difficult to make and have to be absolutely precise so as not to mess up the interference and even the best mirrors absorb rather than reflect some light. Over a path of multiple mirrors that adds up thus reducing usable light and thus sensitivity . Fibre optic cables are not refined enough to do this job yet but are getting closer. Producing an electric field with a set ratio to the real one , but at lower manageable energy can act as a substitute for individual unit pathways but not the final “beam combiner” . Almost there ! This is a “heterodyne” interferometer and represents the move forwards probably with better fibre optics . Perfect to back up ALMA’s great protoplanetary sub millimeter images with visible of the critical protoplanetary disks exoplanets form from . In space it will be done by Lasers or masers or some other electromagnetic source hopefully allowing big baselines and large “dilute apertures ” . That’s what the aim was for TPF-I. Great idea , twenty years too soon . That’s why we need “formation flying” too as I said , not just for star shades exciting as they would be short term at least . Hope I’ve explained that satisfactorily for any optics or physics experts I know will be watching ! Took me ages to grasp this obscure but vital issue that will only grow and that I’ve made it a bit quicker to grasp than for me ! The mistakes as they say ” are my own.”
Ashley thank you very much for these interesting posts. I didn’t knew about ARIEL-good news.
As to Enceladus, indeed we will see how it goes, but with the wealth of information we are receiving I certainly hope we will see a movement to at least start designing something soon for the next decade.
I hope so ! Looks like the $2 billion of Europa Clipper is the absolute lowest a ” full scale ” mission can be done , by Nasa anyway. Hopefully boosted by nano sats in future. I guess the radiation environment round Enceladus is somewhat better then Europa. Through the plumes too. Orbiter too difficult and expensive , lander much the same though much shorter duration so probably cheaper if you want a Huygens style 2-3 hours of data while carrier/relay above horizon . I I intend to look at Enceladus as I know a number of teams are looking at It now very seriously .
Nasa MIDEX next year. I’m sure we will see atLeast one transit spectroscopy bid . Cowan et al and Nasa Ames published recently on this area proposing a 1m telescope. JPL still have 0.75m FINESSE plans from last time. With the new , enlarged budget plus a free launch to a TESS style near Earth compromise viewing orbit that’s probably doable. Difficult to get beyond gas or ice Giants at the aperture though . If they used Astriums low mass and cheap high quality silicon carbide telescopes ( now have superior rms to proven Euclid ), bolted onto US spacecraft they could probably bump up the aperture considerably to “Discovery” levels ( with a decent band pass too )still within the MIDEX envelope but still remain in non US technology constraints . I know Astrium are very keen to get into the U.S.
This is an outstanding article. My thanks to the editors for publishing it.
On another note, I read somewhere that old space probes were being retasked by colleges and private firms to do research beyond their original missions. I would appreciate an article on the possibility of using older probes for some of the work mentioned in the above article as well as what probes are viable for retasking. In addition, not to be that guy, but I wonder if new mission launches are designed to be more ECO FRIENDLY to reduce the amount of NEO space junk. It would be a shame for space junk to collide with a brand new multi-million dollar probe.
Enceladus seems the names on everyone’s lips. The various mission options were commissioned from the Goddard Space flight centre for the Nasa Planetary Science division in the 2007 “Enceladus flagship concept study”.
Long but readable. 2006 prices but the comparisons are the same and with a Falcon Heavy many of the costs will be reduced by a much shorter flight time ,reducing the operations and engineering ” running” costs that get forgotten. Again as with Europa Clipper, the multiple fly by option is cheapest high science return and despite distance the lower radiation means it comes out at THAT figure again: $2 billion. Google it and see. A hunred and fifty pages but very readable and good education tool for obstacles facing deep space planetary missions ( hopefully minus one soon thanks to “Heavy” – no more multiple sling shots and long ” round the houses” journeys .
Lots of concepts being developed for “cleaning up space “.not just to be ecofriendly but to make it safer. Lucy Rogers of “it’s only rocket science ” fame is heavily into that and her website will have plenty to say on the matter. First part if problem is identifying it all. Luckily Congress have made it a priority for Nasa to find all potentially dangerous “Near Earth objects ” and the technology. Works nicely to spot space junk too. Then it’s out with Space vacuums . Not so much Dyson spheres as Dyson Hoovers !
Let us not forget the planet with the name that teenage boys and those with that mentality still find amusing:
This was an incredibly thorough article, thanks Ashley for writing it! I only finished my first pass of it this morning, and it took me a couple of sittings to digest all the info. I will definitely be re-reading the whole article later.
For follow-up discussion, how about we consider potential game changers? Here are a couple of obvious potential upsides:
-SpaceX’s reusable rockets and the potential further cost reductions they could bring haven’t been mentioned here yet, unless I missed it.
-Cooperation between the Chinese and Indian space agencies with the currently collaborating trio of NASA/ESA/JAXA would add extra resources and could substantially reduce costs. The indian space agencies’ mission to Mars that arrived in the same week as MAVEN cost just a tenth of the latter mission, and a huge chunk of that was R&D staff and operational stuff costs
The most obvious potential downside is the risk of another global financial crisis
I appreciate the comments regarding a probe going out to Saturn’s neighborhood – Enceladus and Titan in particular. Super high radiation levels may make human crewed exploration around Europa and Jupiter more dicey. While the Saturn explorations are no cheap and easy walk in the park for either unmanned or human space exploration, I suspect that Euceladus and Titan may eventally be easier for human boots on the ground so to speak.
I’ve spoken to several scientists this week about missions , to Enceladus in particular . I think Paul has something exciting lined up in that direction for everyone to whet the appetite ….so watch that space . It’s not a well known fact but non U.S institutions can bid for US funding pots like New Frontiers . The mission just has to have a high US technological contribution to keep US business and Congress happy. It can also be topped up with partner organisations . JAXA and the Canadian Space Agency are the big two at present . Im sure they helped make WFIRST possible with generous contributions . It wouldn’t take much from them . Plus some lightweight , cheap European silicon carbide composite ,combined with Space X rockets and Enceladus becomes doable . Silicon carbide is the the real deal and if Nasa embraced it as the ESA phave then a $1.5 billion mission to Saturn becomes realistic .Reusable technology is great though not yet matured , but it does lower payload as well as cost which and for a Saturn mission of substance this is important as The Falcon Heavy payload , non reusable to Saturn ,is about 5 tonnes which is just enough with low mass silicon carbide material to allow carriage of the large amount of propellant required for orbital manoeuvres . There is even talk of solar power but the array would need to be enormous and add to an already near the margin mass. So it’s RTGs if any are available. Hopefully we will see Cube sats or a Titan Balloon deployed for the first time too, massively increasing mission science at little extra cost and eminently possible away from .Jupiter’s infernal radiation . Lots of options. I think next Octobers 30 mile Enceladus Cassini pass designed to go right through the southern plumes will decide what happens next . I’m sure there will be lots of coverage .Watch that space .
Uranus/Neptune . Always the bridesmaid, never the bride. Always in Decadel but never high up enough as au say in the article in a great lament, so much to learn about the commonest planet type in the galaxy. On our doorstep yet TESS/JWST and WFIRST will probably tell us more about such planets first in other systems. It may even be that a 16m 2035 ATLAST will be the next time we get an information boost on Uranus and Neptune. I suppose the only realistic option would be a New frontiers funded Falcon Heavy launched flyby, perhaps aided by Cube sats , but nothing Even on the provisional list for New Frontiers 4 and 5. Just ODINUS unsuccessfully for the ESA L round. Doomed by the previous selection of JUICE , giving cosmology its chance in subsequent rounds.