Eyes Turned Skywards, Part IV: Post #21
Even as their colleagues elsewhere were fighting to keep the Pioneer program going, the scientists and engineers working on the Hermes Mercury orbiter mission were steadily working towards their mission’s launch. Optimistic and aggressive early projections of launching in 2005 had run into the cold--or in this case, hot--reality of dealing with the harsh environment of Mercury orbit and forced a slip, but after recalibrating expectations mission development was going smoothly and on-time. The largest impact had been the addition of an Earth flyby before beginning the main flyby sequence to reach Mercury orbit, an optimization that permitted a slip of only seven months instead of nearly two years to the next Venus launch window. This would, admittedly, increase mission duration and risk, but the extra time would be spent in a relatively calm and quiet region of space, hopefully keeping the spacecraft safe and operational.
Unfortunately, budgetary impacts were not so limited; as the first and possibly the only spacecraft to reach Mercury orbit for some time, the Hermes proposal had included a relatively large number of instruments in order to probe the entire geophysical environment of the planet. Although most of the instruments had been relatively well understood and developed, the complications of modifying them to deal with the Mercury environment and integrating them into the spacecraft had proven more difficult than expected, another reason for the mission’s slip. To avoid further delays, additional funds were poured into the project, one of the factors behind the delayed 2006 mission selection. Although effective at keeping the program on-track, the cost growth of the mission had led to questions during the reorganization of the Pioneer program about whether it was meeting its goals of enabling cheap, rapid exploration, despite the spacecraft’s successful launch only a few months after the cancelled selection.
As NASA organized an abbreviated selection in 2007 to compensate for the cancellation of the 2006 selection, the board responsible was acutely aware that future Congressional support could very well be riding on whether the mission they picked was a successful exemplar of the program’s purpose or bloated and delayed by unexpected cost growth and technical issues. In a stroke of what could be called fortune, however, all of the proposals for the 2007 selection were repeats of proposals from the planned 2006 selection, as it was not possible for other teams to assemble their proposals fast enough to meet submission deadlines, and in turn were usually submissions of proposals that had previously gone through at least one Pioneer competition, since only larger, better-resourced teams could invest in suddenly updating their proposal documents to account for the new date. As a result, when the board met to consider its choices, it was selecting from a list of well-studied missions with extensive costing data, leaving very few unknown unknowns to anticipate. Even with this confidence, however, the selection of the Mars Polar Lander, or MPL, indicated that the board was breaking for the safe choice over more adventurous alternatives.
Proposed in every competitive Pioneer selection from 1999 onwards, MPL was exactly and precisely what its name indicated, a fixed lander, like the Vikings, designed to land near one of the Martian poles and investigate the near-polar environment of Mars. Landing constraints on all previous Mars missions, whether Soviet or American, had prevented spacecraft from landing near either pole, a disappointment to scientists who wanted to explore the only polar ice caps in the Solar System aside from Earth’s. Besides being interesting subjects of exploration in their own right, their growth and shrinkage over the course of the Martian year has a measurable impact on the Martian atmosphere, with nearly a third of the atmosphere’s entire mass freezing out during winters and sublimating back into gas during the spring, piquing the interest of climatologists, while they are surrounded by and contain many complex and interesting geological structures, like layered terrain and underground water ice deposits. An offshoot of the pre-Pioneer Mars/Phobos ‘98 Ares Program mission proposal, which was ended by Gore’s election and reorganization of Project Constellation, the JPL-led spacecraft would land during the northern summer, spending several months exploring the weather and surface of a polar site before dying as temperatures plunged with the onset of winter.
Although the mission had seen a great deal of study and refinement in the decade and a half it had taken to go from proposal to selection, and promised to stick to well-understood technology and well-understood risks, for this very reason its selection immediately saw criticism from some corners of the planetary science community who thought it showed a stodgy, conservative attitude completely at odds with the purpose of the Pioneer program. Probes like Barnard, still three years from its encounter with Comet Encke, or Hermes, about to flyby Earth on the way to Venus, had pushed the envelope, venturing to new places and daring to do new things that would be impossible with more expensive missions. A spacecraft that would recapitulate probes from thirty years earlier hardly had their air of romanticism and exploration, even if it was venturing to a new destination on Mars; even, perhaps especially, if it was a firmer budgetary and schedule choice than more adventurous missions. Nevertheless, most members of the community, aware of the criticism that had been leveled at Hermes, understood NASA’s desire to stick to the tried-and-true, and lined up behind the selection, leaving the critics as persistent gadflies, but nothing more for the moment. As work at Pasadena got underway, however, and attention elsewhere turned towards the next selection, their position would become increasingly important and influential.
Thus, as the next set of Pioneer proposals began to roll in the next year, the attitude of the selection board had moved from sheer conservatism towards an attempt at blending careful conservatism and adventurousness in a single mission, much like Hermes had done. Although selecting missions unlikely to overrun their estimated budgets was important, so was a sense of adventure. Accommodating both of these desires was difficult, with many worthy missions at hand, but ultimately the board decided that the best balance for the 2009 selection was offered by the Venus Atmospheric System Explorer, or VASE, mission, an update of 1978’s Pioneer Venus Multiprobe mission to meet a new era of technology and a new set of scientific questions. By using a well-understood mission profile and operating inside the envelope, the board felt that it posed few financial or schedule risks, while at the same time it offered attractive prospects for novelty by traveling to one of the harshest planets in the solar system, and one that no American spacecraft had traveled to in fifteen years.
VASE itself had grown out of a series of studies and mission concepts developed by the Venus science community since the demise of VOIR, which had developed a consensus that the most important questions about Venus concerned its atmosphere. Despite the Eos Franco-Soviet balloon mission of the early 1980s, the Pioneer Venus multiprobe mission a few years earlier, and even earlier Soviet atmospheric probes, much was still unknown about the structure and fine composition of the atmosphere, and therefore about the history of the planet. Compared to orbiters like the recent Japanese Akatsuki and Chinese Jinxing spacecraft, atmospheric probes could explore the denser, higher-pressure region under the cloud deck, providing otherwise unobtainable information and complementing orbital observations. Similarly, a modern balloon mission, using more advanced electronics and equipment than the old Eos mission, could provide more information on the atmosphere in more places at the same time. Despite this scientific attraction, atmospheric missions were also much less ambitious than many of the alternatives, avoiding the harsher regions of Venus or the need to survive them for long periods of time.
However, even lower ambition only went so far in reducing cost and schedule risks. Although the Venus Exploring Inflatable Lifter, or VEIL, mission had proposed a Venus balloon and at first glance seemed a strong competitor to VASE, it had been heavily compromised in order to fit in the Pioneer budget box. Venus scientists wanted multiple balloons at multiple latitudes and longitudes in order to track wind currents at different locations on Venus, grist for the mill of computational models that they could then use to extend their observations to the rest of the atmosphere. In addition, they wanted the ability to track balloon movement anywhere on the planet, in turn requiring a communications relay orbiter for when the balloons were inconveniently on the side facing away from Earth. Together, this meant much higher costs, in the range of a Cornerstone mission, so that VEIL had pared the mission back dramatically, only delivering a single balloon with no communications relay satellite. Although this managed to reduce the mission’s projected cost to acceptable levels, it also reduced its scientific value so much that it hardly seemed worthwhile any more, while still throwing up a number of red flags for potential overruns and schedule slips in the making. As much as many people wanted the Pioneer missions to push the envelope, they could only push so far. Ultimately, even one balloon had proved a bridge too far for Pioneer’s budgets, and VEIL had lost out in favor of VASE.
For more ambitious missions, scientists would have to look towards the Planetary Science Prioritization Panel, or PSP^2, as it began working on its legally-mandated report on the future of planetary science soon after the selection of VASE. Since the 1960s, the National Academy of Sciences COMmittee on Planetary and Lunar EXploration, or COMPLEX, had periodically produced reports on recommended future planetary science missions, many of which had eventually been flown, but in a haphazard and demand-driven process. Unlike other expensive fields like particle physics, nuclear physics, or astronomy, there was no statutory structure for providing recommendations to guide and shape NASA’s planetary science program, with the result that it had evolved to launch missions based at least as much on political as scientific criteria. This had worked well in the afterglow of Apollo and the Vulkan Panic, when relatively loose budgets had permitted a wide-ranging and pioneering program of exploration, but had become ineffective in the more straitened circumstances of the 1990s. One of the primary recommendations of the Cornell Plan had been to establish a permanent advisory body like the Particle Physics Project Prioritization Panel or Nuclear Science Advisory Committees advising the Department of Energy and National Science Foundation on their fields, but for planetary science. This body would be responsible for regularly providing a list of recommended missions to NASA, which the agency could then choose from. With its establishment by Congress, PSP^2 was now beginning to draw up its first report with the development of studies on a wide range of possible missions and destinations by specialized panels including many of the most distinguished scientists in the field. Each of the five major groups of target bodies--terrestrial planets, Mars, gas giants, icy bodies, and minor planets--had its own survey panel, along with “interdisciplinary” survey panels covering technology development and supporting infrastructure. Over the course of the year, PSP^2 sorted out the responsibilities of the panels and began a concerted program of community outreach, even as the panels, in turn, began to write up their own studies for the main committee.
As the first drafts of the panel studies began to come in later in the year, it became clear that PSP^2 would, at least, not suffer from a lack of mission possibilities to choose from. Over two dozen serious proposals had been mooted and studied by the target panels, ranging from a large mission to follow up Hermes and perhaps even attempt a landing on Mercury’s surface to an ion-propelled, Saturn Heavy-boosted spacecraft that would zoom past Jupiter before screaming out into interstellar space at a clip far exceeding either the Voyagers or the earlier Pioneer probes. Along with the variety of missions, cost estimates fluctuated wildly: the proposed Mars Geophysical Network came in only a little above the Pioneer cost cap, while others, like the behemoth Neptune-Triton System Mission, promised to break Cassini’s three billion dollar record and become the most expensive planetary mission in NASA’s history. With such a wide range of proposals, the most pressing question had become how to evaluate and rank so many missions.
Even as PSP^2 was considering how to manage the flood of proposals, MPL’s launch window was finally rolling around in October 2009, over half a year since VASE’s approval. Fitting for a mission that had fifteen years of design heritage behind it, it had experienced few difficulties in development, with comparatively smooth sailing on all fronts whether schedule or budgetary. Launch was equally smooth, though marked by a major first for the space program; instead of the traditional Deltas or Saturns, MPL was lifted into orbit by a Star Launch Thunderbolt, with a solid third stage attached to the spacecraft’s aeroshell completing the injection to a fast Mars-crossing trajectory that would reach the Red Planet in just six months instead of the usual eleven, so that MPL would reach the Martian north pole just as spring was turning into summer. The successful launch marked the first time that a NASA planetary science mission had ever been launched on a reusable vehicle, and a significant cost savings compared to more conventional vehicles. After launch, MPL settled into dormancy as it cruised towards Mars.
While one of the most recent Pioneer missions was nearing Mars, one of the oldest was finally reaching its destination after an epic, decade-long journey. Although reaching Encke had been time-consuming, the reward was sweet, as after multiple flybys of Venus and Earth to pump down the spacecraft’s orbital energy, Barnard became the second spacecraft in history to land on a comet in March of 2010, a month after reaching and putting itself into orbit around Encke. After a tense landing sequence, punctuated by a brief scare when it appeared that the mechanism designed to anchor the spacecraft to the comet had malfunctioned and Barnard had bounced back into orbit, it quickly set to work. Although the first images sent back from the lander showed jagged spires of relatively solid rock and other materials jutting ominously out of the comet’s surface, leading commentators to compare Encke to Mordor from J.R.R. Tolkien's Lord of the Rings books, further exploration over the next few weeks showed that this outwards appearance was only a surface illusion. Instead, most of the surface was covered in a thick, refractory layer of rocky dust, extending tens of centimeters into the comet and protecting its icier core from the harsh conditions of space, making the comet a kind of “icy dirtball,” as Helios-Encke some thirty years earlier had indicated. Barnard also built on Kirchhoff’s data on Tempel 2, showing that Encke-type comets also had little if any intrinsic magnetic field and an elevated level of “heavy hydrogen,” deuterium, compared to ordinary hydrogen, providing more evidence against the theory that cometary impacts had supplied most of the Earth’s water.
Just a month after Barnard touched down on Encke, MPL entered the atmosphere of Mars, streaking through nearly cloudless skies before safely descending to a landing point near the planet’s north pole. In a spectacular example of inter-agency cooperation, Japan’s Hayabusa[/] orbiter, which had only recently reached the planet itself, managed to successfully image the probe while it was descending under its parachute, the first time a spacecraft around another planet had recorded another, let alone while it was passing through the atmosphere. After this high note, MPL’s mission continued from success to success, with the probe’s robotic arm quickly revealing hoped-for evidence of water ice just under the Martian surface and the chemistry lab definitively confirming that perchlorates, believed to be responsible for Viking’s inconclusive biological results, were present in Martian soil. Although a blow to those few who hoped life might be present there, most scientists were pleased that this mystery had finally been definitively resolved, and focused more on the geological and climatological implications of MPL’s other data. MPL’s meteorological suite also provided important information on ground-level conditions near the Martian poles, complementing Viking and Mars Traverse Rover point data and orbital observations of the entire globe to help build refined atmospheric models, both of Mars and of Earth. After nearly six months of observations, MPL finally succumbed to dropping temperatures and dimming sunlight as Mars neared its autumnal equinox, shutting down for the final time in late September of 2010. Hayabusa observations of the site showed that dry ice formed around and over the probe that winter, as expected, and most likely destroyed MPL’s solar panels from having to support excessive, beyond-design weights. Between that and cold damage to the electronics, the spacecraft was permanently disabled, explaining why attempts to revive the spacecraft during the next Martian summer in summer of 2012 were unsuccessful.
Meanwhile, PSP^2 was nearing the completion of its final report after a long sequence of community outreach events, communications with NASA and other space agencies, and internal studies. Based on the scientific priorities it had drawn up with involvement from the wider planetary science community, the panel was generating a list of broad recommendations supplemented by a ranking of mission proposals according to cost and scientific value. Finally, after nearly two years of work, it published its draft final report in early 2011, prompting a final round of feedback before the publication of the final report that summer. As might have been expected after the Cornell Plan, it urged NASA in the strongest tones to launch at least one larger mission over the next decade and continue the Pioneer program with a cadence of one mission selection every other year, along with establishing an intermediate-cost program for missions like the Mars Geophysical Network or Venus Atmosphere Circulation Mission that were too large for Pioneer but, at least in the judgement of the committee, too small for a full-scale Cornerstone mission. Additionally, it recommended that NASA establish an ongoing technology development program rather than leaving it up to each individual mission to pay for whatever new instruments or technologies that it might need, and for NASA to seek more international partnerships with other space agencies. Finally, for the next Cornerstone mission the committee recommended that NASA immediately begin work on a Europa Orbiter mission, especially if further study could reduce the estimated price tag, followed by a Mars Sample Return campaign later in the decade.
Crucially for this recommendation, icy moons and Mars scientists had held the balance of power on PSP^2 and in the wider community; the United States had launched more missions to Mars than to any other planet or heavenly body aside from the Moon, and Galileo and Cassini’s missions to Jupiter and Saturn, respectively, had maintained a healthy community of scientists interested in Europa, Titan, Enceladus, Triton, and other, similar bodies. Compared to the relatively small and marginalized Venus or ice giants communities, icy moons and Mars had a large number of advocates able to push their case and develop mission concepts, while being simpler in a number of respects than missions to these other locations. Additionally, Mars and icy moons had built-in public relations advantages; Mars had been the destination for interplanetary spaceflight of any kind for over a century, while the icy moons, especially Europa, were widely regarded as the most likely place for alien life to exist in the solar system, both tempting attractions for the public and for planetary scientists. Although advocates of other destinations could make powerful arguments in their favor, they lacked the sheer magnetic draw of Mars or Europa as destinations, and had fallen behind in advocacy despite their best efforts. The result was a compromise between these two groups, based on the fact that the Europa Orbiter would be a cheaper and simpler mission than the multi-mission Mars Sample Return campaign JPL had envisioned since the 1980s. Combined with their recommendation of an active Pioneer program, which could easily support smaller Mars missions, Venus missions, and minor planets missions, and an intermediate category that could cover larger and gas giants missions, the final report had something for just about everyone in the planetary science community, thus preserving the unified voice that had led to the creation of PSP^2 in the first place.
While Congress had already approved and funded an ongoing frequent Pioneer program, the board’s other recommendations would require approval from the Hill, so that the publication of the report in early 2011 only marked the beginning of a new advocacy campaign. As they had in previous years, planetary scientists alternated pilgrimages to Washington with work in the lab focusing on addressing Congressional concerns with their recommendations. Despite the estimated cost of a Europa mission, Congress proved receptive to the idea of a new mission focused on Europa’s postulated under-ice sea, perhaps inspired by the idea of discovering alien life, though they had concerns over the cost. Despite being operationally simpler and having a projected cost less than Mars Sample Return, the Europa Orbiter was still expected to cost considerably more than Cassini, a result of the complex mission requirements, the difficulty of reaching Europa orbit, and the extremely harsh conditions of near-Jovian space, especially the radiation environment. Prompted by these Congressional concerns, interested scientists refined the mission concept, dredging up an idea from the early days of Europa mission planning in the 1990s to have a Jovian orbiter make many Europa flybys instead of actually putting itself into Europa orbit, thus reducing the amount of propellant needed and simplifying the mission. Moreover, by spending only brief periods of time deep inside the Jovian radiation belts instead of being forced to continually reside in them, the lifetime of the spacecraft could be greatly increased and it could perform some incidental science focused on the outer moons Ganymede and Callisto, and on Jupiter itself. NASA study of the concept also showed that this option’s impact on science would be minimal or, in some cases, actually positive compared with the orbiter option, while the cost of the mission could be slashed by more than half. With such positive results, Congress approved a new start on the Europa Systems Mission, or ESM, last year, with a Saturn Heavy launch planned to boost the probe towards Jupiter in 2019 or 2020.
In the meantime, however, other new recommendations by PSP^2 suffered. Despite the panel’s strong insistence on a new intermediate-class program to fill the gap between cheap Pioneer missions and expensive Cornerstones, Congress proved cool to the idea and it was dropped by advocates shortly after the report’s publication, as were the establishment of a stable technology development budget line and the creation of a budget line for supporting data archiving and release and facilitating the development of new planetary scientists. Even the projected Mars Sample Return mission suffered, with serious study work not beginning until after the approval of ESM in 2014, and no flight now expected until the mid-2020s at best, possibly slipping mission completion to the late 2020s or even the early 2030s at earliest, about when some of the more optimistic recent projections put humans on or around Mars.
On the other hand, the Pioneer program has continued from success to success; even as PSP^2’s final report was being published, the Pioneer selection board announced that it had chosen the Mars Ice Orbiter, or MIO, for launch in 2013. Building on the detection of ice at MPL’s landing site, MIO is designed to use a ground-penetrating radar system to detect ice all over the planet, expanding MPL’s observations towards a global inventory of Martian subsurface ice. Since its arrival last year, MIO has been aerobraking into its final observation orbit, which it is expected to reach in October. In the 2013 selection, the selection board opted to return to the minor planets by choosing the Comet Tour mission, a multi-flyby spacecraft utilizing electric propulsion to visit several cometary nuclei to compare them with Encke and Tempel 2 and build a broader baseline of cometary properties for comparative paleontological analysis. Data from 2010’s private NEOSearch spacecraft has been very useful for constructing a target list, and launch is scheduled for later this year. Most recently, this year’s selection broke the pattern of alternation between Mars and other targets that had been beginning to draw some criticism from planetary scientists, instead opting for the Aeneas mission to the Trojan asteroids. Clustered before and behind Jupiter in its orbital path, the Trojans are believed to be relatively volatile-rich remnants of the early solar system, and windows into our solar system’s past, so that Aeneas may shed important light on the formation of the gas giants and other outer system bodies.
Farther afield, planetary scientists are already gearing up for the next PSP^2 survey, expected to begin in 2019, and for the Mars Sample Return mission planned for the next decade. Recent MSR studies have shown a need for at least one precursor mission, given the large, sophisticated rover planned for use in gathering samples and the complexity of precision landing on Mars, so that support is growing for a large rover mission in the early 2020s, following the launch of ESM, while cost issues have led NASA to approach ESA, Roscosmos, and JAXA about cooperating on the sample return itself. The idea of creating an intermediate mission class has also returned, though as of yet it lacks significant Congressional support. Nevertheless, should their new process continue functioning, the future of planetary science looks brighter than it has in decades, with a steady stream of missions set to head skywards and explore new--or old--worlds.