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solar sail illustration
Solar sail technology, still in its early phases of development today, could support missions to the far reaches of the solar system to allow for direct imaging of exoplanets.

Future exoplanet missions: NASA and the world (part 2)

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The lessons of SIM

SIM was a mission endorsed by two decadal surveys. These endorsements led to a project start in 1997. Over the next decade, SIM progressed through phases A and B, preliminary analysis and definition. On the brink of entering Phase C, or design, in 2005, the NASA administrator decided to disregard those decadal directives and put SIM into limbo. The space agency was faced with a Space Shuttle program that was struggling to return to flight, a proposition that was taking longer and costing more than anticipated. In addition, the Constellation human spaceflight program was gearing up. These two fiscal burdens convinced NASA administrator Mike Griffin to “borrow” funds from the space science division. Those funds have never been returned. Faced with a constrained budget, NASA chose to cut SIM’s funds to the bone. Congress intervened and ordered NASA to continue with SIM. The project continued for five more years, bravely using its trickle of funding to buy down risk. In spite of the odds, the SIM team developed the technology needed to fly the mission. In fact, the technology was so advanced that they were able to propose a faster, better, cheaper version of the original design. This was the SIM-Lite spacecraft. After the expenditure of $600 million, this mission was technologically ready to proceed to construction. Nevertheless, the axe came in 2010, with the recommendation from the latest astrophysics decadal survey, Astro 2010, to discontinue SIM-Lite. What is telling about this event is that the fate of a major exoplanet project was decided by a committee of astronomers with a marginal interest in exoplanets.

There has been no comment in the media about an unusual aspect of Astro 2010’s final report. There were several panels reporting to the main decadal committee. The Electromagnetic Observations from Space (EOS) panel was set up to prioritize space telescope missions. Future exoplanet missions were included in that category. Comments from their report to the executive committee are revealing. When treating the subject of which exoplanet mission NASA should pursue in the coming decade, their comments included the following:

  • “The panel is enthusiastic about one such program, SIM Lite.”
  • “A mission like SIM-Lite would be the current best choice for a new exoplanet mission.”
  • “In the independent cost-appraisal process of Astro 2010, SIM-Lite was judged to be low-risk and technically ready for Phase C.”

These quotes give a taste of the positive appraisal of the SIM-Lite project by Astro 2010’s space telescope expert panel. In addition, the EOS panel essentially endorsed the findings of the Exoplanet Task Force, or EPTF. This was an effort by the exoplanet community to define their mission priorities. It was conducted two years before the Astro 2010 Decadal study was launched. The EPTF involved extensive input from the exoplanet community and was in many ways the exoplanet’s version of a decadal report. The resulting report, “Worlds Beyond,” stated that an astrometry mission such as SIM was the exoplanet community’s number one priority.

The fate of SIM serves as a cautionary tale for future exoplanet projects. If SIM could be cancelled, then no exoplanet project is safe.

Besides what Astro 2010 had to say—or not say—about SIM, there is the question of whether the fate of SIM should have been part of Astro 2010’s purview. It seems that this practice has caught the attention of Congress. In language accompanying this year’s appropriations bill, the Senate made its concerns known. Under the “Decadal Surveys and Mid-Session Reviews” heading, the Senate stated that, “once NASA has committed to a mission with an executable funding profile, the Committee does not believe mid-session reviews and other management tools that serve to undermine established missions with broad consensus within their scientific discipline do anything more than unnerve the scientific community.” These are frank observations. The Committee also encourages NASA to focus its efforts so that it can meet its commitments. This strong language is perhaps the committee’s reaction to NASA’s mismanagement of SIM-Lite.

These additional details on the saga of SIM are not being presented in order to argue for its reinstatement. That train has already left the station, and NASA now has its focus on a direct imaging mission. However, these events should be brought to the attention of the wider space community, and perhaps to many in the exoplanet community who were not aware of the EOS Panel’s endorsement of SIM. Even more importantly, the fate of SIM serves as a cautionary tale for future exoplanet projects. If SIM, a mission that had progressed through Phases A and B, had an investment of $600 million of technology development, and had passed all engineering milestones with flying colors, could be cancelled, then no exoplanet project is safe.

other solar system illustration
Missions like those discussed here could turn illustrations like the above eventually into actual images.

The need for an Exoplanet Exploration Division

That is, they are not safe as long as exoplanet exploration remains within NASA’s Astrophysics division. Perhaps the best thing that John Grunsfeld, NASA’s associate administrator for science, could do for exoplanet exploration is to create a separate division for it. Right now, this line item is contained within NASA’s Astrophysics Division. In that division, exoplanet exploration occupies a very small wedge. Its budget of $40 million per year is 4% of the Astrophysics budget total of $1 billion (including JWST). This corresponds to only 1% of NASA’s total Science Mission Directorate budget, or a quarter of a percent of NASA’s overall budget. If exoplanet exploration remains in Astrophysics, then it will get nowhere. There are many priorities in Astrophysics that have a higher priority for funding, not the least of which is JWST. After its launch, the dark energy mission WFIRST received the Astro 2010’s endorsement to be NASA’s next astronomy priority. In addition, NASA must fund the de-orbiting of HST later this decade. That effort, with a required backup, will likely cost $200–400 million. In that budget environment, there is little chance that astrophysicists will allow exoplanet exploration to grow, let alone use up a precious flagship slot for an exoplanet mission. If NASA wants to make real progress in this field, it must set up an Exoplanet Exploration division equal in status and importance to the Astrophysics and Planetary Science divisions. This should be done immediately. To get things moving, this new division could be started with a budget of $200 million.

This level would support a robust investment in New Worlds technology, allowing technology development to begin early and in earnest. Within a few years, as the budget for JWST ramps down, the budget for the Exoplanet Exploration division could be increased to $500 million. That funding would then begin to approach the commitment that this new field of science demands. This money could be phased in with contributions from the other science divisions, or with a return of the funds that human spaceflight “borrowed” in 2005. Even at that level, Exoplanet Exploration would still be the lowest funded level in the Science Mission Directorate. Besides funding, the other benefit of an independent exoplanet division is the issue of priority. An independent division, with a budget of $500 million would be able to launch significant exoplanet missions. Also, an exoplanet division could conduct its own decadal survey. Instead of relying on decisions made by a mostly disinterested group, the exoplanet community would have its peers judge the priority of planned missions.

Even though the subject of exoplanets is very popular with the public, there is little appreciation for how little money NASA invests in this area.

An independent Exoplanet Exploration division could also be given the task of managing the very first robotic interstellar missions. In 2011, Geoff Marcy proposed a robotic mission to Alpha Centauri by the end of this century, as a way to focus high technology efforts at NASA and to serve as an inspiration for the next generation. It is a daunting challenge. To prepare for such a mission, an Exoplanet Exploration division could fund pioneer interstellar missions that could begin sometime in the 2020s. In fact, a group of engineers, affiliated with The Planetary Society, has already proposed a roadmap of increasingly capable interstellar pathfinders utilizing the technique of solar sailing (see “Mind Expansion”, The Space Review, November 21, 2011; “Stepping Lightly to the Stars,” The Planetary Report, March 2012). Both The Planetary Society and NASA’s Office of the Chief Technologist are working on projects to test fly these sails. Crewed “world ships” may come someday, but in the meantime, a robotic interstellar pioneer can be launched with technology that is available today, or will soon be within reach.

As we review these exoplanet missions, it is good to keep in mind the daunting challenges involved in detecting, let alone traveling to, planet-sized objects at interstellar distances. If our solar system was shrunk down in size so that the distance from the Earth to the Sun was 1 foot (30 centimeters), then the nearest star system, Alpha Centauri, nearly 4.4 light-years, would be more than 52 miles (85 kilometers) away. These interstellar pioneers could use a closer target as their first milestone. At a distance of only 500–600 AU lies a virtual sphere around the Sun at which visible light is magnified by the bending of space caused by the gravity of the Sun, per Einstein’s general theory of relativity. This is the same principle that is used in microlensing. In this case the Sun’s gravity acts as a lens that provides an astonishing degree of magnification. Theoretically, with a space telescope at 550 AU, one could image fine details on nearby exoplanets. For example, at the distance of Alpha Centauri, the resolution would be an almost unimaginable one meter! In addition, the spacecraft need not stop at 550 AU since the virtual lens begins at that distance and continues outward.

However, there are several hurdles to obtaining such images. First, a telescope would have to “fly around” the focal line, i.e., “raster scan,” in order to assemble an image. This may necessitate using a swarm of micro-probes to image a collection of “pixels.” Second, the target planet must be lined up with the Sun. We would need to know which one of the nearby worlds would be the best target because only one target is visible per mission, since the mission’s trajectory must lie on a line through the Sun and the target planet. NEAT or New Worlds would find that target. An Interstellar pioneer need carry only a modest telescope to ascertain if the Sun’s gravity lens can provide the high-resolution images predicted by theory. If this proves to be feasible, then later missions can attempt to gather a more complete image of a distant Earth.

hree decades ago, Carl Sagan—the patron saint, if you will, of exoplanet exploration—envisioned the future of that quest. Sagan described them as “beckoning worlds.” They beckon still.

Then, there is the issue of public awareness of the struggles for funding for exoplanet missions. Even though the subject of exoplanets is very popular with the public, there is little appreciation for how little money NASA invests in this area. This is in contrast to the planetary science community. When NASA’s planetary science budget was targeted for massive cutbacks this year, there was an outcry from both planetary scientists and the public. Congress has reacted to this public pressure and has restored some of the cuts proposed by the Obama Administration.

However, when the SIM project was terminated at the end of 2010, the silence from the media was profound. In addition, there was little, if any, protest from the exoplanet community. As a result, Congress essentially gave no attention to the dire condition of exoplanet exploration. It is difficult enough to get Congress to act, but, if there is no evidence to the contrary, then Congress will usually assume that there is no need for action. This lack of interest is reflected in the near-zero level of funding for this effort. Steve Squyres has remarked that the appearance of disunity, disarray, and disagreement will give the Congress reason to go after a program’s funding. He was speaking of planetary science, but the same applies to exoplanet exploration.

In closing, it is sobering to consider that today’s exoplanet researchers are truly modern Columbuses. The nearby Earths that they should discover in the next decades will be the frontiers that will be explored by our descendants for centuries, either in person or by proxy. However, like Columbus 500 years ago, today’s torchbearers struggle to find the funding necessary to achieve their dreams.

Three decades ago, Carl Sagan—the patron saint, if you will, of exoplanet exploration—envisioned the future of that quest. Years before the discovery of the first exoplanet, his TV series Cosmos presented accurate forecasts of what would be found. He proposed that our type of solar system wasn’t the only design possible. He accurately forecast the discovery of “hot Jupiters” as well as systems that had jovian planets intermixed with terrestrial worlds. In addition, he foresaw that direct imaging by using a starshade and indirect detection via astrometry will be the way that our civilization will find nearby twins of our home world. Sagan described them as “beckoning worlds.” They beckon still.


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