The recent burst of interest in interstellar flight has surely been enhanced by the exoplanet discoveries that have become almost daily news. Finding interesting planets, some of them with the potential for water on their surfaces, inevitably raises the question of how we might find a way to get there. We can only imagine this accelerating as missions like the Transiting Exoplanet Survey Satellite (TESS) and the James Webb Space Telescope begin to fill in not just our inventory of nearby planets but our understanding of their compositions.
Find a terrestrial class planet around another star — we may find that there is more than one around the Alpha Centauri stars — and the interstellar probe again becomes a topic of lively conversation. Breakthrough Starshot, the hugely ambitious attempt to develop a concept for tiny payloads being delivered through beamed laser propulsion to a nearby star, is by now a major part of the discussion. And as I said in my closing remarks at the recent Tennessee Valley Interstellar Workshop in Huntsville, there is a synergy among these developments.
Here’s a bit of what I said in Huntsville:
The emergence of Breakthrough Starshot clearly changes the game for everyone in the interstellar community. We have a congressional subcommittee report that ‘encourages NASA to study the feasibility and develop propulsion concepts that could enable an interstellar scientific probe with the capability of achieving a cruise velocity of 10 percent of the speed of light.’ I doubt seriously that that phrasing would have emerged without the powerful incentive of the funding provided by Breakthrough, nor would the Tau Zero Foundation’s recent grant.
Let’s take this apart and look at the pieces. We all know that Breakthrough Starshot lit up media coverage of the interstellar idea at the same time that we were finding an interesting planet not so much larger than Earth in what appeared to be a habitable zone orbit around Proxima Centauri — being at one of the Breakthrough Starshot sessions when the announcement was made was an energizing experience, and I remember staying up late one night in Palo Alto writing the article on the Proxima Centauri discovery that I would post when the embargo lifted.
Image credit: Manchu.
The subcommittee report I referred to was the work of representative John Culberson (R–TX), long known for his interest in the space program and a panelist at the TVIW 2017 gathering. Culberson submitted a report to the Committee on Appropriations to accompany a bill setting NASA’s budget for the 2017 fiscal year, which began on October 1 of that year.
The bill sets down a futuristic agenda:
Interstellar propulsion research.—Current NASA propulsion investments include advancements in chemical, solar electric, and nuclear thermal propulsion. However, even in their ultimate theoretically achievable implementations, none of these could approach cruise velocities of one-tenth the speed of light (0.1c), nor could any other fission-based approach (including nuclear electric or pulsed fission). The Committee encourages NASA to study and develop propulsion concepts that could enable an interstellar scientific probe with the capability of achieving a cruise velocity of 0.1c.
Part of this study would be focused on Alpha Centauri, as the report makes clear:
These efforts shall be centered on enabling such a mission to Alpha Centauri, which can be launched by the one-hundredth anniversary, 2069, of the Apollo 11 moon landing.
And there is this about propulsion prospects:
Propulsion concepts may include, but are not limited to fusion-based implementations (including antimatter-catalyzed fusion and the Bussard interstellar ramjet); matter-antimatter annihilation reactions; multiple forms of beamed energy approaches; and immense ‘sails’ that intercept solar photons or the solar wind. At the present time, none of these are beyond technology readiness level (TRL) 1 or 2. The NASA Innovative Advanced Concepts (NIAC) program is currently funding concept studies of directed energy propulsion for wafer-sized spacecraft that in principle could achieve velocities exceeding 0.1c and an electric sail that intercepts solar wind protons.
The report notes work at the NASA Innovative Advanced Concepts program, pointing to studies Phil Lubin (UC-Santa Barbara) has performed on the whole issue of beamed propulsion using lasers. This work is repeatedly cited by Breakthrough Starshot and Lubin is actively involved in Breakthrough’s work on laser technologies. Thus there is some overlap even here between NASA and a privately funded venture that is putting the beamed sail idea to the test and examining the infrastructure needed.
What Culberson’s report went on to do was to tell NASA to submit an “interstellar propulsion technology assessment report” with a draft roadmap that could include an overview of the propulsion concepts considered viable, one that would include the technical challenges, assessments of technology readiness levels, near-term goals and funding requirements.
If this sounds familiar, it is because of the tie-in with the grant recently awarded to the Tau Zero Foundation to compile just such a technology roadmap, work which is now in progress. But despite overstatements in many media outlets (along the lines of ‘NASA Planning Interstellar Mission’ and the like), funding breakthrough propulsion ideas is difficult at the best of times, as Tau Zero founder Marc Millis knows all too well. The former head of NASA’s Breakthrough Propulsion Physics project, Millis told me that acquiring the Tau Zero grant was an extended process that took a number of years to complete. From a recent email:
“A part of this story is the funding process. Those processes are not as singular or straight forward (or fast) as many envision. For example, the grant awarded to Tau Zero in January 2017 was proposed to NASA five years earlier, in February 2012. At that time NASA agreed that such work was needed, but was out of scope for its current funding categories. As those five years passed, the details of the work were iterated with NASA four times, each time getting closer to being funded. The last requested revision was December 2016, where Culberson’s interest added the last nudge. The other part of this story is that funding can vanish faster than it is awarded. In multi-year grants, like the one to Tau Zero, there is no guarantee that funding will exist for its second and third years. That is all part of the realities that we have to deal with.”
In other words, although I’ve seen the ‘NASA to the stars’ story pitched as a reprise of the Apollo program, it is actually a very small step in the direction of assessing what would be required to get an interstellar option in motion. This is certainly not a funded effort to build and launch specific hardware, or even a detailed mission study of the sort Breakthrough Starshot will be creating. But we do have recent reports that a small team based at the Jet Propulsion Laboratory is working on further ideas. JPL’s Anthony Freeman spoke of the possibilities at the 2017 American Geophysical Union conference. At the Huntsville TVIW meeting, JPL’s Stacy Weinstein-Weiss discussed the science prospects for an interstellar probe.
Obviously, we’ll follow such efforts with great interest. Meanwhile, my assumption on the background of all this is that Breakthrough Starshot’s sudden emergence prompted questions about NASA’s interest in interstellar matters on the part of Rep. Culberson, who off-loaded the idea to the committee report, which led to the awarding of the Tau Zero grant, perhaps intensifying the JPL investigations as well. A cynic might question whether the whole story hasn’t received far too much attention, given the excesses of many headline writers. But I have a different take.
In my view, keeping deep space in front of the public is helpful as long as we are pointing to legitimate research that moves the ball forward. The idea that NASA has a large interstellar program in place is incorrect, but that it takes even small steps in this direction by way of early conceptualizations and roadmaps is encouraging. Meanwhile, a vigorous private effort to put theoretical technologies to actual prototype and testing is all to the good, perhaps pointing toward future synergies between space agencies and non-traditional space organizations.
Everything gets blown out of proportion somewhere on the Internet, a challenge we all have to live with as we pursue ideas as futuristic as travel to other stars. But on balance, I’d say that 2017’s flurry of media attention was a good thing, and one that may remind us how much it would take to actually build serious interstellar hardware by 2069 or sooner. Technologies need development at every level, but there is nothing wrong with the Starshot model, beginning with conceptual studies and progressing to laboratory work that could point to eventual starflight.