Typically all it takes to spawn a brand new concept is a tiny smudge in a telescopic picture. What counts, in fact, is simply what that smudge implies. Within the case of the item known as ‘Oumuamua, the implication was interstellar, for no matter it was, this smudge was clearly on a hyperbolic orbit, that means it was simply passing via our Photo voltaic System. Jim Bickford wished to see the departing customer up shut, and that was a part of the inspiration for a novel propulsion idea.
Now transferring right into a Section II examine funded by NASA’s Revolutionary Superior Ideas workplace (NIAC), the thought is dubbed Skinny-Movie Nuclear Engine Rocket (TFINER). Not the world’s most pronounceable acronym, but when the thought works out, that can hardly matter. Working on the Charles Stark Draper Laboratory, a non-profit analysis and growth firm in Cambridge MA, Bickford is understood to long-time Centauri Goals readers for his work on naturally occurring antimatter seize in planetary magnetic fields. See Antimatter Acquisition: Harvesting in House for extra on this.
Picture: Draper Laboratory’s Jim Bickford, taking a deep house propulsion idea to the following degree. Credit score: Charles Stark Draper Laboratory.
Harvesting naturally occurring antimatter in house provides some hope of easing one of many greatest issues of such propulsion methods, specifically the problem in producing sufficient antimatter to gas an engine. With the Skinny Movie Nuclear Engine Rocket, Bickford once more tries to alter the sport. The notion is to make use of energetic radioisotopes in skinny layers, permitting their pure decay merchandise to propel a spacecraft. The correct substrate, Bickford believes, can management the emission path, and the sail-like system packs a punch: Velocity adjustments on the order of 100 kilometers per second utilizing mere kilograms of gas.
I started this piece speaking about ‘Oumuamua, however that’s only for starters. As a result of if we are able to create a dependable propulsion system able to such tantalizing velocity. we are able to begin serious about mission targets as distant because the photo voltaic gravitational focus, the place excessive magnifications grow to be doable. As a result of the lensing impact for sensible functions begins at 550 AU and continues with a focal line to infinity, we’re taking a look at an extended journey. Keep in mind that Voyager 1, our most distant working spacecraft, has taken virtually half a century to succeed in, as of now, 167 AU. To picture multiple planet on the photo voltaic lens, we’ll additionally want a excessive diploma of maneuverability to shift to a number of exoplanetary programs.
Picture: That is Determine 3-1 from the Section 1 report. Caption: Idea for the skinny movie thrust sheet engine. Alpha particles are selectively emitted in a single path at roughly 5% of the velocity of sunshine. Credit score: NASA/James Bickford.
So we’re taking a look at a extremely fascinating know-how if TFINER could be made to work, one that might supply imaging of exoplanets, outer planet probes, and encounters with future interstellar interlopers. Bickford’s Section 1 work might be prolonged within the new examine to refine the mission design, which is able to embrace thruster experiments in addition to what the Section II abstract refers to as ‘isotope manufacturing paths’ whereas additionally contemplating alternatives for hybrid missions that might embrace the Oberth ‘photo voltaic dive’ maneuver. Extra on that final merchandise quickly, as a result of Bickford might be presenting a paper on the prospect this summer time.
Picture: Artist idea highlighting the novel strategy proposed by the 2025 NIAC awarded collection of the TFINER idea. That is the baseline TFINER configuration used within the system evaluation. Credit score: NASA/James Bickford.
However let’s drop again to the Section I examine. I’ve been perusing Bickford’s closing report. Creating out of Wolfgang Moeckel’s work at NASA Lewis within the Nineteen Seventies, the TFINER design makes use of skinny sheets of radioactive components. The answer leverages exhaust velocities for alpha particle decays that may exceed 5 % of the velocity of sunshine. You’ll recall my touch upon house sails within the earlier submit, the place we appeared on the benefit of inflatable elements to make sails extra scalable. TFINER is extra scalable nonetheless, with adjustments to the quantity of gas and sheet space being key variables.
Let’s start with a ~10-micron thick Thorium-228 radioisotope movie, with every sheet containing three layers, integrating the lively radioisotope gas layer within the center. Let me quote from the Section I report on this:
It have to be comparatively skinny to keep away from substantial vitality losses because the alpha particles exit the sheet. A skinny retention movie is positioned over this to make sure that the residual atoms don’t boil off from the construction. Lastly, a substrate is added to selectively take in alpha emission within the ahead path. Since decay processes haven’t any directionality, the substrate absorber produces the differential mass movement and ensuing thrust by limiting alpha particle trajectories to at least one path.
The TFINER baseline makes use of 400 meter tethers to attach the payload module. The sheet’s energy comes from Thorium-228 decay (alpha decay) — the half-life is 1.9 years. We get a ‘decay cascade chain’ that produces daughter merchandise – 4 extra alpha emissions end result with half-lives starting from 300 ns to three days. The uni-directional thrust is produced due to the beryllium absorber (~35-microns thick) that coats one aspect of the skinny movie to seize emissions transferring ahead. Efficient thrust is thus channeled out the again.
Observe as nicely the tethers within the illustration, crucial to guard the sensor array and communications part to reduce the radiation dose. Manipulation of the tethers can management trajectory on single-stage missions to deep house targets. Reconfiguring the thrust sheet is what makes the design maneuverable, permitting thrust vectoring, at the same time as longer half-life isotopes could be deployed within the ‘staged’ idea to realize most velocities for prolonged missions.
Picture: That is Determine 7-8 from the report. Caption: Instance thrust sheet rotation utilizing tether management. Credit score: NASA/James Bickford.
From the Section I report:
The payload module is linked to the thrust sheet by lengthy tethers. A winch on the payload module can individually pull-in or let-out line to govern the sail angle relative to the payload. The thrust sheet angle will rotate the imply thrust vector and function very similar to trimming the sail of a ship. In fact, on this case, the sail (sheet) strain comes from the nuclear exhaust somewhat than the wind
It’s arduous to think about the diploma of maneuverability right here being replicated in any present propulsion technique, an enormous payoff if we are able to learn to management it:
This strategy permits the thrust vector to be rotated relative to the middle of mass and velocity vector to steer the spacecraft’s essential propulsion system. Nevertheless, that is more likely to require very complicated controls particularly if the payload orientation additionally must be modified. The maneuvers would all be gradual given the lengthy traces lengths and separations concerned.
Spacecraft pointing and management is an space as important because the propulsion system. The Section I report goes into the above choices in addition to thrust vectoring via sheets configured as panels that might be folded and adjusted. The report additionally notes that thermo-electrics throughout the substrate could also be used to generate electrical energy, though a radioisotope thermal generator built-in with the payload could show a greater answer. The report provides a superb roadmap for the design refinement of TFINER coming in Section II.
Picture: TFINER imaged as within the Section I examine utilizing a panel configuration. Credit score: NASA/James Bickford.
The baseline TFINER idea thought of within the report deploys 30 kg of Thorium-228 in a sheet space measuring over 250 sq. meters, a configuration able to offering a delta-v of 150 km/s to a 30 kg payload. Bickford’s emphasis on maneuverability is nicely taken. A mission to the photo voltaic gravitational focus might make the most of this functionality by aligning with not only one however a number of targets via persevering with propulsive maneuvers. Isotopes with an extended half-life (Bickford has studied Actinium-227, however different isotopes are doable) can present for ‘staged’ mixed architectures permitting nonetheless longer mission timeframes. A high-flux particle accelerator is assumed as the very best manufacturing pathway to create the required isotopes.
Clearly we’re within the early levels of TFINER, however what an thrilling idea. To return to ‘Oumuamua, the report notes {that a} mission to check it “…isn’t doable with out the power to decelerate and carry out a search alongside the trajectory because the uncertainty bubble in its trajectory is bigger than the vary of any sensors that will work throughout a flyby. The isotope gas could be chosen to optimize for greater accelerations early within the mission or longer half-life choices for prolonged missions.” Because the Section II report lays out the event path, questions of gas manufacturing and substrate optimization might be absolutely explored.
I requested Dr. Bickford about how the Section II examine will proceed. In an electronic mail on Wednesday, he pointed to persevering with evaluation of the thrust sheet, gas manufacturing and spacecraft design, which ought to contain potential mission architectures. However he handed alongside a number of different factors of curiosity:
- Northwestern and Yale Universities have joined the group to function a ~1 cm2 scale thruster demonstration to validate the pressure fashions and higher perceive the sheet’s electrical charging conduct.
- Draper Laboratory has expanded its work with Los Alamos Nationwide Laboratory to discover novel manufacturing approaches together with new particle accelerators and gas manufacturing architectures.
- ”We’ve added NASA MSFC as consultants to discover hybrid mission architectures which exploit photo voltaic strain through the shut photo voltaic flyby of an Oberth maneuver.”
Ideas like TFINER push the envelope within the type of ways in which repay not solely in a financial institution of latest technical data however novel applied sciences that can bear on how we discover the Photo voltaic System and ultimately transcend it. I’m reminded of Steve Howe and Gerald Jackson’s antimatter sail idea, which produces fission by permitting antimatter, saved in all probability as antihydrogen, to work together with a sheet of U-238 coated with carbon (see Antimatter and the Sail). TFINER makes use of no antimatter, however in each circumstances we’ve got what seems to be like a sail floor being reinvented to supply missions that might put unique targets inside attain.
The opposite motive the antimatter sail involves thoughts is that Jim Bickford is the person who reminded us how a lot naturally occurring antimatter could also be accessible for harvest within the Photo voltaic System. The Howe/Jackson idea might work with milligrams of antimatter, which is conceivably accessible trapped in planetary magnetic fields, together with that of Earth. In earlier work, Bickford has calculated that a few kilogram of antiprotons enter our Photo voltaic System each second, and any planet with a powerful magnetic subject is truthful recreation for assortment.
We hammer away at propulsion points hoping for the breakthrough that can get us to the photo voltaic gravitational lens and the outer planets with a lot shorter mission timelines than accessible right this moment. The considered catching an interstellar interloper like ‘Oumuamua provides spice to the TFINER idea because the work continues. I look with nice curiosity within the path Bickford is taking with the Oberth maneuver, which we’ll be discussing additional this summer time.
