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Heliophysics with Interstellar Implications

You would think that heading toward the Sun, rather than away from it, would not necessarily fall under Centauri Dreams’ purview, but missions like the Parker Solar Probe have reminded us that extreme environments are ideal testing grounds for future missions. Build a heat shield that can take you to within 10 solar radii of our star and you’re also exploring possibilities in ‘sundiver’ missions that all but brush the Sun in a tight gravity assist.

Or consider the two proposals NASA has just selected in the area of small satellite technologies, which grow directly out of its heliophysics program. Here, the study of the Sun’s interactions with the Solar System, and the consideration of Sun, planets and heliosphere as a deeply interconnected system, takes pride of place. Let’s start with a mission called SETH — Science-Enabling Technologies for Heliophysics. One of its two technology demonstrators, called the HELio Energetic Neutral Atom (HELENA) detector, involves solar energetic neutral atoms, which can provide advanced warnings of potential radiation threats to astronauts.

The other demonstrator aboard SETH is an optical communications technology expressly designed for CubeSats and other small satellites, one that could allow a hundred-fold increase in the return of deep space data. Building out a robotic infrastructure in the Solar System will involve increasingly miniaturized technologies. We can envision small satellite constellations that can network and operate one day in ‘swarm’ fashion to create a continuous presence around targets ranging from asteroids to the gas and ice giants that can shape their orbits.

Image: NASA has selected two proposals to demonstrate technologies to improve science observations in deep space. The proposals could help NASA develop better models to predict space weather events that can affect astronauts and spacecraft, such as coronal mass ejections (CMEs). In this image, taken by the Solar and Heliospheric Observatory on Feb. 27, 2000, a CME is seen erupting from the Sun, which is hidden by the disk in the middle, so the fainter material around it can be seen. Credit: ESA/NASA/SOHO.

Toward a Large Solar Sail

But if you’re looking for a mission with real interstellar punch, consider Solar Cruiser, whose two technology demonstrations involve measurements of the Sun’s magnetic field structure and the velocity of coronal mass ejections (CMEs), those vast explosions of plasma that can create space weather nightmares for utility grids on Earth. Making this mission possible will be a solar sail of almost 1,700 square meters. The timing on this proposal seems propitious given The Planetary Society’s recent success at raising the orbit of LightSail-2 using sunlight. Pushing toward much larger designs is the next step.

“This is the first time that our heliophysics program has funded this kind of technology demonstration,” said Peg Luce, deputy director of the Heliophysics Division at NASA Headquarters. “Providing the opportunity to mature and test technologies in deep space is a crucial step towards incorporating new techniques into future missions.”

Lots to work with here, and I’m drawing together more information about Solar Cruiser, which would not only be by far the largest solar sail yet deployed, but would also experiment with using the momentum of sunlight to continuously modify its orbit. This would allow us to obtain views of the Sun that orbits involving gravity alone would not make possible. Robert Forward explored the original concept and introduced it to the public first in the pages of Analog and then in his book Indistinguishable from Magic (1995), where he considered how we might use such spacecraft near the Earth. He called a spacecraft that uses a solar sail to hover over a region rather than orbiting the Earth a ‘statite,’ and explained it this way:

…I have the patent on it — U.S. Patent 5,183,225 “Statite: Spacecraft That Utilizes Light Pressure and Method of Use”… The unique concept described in the patent is to attach a television broadcast or weather surveillance spacecraft to a large highly reflective lightsail, and place the spacecraft over the polar regions of the Earth with the sail tilted so the light pressure from the sunlight reflecting off the lightsail is exactly equal and opposite to the gravity pull of the Earth.

Here we are using a solar sail for station-keeping rather than transport, and Solar Cruiser may turn out to be the first time we experiment with the technique, which offers options that other kinds of satellite do not:

With the gravity pull nullified, the spacecraft will just hover over the polar region, while the Earth spins around underneath it. Since the spacecraft is not in orbit around the Earth, it is technically not a satellite, so I coined the generic term ‘statite’ or ‘-stat’ to describe any sort of non-orbiting spacecraft (such as a ‘weatherstat’ or ‘videostat’ or ‘datastat’).

Image: Analog‘s December, 1990 issue contained an article by Robert Forward describing the ‘polesitter’ concept, one of many innovative ideas the scientist introduced to a broad audience. Credit: Condé Nast.

Can Solar Cruiser push these ideas forward in orbits near the Sun? Forward called orbits that are non-Keplerian ‘displaced orbits’ and also referred to such satellites as ‘polesitters.’ It will be fascinating to see how far Solar Cruiser will explore such capabilities as part of its larger mission, which should also teach us much about large sail materials and deployment.

What will follow is a nine-month study period, with both proposals funded at $400,000 for concept studies, after which one of the two proposals will be selected to go into space. Launch will take place in October of 2024 as a secondary payload along with the Interstellar Mapping and Acceleration Probe (IMAP) probe, another mission we’ll be following closely as it investigates the interactions of the solar wind with the local interstellar medium (the spacecraft will orbit the Sun-Earth L1 Lagrangian point and will also be used to monitor space weather).

Also of interest: Baig and McInnes, “Light-Levitated Geostationary Cylindrical Orbits are Feasible,” Journal of Guidance, Control and Dynamics, Vol. 33, No. 3 (2010), pp. 782-793 (abstract).

{ 13 comments… add one }
  • Alex Tolley August 19, 2019, 13:27

    I look forward to reading more about Solar Cruiser. That is a large sail. If it is square, the sail would be over 130 meters on a side. Solar sailing is a tarting to get serious.

  • Thomas Goodey August 19, 2019, 14:10

    You wrote “Build a heat shield that can take you to within 10 solar radii of our star and you’re also exploring possibilities in ‘sundiver’ missions that all but brush the Sun in a tight gravity assist.”

    You mean, like Oumuamua?

    • Paul Gilster August 19, 2019, 14:48

      ‘Oumuamua’s gravity assist was anything but ‘tight’ compared to a true sundiver. Perihelion at 38,100,000 km.

  • Harry R Ray August 19, 2019, 14:53

    Speaking of the interstellar IMPLICATIONS of Heliophysics: The Spitzer Space Telescope has managed to pull off an incredible feat – measure the albedo of the SURFACE of an Earth-sized exoplanet. LHS 3844b orbits a red dwarf star every 11 hours. Spitzer monitored the planet CONTINUOUSLY for 100 hours. Thw things popped out! One, the dayside temperature is ~1500 degrees farenheidt whereas the nightside temperature approaches absolute zero, indicating NO transport of heat from the dayside to the nightside. Two, the albedo is very low, indicative of volcanic basalts completely covering the surface!

    • Alex Tolley August 19, 2019, 19:55

      Does this imply there is no atmosphere?

      • Harry R Ray August 20, 2019, 9:16

        Yes. The paper is now up on the exoplanet.eu website.

  • Andrew Palfreyman August 19, 2019, 15:30

    Dr. Kipping of Cool Worlds has coined the name “quasites” also.

  • Christopher Phoenix August 19, 2019, 16:01

    Robert Forward explored the original concept… He called a spacecraft that uses a solar sail to hover over a region rather than orbiting the Earth a ‘statite,’ and explained it this way:

    The “statite” is one of my favorite of Robert Forward’s proposals, even compared with the true exotica like using rotating super-dense matter to generate dipole gravitational fields. For me, it drove home just how far a photon sail breaks free from the limitations of rockets. Given proximity to a star, a photon sail can provide thrust forever, for free. We can contemplate missions that would never be possible with any propulsion system that requires propellant.

    What will follow is a nine-month study period, with both proposals funded at $400,000 for concept studies, after which one of the two proposals will be selected to go into space.

    It’s a pity we must choose between SETH and the Solar Cruiser, but resources (and mass budgets) are always limited! Both proposals carry fascinating technology demonstrators. But whichever one is ultimately selected will certainly push both our knowledge of the sun and space technology forward.

  • ljk August 20, 2019, 8:58

    A Review of Past Insights by Robert L. Forward, PhD:
    Emerging Technologies and Future Concepts

    Tony Robertson1 and Gerald D. Nordley2

    1NASA/MSFC, Propulsion Research Center, Huntsville, AL 35812
    2Consultant, 1238 Prescott Avenue, Sunnyvale CA 94089-2334
    1256-544-7102, Glen.A.Robertson@nasa.com


    A review of various technologies discussed by Dr. Robert Forward is presented as a tribute to Dr. Forward, and is based on selections from his writings and those of subsequent investigators. Some emphasis is placed on the new frontiers of space propulsion, power and communication.

    Many of these concepts and technologies are presented within the STAIF 2004 “1st Symposium on New Frontiers and Future Concepts.”

    These range from highly speculative notions to hardware that has now been demonstrated in space flight. Among these concepts and technologies to be discussed are future communications, antimatter propulsion, space elevators and tethers, beamed energy propulsion,
    and emerging gravity theories and concepts.


  • ljk August 20, 2019, 9:05


    The Science and Fiction of Robert L. Forward

    Article (PDF Available) in Physics Procedia 38:109-115 ·

    December 2012 with 345 Reads

    DOI: 10.1016/j.phpro.2012.08.016

    By Charles A. Lundquist


    One way to examine a relationship between science and science fiction is to look at the works of individuals who simultaneously were practicing scientists and authors of science fiction. Dr. Robert L. Forward is such an individual.

    From 1980 through 1997 he wrote and published about twelve science fiction novels. During the same time interval, he produced many scientific and technical papers. Writing science fiction was essentially a byproduct of his scientific research.

    His early research concerned gravitation and astronomical objects. Later he studied space transportation technologies, including photon propelled sails, antimatter rockets and long tethers.

    An immediate observation is that Dr. Forward, in his science fiction, took particular care that the circumstances and technologies used had reasonable scientific bases. A prime example is his use of antimatter propulsion in his fiction.

    In his scientific career, Dr. Forward was a leading proponent that antimatter propulsion was possible, but very expensive. Enormous sails propelled in space by astronomical photons or laser beams is another propulsion technology employed in his novels.

    If a distinction is made between fiction based on sound scientific principles and fiction that is pure fantasy, the works of Robert Forward clearly fall in the first grouping.

    The paper online here:


  • Harry R Ray September 4, 2019, 9:58

    Paul Gilster: WE MAY HAVE A SUNDIVER! 322P/SOHO is NOT a periodic sundiving comet after all! It has just been reclassified as the FIRST sundiving ASTEROID. Furthermore, its size is almost EXACTLY that of `Oumuamua and its aspect ratio is ~50% that of `Oumuamua. Could it have origionally come from another star and then DELIBERATELY passed close enough to Jupiter to slow it down to the point that it was subsequently captured in its current orbit. This is obviously WILD SPECULATION, but please ask Avi Loeb if this scenario is plausible. Whether it is or not, this object should be made a prime target for a future space mission.

    • Paul Gilster September 4, 2019, 15:49

      Dr. Loeb replies:

      “In a paper with my undergraduate student, Amir Siraj, we explored the orbits of interstellar objects that are trapped by the Solar system as a result of a close encounter with Jupiter. As illustrated in Figure 1 of that paper, the distinguishing signature of an interstellar origin is a high inclination relative to the orbital plane of the planets. The distributions of semi-major axis and eccentricity are described by equations 6-8. By comparing the parameters of 322P/SOHO to our results, one can decide whether it is most likely to be a common Solar system Centaur (most likely case) or a rare interstellar visitor that was trapped by Jupiter.

      Aside from orbital parameters, one can use the composition of its burnt out gases to infer its origin, as described in another paper we wrote recently with my postdoc, John Forbes.”

      The URLs are:



      Many thanks to Dr. Loeb for this thoughts on this.

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