The very low Energy Efficiency seems to make it not worthwhile. It is important to have station keeping like the Quasite system but this can also be dynamically maintained. The low efficiency makes the dynamo storage idea via TARS not worthwhile.
The TARS (Torqued Accelerator Using Radiation from the Sun) launching catapult concept can be augmented with solar photovoltaic (PV) power to increase spin speed more efficiently than the baseline passive design. The original TARS proposal relies on differential solar radiation pressure to generate torque, spinning up the tethered system over weeks to months (or longer for current materials) to achieve tip speeds of 10-20 km/s for payload release. This passive method has inherently low efficiency (0.001-0.1% solar-to-kinetic conversion) due to the weak radiation pressure (~4.5 μN/m² at 1 AU). Integrating solar PV panels to generate electricity for active spin-up—via electric motors, ion thrusters, or electromagnetic torquers—could accelerate the process to days or hours, with overall efficiencies of 15-25%, while maintaining the system’s solar-powered nature.The TARS paper itself acknowledges this potential and talks about using microthruster to get it up to speed.
A solar PV-only version of the TARS (Torqued Accelerator Using Radiation from the Sun) catapult launch system, incorporating a magnetic spinning mechanism, could fully eliminate the need for passive solar spin-up via radiation pressure. The original TARS design relies on differential solar radiation pressure to generate torque for gradual spin-up (over weeks to years), but this passive method has limitations like slow charging, orbital instability during early phases, and low efficiency (~0.001-0.1%).
By shifting to an active system powered solely by solar PV panels—generating electricity to drive magnetic mechanisms for torque—you can achieve faster, more reliable spin-up without any reliance on radiation pressure. This would transform TARS into a fully active rotational tether catapult, still using centrifugal force for payload launch, but with enhanced control and scalability.
Lightweight, high-efficiency PV panels (e.g., multi-junction GaAs cells, 30-35% efficient, ~100-300 W/kg) mounted on the paddles or central hub generate power (e.g., 1-10 kW from 1-10 m² at 1 AU). This electricity powers the spinning mechanism, eliminating passive torque entirely.
Near-Term and Long-Term Prospects
Near-Term (2025-2035): Prototypes viable using COTS PV and magnetic torquers (e.g., from missions like TEPCE). NASA/DARPA could demo hybrids soon, with Starship enabling cheap deployment. Costs: ~$10-100M per unit.
Long-Term (2035+): Advances solar for 50% PV efficiency and nanomaterials and electrical strength augmentation enable higher speeds (the 1000 km/s in the paper). Could evolve into solar-powered rotovators for orbital transfers, outpacing passive TARS.
Can Sequenced Rotovators With Higher and Higher Speeds Be Used to Boost Missions?
Rotovators, also known as momentum exchange tethers or rotating skyhooks, are advanced space infrastructure concepts designed to facilitate efficient orbital transfers without relying heavily on traditional rocket propulsion. The PV enhanced spinning systems could be used to provide more speed to missions without having to go to planets for gravitational boosts.
A solar-powered variant integrates solar energy—via photovoltaic (PV) panels or solar sails—to generate electricity or thrust for maintaining rotation, reboosting momentum, and adjusting orbits or just increasing speed making the system sustainable and propellant-efficient. The arbitrary position keeping of spinning systems could allow for flexibly increasing speed if the docking and release systems are mastered.
Magnetic Spinning Mechanism Options
Systems using electromagnetic forces for torque, which are well-established in spacecraft attitude control and tether dynamics.
PV electricity drives electric motors at the tether hub or electromagnetic coils along the tether to apply direct torque. Magnetotorquers (coils that interact with external magnetic fields) have historically been used to spin up satellites, including for replenishing angular momentum in spin-stabilized systems.
Electrodynamic Tether (EDT) Adaptation: Run PV-generated current through the conductive tether to interact with ambient magnetic fields (e.g., solar wind IMF) via Lorentz force, generating rotational torque. EDTs are proven for propulsion and attitude control (e.g., TEPCE CubeSat experiment), and spinning variants exist for orbital maneuvering
Superconducting magnetic levitation (maglev) bearings enable frictionless rotation, while PV-powered reaction wheels (with magnetic suspension) build angular momentum. This is common in satellites for precise spin control.
These mechanisms provide all required torque actively, bypassing radiation pressure. Spin-up could occur in hours to days (vs. passive’s weeks-years), limited only by power output and material strength (or electrically enhanced strength.)
The catapult launch remains the same: Release payload at peak rotation for interstellar velocities.
Why Solar PV + Alternatives Are Better
TARS’s efficiency is fundamentally limited by the weak radiation pressure (orders of magnitude weaker than PV’s direct photon-to-electron conversion). PV systems capture ~20% of solar energy as usable electricity immediately, vs. TARS’s <<1% over long periods. Kinetic storage via flywheels adds minimal losses and allows rapid cycling, unlike TARS’s years-long spin-up.
Extremely low energy conversion efficiency: The process relies on radiation pressure (≈4.5 μN/m² at 1 AU from the Sun), leading to efficiencies on the order of 0.001-0.1% (proportional to v/c, where v is rotational tip speed and c is the speed of light). For typical speeds of 10 km/s, efficiency is ≈0.006%.
Slow charging: Spin-up takes days to years, depending on material areal density (mass per unit area) and orbit. For advanced materials like graphene (areal density ≈0.2 g/m²), it might reach usable speeds in ~7 days, but for current materials (≈140 g/m²), it takes months to years.
Material limits: Rotational speed is capped by tensile strength to avoid structural failure (critical velocity v_crit = √(2σ/ρ), where σ is tensile strength and ρ is density; e.g., ≈10-20 km/s for carbon nanotubes or graphene).
Losses: 20-30% heat dissipation in vacuum during extraction, plus stability challenges (e.g., tumbling risk).
Scale and context: Suited for space (e.g., Mars bases or microwave power beaming), but requires enormous areas for meaningful energy (e.g., tens of GWh over 10 years per system, needing fleets of 1,700-ton units for TWh-scale storage).
TARS’s primary advantage is passivity—no fuel or electronics needed—but this comes at the cost of inefficiency for power generation or storage compared to active systems.
Near-Term Efficiency/Prospects
PV-based (photovoltaic) systems are commercial now, with global capacity over 1 TW and storage costs falling rapidly. TARS remains theoretical, with prototypes years away and inefficiencies making it unsuitable for near-term power needs.
Long-Term Efficiency/Prospects
Advances in materials could shorten TARS charge times (e.g., to days), but efficiency won’t exceed ~1% due to physical limits. PV and storage will likely reach 30-40% overall, with hybrids (e.g., space-based PV beaming power to Earth) outpacing TARS. Alternatives like lunar drivers could offer better kinetic yields in space.
Brian Wang is a Futurist Thought Leader and a popular Science blogger with 1 million readers per month. His blog Nextbigfuture.com is ranked #1 Science News Blog. It covers many disruptive technology and trends including Space, Robotics, Artificial Intelligence, Medicine, Anti-aging Biotechnology, and Nanotechnology.
Known for identifying cutting edge technologies, he is currently a Co-Founder of a startup and fundraiser for high potential early-stage companies. He is the Head of Research for Allocations for deep technology investments and an Angel Investor at Space Angels.
A frequent speaker at corporations, he has been a TEDx speaker, a Singularity University speaker and guest at numerous interviews for radio and podcasts. He is open to public speaking and advising engagements.
I did some updating of some of the wordpress plug-in software components. I did not delete published comments. I apologize if this caused some comments to be lost. Goatguy informed me of that some comments he saw were lost. Brett please republish your comment on this post.
Well, as I said in the other thread, the solar TARS was an idea I examined literally decades ago, when I first heard of solar sails. Not really practical, as it’s a horribly inefficient way to capture solar energy. It’s the sort of thing where you get the idea, run the numbers, and then laugh and move on, frankly. PV and motor driven flywheels would be wildly more efficient, but you’re probably better off just investing the extra mass in more power generation and forgetting about storage.
The lunar mass driver idea is something I came up with back when I was involved in the L-5 society. Lunar escape velocity is less than 3 kps, orbital velocity around Earth 1 kps. With under 4 kps you can launch a payload from the lunar surface to a grazing passage past the Earth.
You arrive at perigee around Earth at about 11 kps, with about 7.5 times as much kinetic energy as had to be provided to leave the Moon. That’s an excellent EROEI, and if you’re doing mining on the Moon, your ‘waste product’ is lunar resources in LEO.
It does require some serious infrastructure in LEO, though, an orbital ring with a reverse mass driver extracting the energy. Can’t just be a satellite because the perigee location goes around the Earth as fast as the Moon.