Solar thermal rocket
A solar thermal rocket is a theoretical
In the shorter term, solar thermal propulsion has been proposed both for longer-life, lower-cost, more efficient use of the
Solar-thermal design concepts
There are two solar thermal propulsion concepts, differing primarily in the method by which they use solar power to heat up the propellant:[citation needed]
- Indirect solar heating involves pumping the propellant through passages in a heat exchanger that is heated by solar radiation. The windowless heat exchanger cavity concept is a design taking this radiation absorption approach.
- Direct solar heating involves exposing the propellant directly to solar radiation. The rotating bed concept is one of the preferred concepts for direct solar radiation absorption; it offers higher specific impulse than other direct heating designs by using a retained seed (tantalum carbide or hafnium carbide) approach. The propellant flows through the porous walls of a rotating cylinder, picking up heat from the seeds, which are retained on the walls by the rotation. The carbides are stable at high temperatures and have excellent heat transfer properties.
Due to limitations in the temperature that heat exchanger materials can withstand (approximately 2800
Small-scale hardware has been designed and fabricated for the
Reusable Orbital Transfer Vehicles (OTV), sometimes called (inter-orbital) space tugs, propelled by solar thermal rockets have been proposed. The concentrators on solar thermal tugs are less susceptible to radiation in the Van Allen belts than the solar arrays of solar electric OTV.[3]
An initial proof of concept was demonstrated in 2020 with helium at the Johns Hopkins University Applied Physics Laboratory solar simulator.[4]
Propellants
Most proposed designs for solar thermal rockets use
Conventional thought has been that hydrogen—although it gives excellent specific impulse—is not space storable. Design work in the early 2010s has developed an approach to substantially reduce hydrogen boiloff, and to economically utilize the small remaining boiloff product for requisite in-space tasks, essentially achieving zero boil off (ZBO) from a practical point of view.[6]: p. 3, 4, 7
Other substances could also be used. Water gives quite poor performance of 190 seconds (1.9 kN·s/kg), but requires only simple equipment to purify and handle, and is space storable and this has very seriously been proposed for interplanetary use,
Ammonia has been proposed as a propellant.[8] It offers higher specific impulse than water, but is easily storable, with a freezing point of −77 degrees Celsius and a boiling point of −33.34 °C.
A solar-thermal propulsion architecture outperforms architectures involving electrolysis and liquification of hydrogen from water by more than an order of magnitude, since electrolysis requires heavy power generators, whereas distillation only requires a simple and compact heat source (either nuclear or solar); so the propellant production rate is correspondingly far higher for any given initial mass of equipment. However its use does rely on having clear ideas of the location of water ice in the solar system, particularly on lunar and asteroidal bodies, and such information is not known, other than that the bodies within the asteroid belt and further from the Sun are expected to be rich in water ice.[9][10]
Solar-thermal for ground launch
Solar thermal rockets have been proposed [11] as a system for launching a small personal spacecraft into orbit. The design is based on a high altitude airship which uses its envelope to focus sunlight onto a tube. The propellant, which would likely be ammonia, is then fed through to produce thrust. Possible design flaws include whether the engine could produce enough thrust to overcome drag, and whether the skin of the airship wouldn't fail at hypersonic velocities. This has many similarities to the orbital airship proposed by JP Aerospace.
Proposed solar-thermal space systems
As of 2010[update], two proposals for utilizing solar-thermal propulsion on in-space post-launch spacecraft systems had been made.
A concept to provide
Solar-thermal monoprop hydrogen thrusters are also integral to the design of the next-generation cryogenic
The viability of various trips using Solar Thermal propulsion was investigated by Gordon Woodcock and Dave Byers in 2003.[clarification needed][12]
A subsequent proposal in the 2010s was the Solar Moth spacecraft that would use lightweight mirrors to focus solar radiation on a solar thermal engine.[13][14]
See also
References
- ^ Solar Thermal Propulsion for Small Spacecraft - Engineering System Development and Evaluation PSI-SR-1228 publisher AIAA July 2005
- ^ Webpage DLR Solar Thermal Propulsion of the Institut für Raumfahrtantriebe Abteilung Systemanalyse Raumtransport (SART) date = November 2006 Archived 2007-07-06 at the Wayback Machine
- ^ John H. Schilling, Frank S. Gulczinski III. "Comparison of Orbit Transfer Vehicle Concepts Utilizing Mid-Term Power and Propulsion Options" (PDF). Retrieved May 23, 2018.
- ^ Oberhaus, Daniel (20 November 2020). "A Solar-Powered Rocket Might Be Our Ticket to Interstellar Space". Wired.
- ^ Ultramet. "Advanced Propulsion Concepts - Solar Thermal Propulsion". Ultramet. Retrieved June 20, 2012.
- ^ a b c
Zegler, Frank; Bernard Kutter (2010-09-02). "Evolving to a Depot-Based Space Transportation Architecture" (PDF). AIAA SPACE 2010 Conference & Exposition. AIAA. p. 3. Retrieved March 31, 2017.
the waste hydrogen that has boiled off happens to be the best known propellant (as a monopropellant in a basic solar-thermal propulsion system) for this task. A practical depot must evolve hydrogen at a minimum rate that matches the station keeping demands.
- ^ NASA. "Robotic Asteroid Prospector NIAC Phase 1 Final Report" (PDF). NASA. Retrieved March 11, 2021.
- ^ PSI. "Solar Thermal Propulsion for Small Spacecraft_Engineering System Development and Evaluation" (PDF). PSI. Retrieved August 12, 2017.
- ^ Zuppero, Anthony (2005). "Propulsion to Moons of Jupiter Using Heat and Water Without Electrolysis Or Cryogenics" (PDF). Space Exploration 2005. SESI Conference Series. 001. Retrieved June 20, 2012.
- ^ Zuppero, Anthony. "new fuel: Near Earth Object fuel (Neofuel, using abundant off-earth resources for interplanetary transport)". Retrieved June 20, 2012.
- ^ "Interplanetary transportation» Solar Thermal Ground to Orbit - Solar Thermal Tech to launch". NewMars. Retrieved January 19, 2023.
- )
- ^ Nick Stevens Graphics, 18 January 2018, accessed 20 January 2019.
- ^ Rocket engine performance as a function of exhaust velocity and mass fraction for various spacecraft, Project Rho, accessed 20 January 2019.
External links
- Solar Thermal Propulsion for Small Spacecraft - Engineering System Development and Evaluation (2005)
- Pratt & Whitney Rocketdyne Wins $2.2 Million Contract Option for Solar Thermal Propulsion Rocket Engine (Webpage quoting press release,
June 25, 2008, Pratt & Whitney Rocketdyne)