Nuclear reactors in space!
Zara Hodgson
NNL Technical Conference 2015
Nuclear Reactors in Space!
Map of the Solar System with approximate location of Spacecraft (image courtesy of NASA)
Nuclear Reactors in Space!
Inactive Prototype of
SNAP-10A
National Museum of
Nuclear Science and
History, Albuquerque,
USA
And Tim Tinsley, Chris Rhodes and Mark
Sarsfield
Nuclear Reactors in Space!
• 1965 SNAP 10A launched. First (and only) USA
reactor in space.
• Thermal spectrum, NaK coolant, 590We maximum operation,
43 days
• 1967 – 1988 RORSAT series launched by Russia.
• Fast spectrum, NaK coolant, Up to 3kWe, UC2 and UMo,
~90%HEU
• 1987 TOPAZ launched by Russia
• Fast spectrum, NaK coolant, 5kWe, UO2 ,~96%HEU, Plans for
US-Russia 40kWe reactor abandoned in 1992
• Russia has launched 33 reactors: 31 of BES-5 and 2
of TOPAZ)
Why? Solar irradiance
There are two important classes of existing space mission that cannot rely only on solar photovoltaics for power:
1. Outer solar system missions, due to the 1/r2 weakening of the solar flux.
- ESA’s Rosetta spacecraft requires 64m2 of solar array to just survive at ~5 a.u.
2. Mars or moon lander/rover missions that wish to survive and/or operate through the night, or the Martian dust
storms.
Rosetta
32m wingspan
Why - Power?
• Solar
•
•
Proven and cheap
Beyond Mars ineffective or in dark
(Rosetta’s Philae lander!)
•
Easily damaged; large complex
deployment
• Chemical
•
•
ESA’s Rosetta and Philae lander
powered using solar
Low power density
Short lifetime, or large/heavy fuel load
• Nuclear
•
•
•
•
Independent of orbit and location
Proven and reliable – but launch safety!
High power density
Potential to provide power, heat and
thrust
NASA’s Mars Curiosity Rover - powered
using Nuclear RTG system
Image courtesy of ESA and NASA
Nuclear - proven in space
1. Direct production of heat by
radioactive decay (Radioisotope
Heater Unit, RHU)
2. Electrical power generation
via radioactive decay heat
(Radioisotope Power System, RPS)
• Radioisotope Thermoelectric
Generator (RTG)
• Stirling Radioisotope Generator
(SRG)
Image courtesy of US DoE and NASA
Nuclear –proven in space
3. Nuclear reactor system
• Electrical power & Electrical
Propulsion (NEP)
• Thermal Propulsion (NTP)
Reactor Power Systems
Reactor power systems are seen as an exciting enabling
technology for large-scale exploration missions:
• Power for moon or Mars bases?
• Power for electrical thrusters on interplanetary craft?
Studies and design exercises have produced credible reactor
concepts in the power range ~1kW ~ 1MW.
NASA’s Fission
Surface Power
System is the most
advanced
development
programme in this
field.
Image courtesy of NASA
Nuclear Propulsion in Space
Nuclear Electric Propulsion
Deployable construction
Nuclear Thermal Propulsion
Keldysh Centre- Nuclear Power
Propulsion System prototype
NASA’s Bimodal Nuclear Thermal
Rocket
Image courtesy of KeRC and NASA
Nuclear Electric Space Propulsion
Systems
• Why nuclear propulsion ?
• Energy density of nuclear systems is considerably higher
than fossil (chemically) systems – lower mass of fuel
required; enables greater distances from sun and speed
• Why electric propulsion ?
• Since the early days of nuclear power, nuclear rocket engines
have been considered – Nuclear Thermal Propulsion – NTP
• With electric thrusters (Nuclear Electric Propulsion NEP)
propellant is accelerated to considerably higher velocities
requiring a smaller mass of propellant to be carried – high
specific impulse.
• NTP – High thrust but short duration owing to mass of propellant
required
• NEP – Low thrust but high specific impulse – long duration
Current UK activities
• RPS
• The UK is a major contributor to the ESA radioisotope power
programme
• NEP
• The UK is a collaborator on the European Framework 7
programme on nuclear electric propulsion, MEGAHIT
• And now DEMOCRITOS, a Horizon 2020 project
MEGAHIT project overview
MEGAHIT is funded by the European Commission, under the 7th Framework
Programme for Research and Technological Development (FP7), under grant
agreement n° 313096.
MEGAHIT is an EC – Russia supporting action, in preparation of the Horizon
2020 programme.
The MEGAHIT Consortium is composed of 6 partners
Project objectives
The MEGAHIT project started in March 2013 and concluded
in September 2014.
Its objectives were:
to construct a road-map for nuclear electric in-space
propulsion activities within the EC Horizon 2020
programme – at MWe power
to create a European community including Russian
partners around Nuclear Space Power systems
To analyse the potential collaboration opportunities
at international level
Possible mission scenarios
Near Earth Object deflection:
Depending on the mass and trajectory
of the NEO, a MW class system may be
required to deflect it to protect the
Earth.
Robotic Exploration: A
MW class vehicle would open
new exploration mission
classes like sample return
from Jovian moons.
Image courtesy of NASA and Touchstone Pictures
Possible mission scenarios
Space tugs: for the removal of ‘dead’
spacecraft or debris, orbital station
assembly (lunar orbit or in L points)
and general mission support.
Manned Mars Missions: A manned
exploration mission to Mars would
require several tens of tons to be put
on the surface of the planet. Multi-MW
power electric propulsion offers the
possibility of reducing the number of
launches needed
Image courtesy of ESA and NASA
Topic areas
The topics addressed by MEGAHIT cover all the areas of space nuclear electric
propulsion. The technological plans were organised within eight topics
1.
2.
3.
4.
5.
6.
7.
8.
Fuel and core
Thermal control
Conversion
Propulsion
Power management and distribution
Structure and spacecraft arrangement
Safety and regulations
Communication and public awareness
Image courtesy of CNES
NEP System Layout
Nuclear Electricity
Generation in Space
• A 1MWe system required to generate the thrust
levels to satisfy a reasonable range of missions
• 2nd Law of Thermodynamics requires some heat to
be rejected in order to convert heat into electricity
(regardless of the technology used)
• Heat rejection in space can only be achieved by
thermal radiation or by through the ejection of
heated matter from the spacecraft
• NTP = heat rejection occurs by ejecting hot propellant
(forced convection)
• NEP = heat rejection has to occur by thermal radiation (mass
flow rate of ejected propellant is too low to convect sufficient
heat)
The Radiator Problem : the need for
high temperature reactors
• For a system thermal efficiency of about 33%
2 MW of heat will be rejected for 1 MWe generated.
• The radiator is the main contributor to the mass of the system
so there is a strong driver to reduce the radiator area and
hence radiator mass.
• For a given temperature the radiator area is proportional to
the amount of heat rejected.
• For a given amount of heat rejected the radiator area is
inversely proportional to T4
» There is a conflicting requirement to both maximise thermal
efficiency and maximise the temperature at which heat is rejected.
Need to maximise the reactor outlet temperature.
Tail wagging the dog ? - legitimate in this case
Reactor design is driven by the need to optimise
radiator performance.
Requirements for the reactor
and power conversion system
• Power conversion system – Recuperated gas
turbine Brayton cycle (He-Xe) with turbine inlet
temperature 1300K – only high TRL technology
that can offer ηTH ~ 30%
• Reactor options:
• Direct cycle - He-Xe gas-cooled reactor with epithermal to
fast spectrum and core outlet temperature of 1300K.
• Indirect cycle - Lithium liquid metal-cooled reactor with
fast spectrum with core outlet temperature 1350K.
• Fuel options – HEU, Oxide, Carbide, Nitride
Reactor with
4 sub-critical parts
OPUS by CEA
Demonstration of INPPS
• DEMOCRITOS project, EC Horizon 2020
project
• Started March 2015
• Builds on the MEGAHIT roadmap
• Ground Demonstrator
• Core Demonstrator
• Space Architecture Demonstrator
•
Returning to Earth….
• Reactors for space applications are:
• Sealed for life (for a 10 year mission)
• Small, lightweight, self-contained, safe and autonomous
• A given space reactor will be more efficient on Earth as one
can provide a more effective heat sink (should be ~ 50%
efficient)
• Terrestrial applications could be based on transportable high
density power supply, e.g.:
•
•
•
•
•
Power in remote locations
Ship propulsion
De-centralised power
Power on the seabed
Temporary power for disaster relief
• Technology transfer for improved terrestrial nuclear safety
Conclusion
• Nuclear in space has
enabled science and
discovery that would have
been impossible without
• Nuclear will remain essential
for future discovery
• Nuclear in space is a
challenge
• Great potential for space
and terrestrial power
advances
Image courtesy of NASA
Acknowledgements
The work leading to part of this presentation has received funding
from the European Union Seventh Framework Programme and
Horizon 2020.