RTG - and its subject wise relation and how its used in nanosatellite.

1. Radioisotope Thermoelectric
Generator in Nanosatellite
-By
Shubhankar S Kulkarni
Roll no.39
L-Section
Electrical and Electronics Engineering
RVCE

2. RTG’s used in Nanosatellite
RTG in Nanosatellite

3. RTG in Nanosatellite
Electronics Aspect
Seebeck Effect
1.
The Seebeck effect is the conversion of temperature differences directly into electricity.
2.
The Seebeck effect is a classic example of an electromotive force (emf) and leads to measurable currents or voltages
in the same way as any other emf.
Electromotive forces modify Ohm's law by generating currents even in the absence of voltage differences (or vice
versa); the local current density is given by
3.
where V is the local voltage and σ is the local conductivity.
•
In general the Seebeck effect is described locally by the creation of an electromotive field
where S is the Seebeck coefficient (also known as thermo power), a property of the local material, and is
the gradient in temperature .The Seebeck coefficients generally vary as function of temperature, and depend
strongly on the composition of the conductor. For ordinary materials at room temperature, the Seebeck coefficient
may range in value from −100 μV/K to +1,000 μV/K.

4. RTG in Nanosatellite
Mechanical Aspect
The casing of the nuclear fuel:
•An RHS-90 is a sealed radiation source in which the fuel composition is sealed hermetically and two-fold into a capsule
using argon welding.
•Several RTGs use strontium-90 in the form of strontium borosilicate glass.
•The capsule is protected against external impact by the thick shell of the RTG, which consists of stainless
steel, aluminium and lead.
•Although molybdenum has several metallurgical characteristics that make its fabrication (especially by welding)
difficult, it has some important properties that give it good potential for use in the next generation of nuclear reactors or
in radioisotope thermoelectric generators.

5. RTG in Nanosatellite
Programming Aspect
An automatic, nuclear powered underwater acoustic beacon and data telemetry system:
•The system's primary function is to provide timed acoustic pulses for the exact positioning determination of various
hydrophones on an underwater array.
•The second function is to measure internal temperatures of the nuclear generator along with other parameters.
• On a predetermined schedule, these data are converted to a coded binary bit form and are acoustically transmitted aspulse tones to the array.
• The coded signal is received by the array and then relayed to a manned shore station via cable to be decoded and
displayed.
•The system was designed Incorporate circuitry for the automatic coding and acoustic telemetry of data concerning the
RTG and power circuits to an array that is linked to shore via cable for subsequent evaluation of the RTG's operating
characteristics.

6. RTG in Nanosatellite
Mathematical Aspect
Fermi Dirac Distribution:
Using the Fermi-Dirac distribution, the average energy Eav per electron in a metal is given by,
where EF0 is the Fermi energy at 0 K. The average energy in the hot end is greater, and energetic electrons in the hot
end diffuse toward the cold region until the potential prevents further diffusion. This Fermi-dirac distribution is derived
using binomial coefficient principle and Lagrange’s multipliers.

7. Fermi-Dirac Distribution Derivation using Lagrange’s
Multipliers and Sterlings Approximations
RTG in Nanosatellite
The number of ways of distributing ni indistinguishable particles among the gi sublevels of an energy level, with a maximum
of one particle per sublevel, is given by the binomial coefficient, using its combinatorial interpretation
For example, distributing two particles in three sublevels will give population numbers of 110, 101, or 011 for a total of three
ways which equals 3!/(2!1!).
The number of ways that a set of occupation numbers ni can be realized is the product of the ways that each individual energy
level can be populated:
Following the same procedure used in deriving the Maxwell–Boltzmann statistics, we wish to find the set of ni for which W is
maximized, subject to the constraint that there be a fixed number of particles, and a fixed energy. We constrain our solution
using Lagrange multipliers forming the function:

8. RTG in Nanosatellite
Using Stirling's approximation for the factorials, taking the derivative with respect to ni, setting the result to zero, and
solving for ni yields the Fermi–Dirac population numbers:
By a process similar to that outlined in the Maxwell-Boltzmann statistics article, it can be shown thermodynamically
that
and
where µ is the chemical potential, k is Boltzmann's constant and T is
the temperature, so that finally, the probability that a state will be occupied is:

9. Safety
RTG in Nanosatellite
•More than 35 years have been researched in the engineering concepts and testing of RTG.
•Multiple layers of protective materials, including iridium capsules (or platinium-sodium capsules for RHUs) and high
strength, heat-resistant graphite blocks are used to protect the radionuclide and prevent its release.
• Iridium is a strong, corrosion-resistant metal that is chemically compatible with plutonium dioxide.
•In addition, graphite is used because it is lightweight and highly heat-resistant.
•Several test for potential accident scenarios to know how RTG responses has been developed.

10. Conclusion
RTG in Nanosatellite
•In space application, Radioisotope Power Systems takes some advantages over solar panels.
•In several space operations there are long periods of darkness, and RPS will be the best actual technology.
•For outer planet missions, RTGs are more useful than solar panels to generate electric power for feeding
communication systems and scientific instruments on the spacecraft.
•Additionally, there are new space technologies that use natural resources with/without radioisotope power systems.
•Actual high-magnitude earthquakes events occurred in Japan in 2011, has severally damaged the Fukushima reactor.
This marks the difficult to change the public opinion about nuclear energy. Besides, the low disposal of Plutonium-238
is a serious drawback.
•The re-establishment of this man-made radioisotope production will be more difficult with these events.
•For using less plutonium than required, RPS efficiency must improve.
•Using low conductivity materials and high thermoelectric rating, Z, RPS efficiency would improve.
•A high-efficiency Stirling-type system would give an apparent mass/power benefit, as well as using less plutonium
for a similar power output.

11. Reference
• Radioisotopes - Applications in Physical Sciences(Book by Prof.Nirmal Singh)
• www.ieeexplore.org- for the scientific papers.
• www.google.com-for its vast number of images and path to all other websites.
• www.wikipedia.org- for the derivations and explanations it provided.
• Elseivers Publications- For providing ennumerable scientific journals.
• www.aws.org
• www.bellona.org
• www.nasa.gov
RTG in Nanosatellite