Ambrosi, Richard M.

Cunningham, Karen

Kim, Tony

Love, Lloyd

Robertson, Glen

Williams, Hugo R.

Young, David

NASA Technical Reports Server

Glen Robertson, David Young, Lloyd Love, Karen Cunningham, Tony Kim
Marshall Space Flight Center, Huntsville Alabama
Richard M. Ambrosi, and Hugo R. Williams 
University of Leicester, Space Research Centre, Leicester, UK.
Preliminary Analysis: Am-241 
RHU/TEG Electric Power Source 
for Nanosatellites
Nuclear and Emerging Technologies for Space 2014
Infinity Science Center, Stennis, MS - February 24-26, 2014
glen.a.robertson@nasa.gov; 256-544-7102
https://ntrs.nasa.gov/search.jsp?R=20140008797 2019-08-31T20:22:18+00:00Z
Nuclear and Emerging Technologies for Space 2013 – Infinity Science Center, Stennis, MS - February 24-26, 2014 
Nanosatellites (NanoSats)
2
 Nanosatellites (NanoSats) are small spacecraft in
the 1-10 kg range, which present a simple, low-cost
option for developing quickly-deployable satellites.
CubeSats, a special category of NanoSats, are
even being considered for interplanetary missions.
However, the small dimensions of CubeSats and
the limited mass of the NanoSat class in general
place limits of capability on their electrical power
systems (especially where typical power sources
such as solar panels are considered) and stored
energy reserves; restricting the power budget and
overall functionality.
Staehle, R., et al., “Interplanetary NanoSat: Opening the Solar System to a Broad Community at Lower Cost,” JoSS, 
Vol. 2, No. 1, pp. 161-186, 2013.
Mass: 46 kg
Mass: 1 kg
Nuclear and Emerging Technologies for Space 2013 – Infinity Science Center, Stennis, MS - February 24-26, 2014 
CubeSats
3
 CubeSats are nano-satellites categorized by size and 
weight
 1U: 10cm x 10cm x 10cm and less than 1Kg
 2U: 10cm x 10cm x 20cm and less than 2Kg
 3U: 10cm x 10cm x 30cm and less than 3Kg
 Limited surface area restricts area for solar panels
and power production capabilities
 1U: 1-2.5 Watts; 2U: 2-5 Watts; 3U: 7-20 Watts
 Power budgets for CubeSat subsystems
 Primary CubeSat subsystems:
 Attitude determination and control (ADCS) 
 Command and data handling (C&DH) 
 Communications
 Electrical power supply (EPS)
 Technical payload
Nuclear and Emerging Technologies for Space 2013 – Infinity Science Center, Stennis, MS - February 24-26, 2014 
Shifting Trends in CubeSat Usage
4
 Typical, past CubeSat mission scopes
 Commercial-off-the-shelf (COTS) component testing in space environment
 Novel technology testing (e.g., ion thrusters, radiation detectors)
 Telemetric sensor data acquisition (e.g., atmospheric data, GPS locating)
 Increasing interest in CubeSats due to proven mission successes and low-cost 
imposed by strict design standards
 New, emerging CubeSat mission scopes
 Trending towards useful scientific data acquisition (i.e., increased high-performance 
requirements for on-board data processing)
 Trending away from simple verification and usage experiments
SpaceWorks_NanoMicrosat_Market_Feb2013.pdf
Nuclear and Emerging Technologies for Space 2013 – Infinity Science Center, Stennis, MS - February 24-26, 2014 
Am-241 RHU/TEG  Power System
5
 United Kingdom (UK) evaluation of several isotopes have concluded that Am-241 is a good
replacement for Pu-238 in space missions. Am-241 has a half-life that is approximately five
times greater than that of Pu-238 and it has been determined that the neutron yield of a
241-AmO2 source is approximately an order of magnitude lower than that of a 238-PuO2
source of equal mass and degree of 16O enrichment. It has been demonstrated that
shielded heat sources fuelled by oxygen-enriched 238-PuO2 have masses that are up to
10 times greater than those fuelled by oxygen-enriched 241-AmO2 with equivalent thermal
power outputs and neutron dose rates at 1 m radii. [1].
 Am-241 radioisotope heat unit and thermal electrical generator (RHU/TEG) are being
developed in the UK as the electrical power source (EPS), where studies have identified
Am-241 as the isotope of choice for a European program [2].
 The UK reports that Am-241 fuel can be produced economically and at high isotopic purity
by separation from stored separated plutonium (Pu) produced during the reprocessing of
civil fuel [3].
1. O’Brien, R. C., et al., “Safe radioisotope thermoelectric generators and heat sources for space applications,” 
Journal of Nuclear Materials, 377, pp. 506–521, 2008. 
2. Sarsfield, M. J. et al., “Progress on 241Am production for use in Radioisotope Power Systems,” Paper 6750 in the 
Proceedings of Nuclear and Emerging Technologies for Space 2013 Albuquerque, NM, February 25-28, 2013. 
3. Ambrosi, R. M. et al., “Development and Testing Of An Americium-241Radioisotope Thermoelectric Generator,” 
Paper 6780 in the Proceedings of Nuclear and Emerging Technologies for Space 2013 Albuquerque, NM, February 
25-28, 2013. 
Nuclear and Emerging Technologies for Space 2013 – Infinity Science Center, Stennis, MS - February 24-26, 2014 
6
 In the US, the Idaho National Laboratory, Center for Space Nuclear 
Research reports [1] that: 
 Am-241 is available at around 1 kg/yr commercially,
 Am-241 produces 59 keV gammas which are stopped readily by tungsten so 
the radiation field is very low. Whereby, an Am-241 source could be placed in 
among the instruments and the waste heat used to heat the platform, and
 Amounts of isotope are so low that launch approval may be easier, especially 
with tungsten encapsulation.
Am-241 RHU/TEG  Power System
1. Howe, S. D., et al., “Compact, Low Specific-Mass Electrical Power Supply for Hostile Environments,” presented at 
the 9th Annual Polar Technology Conference, 2-4 April 2013. 
Nuclear and Emerging Technologies for Space 2013 – Infinity Science Center, Stennis, MS - February 24-26, 2014 
7
Am-241 RHU/TEG  Power System
 For these reasons, Am-241 is well suited to missions that demand long
duration electrical power output, such as deep spaceflight missions and
similar missions that use radiation-hard electronics and instrumentation
that are less susceptible to neutron radiation damage.
Nuclear and Emerging Technologies for Space 2013 – Infinity Science Center, Stennis, MS - February 24-26, 2014 
5 We CubeSat Am-241 RHU/TEG  PS
8
O’Brien, R. C., et al., “Safe radioisotope thermoelectric generators and heat sources for space applications,” Journal of 
Nuclear Materials, 377, pp. 506–521, 2008. 
Radiation shielding: Outermost shield for neutrons would be composed of 5 cm thick boron loaded polyethylene 
Nuclear and Emerging Technologies for Space 2013 – Infinity Science Center, Stennis, MS - February 24-26, 2014 
9
 To overcome the dimension limitation, part of the neutron shielding could be placed
around the CubeSat while only in the carrier/launcher to provide adequate radiation
safety during handling and ground operations, and left in the launcher after the
CubeSat is deployed.
 For smaller Wattage (<5 We) RHU/TEGs, some reduction in the size would be
expected. But the 5 cm thick boron loaded polyethylene neutron shielding required
would still push the overall size outside CubeSat dimensions.
 Need to determine if the 5 cm thick boron loaded polyethylene neutron shielding
would be reduced by the carrier/launcher.
5 We CubeSat Am-241 RHU/TEG  PS
Nuclear and Emerging Technologies for Space 2013 – Infinity Science Center, Stennis, MS - February 24-26, 2014 
Energy Budgeting Analysis
10
Arnold, S.S., Nuzzaci, R., and Gordon-Ross, A., 
“Energy budgeting for NanoSat with an integrated FPGA,” 
Aerospace Conference, 2012 IEEE, 3-10 March 2012.
 1U case study based on the M-Cubed (Orbital) project
 3U case study based on the QuakeSat CubeSat (Orbital) project
Nuclear and Emerging Technologies for Space 2013 – Infinity Science Center, Stennis, MS - February 24-26, 2014 
1U Case Study
 1U case study based on the M-Cubed (Orbital) project [1]
 Power usage between 4-6 Watts on average [2]
11
[1]D. Bekker, T. Werner, T. Wilson, P. Pingree, K. Dontchev, M. Heywood, et al,”A CubeSat design to evaluate the Virtex-5 FPGA 
for Spaceborne Image Processing,” Aerospace Conference, 2010 IEEE, Big Sky, MT, 6-13 March 2010
[2]P. Pingree, T. Werne, D. Bekker, T. Wilson, J. Cutler, M. Heywood, ”The Prototype Development Phase of the CubeSat On-
board processing Validation Experiment” in IEEE Proc. 2011 Aerospace Conference, Big Sky, MT, 2011
1U Power Budget [1]
Nuclear and Emerging Technologies for Space 2013 – Infinity Science Center, Stennis, MS - February 24-26, 2014 
1U Energy Budget
12
 Power usage between 4-6 Watts on average is achievable with a 5 We 
Am-241 RHU/TEG power systems.
 Note. It is believed that the power budget equation used in [1] was not 
correct, which may have lead to it not working with the increase power 
requirement of the FPGA for the 1U case. With correction to the equation 
and using the 5 We continuous Am-241 RHU/TEG power source, it did 
work.
[1] Arnold, S.S., Nuzzaci, R., and Gordon-Ross, A., “Energy budgeting for NanoSat with an integrated FPGA,” 
Aerospace Conference, 2012 IEEE, 3-10 March 2012.
Nuclear and Emerging Technologies for Space 2013 – Infinity Science Center, Stennis, MS - February 24-26, 2014 
3U Case Study
 3U case study based on the QuakeSat CubeSat (Orbital) project [1]
 Estimated maximum power consumption of 12.6 Watts when all components were operating.
13
3U Power Budget [1]
[1] T. Bleier, P. Clarke, J Cutler, L. DeMartini, C. Dunson, et al, QuakeSat Lessons Learned: Notes from the 
Development of a Triple CubeSat, White Paper, June 4, 2003
Nuclear and Emerging Technologies for Space 2013 – Infinity Science Center, Stennis, MS - February 24-26, 2014 
3U Energy Budget
14
   produced store 1 2 1 1 2 2
processing
payload store
... ...n n nJ P t t t Pt P t P tt
P P
         
Orbital Period
t Payload Operational Time
P Payload Power
n
n
 


3U Equatorial Orbital
The P's in the equations are entered as positive numbers. This is opposed to the negative load power numbers 
given in the tables on slides 11 and 13.
Nuclear and Emerging Technologies for Space 2013 – Infinity Science Center, Stennis, MS - February 24-26, 2014 
3U Energy Budget
15
produced store
processing
payload store
J P
t
P P
 
3U Equatorial Orbital
Nuclear and Emerging Technologies for Space 2013 – Infinity Science Center, Stennis, MS - February 24-26, 2014 
Future Work
16
 Establish collaboration between NASA/MSFC and US/UK 
researchers developing Am-241 RHU/TEG power systems.
 Establish Power Board Development at NASA/MSFC by:
 Leveraging MSFC Solid State Ultra-Capacitor Development**, and
 Leveraging MSFC Avionics Heritage.
 Standardize  a 5 We Am-241 RHU/TEG power system for long term 
NanoSat missions.
 Flight Test by 2019 or earlier.
** For more information contact Dr. Terry Rolin at MSFC


Preliminary Analysis: Am-241 RHU/TEG Electric Power Source for Nanosatellites

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