Jennifer M. Nappier

Glenn Research Center, Cleveland, Ohio

Molly C. Wilson

The University of Michigan, Ann Arbor, Michigan

Long Term Performance Metrics of the GD SDR

on the SCaN Testbed

The First Year on the ISS

NASA/TM—2014-216643

March 2014
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Jennifer M. Nappier

Glenn Research Center, Cleveland, Ohio

Molly C. Wilson

The University of Michigan, Ann Arbor, Michigan

Long Term Performance Metrics of the GD SDR

on the SCaN Testbed

The First Year on the ISS

NASA/TM—2014-216643

March 2014

National Aeronautics and

Space Administration

Glenn Research Center

Cleveland, Ohio 44135
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7115 Standard Drive

Hanover, MD 21076–1320

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Level of Review: This material has been technically reviewed by technical management. 
NASA/TM—2014-216643 1 

Long Term Performance Metrics of the GD SDR 

on the SCaN Testbed 

The First Year on the ISS 

Jennifer M. Nappier 

National Aeronautics and Space Administration 

Glenn Research Center 

Cleveland, Ohio 44135 

Molly C. Wilson 

The University of Michigan 

Ann Arbor, Michigan 48109 

Abstract 

The General Dynamics (GD) S-Band software defined radio (SDR) in the Space Communications 

and Navigation (SCaN) Testbed on the International Space Station (ISS) provides experimenters an 

opportunity to develop and demonstrate experimental waveforms in space. The SCaN Testbed was 

installed on the ISS in August of 2012. After installation, the initial checkout and commissioning phases 

were completed and experimental operations commenced. One goal of the SCaN Testbed is to collect 

long term performance metrics for SDRs operating in space in order to demonstrate long term reliability. 

These metrics include the time the SDR powered on, the time the power amplifier (PA) is powered on, 

temperature trends, error detection and correction (EDAC) behavior, and waveform operational usage 

time. This paper describes the performance of the GD SDR over the first year of operations on the ISS. 

1.0 Introduction 

As of August 2013, the GD SDR has been operating on the ISS for one year. Long term performance 

metrics for the GD SDR on the ISS have been captured and analyzed from the SCaN Testbed telemetry, 

which is collected and stored in a database at a rate of one sample per second when the SDR and Avionics 

are powered on. The long term performance metrics of interest include the SDR and PA power on time, 

receive and transmit waveform operational use time, and temperature trending. This paper provides an 

overview of the GD SDR, the temperature sensors, and the transmit and receive waveforms in Section 2.0. 

The results are discussed in Section 3.0. Suggested future work is described in Section 4.0 and a summary 

is given is Section 5.0. 

2.0 Background Information 

2.1 GD SDR Overview 

The GD S-Band SDR is one of three SDRs in the SCaN Testbed (Ref. 1) on the ISS. The GD SDR 

contains five hardware slices—a digital electronics slice, two power conditioning slices, a power 

amplifier (PA) slice, and an S-Band RF up and down converter slice. There are four temperature sensors 

for the GD SDR, and they are located both internal and external to the radio. The digital electronics slice 

consists of an Actel RTAX field programmable gate array (FPGA), a Xilinx Virtex II FPGA and a 

ColdFire microprocessor. The memory consists of EEPROM for permanent storage as well as SDRAM 

and SRAM for volatile storage. The GD SDR is capable of compensating for single event upsets (SEUs) 

in memory caused by radiation in space. A SEU in the memory would be seen in the EDAC telemetry. 

The waveforms running on the GD SDR are compatible with the Tracking Relay Data Satellite System 

(TDRSS) (Ref. 2). 
NASA/TM—2014-216643 2 

2.2 Temperature Sensors 

There are four temperature sensors for the GD SDR on the SCaN Testbed. The temperature sensors 

internal to the SDR are located on the PA and the temperature controlled crystal oscillator (TCXO). These 

sensors are named GD PA TEMP and GD TCXO TEMP. The telemetry from these temperature sensors is 

sent from the SDR to the Avionics to be transmitted to the ground, so measurements from these sensors 

are only available when the SDR is powered on. There are also two temperature sensors placed on the 

baseplate of the SDR. These sensors are connected directly to the Avionics, so readings are available 

anytime the Avionics is powered on. The Avionics sensor names are AV GD TEMP1 and AV GD TEMP2. 

2.3 Error Detection and Correction 

There is telemetry for both correctable and uncorrectable error detection and corrections (EDACs) 

from the GD SDR. The telemetry is for the EEPROM, the SDRAM, and the SRAM memories. A single 

error in memory is correctable while a double error in memory is not correctable, but it is detectable. 

EDACS are caused by radiation in space. 

2.4 GD SDR Waveform Description 

2.4.1 Receive Waveform 

The initial GD SDR receive waveform includes three reconfigurable parameters—data rate, coding 

on/off, and center frequency. The S-Band RF center frequency can be changed to operate with the TDRSS 

Single Access (SA) or Multiple Access (MA) modes. The receive waveform can be configured to operate 

at two data rates—18 and 72 kbps. The Viterbi decoder for forward error correction can be enabled and 

disabled. These three parameters lead to the eight different receive waveform mode combinations. 

2.4.2 Transmit Waveform 

The transmit waveform is capable of operating in the TDRSS Data Group (DG) 1, Modes 1, 2, and 3, 

as well as DG 2 configurations. The data rates can be configured to 24, 192, and 1 Mbps and forward 

error correction can be enabled and disabled. The RF center frequency can be selected to operate with the 

TDRSS SA or MA modes. These parameters lead to 28 different waveform mode combinations. For the 

SCaN Testbed operations, each unique transmit and receive waveform mode combination was given a 

unique waveform number, which can be seen in the waveform tables in Section 3.0 (Tables 4 and 5). 

3.0 Results 

The telemetry from the first year on ISS was processed and results for the SDR power on time, the 

PA power on time, EDAC occurrence, waveform operational use, as well as temperature were analyzed. 

These performance metrics for the first year of on-orbit operation on the ISS are discussed in this section. 

3.1 SDR Power on Time 

The GD SDR has been powered on and operating in space for a total of 268.7 hr. The power on time 

by calendar month is shown in Table 1. The SDR was powered on for the first time in August 2012 and 

initial checkout tests were completed in September and October 2012. In November, the GD SDR was 

primarily used during the RF subsystem checkout. The SDR was not used in the month of December 

2012 due to a project stand down. The testing in 2013 included commissioning, RF characterization, and 

the start of experiments on the GD SDR. 
NASA/TM—2014-216643 3 

3.2 PA Power on Time 

The PA on the GD SDR has been powered on and transmitting in space for 41.3 hr. The power on 

time by calendar month is shown in Table 2. Transmit tests started in October 2012 during the checkout 

phases of the project. The testing completed in 2013 is listed in Section 3.1. 

3.3 Temperature 

This section details the results of the temperature sensor analysis. Table 3 contains some overall 

statistics for each temperature sensor for the GD SDR during the year from August 2012 to August 2013. 

Figure 1 shows histograms of the temperatures recorded from each sensor over the year. The mean 

temperatures were between 7.5 to 11.5 °C. The temperature operating range was primarily between 

0 to 20 °C. 

The GD radio was not powered on during December, so data from this month can be used as a control 

group against which data from when the radio was powered on can be compared. In all of the temperature 

data from December, a 90 min period was observed during which the temperature increases and decreases 

(Fig. 2). This temperature change corresponds to the ISS’s 90-min orbit around Earth. This trend is also 

evident in most other temperature plots. 

TABLE 1.—GD SDR POWER ON TIME 

Month Year Time on, 

hr 

August 2012 5.7 

September 2012 14.3 

October 2012 11.4 

November 2012 70.4 

December 2012 0.0 

January 2013 11.0 

February 2013 24.5 

March 2013 51.9 

April 2013 15.8 

May 2013 30.0 

June 2013 5.4 

July 2013 28.2 

Total 268.7 

TABLE 2.—GD SDR PA POWER ON TIME 

Month Year Time on, 

hr 

August 2012 0.0 

September 2012 0.0 

October 2012 1.6 

November 2012 7.9 

December 2012 0.0 

January 2013 2.5 

February 2013 3.7 

March 2013 8.3 

April 2013 2.8 

May 2013 4.9 

June 2013 1.2 

July 2013 8.4 

Total 41.3 

TABLE 3.—GD SDR TEMPERATURE STATISTICS 

 AV GD TEMP1,

C 

AV GD TEMP2

°C 

GD PA TEMP,

°C 

GD TCXO TEMP, 

°C 

Mean 7.6 7.5 11.5 9.8 

Median 7.1 7.1 10.8 10.0 

Max 24.1 24.9 24.6 23.8 

Min 0.3 –1.2 3.3 –2.8 

Standard deviation 3.3 3.3 3.5 3.5 
NASA/TM—2014-216643 4 

Figure 1.—GD SDR temperature histograms. 

Figure 2.—GD SDR baseplate temperature (December 3, 2012). 

 

-10 0 10 20 30

0

2

4

6

8

10 x 105

AV GD TEMP1

Occurrences

-10 0 10 20 30

0

2

4

6

8

10 x 105

AV GD TEMP2

Occurrences

-10 0 10 20 30

0

0.5

1

1.5

2

2.5 x 105

GD PA TEMP

Occurrences

-10 0 10 20 30

0

1

2

3

4 x 105

GD TCXO TEMP

Occurrences

14:00 15:00 16:00 17:00 18:00 19:00 20:00 21:00 22:00

-10

0

10

20

30

GMT

Temperature (°C)

AV GD TEMP1

AV GD TEMP2

ISS 90 minute

orbit around Earth
NASA/TM—2014-216643 5 

Figure 3 shows an example of the behavior of all four temperature sensors after the SDR has been 

powered on. In 17 out of 40 cases where the radio is powered on, the overall temperature increases after 

power on and this can be seen in Figure 3. However, there are 19 cases where the radio is powered on and 

the temperature does not change outside of the 90-min period, and 4 cases where the radio is powered on 

and the temperature decreases overall. In addition, there are 8 cases where the radio is powered off and 

the temperature increases. 

When the PA is powered on and the SDR is transmitting, an increase in temperature can be seen. In 

Figure 4, the vertical lines indicate when the power amplifier is being powered on or off; when the line is 

horizontal at 25, the PA is on, and when it is horizontal at 0, the PA is off. There is a clear increase in 

temperature when the radio is transmitting. This increase is most noticeable in the PA sensor, but can also 

be observed more subtly in the data from the other sensors. 

Figure 3.—GD SDR temperature after power on (November 6, 2012). 

Figure 4.—Temperature increase when the SDR is transmitting (November 2, 2012). 

 

09:00 12:00 15:00 18:00 21:00

-10

-5

0

5

10

15

20

25

30

GMT

Temperature (°C)

AV GD TEMP1

AV GD TEMP2

GD PA TEMP

GD TCXO TEMP

PA On/Off

PA On

PA Off

09:00 12:00 15:00 18:00 21:00

-10

-5

0

5

10

15

20

25

30

GMT

Temperature (°C)

AV GD TEMP1

AV GD TEMP2

GD PA TEMP

GD TCXO TEMP

PA On/Off

PA On

PA Off
NASA/TM—2014-216643 6 

It was hypothesized that there would be a correlation between the beta angle of the ISS and the 

temperature of the payload. The beta angle (seen in the upper portion of the figure) and the mean 

temperature from the GD SDR temperature sensor 1 (seen in the lower portion of the figure) are plotted in 

Figure 5. There was no correlation between the beta angle of the ISS and the mean temperature from 

Avionics GD Temperature Sensor 1. 

3.4 Error Detection and Correction 

As of August 1, 2013, no EDACs have been detected on the GD SDR. This means that any radiation 

in space has not caused either a correctable or detectable error in memory. Since the GD SDR is operating 

on the ISS in low Earth orbit, which is a low radiation environment, the fact that no EDACS have been 

detected is consistent with expectations. 

3.5 Waveform Operational Time 

The operational time for the receive and transmit waveforms can be seen in Tables 4 and 5. The most 

used waveform pair was the low rate (18 kbps receive; 24 kbps transmit), uncoded, SA, DG1 M2 

waveform. This waveform was used frequently during the RF Subsystem checkout tests. 

Figure 5.—Beta angle and GD SDR baseplate temperature. 

TABLE 4.—GD SDR RECEIVE WAVEFORM OPERATIONAL TIME 

Waveform 

number 

Data rate, 

kbps 

Forward error 

correction 

Frequency Time used, 

hr 

180/182 18 Uncoded SA 26.4 

179/181 18 Coded SA 3.0 

184/186 18 Uncoded MA 3.8 

183/185 18 Coded MA 3.5 

204/206 72 Uncoded SA 4.4 

203/205 72 Coded SA 1.2 

208/210 72 Uncoded MA 1.4 

207/208 72 Coded MA 1.5 

 

Aug Sep Oct Nov Dec Jan Feb Mar Apr May Jun Jul

-100

0

100

GMT

Beta Angle (°)

Aug Sep Oct Nov Dec Jan Feb Mar Apr May Jun Jul

-10

0

10

20

30

GMT

Temperature (°C)
NASA/TM—2014-216643 7 

TABLE 5.—GD SDR TRANSMIT WAVEFORM OPERATIONAL TIME 

Waveform 

number 

Frequency Waveform 

type 

Data rate, 

kbps 

FEC Coherency Time used, 

hr 

165 SA DG1, Mode 1 and 2 24 Coded Enabled 0.4 

213 SA DG1, Mode 1 and 2 24 Coded Disabled 1.9 

166 SA DG1, Mode 1 and 2 24 Uncoded Enabled 0.0 

214 SA DG1, Mode 1 and 2 24 Uncoded Disabled 23 

173 MA DG1, Mode 1 and 2 24 Coded Enabled 0.9 

221 MA DG1, Mode 1 and 2 24 Coded Disabled 2.3 

174 MA DG1, Mode 1 and 2 24 Uncoded Enabled 0.6 

222 MA DG1, Mode 1 and 2 24 Uncoded Disabled 3.2 

189 SA DG1, Mode 1 and 2 192 Coded Enabled 1.1 

237 SA DG1, Mode 1 and 2 192 Coded Disabled 0.0 

190 SA DG1, Mode 1 and 2 192 Uncoded Enabled 1.6 

238 SA DG1, Mode 1 and 2 192 Uncoded Disabled 0.7 

197 MA DG1, Mode 1 and 2 192 Coded Enabled 1.3 

245 MA DG1, Mode 1 and 2 192 Coded Disabled 0.0 

198 MA DG1, Mode 1 and 2 192 Uncoded Enabled 0.0 

246 MA DG1, Mode 1 and 2 192 Uncoded Disabled 1.3 

299 SA DG1, Mode 3 1000 Coded Enabled 0.0 

300 SA DG1, Mode 3 1000 Uncoded Enabled 1.1 

303 MA DG1, Mode 3 1000 Coded Enabled 0.0 

304 MA DG1, Mode 3 1000 Uncoded Enabled 0.0 

261 SA DG2 1000 Coded Enabled 0.0 

262 SA DG2 1000 Uncoded Enabled 0.0 

381 SA DG2 1000 Coded Disabled 0.0 

382 SA DG2 1000 Uncoded Disabled 2.0 

385 MA DG2 1000 Coded Enabled 0.0 

386 MA DG2 1000 Uncoded Enabled 0.0 
NASA/TM—2014-216643 8 

4.0 Future Work 

While there were many temperature trends that are easily explainable as described in Section 3.3, 

there are also several unexplained trends. This section suggests possible investigations relating to the 

behavior of the GD SDR temperature in space. Figure 6(b) is a magnified section of the Figure 6(a). 

From the magnified image, we can see that the period of temperature increase and decrease due to the ISS 

orbit around the Earth is still about 90 min, as it should be. The unusual behavior seen in this graph is the 

miniscule change in the temperature magnitude. It is less than half a degree, where in December (the 

baseline in Figure 2) the change in temperature due to being exposed to Sun and shade was about 2or 

3. In other months, the change is greater than this, but only on a few days in June is the change so small. 

(a) 

(b) 

Figure 6.—(a) Baseplate temperature magnitude, (b) zoomed (June 4, 2013). 

00:00 06:00 12:00 18:00 00:00

-10

-5

0

5

10

15

20

25

30

GMT

Temperature (°C)

AV GD TEMP1

AV GD TEMP2

06:00 12:00 18:00 00:00

3.5

4

4.5

5

5.5

6

6.5

7

7.5

GMT

Temperature (°C)

AV GD TEMP1

AV GD TEMP2
NASA/TM—2014-216643 9 

In Figure 7, the temperature is trending down even though the radio is on. This decrease while the 

radio is on happens four times during the year of data. This is the biggest decrease; in the other three 

occurrences, the decrease is very slight (the other occurrences are July 8, July 11, and September 13). 

In Figure 8, the overall temperature is trending up even though the radio is not on. Perhaps another 

radio has in the testbed has been turned on and is causing the increase in temperature. 

Figure 7.—Downward temperature trend (March 18, 2013). 

Figure 8.—Upward temperature trend (May 6, 2013). 

 

12:00 15:00 18:00 21:00 00:00

-10

-5

0

5

10

15

20

25

30

GMT

Temperature (°C)

AV GD TEMP1

AV GD TEMP2

GD PA TEMP

GD TCXO TEMP

PA On/Off

PA On

PA Off

14:00 15:00 16:00 17:00 18:00 19:00 20:00 21:00 22:00

-10

-5

0

5

10

15

20

25

30

GMT

Temperature (°C)

AV GD TEMP1

AV GD TEMP2
NASA/TM—2014-216643 10 

Figure 9.—Unexplained temperature trend pattern (February 12, 2013). 

Figure 9 shows a longer 3-hr temperature pattern consisting of a longer maximum followed by a 

shorter, local maximum. This occurs on 34 of the 124 days on which data was taken. It happens when the 

radio is both on and off; six of the times this pattern occurs the radio is on, and 28 of the times the radio is 

off. It happened throughout the year; the only months that do not have temperature data that follow this 

pattern are November and December. 

5.0 Summary 

The GD SDR long term performance metrics analysis for the first year on the ISS has been 

completed. The analysis included SDR (269 hr) and PA (41 hr) power on time; and waveform operational 

time. A check on the EDAC counts showed that there have been no EDACs so far. The temperature 

analysis revealed a warming and cooling period consistent with the revolution of the ISS around the 

Earth. There does not appear to be a correlation between beta angle and SDR temperature. The future 

work section (Section 4.0) lists some unexplained temperature trends that could be the subject of further 

investigation. 

References 

1. S. Johnson, R. Reinhart, and T. Kacpura. “CoNNeCT’s Approach for the Development of Three 

Software Defined Radios for Space Application,” presented at the IEEE Aerospace Conference, 

March 2012. 

2. Space Network (SN) User’s Guide, 450-SNUG (Revision 9, August 2007). 

15:00 18:00 21:00

-10

-5

0

5

10

15

20

25

GMT

Temperature (°C)

AV GD TEMP1

AV GD TEMP2

GD PA TEMP

GD TCXO TEMP

PA On/Off

PA On

PA Off