**5. Space vehicle link services**

and the receiver, a good indication of the signal strength is given by the received isotropic power. RIP is simply the transmitter EIRP after subtracting off the losses

where LA is the atmospheric loss extracted from tables or curves, in negative dB

The last portion of **Table 3** addresses the receiving system and assesses how well it performs. This section involves with the calculation of the signal strength and the noise strength, resulting in the ratio of signal power over noise power density (C/N0). In general, we first address the signal power and then the noise power density. Line 21 provides for the receive antenna size consistent with the receive antenna gain to be calculated later. The next parameter in **Table 3** is the polarization loss, which accounts for the mismatching between the polarization axial ratios of the received signal and the receiving system. The axial ratio is the ratio of the major axis of an ellipse to its minor axis. For circularly polarized signal, the ratio should be 0 dB. Any deviation from 0 dB results in a polarization loss. Line 23 shows the values of receive antenna gain. For downlink in which the receive antenna is a dish antenna located at GS, Gr is calculated using the standard dish antenna equa-

(very small at 0.02 dB/Km per Datron chart in L and S bands). Ls can also be

*Gr* <sup>¼</sup> <sup>10</sup> <sup>∗</sup> log 10 <sup>η</sup> <sup>∗</sup> <sup>π</sup> <sup>∗</sup> <sup>f</sup>*<sup>C</sup>* <sup>∗</sup> <sup>D</sup>

**Table 3**); fC = downlink frequency, in Hz; D = antenna diameter, in m; and

the polarization loss, plus the receive antenna gain, i.e.

where LP is the polarization loss, in negative dB.

of SV antenna, with a gain of 2 dBi (see line 23 of **Table 3**).

*TS* <sup>¼</sup> *TA* <sup>þ</sup> <sup>10</sup>ð Þ *LL*þNF *<sup>=</sup>*<sup>10</sup> � <sup>1</sup>

where NF = low noise amplifier noise factor, in dB and LL = line loss, in dB.

where η = average antenna efficiency (assumed to be 0.6 in the calculation in

At the end, the received power at the antenna feed is just the sum of RIP, minus

For the downlink transmit antenna on the SV, as in the case of uplink receive antenna, the SV antenna is a broad beam Earth coverage (EC) omnidirectional type

For the noise power density (N0), we need to calculate the system temperature (TS) measured at the antenna feed. The system temperature is the sum of antenna sky temperature (TA) and the composite temperature from antenna line loss (LL) and low noise amplifier noise figure (NF) which are referred to the antenna feed. In

*c* 

*C* ¼ RIP þ *LP* þ *Gr* in dBW (9)

in dBi (8)

∗ 290 in Deg � K (10)

RIP ¼ EIRP þ *LS* þ *LA* in dBW (7)

of the transmission medium, i.e.

obtained from the Datron calculator [8].

*Satellite Systems - Design, Modeling, Simulation and Analysis*

**4.3 Receive system and performance**

tion (similar to Eq. (6) for Gt).

c = velocity of light, in m/s.

linear quantity, TS is given by [1].

**170**

The noise density (N0) is given by

For many SVs, we are interested in their uplink and downlink services. **Table 2** shows an example, taken from an IEEE paper [4]. This is the standard link budget, where the ground station is an AFSCN [3] remote tracking station (RTS) using SGLS waveform [3, 4]. The waveform is described in an AFSCN interface control document (ICD) [3] and is implemented in DLA, although other waveforms can be readily incorporated. The uplink has two services of interest—carrier and command —while the downlink has three services of interest: carrier, ranging, and telemetry. In general service margins are calculated for these five services. For the SGLS waveform, command is coupled with ranging and modulated on the uplink carrier; therefore command is also turned around at the SV along with ranging. This SGLS turnaround process explains the reason that **Table 2** shows a power allocation for command in the downlink and no calculation for its margin. As a result, downlink power allocated to command is essentially wasted while robbing power from other downlink services. The requirements and service margins for command and telemetry are expressed in Eb/N0, since it is the bit error rate (BER) that counts for both cases. The carrier and ranging are expressed in C/No given by a specific station. For ranging, it is the autocorrelation value between the decoded ranging code and the transmitted ranging code that needs to be maximized in order to successfully perform accurate ranging.

**Table 2** represents uplink and downlink budgets for SGLS TT&C. Let us address the important aspects of the calculation of uplink and downlink services in the next few subsections. The role of modulation indices is to divide up the power for allocation to services. The modulation index is expressed in radians so that it can go right in as an argument in a sinusoidal or Bessel expression. If the modulation indices of all services are zero radians, no power is allocated to the services, and the carrier retains all the link power calculated in Section 4. If the modulation indices of services are not zero, portions of the power are taken from the carrier and allocated to the services. The remaining power stays with the carrier as the "residual carrier power."

#### **5.1 SNR and link margin calculation**

After SV separation, we are dealing with the SV uplink and downlink using SGLS or NASA Unified S-Band waveforms as described in [3, 4]. For telemetry service, the requirement is SNR = Pservice/NoB = Eb Rb/NoB = Eb/No in dB. For carrier and ranging, the requirements are stated in terms of C/No as mentioned before. For acquisition, the uplink carrier loop bandwidth could be as high as +/� 100 KHz, while its tracking bandwidth could be as small as a few Hz. For the station the carrier tracking loop bandwidth is about 20–50 Hz, as in **Table 2** in line 36. For ranging, the bandwidth of 10 Hz represents ranging tracking loop bandwidth (**Table 2**, line 56), which corresponds to the sampling rate of the autocorrelation


#### **Table 4.**

*Uplink and downlink service modulation losses for SGLS and NASA USB.*

value between the detected ranging code and the transmitted ranging code. For command and telemetry, the requirements are expressed in terms of Eb/N0. The command and telemetry data bit rates of 1000 bps each are representing the lower end of their SGLS choices. As shown in **Table 2**, the results from the SNR calculation are the values of C/N and Eb/N0 for various received uplink services (lines 37 and 48 for command C/N or Eb/No) and for various downlink services (line 55 for ranging service Prng/No and line 70 for telemetry service Eb/No). The uplink service modulation losses for SGLS and NASA USB with subcarrier (S/C) [3, 4, 9] are shown in **Table 4**. The downlink service modulation losses for SGLS and NASA USB with subcarrier (S/C) [3, 4, 9] are shown in **Table 4**. Also note that β1, β2, and β<sup>3</sup> represent the modulation indices for command (CMD), ranging (RNG), and telemetry (TLM), respectively, per [3, 4, 9]. These uplink and downlink modulation losses are in lines 34, 44, and 54 in **Table 2**.

are displayed together. As an example a specific LV to TDRSS BPSK link using

*Dynamic Link from Liftoff to Final Orbital Insertion for a MEO Space Vehicle*

*DOI: http://dx.doi.org/10.5772/intechopen.92462*

put on the I channel and the ranging signal is on the Q channel.

This chapter discusses the required three DLAs and related tracking waveforms to cover the three launch stages, namely, (a) the launch vehicle tracking link from liftoff to its end LOS using the digital FM or BPSK signal, (b) the launch vehicle tracking link from LOS to TDRSS at BLOS using NASA USB signal, and (c) the final tracking link from SV to an AFSCN ground station using AFSCN SGLS, AFSCN NSGLS, or NASA USB waveforms. In the third tracking link case, BPSK, QPSK, or AQPSK waveforms were used, in which for QPSK and AQPSK, the telemetry data is

The chapter shows that good telemetry link margins from LV to tracking stations such as TEL4, JDMTA, and ANT or to a NASA TDRSS relay satellite can be achieved using digital FM, BPSK, QPSK, or AQPSK signals, after SV separation. The chapter also shows that good tracking link margins can be achieved from SV to AFSCN ground stations, including IOS or DGS as the first contact station.

NASA data is shown in **Table 1**.

*LV slant range received TLM Eb/No and TLM link margin.*

**7. Conclusion**

**173**

**Figure 4.**

For NSGLS waveforms such as the direct mod BPSK, QPSK, and AQPSK, the service mod losses are negligible. Finally, the calculated service SNR in **Table 2** is compared with the required SNR to obtain the link margin for each service. The required SNR values capture all the performance requirements for the services, such as ranging accuracy, tracking loop loss likelihood, bit error rate, and others.

#### **6. Launch vehicle dynamic link**

Before SV separation from the LV, we are also interested in the dynamic link from a ground station to the LV, from liftoff to the SV after separation, along the entire LV flight path using the tracking stations in the line of sight (TEL4, JDMTA, ANT, DGS, TDRSS). The waveforms for this LV tracking are described in Range Commander Council (RCC) handbook [2]. One must ensure that the downlink telemetry link from the launch vehicle to these ground stations and TDRSS relay satellite are positive as can be seen in **Figure 3**. The basic LV range modulations are digital FM, BPSK, QPSK, AQPSK, etc. as discussed in RCC [2]. In **Figure 4**, dynamic LV slant range "received TLM Eb/No" and "TLM link margin" for a specific mission *Dynamic Link from Liftoff to Final Orbital Insertion for a MEO Space Vehicle DOI: http://dx.doi.org/10.5772/intechopen.92462*

**Figure 4.** *LV slant range received TLM Eb/No and TLM link margin.*

are displayed together. As an example a specific LV to TDRSS BPSK link using NASA data is shown in **Table 1**.

### **7. Conclusion**

value between the detected ranging code and the transmitted ranging code. For command and telemetry, the requirements are expressed in terms of Eb/N0. The command and telemetry data bit rates of 1000 bps each are representing the lower end of their SGLS choices. As shown in **Table 2**, the results from the SNR calculation are the values of C/N and Eb/N0 for various received uplink services (lines 37 and 48 for command C/N or Eb/No) and for various downlink services (line 55 for ranging service Prng/No and line 70 for telemetry service Eb/No). The uplink service modulation losses for SGLS and NASA USB with subcarrier (S/C) [3, 4, 9] are shown in **Table 4**. The downlink service modulation losses for SGLS and NASA USB with subcarrier (S/C) [3, 4, 9] are shown in **Table 4**. Also note that β1, β2, and β<sup>3</sup> represent the modulation indices for command (CMD), ranging (RNG), and telemetry (TLM), respectively, per [3, 4, 9]. These uplink and downlink modula-

**No. Uplink modulation Carrier Ranging Command**

*J* 2

J0 2 (*β*1)cos<sup>2</sup>

J0 2 (*β*1) J0 2 (*β*2) 2J0 2 (*β*1)J1 2 (β2)

**No. Downlink modulation Carrier Ranging Telemetry**

J0 2 (*β*<sup>0</sup> 1)J0 2 (*β*<sup>0</sup> 2)

J0 2 (*β*3)

J0 2 (*β*3)J0 2 (*β*<sup>0</sup> 2) 2J0 2 (*β*3)J1 2 (*β*<sup>0</sup> 2) 2J0 2 (*β*<sup>0</sup> 2)J1 2 (*β*3)

*<sup>o</sup> <sup>β</sup>*<sup>1</sup> ð Þ*:cos* <sup>2</sup> *<sup>β</sup>*<sup>2</sup> ð Þ *<sup>J</sup>*

2

+ … …

2J0 2 (*β*<sup>0</sup> 1) J1 2 (*β*<sup>0</sup> 2)

J0 2 (*β*3)

(*β*2) J0 2 (*β*1) sin<sup>2</sup>

*<sup>o</sup> <sup>β</sup>*<sup>1</sup> ð Þ*: sin* <sup>2</sup> *<sup>β</sup>*<sup>2</sup> ð Þ <sup>2</sup>*<sup>J</sup>*

2

2J0 2 (*β*2) J1 2 (*β*1)

2J0 2 (*β*<sup>0</sup> 1)J0 2 (*β*<sup>0</sup> 2)

J1 2 (*β*3)

+ … ..

(*β*2) 2J1 2 (*β*1) cos<sup>2</sup>

<sup>1</sup> *<sup>β</sup>*<sup>1</sup> ð Þ*:cos* <sup>2</sup> *<sup>β</sup>*<sup>2</sup> ð Þ

(*β*2)

For NSGLS waveforms such as the direct mod BPSK, QPSK, and AQPSK, the service mod losses are negligible. Finally, the calculated service SNR in **Table 2** is compared with the required SNR to obtain the link margin for each service. The required SNR values capture all the performance requirements for the services, such as ranging accuracy, tracking loop loss likelihood, bit error rate, and others.

Before SV separation from the LV, we are also interested in the dynamic link from a ground station to the LV, from liftoff to the SV after separation, along the entire LV flight path using the tracking stations in the line of sight (TEL4, JDMTA, ANT, DGS, TDRSS). The waveforms for this LV tracking are described in Range Commander Council (RCC) handbook [2]. One must ensure that the downlink telemetry link from the launch vehicle to these ground stations and TDRSS relay satellite are positive as can be seen in **Figure 3**. The basic LV range modulations are digital FM, BPSK, QPSK, AQPSK, etc. as discussed in RCC [2]. In **Figure 4**, dynamic LV slant range "received TLM Eb/No" and "TLM link margin" for a specific mission

tion losses are in lines 34, 44, and 54 in **Table 2**.

**Uplink service modulation losses for SGLS and NASA USB**

*Satellite Systems - Design, Modeling, Simulation and Analysis*

1 AM-3FSK/PRN RNG/PM (SGLS unfiltered

2 BPSK/PRN RNG/PM (USB filtered case) (Eqs. (1-22) and (1-23)) [9]

3 BPSK/Tone RNG/PM (USB unfiltered

4 PRN RNG/PSK TLM/PM (SGLS filtered

5 Tone RNG/PSK TLM/PM (USB filtered

(Eqs. (2-18) and (2-20)) [4]

(Eqs. (2-18) and (2-21)) [9]

**Downlink modulation losses for SGLS and NASA USB**

*Uplink and downlink service modulation losses for SGLS and NASA USB.*

(Eqs. (1-18) and (1-21)) [9]

uplink) [3, 4]

case)

case)

case)

**Table 4.**

**172**

**6. Launch vehicle dynamic link**

This chapter discusses the required three DLAs and related tracking waveforms to cover the three launch stages, namely, (a) the launch vehicle tracking link from liftoff to its end LOS using the digital FM or BPSK signal, (b) the launch vehicle tracking link from LOS to TDRSS at BLOS using NASA USB signal, and (c) the final tracking link from SV to an AFSCN ground station using AFSCN SGLS, AFSCN NSGLS, or NASA USB waveforms. In the third tracking link case, BPSK, QPSK, or AQPSK waveforms were used, in which for QPSK and AQPSK, the telemetry data is put on the I channel and the ranging signal is on the Q channel.

The chapter shows that good telemetry link margins from LV to tracking stations such as TEL4, JDMTA, and ANT or to a NASA TDRSS relay satellite can be achieved using digital FM, BPSK, QPSK, or AQPSK signals, after SV separation. The chapter also shows that good tracking link margins can be achieved from SV to AFSCN ground stations, including IOS or DGS as the first contact station.

*Satellite Systems - Design, Modeling, Simulation and Analysis*

**References**

[1] Sklar B. Digital Communications Fundamentals and Applications. New Jersey: Prentice Hall; 1988. p. 221

*DOI: http://dx.doi.org/10.5772/intechopen.92462*

*Dynamic Link from Liftoff to Final Orbital Insertion for a MEO Space Vehicle*

[2] RCC, Range Commander Council, Telemetry Group. Document 119-88; 1988. (approved for public release)

[3] Air Force Satellite Control Network (AFSCN) Interface Control Document: Range Segment to Space Vehicle, ICD-000502A, prepared by The Aerospace Corporation for Space and Missile

[4] Kreng JK, Ardeshiri MM. Effects of turnaround command on SGLS C/No and SNR performance. In: 2018 IEEE Aerospace Conference, Paper #2513;

[5] Krikorian YY et al. Dynamic link analysis tool for a telemetry downlink system. In: 2004 IEEE Aerospace Conference Proceedings; 2004.

[6] Spiegel MR, Lipschutz S, Liu J. Mathematical Handbook of Formulas and Tables, Third Edition, Section 10. New York: McGraw Hill; 2009

[7] Kreng J, Do S, Mathur A. USB Command Link Via TDRSS to Satellites and Possibly Space Launch Vehicles

[8] Datron/Transco Inc., USA. Antenna, Space and Atmospheric Calculator

[9] Kreng J, Krikorian Y, Raghavan S. Telemetry, tracking, and command link

performance using USB/STDN waveform. IEEE/Aerospace Journal.

Systems Center; 2011

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**175**
