# Presentation: 372554

## Terra Operational Solution

**to Potential RFI with DSN**

**Bob Kozon**
**Terra Flight Operations Director**
**GSFC Code 428**
**(301) 614-5045**
**bob.kozon@gsfc.nasa.gov**

## Terra Direct Broadcast (DB) system was recognized as a potential source of RFI for Deep Space Network (DSN) X-band user spacecraft
A total of nine (9) DSN user spacecraft would potentially be impacted at the time of initial turn-on of Terra DB
Cassini
NEAR
Voyager 1 and 2
Ulysses
Mars Global Surveyor
Stardust
Nozomi (Planet-B)
Deep Space 1
Mars Odyssey was launched after Terra, following termination of operations for the NEAR mission

*A total of nine (9) DSN user spacecraft would potentially be impacted at the time of initial turn-on of Terra DB*
*Cassini*
*NEAR*
*Voyager 1 and 2*
*Ulysses*
*Mars Global Surveyor*
*Stardust*
*Nozomi (Planet-B)*
*Deep Space 1*
*Mars Odyssey was launched after Terra, following termination of operations for the NEAR mission*

**Potential DSN RFI Problem for Terra**

## An operational solution to the potential DSN RFI problem was required to be in place upon activation of the Terra DB system
Horizon-to-Horizon turn-off of Terra DB while over DSN was requested
Operational procedure to accommodate this requirement was implemented on the Terra Flight Dynamics System (FDS) operating in the EOS Operations Center (EOC)
Ground Station masks consisting of  36 azimuth/elevation points were acquired for each DSN dish with X-band downlink capability for the Goldstone, Madrid, and Canberra sites
Masks were incorporated into Terra FDS, enabling generation of output products containing Terra AOS/LOS times for each dish
Software was written to extract the earliest AOS and latest LOS time for each Terra pass over each of the DSN sites
These values were used as input to the Absolute Time Command (ATC) load generation process for the turn-off and turn-on of Terra DB over the DSN sites

*Horizon-to-Horizon turn-off of Terra DB while over DSN was requested*
*Operational procedure to accommodate this requirement was implemented on the Terra Flight Dynamics System (FDS) operating in the EOS Operations Center (EOC)*
*Ground Station masks consisting of  36 azimuth/elevation points were acquired for each DSN dish with X-band downlink capability for the Goldstone, Madrid, and Canberra sites*
*Masks were incorporated into Terra FDS, enabling generation of output products containing Terra AOS/LOS times for each dish*
*Software was written to extract the earliest AOS and latest LOS time for each Terra pass over each of the DSN sites*
*These values were used as input to the Absolute Time Command (ATC) load generation process for the turn-off and turn-on of Terra DB over the DSN sites*

**Initial Solution to DSN RFI Issue**

## Initial solution was good for JPL, but bad for Terra and DB user community
Horizon-to-Horizon turn-off of DB during each Terra pass over Goldstone, Madrid, and Canberra resulted in significant data loss over these regions
Large number of DB system On-Off cycles increased operator-intensive nature of ATC load verification process
Large number of DB system On-Off cycles raises hardware life concerns
Alternate solutions were implemented and proposed to JPL
Software was written at GSFC to read the DSN schedule from the JPL Web page and compute DB On/Off times based upon scheduled DSN contacts with X-band user spacecraft
Solution was unacceptable to JPL because the Web-based schedule cannot accommodate late schedule changes and/or emergency contact scheduling

*Horizon-to-Horizon turn-off of DB during each Terra pass over Goldstone, Madrid, and Canberra resulted in significant data loss over these regions*
*Large number of DB system On-Off cycles increased operator-intensive nature of ATC load verification process*
*Large number of DB system On-Off cycles raises hardware life concerns*
*Alternate solutions were implemented and proposed to JPL*
*Software was written at GSFC to read the DSN schedule from the JPL Web page and compute DB On/Off times based upon scheduled DSN contacts with X-band user spacecraft*
*Solution was unacceptable to JPL because the Web-based schedule cannot accommodate late schedule changes and/or emergency contact scheduling*

**Problems with Initial Solution**

## Actual Terra X-band data was acquired at the DSN Goldstone site
Analysis of data indicated that the “zone of exclusion” for the DSN did not need to encompass the entire Horizon-to-Horizon circle
Zone could be confined to a much narrower cone centered on each of the 9 DSN user spacecraft with X-band downlink capability
Compromise solution was implemented at GSFC
Ephemerides for all 9 spacecraft were acquired from the JPL-based HORIZONS Web page
Data was incorporated into the Terra FDS to model the position of the X-band user spacecraft with respect to the earth and celestial sphere
A 20 ̊ half-angle cone (centered on the location of each of the X-band user spacecraft) was used as the new “zone of exclusion”
Cone was reduced from 20 ̊ to 10 ̊ after acquiring confidence in the compromise solution (i. e., no RFI incidents)

*Analysis of data indicated that the “zone of exclusion” for the DSN did not need to encompass the entire Horizon-to-Horizon circle*
*Zone could be confined to a much narrower cone centered on each of the 9 DSN user spacecraft with X-band downlink capability*
*Compromise solution was implemented at GSFC*
*Ephemerides for all 9 spacecraft were acquired from the JPL-based HORIZONS Web page*
*Data was incorporated into the Terra FDS to model the position of the X-band user spacecraft with respect to the earth and celestial sphere*
*A 20 ̊ half-angle cone (centered on the location of each of the X-band user spacecraft) was used as the new “zone of exclusion”*
*Cone was reduced from 20 ̊ to 10 ̊ after acquiring confidence in the compromise solution (i. e., no RFI incidents)*

**Compromise Solution**

## Terra DB is now on at all times except when Terra passes within one of the 10 ̊ half-angle cones in the line of sight of a DSN dish that is in-view of one or more of the X-band user spacecraft
This has minimized DB off time to minutes or seconds per day instead of almost 2 hours per day for a Horizon-to-Horizon mask
Operations Agreement (OA) between GSFC and JPL has been developed and signed off
OA details the specifics of the implemented solution and the working relationship between GSFC and JPL on this issue
OA outlines a “fall-back” procedure involving a return to Horizon-to-Horizon turn-off while potential RFI “incidents” are investigated
NO RFI INCIDENTS BETWEEN TERRA AND THE DSN HAVE OCCURRED SINCE TERRA LAUNCH

*This has minimized DB off time to minutes or seconds per day instead of almost 2 hours per day for a Horizon-to-Horizon mask*
*Operations Agreement (OA) between GSFC and JPL has been developed and signed off*
*OA details the specifics of the implemented solution and the working relationship between GSFC and JPL on this issue*
*OA outlines a “fall-back” procedure involving a return to Horizon-to-Horizon turn-off while potential RFI “incidents” are investigated*
**NO RFI INCIDENTS BETWEEN TERRA AND THE DSN HAVE OCCURRED SINCE TERRA LAUNCH**

**Current Procedure in Place**

## Sample of Weekly DB Turn-off Product

**Sample of Weekly DB Turn-off Product**