**Doc. No. 028-600766**

**CAGE Code: 9M715**

**July 31, 2003**

**Final Report for the**

**Communications and Navigation**

**Demonstration on Shuttle (CANDOS)**

**Experiment**

**Revision "-"**

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![](media/image2.wmf)

Change Record

  ------------ ---------------------- ----------------- ------------------
  Revision     Description            Date              Approved

  \-           Originated per         September 8, 2003 Marc Harlacher
               ECF-AE0551                               

                                                        

                                                        

                                                        

                                                        
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table of contents

[1 Introduction and System Overview
5](#introduction-and-system-overview)

[1.1 CANDOS Overview 5](#candos-overview)

[1.2 General Observations 5](#general-observations)

[2 Space Network Communications Objective
7](#space-network-communications-objective)

[2.1 Summary 7](#summary)

[2.2 Analysis #1: 8](#analysis-1)

[2.3 Analysis #2: 9](#analysis-2)

[2.4 Analysis #3: 10](#analysis-3)

[2.5 Analysis #4: 10](#analysis-4)

[3 Ground Network Communications Objective
12](#ground-network-communications-objective)

[3.1 Summary 12](#summary-1)

[3.2 Analysis #5: 13](#analysis-5)

[3.3 Analysis #6: 13](#analysis-6)

[4 Mobile IP Objective 15](#mobile-ip-objective)

[5 On-Orbit Reprogramming Objective
17](#on-orbit-reprogramming-objective)

[6 Range Safety Objective 18](#range-safety-objective)

[6.1 Summary 18](#summary-2)

[6.2 Analysis #7: 19](#analysis-7)

[7 GPS Objective 21](#gps-objective)

[7.1 Summary 21](#summary-3)

[7.2 Navigation Software Overview 21](#navigation-software-overview)

[7.3 GPS Experiment Overview 22](#gps-experiment-overview)

[7.4 JSC Ground Navigation Vector Comparisons
23](#jsc-ground-navigation-vector-comparisons)

[7.5 BET Comparisons 23](#bet-comparisons)

[7.5.1 Experiment 1 24](#experiment-1)

[7.5.2 Experiment 2 25](#experiment-2)

[7.5.3 Experiment 3 27](#experiment-3)

[7.5.4 Experiment 4 29](#experiment-4)

[7.5.5 Orbit 64 30](#orbit-64)

[7.5.6 Orbit 156 32](#orbit-156)

[7.5.7 BET Comparison Summary 34](#bet-comparison-summary)

[7.6 Navigation Telemetry 36](#navigation-telemetry)

[7.7 Conclusions 36](#conclusions)

[7.8 References 36](#references)

[Appendix A. Navigation Telemetry 37](#__RefHeading___Toc50791752)

[7.9 GPS Experiment #1 38](#gps-experiment-1)

[7.10 GPS Experiment #2 45](#gps-experiment-2)

[7.11 GPS Experiment #3 52](#gps-experiment-3)

[7.12 GPS Experiment #4 60](#gps-experiment-4)

[7.13 Orbit 64 67](#orbit-64-1)

[7.14 Orbit 156 73](#orbit-156-1)

# Introduction and System Overview

This document provides a detailed summary of results from the Low Power
Transceiver (LPT) on-orbit experiment termed the Command And Navigation
Demonstration On Shuttle (CANDOS, pronounced: CAN-DUES) system. The
purpose of this document is to present the detailed analysis that
verifies each mission objective and to identify the causes of anomalies
observed during the flight. For each anomaly, an assessment is presented
regarding applicability to the current 3rd Generation LPT design and
recommended resolutions. This document is intended to accompany the
numerous CANDOS flight results papers and presentations generated by the
various team members, and is therefore not a comprehensive analysis
summary of all aspects of the demonstration. The specific focus of this
summary is the performance and functionality of the LPT in its CANDOS
configuration.

A brief overview of the CANDOS system is presented below. Sections 2
through 7 each summarize results from the primary experiment objectives,
and include Space Network Communications, Ground Network Communications,
Mobile-IP, On-Orbit Reprogramming, Range Safety and GPS. The appendix
contains additional detailed results from the GPS experiment.

## CANDOS Overview

The LPT represents an enabling technology for emerging, cost effective
space operations, providing integrated communications and GPS navigation
functions in a space qualified design developed by NASA/GSFC and ITT
Industries under sponsorship of the NASA Office of Space Flight. The LPT
employs a modular architecture using PC/104-sized cards to build a stack
with flexible functionality. The CANDOS LPT is capable of simultaneously
processing GPS signals received at the L1 frequency, and Tracking and
Data Relay Satellite System (TDRSS) and Ground Network (GN) signals
received at S-band. Additionally, the LPT can transmit S-band signals
through TDRSS or GN.

The CANDOS experiment flew on-board NASA Space Shuttle Columbia mission
STS-107, and was the first space demonstration of the LPT. Figure 1
illustrates the top-level experiment concept, and Figure 2 depicts the
experiment hardware in its flight configuration. The experiment operated
from launch day, January 16, 2003 until completing its mission on
January 31, 2003. In the words of our NASA customer "the experiment was
a great success."

## General Observations

The CANDOS flight hardware demonstrated it's capability to survive the
launch and open space environment for 16 days, thereby accomplishing a
significant secondary objective of surviving the space environment.
During this time, the only generic anomalies observed include two
apparent "hangs" and a number of COTS CPU-induced resets of the LPT
portion of the experiment. As described in section 2, both system hangs
required that experiment power be cycled. One of these was caused by the
serial interface between the LPT and the COTS CPU (unclear which side
was the cause), and the other has been isolated to the COTS CPU or it's
software. The 19 occurrences of the CAM-induced resets of the LPT have
also been investigated. For all events CAM asserted the toggle bank
almost without warning. CAM requires that the LPT not send a status
message for 6 seconds before it issues a reset command. The reset
command was accepted by the LPT, which reset itself in every instance.
The ability of the LPT to respond to the reset command indicates that
the LPT itself was not "hung," though something in the serial interface
from the LPT to the COTS CPU apparently was. Whether this anomaly is
related to the similar anomaly requiring an experiment power cycle has
not been determined. Attempts to reproduce this anomaly with the spare
CANDOS unit were unsuccessful. The prototype unit ran for 8 days and did
not issue a single toggle bank command.

![](media/image3.wmf){width="6.622222222222222in"
height="4.166666666666667in"}

Figure 1. CANDOS Experiment Concept Diagram

![](media/image4.wmf){width="6.634722222222222in"
height="2.904861111111111in"}

Figure 2. CANDOS Experiment Hardware

# Space Network Communications Objective

## Summary

This section presents the Tracking and Data Relay Satellite System
(TDRSS) communication results from the CANDOS experiment. The mission
timeline provided 97 communications opportunities, 52 using the TDRSS
S-Band Single Access (SSA) service and 45 using the S-Band Multiple
Access (MA) service. The purpose of this objective was to verify that
the LPT is capable of closing a two-way link with the TDRSS while in
orbit. Of the 52 SSA events, 47 were considered 100% successful and
resulted in two-way communications flow. Of the 45 MA events, four were
unsupportable as a result of Shuttle attitude at the time of the event
and limitations in the experiment field of view. Of the 41 MA events
that were supportable, 39 were considered 100% successful and resulted
in two-way (35 forward and return link) or one-way (4 return link only)
communications flow as intended. All of the one-way services were
scheduled as return-only services (no forward link scheduled). Of the
seven remaining events (5 SSA and 2 MA), four were considered partially
successfully in that at least one of the forward or return links
operated without anomaly. The three unsuccessful events were not
supported by the experiment as a result of the need to cycle power, as
explained below.

  ------------ ----------------------------- -----------------------------
  **Event      **Number of Supportable       **% Successful**
  Type**       Opportunities**               

  SSA          52                            90%

  MA           41                            95%
  ------------ ----------------------------- -----------------------------

In total, more than 52 hours of TDRSS communications were accomplished.
Both the SSA and MA services were used successfully, using both high and
low gain antennas and both transmitters in the LPT (one at a time). It
seems clear that the mission objective of demonstrating successful Space
Network communications has been amply verified. Of the problems
observed, five of seven were caused by experiment mis-configurations.
Only one of the anomalies has been attributed to the LPT itself, and it
has been characterized and is easily corrected through software.

+------+--------+------------------+---------------------+------------+
| **E  | **Gr   | **Description**  | **Identified        | **Impact   |
| vent | ound** |                  | Cause**             | on         |
| Numb |        |                  |                     | Subsequent |
| er** | **Sta  |                  |                     | LPT        |
|      | tion** |                  |                     | Gen        |
|      |        |                  |                     | erations** |
+------+--------+------------------+---------------------+------------+
| 24 & | STGT & | LPT portion of   | See Analysis #1     | Unknown    |
| 25   | GRGT   | experiment would | below               |            |
|      |        | not respond to   |                     |            |
|      |        | configuration    |                     |            |
|      |        | commands         |                     |            |
+------+--------+------------------+---------------------+------------+
| 47   | WSGT   | Experiment       | See Analysis #2     | None,      |
|      |        | became           | below               | non-LPT    |
|      |        | completely       |                     | hardware   |
|      |        | unresponsive and |                     | crashed    |
|      |        | required power   |                     | (COTS CPU) |
|      |        | cycle            |                     |            |
+------+--------+------------------+---------------------+------------+
| 51   | WSGT   | Never achieved   | The frequency       | None,      |
|      |        | return link      | offset parameter in | problem    |
|      |        | signal           | the SN              | occurred   |
|      |        | acquisition/lock | configuration code  | in ground  |
|      |        |                  | was invalid         | station    |
|      |        |                  |                     | conf       |
|      |        |                  |                     | iguration. |
+------+--------+------------------+---------------------+------------+
| 95   | GRGT   | Intermittent     | Hitchhiker control  | None,      |
|      | (T     | forward and      | link was            | problem    |
|      | DRS-Z) | return link      | unavailable to      | was caused |
|      |        | communications   | configure in time   | by         |
|      |        |                  | for event start.    | inability  |
|      |        |                  |                     | to         |
|      |        |                  | Transmitter-enable  | properly   |
|      |        |                  | script problem      | configure  |
|      |        |                  | mis-configured the  | the LPT    |
|      |        |                  | LPT receiver.       |            |
+------+--------+------------------+---------------------+------------+
| 141  | WSGT   | Never achieved   | See Analysis #3     | None,      |
|      |        | return link      | below               | problem    |
|      |        | signal           |                     | caused by  |
|      |        | acquisition/lock |                     | an LPT     |
|      |        |                  |                     | con        |
|      |        |                  |                     | figuration |
|      |        |                  |                     | error. CAM |
|      |        |                  |                     | is not     |
|      |        |                  |                     | a          |
|      |        |                  |                     | nticipated |
|      |        |                  |                     | to be used |
|      |        |                  |                     | in future  |
|      |        |                  |                     | app        |
|      |        |                  |                     | lications. |
+------+--------+------------------+---------------------+------------+
| 150  | WSGT   | Unable to        | See Analysis #4     | Correct    |
|      |        | maintain forward | below               | LPT        |
|      |        | link decoder     |                     | firmware   |
|      |        | lock             |                     | bug that   |
|      |        |                  |                     | allocates  |
|      |        |                  |                     | the        |
|      |        |                  |                     | Viterbi    |
|      |        |                  |                     | decoder    |
|      |        |                  |                     | resource.  |
+------+--------+------------------+---------------------+------------+

## Analysis #1: 

CAM on board was not able to send or receive telemetry from DSP module
of LPT. Experiment had to be power cycled to bring it back.

Sequence of events:

+----------+-----------------------------------------------------------+
| 20/04:09 | CAM successfully configures LPT for receive (sn_rx0_4)    |
|          | and transmitter (sn_tx1_64) modes for upcoming event.     |
+----------+-----------------------------------------------------------+
| 20/04:33 | Event starts; Forward link closes.                        |
+----------+-----------------------------------------------------------+
| 2        | 10 Blinds commands issued to turn on TX1. The first 9     |
| 0/04:34- | commands were wrong (omni_tx1_enable.sh was used instead  |
|          | of OMNI_tx1_enable.sh). The 10^th^ command was typed in   |
| 20/04:38 | correctly and accepted by the blindcommander utility and  |
|          | 4:38:32. According to the log, a tx1_enable.sh command    |
|          | was also issued at least once via the HH link. No time    |
|          | was given for this.                                       |
+----------+-----------------------------------------------------------+
| 20/04:37 | Last GPS/caminterface command transmitted by CAM.         |
+----------+-----------------------------------------------------------+
| 20/      | CAM transmits command to LPT. This command was 2 bytes    |
| 04:38:32 | too long, but looks like it was originally a disable      |
|          | transmitter 2 command (see below).                        |
+----------+-----------------------------------------------------------+
| 20/      | CAM transmits command to turn on transmitter 1. The       |
| 04:38:33 | settings match sn_tx1_64.sh script                        |
+----------+-----------------------------------------------------------+
| 20/      | CAM transmits command to turn off transmitter 2. The      |
| 04:38:34 | settings match sn_tx1_64.sh script                        |
+----------+-----------------------------------------------------------+
| 20/      | CAM transmits command to turn on transmitter 1. The       |
| 04:38:34 | settings match sn_tx1_64.sh script                        |
+----------+-----------------------------------------------------------+
| 20/      | Last new update of OMNI UDP telemetry program (the        |
| 04:28:37 | telemetry program continued to run).                      |
+----------+-----------------------------------------------------------+
| 20/      | Toggle bank and reset command issued from CAM to LPT.     |
| 04:38:39 |                                                           |
+----------+-----------------------------------------------------------+
| 20/05:01 | CAM/caminterface restarted. Before it quits, caminterface |
|          | processes 46 GPS messages within 14 seconds.              |
+----------+-----------------------------------------------------------+
| 20/05:07 | Toggle bank command issued by CAM. No data from LPT.      |
+----------+-----------------------------------------------------------+
| 20/06:39 | LPT turned off. When turned back on, the LPT and CAM work |
|          | normally.                                                 |
+----------+-----------------------------------------------------------+

The problem can be sourced to the erroneous command issued by CAM to the
LPT. After receiving the command, it looked like the LPT stopped
transmitting and receiving messages. There are two signs that point to
this:

1)  CAM issues a command to reset the LPT 6-7 seconds (the length of the
    CAM timeout) after this message was issued.

2)  The transmitter enable and disable messages following the erroneous
    message have a subcarrier frequency offset of 0 Hz. This is
    significant because the "tx1_enable" script only changes the
    transmitter enable variable; all other variables should have matched
    the erroneous configuration message. The fact that they do not
    indicates that the LPT never responded with a transmitter status
    message after the erroneous message was issued (which is not a
    normal occurrence).

There is nothing definite that explains why CAM would transmit data
incorrectly. However, because the four transmitter commands were
executed so close together, it can be guessed that multiple people were
commanding the LPT at one time. The problem may have been caused when
more than one transmit enable command was issued at the same time from
both the HH link and through blind commanding.

The erroneous configuration message sent to the LPT was the following

+------+-------+------------------------------------------------------+
| Nu   | Word  | Meaning                                              |
| mber |       |                                                      |
+------+-------+------------------------------------------------------+
| 1    | 000C  | Transmitter Header                                   |
+------+-------+------------------------------------------------------+
| 2    | 0121  | Sets transmitter to:                                 |
|      |       |                                                      |
|      |       | GN, Uncoded I, Uncoded Q, NRZ-L I, NRZ-M Q, NRZ I,   |
|      |       | Bi-Phase Q, 1X External Clock Freq., 1:1 QPSK, No    |
|      |       | LPT Reset                                            |
|      |       |                                                      |
|      |       | Note: This seems to be the inserted byte.            |
+------+-------+------------------------------------------------------+
| 3    | 762A  | PN Code of 30,250. Note this violates the range of   |
|      |       | the DSP and will be rejected (previous value will be |
|      |       | used).                                               |
+------+-------+------------------------------------------------------+
| 5,4  | 190   | Data rate of 4,194,304,200 on I Channel. Note this   |
|      | 00014 | violates the range of the DSP and will be rejected   |
|      |       | (previous value will be used).                       |
+------+-------+------------------------------------------------------+
| 7,6  | 000   | Data rate of 0 on Q channel.                         |
|      | 00000 |                                                      |
+------+-------+------------------------------------------------------+
| 8    | 0000  | Ext. Data, Normal Operations, TX1, Transmitter       |
|      |       | Disable, No I Data Scrambling, No Q Scrambling       |
+------+-------+------------------------------------------------------+
| 9,10 | 002   | RX Max. Data Rate of 40 bps                          |
|      | 80000 |                                                      |
+------+-------+------------------------------------------------------+
| 1    | 000   | Receiver Clock Bias set to 0                         |
| 1,12 | 00000 |                                                      |
+------+-------+------------------------------------------------------+
| 13   | 0000  | Modulation Index set to 0                            |
+------+-------+------------------------------------------------------+
| 1    | 006   | Subcarrier Frequency Offset set to 100 Hz.           |
| 4,15 | 40000 |                                                      |
+------+-------+------------------------------------------------------+
| 16   | 0000  | Extra Message                                        |
+------+-------+------------------------------------------------------+

An identical message was issued to the spare CANDOS unit and there was
no effect on the operation of the LPT. Unfortunately, there is no way to
recreate the exact sequence of events starting with the possible
simultaneous commanding of the LPT. Note that while the anomaly looks
like it originated when the erroneous message was issued, it is
certainly possible that CAM did not report the issued command
accurately, and therefore the true fault may lie elsewhere.

## Analysis #2:

The COTS CPU hung. Experiment power had to be recycled in order to
restore normal operations.

Sequence of Events:

+--------+-------------------------------------------------------------+
| 21     | Last recorded system event in /var/log/messages             |
| /16:33 |                                                             |
+--------+-------------------------------------------------------------+
| 21     | System appears to back to normal. There are no startup      |
| /17:20 | messages in /var/log/messages and the first is CAM toggling |
|        | the LPT bank as a result of booting up.                     |
|        |                                                             |
|        | CAM also starts recording data.                             |
+--------+-------------------------------------------------------------+

**Analysis**:

Although it is curious that the system log resumes recording events at
the end of the startup sequence (as opposed to immediately following
application of power, there is simply no information regarding what
caused the system to crash. All log files stopped recording at 16:33 and
resumed at 17:20.

**Conclusion**:

There is not enough information to debug this anomaly.

## Analysis #3:

White Sands (WSGT) was unable to acquire or track the CANDOS return
link. Observations during the anomaly noted that the transmitter was not
drawing the expected amount of power.

**Results**:

Preliminary analysis during the mission indicated that the transmitter
enable script was being executed by CAM incorrectly. Specifically, the
intended transmitter (TX1) was first enabled and then the unintended
transmitter was disabled. This effectively "turned off" the modulator,
and explains the reduced power scenario observed during the mission (the
proper order and the way the script is written is to first disable the
undesired transmitter and then enable the desired one). During the
actual on-orbit event, CAM was running in a "command line" mode in order
to restrict the amount of file I/O used for logging. This was thought to
be desireable in order to increase the likelihood of success of a
reprogram of the DSP (less processor load means more time to service the
UART), but prevented any logging of CAM during this time period. This
anomaly could not be reproduced with the spare CANDOS unit. CAM was
configured for "command line" mode, a telnet session was opened to CAM
and the transmitter could be turned off and on. Unfortunately, using the
telnet session to configure the transmitter was not part of the
procedures manual, so there is no way to know if the configuration
process was done correctly.

## Analysis #4:

LPT receiver Viterbi Decoder configuration seems to change "by itself,"
resulting in intermittent data flow.

**Results**:

This anomaly was reproduced with the spare CANDOS unit. Sending a TDRSS
configuration with the Viterbi decoder enabled to a receiver channel
that is already configured with the Viterbi enabled causes the Viterbi
decoder to be deactivated. However, turning the channel off and then
configuring it is always successful and the Viterbi decoder remains
enabled and operates properly.

Because the 1^st^ Generation has only one Viterbi decoder, the DSP on
the LPT determines whether or not the Viterbi decoder is being used when
it receives a new receiver configuration command (regardless of the
channel being configured). In order to eliminate a resource conflict, if
it finds that the decoder has already been allocated the DSP will modify
the new receiver configuration command by disabling the Viterbi decoder
parameter and will then configure the intended receiver channel with the
modified configuration. This occurs even if the new receiver command is
for the same channel that is actively using the decoder.

The problem seems to occur when the new command is processed. If the LPT
is configured to use the Viterbi decoder, a new receiver command which
configures the Viterbi decoder will fail the check to see if the Viterbi
decoder is available. When the receiver is configured with the newly
received command, the DSP effectively disables the Viterbi decoder. This
is an LPT firmware bug that should be corrected in all affected units.

# Ground Network Communications Objective

## Summary

This section presents the NASA Ground Network (GN -- also referred to as
the Spaceflight Tracking and Data Network (STDN)) communication results
from the CANDOS experiment. The mission timeline provided 37
communications opportunities, utilizing either the Wallops Flight
Facility or the Merritt Island ground stations. The purpose of this
objective was to verify that the LPT is capable of closing a two-way
link with a GN station while in orbit. Of the 37 events, one was
unsupportable as a result of Shuttle attitude at the time of the event
and limitations in the experiment field of view. Of the 36 events that
were supportable, 27 were considered 100% successful and resulted in
two-way (26 forward and return link) or one-way (1 forward link only)
communications flow as intended. Of the nine remaining events, eight
were considered partially successfully in that at least one of the
forward or return links operated without anomaly.

  ------------ ----------------------------- -----------------------------
  **Event      **Number of Supportable       **% Successful**
  Type**       Opportunities**               

  Wallops      21                            71%

  MILA         15                            87%
  ------------ ----------------------------- -----------------------------

In total, more than 6 hours of GN communications were accomplished. Both
Wallops and MILA ground stations were used successfully. It seems clear
that the mission objective of demonstrating successful Ground Network
communications has been amply verified. Of the problems observed, six of
nine were caused by experiment mis-configurations or inconsistencies
between the operations concept and the way that the experiment was
configured. A single issue addresses all three remaining anomalies
(subcarrier acquisition).

+------+--------+------------------+---------------------+------------+
| **E  | **Gr   | **Description**  | **Identified        | **Impact   |
| vent | ound** |                  | Cause**             | on         |
| Numb |        |                  |                     | Subsequent |
| er** | **Sta  |                  |                     | LPT        |
|      | tion** |                  |                     | Gen        |
|      |        |                  |                     | erations** |
+------+--------+------------------+---------------------+------------+
| 7    | MILA   | LPT unable to    | The single LPT      | A          |
|      |        | acquire the      | acquisition engine  | cquisition |
|      |        | forward link     | was allocated to    | priority   |
|      |        | carrier          | GPS signal          | scheme     |
|      |        |                  | acquisition for the | must       |
|      |        |                  | vast majority of    | account    |
|      |        |                  | the pass. Because   | for        |
|      |        |                  | of the orbiters     | operations |
|      |        |                  | attitude for a GN   | concept    |
|      |        |                  | pass, no GPS SVs    |            |
|      |        |                  | were in view        |            |
|      |        |                  | resulting in        |            |
|      |        |                  | extended            |            |
|      |        |                  | acquisition         |            |
|      |        |                  | intervals           |            |
|      |        |                  | (timeouts).         |            |
+------+--------+------------------+---------------------+------------+
| 12,  | WLPS   | LPT unable to    | The single LPT      | A          |
| 15 & |        | acquire the      | acquisition engine  | cquisition |
| 57   |        | forward link     | was allocated to    | priority   |
|      |        | carrier          | GPS signal          | scheme     |
|      |        |                  | acquisition for the | must       |
|      |        |                  | vast majority of    | account    |
|      |        |                  | the pass. Because   | for        |
|      |        |                  | of the orbiters     | operations |
|      |        |                  | attitude for a GN   | concept    |
|      |        |                  | pass, no GPS SVs    |            |
|      |        |                  | were in view        |            |
|      |        |                  | resulting in        |            |
|      |        |                  | extended            |            |
|      |        |                  | acquisition         |            |
|      |        |                  | intervals           |            |
|      |        |                  | (timeouts).         |            |
+------+--------+------------------+---------------------+------------+
| 43   | MILA   | LPT unable to    | See Analysis #5     | Unknown    |
|      |        | acquire the      | below               |            |
|      |        | forward link     |                     |            |
|      |        | subcarrier       |                     |            |
+------+--------+------------------+---------------------+------------+
| 70   | WLPS   | LPT unable to    | Post pass           | None,      |
|      |        | acquire the      | investigation       | problem    |
|      |        | forward link     | revealed that       | caused by  |
|      |        | subcarrier       | Wallops incorrectly | a ground   |
|      |        |                  | configured the      | station    |
|      |        |                  | forward modulation  | con        |
|      |        |                  | index.              | figuration |
|      |        |                  |                     | error      |
+------+--------+------------------+---------------------+------------+
| 91 & | WLPS   | LPT unable to    | See Analysis #5     | Unknown    |
| 92   |        | acquire the      | below               |            |
|      |        | forward link     |                     |            |
|      |        | subcarrier       |                     |            |
+------+--------+------------------+---------------------+------------+
| 142  | WLPS   | Never achieved   | See Analysis #6     | None,      |
|      |        | return link      | below               | problem    |
|      |        | signal           |                     | caused by  |
|      |        | acquisition/lock |                     | an LPT     |
|      |        |                  |                     | con        |
|      |        |                  |                     | figuration |
|      |        |                  |                     | error. CAM |
|      |        |                  |                     | is not     |
|      |        |                  |                     | a          |
|      |        |                  |                     | nticipated |
|      |        |                  |                     | to be used |
|      |        |                  |                     | in future  |
|      |        |                  |                     | app        |
|      |        |                  |                     | lications. |
+------+--------+------------------+---------------------+------------+

## Analysis #5:

Unable to track GN subcarrier.

A TURFTs available at ITT was configured for GN mode as follows:

Mod-Index: 1.0 and 1.7

Sub-Carrier: 16 KHz

Data Rate: 2 kbps

Data Format: NRZ-L

Convolutional Encoding: OFF

Carrier Doppler: +-60KHz

Doppler Rate: 1 KHz/Sec

Return Link Output Level at: -100 dBm

Configured CANDOS Unit #1 as follows (consistent with CANDOS
configuration logs):

Ch0 and Ch1 for GN mode

Data Rate: 2kbps

Data Format: NRZ-L

Viterbi Decoder: OFF

Sub-Carrier: 16 KHz

In addition, all other LPT channels were turned off in order to
eliminate the potential for acquisition engine conflicts. We were unable
to recreate any acquisition anomalies. Both Mod-Indexes of 1.0 and 1.7
were used successfully, and both appeared to work equally well. At this
time we are unable to verify ground network configuration, though verbal
inquiry during the mission indicated that the proper configuration was
in place.

## Analysis #6: 

Wallops was unable to acquire or track the CANDOS return link.
Observations during the anomaly by Wallops personnel noted that the
transmitter waveform appeared to have a TDRSS-like waveform.

**Results**:

This anomaly may be closely related to that described in Anomaly #3, as
it occurred on the subsequent communications event and shares similar
circumstances. During the actual on-orbit event, CAM was running in a
"command line" mode in order to restrict the amount of file I/O used for
logging. This was thought to be desireable in order to increase the
likelihood of success of a reprogram of the DSP (less processor load
means more time to service the UART), but prevented any logging of CAM
during this time period. This anomaly could not be reproduced with the
spare CANDOS unit. CAM was configured for "command line" mode, a telnet
session was opened to CAM and the transmitter could be turned off and on
and configured at will. Unfortunately, using the telnet session to
configure the transmitter was not part of the procedures manual, so
there is no way to know if the configuration process was done correctly.

# Mobile IP Objective

This section summarizes the Mobile IP communication results from the
CANDOS experiment. Detailed results for this objective are documented
elsewhere. Figure 3 illustrates the mobile IP concept for the
experiment.

![](media/image5.jpeg){width="5.669444444444444in"
height="4.252083333333333in"}

Figure 3. CANDOS Mobile IP Experiment Concept Diagram

The experiment accomplished the following achievements:

-   All operations were conducted according to the GSFC IT Security
    Branch approved CANDOS security plan.

-   Mobile IP utilized on all two-way SN and GN passes.

    -   Packet routing established automatically and securely using the
        standard Mobile IP protocol that comes with Cisco routers

    -   Automatically setup IP routing tunnels for SN & GN stations as
        the Shuttle came into view

-   The standard off-the-shelf IP stack built into the on-board COTS
    operating system supported all data communications. Standard HDLC
    packet framing was used on all links.

-   Blind commanding using UDP-based command uplink

    -   Turned transmitter on using UDP command over static IP tunnel

-   Real time telemetry delivered using UDP

-   Reliable file delivery from CANDOS payload to POCC (navigation
    system logs, comm system logs) and from POCC to CANDOS payload
    (stored commands, data files, software updates) using both TCP/IP
    based 2-way file transfer protocols - Secure Copy Protocol (SCP) and
    one and 2-way UDP-based Multicast Dissemination Protocol (MDP)

-   On-board clock synchronization to ground time standard using Network
    Time Protocol (NTP)

-   Autonomous on-board message data routing demonstration

-   Secure LPT commanding from, and reliable file delivery to, a remote
    site (NASA/MSFC)

-   Multiple simultaneous secure sessions between the POCC and the
    spacecraft conducting commanding & reliable file transfers

-   Multi-station reliable file transfers (automatic resumption after
    handover)

-   File delivery across one-way links with application-level Reed
    Solomon coding

In summary, all planned primary and secondary objectives were
accomplished.

# On-Orbit Reprogramming Objective

This section presents the results from the on-orbit reconfiguration of
the LPT's digital signal processor (DSP). The first demonstration
involved uploading an identical Flash bootable image of the flight DSP
firmware to the experiment during an SN communications event, followed
by the programming of this firmware into the secondary Flash memory bank
in the LPT and a reset of the LPT electronics. The first attempt at
programming the Flash memory was unsuccessful due to a higher than
tolerance error rate on the asynchronous serial port between the COTS
CPU and the LPT itself. This anomaly is a known issue with the CANDOS
COTS CPU software and was anticipated. A second attempt proved
successful, after which commands to the COTS CPU were issued to toggle
the boot bank and to reset the LPT. The LPT was able to boot from the
new Flash memory bank and the proper version number was verified. A
successful subsequent communications event confirmed proper operation of
the LPT using this boot image.

The second demonstration used functionally identical firmware that was
modified to reflect an incremented version number. The same process of
uploading the Flash bootable image to the experiment, programming the
LPT over the asynchronous serial port, toggling boot banks and resetting
the LPT was repeated. The programming was successful on the first
attempt, and following the boot of the newly programmed image, the
modified version number was verified. As before, a successful subsequent
communications event confirmed the functionality of the new firmware
upload.

It seems clear that the mission objective of demonstrating an on-orbit
reprogram of the LPT DSP has been verified. No unexpected anomalies were
observed during either demonstration.

# Range Safety Objective

## Summary

This section presents the range safety communication results from the
CANDOS experiment. The mission timeline provided 12 communications
opportunities, utilizing the Dryden Flight Research Center (DFRC) ground
station and/or the TDRSS. The purpose of this objective was to verify
that the LPT is capable of closing a two-way link, with greater than 9
dB of link margin, simultaneously with both a ground-based and
space-based relay. Of the 12 events, only six actually included both
DFRC and a TDRS. The remaining six included only a single TDRSS (1
event) or only DFRC (5 events). All 12 events were successful in
accomplishing error-free, two-way communications. A more thorough
analysis of the effectiveness of the commanding, telemetry and link
margin is documented in a separate report. However, a preliminary
assessment is provided here. In general, for events where both a TDRS
and DFRC were available, link margins significantly exceeded 9 dB,
except at event boundaries when antenna gain resulted in substantial
pointing loss to one target or the other. The following table summarizes
Eb/No estimates based on the LPT's coherent AGC for the each of the
range safety events. Note that for events where only a TDRS or DRFC were
in view, the LPT receiver channel configured for the target not in view
false locked to the signal from the target that was in view. The Eb/No
difference observed in these cases (typically \~23 dB) closely
approximates the cross-correlation protection provided by the 1023-chip
long PN spreading codes used for this demonstration.

  ------------ ------------------ -------------------- -------------------
  **Event      **Estimated TDRS   **Estimated DFRC     **Achieved Link
  Type**       Eb/No**            Eb/No**              Margin**

  DFRC         9-10 (false lock)  34-36                \>24 dB

  DFRC         9-12 (false lock)  32-36                \>22 dB

  DFRC         10-13 (false lock) 32-36                \>22 dB

  DFRC         7-12 (false lock)  30-36                \>20 dB

  WSGT         30-32              6-9 (false lock)     \>20 dB

  DFRC         9-12 (false lock)  31-34                \>21 dB

  DFRC/STGT    21-32              30-35                \>11 dB

  DFRC/STGT    24-25              34-35                \>14 dB

  DFRC         No Lock            21-35                \>11 dB

  DFRC         No Lock            26-32                \>16 dB

  DFRC/STGT    25-31              34-36                \>15 dB

  DFRC/STGT    20-32              28-36                \>10 dB

  DFRC/WSGT    6-30               22-29                0-18 dB
  ------------ ------------------ -------------------- -------------------

Note that the use of the LPT's coherent AGC to estimate Eb/No poses a
limit on the range of valid estimation. Because the LPT utilizes a
wideband, non-coherent AGC in addition to the data-bandwidth-matched
coherent AGC, the estimator will saturate when the signal level begins
to approach the noise level in the 6 MHz bandwidth of the LPT's TDRSS
receiver. The approximate noise level in the receiver is --105 dBm. To
illustrate this effect, the spare CANDOS unit was used to measure the
effect over a range of input signal power while configured for the
CANDOS Range Safety mode. The results, shown in Figure 4, indicate that
the AGC-based estimator will saturate at approximately 36 dB Eb/No. Note
that the estimator begins to become non-linear at an input signal level
of approximately --107 dBm, at a corresponding Eb/No of 32 dB. One
should therefore conclude that the accuracy of the Eb/No estimates
provided using this method will degrade above this level, as is the case
for much of the DFRC link cases.

![](media/image6.wmf){width="5.450694444444444in"
height="3.626388888888889in"}

Figure 4. Saturation Effect of the LPT's AGC

## Analysis #7: 

The final range safety event was unable to maintain the required 9 dB
link margin as a result of Shuttle attitude preventing good boresight
antenna pointing. This fact was observed during the event (as well as
the previous WSGT SSA event) and documented in the pass summary.
Nevertheless, both the TDRSS and ground station links closed and range
safety commands were observed at the CANDOS experiment. An analysis of
the 10-second telemetry collected from the experiment revealed an
interesting Doppler profile during a portion of this pass.

**Results**:

The impact of the poor antenna pointing during this event is easily
observed in Figure 5. The yellow line shows the received Eb/No for the
TDRSS link. While in general there was sufficient link margin to receive
commands, this margin was not maintained and in fact varied dramatically
over very short time intervals. The figure also illustrates the Doppler
profiles observed by both receiver channels during the event. Visibility
of the TDRSS link was maintained for the duration of the event, and, as
was typical for many Range Safety events, visibility of the ground
station link was limited by the horizon. As a result the ground station
link false locked to another signal until the ground station signal was
visible. The interesting aspect of this situation was that the signal
that the ground station channel false locked to does not appear to be
the TDRSS signal. This unknown signal is offset from the TDRSS signal by
almost exactly 3KHz, and follows a nearly identical Doppler rate of
change. It is tempting to suggest that this signal may in fact have been
the TDRSS signal, however, the TDRSS channel remained locked to the true
TDRSS signal for a period of time after the ground station channel false
locked to the unknown signal. In order to prove that the TDRSS channel
was truly locked to the authentic TDRSS signal, Figure 5 also
illustrates the Doppler profile from the TDRSS SSA event that
immediately preceded this Range Safety event. Fortunately, the same
TDRSS was used for both events and the figure clearly shows a consistent
Doppler track for the duration of both events. At the time marked event
A in the figure, the TDRSS receiver channel also false locked to the
unknown signal, and both channels tracked this third signal until event
B when the ground station signal was acquired. During this time period,
it can be seen that the Eb/No of the TDRSS channel slowly degraded until
the time marked event C when the TDRSS receiver channel reacquired the
true TDRSS signal, which it tracked for the duration of the event.

While it is tempting to attempt to identify the third signal, no attempt
has been made to do so other than to note that it almost certainly
originated from the same TDRSS given it's extremely similar Doppler
profile. Perhaps it was the Shuttle's S-Band forward link, or perhaps it
was a frequency-shifted artifact of the true Range Safety command link,
though the mechanism that would cause such a frequency shift is not
known to the author.

![](media/image7.wmf){width="7.002083333333333in"
height="4.440972222222222in"}

Figure 5. Final Event (#13) Doppler Profile with Eb/No Data

In summary, twelve of the thirteen Range Safety communications events
attempted were successful in achieving the required 9 dB link margin,
and all 13 were successful in flowing data via the scheduled links. Poor
Shuttle attitude resulted in sub-optimal antenna pointing for the final
event, which prevented the link from maintaining the desired link
margin. The Dryden ground station was also used successfully. Other than
the unknown signal observed during the last event, no anomalies were
noted during any of the events, resulting in a 92% success rate (12/13)
for all Range Safety events.

# GPS Objective

## Summary

This report presents the GPS navigation results from the CANDOS
experiment on STS-107. The mission timeline provided 4 periods of at
least 2 orbits with no orbiter maneuvering for the GPS experiments. The
CANDOS objectives during the GPS experiment periods were to:

-   maintain track of at least 4 satellites,

-   achieve GEODE convergence,

-   demonstrate using an uplinked attitude timeline to select which
    satellites to track,

-   demonstrate GEODE propagation during GPS outages and subsequent
    filter processing when at least 4 GPS satellites come back into view

-   compare the GEODE solution to the JSC ground navigation solution,

-   compare the GEODE solution to the post-flight Best Estimate of
    Trajectory (BET).

All objectives were met and are documented in this report.

## Navigation Software Overview

The LPT navigation software is comprised of 4 main functions: 1) point
solution, 2) orbit determination, 3) channel assignment, and 4) data
logging. The point solution function is a standard weighted least
squares algorithm for computing position and clock bias when at least 4
GPS satellites are tracked. Velocity and clock drift are computed from a
polynomial fit to 3 successive position/bias solutions. The point
solution algorithm was designed for both ground and orbital scenarios.

The GPS Enhanced Orbit Determination Experiment (GEODE) software,
developed at NASA GSFC, provides the orbit determination function. GEODE
consists of a 9-element Kalman filter that solves for position,
velocity, drag coefficient, clock bias, and clock drift. It also
provides high-fidelity force models for the geopotential, atmospheric
drag, and sun/moon gravitational perturbations. The expected GEODE
position accuracy is 20 m one-sigma.

The channel assignment function determines which satellites are to be
tracked. When less than 4 satellites are tracked and a position is
unavailable, the function will perform an open-sky search until at least
4 satellites are tracked. Once at least 4 satellites are tracked and
position solution is available, the channel assignment function will use
the current position, GPS almanac, and current orbiter attitude to
determine which satellites are in view and then command the LPT to track
them. An initial GPS almanac file is available onboard the LPT, and is
updated as new data is received from the GPS constellation. An uplinked
attitude timeline file provides the orbiter's attitude base on the
mission timeline. This file allows the operator to set the orbiter's
attitude via roll-pitch-yaw angles as a function of time such that the
software can determine the direction the GPS antenna is pointing with
respect to the GPS constellation.

The data logging function logs various database messages for post-flight
analysis. The message types and logging frequency are determined by a
database logging configuration file that can be uplinked to the LPT as
needed. All available messages were logged during the GPS experiments,
but only a minimal set was logged at other times to conserve disk space
on the LPT.

## GPS Experiment Overview

Table 1 summarizes the four GPS experiment periods, along with two
unscheduled GPS tracking opportunities (orbits 64 and 156). As shown,
the orbiter provided a stable attitude for tracking the GPS
constellation during each of the 4 experiments. The attitude column
shows which orbiter body axis is in the direction of the local vertical
(LV; points toward the Earth) and which is in the direction of the
velocity vector (VV). The orbiter body coordinates convention is +X axis
out the nose, +Y axis out the right wing, and +Z completing the
right-hand rule (out the bottom). The GPS antenna boresight is along the
orbiter's -Z body axis (outward from the payload bay). The experiment
start and stop times are listed in both GMT (day of
year/hour:minute:second) and GPS time (GPS week/time of week).

Table 1: GPS Experiment Timeline

+------------+---------------+--------------+--------------+----------+
| **GPS**    | **Attitude**  | **Start      | **Stop       | **Du     |
|            |               | Time**       | Time**       | ration** |
| **Ex       |               |              |              |          |
| periment** |               |              |              | **       |
|            |               |              |              | (H:MM)** |
+------------+---------------+--------------+--------------+----------+
|            |               |              |              |          |
+------------+---------------+--------------+--------------+----------+
| #1         | +ZLV -YVV     | 20/00:15:00  | 20/03:22:00  | 3:07     |
|            |               |              |              |          |
|            |               | 1202/87313   | 1202/98533   |          |
+------------+---------------+--------------+--------------+----------+
|            |               |              |              |          |
+------------+---------------+--------------+--------------+----------+
|            |               |              |              |          |
+------------+---------------+--------------+--------------+----------+
| #2         | +ZLV +YVV     | 22/20:19:00  | 23/00:29:00  | 4:10     |
|            |               |              |              |          |
|            |               | 1202/332353  | 1202/347353  |          |
+------------+---------------+--------------+--------------+----------+
|            |               |              |              |          |
+------------+---------------+--------------+--------------+----------+
|            |               |              |              |          |
+------------+---------------+--------------+--------------+----------+
| #3         | +ZLV +YVV     | 23/20:14:00  | 23/23:24:00  | 3:10     |
|            |               |              |              |          |
|            |               | 1202/418453  | 1202/429853  |          |
+------------+---------------+--------------+--------------+----------+
|            |               |              |              |          |
+------------+---------------+--------------+--------------+----------+
|            |               |              |              |          |
+------------+---------------+--------------+--------------+----------+
| #4         | +ZLV +YVV     | 24/19:57:42  | 24/23:59:00  | 3:51     |
|            |               |              |              |          |
|            |               | 1202/503875  | 1202/517753  |          |
+------------+---------------+--------------+--------------+----------+
|            |               |              |              |          |
+------------+---------------+--------------+--------------+----------+
|            |               |              |              |          |
+------------+---------------+--------------+--------------+----------+
| Orbit 64   | -Z Solar      | 20/13:45:00  | 20/15:43:00  | 1:58     |
|            | Inertial      |              |              |          |
|            |               | 1202/135913  | 1202/142993  |          |
+------------+---------------+--------------+--------------+----------+
|            |               |              |              |          |
+------------+---------------+--------------+--------------+----------+
|            |               |              |              |          |
+------------+---------------+--------------+--------------+----------+
| Orbit 156  | -XLV +YVV     | 26/11:50:00  | 26:14:10:00  | 2:20     |
|            |               |              |              |          |
|            |               | 1203/42613   | 1203/51013   |          |
+------------+---------------+--------------+--------------+----------+
|            |               |              |              |          |
+------------+---------------+--------------+--------------+----------+

Prior to each GPS experiment period, any necessary files were uplinked
(e.g., updates to the navigation configuration, attitude timeline, or
logging configuration). At the beginning of each GPS experiment period,
the navigation software was initialized from a cold-start. Once the
open-sky search algorithm acquired at least 4 GPS satellites, a point
solution was computed and used to initialize GEODE.

All experiments were run with the same navigation configuration except
the first. For the first experiment, the GEODE drag coefficient's a
priori variance and process noise were constrained so as not to estimate
a correction to the drag coefficient. For the other experiments, the
drag coefficient's a priori variance and process noise were increased
such that GEODE would estimate the drag coefficient correction.

## JSC Ground Navigation Vector Comparisons

JSC provided the current ground navigation batch solution vector once
per orbit for comparison with the GEODE estimate. Table 2 shows the
vector comparisons for each of the experiments. The one-sigma JSC vector
accuracies are approximately 360 m in position and 0.314 m/s in velocity
(for 2 hours following an attitude maneuver). The GEODE solution was not
corrected for the distance between the GPS antenna and the orbiter's
center of mass for these comparisons. All but one of the GEODE vectors
were within the 1-sigma uncertainty of the JSC vectors, with the first
comparison of the fourth experiment being less than 2-sigma.

Table 2: JSC Vector Comparisons

+--------+------------+--------------------+-------------+-------------+
| **O    | **GPS**    | **GPS**            | *           | **Velocity  |
| rbit** |            |                    | *Position** | Difference  |
|        | **Ex       | **Time**           |             | (m/s)**     |
|        | periment** |                    | *           |             |
|        |            |                    | *Difference |             |
|        |            |                    | (m)**       |             |
+--------+------------+--------------------+-------------+-------------+
| 55     | 1          | 1202/88813         | 179.0       | 0.170       |
+--------+------------+--------------------+-------------+-------------+
| 56     | 1          | 1202/94633         | 149.6       | 0.186       |
+--------+------------+--------------------+-------------+-------------+
| 57     | 1          | 1202/100453        | 248.0       | 0.270       |
+--------+------------+--------------------+-------------+-------------+
|        |            |                    |             |             |
+--------+------------+--------------------+-------------+-------------+
| 64     | --         | 1202/137714        | 47.1        | 0.063       |
+--------+------------+--------------------+-------------+-------------+
|        |            |                    |             |             |
+--------+------------+--------------------+-------------+-------------+
| 101    | 2          | 1202/341594        | 25.1        | 0.078       |
+--------+------------+--------------------+-------------+-------------+
| 102    | 2          | 1202/347893        | 97.8        | 0.122       |
+--------+------------+--------------------+-------------+-------------+
|        |            |                    |             |             |
+--------+------------+--------------------+-------------+-------------+
| 116    | 3          | 1202/423271        | 132.4       | 0.141       |
+--------+------------+--------------------+-------------+-------------+
| 117    | 3          | 1202/429126        | 225.2       | 0.283       |
+--------+------------+--------------------+-------------+-------------+
|        |            |                    |             |             |
+--------+------------+--------------------+-------------+-------------+
| 132    | 4          | 1202/509701        | 439.8       | 0.520       |
+--------+------------+--------------------+-------------+-------------+
| 133    | 4          | 1202/515532        | 243.2       | 0.212       |
+--------+------------+--------------------+-------------+-------------+
|        |            |                    |             |             |
+--------+------------+--------------------+-------------+-------------+
| 156    | --         | 1202/636373        | 80.2        | 0.154       |
+--------+------------+--------------------+-------------+-------------+
| 157    | --         | 1202/642193        | 110.6       | 0.071       |
+--------+------------+--------------------+-------------+-------------+

## BET Comparisons

The GEODE state vectors were compared to the Postflight Attitude and
Trajectory History (PATH), also known as a Best Estimate of Trajectory
(BET), generated by the NASA Johnson Space Center (JSC). \[2\] The
estimated accuracy of the BET's position and velocity in radial,
intrack, and crosstrack components is shown in Table 3. \[3\] Because of
the large uncertainties in the BET relative to predicted GEODE
accuracies, no corrections for antenna location or shuttle attitude we
made to the GEODE states.

Table 3 : BET 3σ Accuracies

+-----------------------+-----------------------+-----------------------+
| **Component**         | **Position**          | **Velocity**          |
|                       |                       |                       |
|                       | **(m)**               | **(m/s)**             |
+-----------------------+-----------------------+-----------------------+
| Radial                | 200                   | 0.45                  |
+-----------------------+-----------------------+-----------------------+
| Intrack               | 450                   | 0.20                  |
+-----------------------+-----------------------+-----------------------+
| Crosstrack            | 200                   | 0.25                  |
+-----------------------+-----------------------+-----------------------+

### Experiment 1

Figure 1 and Figure 2 show the radial, intrack, and crosstrack position
and velocity differences for the first GPS experiment. The shuttle
attitude is indicated along the top of the figure, and the "x" symbols
on each curve indicate where GEODE was not converged. GEODE converged
within 25 minutes of being initialized. At the end of the experiment,
the shuttle transitioned to an inertial attitude hold (approximately
98,500 seconds time of week) and GEODE became unconverged as the LPT
dropped satellites due to poor visibility. However, as the shuttle's
attitude improved for tracking GPS satellites, GEODE reconverged from
approximately 100,300 to 102,300 seconds time of week before the
attitude caused the LPT to lose track of GPS again.

![](media/image8.wmf){width="5.25in" height="3.9375in"}

Figure 1: Experiment 1 Position Difference

![](media/image9.wmf){width="5.25in" height="3.9375in"}

Figure 2: Experiment 1 Velocity Difference

### Experiment 2

Figure 3 and Figure 4 show the radial, intrack, and crosstrack position
and velocity differences for the second GPS experiment. Even though the
experiment was only for the duration of the +ZLV +YVV attitude hold, the
subsequent --XLV --YVV attitude hold allowed the LPT to track enough
satellites to maintain GEODE convergence for an additional 2.5 hours.

At the end of this period, the navigation software continued to run for
an additional 9 hours. Figure 5 shows the resulting position differences
with the BET. The shuttle attitude was not favorable to tracking at
least 4 GPS satellites after the --XLV --YVV attitude hold, and the
GEODE position error increased as a result of unmodeled translational
forces from multiple attitude maneuvers during this timeframe. The
intrack position error relative to the BET grew to 9 km before the LPT
again tracked 4 or more GPS satellites, and within 13 minutes, GEODE had
reconverged. This demonstrated the ability of GEODE to propagate through
extended outages and reconverge when new measurements are available.

![](media/image10.wmf){width="5.25in" height="3.9375in"}

Figure 3: Experiment 2 Position Difference

![](media/image11.wmf){width="5.25in" height="3.9375in"}

Figure 4: Experiment 2 Velocity Difference

![](media/image12.wmf){width="5.25in" height="3.9375in"}

Figure 5: Extended Experiment 2 Position Difference

### Experiment 3

Figure 6 and Figure 7 show the radial, intrack, and crosstrack position
and velocity differences for the third GPS experiment. Even though the
experiment was only for the duration of the +ZLV +YVV attitude hold, the
subsequent --XLV +YVV attitude hold allowed the LPT to track enough
satellites to maintain GEODE convergence for an additional 3 hours.
During the latter attitude hold, GEODE became unconverged for 12 minutes
due to poor GPS constellation visibility, but then reconverged as more
satellites were eventually tracked.

![](media/image13.wmf){width="5.25in" height="3.9375in"}

Figure 6; Experiment 3 Position Difference

![](media/image14.wmf){width="5.25in" height="3.9375in"}

Figure 7: Experiment 3 Velocity Difference

### Experiment 4

Figure 8 and Figure 9 show the radial, intrack, and crosstrack position
and velocity differences for the fourth GPS experiment. The experiment
ended at the end of the +ZLV +YVV attitude hold, and the subsequent
--XLV +YVV attitude hold was not favorable for tracking the GPS
constellation. As a result, GEODE became unconverged, but continued to
propagate for another 4.5 hours until the navigation software was
disabled. The lack of measurements prevented GEODE from correcting the
state for the unmodeled translational forces from the attitude maneuver,
and a 6 km intrack position and 6.5 m/s radial velocity difference
between the BET and GEODE was observed at the end of the data arc.

![](media/image15.wmf){width="5.25in" height="3.9375in"}

Figure 8: Experiment 4 Position Difference

![](media/image16.wmf){width="5.25in" height="3.9375in"}

Figure 9: Experiment 4 Velocity Difference

### Orbit 64

Figure 10 and Figure 11 show the radial, intrack, and crosstrack
position and velocity differences for the data collected starting at
orbit 64.

![](media/image17.wmf){width="5.25in" height="3.9375in"}

Figure 10: Orbit 64 Position Difference

![](media/image18.wmf){width="5.25in" height="3.9375in"}

Figure 11: Orbit 64 Velocity Difference

### Orbit 156

Figure 12 and Figure 13 show the radial, intrack, and crosstrack
position and velocity differences for the data collected starting at
orbit 156. This was a unique opportunity in evaluating GEODE's
performance under sporadic tracking periods. GEODE was initialized
during the --ZLV +YVV attitude hold with the point solution, converged,
and processed data for just under 1 hour before the LPT lost track of
the GPS constellation at 27,100 seconds TOW due to an attitude
transition. Due to the poor tracking geometry and shuttle attitude,
GEODE did not reconverge until 43,000 seconds TOW when the --XLV +YVV
attitude hold was more favorable for tracking the GPS constellation,
even though GPS satellites were tracked and processed in the meantime.
Figure 14 shows 2 discretes generated by GEODE that illustrate this. The
first is a flag indicating whether or not GEODE has converged, and the
other indicates whether or not GEODE processed a measurement (GEODE will
process a measurement if at least 4 satellites are tracked).

![](media/image19.wmf){width="5.25in" height="3.9375in"}

Figure 12: Orbit 156 Position Difference

![](media/image20.wmf){width="5.25in" height="3.9375in"}

Figure 13: Orbit 156 Velocity Difference

![](media/image21.wmf){width="5.25in" height="3.9375in"}

Figure 14: Orbit 156 GEODE Processing Discretes

### BET Comparison Summary

Figure 15 and Figure 16 show statistics for the radial, intrack, and
crosstrack components of the position and velocity differences between
the BET and GEODE for the four GPS experiments and the data collected at
orbits 64 and 156. Also shown are the average statistic values over all
of the data, along with the predicted BET 3σ uncertainties listed in
Table 1 (red horizontal solid line). Figure 17 shows the same statistics
for the root sum square (RSS) position and velocity differences.

Experiment 4 compared the worst against the BET. The maximum value for
all three components of position and velocity exceeded the predicted BET
thresholds, with the crosstrack component being the worst offender. The
crosstrack position and velocity differences also exceeded the expected
BET uncertainties in Experiment 3. All other periods were well bounded
by the BET uncertainty thresholds.

![](media/image22.wmf){width="5.25in" height="3.9375in"}

Figure 15: GEODE-BET Position Difference Statistics

![](media/image23.wmf){width="5.25in" height="3.9375in"}

Figure 16: GEODE-BET Velocity Difference Statistics

![](media/image24.wmf){width="5.25in" height="3.9375in"}

Figure 17: GEODE-BET RSS Position and Velocity Difference Statistics

## Navigation Telemetry

Over 150 Mbytes of navigation telemetry was collected during the
mission. Appendix A shows plots of various telemetry points for each of
the GPS tracking periods.

Other than external references for comparison, such as the ground
navigation vector or BET, the best indication of GEODE's performance are
the pseudorange residual statistics, which are shown in Table 4 for each
GPS experiment. The 95% value was computed as the 95% point of the
absolute residuals when ranked in ascending order. The first measurement
at each processing epoch included significant errors from the LPT clock
(up to 600 m) and was excluded from the statistics. The near-zero mean
and approximately 13 m standard deviation indicates that the Kalman
filter performed well.

Table 4: Measurement Residual Statistics

+----------------+-----------------+-----------------+-----------------+
| **GPS**        | **Mean**        | **Sigma**       | **95%**         |
|                |                 |                 |                 |
| **Experiment** | **(m)**         | **(m)**         | **(m)**         |
+----------------+-----------------+-----------------+-----------------+
| 1              | -0.4            | 12.6            | 25.3            |
+----------------+-----------------+-----------------+-----------------+
| 2              | 0.2             | 12.2            | 24.5            |
+----------------+-----------------+-----------------+-----------------+
| 3              | -0.9            | 12.7            | 25.4            |
+----------------+-----------------+-----------------+-----------------+
| 4              | 1.2             | 11.4            | 22.7            |
+----------------+-----------------+-----------------+-----------------+

## Conclusions

The differences between GEODE and the ground navigation and BET
reference vectors were in general well within the expected uncertainties
of those sources. However, it is not known to what level of confidence
the uncertainty of the ground navigation and BET vectors are defined,
and those uncertainties are general in nature. One typically prefers the
reference source accuracy to be of the same order or better than what is
being tested. This is clearly not the case in this instance, as the
expected one-sigma uncertainty in GEODE's position is 20 m. The GEODE
pseudorange residual statistics are consistent with a one-sigma
positioning accuracy of 20 m.

## References

1.  "Global Positioning System (GPS) Enhanced Orbit Determination
    (GEODE) Mathematical Specifications," Version 5, Update 3, NASA GSFC
    document CSC-5506-06R0UD0, March 2001.

2.  "STS-107 PATH Final Report", internal JSC memo.

3.  "Internal ICD: PATH Product", NASA JSC Doc. No. ICD-I-TOP-002C, Rev.
    CPN-1, May 4, 2001.

```{=html}
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```
A.  []{#__RefHeading___Toc50791752 .anchor}Navigation Telemetry

The following subsections provide plots of the GEODE telemetry obtained
from each experiment. A brief description of each plot is as follows:

-   Filter Converged Discrete: indicates when GEODE is converged (1) or
    not converged (0). The filter converged discrete is set when the
    position sigma is less than 100 m, the velocity sigma is less than
    0.2, and the semi-major axis sigma is less than 50 m.

-   Position Comparison Test Discrete: The difference between the point
    solution and filter solution is less than (1) or greater than (0)
    500 m.

-   Position Variances: filter position variances (J2000 X, Y, and Z
    position components)

-   Velocity Variances: filter velocity variances (J2000 X, Y, and Z
    velocity components)

-   Drag Coefficient Variance

-   Clock Bias Variance

-   Semi-Major Axis Sigma

-   Pseudorange Residuals (1 -- 14): measurement residuals for PRNs 1 --
    14

-   Pseudorange Residuals (15 -- 31): measurement residuals for PRNs 15
    -- 31

-   Filter-Point Solution Position Difference: difference between the
    GEODE filter and the point solution position estimates (input to the
    Position Difference Test discrete)

-   Filter-Point Solution Clock Bias Difference

-   Filter-Point Solution Clock Drift Difference

-   GEODE Clock Drift Estimate

-   GEODE Drag Coefficient Correction Estimate

## GPS Experiment #1

![](media/image25.wmf){width="4.375in" height="3.5in"}Figure 18: Exp. 1
Filter Converged Discrete

![](media/image26.wmf){width="4.375in" height="3.5in"}

Figure 19: Exp. 1 Position Comparison Test Discrete

Figure : Exp. 1 Position Variance![](media/image27.wmf){width="4.375in"
height="3.5in"}s

Figure ![](media/image28.wmf){width="4.375in" height="3.5in"}: Exp. 1
Velocity Variances

Figure ![](media/image29.wmf){width="4.375in" height="3.5in"}: Exp. 1
Drag Coefficient Variance

Figure ![](media/image30.wmf){width="4.375in" height="3.5in"}: Exp. 1
Clock Bias Variance

![](media/image31.wmf){width="4.373611111111111in"
height="3.498611111111111in"}

Figure 24: Exp. 1 Semi-Major Axis Sigma

Figure ![](media/image32.wmf){width="4.375in" height="3.5in"}: Exp. 1
Pseudorange Residuals (PRN 1 - 14)

![](media/image33.wmf){width="4.375in" height="3.5in"}

Figure 26: Exp. 1 Pseudorange Residuals (PRN 15 -- 31)

Figure ![](media/image34.wmf){width="4.375in" height="3.5in"}: Exp. 1
Filter-Point Solution Position Difference

Figure : Exp. 1 ![](media/image35.wmf){width="4.375in"
height="3.5in"}Filter-Point Solution Clock Bias Difference

![](media/image36.wmf){width="4.375in" height="3.5in"}

Figure 29: Exp. 1 Filter-Point Solution Clock Drift Difference

![](media/image37.wmf){width="4.375in" height="3.5in"}

Figure 30: Exp. 1 Clock Drift

![](media/image38.wmf){width="4.375in" height="3.5in"}

Figure 31: Exp. 1 Drag Coefficient

## GPS Experiment #2

![](media/image39.wmf){width="4.373611111111111in"
height="3.498611111111111in"}

Figure 32: Exp. 2 Filter Converged Discrete

![](media/image40.wmf){width="4.373611111111111in"
height="3.498611111111111in"}

Figure 33: Exp. 2 Position Comparison Test Discrete

![](media/image41.wmf){width="4.373611111111111in"
height="3.498611111111111in"}

Figure 34: Exp. 2 Position Variances

![](media/image42.wmf){width="4.373611111111111in"
height="3.498611111111111in"}

Figure 35:Exp. 2 Velocity Variances

![](media/image43.wmf){width="4.373611111111111in"
height="3.498611111111111in"}

Figure 36: Exp. 2 Drag Coefficient Variance

![](media/image44.wmf){width="4.373611111111111in"
height="3.498611111111111in"}

Figure 37: Exp. 2 Clock Bias Variance

![](media/image45.wmf){width="4.373611111111111in"
height="3.498611111111111in"}

Figure 38: Exp. 2 Semi-Major Axis Sigma

![](media/image46.wmf){width="4.375in" height="3.5in"}

Figure 39: Exp. 2 Pseudorange Residuals (PRN 1 -- 14)

![](media/image47.wmf){width="4.375in" height="3.5in"}

Figure 40: Exp. 2 Pseudorange Residuals (PRN 15 -- 31)

![](media/image48.wmf){width="4.375in" height="3.5in"}

Figure 41: Exp. 2 Filter-Point Solution Position Differences

![](media/image49.wmf){width="4.375in" height="3.5in"}

Figure 42: Exp. 2 Filter-Point Solution Clock Bias Difference

![](media/image50.wmf){width="4.375in" height="3.5in"}

Figure 43: Exp. 2 Filter-Point Solution Clock Drift Difference

![](media/image51.wmf){width="4.375in" height="3.5in"}

Figure 44: Exp. 2 Clock Drift

![](media/image52.wmf){width="4.373611111111111in"
height="3.498611111111111in"}

Figure 45: Drag Coefficient

## GPS Experiment #3

![](media/image53.wmf){width="4.373611111111111in"
height="3.498611111111111in"}

Figure 46: Exp. 3 Filter Converged Discrete

![](media/image54.wmf){width="4.373611111111111in"
height="3.498611111111111in"}

Figure 47: Exp. 3 Position Comparison Test Discrete

![](media/image55.wmf){width="4.373611111111111in"
height="3.498611111111111in"}

Figure 48: Exp. 3 Position Variances

![](media/image57.wmf){width="4.373611111111111in"
height="3.498611111111111in"}

Figure 49:Exp. 3 Velocity Variances

![](media/image59.wmf){width="4.373611111111111in"
height="3.498611111111111in"}

Figure 50: Exp. 3 Drag Coefficient Variance

![](media/image60.wmf){width="4.375in" height="3.5in"}

Figure 51: Exp. 3 Clock Bias Variance

![](media/image61.wmf){width="4.373611111111111in"
height="3.498611111111111in"}

Figure 52: Exp. 3 Semi-Major Axis Sigma

![](media/image62.wmf){width="4.375in" height="3.5in"}

Figure 53: Exp. 3 Pseudorange Residuals (PRN 1 -- 14)

![](media/image63.wmf){width="4.375in" height="3.5in"}

Figure 54: Exp. 3 Pseudorange Residuals (PRN 15 -- 31)

![](media/image64.wmf){width="4.375in" height="3.5in"}

Figure 55: Exp. 3 Filter-Point Solution Position Differences

![](media/image65.wmf){width="4.375in" height="3.5in"}

Figure 56: Exp. 3 Filter-Point Solution Clock Bias Difference

![](media/image66.wmf){width="4.375in" height="3.5in"}

Figure 57: Exp. 3 Filter-Point Solution Clock Drift Difference

![](media/image67.wmf){width="4.375in" height="3.5in"}

Figure 58: Exp. 3 Clock Drift

![](media/image68.wmf){width="4.375in" height="3.5in"}

Figure 59: Exp. 3 Drag Coefficient

## GPS Experiment #4

![](media/image69.wmf){width="4.375in" height="3.5in"}

Figure 60: Exp. 4 Filter Converged Discrete

![](media/image70.wmf){width="4.375in" height="3.5in"}

Figure 61: Exp. 4 Position Comparison Test Discrete

![](media/image71.wmf){width="4.375in" height="3.5in"}

Figure 62: Exp. 4 Position Variances

![](media/image72.wmf){width="4.375in" height="3.5in"}

Figure 63:Exp. 4 Velocity Variances

![](media/image73.wmf){width="4.375in" height="3.5in"}

Figure 64: Exp. 4 Drag Coefficient Variance

![](media/image74.wmf){width="4.375in" height="3.5in"}

Figure 65: Exp. 4 Clock Bias Variance

![](media/image75.wmf){width="4.373611111111111in"
height="3.498611111111111in"}

Figure 66: Exp. 4 Semi-Major Axis Sigma

![](media/image76.wmf){width="4.375in" height="3.5in"}

Figure 67: Exp. 4 Pseudorange Residuals (PRN 1 -- 14)

![](media/image77.wmf){width="4.375in" height="3.5in"}

Figure 68: Exp. 4 Pseudorange Residuals (PRN 15 -- 31)

![](media/image78.wmf){width="4.375in" height="3.5in"}

Figure 69: Exp. 4 Filter-Point Solution Position Differences

![](media/image79.wmf){width="4.375in" height="3.5in"}

Figure 70: Exp. 4 Filter-Point Solution Clock Bias Difference

![](media/image80.wmf){width="4.375in" height="3.5in"}

Figure 71: Exp. 4 Filter-Point Solution Clock Drift Difference

![](media/image81.wmf){width="4.375in" height="3.5in"}

Figure 72: Exp. 4 Clock Drift

![](media/image82.wmf){width="4.375in" height="3.5in"}

Figure 73: Exp. 4 Drag Coefficient

## Orbit 64

![](media/image83.wmf){width="4.373611111111111in"
height="3.498611111111111in"}

Figure 74: Orbit 64 Filter Converged Discrete

![](media/image84.wmf){width="4.373611111111111in"
height="3.498611111111111in"}

Figure 75: Orbit 64 Position Comparison Test Discrete

![](media/image85.wmf){width="4.373611111111111in"
height="3.498611111111111in"}

Figure 76: Orbit 64 Position Variances

![](media/image86.wmf){width="4.373611111111111in"
height="3.498611111111111in"}

Figure 77: Orbit 64 Velocity Variances

![](media/image87.wmf){width="4.373611111111111in"
height="3.498611111111111in"}

Figure 78: Orbit 64 Drag Coefficient Variance

![](media/image88.wmf){width="4.373611111111111in"
height="3.498611111111111in"}

Figure 79: Orbit 64 Clock Bias Variance

![](media/image89.wmf){width="4.373611111111111in"
height="3.498611111111111in"}

Figure 80: Orbit 64 Semi-Major Axis Sigma

![](media/image90.wmf){width="4.373611111111111in"
height="3.498611111111111in"}

Figure 81: Orbit 64 Filter-Point Solution Position Differences

![](media/image91.wmf){width="4.373611111111111in"
height="3.498611111111111in"}

Figure 82: Orbit 64 Filter-Point Solution Clock Bias Difference

![](media/image92.wmf){width="4.373611111111111in"
height="3.498611111111111in"}

Figure 83: Orbit 64 Filter-Point Solution Clock Drift Difference

![](media/image93.wmf){width="4.373611111111111in"
height="3.498611111111111in"}

Figure 84: Orbit 64 Clock Drift

![](media/image94.wmf){width="4.373611111111111in"
height="3.498611111111111in"}

Figure 85: Orbit 64 Drag Coefficient

## Orbit 156

![](media/image95.wmf){width="4.373611111111111in"
height="3.498611111111111in"}

Figure 86: Orbit 156 Filter Converged Discrete

![](media/image96.wmf){width="4.373611111111111in"
height="3.498611111111111in"}

Figure 87: Orbit 156 Position Comparison Test Discrete

![](media/image97.wmf){width="4.373611111111111in"
height="3.498611111111111in"}

Figure 88: Orbit 156 Position Variances

![](media/image98.wmf){width="4.373611111111111in"
height="3.498611111111111in"}

Figure 89: Orbit 156 Velocity Variances

![](media/image99.wmf){width="4.373611111111111in"
height="3.498611111111111in"}

Figure 90: Orbit 156 Drag Coefficient Variance

![](media/image100.wmf){width="4.373611111111111in"
height="3.498611111111111in"}

Figure 91: Orbit 156 Clock Bias Variance

![](media/image101.wmf){width="4.373611111111111in"
height="3.498611111111111in"}

Figure 92: Orbit 156 Semi-Major Axis Sigma

![](media/image102.wmf){width="4.373611111111111in"
height="3.498611111111111in"}

Figure 93: Orbit 156 Clock Drift

![](media/image103.wmf){width="4.373611111111111in"
height="3.498611111111111in"}

Figure 94: Orbit 156 Drag Coefficient