REG NASA-LLIS-0878--2000 Lessons Learned Orbiter S-Band Uplink Monitoring System.pdf

1、Best Practices Entry: Best Practice Info:a71 Committee Approval Date: 2000-04-24a71 Center Point of Contact: KSCa71 Submitted by: Wilson HarkinsSubject: Orbiter S-Band Uplink Monitoring System Practice: The S-Band Uplink Monitoring System provides the means to verify the voice and data communication

2、s received by the Orbiter while at the launch pad are complete and error-free.Programs that Certify Usage: This practice has been used on the Space Shuttle Program.Center to Contact for Information: KSCImplementation Method: This Lesson Learned is based on Maintainability Technique number OPS-18 fro

3、m NASA Technical Memorandum 4628, Recommended Techniques for Effective Maintainability.Maintainability of the S-Band Uplink Monitoring System is enhanced by providing a means to pinpoint faults should they occur. Reliability is also enhanced by ensuring the communication signals are transmitted as i

4、ntended.The Goddard Unified S-Band (GUSB) system transmits voice and data signals via free space to two antennas at the launch pad; the Orbiter S-Band Antenna and the Monitor S-Band Antenna on the Fixed Service Structure (FSS). Both antennas receive the same signal. The signal from the Monitor Anten

5、na is retransmitted over an optional link, demodulated at the Orbiter Processing Facility (OPF) and compared to the signal being sent from GUSB (See Figure 1).Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-refer to D descriptionD Provided by IHSNot

6、for ResaleNo reproduction or networking permitted without license from IHS-,-,-Figure 1. S-Band Uplink Monitoring System Block Diagram The GUSB voice and data communications are critical, particularly during launch countdown. However, transmissions can be distorted because of a transmission frame er

7、ror, a discontinuity in Radio Frequency (RF) signal level, or a response to harmonics. Concerns arise about the information reaching the Orbiter: Is it error free? Is it identical to that which was transmitted? The S-Band Uplink Monitor System answers these questions continuously throughout launch c

8、ountdown. This system detects such problems; furthermore, it provides a frame of reference whereby engineers can troubleshoot and pinpoint the errors to the following areas:a71 The GUSB transmittera71 The receiver on-board the Orbitera71 The Orbiters on-board sensora71 The monitoring receiver in the

9、 OPFThis capability enhances the maintainability of the monitoring system, as well as the GUSB transmission system, by providing this pinpointing capability.RF TransmissionThe GUSB antenna transmits the modulated S-Band signal (2106 or 2041 MHZ, payload dependant) at several levels during the countd

10、own: 10KW, 1KW, 200 W, 16 W. The Uplink Monitor S-Band Antenna receives the incoming S-Band Signal at the 295-foot level of the FSS. The antenna was designed to be located as close as possible to the Orbiter S-Band Antenna in order to receive the same signal in terms of strength and noise content. T

11、he signal is then split at half power between two channels.The channel selected depends on the GUSB signal power. The channels are identical except for their variable attenuator settings. The high power channel has high attenuation so the optical transmitter does not saturate; the low power channel

12、has low attenuation so the signal has considerable strength when it reaches the optical transmitter input.After the signal passes through the directional coupler, the RF amplifier in each channel boosts the signal with a +52dB gain to acquire optimum signal strength through the optical link. This as

13、sures an adequate signal strength at the receiver in the OPF after passing through the final directional coupler.Fiber-Optic LinkThe signal is now transmitted to the OPF through an optical link. The use of fiber over a long distance minimizes both attenuation and noise interference. In addition, ele

14、ctromagnetic interference is non-existent when transmitting over fiber optics. For these reasons, the fiber-optical link covers a sizable distance of the systems total transmission range (up to 8 KM for Pad B).Provided by IHSNot for ResaleNo reproduction or networking permitted without license from

15、IHS-,-,-The optical power at the transmitter is set to allow for losses in the optical link and still be above the sensitivity of the optical receiver in the OPF. The number of patch panels and fiber optic connectors are kept to a minimum to minimize losses during the routing of the signal to the OP

16、F.Two fiber optic couplers are used because the system is required to transmit the signal from either launch pad to OPF-1, 2 or OPF-3. The first coupler is a single-mode 2X2 which allows two inputs such as the low-power channels from Pads A and B to transmit to OPF 1, 2 on output 1 and to OPF-3 on o

17、utput 2. The second coupler is configured similarly, except that the high power channels feed the inputs.The fiber optical receivers in the OPF communications and Tracking Laboratory receive the modulated optical signal. At this point the signal is demodulated off the light wave and coupled to the S

18、-Band receiver in the OPF where it is compared with that coming off an S-band receiver that is monitoring the GUSB. Information is demodulated from the carrier and recorded by a frame-check computer that indicates the bit-error count. It is at this point that engineers can determine if the S-Band si

19、gnal received at the Orbiter is accurate and detectable.Reference:1. KSC Drawing 80K54080.Impact of Non-Practice: During the Space Shuttle launch countdown, various computers and multilogic Command Control Units (CCUs) aboard the Orbiter await data feeds from Control Centers at both Kennedy and John

20、son Space Centers. These CCUs activate Orbiter sensors that provide the launch team with vital data such as temperature and pressure readings. In addition to data, voice communications from JSC are transmitted directly to the Orbiter Flight Crew.The S-Band Monitoring System provides verification tha

21、t these signals arrive at the launch pad error-free. It also provides the means to pinpoint the source of any errors, should they occur.Related Practices: N/AAdditional Info: Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-Approval Info: a71 Approval Date: 2000-04-24a71 Approval Name: Eric Raynora71 Approval Organization: QSa71 Approval Phone Number: 202-358-4738Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-