Simulation Studies in support of an ISS GWOS mission: TropWinds

1. Simulation Studies in support of an ISS GWOS mission: TropWinds Emmitt, Wood, Greco (SWA) Gentry (GSFC/NASA) Kavaya (LaRC/NASA) DWL WG Meeting 24 – 26 August 2010 Bar Harbor, Me

2. Outline • General TropWinds concept including options • DWL alone • DWL and scatterometer • Scaled down GWOS/NWOS for ISS accommodations • Latest instrument parameters for GWOS • ISS configuration/accommodation issues • Implications of CALIPSO study • Aerosols in the tropics • Tropical clouds (upper troposphere) • Current DWL simulation results

3. Mission Definition Team • Established to develop a path to space for a Doppler wind lidar. • Oversaw IDL evaluation of GWOS (Global Wind Observing System) and NWOS (NPOESS Wind Observing System). • Currently considering a science mission using a combination of GWOS and NWOS instrument designs • NWOS telescope cluster concept; GWOS hybrid transceiver technology; scaled to ISS orbit altitude.

4. OSSE evaluation of TropWinds • Papers presented by Lars Peter and Michiko. • Uses the T511 Nature Run and the GWOS instrument parameters adjusted to 350km orbit.

5. TropWinds Instrument Parameters *At the fundamental 1.06um for direct detection. The utility wavelength is .355um ** Includes: Pre LRE optics (.48), IF (.7) and LRE throughput (.74)

6. Mission and Accommodation Issues

7. Assumptions • A demonstration mission that will not held to operational lifetime, duty cycle and data download requirements. • Instrument would be based upon existing GWOS and NWOS concepts, both using the hybrid approach. • The pointing issues would be handled with “knowledge” rather than “control” (i.e. no gimbaling)

10. External payload attachment sites • The US integrated truss segment (ITS) provides logistics and maintenance as well as payload attachment sites. The attachment sites accommodate logistics and maintenance and payloads carriers, both zenith and nadir. • The U.S-provided ExPRESS Logistics Carrier ELC is designed to carry a variety of orbital replacement units (ORUs or spares), first-time outfitting cargo, and external payloads (science experiments). • The ESA Columbus-EPF is another back-porch-like platform that can accommodate two zenith-and two nadir-looking payloads. • The Japanese JEM-EF, a back-porch-like attachment to the JEM pressurized module, accommodates up to eight payloads, which can be serviced by the crew via the JEM PM airlock and dedicated robotic arm.

11. External payload attachments • EXpedite the PRocessing of Experiments to the Space Station (EXPRESS) Logistics Carrier (ELC) • 4 sites allowing multiple payloads • 4,445Kg • 3kW • 95Mbps • 30M3 • Columbus-EPF • 4 sites: 1 zenith, 1 nadir, 2 starboard • 290Kg per site (includes EXPRESS, ExPA and FRAM) • 1.25kW at each site (120 VDC) • High data rate line 32Kbits/second • .9 x 1.2 x 1.2 meters dimensions

12. External payload attachments • Japanese JEM-EF • Accommodates 9 experiment payloads • Nominal 500kg payloads • 3kW 120VDC • ?? download data rates • .8 x 1.0 x 1.8 meters

13. ELC 1 and ELC2

15. JEM-EF

16. Key accommodation issues related to instrument performance • High frequency vibrations (> 1 Hz) • Slow attitude changes (drifts; re-boosts) • Power to PL (average and peak) • Thermal management • Orbital debris • Data rates and latency (uplink and downlink)

17. High frequency vibrations • Current interest is in the energy in vibrations with frequencies > 1 Hz; may introduce coherent detection velocity errors depending upon amplitude; may exceed thresholds for direct detection Fabry Perot interferometer. • Understanding: • Max amplitude of >1 Hz is ~ .5 urad as measured on the ISS • Potential resolution: • Use standard vibration damping technology

18. Changes of attitude • Concern is driven mainly by the pointing stability during the 4.15 msec round trip time for laser pulse. • < 3.08 urad/4.15 millisec is needed (= .74 urad/ms = .04 d/sec) • Coherent detection subsystem requires better than 3.08 urad to keep losses < 3 dB. • Understanding: • +- 20 degrees Pitch; .02 degree/sec per axis max • Nominal attitude changes < 1 degree in each axis per orbit • Solutions: • Need pointing knowledge within ~ 25 urad

19. Electrical power (1) • The coherent and direct detection subsystems in the hybrid-DWL require ~ 125 and 885 watts maximum power respectively. • Standby power is needed if orbit average power available is below that needed for continuous wind profiling. • Can operate only in sunlit hours if necessary.

20. Electrical power (2) • Understanding: • The total single orbit-averaged power, to include eclipse operations, provided to the Payload (PL) during normal operations will not exceed 200 watts for HEO and 400 watts for LEO combined over all power services. • Daily average power for LEO will not exceed 200 watts over all. • The total peak power provided to the PL during normal operations shall not exceed 700 watts, combined over all power services.   • The energy provided to the PL during normal eclipse operations shall be limited to 350 W-hr combined over all power services.   •   Recommend flexibility to ~1400 Watts using scalable SB Power to accommodate high consumption payloads (e.g. RF or SAR) • Solution(s): • Can operate to meet power limitations

21. Thermal management • The hybrid DWL is, at best, 2 - 5% wall plug efficient for the entire PL (includes laser cooling, communications, data system, etc.) • Understanding: • Needs to be discussed in depth • Solution: • TBD

22. Near FOV space debris • Concern is that any space debris within the first few hundred meters of the ISS may cause damage to the instrument, especially on the JEM. • Understanding: • none • Solution: • TBD

23. Data rates (up/down) • There will be a desire to downlink all raw data: ~20Mbits/second if all data taken is retrieved and downlinked. • Uploading commands is not a major issue. • Understanding: • S-band command uplink = ~ 75kb/s • Ku-band data downlink = ~100Mb/s (max) • Solution(s): • Some on-board processing could be used to reduce orbit average downloads

24. ISS GWOS Coverage for three orbits

25. DLSM simulations for TropWinds • Emphasis on the tropics. • Scaling GWOS down to 350km • Uses GWOS instrument performance parameters listed in prior slide • Clouds in T511 Nature Run modified to conform to ISCCP coverage statistics • Understates very thin to subvisual cirrus effects which would be very positive for coherent coverage and slightly negative for direct accuracies.

28. Cloud statistics for the tropics using CALIPSO • Using CALIPSO (V3.1) profile data set • Understates “very thin” cirrus and sub-visual cirrus. • Appropriate for direct (molecular) detection assessment; understates coherent performance.

41. Summary • Platform attitude drift does not appear to be a major factor in DWL data quality using pointing knowledge over pointing control • Clouds will be a major modulator of DWL coverage • Direct detection is most effected by the high clouds in the tropics. • Coherent provides winds within some of the high level clouds and within the lower troposphere below.