# Presentation: 437397

## Mission Operations Working Group Meeting______________Bob E. Schutz, University of TexasScience Team Leaderschutz@csr.utexas.edu

## Science Summary

**Growth or shrinkage of Greenland and Antarctica ice sheets is unknown; contributes to sea-level**
**Altimeter profiles to 13 cm and spatial averaging over 100 km x 100 km areas to 1.5 cm/yr**
**Global topography at high resolution and accuracy**
**Measure vertical structure of radiatively significant clouds and aerosols, determine optical depth and height of the planetary boundary layer**

## General Science Requirements: I

**Altimeter precision ~10 cm**
**Global, continuous day/night operation**
**Determine GLAS reference point (GRP) position with respect to Earth center of mass to accuracy < 5 cm radial PAD; GRP known with respect to observatory center of mass (~cg) to 5 mm; GPS antennas and LRA reference points with respect to cg to 5 mm **
**Determine laser pointing direction in inertial space to an accuracy of 1.5 arcsec**
**Orbit: 94 deg (covers most of the polar regions, provides crossovers for analysis); frozen (altitude is function of latitude)**
** ****Off-nadir pointing at a reference ground track, which allows generation of very nearly repeating tracks (compromise: polar regions on every track; intermittent use elsewhere)**
**Off-nadir pointing for special applications (e.g., calibration/validation maneuvers, targets of opportunity)**

**Notes:**
Some of the requirements can be identified with, for example, the GLAS instrument. But in subtle ways, the 

## General Science Requirements: II

**Launch window: NLT 6 pm PST, earlier is preferred**
**Solar array articulation: inhibit well before start of polar region pass; inhibit on selected Cal/Val site passes (rare occurrence to assess solar array induced jitter)**
**Perform conical scan maneuvers over ocean for Cal/Val**
**Location of ********V (orbit adjust maneuvers); not in south polar region, north polar region acceptable when subsequent track does not cross Greenland**
**Coordinate time and location of maneuvers with Science Team for science impact assessment**

**Notes:**
Some of the requirements can be identified with, for example, the GLAS instrument. But in subtle ways, the 

## Commissioning Phase

**Launch + 30 days**
- Science Team assessment of GPS receiver performance and early assessment of POD and BJ receiver performance (no expectation to reach 5 cm radial accuracy at this stage due to outgassing, etc); comparisons with operational OD (OOD)
- Desirable for IST (and LRC) to be activated for early assessment of PAD, comparison with on-board quaternions
- GLAS laser power up with LPA; initial assessment of data
- What is schedule for instrument component power on? (Purpose is to obtain initial performance assessments prior to Cal/Val Phase)
- Outstanding issues?
- From “long duration simulation” run in September, various questions came up about constants and scale parameters in PRAP (referred to in PRAP documentation): who will provide this information or where will it be documented
- Do we need an ICD for exchange of orbit results between UTCSR and LASP? (Preference: no special formats for exchange, but may need that formats be “change controlled”
- Flight reference orbits provided to LASP; if launch conditions require change, new reference orbits would be in same format

## Cal/Val Phase

**Commissioning to ~120 days**
- Initial cal/val orbit is 8 day repeat with ascending pass over White Sands and Bonneville
- Approximate transition to 183 day repeat at about 60-90 days after Commissioning
- Ongoing assessment of laser performance with LPA and digitized pulses; GPS and other components of GLAS, e.g., IST, LRC.
- Ongoing exchange of information between LASP and Science Team
- First experiments ASAP with overflights of Cal/Val sites and ocean scans; requires GLAS laser operation

## Cal/Val Considerations

**Verify instrument performance**
- Possible altitude dependencies
- White Sands (~ min altitude), Antarctica (~ max altitude)
- Possible thermal effects
- Ascending passes (night during Cal/Val)
- Descending passes (day during Cal/Val)
- Other effects or testing (e.g., several tens of degree off-nadir; point at South Pole)
**Other effects**
- Spacecraft jitter during solar array articulation
- Inhibit or activate articulation during some Cal/Val site overflights
**Other Cal/Val**
- Ocean sweeps (conical motion about nadir direction)

## Cal/Val Sample Timeline

**Assume times are elapsed time since start of 8 day cycle**
- Day 0
- 0.13 d, Pacific ocean scan, descending  (15 min duration)
- 0.45 d, Amery (Antarctica), descending, 3.5 off-nadir
- 0.64 d, Pacific ocean scan, ascending (15 min)
- Day 1
- 1.14 d, Pacific ocean scan, descending (15 min)
- 1.45 d, Bonneville, ascending, `0.4 off-nadir
- 1.64 d, Pacific ocean scan, ascending (15 min)
- 1.80 d, Greenland summit, descending, 1.8° off-nadir
- 1.81 d, Salinas Grandes (Argentina), descending, 0.8° off-nadir
- Day 2
- 2.15 d, Pacific ocean scan, descending (15 min)
- 2.65 d, Pacific ocean scan, ascending (15 min)
- 2.94 d, White Sands-secondary, descending, ~0° off-nadir
- 2.97 d, Amery (Antarctica), ascending, 0.5° off-nadir

## Cal/Val Sample Timeline: continued

**Times from start of 8 day cycle**
- Day 3
- 3.16 d, Pacific ocean scan, descending (15 min)
- 3.57 d, Antarctic site 2, descending, 0.5° off-nadir
- 3.66 d, Pacific ocean scan, ascending (15 min)
- Day 4, etc.
- Similar
**Preliminary timeline plan being developed with objectives and requirements (e.g., offnadir pointing, solar array articulation inhibited, etc.). Goal: draft by ~May/June Science Team meeting (inflight circumstances may require changes, but a startup plan is needed)**
**Midterm Cal/Val Workshop to assess results and decide on transition to 183 day orbit and tentative completion of Cal/Val Phase**

## Main Mapping Phase

**183 day repeat orbit**
**Cal/Val Phase final workshop and initial mapping phase workshop to review readiness for generating science products**
**Cal/Val continues throughout the mission**

## Status

**POD/PAD pre-readiness review (Austin, Feb. 20, 2002)**
**Preliminary Cal/Val timeline and Cal/Val pre-readiness review (~May/June 2002)**
**Data flow tests, progressively with higher fidelity underway (Hancock, et al., + ICD status)**
**Fall 2002:**
- POD/PAD readiness review
- Cal/Val launch readiness workshop
- Prelaunch end to end simulation to test the readiness of all operations components?