October 5, 2001
To: Landing Site Workshop Participants
From: M. Golombek and J. Grant, Chairs Landing Site Steering Committee
Re: MER Landing Sites Ellipse Sizes
Below is a memorandum describing updated landing site ellipse sizes and orientations to be used at the upcoming Landing Site Workshop. Most of these ellipses are slightly larger than those distributed earlier. Most ellipses are within 10 km of previous estimates, although a few approach 20 km.
The PDF file includes the ellipse sizes and azimuths for all ROTO and Nadir sites as well as the Elysium Flow site. The Excel file includes a worksheet for determining the ellipse size and orientation from latitude for any site not on the list. I have taken the liberty of adding the approximate latitudes for Ares Vallis Tributary, Sinus Meridiani and Highlands to the worksheet for your convenience, so all sites to be discussed at the Landing Site Workshop should have ellipse sizes and orientations.
Subject: Updated Site Ellipse Dimensions for Site Selection Workshop
Introduction, Assumptions, and References:
Attached are updated landing ellipse dimensions and other supporting data for use in the Site Selection Workshop 10/17-18/2001. Site coordinates were provided by Matt Golombek in his September 26,2001 memo ["Mars Exploration Rover Landing Site Memorandum"]. Nav performance is based on the nav baseline established at the end of August, and includes a correction to ionosphere modeling inputs noted in mid September.
NOTE: These results supercede the site ellipse data provided 9/10/01.
The following assumptions for generating the Site Selection Workshop ellipses were agreed to at the 9/4/01 Project Design Team meeting:
The EDL margins were added to the 99% Monte Carlo dimensions to produce the ellipse data shown in the attached documents.
Analyses:
Over 50 EDL Monte Carlo analyses went into these results, including LARC 60DOF and JPL 3DOF Monte Carlos. Wherever feasible, redundant analyses at LARC and JPL were used to crosscheck results.
Sets of 2000 entry states were provided by JPL NAV for Monte Carlo analyses at seven of the ROTO sites. These data were used to generate approximate entry states for Monte Carlo analyses at the remaining ROTO sites, plus the Elysium Flow site EP49B. [See Additional Analysis Notes at the end of this e-mail for more details.]
Ellipses for ROTO and Nadir Sites
The PDF presentation summarizes total [end-to-end] downtrack and crosstrack ellipse dimensions, and azimuths with respect to true North. The first page contains ellipse dimensions for the ROTO sites, plus Elysium Flow. The last page shows ellipse sizes for the Nadir sites, based on curve fit approximations.
Spreadsheet Tool for Calculating Ellipse Dimensions as a Function of Latitude
The Excel spreadsheet is provided as a tool for calculating ellipse dimensions as a function of latitude. Twelve quadratic curve fits are included in this spreadsheet, covering open and close of launch period for MER-A, MER-B, downtrack, crosstrack, and azimuth data. The ROTO ellipses, plus an ellipse calculated at 10°N, were used to construct the curves.
The Nadir sites are shown at the top of the spreadsheet. At the bottom are "work" areas, to be used for calculating dimensions at other latitudes. The user enters planetocentric latitude and the spreadsheet calculates ellipse dimensions at open and close of the launch period. Note: dimensions for MER-A are slightly different than those for MER-B. The user should be sure the correct curve fits are used; an example of the difference is shown in the work areas.
Ellipse Size Uncertainties for Curve Fit Approximations Since the curve fits represent approximations as a function of latitude only, they will not include the effects of small ellipse variations due to site longitude. The combined effects of different arrival times, approach geometries, nav tracking schedules, and other effects can produce small deviations from ellipse sizes calculated with the curve fits. The approximate size of such errors is:
±5 km in downtrack,
±1 km crosstrack,
±1 degree in azimuth.
Philip Knocke
Sets of 2000 entry states were generated by JPL NAV for EDL Monte Carlo analyses at launch period open and close, for the following ROTO sites: IP85A, TM10A, VM53A, EP55A, IP98B, TM20B, and Melas B Site. B-plane dispersions generated from the above data, plus new nominal entry states, were used to generate approximate dispersed states for Monte Carlo analyses at the remaining ROTO sites.
Curve fits based on all the above, plus one MERB Monte Carlo at 10°N, were employed to provide approximate landing ellipse dimensions for the Nadir sites. The following table summarizes the source of results for all ROTO sites plus Elysium Flow:
Curve fits based on all the above were employed to provide approximate landing ellipse dimensions for TM9A, TM19B, and the Nadir sites. The following table summarizes the source of results for all ROTO sites.
| MER-A Site | Analysis | ||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| IP85A | MC
| TM9A
| ~MC
| TM10A
| MC
| EP82A
| ~MC
| VM53A
| MC
| VM41A
| ~MC
| EP55A
| MC
| |
| MER-B Site | Analysis | ||||||||
|---|---|---|---|---|---|---|---|---|---|
| EP49B | ~MC
| IP98B
| MC
| TM19B
| ~MC
| TM20B
| MC
| Melas B site
| MC
| |
| Legend: | MC | = | Monte Carlo based on 2000 entry states from NAV |
| ~MC | = | Monte Carlo based on approx B-plane dispersions |
voice: 818-393-1021
e-mail: philip.c.knocke@jpl.nasa.gov
mail: JPL, 4800 Oak Grove Drive, MS 301-125, Pasadena CA 91109