September 10, 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 the memorandum describing the landing site ellipse sizes and orientations to be used for next weeks Landing Site Workshop. Ellipses are fairly close to the approximations we sent out last week (e-mail dated Sept. 6).
The Power Point presentation includes the ellipse sizes and azimuths for all ROTO and Nadir sites. The Excel file includes a worksheet for determining the ellipse size and orientation from latitude for any site not on the list (e.g., the 6 additional sites with small ellipses described in our e-mail of August 24: Isidis, Elysium Flow I and II, Ares Vallis Tributary, Sinus Meridiani and Highlands).
Subject: Site Ellipse Dimensions for Site Selection Workshop
Introduction, Assumptions, and References:
Attached are landing ellipse dimensions and other supporting data for use in the upcoming Site Selection Workshop. Site coordinates were provided by Matt Golombek in his July 30,2001 memo ["MER Landing Site Memorandum, Re: Center Ellipse Locations in MOLA Reference Frame"]. Nav performance is based on the new nav baseline established at the end of August.
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 40 EDL Monte Carlo analyses went into these results, including LARC 6DOF 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 five of the ROTO sites. These data were used to generate approximate entry states for Monte Carlo analyses or curve fit approximations at the remaining sites. [See Additional Analysis Notes at the end of this e-mail for more details.]
Ellipses for ROTO and Nadir Sites
The Powerpoint presentation summarizes total [end-to-end] downtrack and crosstrack ellipse dimensions, and azimuths with respect to true North. ROTO site dimensions are shown, with asterisks for those ellipses calculated via curve fit approximations rather than Monte Carlos. The last page shows ellipse sizes for the Nadir sites, based on curve fits to the ROTO data.
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 curve fits are included in this spreadsheet, covering open and close of launch period for MER-A, MER-B, downtrack, crosstrack, and azimuth data. When compared with the ROTO Monte Carlo data, these curve fits produce a maximum error of < 2 km in downtrack, and negligible errors in crosstrack and azimuth.
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.
Philip Knocke
Sets of 2000 entry states were generated by JPL NAV for EDL Monte Carlo analyses at the following ROTO sites: IP85A [launch period open and close], EP55A [open and close], IP98B [open and close], TM20B [open only], and Melas B Site [open and close].
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 following ROTO sites: TM20B[close], TM10A, EP82A, VM53A, and VM41A.
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 | Open | Close | ||||||||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| IP85A | MC | MC
| TM10A
| ~MC
| ~MC
| TM9A
| CF
| CF
| EP82A
| ~MC
| ~MC
| VM53A
| ~MC
| ~MC
| VM41A
| ~MC
| ~MC
| EP55A
| MC
| MC
| |
| MER-B Site | Open | Close | |||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|
| IP98B | MC | MC
| TM19B
| CF
| CF
| TM20B
| MC
| ~MC
| Melas B site
| MC
| MC
| |
| Legend: | MC | = | Monte Carlo based on 2000 entry states from NAV |
| ~MC | = | Monte Carlo based on approx B-plane dispersions | |
| CF | = | Curve fit |
voice: 818-393-1021
e-mail: philip.c.knocke@jpl.nasa.gov
mail: JPL, 4800 Oak Grove Drive, MS 301-125, Pasadena CA 91109