# Presentation: 532995

## Mars Exploration Rover Landing Site Ellipse Update

**P. Knocke**
**3rd MER Landing Site Selection Workshop****March 26, 2002**

## 10/2001 Site Ellipse Analyses and Assumptions

**Entry dispersions were for TCM5 at Entry - 2 days [data cutoff at Entry - 2.5 days]**
**Assumes Auto-TCM:  designed maneuver  instead of library of fixed maneuvers**** **
**Approach Nav estimates include ∆DOR and peer-reviewed orbit determination filter inputs**
**A "no margin" floor capability was established, then margins were added for Navigation robustness. **
**Nav delivery capabilities are strongly dependent on spacecraft dynamics **
- ACS events, non-grav acceleration uncertainty, maneuver execution error
**Nav delivery capabilities do not apply in the event of a thruster failure**
- Unbalanced turns produce non-zero net ∆V from each ACS event, resulting in degraded performance.
**LARC 6DOF and/or JPL 3DOF Monte Carlo analyses were performed for all ROTO sites plus Athabasca.  99% landing ellipses were calculated.**
**Sets of 2000 entry states were provided at:   IP85A, TM10A, VM53A, EP55A, IP98B, TM20B, Melas B Site**
**B-plane dispersions generated from these data, plus new nominal entry states, were used to create approximate dispersed states for Monte Carlo analyses at the other ROTO sites.**
**Curve fits based on the ROTO site ellipses were used to provide approximate landing ellipse dimensions for the Nadir sites**
**EDL margins were added to the 99%landing ellipses to account for other potential effects on ellipse dimensions, including:**
**Sustained winds, additional atmospheric density dispersions, potential change in target entry flight path angle, etc.**** **

## EDL Margins

***Total Downtrack EDL Margin is equivalent to an EFPA error of ***
***0.04° - 0.05°***
_***Partial:***_***  5 km Total Downtrack per ***
***±0.01° 3************ EFPA ***

## Gusev Example [10/2001 Site Location]

**Site Ellipse**

**Monte Carlo**
**Scatter Points**

**99%**
**[unmargined]**
**Ellipse**

## Nav Update

**Work done for 10/2001 workshop suggested an uncertainty [i.e. noise] of ~ 0.02° in 3********EFPA errors, based on effects of minor changes to analysis [∆DOR & Doppler/Range scheduling, etc.]**** **
**Covariance Study comparison with Odyssey approach reconstruction **
**Good agreement - no need to change Orbit Determination filter assumptions**** **
**Further refinement of delivery estimates**
**Revision of TCM-5 maneuver execution errors:  1******** reduced by 1 mm/s [MER-A], 2 mm/s [MER-B]**
**Latest Delivery estimates are at level of 10/2001 numbers or better :**
**DSN contention during MER approach phase is high, and may affect quantity of Doppler & Range tracking available for MER.  **
**Worst case impact is up to ~0.03° increase in 3******** EFPA error**

## Updated Landing Error Estimates

**Site locations have changed slightly, with negligible effect on site dimensions**
**EDL Margins are unchanged**
**Likelihood of shallowing the targeted entry flight path angle is somewhat lower, depending on results of the parachute deploy strength tests in May 2002**
**Updated landing error ellipses [including EDL margin] based on new Nav delivery are slightly smaller:**

- *  Estimate based on curve fit from 10/2001 and other data                        ** Based on POST & AEPL Monte Carlos using 2000 entry states generated  3/1/2002.

## Melas [MER-B Open]

***Melas [MER-B Open]***

**EDL-margined TCM-5 Ellipse, from updated Nav ****[88 km x 17 km, 83° Az]**

**Site Ellipse 10/2001**
**[105 km x 20 km, 82° Az]**

## Conclusions

**No change to the Site Ellipse dimensions are recommended**
**New Nav estimates improve 3******** EFPA error by up to ~ 0.04°**
**New uncertainties and potential threats are comparable in magnitude**
**Analysis "noise" [0.02°]**
**Threat to Doppler/Range tracking schedule [≤ 0.03°]**
**Other Issues:**
**Current analyses assume some ground system infrastructure performance beyond levels previously committed to.**
**e.g. Earth orientation parameters, media calibrations, etc.**
**Not currently modeled:**
**Separation ∆V, HRS venting ∆V **
**Operational effects:   in-flight anomalies, targeting process, ...**