Mars Science Laboratory landed Curiosity in Gale Crater on 5 Aug 2012. Curiosity landed successfully only 2.2 km away from the expected target given the onboard navigation state. Better than the average Apollo capsule splashdown miss distance. A late bank reversal and a suspected tail wind contributed to this slight miss. Entry guidance is derived from the Apollo capsule "final phase" logic and adjusts the range flown during entry by varying the direction of the lift vector (i.e., bank angle). Refinement of the guidance gains and alternative parachute deploy triggers to reduce the ellipse size will be studied for future Mars landing missions

McGrew, L.

Mendeck, G.

NASA Technical Reports Server

2/8/2013
Post-Flight EDL 
Entry Guidance Performance for the 
2011 Mars Science Laboratory Mission
G. Mendeck & L. McGrew
NASA Johnson Space Center
2013 AAS/AIAA Spaceflight Mechanics
AAS 13-419
https://ntrs.nasa.gov/search.jsp?R=20130009519 2019-08-31T00:08:08+00:00Z
2Mars Science Laboratory
Introduction
• Mars Science Laboratory landed Curiosity in Gale Crater 
on 5 Aug 2012
– First Mars guided entry to a touchdown ellipse of 19 x 7 km, 
landing 2.2 km away from the expected target
• Entry guidance is derived from the Apollo capsule “final 
phase” logic and adjusts the range flown during entry by 
varying the direction of the lift vector (i.e., bank angle)
– Flight proven algorithm with minor modifications
– Algorithm consistently met ellipse size requirements and 
performance constraints since conceptual development in 2000
2013 AAS/AIAA Spaceflight Mechanics
3Mars Science Laboratory
Entry Interface Occurs
E+0 sec, h=126km, range=632 km, inertial vel=5845 m/s, inertial FPA=-15.47 deg
Peak Heating Occurs
Begin Heading Alignment Phase
Initiate Chute Deploy Sequence
Begin Range Control Phase
Maneuver to Attitude Hold After Cruise Stage Separation
Prior to EI-9 min
Peak Loading Occurs
Event Description & Nominal State Guidance Actions
• Attitude hold at a ground-
commanded bank angle 
until Range Control 
Phase starts
• Command bank angle 
magnitude to minimize 
predicted downrange 
error at deployment
• Command bank reversals 
to manage crossrange
error
• Command bank angle to 
minimize residual 
crossrange & maximize 
deploy altitude
• Initiate sequence on 
velocity trigger to prepare 
for chute deploy
Phase
Pre-Bank
Range 
Control
(Start of
Guided
Entry)
Heading 
Alignment
Chute
Sequence
(End of 
Guided 
Entry)
Filtered drag acceleration ≥ 0.2g
E+51 sec, h=52km, range=350 km, M=29, relative vel=5839m/s
v = 1100 m/s
E+136 sec, h=14 km, range=83km, M=5, load=1.7g
v = 406 m/s
E+259 sec, h=12 km, range=5 km, M=1.7
E+63 sec, h=39 km, range=283 km, M=24, v=5606 m/s, load=4g
Load = 12.5 g
E+80 sec, h=23 km, range=200 km, M=19, v=4189 m/s
MSL Telemetry
2013 AAS/AIAA Spaceflight Mechanics
Guided Entry Phases
4Mars Science Laboratory
 vDLR
depRpRRK
refvD
L
cvD
L



 




 3
,,
Range Control Logic Overview
• Apollo final phase controls to terminal range and velocity target using 
pre-derived influence coefficients with respect to errors about a 
nominal reference trajectory that ends at parachute deploy
• Reference trajectory defined by range-to-go, drag acceleration, and 
altitude rate as a function of relative velocity
• Commanded bank angle varies to control range based on deviations 
in predicted range, altitude rate, and drag from a reference trajectory
 
  21cos KDL
DL C
C 


 
Predict Current Range:
Find Commanded Vertical 
L/D Required to Converge 
Range to Target:
Bank Required For 
Commanded L/D:
   refrefrefp rrrRDDDRRR  • • •
R Range to Target
Rp Range, predicted
Rref Range, reference
Rdep Range, deploy bias
D Drag
Dref Drag, reference
L Lift
r Altitude Rate
rref Altitude Rate, ref
K3 L/D over-control gain
K2 Bank left/right control
•
•
2013 AAS/AIAA Spaceflight Mechanics
5Mars Science Laboratory
MSL Reconstructed Entry Trajectory
2013 AAS/AIAA Spaceflight Mechanics
6Mars Science Laboratory
Commanded Bank Angle Telemetry
2013 AAS/AIAA Spaceflight Mechanics
If Landing 
Short
If Landing 
Long
If Landing 
Short
If Landing 
Long
7Mars Science Laboratory
Range Error Components Telemetry
2013 AAS/AIAA Spaceflight Mechanics
0°
30°
60°
90°
     refrefdepreferror rrrRDDDRRRRR  
If Landing 
Short
If Landing 
Long
If Landing 
Short
If Landing 
Long
180°
8Mars Science Laboratory
Delivery Uncertainties from Entry -8 to -1 days
2013 AAS/AIAA Spaceflight Mechanics
9Mars Science Laboratory
Operations Planning for Delivery Errors
• For a given atmospheric entry point, what guidance reference 
trajectory will perform well to reach the intended landing site?
• Evaluated thousands of combinations before settling on a small 
number of different guidance gain sets to be chosen via the predicted 
entry flight path angle (EFPA)
2013 AAS/AIAA Spaceflight Mechanics
10
Mars Science Laboratory
Contributions to Landing Site Error
Source Data
Guidance 
Prediction, 
Relative (km)
Delta  
(km)
Downrange at 
Deploy, 
Relative (km)
Delta 
(km)
Downrange at 
Landing, 
Relative (km)
Delta 
(km)
Monte Carlo of Pre Entry Trajectory 0.0 -- 0.0 -- 0.0 --
+ Actual EFPA Delivery 0.0 0.0 0.0 0.0 0.0 0.0
+ Actual Onboard Nav State -0.1 -0.1 -0.1 -0.1 -0.1 -0.2
+ Reconstructed Aerodynamics 0.5 0.5 0.7 0.8 0.6 0.7
Best Estimate from 
Reconstructed Trajectory -0.6 -1.0 -2.4 -3.1 -2.3 -2.9
Parachute Deploy Touchdown
2013 AAS/AIAA Spaceflight Mechanics
Negative values are downrange past the target
11
Mars Science Laboratory
Summary & Forward Work
• Curiosity landed successfully only 2.2 km away 
from the expected target given the onboard 
navigation state
– Better than the average Apollo capsule splashdown 
miss distance
– A late bank reversal and a suspected tail wind 
contributed to this slight miss
• Refinement of the guidance gains and alternative 
parachute deploy triggers to reduce the ellipse size 
will be studied for future Mars landing missions
2013 AAS/AIAA Spaceflight Mechanics


Post-Flight EDL Entry Guidance Performance for the 2011 Mars Science Laboratory Mission

The 2011 Mars Science Laboratory was the first Mars guided entry which safely delivered the rover to a landing within a touchdown ellipse of 19.1 km x 6.9 km. The Entry Terminal Point Controller guidance algorithm is derived from the final phase Apollo Command Module guidance and, like Apollo, modulates the bank angle to control the range flown. The guided entry performed as designed without any significant exceptions. The Curiosity rover was delivered about 2.2 km from the expected touchdown. This miss distance is attributed to little time to correct the downrange drift from the final bank reversal and a suspected tailwind during heading alignment. The successful guided entry for the Mars Science Laboratory lays the foundation for future Mars missions to improve upon

McGrew, Lynn Craig

Mendeck, Gavin F.

Post-Flight EDL Entry Guidance Performance of the 2011 Mars Science Laboratory Mission

The 2011 Mars Science Laboratory was the first successful Mars mission to attempt a guided entry which safely delivered the rover to a final position approximately 2 km from its target within a touchdown ellipse of 19.1 km x 6.9 km. The Entry Terminal Point Controller guidance algorithm is derived from the final phase Apollo Command Module guidance and, like Apollo, modulates the bank angle to control the range flown. For application to Mars landers which must make use of the tenuous Martian atmosphere, it is critical to balance the lift of the vehicle to minimize the range error while still ensuring a safe deploy altitude. An overview of the process to generate optimized guidance settings is presented, discussing improvements made over the last nine years. Key dispersions driving deploy ellipse and altitude performance are identified. Performance sensitivities including attitude initialization error and the velocity of transition from range control to heading alignment are presented. Just prior to the entry and landing of MSL in August 2012, the EDL team examined minute tuning of the reference trajectory for the selected landing site, analyzed whether adjustment of bank reversal deadbands were necessary, the heading alignment velocity trigger was in union with other parameters to balance the EDL risks, and the vertical L/D command limits. This paper details a preliminary postflight assessment of the telemetry and trajectory reconstruction that is being performed, and updates the information presented in the former paper Entry Guidance for the 2011 Mars Science Laboratory Mission (AIAA Atmospheric Flight Mechanics Conference; 8-11 Aug. 2011; Portland, OR; United States

Port-Flight EDL Entry Guidance Performance of the 2011  
Mars Science Laboratory Mission 
Gavin F. Mendeck* and Lynn Craig McGrew† 
NASA Johnson Space Center, Houston, Tx, 77058 
  
 
The 2011 Mars Science Laboratory was the first successful Mars mission to attempt a guided entry which safely 
delivered the rover to a final position approximately 2 km from its target within a touchdown ellipse of 19.1 km x 
6.9 km. The Entry Terminal Point Controller guidance algorithm is derived from the final phase Apollo Command 
Module guidance and, like Apollo, modulates the bank angle to control the range flown. For application to Mars 
landers which must make use of the tenuous Martian atmosphere, it is critical to balance the lift of the vehicle to 
minimize the range error while still ensuring a safe deploy altitude. An overview of the process to generate 
optimized guidance settings is presented, discussing improvements made over the last nine years. Key dispersions 
driving deploy ellipse and altitude performance are identified. Performance sensitivities including attitude 
initialization error and the velocity of transition from range control to heading alignment are presented. 
 
Just  prior to the entry and landing of MSL in August 2012, the EDL team examined minute tuning of the reference 
trajectory for the selected landing site, analyzed whether adjustment of bank reversal deadbands were necessary, the 
heading alignment velocity trigger was in union with other parameters to balance the EDL risks, and the vertical L/D 
command limits. This paper details a preliminary postflight assessment of the telemetry and trajectory reconstruction 
that is being performed, and updates the information presented in the former paper Entry Guidance for the 2011 
Mars Science Laboratory Mission (AIAA Atmospheric Flight Mechanics Conference; 8-11 Aug. 2011; Portland, 
OR; United States) 
 
 
 
 
. 
 
 
Figure 1: Nominal simulated velocity, g-load, altitude and bank angle vs time for a MSL entry trajectory to be updated 
with post-flight telemetry data (Entry Guidance for the 2011 Mars Science Laboratory Mission, Figure 8) 
 
https://ntrs.nasa.gov/search.jsp?R=20120015817 2019-08-30T22:56:19+00:00Z
 
 
 
Figure 2: A nominal commanded bank profile for the MSL entry trajectory to be updated with post-flight telemetry data 
(Entry Guidance for the 2011 Mars Science Laboratory Mission, Figure 9) 
 
 
 
 
 
 
 
Figure 3:  Summation of predicted range error components during range control of a nominal trajectory to be updated 
with post-flight telemetry data (Entry Guidance for the 2011 Mars Science Laboratory Mission, Figure 10) 
 


Post-Flight EDL Entry Guidance Performance for the 2011 Mars Science Laboratory Mission

Abstract

Similar works

Full text

Available Versions

NASA Technical Reports Server

NASA Technical Reports Server

NASA Technical Reports Server