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25'107 Intro' to Engineering Session 17: Unit Conversion II

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Title: 25'107 Intro' to Engineering Session 17: Unit Conversion II


1
25.107 Intro. to EngineeringSession 17 Unit
Conversion II
  • David O. Kazmer, P.E., Ph.D.

2
Module ThreeEngineering Analysis
  • Dates/Topics
  • 10/26 Engineering Analysis
  • 10/31 Units Conversion I
  • 11/2 Units Conversion II (quiz)
  • 11/7 Engineering Economics
  • 11/9 Engineering Economics
  • 11/14 Engineering Economics
  • 11/16 Engineering Economics

3
Agenda
  • Unit Conversion Case Study
  • Quiz
  • Project 2 Example

4
Case StudyMars Polar Lander
5
Previous Space Failures
  • Propulsion systems have leaked exploded.
  • Power systems have short-circuited.
  • Observation instruments have failed to work or
    have been pointed in wrong directions.
  • But until 1999 no CFIT had occurred.
  • CFIT is a Controlled Flight Into Terrain
  • It occurs when human error flies a perfectly good
    airplane right into the ground

6
During the CFIT
  • Trajectory errors were accumulating.
  • Systems were assumed to be good.
  • 30-year-old trajectory code was not allowed to be
    run, seen, or verified outside JPL.
  • Mid-course corrections resulted in erratic
    behavior.
  • No fix found given limited time during final
    approach.
  • The spacecraft was almost certainly destroyed
    when its hydrazine propellant tank heated to the
    point of self-ignition of the remaining fuel.
  • "There was enough explosive force there to level
    a city block, so the spacecraft probably was
    blown apart into shards of scrap metal that soon
    burned up in the Martian atmosphere.
  • Whether the debris burned up, fell to the
    surface, or grazed the atmosphere fast enough to
    have passed out into space on the other side of
    Mars is not known.
  • For now, it is truly "lost in space."

7
After the CFIT
8
The Source of ErrorUnit Conversion!!!
  • The Mars Climate Orbiter performed momentum dump
    operations to slow the aircraft at its
    destination. According to NASA, the trajectory
    problem began at this point.
  • The unit that JPL wanted was the Newton (the
    force that accelerates a 1 kilogram mass at a
    rate of 1 meter per second per second).
  • Engineers at Lockheed Martin Astronautics Co.,
    Denver, Colo., had used pounds force, and these
    figures would have been too large by a factor of
    4.45.
  • In engineering terms, these two values are on the
    same order of magnitude.
  • There was no large mismatch in the scale of
    calculations made with the one or the other.
  • These two units were close enough in magnitude
    that the unintentional substitution of one for
    the other apparently rang no warning bells.

9
The Failure Mode?Adaptive Computer Control
  • According to a JPL spokesman, every maneuver
    intended to dump momentum added a velocity error
    of about 0.001 meter per second, on a probe that
    was traveling at a rate of tens of kilometers per
    second.
  • These deflections themselves were not the
    problem, but their incorrect modeling was, when
    the computer was told the spacecraft had received
    a force of four or five times as great as it
    really had.
  • "Every momentum dump will introduce an additional
    bogus force into the navigation software.
    Ultimately the real-time model of the spacecraft
    was warped by this application of a non-existent
    force."
  • At the 10 November press conference, chief
    investigator Arthur Stephenson explained "Had we
    done end-to-end testing, we believe this error
    would have been caught." But the rushed and
    inadequate preparations left no time to do it
    right.

10
Agenda
  • Unit Conversion Case Study
  • Quiz
  • Project 2 Example

11
830 Quiz
  • Convert
  • Needed conversions
  • 1 meter 3.28 ft
  • 1 Acre 43560 ft2
  • 1 W Hr 3600 J
  • 1 gallon of gasoline 131,000,000 J

12
930 Quiz
  • Convert
  • Needed conversions
  • 1 meter 3.28 ft
  • 1 W Hr 3600 J
  • 1 barrel of gasoline 44 gallons of gasoline
  • 1 gallon of gasoline 131,000,000 J

13
Agenda
  • Unit Conversion Case Study
  • Quiz
  • Project 2 Example

14
25.108Introduction to Engineering II
15
25.108 Pre-RegistrationBy Major
  • Chemical
  • Lecture 25.108.103
  • Lab
  • 25.108.807 or
  • 25.108.808
  • Civil
  • Lecture 25.108.104 (phantom)
  • Lab
  • 25.108.813 or
  • 25.108.814
  • Electrical/Computer
  • Lecture
  • 25.108.101
  • 25.108.601 (honors)
  • Lab
  • 25.108.801
  • 25.108.802
  • 25.108.803
  • 25.108.804
  • Mechanical
  • 2 Hour Lecture
  • 25.108.816 or
  • 25.108.817 or
  • 25.108.818
  • Plastics
  • Lecture 25.108.102
  • Lab
  • 25.108.810
  • 25.108.811
  • Nano
  • Lecture 25.130.201
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