Lessons Learned in System Engineering: A Retrospective Look at TDRSS

System Engineering Follies INCOSE MEETING (Enchantment Chapter) March 16, 2005 Murray Elowitz JJ & E Research Corp 11045 Greenview NE Albuquerque, NM 87111 (505) 856-7247 melowitz@comcast.net

INCOSE Journal Article • First Article in the new issue M. Elowitz

Lessons Get Learned - And Learned - And Learned • Tracking Data Relay Satellite • Sync Eq orbit to be a bent pipe from flying aircraft and spacecraft to single earth station, with signal distribution from there • Circa 1977 – don’t trust my memory • Humongous satellite, very complex, filled Shuttle bay (with upper stage) • 60 ft. Here would be The Picture If I could Have Found It M. Elowitz

Meet or Exceed Requirements • TDRSS was the first payload on the “Inertial Upper Stage • Co-packaged in Shuttle bay • Acts as upper rocket stage to go from LEO to Sync Eq • Hohman transfer, two impulse, etc. for the orbital mechanics • Shuttle gave it a beautiful ride • IUS did not Burned a hole thru bell Gases Bell Housing OOOPS Other Gases M. Elowitz

What does torque do? • Torque creates a rotational acceleration! • In other words, the IUS spun the mated vehicles end over end!! • There is no way to shut off a solid rocket motor • Etc • etc/ • Now for the good part. M. Elowitz

Good System Engineering 1. TDRSS had a function to separate itself from the booster • A backup to IUS primary • It separated (Might have gotten banged on the way off) 2. The control system requirements was to stabilize TDRS from an initial rate of ?? 1.5/sec • BUT Separation rate was about FIVE TIMES that! • Terrible overdesign! It stabilized with a lot of sweat and pain from the ground controllers. • Months later, using only the satellite 10 lb engines, it limped up to sync eq • It gave two years of limited reduced capability Note: Numbers made up, but indicative M. Elowitz

Lessons Get Learned - And Learned And Learned • Another TDRSS Story – Revisit requirements, especially environmental • Ref: System Engineering 1st article, reference to Tacoma Narrows Bridge M. Elowitz

Once upon a time … … spacecraft had minimal computing … semiconductors had big features Later, more digital processing was added And components used more dense silicon Then, in the late ’70’s NASA JPL sent a spacecraft to a planet And were shocked. Solar radiation particles upset the memory states of its computer!!! The solution was to frequently upload the memory from the ground -- very frequently M. Elowitz

Not My Problem • At that time TDRSS was in full scale development • JPL was not that far away – Redondo Beach to Pasadena • The problem was well known • CONCLUSION • NOT MY PROBLEM • THEY WENT WAY OUT TOWARD THE SUN AND WE ARE ONLY GOING TO SYNC EQ • THUS, The lesson was relearned M. Elowitz

Bad System Engineering M. Elowitz

System Engineering Follies II INCOSE MEETING (Enchantment Chapter) March 16, 2005 • Murray Elowitz • JJ & E Research Corp • 11045 Greenview NE • Albuquerque, NM 87111 • (505) 856-7247 • melowitz@comcast.net M. Elowitz

How To Lose Your Proposal • Case History • System Engineering defines requirements, architecture, design features • System Engineering also verifies that its solution meets the customer needs M. Elowitz

HF Comm System • RFP Spec called for multiple strings of equipment for • 10 Critical Priority • 4 high Priority • 8 Normal Priority • Statement of Need defined Blocking factors • Probability of call going through • By Priority Type M. Elowitz

Too Much Knowledge • To meet the blocking factors – 0%, 5%, 15% - takes 16 strings of equipment • Plus one for hot spare • Winner bid 10 strings • Total program cost MUCH LOWER • THE CUSTOMER DID NOT SPECIFY BLOCKING FACTORS • The winner did not even account for outages M. Elowitz

Lessons Learned in System Engineering: A Retrospective Look at TDRSS