Q&A with Chuck Phillips, Apex Thermal Engineer

Published on
February 28, 2023
Chuck Phillips, Apex Thermal Engineer
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Chuck spent his career as a top thermal spacecraft engineer at JPL, and has recently joined Apex. Satellites have to handle a lot of thermal stress, and in this blog post, Chuck tells us more about the importance of thermal engineering.

Q: You spent 25 years at JPL– and now decided to come to Apex. What drove you to Apex?

I see the overall aerospace market changing rapidly.  Larger aerospace firms will struggle to evolve as quickly as smaller, more nimble companies can. While there will always be a place for large multi-billion dollar programs, most budgets will no longer support this sole mode of operation.  What Apex will provide are options that previously did not exist to the small satellite operator.  

I am interested in leveraging the latest low-cost technologies and in taking more risk.  I have always been drawn to the smaller projects that are run by a core talented team.  I see that environment here in Apex.  

Q: What is thermal engineering? Explain like I’m five.

It is the responsibility of the Thermal Engineer to maintain all spacecraft temperature within a comfortable range.  It’s really more than that however, as the thermal engineer needs to take into account limitations from many different disciplines, such as available electrical power,  what environment will the spacecraft fly in, how the spacecraft flies (CONOPS), and how much mass is available to work with.  Having to have an understanding of some many different areas really means the Thermal Engineer is a Thermal “Systems” Engineer.  

Q: Why do satellites have to worry about thermal engineering? What could go wrong?

Many things can go wrong, and have.  Failures can either be catastrophic or more subtle.  Failure to maintain proper temperature can cause numerous problems such as:

  1. Battery failure; Reduction in battery life
  2. Avionics failure; Decreased avionics reliability
  3. Actuator failure; Deployment failure; Increased torque
  4. Frozen propellant lines, failure of the prop subsystem
  5. Structural warping; Not meeting pointing requirements
  6. Deformation of optics; Not meeting optical throughput requirements
  7. Excessive energy consumption; spacecraft brown-out
  8. etc.

Q: Speaking of which, what’s been the worst thermal-related satellite anomaly you’ve seen… and what could have prevented it?

I’ve seen many thermal failures, none catastrophic thankfully beyond a launch vehicle failure, so that satellite (OCO-1) never got a chance.  One of the more interesting failures that I can recall had to do with the highly successful Opportunity Mars Rover.  Right after landing, it became evident that a warm-up heater designed to bring a component called the IDD (Instrument Deployment Device) was stuck on over the Mars nighttime, needlessly draining the battery’s power and detracting from available power for scientific measurements during the following Sol.  This was to be a repeating failure due to hastily implemented mechanical thermostat designed, ironically to prevent actuator overheating.  Flight software needed to be modified to allow for a “Deep-Sleep” mode which actually took the battery (as well as other heaters) fully offline at night.  The rover would then wake up when the solar arrays became “power-positive” at the start of the next Sol.  This mode was somewhat risky, and we certainly celebrated when the rover successfully woke up after trying Deep Sleep for the first time.  

The lesson here is that late fixes can often have unintended consequences.  We always have to ask when schedule is tight, “is your proposed change to make better or to make work?”  This is the game that every project plays, trading technical risk for system benefits.  In this rare case, it may have been more beneficial to do nothing and to accept a wider potential temperature range for the IDD actuator.  Hindsight is always 20-20 though.  

Q: What are you most proud of from your career?

I am most proud of the fact that the missions that I was able to support have had a positive impact in some way.  The Mars Exploration Rovers uncovered unequivocal evidence of a Mars once covered with water.  Orbiting Carbon Observatory-2 is currently measuring CO2 concentration in our atmosphere.  GRAIL measured the gravitational field of the moon to better understand the Moon’s composition and origin.  DoD projects have kept our country far ahead or potential adversaries.

I am also proud of the mentoring that I have been able to provide to younger engineers.  I believe it is best to learn by doing, and it’s very satisfying to see younger engineers make mistakes, correct for them and safely learn.  

Q: What do most people get wrong about thermal engineering?

Thermal Engineers are indeed Systems Engineers.  A common misconception is that the thermal engineer is only responsible for thermal analysis.  Anyone can analyze a point design to see if it will work or not.  It is the job of the thermal engineer to drive towards an architecture that will work before any analysis is even started.  

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