Using the Satellite Lifetime Tool versus HPOP for Re-Entry Prediction

I recently had a customer ask about the differences he was seeing in a satellite’s predicted decay time when using the Satellite Lifetime Tool versus propagating the satellite using HPOP. This particular customer was seeing a variance of about two months. I helped him realize the large time gap in this instance was due to inconsistent setup of the Lifetime Tool and HPOP Force Models. This customer inquiry led me to realize we should create a “best practices” article for using these tools for comparison. I’ve laid these practices out in an FAQ here.

Eventually another question was brought up: When would I use the Satellite Lifetime Tool instead of HPOP or vice versa? Both the Satellite Lifetime Tool and HPOP are included with the STK SatPro license, so it’s not a matter of not having access to one or the other. When you read the Help documentation on the Satellite Lifetime Tool, we include this note “The algorithms behind the Lifetime tool are designed to compute an estimate of duration of time that a satellite will remain in orbit when re-entry is not imminent. This tool is not designed to produce a precise time or location of re-entry. Full fidelity orbit propagation methods such as those available in HPOP and Astrogator are better suited for re-entry prediction.” The text in bold is the key phrase for the takeaway: the Satellite Lifetime tool is best suited for a decay time estimate, while HPOP and Astrogator can be used for decay time and location prediction. HPOP and Astrogator will need to fully propagate the satellite forward until it reaches its decay altitude. This can become time consuming if your satellite doesn’t decay for a few months or even years. What I’d recommend is to define your satellite using either HPOP or Astrogator using the default scenario time period (~24 hours). Then use the Satellite Lifetime Tool to obtain an initial estimate of the satellite decay time and be sure to use my best practices. If you’d like to explore the decay time and location more precisely with HPOP or Astrogator, then you’ll know an estimated analysis period needed and can change that accordingly to allow STK to propagate the satellite forward to that time.


Design and operate satellite systems with specialized propagators, attitude profiles, and satellite engineering tools.


Design high-fidelity spacecraft trajectories for mission planning and operations.