# Satellite Remaining Life

How can I know the remaining life of a satellite? I have been using satbeam, and try to calculate it based on launch date + expected life, but it seems to have some problems. For example, for this satellite:

The launch date is 1999 and the expected lifetime is 12 years, so the expected end year is 2011, but it is still active now. How should I know when this satellite would retire? Thank you.

• I feel like it depends on whether or not the satellite has any fuel it can use to reboost. Commented Aug 11, 2016 at 3:05
• So it is not possible for me to learn the expected retirement date? Since I cannot know the amount of remaining fuel. And am I correct that, a lower utilization of fuel (such as renting less transponder out), would lead to a longer life span as less fuel is used? Thanks. Commented Aug 11, 2016 at 3:08
• I wouldn't say that. It may not have reboosting fuel, and even if it does, you might still be able to calculate it if you know how much fuel it started with and how often they reboost it. Commented Aug 11, 2016 at 3:21
• So the fuel for rebooting is separated from the fuel for transponder? Then shouldn't the expected lifetime of a satellite is deterministic, since we should be able to calculate the need of rebooting fuel to stay in orbit. Commented Aug 11, 2016 at 3:35
• The transponders do not use propellant. Commented Aug 11, 2016 at 21:10

A satellite should have a planned lifetime, "expected lifetime", or design lifetime, but it's a balance between a number of factors.

Gunter's Space Pages is a great place to read about satellites and get a better idea what they are for and any special information about them. Here is the page for JCSAT-5 and JCSAT-6. Take a look there first.

This satellite is not in a low earth orbit (LEO) so there is no risk of the orbit decaying due to atmospheric friction. It will stay "up there" for a very long time, although not necessarily in the exact location it is supposed to be.

Satellites - including telecommunications satellites like this one - have usually been quite expensive to build and put into orbit, so in this example, if you can't reasonably expect it to keep working for 12 years, then it may not be economically worth paying for it to be 1) designed, 2) built, 3) application for and receiving a "spot" in the geostationary space obtained, 4) launched, and 5) maintained by ground control. Business plans to use this telecommunications bandwidth also rely on it's stability.

There is a huge amount of experience with telecom satellite orbital station keeping to maintain them in their assigned geostationary orbit position and pointing in the correct direction - attitude control. The satellite usually has more propellant than it is expected to need during its expected lifetime, because if it lasts longer, you can usually or at least often make more money maintaining it and selling the bandwidth.

But there is an expense to maintaining a satellite, so if you are not making money, sometimes you change to an inactive mode so that you don't have to pay nearly as much for regular ground communication bandwidth and control.

• Thanks. One more question, am I correct that the fuel for transponder is separated from the fuel for reboost? So that utilization rate is independent from expected lifetime. Commented Aug 11, 2016 at 4:09
• You might ask that as a new question, the answer might be a little more complicated than just yes or no for satellites like this one that are in orbits higher than LEO.
– uhoh
Commented Aug 11, 2016 at 4:17
• Transponders don't use 'fuel.' They operate using electricity. Transponders, and any electronic system, can fail in a few ways. An internal component can break rendering it useless, and interface with an eternal system can fail rendering it useless, or it receives insufficient power to continue operating. All of these problems are overcome using redundancy and avoiding single points of failure (failures that have larger impacts). The redundancy required is based on the design / expected life of each component, subsystem, system, the satellite, etc. Commented Aug 11, 2016 at 15:50
• @AndrewW. woa - how does transponders don't use 'fuel' fit in here? The question is about "expected lifetime" and that's comes from the engineering, sales, and marketing departments to name a few. If sales says they need it to last 12 years or they won't make money, then the engineers will design for say >95% probability 12 years minimum performance for example. it's quite a substantial statistical analysis, but that's roughly how it goes. You are just listing a few of the many failure modes that have to be evaluated. Do you really think that I believe transponders run on fuel? :-)
– uhoh
Commented Aug 11, 2016 at 16:04
• @uhoh Sorry for the confusion, and not doubting your knowledge. (I see you post answers often) :) I was trying to respond to StephenChung's comment above yours where he says "One more question, am I correct that the fuel for transponder is separated from the fuel for reboost?" as well as another below his question. That's what made me say 'woa' to myself. Also, your answer is spot on. Gave it an upvote. Commented Aug 11, 2016 at 16:23