Fuel Level Measurement On Spacecraft, discussion & ideas Options

[Doug M.]

We got answers!

Here's what the good people at Mars Outreach have to say.

1) As of today (having just completed an Orbit Trim Maneuver (OTM)), Odyssey has 17.3 kg, +3.0 / -5.0 propellant.

2) 1.9 kg is obligated for a follow-on OTM in January 2014. Odyssey utilizes approximately 1 kg / year and historically has budgeted 1 kg / year for unexpected safing events. So, propellant life should be between 5.2 to 9.2 years. These numbers are based on no onboard anomalies that would require propellant above the safing budget, no changes in Odyssey's basic operations (three operating reaction wheels, high gain antenna and solar array servos (motors) continue to function normally, etc.) and no further programmatic maneuvers. Consideration is being given to performing a procedure in the future that has the potential to refine the +3 / -5 uncertainty of fuel remaining.

When prop is exhausted, the mission ends because the spacecraft is no longer able to desaturate the reaction wheels and / or provide thruster control; the spacecraft can no longer be pointed to maintain communications and solar panel illumination.

3) The statement is basically correct: THEMIS, which is comprised of two imagers, visible and infrared, and two instruments of the Gamma Ray Suite, High Energy Neutron Detector and the Neutron Spectrometer, all continue to operate and gather science data. The Gamma Ray Spectrometer of the Gamma Ray Suite and Marie have both been decommissioned.


Thanks again for your questions and your interest in Mars exploration!

Wow! Okay, so what comes to mind from this?

Well, the first thing is that there's an awfully large uncertainty in the amount of fuel left. 17.3 kg +3 / -5 ? The range of uncertainty is almost half the total amount of fuel. I wonder why; and I also wonder what the "procedure" might be to narrow the range.

Second is, they have a fair amount of propellant left -- enough for at least another five years of operation. So, barring mechanical failure, Odyssey should see the arrival of MAVEN (2014) and quite possibly of Mars Insight (September 2016 if they make their launch window) and ExoMars Part One (ditto).



Doug M.