Three Times I Measured Nothing

Builder Journal · Mars Environmental Dynamics Analyzer (MEDA) Virtual Sensor Recovery Ten times in a row I predicted what my next submission would score before I uploaded it. The worst miss was 0.0025 on a number around nineteen. I took that as confirmation that the physics underneath was correct. It was confirmation that I can do arithmetic. Two days before this competition closed I pointed a review at my own endgame, expecting notes about the code. It came back with three errors and none of them were in the code. All three were in my reasoning, and all three had the same shape: I had run something that felt like a measurement and was not one. This is the fourth entry in this series and the one I would keep if I had to burn the other three. The models are competition-specific. This part is not. The competition in one breath Perseverance carries an environmental station called MEDA. Some of its surface pressure readings are missing, and the competition is to reconstruct them. Scored on mean squared error. The wrinkle is the split. Training covers sols 1 through 100, when pressure is climbing toward its seasonal peak. Test covers sols 201 through 300, when it is falling hard toward the aphelion minimum. Sols 101 through 200 do not exist in either file. Every prediction is outside the range the model was fit on. The first entry covers the first submission, which contained no machine learning at all and took the top of the board at 61.04. Six weeks and seven versions later the public score was 18.99. Almost everything in between was selected by one signal. Not cross-validation. Cross-validation here can only hold out sols from the rising limb, so it is structurally blind to the regime I am scored on. The leaderboard was the only thing that could see the falling limb, so the leaderboard picked every scalar that mattered: the residual shrink, the blend weight, a constant seasonal offset, a diurnal scaling. Hold onto that. It becomes the joke about four hundred words from