PhysWall inverts a closed, non-linear physical law at a single measurement point — and refuses when the inverse is not unique.
NASA's Deep Space Network publishes, every minute, which antenna is talking to which spacecraft and how long a signal takes to get there and back. That number is a measurement, and it is one arithmetic step from a distance.
This page does that step, and then refuses the three questions it cannot answer.
⚠ worked out in your browser
Move a control and the answer below updates. There is nothing to press.
distance = RTLT × c / 2
185 daily states for JWST, March to September 2026, projected onto the plane perpendicular to the Sun-Earth line. Move the slider and the marks move — they sit wherever the telescope was that far away.
Light time gives one number: how far away. An orbit needs six, so five are missing, and none of the five follows from a distance. The three questions below are what those five prevent you from answering.
| Question | From light time? | Needs |
|---|
So the honest verdict on any of those is no verdict, with the missing input named. A distance that sits inside its band tells you the spacecraft is where it should be along one axis, and nothing about the other two.
These are published constraints for one L2 mission, written down before launch. Each carries its source, because a bound with no citation cannot fail a measurement.
| Constraint | Range | Source |
|---|
⚠ Most of these come from a 2017 design paper, for a spacecraft that weighed 7,728 kg. The one that flew weighs 9,174 kg at launch (30 Aug 2026, COSPAR 2026-199A) — a 19% gap, not the 36% we first wrote from a figure that turned out to be wrong. The shape of the orbit is unlikely to have changed; the numbers have almost certainly been recomputed. If a measurement lands outside this box, the first explanation is that the box is out of date.
Not thermal, which is the usual guess. The 2024 paper from the mission's own flight dynamics team says the requirement that most constrains the design is the ability to downlink at least 1.3 terabytes of science data a day through one ground station — and that this restricts the mission to unusually small-amplitude orbits compared with JWST.
Which makes the data rate, also published live by the DSN, the most interesting number on the feed.
The same tool, run against three more ephemerides pulled from JPL Horizons. None of them was chosen because it would work.
Twenty-five hourly states for JWST, pulled from JPL Horizons on 30 August 2026. Reconstructed from tracking data by Goddard's Flight Dynamics Facility — not a prediction, and not ours.
⚠ The distance falls 10,064 km across the day and the angle closes by three quarters of a degree. Both sit inside their published bounds the whole time, which is what you would expect and is not the interesting part.
What is interesting is the third row. Ask this ephemeris for a semi-major axis and the tool refuses: at 1.3 million km the Sun holds the orbit as much as the Earth does, and a two-body conversion returns a number that is arithmetic rather than measurement.
Published orbital parameters for at least one L2 mission carry a perigee that falls exactly in the range that conversion produces. Somebody ran it and printed the output.
185 daily states for JWST, March to September 2026, projected onto the plane perpendicular to the Sun-Earth line. This is the halo — one full loop, measured, not modelled.
The circle is the published bound: at the L2 x-coordinate the orbit must stay inside 1.09 million km of the Sun-Earth line. That figure and the 36-degree angle limit are the same constraint written twice — 1.5e6 × tan(36°) is 1,089,814 km, which is the published number to four figures.
⚠ The two constants this page runs on, written out. The speed of light is 299,792.458 km/s (written in the code as 299792.458) — an SI definition, not a measurement, and the metre is defined from it rather than the other way round. The halo bound is 1,089.814 thousand km (in the code as 1089.814), which is 1.5×106 × tan(36°) and is derived above. Both appear in the code as numbers with those exact digits, and a reader who cannot find them written down cannot check them.
Maturity: validated. c is exact by definition, so the only uncertainty is the reading.
A checking tool, not professional advice. It tells you what a measurement does and does not support; what to do about that is your decision.