--- title: "Orbital lifetime with NASA DAS versus a tracked re-entry forecast | Descent" description: "NASA DAS estimates orbital lifetime before launch from assumed parameters. A tracked re-entry forecast re-predicts the decay date from live TLE and OMM data after launch. What each one is, what goes into it, and where each belongs in a mission." url: https://descent.space/learn/nasa-das-vs-tracked-reentry-forecast --- Learn # Orbital lifetime with NASA DAS versus a tracked re-entry forecast NASA DAS estimates orbital lifetime before launch from assumed parameters. A tracked re-entry forecast re-predicts the decay date from live TLE and OMM data after launch. What each one is, what goes into it, and where each belongs in a mission. Published 8 September 2026 NASA’s Debris Assessment Software (DAS) estimates a satellite’s orbital lifetime before launch from assumed parameters. A tracked re-entry forecast re-predicts the decay date after launch from the satellite’s own tracking data. The two are not competing answers to the same question: one belongs in the licence application, the other in operations and the post-mission disposal record. This article describes what each one takes in, what it puts out, and when a mission needs which. ## What NASA DAS is DAS is a utility NASA’s Orbital Debris Program Office maintains to verify that a spacecraft, upper stage, or payload complies with NASA-STD-8719.14, NASA’s technical standard for limiting orbital debris. It covers several requirements in that standard: debris released in normal operations, vulnerability to impacts, post-mission orbital lifetime, and re-entry casualty risk. The post-mission lifetime assessment is the part that matters for the FCC 5-year rule and its 25-year predecessor. The current version at the time of writing is DAS 3.2.7, updated in April 2026 for Windows 11 and distributed through the NASA Software Catalog under a software user agreement. NASA publishes solar flux table updates for it quarterly. ## What goes into a DAS lifetime estimate A DAS orbital lifetime run takes three kinds of input. The first is the initial orbit: apogee altitude, perigee altitude, inclination, and the start date. The second is the spacecraft’s area-to-mass ratio, which sets how strongly drag acts on it; the operator supplies mass and a cross-sectional area, usually an average over the expected tumbling attitude. The third is the atmosphere, which DAS derives from a solar flux projection in the table NASA ships with the tool. DAS then propagates the orbit under drag until it reaches the surface and reports the lifetime in years. Because the run starts from a planned orbit and an assumed attitude, it is an estimate of what the satellite would do, and the standard practice is to make it conservative. The US Government Orbital Debris Mitigation Standard Practices say the disposal orbit should be chosen “using conservative projections for solar activity”, and the same logic applies to the area-to-mass ratio. DAS is not a tracking tool. It does not read element sets, it does not update as the satellite flies, and it produces one lifetime figure per run rather than a date that changes over time. That is the correct design for its purpose, which is to bound the post-mission lifetime of a satellite that has not yet been built. ## What a tracked re-entry forecast is A tracked re-entry forecast starts once the satellite is in the public catalogue. The 18th Space Defense Squadron tracks objects in low Earth orbit and publishes general-perturbations (GP) orbital element sets through Space-Track; CelesTrak redistributes them. The classic format is the two-line element set (TLE); the same data is also published as an Orbit Mean-elements Message (OMM). For a low, decaying object, new element sets typically arrive several times a day. Each element set carries the observed mean orbit at an epoch and a drag term (B\* in a TLE). Across a sequence of element sets, the drag term and the falling semi-major axis show how the real satellite responds to the real atmosphere: its effective ballistic coefficient, which depends on its actual attitude, and the density it is flying through, which depends on the solar activity that actually occurred. A tracked forecast propagates from the latest observed orbit, with a ballistic coefficient fitted to the recent trend and a space-weather model for the atmosphere ahead, to a predicted re-entry date. When the next element set arrives and the orbit has changed, it re-predicts. The output is different in kind from a DAS lifetime. It is a date with a countdown, it moves, and the record of how it moved is itself useful: it shows whether the satellite is decaying faster or slower than the pre-launch estimate and by how much. ## What Descent does Descent is a tracked re-entry forecast service. An operator adds a satellite by mission name or NORAD catalogue number. Descent ingests TLEs every hour, with a five-year backfill of the historical record, and re-predicts the re-entry date whenever the orbit changes. The prediction engine models space weather rather than assuming a drag-only scenario. The product surface is the predicted re-entry date with a live countdown, an orbital decay chart (altitude over time), a ballistic-coefficient trend across predictions, and an append-only history in which every prediction stores the TLE inputs it used, when they were fetched, and the engine version. For a satellite that has already re-entered, Descent can package the full dated prediction history, the actual decay date, the TLE record, and the engine version as a post-mission report; the prediction history for re-entered satellites is free. Descent has not published a benchmark of its predicted re-entry dates against observed re-entries. Until it does, this article makes no claim about how close its forecasts land, and no comparison of that kind against DAS or any other tool. ## Where each one belongs Stage Question Instrument Mission design and licence application Will the satellite re-enter within five years of end of mission? DAS or an equivalent lifetime tool, run on the planned orbit with conservative inputs Operations When will it re-enter, given how it is actually decaying? Tracked re-entry forecast from GP element sets End of mission Is the five-year deadline still met, and what changed? Tracked forecast history against the pre-launch estimate After re-entry What was predicted, what happened, and from which data? Post-mission report: prediction history, actual decay date, TLE record The pre-launch estimate and the tracked forecast disagree by design, because the second one knows things the first one had to assume. A CubeSat that tumbles more than expected, or flies through a stronger solar maximum than the projection, will come down earlier than its DAS lifetime; a quiet sun will keep it up longer. Neither outcome makes the DAS run wrong. It bounded the case with the information available, and the tracked record shows what the case turned out to be. In the last days before re-entry, Space-Track additionally publishes Tracking and Impact Prediction (TIP) messages for decaying objects, giving a predicted decay time and window from the tracking network’s own re-entry assessment. A tracked forecast service is upstream of that: it covers the months and years between the last DAS run and the final TIP. ## Sources - NASA Debris Assessment Software: [orbitaldebris.jsc.nasa.gov](https://orbitaldebris.jsc.nasa.gov/mitigation/debris-assessment-software.html) and the NASA Software Catalog entry [software.nasa.gov/software/MSC-26690-1](https://software.nasa.gov/software/MSC-26690-1) - NASA-STD-8719.14, Process for Limiting Orbital Debris: [standards.nasa.gov](https://standards.nasa.gov/standard/NASA/NASA-STD-871914) - US Government Orbital Debris Mitigation Standard Practices, November 2019 update: [orbitaldebris.jsc.nasa.gov](https://orbitaldebris.jsc.nasa.gov/library/usg_orbital_debris_mitigation_standard_practices_november_2019.pdf) - FCC 22-74, Second Report and Order on the five-year post-mission disposal rule: [docs.fcc.gov/public/attachments/FCC-22-74A1.pdf](https://docs.fcc.gov/public/attachments/FCC-22-74A1.pdf) - CelesTrak, GP data formats (TLE and OMM): [celestrak.org](https://celestrak.org/NORAD/documentation/gp-data-formats.php) - Space-Track documentation, including TIP messages: [space-track.org/documentation](https://www.space-track.org/documentation) ## Questions ### Can a tracked re-entry forecast replace NASA DAS in a licence application? No. A licence application is filed before launch, when there is no tracking data. DAS, or an equivalent lifetime tool, is the right instrument for that estimate. A tracked forecast starts when the satellite has a catalogue number and element sets, and serves the operations and post-mission disposal record. ### Why does the tracked re-entry date move? Because the inputs move. Each new element set carries the observed orbit and drag, and the atmosphere changes with solar activity on timescales from days to years. A forecast that re-predicts on every orbit change will show a date that shifts, and the history of those shifts is part of the record. ### Which one is more accurate? They answer different questions and are not compared on the same axis. DAS gives a bound on post-mission lifetime for an orbit that does not yet exist; a tracked forecast gives a re-entry date for an orbit that does. Descent has not published a benchmark of its forecasts against observed re-entries, and makes no comparative claim until it does. ## More from Descent - [The FCC 5-year rule: what a CubeSat operator must demonstrate](https://descent.space/learn/fcc-5-year-rule) Private beta ## Need a tracked re-entry date for a live satellite? Descent is in private beta. Leave your email and we will invite you in mission order.