Moving Target APT Instructions

Details of how the JWST Astronomer's Proposal Tool (APT) can be used by Solar System observers, with descriptions of current APT limitations and walkthrough examples for creating a proposal for various classes of Solar System targets.

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See also: JWST Astronomers Proposal Tool Overview

The JWST Astronomer's Proposal Tool (APT) is used for designing JWST proposals and contains special options for Solar System ("moving") target observations. Before using APT, you should estimate exposure times with the Exposure Time Calculator and take a quick look at your target's visibility using JPL Horizons and the Moving Target Visibility Tool (MTVT). The latter tools could cut down the time you spend testing the schedulability of observations in APT.

With these pre-steps complete, you will be ready to start designing your APT proposal. A typical workflow would be:

  1. Define the target. You have tremendous flexibility to identify specific targets and pointing positions relative to targets using a system of target Levels. Level 1 targets are Solar System bodies directly orbiting the Sun (planets, comets, and asteroids), while Level 2 and Level 3 targets are moons of, or positions on, or relative to, the specified Level 1 or Level 2 target. Moving targets are also divided in APT between standard targets and minor bodies (asteroids and comets). For standard targets, ephemerides can be computed using information directly accessible to and maintained by APT. For the minor bodies, you must supply orbital elements, either manually or by retrieving them from the JPL Horizons system using the built-in APT tool. See Tutorial on Creating Solar System Targets in APT

  2. Define the observations. For each observation, you must select a target, an instrument, and a science template. Note that moving targets can be observed with any instrument and any observing template, although not all templates are optimal for Solar System observations; see Moving Target Observing Strategies. Also see Tutorial on Creating Solar System Observations in APT.

  3. Define scheduling constraints on the observations. These include date, time, separation from another body, apparent rate of motion, rotational phase, phase angle, etc. See the Tutorial on Creating Solar System Observations in APT. A full list of generic and moving target-specific special requirements can be found in Special Requirements and Solar System Special Requirements, respectively.

  4. Evaluate the schedulability of observations.

  5. Submit your proposal.

You are advised to first read the JWST Astronomers Proposal Tool Overview article for a general understanding of APT.

On this page, we describe APT's current limitations for moving targets and walk through the creation of moving target proposals.

APT limitations for Solar System observations

APT is always under development and for moving targets some capabilities are not expected to be available until later cycles. The following list is not exhaustive. If you have questions please contact the help desk

  1. APT does not (and is not planned to) provide sensitivity information. You must use the JWST Exposure Time Calculator (ETC). See Moving Target ETC Instructions.

  2. Currently, APT does not allow observation visualization against all-sky images/catalogs for moving targets. This includes visualization of the object ephemeris. You must use a fixed target as a proxy to examine dithers, coverage, and orientation. A workaround is described in Tutorial on Visualizing Dithers of a Solar System Observation in APT. Accurate orientations for the Aladin viewer can be determined using the Moving Target Visibility Tool (MTVT).

  3. APT does not currently support shadow observations. See Moving Target Acquisition and Tracking for information on a workaround until this is implemented.

General APT information

Download APT

Words in bold are GUI menus/
panels or data software packages; 
bold italics are buttons in GUI
tools or package parameters.

The most recent release of APT is available at

Begin a JWST proposal

Click on the New Document button in the upper left. You will have the option of starting either a new HST or new JWST proposal.

Figure 1. Starting a new JWST proposal

Edit proposal information

More extensive directions for filling out this form can be found at JWST Astronomers Proposal Tool Overview. Moving target observers should select Solar System as either the Scientific Category or Alternate Category.

Figure 2. Proposal Information page

Submit proposal

When you are ready to submit, click the paper plane icon, and fill in the form. Proposals can be re-submitted as needed up to the deadline. Any outstanding errors or warnings must be explained to complete the submission process.

Figure 3. Submitting a proposal

Tutorials and tools

For additional information on APT, see JWST Astronomers Proposal Tool Overview. The following will only concern the unique case of specifying a moving target observation. 

Create targets

Moving targets have unique parameters in APT. Some examples are illustrated in Tutorial on Creating Solar System Targets in APT.

You can also read in-depth about Solar System targets for APT and look at the list of Solar System standard targets.

Create observations and define scheduling constraints

See Tutorial on Creating Solar System Observations in APT.

You can read about moving target APT constraints in Solar System Special Requirements. To learn about the observation templates available for each instrument, see APT Observations

Visualize dithers and mosaics using a fixed target as a proxy for your moving target 

Currently APT does not have the capability to display a visualization of moving target dithers with the Aladin viewer. For a workaround, see Tutorial on Visualizing Dithers of a Solar System Observation in APT.

Target acquisition

Target acquisition (TA) is not required (or recommended) for standard targets or most numbered minor bodies for IFU observing modes (MIRI MRS, NIRSpec IFU) or the NIRSpec MSA "long slit" but may be necessary for other long slit observing modes (MIRI LRS, NIRSpec fixed slit). NIRSpec TA for moving targets will use the 1.6” S1600A1 aperture and the observer can then put the target in any fixed slit, IFU, or MSA “long slit.” See Moving Target Observing Strategies for more information and additional links.

More general information about APT target acquisition is in the article APT Target Acquisition.

Evaluate the schedulability of observations

APT has tools to visualize and check the schedulability of your observations (to visualize dithers, read the Tutorial on Visualizing Dithers of a Solar System Observation in APT). You can also check for duplications and estimate the total time needed to execute your proposal.


Download the Astronomer's Proposal Tool

Go to the online JWST Exposure Time Calculator

Latest updates

  • Minor wording changes.

  • Removed warning about the long run time of the Visit Planner for nearby objects, as this is no longer applicable.

    Added wording about the Moving Target Visibility Tool (MTVT).
Originally published