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Every motor simulation in OpenRocket is driven by a thrust curve — a time-series record of thrust output over the motor’s burn. OpenRocket ships with a large built-in database of certified motor thrust curves, and also lets you import your own.

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Motor naming convention

Model and high-power rocket motors follow a standardized naming convention defined by the National Fire Protection Association (NFPA 1125). Understanding the designation helps you quickly gauge what a motor can do. A typical designation looks like: D12-5
PartExampleMeaning
Impulse class letterDTotal impulse range. Each letter doubles the previous: A = 1.26–2.5 Ns, B = 2.51–5 Ns, C = 5.01–10 Ns, D = 10.01–20 Ns, and so on up through O and beyond.
Average thrust (N)12Average thrust in Newtons over the burn time.
Ejection delay (s)5Delay in seconds from burnout to ejection charge firing. A 0 means no delay; a P means plugged (no ejection charge).
For reload motors, the designation often separates the casing from the propellant grain. For example, an AeroTech J800T-P is a J-class motor with 800 N average thrust, using a Blue Thunder (T) propellant, with a plugged delay (P).
The burn time is defined by NFPA 1125 as the duration during which the motor produces more than 5% of its maximum thrust. This is the threshold used internally by OpenRocket when calculating average thrust and burn time.

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The built-in motor database

OpenRocket includes a comprehensive built-in database of certified motor thrust curves, sourced from manufacturers and certification bodies. The database covers motors from:
  • Single-use solid propellant motors (e.g., Estes, Quest)
  • Reloadable solid propellant motors (e.g., AeroTech RMS, Cesaroni Pro)
  • Hybrid motors
The database is accessible from the Motor Selection panel in the Motors & Configuration tab. You can filter it by manufacturer, impulse class, and motor dimensions, or search by designation. See Basic flight simulation for details on using the Motor Selection panel.

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Importing custom thrust curves

OpenRocket supports importing motor thrust curves from two file formats:

RASP (.eng)

The RASP format is a plain-text format used by many certification databases and motor simulation tools. Files use the .eng extension.

RockSim (.rse)

The RockSim format is an XML-based format used by the RockSim simulation software. Files use the .rse extension.
Both formats are widely available from motor manufacturers’ websites, the ThrustCurve.org database, and other rocketry resources.

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Configuring the thrust curves folder

OpenRocket scans one or more folders on your disk for custom thrust curve files at startup. To configure which folders are scanned:
1

Open Preferences

Go to Edit → Preferences (Windows/Linux) or OpenRocket → Preferences (macOS).
2

Go to the Thrust curves tab

Click the Thrust curves tab in the Preferences window.
3

Add or remove folders

Use the Add button to add a directory containing your .eng or .rse files. Use Remove to remove a directory from the scan list. You can add multiple directories.
4

Restart or reload

After making changes, restart OpenRocket (or use the reload option if available) for the new files to appear in the Motor Selection panel.
Custom thrust curve files are merged with the built-in database. If a custom file defines a motor with the same designation as a built-in motor, both entries will appear in the Motor Selection panel — you can choose which thrust curve to use.

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RASP (.eng) file format

The RASP format is a simple line-based text format. A typical .eng file looks like this: 
; Custom motor example
; Name Diam(mm) Len(mm) Delays Prop-mass(g) Total-mass(g) Manufacturer
D12 24 70 0,3,5,7 12.0 25.8 Estes
0.000 0.0
0.015 12.5
0.060 14.4
0.100 13.5
0.150 12.8
0.900 0.5
0.950 0.0
;
  • Lines starting with ; are comments
  • The header line provides the motor designation, dimensions, available delays, propellant mass, total mass, and manufacturer
  • Each subsequent data line gives a time (seconds) and thrust (Newtons) pair
  • A trailing ; ends the motor definition; multiple motors can appear in one file

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RockSim (.rse) file format

The RockSim format is XML-based. Each motor entry is an <engine> element with attributes for the motor’s physical parameters and nested <data-point> elements for the thrust curve: 
<engine-database>
  <engine-list>
    <engine mfr="Example" code="D12" len="70" dia="24"
            initWt="25.8" propWt="12.0" delays="0,3,5,7"
            avgThrust="12" peakThrust="19.5" throatDia="0"
            exitDia="0" Itot="8.82" burnTime="0.95" massFrac="0.465"
            Type="single-use">
      <comments>Example motor</comments>
      <data>
        <eng-data t="0.000" f="0.0"/>
        <eng-data t="0.015" f="12.5"/>
        <eng-data t="0.100" f="13.5"/>
        <eng-data t="0.950" f="0.0"/>
      </data>
    </engine>
  </engine-list>
</engine-database>

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Viewing a motor’s thrust curve

To see the thrust curve for any motor in the Motor Selection panel, select the motor in the list and check the Show Details section at the bottom of the panel. This displays:
  • A graph of thrust (N) versus time (s)
  • Average thrust, peak thrust, and burn time
  • Total impulse
  • Certification information (if available)

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