aalyria · jimsweeney · Sep 15, 2026
diff --git a/contrib/README.md b/contrib/README.md
@@ -4,3 +4,4 @@ This is an open-source directory of real hardware that has been modeled in Space
 
 For example:
 - [loon/antenna_pattern.textproto](loon/antenna_pattern.textproto): An antenna pattern specified using phi, theta, and gain, with separate patterns for near- and far- field. This pattern models the millimeter-wave antennas used by Loon's balloons for gateway and inter-platform links.
+- [sda_oct_class_terminal/](sda_oct_class_terminal/): a free-space optical terminal of the class defined by the public SDA Optical Communication Terminal Standard 3.1.0 (ITU C-band grid, irradiance and BER requirements taken from the standard, optics and detector values assumed and tagged as such), with a matching optical ground station: antenna patterns, band profile, platform definitions and network nodes.
diff --git a/contrib/sda_oct_class_terminal/README.md b/contrib/sda_oct_class_terminal/README.md
@@ -0,0 +1,50 @@
+# SDA OCT Standard 3.1.0 class optical terminal, modeled in Spacetime
+
+Entities for a free-space optical communication terminal of the class defined by the Space Development Agency's
+Optical Communication Terminal (OCT) Standard, version 3.1.0 (public document, June 2023), plus a ground optical
+station to close a space-to-ground link. The standard defines interoperability requirements, not a hardware design,
+so every number below is tagged either **spec** (taken from the standard, requirement number given) or **assumed**
+(a representative value consistent with the standard). Replace the assumed values with your terminal's datasheet.
+
+## Files
+
+| File | Entity | Notes |
+| --- | --- | --- |
+| `oct_antenna_pattern.textproto` | ANTENNA_PATTERN | Gaussian optical aperture, space terminal |
+| `ogs_antenna_pattern.textproto` | ANTENNA_PATTERN | Gaussian optical aperture, ground station |
+| `oct_band_profile.textproto` | BAND_PROFILE | One ITU C-band channel, rate table from the irradiance requirement |
+| `oct_platform_definition.textproto` | PLATFORM_DEFINITION | Satellite transceiver model: transmitter, APD receiver, antenna, targeting |
+| `ogs_platform_definition.textproto` | PLATFORM_DEFINITION | Ground station transceiver model with an elevation mask |
+| `oct_network_node.textproto`, `ogs_network_node.textproto` | NETWORK_NODE | Interfaces bound to the transceiver models |
+
+## Values and their provenance
+
+| Quantity | Value | Source |
+| --- | --- | --- |
+| Spectral grid | ITU-T G.694.1, 193.1 THz + M x 100 GHz, C-band 1530 to 1565 nm, 100 GHz channel width | spec, OCT-022 |
+| Channel modeled | M = 0, 193.1 THz (1552.52 nm) | spec grid, channel choice assumed |
+| Modulation | OOK-NRZ | spec, section 2 |
+| Required irradiance at the remote aperture | at least 25 uW/m^2 mean, including platform jitter, at 5,500 km | spec, OCT-038 |
+| Maximum irradiance at the remote aperture | 10 mW/m^2 at any established link distance | spec, OCT-037 |
+| Receiver performance | post-FEC BER <= 1e-6 at 25 uW/m^2 at all required rates | spec, OCT-039 |
+| User throughput | continuous 1 Gbps bidirectional Ethernet through turbulence fades | spec, section 3 |
+| Transmit power | 1.0 W | assumed |
+| Transmit 1/e^2 half-angle divergence | 20 urad | assumed |
+| Pointing error (rms) | 4 urad | assumed |
+| Space terminal aperture | 0.08 m, 60 percent efficiency | assumed |
+| Ground station aperture | 0.40 m, 60 percent efficiency, 20 deg elevation mask | assumed |
+| Photodetector | APD, 80 percent quantum efficiency, 2.5 GHz bandwidth, 100 urad field of view, 100 GHz optical bandpass | assumed (bandpass = channel width, spec) |
+| Minimum sun angle | 5 deg | assumed |
+| Slew rates | 2 deg/s azimuth and elevation | assumed |
+
+Consistency check (Gaussian beam, far field): with 1.0 W and a 20 urad 1/e^2 half-angle the beam radius at 5,500 km
+is 110 m and the on-axis irradiance 52.6 uW/m^2; averaged over a 4 urad rms pointing error the mean irradiance is
+48.7 uW/m^2, which meets OCT-038 (25 uW/m^2) with 2.9 dB of margin. The rate table's top step is the received power
+that 25 uW/m^2 delivers through the modeled aperture: -69.0 dBW for the 0.08 m space terminal and -55.0 dBW for the
+0.40 m ground station. Lower steps are assumed.
+
+## What is not modeled here
+
+Acquisition and tracking (spiral search, beacon), the burst-mode waveform of version 4.0.0, atmospheric attenuation
+and turbulence on the ground link (those belong to the link evaluation, not the terminal), and any specific vendor's
+terminal. The SDA standard is cited from the public web version; see the standard for the authoritative text.
diff --git a/contrib/sda_oct_class_terminal/oct_antenna_pattern.textproto b/contrib/sda_oct_class_terminal/oct_antenna_pattern.textproto
@@ -0,0 +1,28 @@
+# Copyright 2026 James Sweeney.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+# SDA OCT Standard 3.1.0 class space terminal aperture. Aperture and divergence are ASSUMED representative
+# values (see README.md); the standard fixes the delivered irradiance (OCT-038), not the optics.
+group {
+  type: ANTENNA_PATTERN
+}
+id: "gain/payload/optical/sda-oct-class-terminal"
+antenna_pattern {
+  gaussian_optical_pattern: {
+    diameter_m: 0.08                 # assumed
+    efficiency_percent: 0.60         # assumed
+    divergence_angle_rad: 0.00002    # assumed, 20 urad 1/e^2 half-angle
+    pointing_error_rad: 0.000004     # assumed, 4 urad rms
+  }
+}
diff --git a/contrib/sda_oct_class_terminal/oct_band_profile.textproto b/contrib/sda_oct_class_terminal/oct_band_profile.textproto
@@ -0,0 +1,40 @@
+# Copyright 2026 James Sweeney.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+# One ITU-T G.694.1 C-band channel (SDA OCT Standard 3.1.0, OCT-022): 193.1 THz + M x 100 GHz, M = 0 here.
+# Rate table: the top step is the received power delivered by the required irradiance of 25 uW/m^2 (OCT-038)
+# through the modeled 0.08 m space-terminal aperture, -69.0 dBW, at which the receiver must reach a post-FEC
+# BER of 1e-6 at all required rates (OCT-039); the user throughput target is 1 Gbps (section 3). Lower steps
+# are ASSUMED fallback rates.
+group {
+  type: BAND_PROFILE
+}
+id: "band/optical/sda-oct-c-band-ch0"
+band_profile {
+  channel_width_hz: 100000000000     # spec, OCT-022: 100 GHz
+  rate_table: {
+    received_signal_power_steps: {
+      min_received_signal_power_dbw: -79
+      tx_data_rate_bps: 1e8            # assumed fallback
+    }
+    received_signal_power_steps: {
+      min_received_signal_power_dbw: -74
+      tx_data_rate_bps: 5e8            # assumed fallback
+    }
+    received_signal_power_steps: {
+      min_received_signal_power_dbw: -69
+      tx_data_rate_bps: 1e9            # spec: 1 Gbps at 25 uW/m^2 through a 0.08 m aperture
+    }
+  }
+}
diff --git a/contrib/sda_oct_class_terminal/oct_network_node.textproto b/contrib/sda_oct_class_terminal/oct_network_node.textproto
@@ -0,0 +1,31 @@
+# Copyright 2026 James Sweeney.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+group {
+  type: NETWORK_NODE
+}
+id: "node/leo/sda-oct-class-terminal"
+network_node {
+  name: "leo-oct"
+  type: "LEO"
+  node_interface: {
+    interface_id: "optical-link"
+    wireless: {
+      transceiver_model_id: {
+        platform_id: "platform/leo/sda-oct-class-terminal"
+        transceiver_model_id: "oct-optical-transceiver"
+      }
+    }
+  }
+}
diff --git a/contrib/sda_oct_class_terminal/oct_platform_definition.textproto b/contrib/sda_oct_class_terminal/oct_platform_definition.textproto
@@ -0,0 +1,76 @@
+# Copyright 2026 James Sweeney.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+# SDA OCT Standard 3.1.0 class space terminal on a low-Earth-orbit platform. Motion is left to the scenario
+# (attach a TLE or ephemeris in `coordinates`); the transceiver model is what this contribution provides.
+group {
+  type: PLATFORM_DEFINITION
+}
+id: "platform/leo/sda-oct-class-terminal"
+platform {
+  name: "leo-oct"
+  type: "LEO"
+  transceiver_model: {
+    id: "oct-optical-transceiver"
+    transmitter: {
+      name: "oct-tx"
+      channel_set: {
+        key: "band/optical/sda-oct-c-band-ch0"
+        value: {
+          channel: {
+            key: 193100000000000        # spec grid, M = 0: 193.1 THz (1552.52 nm)
+            value: {
+              max_power_watts: 1.0     # assumed
+            }
+          }
+        }
+      }
+    }
+    receiver: {
+      name: "oct-rx"
+      channel_set: {
+        key: "band/optical/sda-oct-c-band-ch0"
+        value: {
+          center_frequency_hz: 193100000000000
+        }
+      }
+      signal_processing_step: {
+        photodetector: {
+          avalanche_photodiode: {
+            field_of_view_rad: 0.0001                    # assumed
+            bandwidth_hz: 2500000000                     # assumed, 2.5 GHz
+            noise_temperature_k: 300                     # assumed
+            efficiency_percent: 0.80                     # assumed
+            dark_current_amp: 1e-9                       # assumed
+            load_impedance_ohm: 50                       # assumed
+            noise_factor: 4                              # assumed
+            gain_db: 10                                  # assumed
+            optical_bandpass_filter_bandwidth_hz: 100000000000   # spec channel width, OCT-022
+            wavelength_m: 0.0000015525                   # spec grid, M = 0 (193.1 THz)
+          }
+        }
+      }
+    }
+    antenna: {
+      name: "oct-aperture"
+      antenna_pattern_id: "gain/payload/optical/sda-oct-class-terminal"
+      targeting: {}
+      constraints: {
+        azimuth_angle_rate: { maximum_rate_deg_per_sec: 2.0 }      # assumed
+        elevation_angle_rate: { maximum_rate_deg_per_sec: 2.0 }    # assumed
+        minimum_sun_angle_deg: 5.0                                  # assumed
+      }
+    }
+  }
+}
diff --git a/contrib/sda_oct_class_terminal/ogs_antenna_pattern.textproto b/contrib/sda_oct_class_terminal/ogs_antenna_pattern.textproto
@@ -0,0 +1,27 @@
+# Copyright 2026 James Sweeney.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+# Optical ground station aperture for the space-to-ground link. All values ASSUMED (see README.md).
+group {
+  type: ANTENNA_PATTERN
+}
+id: "gain/ground/optical/ogs-0.4m"
+antenna_pattern {
+  gaussian_optical_pattern: {
+    diameter_m: 0.40                 # assumed
+    efficiency_percent: 0.60         # assumed
+    divergence_angle_rad: 0.00002    # assumed (uplink beacon-class beam)
+    pointing_error_rad: 0.000004     # assumed
+  }
+}
diff --git a/contrib/sda_oct_class_terminal/ogs_network_node.textproto b/contrib/sda_oct_class_terminal/ogs_network_node.textproto
@@ -0,0 +1,31 @@
+# Copyright 2026 James Sweeney.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+group {
+  type: NETWORK_NODE
+}
+id: "node/ground/ogs-0.4m"
+network_node {
+  name: "ogs"
+  type: "GROUND_STATION"
+  node_interface: {
+    interface_id: "optical-link"
+    wireless: {
+      transceiver_model_id: {
+        platform_id: "platform/ground/ogs-0.4m"
+        transceiver_model_id: "ogs-optical-transceiver"
+      }
+    }
+  }
+}
diff --git a/contrib/sda_oct_class_terminal/ogs_platform_definition.textproto b/contrib/sda_oct_class_terminal/ogs_platform_definition.textproto
@@ -0,0 +1,83 @@
+# Copyright 2026 James Sweeney.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+# Optical ground station for the space-to-ground link. Place it with `coordinates.geodetic_wgs84` in the scenario.
+group {
+  type: PLATFORM_DEFINITION
+}
+id: "platform/ground/ogs-0.4m"
+platform {
+  name: "ogs"
+  type: "GROUND_STATION"
+  transceiver_model: {
+    id: "ogs-optical-transceiver"
+    transmitter: {
+      name: "ogs-tx"
+      channel_set: {
+        key: "band/optical/sda-oct-c-band-ch0"
+        value: {
+          channel: {
+            key: 193100000000000
+            value: {
+              max_power_watts: 1.0     # assumed
+            }
+          }
+        }
+      }
+    }
+    receiver: {
+      name: "ogs-rx"
+      channel_set: {
+        key: "band/optical/sda-oct-c-band-ch0"
+        value: {
+          center_frequency_hz: 193100000000000
+        }
+      }
+      signal_processing_step: {
+        photodetector: {
+          avalanche_photodiode: {
+            field_of_view_rad: 0.0002                    # assumed
+            bandwidth_hz: 2500000000                     # assumed, 2.5 GHz
+            noise_temperature_k: 300                     # assumed
+            efficiency_percent: 0.80                     # assumed
+            dark_current_amp: 1e-9                       # assumed
+            load_impedance_ohm: 50                       # assumed
+            noise_factor: 4                              # assumed
+            gain_db: 10                                  # assumed
+            optical_bandpass_filter_bandwidth_hz: 100000000000   # spec channel width, OCT-022
+            wavelength_m: 0.0000015525                   # spec grid, M = 0 (193.1 THz)
+          }
+        }
+      }
+    }
+    antenna: {
+      name: "ogs-aperture"
+      antenna_pattern_id: "gain/ground/optical/ogs-0.4m"
+      targeting: {}
+      azimuth_elevation_mask: {
+        azimuth_deg: 0
+        maximum_obscured_elevation_deg: 20      # assumed 20 deg elevation mask, all azimuths
+      }
+      azimuth_elevation_mask: {
+        azimuth_deg: 360
+        maximum_obscured_elevation_deg: 20
+      }
+      constraints: {
+        azimuth_angle_rate: { maximum_rate_deg_per_sec: 5.0 }      # assumed
+        elevation_angle_rate: { maximum_rate_deg_per_sec: 5.0 }    # assumed
+        minimum_sun_angle_deg: 5.0                                  # assumed
+      }
+    }
+  }
+}
Original file line number	Diff line number	Diff line change
Expand Up		@@ -4,3 +4,4 @@ This is an open-source directory of real hardware that has been modeled in Space

		For example:
		- [loon/antenna_pattern.textproto](loon/antenna_pattern.textproto): An antenna pattern specified using phi, theta, and gain, with separate patterns for near- and far- field. This pattern models the millimeter-wave antennas used by Loon's balloons for gateway and inter-platform links.
		- [sda_oct_class_terminal/](sda_oct_class_terminal/): a free-space optical terminal of the class defined by the public SDA Optical Communication Terminal Standard 3.1.0 (ITU C-band grid, irradiance and BER requirements taken from the standard, optics and detector values assumed and tagged as such), with a matching optical ground station: antenna patterns, band profile, platform definitions and network nodes.