SDA Tranche 1 Transport Layer B

Mission

SDA Tranche 1 Transport Layer B on Falcon 9 Block 5. Wed 10 Sept 2025, 14:12:11 UTC. Reported outcome: Success. Launch site: Space Launch Complex 4E. Source: Launch Library 2.

Tranche 1 Transport Layer B is one of six missions by the United States Space Force Space Development Agency (SDA) for the Proliferated Warfighter Space Architecture (PWSA) Tranche 1 Transport Layer constellation, which will provide assured, resilient, low-latency military data and connectivity worldwide to the full range of warfighter platforms from Low Earth Orbit satellites. The constellation will be interconnected with Optical Inter-Satellite Links (OISLs) which have significantly increased performance over existing radio frequency crosslinks. It is expected to operate over Ka band, have stereo coverage and be dynamically networked for simpler hand-offs, greater bandwidth and fault tolerance. This launch carries 21 satellites manufactured by York Space Systems.

Mission type

Government/Top Secret

Orbit

Polar Orbit

Rocket file imagery

Launch timeline

Times are relative to liftoff.

1. T-38 minWed 10 Sept, 15:34 CEST

   GO for Prop Load

   Launch director verifies go for propellant load

2. T-35 minWed 10 Sept, 15:37 CEST

   Stage 1 LOX Load

   Start of liquid oxygen loading in the first stage

3. T-35 minWed 10 Sept, 15:37 CEST

   Prop Load

   Start of propelland loading

4. T-16 minWed 10 Sept, 15:56 CEST

   Stage 2 LOX Load

   Start of liquid oxygen loading in the second stage

5. T-7 minWed 10 Sept, 16:05 CEST

   Engine Chill

   Start of engine chilling

6. T-1 minWed 10 Sept, 16:11 CEST

   Tank Press

   Fuel tanks are pressurized to flight levels

7. T-1 minWed 10 Sept, 16:11 CEST

   Startup

   The onboard computer takes control over the countdown and runs last checks

8. T-45 sWed 10 Sept, 16:11 CEST

   GO for Launch

   Launch director verifies go for launch

9. T-3 sWed 10 Sept, 16:12 CEST

   Ignition

   Start of the engine ignition sequence

10. T-0Wed 10 Sept, 16:12 CEST

    Liftoff

    First upwards movement of the rocket

11. T+1 min 12 sWed 10 Sept, 16:13 CEST

    Max-Q

    Maximum dynamic pressure

12. T+2 min 30 sWed 10 Sept, 16:14 CEST

    MECO

    Cut-off of the main engine

13. T+2 min 34 sWed 10 Sept, 16:14 CEST

    Stage 2 Separation

    Separation of the second stage from the first

14. T+2 min 42 sWed 10 Sept, 16:14 CEST

    SES-1

    First start of the second engine

15. T+6 min 24 sWed 10 Sept, 16:18 CEST

    Entry Burn Startup

    Start of the atmospheric entry burn

16. T+6 min 47 sWed 10 Sept, 16:18 CEST

    Entry Burn Shutdown

    End of the atmospheric entry burn

17. T+8 min 12 sWed 10 Sept, 16:20 CEST

    Stage 1 Landing Burn

    Start of the first stage landing burn

18. T+8 min 36 sWed 10 Sept, 16:20 CEST

    Stage 1 Landing

    Landing of the first stage

19. T+8 min 38 sWed 10 Sept, 16:20 CEST

    SECO-1

    First cut-off of the second engine

20. T+56 min 43 sWed 10 Sept, 17:08 CEST

    SES-2

    Second start of the second engine

21. T+56 min 51 sWed 10 Sept, 17:09 CEST

    SECO-2

    Second cut-off of the second engine

Slip history

Changes recorded by Space Right Now

No changes since we started tracking on Sat 10 Oct 2026, 11:17 UTC.

Launch pad

Space Launch Complex 4E

Vandenberg SFB, CA, USA (US)

Coordinates: 34.632, -120.611