Anything that leaves the Orbiter gets the FDO’s attention!


This includes:

  • Upper Stage-assisted satellites (Inertial and Spin-stabilized)
  • RMS-deployed spacecraft
  • GAS can deployables or other “mini-ejectables”
  • “Inadvertent” releases (i.e., EVA tools, non-stowable HST solar arrays, etc.)

STS-51 ACTS=TOS Deploy

STS-51 ACTS=TOS Deploy

A specific and additional certification beyond Orbit FDO was established for the first of these scenarios. All Orbit FDOs were trained to handle RMS deploys, GAS cans, or “inadvertent” releases.

The additional nominal and contingency coordination, planning, and operations for Upper Stage deployments required extra training and the Deploy FDO certification.

The FDO maintains an ephemeris of all deployed spacecraft for relative motion monitoring and for predicting tracking coverage in the post-deploy timeframe. This was useful during separation maneuvers for safety concerns (both orbital recontact as well as positioning the Orbiter at a safe stand-off distance prior to and during the upper stage ignition).

There were two primary inertial stage deployment types: The Boeing-built Inertial Upper Stage (IUS) was used for commercial and interplanetary satellite deployments. The Transfer Orbit Stage (TOS), built by Orbital Sciences, was used only once, but had been planned for other missions that were never executed.

Inertial Upper Stage (IUS)

The CSTC (IUS – Sunnyvale) performs a Gamma-Guidance simulation and supplies the FDO with the deploy time.

Transfer Orbit Stage (TOS)

The TOS POCC (at KSC) performs a TOS guidance simulation and supplies the FDO with SRM TIG, from which the FDO computes the deploy time.

In both cases, the FDO is responsible for state vector maintenance, transfer of specified trajectory information to the customer, and separation maneuver computations, including the Deploy and SEP PADs.

Early in the Shuttle program, there were two different types of “spin-stabilized” deployments that required a precise deployment attitude, depending on which axis the satellite spin deployment took.

Payload Assist Module Deployment (PAM-D)

Deployed with the spin axis coincident with the Orbiter -Z axis

Syncom (or “frisbee”-type)

Deployed with spin axis coincident with Orbiter +X axis

The FDO is responsible for computing the deploy time and separation maneuvers.

Typically, two sets of deploy computations are performed:

  1. The preliminary computations are made early in the deploy timeline and are reviewed by the customer.
  2. The final computations are made based on updated target information supplied by the customer to the FDO from the preliminary computations.

RMS Deployables

Typically, the deploy time is specified by some trajectory event such as orbital noon to allow proper crew viewing of the payload or by payload pointing, communication, or sunlight requirements.

The FDO is responsible for computing deploy time, separation maneuvers, and, if applicable, station-keeping and rendezvous maneuvers.

GAS-can ejectables or other “mini-satellites”

The FDO computes deploy time and monitors post-deploy relative motion

Inadvertent release… or “oops!”

The FDO helps recommend best course of action for object retrieval or collision avoidance maneuver

Post-deploy separation maneuvers are payload-specific, but can be grouped into three categories:

Upper stage deploys:

All upper stage deploys require a “final” separation maneuver that places the Orbiter “above and behind” the upper stage prior to SRM ignition.

In addition, IUS and TOS deploys also require a “backaway” separation maneuver to insure adequate clearance prior to the final separation maneuver.

The magnitude of the final separation maneuver is selected to protect for Orbiter tile erosion and payload explosion limits.

RMS deploys:

The typical separation provides a small backaway maneuver (0.5 to 1.0 FPS) followed by a 0.5-3.0 FPS in-plane maneuver.

The exact separation profile will also depend on the payload requirements (e.g., whether the payload will be retrieved later, etc.).

Generic Separation Maneuver (aka 1-2-3 SEP):

Pg. 11-2 Orbit Ops Checklist contains the crew procedures.

Sep sequence consists of a 1 FPS backaway maneuver followed 2 minutes later by a 2 FPS out-of-plane maneuver. A final 3 FPS posigrade maneuver is executed 15 minutes after the out-of-plane maneuver.

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“13 Minutes to the Moon” – an excellent BBC podcast focusing on the behind-the-scenes heroes of Apollo 11 and Apollo 13.

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The space exploration advocacy website of Roger Balettie, former Flight Dynamics Officer in NASA’s Space Shuttle Mission Control Center.

Select a menu tab to the left for detailed links or one of the main sections below:


The Flight Dynamics Officer (FDO, pronounced “fido”) is a Flight Controller in the Mission Control Center responsible for the overall trajectory, or flight path, of the Space Shuttle and all related payloads or other space-bound vehicles associated with the Shuttle.

Read about the:


"Houston… Tranquility Base here. The Eagle has landed."

Since 1965, the Mission Control Center (MCC) has been the nerve center for America’s manned space program.


Space- and NASA-based blog entries.

Last 3 blog posts:
50 Years

50 Years

The Artemis I mission occurred 50 years after Apollo 17. What will it take to not have this happen again?

13 Minutes – a podcast review

13 Minutes – a podcast review

“13 Minutes to the Moon” – an excellent BBC podcast focusing on the behind-the-scenes heroes of Apollo 11 and Apollo 13.



It’s been 40 years since the launch of STS-1, and the excitement of that day never faded.