Redirected from ESPA Ring or ESPA
The Evolved Expendable Launch Vehicle (EELV) Secondary Payload Adapter (ESPA) ring was a joint U.S. Air Force development initiative between the SMC Detachment 12 STP contingency and the AFRL Space Vehicles Directorate. STP worked on the ESPA ring with AFRL under a small business innovative research (SBIR) contract(1) that AFRL had with CSA Engineering. CSA was subsequently acquired by Moog Inc. in late 2008 and now operates under the name of Moog CSA as a wholly owned subsidiary. Standard ESPA rings and their derivative variations are currently manufactured and sold by Moog CSA out of their Mountain View, California facility.

ESPA Concept

ESPA was designed to be installed between the launch vehicle upper stage and the primary spacecraft. To provide minimal impact to the primary, the ESPA duplicates the standard interface plane of the EELV upper stage and has been engineered to be very stiff in all directions. Since the standard ESPA ring is 24 inches high, only a small amount of volume is taken away from the primary. Roughly five feet in diameter and two feet tall, the ESPA is a half-inch thick, machined aluminum forging to which individual satellites can be mounted. ESPAs are available with a variety port configurations and can be manufactured to accommodate up to six standardized secondary satellite mounting locations found along the ring’s outside perimeter. The baseline standard ESPA can support up to six 400-pound satellites.


Many primary satellite payload users are now examining the ESPA concept as a way to generate additional cash flow by selling the unused launch capacity to secondary payload users. This strategy helps improve the primary payload financial bottom line by more fully utilizing the capability of the expensive launch vehicle asset.

ESPA ring under going structural qualification testing
(Photo courtesy of Moog CSA - Albuquerque, NM)

NASA Ames Research Center (ARC) defined ESPA class (180 kg. or less) "Small spacecraft" classifications(2)

Mini-satellite, 100 kilograms or higher
Micro-satellite, 10-100 kilograms
Nano-satellite, 1-10 kilograms
Pico-satellite, 0.01-1 kilograms
Femto-satellite, 0.001-0.01 kilograms

Classes of ESPA Rings

The standard ESPA can accommodate up to a 15,000-pound primary using the standard EELV interface plane bolt pattern: it’s a drop-in component in the launch stack. The simple secondary interface is a 15-inch-diameter bolt circle with 24 fasteners. ESPA can also serve as the structural hub of a satellite or free flyer. ESPA’s standard baseline is a six-port satellite carrier for EELV, but it is compatible with Falcon 9 and Taurus II. In addition, ESPA Rings may be stacked to provide incremental capacity. Modified versions of the adapter are available depending on payload or launch vehicle requirements and are currently offered in the following variant geometries:
  • ESPA Grande – a 4-port adapter that increases capacity from 400 lbm (180 kg) to 660 lbm (300 kg) per satellite
  • Small Launch ESPA – A 38.8 inch ring provides 8- or 15-inch ports for Minotaur IV, Delta II, Falcon 1e and
    Taurus vehicles

Moog CSA is currently pursuing a number of different applications for their ESPA product line with both US Military and civilian customers. This includes the use of up to six secondary “piggyback” payloads when extra capacity exists when the primary payload utilizes less than 100% of the booster’s full capacity. Additionally, the company also offers an integrated vibration isolation system called “SoftRide” to reduce the stresses imposed on the payload during launch. Moog CSA has also developed multi-payload adapters for smaller launch vehicles, targeting government agencies, universities and commercial space organizations with limited budgets.

Missions Flown or scheduled for launch utilizing ESPA

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Mission: STP-1
The inaugural flight of the ESPA ring. The mission’s manifest was the Defense Advanced Research Projects Agency’s Orbital Express, the launch’s largest satellite and primary payload. The ESPA ring carried five auxiliary satellites – MidSTAR-1 (Naval Academy); FalconSAT-3 (U.S. Air Force Academy); NPSAT1 (Naval Post Graduate School); STPSat-1 (STP built with Naval and Air Force Research Laboratory experiments) and CFESat (Los Alamos National Laboratories).

Launch Date: March 2007

Launch Vehicle: Atlas V

ESPA Type: 6 Port

Mission: LCROSS (lunar)
The LCROSS mission was designed to search for water on the moon by sending a payload crashing into the polar lunar surface creating a plume which ejects debris and potentially water vapor or ice above the surface. This debris cloud was then analyzed by a secondary payload.

Launch Date: June 2009

Launch Vehicle: Atlas V

ESPA Type: 6 Port
external image 200px-Demonstration_and_Science_Experiments.png
Mission: DSX (MEO - Free Flyer)
DSX, also known as SSTE-4 (Space Science Technology Experiment-4), is a technology demonstration mission of AFRL (Air Force Research Laboratory) at Kirtland AFB, Albuquerque, NM, USA. DSX will explore the viability of Medium Earth Orbits (MEOs) for communications and surveillance satellites. The satellite’s unique orbit is designed to allow it to study the inner and outer Van Allen radiation belts.

Expected Launch Date: Oct 2012

Launch Vehicle: EELV

ESPA Type: 4 Port

Advanced ESPA Concepts


In October of 2011 the U.S. Air Force released a RFP (Request For Proposal) soliciting contractor designs for a propulsive ESPA based vehicle with the project name of EAGLE. The main objective of the EAGLE Platform program is to develop a maneuverable ESPA Augmented Geostationary Laboratory Experiment (EAGLE) Platform spacecraft bus that utilizes a 6-port standard Evolved Expendable Launch Vehicle (EELV) Secondary Payload Adapter (ESPA) ring as part of its structure and is capable of being launched aboard any variant of the Evolved Expendable Launch Vehicle. The design of the EAGLE Platform will be capable of hosting up to 4 payloads for a period of at least 1 year in geosynchronous (GEO) orbit.

The EAGLE Platform program is an integral part of AFRL’s EAGLE program. The EAGLE program is AFRL’s newest flight program, through the Integrated Experiments and Evaluation Division (RVE) of the AFRL Space Vehicles Directorate located at Kirkland AFB in New Mexico.

For this effort, the EAGLE platform is expected to demonstrate on-orbit the ability to meet the direct inject GEO mission requirements to accommodate a minimum of 600 kg of payload mass. It is anticipated that the EAGLE platform design for this mission will also demonstrate by analysis the ability of the meet both the GTO and LEO mission requirements with minimal hardware changes to the GEO mission design. For the GTO mission, the EAGLE design is expected to accommodate a minimum of 180 kg of payload mass. For the LEO mission, EAGLE is expected to accommodate a minimum of 600 kg of payload mass.

The platform will be able to provide its various payloads with certain life-cycle and mission critical accommodations. This includes reaching payload specific requirements regarding operating power, survival power, slew rate, pointing knowledge, pointing control, jitter, data downlink capability and real-time downlink. Its main communication network will be the Air Force Satellite Control Network (AFSCN). After arrival in EAGLE’s designated orbit, each payload mission will be scheduled and coordinated with the others to ensure unified success amongst the four. None of the payloads will conflict with the mission of another, inhibiting life-cycle functions or mission critical actions. They will not all operate simultaneously, but rather will perform scheduled campaigns of a few days each with one or two payloads operating at the same time.

The government estimates the cost of this program will range from $24M to $28M.

6U Mount ESPA Sum

When ESPA Ring interior volume is available, an ESPA Sum can provide additional capacity for CubeSats or other nanosats behind a 15-inch port, including a pair of 3U packages or a single 6U satellite. This configuration facilitates the launch of multiple 1U, 3U or 6U satellites after the larger Mini or Micro secondary payload satellite has been released from a standard ESPA port.
ESPA Sum.png


  1. AFRL ESPA development summary
  2. NASA Edison Broad Agency Announcement (BAA NNA12ZD0001K)
  3. Moog CSA Engineering, Mountain View, CA., ESPA website
  4. DSX Mission Overview
  5. USAF EAGLE Platform (BAA-RV-12-04), AFRL, Space Vehicles Directorate, Kirtland AFB