Alternate Access To Station (AAS) Performance Requirements Document International Space Station

Status Report From: United Space Alliance
Posted: Wednesday, May 12, 2004

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February 15, 2002
Contract NAS9-20000
Space Flight Operations Contract USA004882



This document identifies the basic functional performance requirements that an Alternate Access to Station System, hereafter termed AAS, is expected to satisfy to perform logistics resupply for the orbiting International Space Station (ISS). It has been developed to provide potential AAS service providers with information to support development of end-to-end AAS concepts.

This document is not intended to and does not serve as the set of detailed design and functional requirements necessary to develop such a system.


The requirements in this document are based on analysis of potential cargos and existing operational rules and criteria. They have been developed to maximize the potential use of the AAS while minimizing the design and cost impact of infrequent or unique cargo items and operational scenarios. Some of the criteria (e.g., power available from the ISS) have been developed based on standardized or normalized ISS allocations with the recognition that the actual specification or Interface Control Document (ICD) limits will be negotiated with the ISS program during the detailed design phase. Those using this document are encouraged to better the criteria rather than depending on negotiated accedences, thereby developing an AAS that is of greater value to the ISS. This document shall not be construed as a commitment by the ISS Program to use any system that satisfies these requirements.

This document provides the following:

a. Basic conceptual requirements
b. Standardized cargo descriptions
c. Cargo processing considerations
d. Representative mission definitions
e. Other ISS interface considerations

The requirements herein have been developed assuming no use of International Partner (IP) assets.


The following reference requirements are intended to ensure that AAS concepts are compatible with the existing ISS design, operations, and utilization concepts and constraints. Deviations from these requirements may have significant implications on the viability of the resulting concept.

2.1 The AAS orbital transfer element will be unmanned.

2.2 The AAS will support the ISS altitude profile from 278 to 460 km (150 to 248 n. mi.) at an inclination of 51.6 degrees.

2.3 The AAS will not require changes to the ISS that adversely affect the ISS performance or capabilities. The AAS will not adversely impact other vehicles that interface with the ISS.

2.4 The AAS service provider is responsible for the purchase and integration of hardware to their vehicle to be compatible with the ISS (e.g., Common Berthing Mechanism (CBM), Flight Releasable Grapple Fixture (FRGF), Power Data Grapple Fixture (PDGF), passive Flight Releasable Attachment Mechanism (FRAM), etc.).

2.5 The AAS orbital transfer element will be required to perform all maneuvers necessary to berth/dock to the on-orbit ISS at the attitudes defined in SSP 50261-01, Generic Groundrules, Requirements and Constraints.

2.6 The AAS will not provide ISS propellant delivery services.

2.7 The AAS will not provide attitude control or ISS reboost while attached to the ISS.

2.8 The AAS orbital transfer element will have a space-to-space communication system compatible with the ISS for the purpose of relaying command and data telemetry.

2.9 The AAS orbital transfer element will have a Guidance, Navigation and Control (GN&C) system commandable from the ISS while in proximity operations.

2.10 External cargo transfers between the AAS orbital transfer element and the ISS will be performed via Extravehicular Robotics (EVR), not by Extravehicular Activity (EVA).

2.11 The ISS can provide resources to the AAS vehicle, depending on the mating location, while the vehicle is attached to the ISS. These resources include electrical power, atmospheric temperature and humidity control, Command and Data Handling (C&DH), and thermal cooling fluids. Resource demand shall not be in excess of those available at a specific interface, and specific allocation will be negotiated with the ISS Program during the detailed design.

2.12 The AAS service provider will be responsible for providing the launch and landing sites for their vehicle and providing the necessary facilities for cargo integration and cargo de-integration of the vehicle that meet the cargo ground handling and environmental requirements.

2.13 In the operational phase, the ISS Program will determine the dates for AAS attached operations and time constraints for returnable cargo.

2.14 The AAS must be capable of delivering cargo to the ISS on any date defined by the ISS Program. It will be available year round.

2.15 Other than nominal approach and departure trajectories, the AAS vehicle will not perform formation flight with the ISS.

2.16 The post assembly complete configuration of the ISS will reflect the Assembly Sequence, Revision F baseline with the exclusion of the Propulsion Module. See Figure 2-1. The ISS elements included are listed below:

  • All truss elements
  • Columbus Operating Facility (COF)
  • Japanese Experiment Module (JEM)
  • Centrifuge Accommodation Module (CAM)
  • Node 3
  • Crew Return Vehicle (CRV)
  • Hab Module
  • Russian Segment with Science Power Platform (SPP)

Additional detailed requirements are defined in subsequent sections of this document.

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