ISS Deorbit USOS Concept of Operations Overview.pdf

Page No. 1

ISS Deorbit Concept of Operations

US Deorbit Options

Page No. 2

Purpose and Agenda

• Purpose ➢Provide a concept of operations to support the development of a US deorbit vehicle capability

• Agenda ➢Background

➢Scenario Overview

➢ Initial ISS Configuration

➢Launch to Dock/Berth

➢Orbit Lowering

➢Deorbit Burn

➢Design Considerations

➢Notional Deorbit Timeline

➢Summary of Key Deorbit Parameters

Page No. 3

Background

• At the completion of ISS operations, currently planned through 2030, the ISS must be safely deorbited via controlled reentry into an unpopulated region. It is the responsibility of all ISS partners to ensure the safe deorbit and reentry of the ISS at its end-of-life (EOL).

• NASA seeks to understand industry’s capability to design, develop, manufacture, launch, and provide the on-orbit operation of a capability to enable a controlled re-entry and safely deorbit the ISS.

• The following slides will outline nominal ISS deorbit strategy to help define capabilities required for development of an alternate disposal capability.

• The proposed US deorbit vehicle will be referred to as the “deorbit vehicle” in further slides.

Page No. 4

Nominal Scenario Overview

• NASA and its International Partners are working through government approvals to extend nominal ISS operations through 2030.

• The deorbit vehicle will attach to ISS at Node 2 Forward approximately one year prior to reentry.

➢ Current nominal ISS operating altitude approximately 416 km

➢ Deorbit vehicle rendezvous estimated to occur above 330 km

• Upon arrival the deorbit vehicle will perform test/checkout objectives and provides capability for attitude control and altitude maintenance.

• ISS altitude will naturally lower over the course of months until the deorbit vehicle is used to perform a series of final deorbit burns.

➢ The Russian Segment will still provide attitude control and altitude maintenance up to the deorbit activities (including lowering ISS altitude to nominal de-orbit start)

➢ The deorbit vehicle will be responsible for the delta-v necessary for controlled reentry (including final orbit shaping)

Page No. 5

Notional Deorbit Timeline

Final Reentry Burn

Min. Rendezvous Altitude

Perigee Lowering Burns (if required)

Deorbit Vehicle Rendezvous

Final ISS Crew Departure

Note: ISS altitude decay rate, deorbit timeframe, and ISS altitude at time of deorbit vehicle rendezvous varies with solar cycle.

https://www.nasa.gov/msfcsolar

Page No. 6

ISS Configuration

• The ISS mass is approximately 450,000 kg.

• Before ISS end-of-life, the Node 2 Forward is planned to be converted from a docking port to a berthing port in support of a commercial element.

➢ The commercial element is planned to depart ISS before deorbit.

• The deorbit vehicle may be required to switch attachment mechanisms at a pre-defined time prior to launch.

➢ Docking to Node 2 Forward International Docking Adapter (IDA)

➢ Robotic capture and berthing to Node 2 Forward Common Berthing Mechanism (CBM)

Docking at Node 2 Forward

Berthing at Node 2 Forward

Page No. 7

Launch to Dock/Berth

• The deorbit vehicle will launch approximately 1 year prior to planned ISS reentry.

• The deorbit vehicle will attach to the ISS via one of the two mechanisms outlined previously:

➢ In the case of a robotic berthing to the Node2 Forward CBM a grapple fixture will need to be placed appropriately on the vehicle to support grappling via the Space Station Remote Manipulator System (SSRMS)

• ISS Crew will provide crew monitoring of the approach (consistent with USOS cargo vehicles)

➢ For a docking case, the deorbit vehicle will provide centerline camera video of approach to the ISS through C2V2 for monitoring.

➢ For a berthing case, the deorbit vehicle will transmit data to the ISS to create crew displays and overlays in support of capture.

• Additional Ground Rules / Assumptions

➢ ISS is crewed.

➢ Common Communications for Visiting Vehicles (C2V2) system is functioning and used for Space-to-Space communication.

➢ ISS retro reflectors remain effective and are located per current baseline.

➢ ISS Global Positioning System (GPS) functions as today (ISS provides data for Relative GPS compatibility).

➢ NASA will provide Tracking and Data Relay Satellite System (TDRSS) support and scheduling for space-to-ground communication.

➢ ISS will provide power and data/command interfaces – No active cooling provided

Page No. 8

Orbit Lowering

• Initial orbit lowering from the rendezvous altitude will be accomplished through a combination of atmospheric drag and Russian Segment burns

• ISS will set up its final deorbit sequence at an altitude of 270 km.

➢ Creates a phase repeat orbit with a 4-day ground track repeat

• Propulsive attitude control is required at altitudes below approximately 220 km.

➢ Beyond this point, CMGs can no longer control attitude.

➢ Russian Segment will be prime for attitude control at this time.

• The De-Orbit vehicle will establish an elliptical orbit of approximately 200 x 145 km through a series of burns to minimize duration of propulsive attitude control.

➢ Total delta-v needed for this orbit setup is approximately 17 m/s.

Key ISS Altitudes for Deorbit

460 km Maximum Rendezvous Altitude (TBD)

330 km Minimum deorbit vehicle rendezvous altitude. (TBD)

270 km Phase repeat orbit (4-day ground track repeat). Natural orbital decay for ISS from this altitude is expected to be approximately one month.

220 km ISS attitude control accomplished via thrusters only. ISS Control

Moment Gyros (CMGs) are no longer able to provide attitude control.

198 km Phase repeat orbit (1-day ground track repeat).

141 km Perigee at which apogee decays at 2 km/orbit: NASA does not plan more than two orbits with perigees below this value.

130 km Estimated minimum operational altitude of USOS external avionics and systems.

110-120 km Altitude at which US solar arrays and radiators are expected to separate (based on observed Mir re-entry).

84-100 km Estimated module rupture altitude [TBC]

70-75 km Maximum allowable vacuum perigee that will cause ISS fragments to lie within a 6000 km footprint [TBC].

50 km Guaranteed capture. 50 km vacuum perigee is the NASA Std 8719.14 requirement for re-entry targeting in all new NASA programs.

Page No. 9

Final Deorbit Burn

• Target de-orbit perigee is 50 km to ensure a small footprint is achieved and all components successfully enter the atmosphere.

➢ This perigee enables for several target locations on the Earth.

• The final burn will target approximately 30 m/s within roughly 40-60 minutes to support a perigee of 50 km and guarantee atmospheric capture.

➢ The final burn will be commanded to the deorbit vehicle by the provider at the time determined by NASA to reenter in the defined footprint.

70 72 74 76 78 80 82 84

Breakup altitude Hbreak (km)

F o o tp ri n t le n g th k m

Hper = 75 km

Hper = 70 km

Hper = 65 km

Hper = 60 km

Hper = 55 km

Hper = 50 km

2008 Aerospace Corporation study as a function of expected break-up altitude and capture perigee

Example Deorbit Target in the South Pacific Ocean(ic) Uninhabited Area

Page No. 10

Design Considerations

• Due to uncertainty in ISS system performance at low altitudes, the deorbit vehicle must provide autonomous operation capabilities for the de-orbit sequence.

➢Power from ISS will be available at higher altitudes, but some questions exist on power capability during final deorbit setup and burn.

➢Additionally, the deorbit vehicle must be capable of providing independent ISS attitude control.

• The deorbit vehicle will need to provide at least 3236 N thrust to hit the target delta-v within a 60-minute time period.

➢To ensure ISS structural integrity, the maximum allowable thrust is 6178 N.

➢Higher max thrust may be permissible if thrust ramps up over time (e.g., throttle capability).

Page No. 11

Design Considerations (continued)

• Controlled reentry is a hazard control for ISS deorbit (public safety), therefore operations of the deorbit vehicle is a must-work function.

➢ISS uses two-fault tolerance for control of catastrophic hazards such as this.

• Given end-of-life, the deorbit vehicle must successfully rendezvous and attach to ISS

➢Current ISS crew transportation vehicles must protect for at least 3 rendezvous attempts to ISS.

➢Given criticality of controlled reentry, a similar (or greater) number of re-rendezvous attempts should be maintained.

Page No. 12

Contingency Response

• As with any long term endeavor, there is risk of a contingency on the ISS that could move up the need to de-orbit the vehicle

• Due to this, the desire is to ensure the de-orbit vehicle is available for launch with a limited call up time as early as possible ➢Potential scenarios exist where call up decision is needed as late as L-6 months

Page No. 13

Summary of Key Deorbit Parameters

• De-orbit vehicle delta-v and prop capability must be between 41-47 m/s

➢ Greater delta-v is preferred

➢ 30 m/s for final de-orbit burn

➢ ~17 m/s delta-v for de-orbit setup

➢ 700-1700 kg of attitude control propellant

• Full deorbit sequence is a must-work function

➢ Due to public safety implications of the deorbit

• Vehicle must remain on orbit attached to the ISS for at least a year

➢ Rendezvous between 330 and 460 km

• Communication with ISS in free flight through C2V2 system

• Capability for multiple rendezvous attempts required to ensure successful attachment to ISS

• Nominal deorbit planned in early 2031 however Launch on Need Call up required to support ISS technical contingencies that lead to early end of life

➢ Need provider input on options to maintain launch on need and possible call up times

• Flexible design to allow transition between docking and berthing with some amount of time before call up.

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