# Presentation: 324698

## An Advanced Cryogenic Cooling System for the Hubble Space Telescope

**Darrell Zimbelman**
**May 7, 2002**

## Agenda

**NICMOS Instrument**
**The Problem**
**Solution(s)**
**NCS Overview**
**Results**
**Summary**

## Instrument installed into HST during Servicing Mission 2 in February 1997
NICMOS is the only Infrared (IR) imaging capability on HST
Designed to take images and low/moderate resolution spectra (/  200) with high angular resolution (0.1 - 0.4 arc-second) at near-IR wavelengths ( = 0.8 to 2.5 μm)
Three cameras designed for simultaneous operations
Each camera contains a dedicated 256 x 256 Pixel HgCdTe detector
Detectors are mounted to the cold optics bench housed in a hybrid dewar (solid nitrogen within aluminum foam) that maintains their temperature at 58 K with a stability of +/- 2 K
Designed for a 5 year mission lifetime

**NICMOS is the only Infrared (IR) imaging capability on HST**
**Designed to take images and low/moderate resolution spectra (********/******** ******** 200) with high angular resolution (0.1 - 0.4 arc-second) at near-IR wavelengths (******** = 0.8 to 2.5 μm)**
**Three cameras designed for simultaneous operations**
- Each camera contains a dedicated 256 x 256 Pixel HgCdTe detector
**Detectors are mounted to the cold optics bench housed in a hybrid dewar (solid nitrogen within aluminum foam) that maintains their temperature at 58 K with a stability of +/- 2 K**
**Designed for a 5 year mission lifetime**

**Near Infrared Camera and Multi-Object Spectrometer (NICMOS) Instrument**

## NICMOS Instrument Continued

**NICMOS Instrument Continued**

## NICMOS Instrument Continued

## NICMOS Installation (Servicing Mission 2)

## A thermal short between the cold baffles and the surrounding Vapor Cooled Shield (VCS) became apparent shortly after installation
Moved the focus of Camera 3 outside the adjustment range which eliminated ability to simultaneously focus all three cameras
However camera 3 was still capable of limited science operations
Increased the parasitic heat loading (~422 mW) which in turn reduced lifetime of the cryogen and thus the anticipated period of science operations (60 months to 22 months)
Post launch investigation concluded that the thermal short was caused by over filling of the dewar followed by expansion of the cryogen during ground cooling operations

- Moved the focus of Camera 3 outside the adjustment range which eliminated ability to simultaneously focus all three cameras
- However camera 3 was still capable of limited science operations
- Increased the parasitic heat loading (~422 mW) which in turn reduced lifetime of the cryogen and thus the anticipated period of science operations (60 months to 22 months)
- Post launch investigation concluded that the thermal short was caused by over filling of the dewar followed by expansion of the cryogen during ground cooling operations

**The Problem**

## NICMOS Dewar

**NICMOS Dewar**

## NICMOS Dewar Continued

**NICMOS Dewar Continued**

**Thermal Short**

## Short Term
A “fast track” call for proposals and increased allocation of HST time to NICMOS science was instituted in May 1997 to maximize potential benefit 
Scientific program concluded on November 15, 1998
Cryogen depleted on January 4,1999
Monitor and quantify detector warm up characteristics

Long Term
Retrieve, repair, and return NICMOS to HST
Replace NICMOS with a new IR instrument
Revive NICMOS with a cryogenic cooling system

**A “fast track” call for proposals and increased allocation of HST time to NICMOS science was instituted in May 1997 to maximize potential benefit **
- Scientific program concluded on November 15, 1998
- Cryogen depleted on January 4,1999
**Monitor and quantify detector warm up characteristics**
_**Long Term**_
**Retrieve, repair, and return NICMOS to HST**
**Replace NICMOS with a new IR instrument**
**Revive NICMOS with a cryogenic cooling system**

**Solution(s)**

## Develop a cryogenic system, the NICMOS Cooling System (NCS), to restore NICMOS scientific performance and extend life of the instrument beyond original plans
Motivation
NICMOS is a critical trailblazer for future IR missions, direct predecessor of NGST
Ideal instrument for observing relatively cool objects (brown dwarf stars and proto-planets)
Possesses ability to peer into molecular clouds and other regions obscured by interstellar dust (star and planet forming regions)
Retains several advantages over ground based telescopes with adaptive optics:
Much lower level of background light - allows higher sensitivity in H and J bands
More accurate photometry - allows for more more precise quantitative measurements
Greater sky coverage and point spread function

**Motivation**
- NICMOS is a critical trailblazer for future IR missions, direct predecessor of NGST
- Ideal instrument for observing relatively cool objects (brown dwarf stars and proto-planets)
- Possesses ability to peer into molecular clouds and other regions obscured by interstellar dust (star and planet forming regions)
- Retains several advantages over ground based telescopes with adaptive optics:
- Much lower level of background light - allows higher sensitivity in H and J bands
- More accurate photometry - allows for more more precise quantitative measurements
- Greater sky coverage and point spread function

**Constructive Intervention**

## Remove 7 W including parasitic heat loads from the NICMOS instrument 
Achieve detector temperatures of < 75 K where effective imaging can occur (balance between quantum efficiency and dark current count)
Thermal stability of 0.1 K/orbit (short term) and 0.5 K/year (long term) for detector calibration
Dissipate 450 W of power
Jitter allocation of 0.89 mas rms (0.77 mas for cooler and 0.45 mas for radiator) of the overall HST jitter performance requirement of 7 mas rms
Interface to existing HST electrical and mechanical systems

**Achieve detector temperatures of < 75 K where effective imaging can occur (balance between quantum efficiency and dark current count)**
**Thermal stability of 0.1 K/orbit (short term) and 0.5 K/year (long term) for detector calibration**
**Dissipate 450 W of power**
**Jitter allocation of 0.89 mas rms (0.77 mas for cooler and 0.45 mas for radiator) of the overall HST jitter performance requirement of 7 mas rms**
**Interface to existing HST electrical and mechanical systems**

**Key System Requirements**

## Develop, test and install a new system that was never intended to be used on HST
No pre-defined interfaces (mechanical or electrical)
EVA compatible
A critical element of the system (i.e. NICMOS) was on-orbit 
Condition of the on-orbit element
Interface issues
Not able to characterize end-to-end system performance
Adhere to a strict “Do No Harm” policy
No added risk to HST
No degradation to the pre-installation HST performance
Minimize cost and accelerate schedule

- No pre-defined interfaces (mechanical or electrical)
- EVA compatible
**A critical element of the system (i.e. NICMOS) was on-orbit **
- Condition of the on-orbit element
- Interface issues
- Not able to characterize end-to-end system performance
**Adhere to a strict “Do No Harm” policy**
- No added risk to HST
- No degradation to the pre-installation HST performance
**Minimize cost and accelerate schedule**

**Challenges**

## Cryo Cooler Technology
Existing systems versus a new technology development effort
Jitter requirement excluded existing systems
New technology effort was selected based on initial assessments of the jitter performance and the ability to satisfy the derived temperature level/stability requirements
Moisture mitigation strategy
Heat Removal System
Heat Pipes versus a Capillary Pumped Loop (CPL)  versus a Loop Heat Pipe (LHP)
LHP and heat pipe designs were incompatible with installation
CPL provided installation flexibility and autonomous control capability
EVA Time
Efficiency versus design versus cost
Maximize time efficiency with simplified designs

- Existing systems versus a new technology development effort
- Jitter requirement excluded existing systems
- New technology effort was selected based on initial assessments of the jitter performance and the ability to satisfy the derived temperature level/stability requirements
- Moisture mitigation strategy
**Heat Removal System**
- Heat Pipes versus a Capillary Pumped Loop (CPL)  versus a Loop Heat Pipe (LHP)
- LHP and heat pipe designs were incompatible with installation
- CPL provided installation flexibility and autonomous control capability
**EVA Time**
- Efficiency versus design versus cost
- Maximize time efficiency with simplified designs

**Key Trades**

## Cryo Cooler
Cooler technology was at a TRL 2/3 when the development began
Matured the cooler technology from a TRL 2/3 to a TRL 7 in 18 months
Flight demonstration during October 1998 (STS-95)
Completed maturation to TRL 9 by February 2002
Fully operational system for HST Servicing Mission 3B

All other elements were at high TRLs

**Cooler technology was at a TRL 2/3 when the development began**
**Matured the cooler technology from a TRL 2/3 to a TRL 7 in 18 months**
- Flight demonstration during October 1998 (STS-95)
**Completed maturation to TRL 9 by February 2002**
- Fully operational system for HST Servicing Mission 3B
_**All other elements were at high TRLs**_

**Technology Readiness**

## Traditional Resource Management 

**Traditional Resource Management **

## NCS Resource Management 

**NCS Resource Management **

## NCS is comprised of three major elements: Electronics Support Module (ESM), NICMOS Cryo Cooler (NCC), CPL/Radiator Assembly
ESM provides the command, control and telemetry functions
NCC cools the NICMOS detectors by circulating Neon through the existing plumbing 
Plumbing was originally used to circulate Helium to freeze the liquid nitrogen in the dewar
EVA friendly bayonet interface between NCC and NICMOS
Removes reliance on expendable cryogens 
CPL/Radiator Assembly transfers heat from the NCC to the external environment
High heat transport capability
Capacity is in excess of that required for the NCC under any operating condition
Excess capacity can be utilized for future needs via an interface plate on the radiator
Associated mechanisms and harnessing to connect elements
Cryo Vent Insert
Ground Strap Adapter
COSTAR Y Harness
Cross Aft Shroud Harness (CASH)
P600 Harness

- ESM provides the command, control and telemetry functions
- NCC cools the NICMOS detectors by circulating Neon through the existing plumbing
- Plumbing was originally used to circulate Helium to freeze the liquid nitrogen in the dewar
- EVA friendly bayonet interface between NCC and NICMOS
- Removes reliance on expendable cryogens
- CPL/Radiator Assembly transfers heat from the NCC to the external environment
- High heat transport capability
- Capacity is in excess of that required for the NCC under any operating condition
- Excess capacity can be utilized for future needs via an interface plate on the radiator
**Associated mechanisms and harnessing to connect elements**
- Cryo Vent Insert
- Ground Strap Adapter
- COSTAR Y Harness
- Cross Aft Shroud Harness (CASH)
- P600 Harness

**NCS Overview**

## NCS Overview

## NCS Installation (-V2)

**ESM**

**COSTAR**
**Y Harness**

## NCS Installation (+V2)

**Neon**
**Flex**
**Lines**

**NCC**

**CPL**
**Line**

**Cryo Vent **
**Insert**

## NCS Installation (-V3)

**NCS**
**Radiator**

**NCS**
**Conduit**

## NCS Internal Layout

**NCS**
**Radiator**

**NCC**

**CPL**

**CASH**

**ESM**

**COSTAR**
**Y Harness**

**Cryo Vent**
**Insert**

## Provides the monitoring and control functions for the NCS
Interfaces with the NCS hardware and HST
Controls the NCC (i.e. the NICMOS detector temperatures) and keeps the turbo-machines within their operating limits
Proportional Integral Derivative control law is used to set the compressor speed, within limits of compressor housing temperature and turbo-alternator speed, to zero the temperature error between the desired NICMOS temperature and a defined set-point
Slip control law for efficient compressor operation
Monitors the CPL and adjusts the heater set-points to provide a stable temperature at the Heat Rejection Interface (HRI) while protecting the loop from deprime

- Interfaces with the NCS hardware and HST
**Controls the NCC (i.e. the NICMOS detector temperatures) and keeps the turbo-machines within their operating limits**
- Proportional Integral Derivative control law is used to set the compressor speed, within limits of compressor housing temperature and turbo-alternator speed, to zero the temperature error between the desired NICMOS temperature and a defined set-point
- Slip control law for efficient compressor operation
**Monitors the CPL and adjusts the heater set-points to provide a stable temperature at the Heat Rejection Interface (HRI) while protecting the loop from deprime**

**ESM**

## HST Electrical Interfaces
Power interface
COSTAR Y harness from COSTAR PDU
Data interface from HST SI C&DH to redundant RIUs
COSTAR Y harness from COSTAR
ESM Electrical Interfaces
Aft Shroud Cooling System (ASCS) harness from the ASCS radiator
COSTARY Y harness from COSTAR
CASH from the NCC
HST Mechanical Interfaces
2 EVA operated latches mounted to the ESM bridge-plate provide interface to aft shroud
Bridge Latch 1 is an EVA actuated rack and pinion plunger design that engages the support standoffs of the center guide rail
Bridge Latch 2 is an EVA actuated ratchet and pawl mechanism that clamps onto the SI connector handhold

- Power interface
- COSTAR Y harness from COSTAR PDU
- Data interface from HST SI C&DH to redundant RIUs
- COSTAR Y harness from COSTAR
**ESM Electrical Interfaces**
- Aft Shroud Cooling System (ASCS) harness from the ASCS radiator
- COSTARY Y harness from COSTAR
- CASH from the NCC
**HST Mechanical Interfaces**
- 2 EVA operated latches mounted to the ESM bridge-plate provide interface to aft shroud
- Bridge Latch 1 is an EVA actuated rack and pinion plunger design that engages the support standoffs of the center guide rail
- Bridge Latch 2 is an EVA actuated ratchet and pawl mechanism that clamps onto the SI connector handhold

**ESM Continued**

## ESM Continued

## Bridge Latches

**Bridge Latch 1**

**Bridge Latch 2**

## Employs two separate cooling loops: Circulator and Cryocooler
Circulator Loop uses a centrifugal circulator to pump a constant flow of neon between the NCC and NICMOS
EVA installed titanium bayonet fittings attach to the Coolant In and Coolant Out female bayonet interfaces on the NICMOS Cryo Interface
Uses neon at a 4 atm design pressure and a nominal operating speed of 1200 rps to provide a flow rate of 0.4 g/s
Removes heat from the NICMOS instrument and conductive parasitics
Heat is transferred from the Circulator Loop to the Cryocooler Loop via the Cold Load Interface
Stainless Steel counter-flow fin-type heat exchanger with a thermal effectiveness is 0.963
Provides structural support for the circulator, turbo-alternator, and recuperator

**Circulator Loop uses a centrifugal circulator to pump a constant flow of neon between the NCC and NICMOS**
- EVA installed titanium bayonet fittings attach to the Coolant In and Coolant Out female bayonet interfaces on the NICMOS Cryo Interface
- Uses neon at a 4 atm design pressure and a nominal operating speed of 1200 rps to provide a flow rate of 0.4 g/s
- Removes heat from the NICMOS instrument and conductive parasitics
**Heat is transferred from the Circulator Loop to the Cryocooler Loop via the Cold Load Interface**
- Stainless Steel counter-flow fin-type heat exchanger with a thermal effectiveness is 0.963
- Provides structural support for the circulator, turbo-alternator, and recuperator

**NCC**

## Cryocooler Loop uses two high-speed turbo-machines to provide compression and expansion of the neon and transfers heat to the HRI
HRI provides a conductive coupling between the NCC and the CPL
Turbo-alternator provides the refrigeration at the cold end of the loop
Work is extracted by expansion of gas across the turbine rotor
Shaft work is then converted to electrical power by the alternator and conveyed to a selectable resistive load where it is dissipated as heat and rejected to the HRI
Compressor provides compression at the warm end of the loop
Centrifugal machine driven by a 3-phase induction motor with a maximum operating speed of 7500 rps
Includes an integral fin-type after-cooler
Bolted to the HRI

- HRI provides a conductive coupling between the NCC and the CPL
- Turbo-alternator provides the refrigeration at the cold end of the loop
- Work is extracted by expansion of gas across the turbine rotor
- Shaft work is then converted to electrical power by the alternator and conveyed to a selectable resistive load where it is dissipated as heat and rejected to the HRI
- Compressor provides compression at the warm end of the loop
- Centrifugal machine driven by a 3-phase induction motor with a maximum operating speed of 7500 rps
- Includes an integral fin-type after-cooler
- Bolted to the HRI

**NCC Continued**

## Recuperator provides heat transfer between the high and low pressure streams of gas in the cryocooler loop
Consists of 300 slotted copper disks equally spaced in a stainless steel outer shell
Flow is separated by stainless steel spacer rings between adjacent pairs of disks
Supported by the CLI on the cold end and the NCC structure on the warm end

- Consists of 300 slotted copper disks equally spaced in a stainless steel outer shell
- Flow is separated by stainless steel spacer rings between adjacent pairs of disks
- Supported by the CLI on the cold end and the NCC structure on the warm end

**NCC Continued**

## Thermal Interface
Copper saddle provides a conductive joint between HRI and CPL evaporator
Evaporator is installed via EVA operations
Pressure required to meet conduction requirement is achieved by EVA installation of a cover plate that bolts to the copper saddle
Cryo Valve Heaters
Provide heat to the NICMOS cryo valve inlet/outlet valve handles to keep the viton o-rings above their leak temperature threshold under all HST environments
EVA installed over NICMOS cryo valve handles

- Copper saddle provides a conductive joint between HRI and CPL evaporator
- Evaporator is installed via EVA operations
- Pressure required to meet conduction requirement is achieved by EVA installation of a cover plate that bolts to the copper saddle
**Cryo Valve Heaters**
- Provide heat to the NICMOS cryo valve inlet/outlet valve handles to keep the viton o-rings above their leak temperature threshold under all HST environments
- EVA installed over NICMOS cryo valve handles

**NCC Continued**

## NCC Electrical Interfaces
Harness from the radiator
CASH from the ESM
HST Mechanical Interfaces
2 EVA operated wing-tab bayonet fittings attached to the NICMOS cryo interface plate
2 EVA operated snap-on valve heater assemblies attached to the NICMOS cryo valve handles
2 EVA operated latches identical to ESM

- Harness from the radiator
- CASH from the ESM
**HST Mechanical Interfaces**
- 2 EVA operated wing-tab bayonet fittings attached to the NICMOS cryo interface plate
- 2 EVA operated snap-on valve heater assemblies attached to the NICMOS cryo valve handles
- 2 EVA operated latches identical to ESM

**NCC Continued**

## NCC Continued

## NCC Continued

## NCC Continued

**NCC Continued**

## NCC Continued

## Thermal Interface & Cryo Valve Heater

## NICMOS Interface Panel

- Coolant IN
- Bayonet Port

- Coolant OUT
- Bayonet Port

- Coolant IN
- Cryo Valve

- Coolant OUT
- Cryo Valve

## CPL/Radiator Assembly interfaces to the NCC at the HRI via the CPL evaporator which carries heat from the NCC to the external radiator
Cold liquid coming from the radiator flows into the evaporator and is vaporized transferring heat from the NCC
Hot vapor carries heat out of the evaporator to the radiator via stainless steel tubing
Vapor enters a heat pipe heat exchanger in the radiator and condenses in header heat pipe
Heat from the header heat pipe is conducted to a series of spreader heat pipes throughout the radiator where heat is then radiated to the space environment
Condensed vapor moves through a subcooler region to cool the liquid prior to exiting the radiator

- Cold liquid coming from the radiator flows into the evaporator and is vaporized transferring heat from the NCC
- Hot vapor carries heat out of the evaporator to the radiator via stainless steel tubing
- Vapor enters a heat pipe heat exchanger in the radiator and condenses in header heat pipe
- Heat from the header heat pipe is conducted to a series of spreader heat pipes throughout the radiator where heat is then radiated to the space environment
- Condensed vapor moves through a subcooler region to cool the liquid prior to exiting the radiator

**CPL/Radiator Assembly**

## HST Electrical Interfaces
P600 Harness 
Power from the HST EPS Test Plug to Radiator Diode Box
CPL/Radiator Electrical Interfaces
Radiator harness to NCC
HST Mechanical Interfaces 
Mounts to exterior of aft shroud
Attached to HST handrails with 3 EVA actuated over-the-center latches
Latches are attached to radiator with titanium flexures
Flex lines from the evaporators feed through the aft shroud cryo vent where they transition to rigid lines running through the conduit which traverses the aft bulkhead
Cryo Vent Insert provides the sole mechanical connection of conduit to aft bulkhead
The rigid lines transition back to flex lines upon exiting the conduit and back to rigid lines at the radiator strain relief bracket

- P600 Harness
- Power from the HST EPS Test Plug to Radiator Diode Box
**CPL/Radiator Electrical Interfaces**
- Radiator harness to NCC
**HST Mechanical Interfaces **
- Mounts to exterior of aft shroud
- Attached to HST handrails with 3 EVA actuated over-the-center latches
- Latches are attached to radiator with titanium flexures
- Flex lines from the evaporators feed through the aft shroud cryo vent where they transition to rigid lines running through the conduit which traverses the aft bulkhead
- Cryo Vent Insert provides the sole mechanical connection of conduit to aft bulkhead
- The rigid lines transition back to flex lines upon exiting the conduit and back to rigid lines at the radiator strain relief bracket

**CPL/Radiator Assembly Continued**

## CPL/Radiator Assembly Continued

**Q ****Radiator**

**Q ****NCC**

**Q ****Heater**

## CPL/Radiator Assembly Continued

**Subcooler Section**
**Isothermalizer heat pipes**
**Heat Pipe Heat Exchangers**
**Reservoir Lines**

**CPL/Radiator Assembly Continued**

## CPL/Radiator Assembly Continued

**CPL/Radiator Assembly Continued**

## CPL/Radiator Assembly Continued

## Radiator Latch Mechanism

**Radiator Latch Mechanism**

## Cryo Vent Insert

- Stove Pipe
- (Attached to conduit)

- Lock Down Ring

- Pawl Levers

**Cryo Vent Insert**

## Flight demonstration to provide system validation and enhanced system knowledge beyond what could be accomplished through ground testing (STS 95, October 1998)
Resulted in 185 hours of anomaly free operation
A minimum temperature of 72.65 K and stability of  0.1 K was reached using a surrogate representation of the NICMOS dewar called the NICMOS Cooling Loop Simulator (NCLS)
Vibration measurements were obtained during various operational and non-operational periods to characterize vibration signatures
Results concluded that disturbances below 2 Hz produce the majority of  contribution to HST jitter, while data resolution and corruption identified the need for further ground testing to reduce uncertainties attributed to mass participation and systematic errors

- Resulted in 185 hours of anomaly free operation
- A minimum temperature of 72.65 K and stability of  0.1 K was reached using a surrogate representation of the NICMOS dewar called the NICMOS Cooling Loop Simulator (NCLS)
- Vibration measurements were obtained during various operational and non-operational periods to characterize vibration signatures
- Results concluded that disturbances below 2 Hz produce the majority of  contribution to HST jitter, while data resolution and corruption identified the need for further ground testing to reduce uncertainties attributed to mass participation and systematic errors

**HST Orbital Systems Test**

## NCS was held to more stringent EMI/EMC test levels to minimize/eliminate risk to the telescope
NICMOS spare detector noise test
Prove that there was no conducted noise into the NICMOS instrument via the NCC
Vibration Emittance Test 
Suspended NCC in micro-g environment to characterize the vibration behavior
Test results showed that NCC induced vibrations were within acceptable HST limits
Radiator RF Emission Test
Developed a grounding plate for the radiator at the telescope entrance
No significant change with or without grounding plate
Thermal Glove Box Testing
Evaluate all EVA interfaces at temperature extremes
High Fidelity Mechanical Simulator/Vehicle Electrical System Test
Crew Training

**NICMOS spare detector noise test**
- Prove that there was no conducted noise into the NICMOS instrument via the NCC
**Vibration Emittance Test **
- Suspended NCC in micro-g environment to characterize the vibration behavior
- Test results showed that NCC induced vibrations were within acceptable HST limits
**Radiator RF Emission Test**
- Developed a grounding plate for the radiator at the telescope entrance
- No significant change with or without grounding plate
**Thermal Glove Box Testing**
- Evaluate all EVA interfaces at temperature extremes
**High Fidelity Mechanical Simulator/Vehicle Electrical System Test**
**Crew Training**

**Specialized Testing**

## System Level Thermal Vacuum Testing

## NBL Training

## Servicing Mission 3B

## Servicing Mission 3B Continued

## Servicing Mission 3B Continued

## Performance

## Summary