# Presentation: 702117

## The Hubble Space TelescopeNICMOS Cooling System (NCS)

**Ed Cheng**
**HST Development Project Scientist**
**05 June 2002**
**AAS Backup Material**

## SM3B Scientific Improvements For HST

**Double the electrical power for science instruments.**
- Combination of the new Solar Arrays and Power Control Unit.
**The Advanced Camera for Surveys (ACS).**
- A new camera improving the (field-of-view x sensitivity) metric by 10x.
- Replaces the ageing WFPC2 camera (and its radiation damaged CCDs).
**The NICMOS Cooling System (NCS).**
- Provides external cooling for the Near Infrared Camera and Multi-Object Spectrograph (NICMOS).
- The NICMOS solid-Nitrogen coolant was used up 2 years after deployment due to a thermal short in the cryostat (expected life was > 5 years).
- Uses a high capacity mechanical cryocooler to provide ~ 75K at the detectors.
- Overall cooling capacity is ~ 7 Watts.
- Power consumption less than 400 Watts.
- Unlike all other HST systems, this is an experimental unit that is flown on a “best effort” basis.

## NICMOS Cooling SystemDevelopment Timeline

**Independent Science Review**
**Completed**

**NICMOS Cooling System****Development Timeline**

**1997**

**14 February 1997**
**NICMOS Installed in HST**

**April 1997**
**NCS Concept Created**

**July 1997**
**NCS Project Approved**

**29 Oct. to 07 Nov. 1998**
**HOST Flight Test**

**06 January 1999**
**NICMOS Cryogen Depleted**

**19 to 27 December 1999**
**HST SM3A**

**1998**

**1999**

**2000**

**2001**

**2002**

**18 May 2002**
**NICMOS Back in Service**

**08 March 2002**
**NCS Installed in HST**

## NICMOS Cooling System Deployment Timeline (2002)

**Jan 2002**

**08 March 2002**
**NCS Installed in HST**

**Feb**

**Mar**

**Apr**

**May**

**18 May 2002**
**NICMOS Back in Service**

**19 March 2002**
**NCS Cooldown Starts**

**12 April 2002**
**Achieved Nominal Temp.**

**11 May 2002**
**Early Release Obs.**

## The NICMOS Instrument

## The NICMOS Cryostat

**This ground servicing plumbing is used to convey the cold gas from the NCS into the instrument.**

## NICMOS Cooling System Block Diagram

## NICMOS Cooling SystemBlock Diagram Description

**The NCS operates with three fluid loops.**
**The Circulator Loop conveys cold Neon gas from the cryocooler to the NICMOS cryostat (and back).**
- The gas is moved by a tiny turbine electrical pump (72,000 RPM).
**The Compressor Loop internal to the cryocooler also uses Neon gas, and implements a reverse Brayton cycle refrigerator.**
- The compressor is a tiny turbine on the hot side driven by electrical power (420,000 RPM).
- The turboalternator is a tiny turbine on the cold side that does electrical work to generate the cooling (180,000 RPM).
**The Capillary Pumped Loop uses anhydrous ammonia gas and liquid to convey the heat (~ 400 Watts) generated by the cryocooler to the external radiator.**
- The CPL includes a flexible portion inside the Aft Shroud, and a rigid length running along the bottom of the HST.

## NCS Cryocooler Mechanical Layout

## NICMOS Cooling SystemComponents in the HST

## NICMOS Cooling SystemComponents Description

**The NCS cryocooler is attached to the HST Aft Shroud next to the NICMOS instrument.**
- Two flexible pipes connect the cold Neon gas in the Circulator Loop to the NICMOS.
- These pipes attach to two ground servicing cryogenic bayonets at the NICMOS.
**The Electronics Support Module (ESM) is attached to the HST Aft Shroud next to the Advanced Camera for Surveys (ACS) instrument.**
- Electrical connections to the NCS cryocooler are made with a Cross Aft Shroud Harness installed by the astronauts.
- Power is provided from a connection to the COSTAR assembly.
**The External Radiator is attached to handrails outside HST.**
- Attached to the NCS cryocooler via the Capillary Pumped Loop.
- Attached to the ESM for electrical control and monitoring.
**The Aft Shroud Cooling System (ASCS) uses a second radiator that is to be installed during a future Servicing Mission.**
- The hardware is fully qualified on the ground.
- ESM control is already in place in the on-orbit hardware.

## NCS Deployment Experience

**Prelaunch and Launch.**
- All planned activities completed without incident.
- Maintained vacuum pumping on the Circulator Loop components until door closure, and then the NCS was purged until T-0.
**EVA.**
- All planned activities completed without incident.
- NCS installed and passed aliveness and functional tests.
- External radiator is skewed a few degrees because of an interference between an MLI skirt and the HST (skirt stiffer than expected).
- Could have been fixed, but EVA time drove the decision to move on to other tasks.
**Servicing Mission Orbital Verification.**
- One transient turboalternator shutdown (by software) shortly after turn-on.
- No additional incidents.
- Cooldown progressed (~2x) slower than expected.
- Discrepancies in modeling the heat extraction efficiency and heat capacity.
- Caused an extended period of “surging”.
- Vibration, even during surging, is negligible.
- NCS/NICMOS reached operating temperature after ~25 days.
- The instrument has been operational ever since.

## NCS On-Orbit Performance

| Parameter |  | Value | Unit |
| --- | --- | --- | --- |
| NICMOS | Detector Temperature | 77.1 | K |
|  | Detector Temperature Stability | +/- 0.07 | K |
|  | Cryostat Cold Dome Temperature | ~ 72.8 | K |
|  | Cryostat Parasitics | ~ 0.4 | Watts |
| Cryocooler | Cold Gas Temperature to NICMOS | ~ 65 | K |
|  | Heat Rejection Temperature | 278 | K |
|  | Total Cooling Power | 6.5 | Watts |
| System | External Radiator Temperature | -28 to -10 | C |
|  | NCS Power Consumption | 375 | Watts |

**All parameters meet specifications and are within expected ranges.**

## The Restored NICMOS

**NICMOS works better than ever.**
- Detector quantum efficiencies increase with temperature.
- Original plan was 58K, driven by the solid Nitrogen cryogen.
- Actual operating temperature was ~ 62K with the cryostat thermal short.
- Current detector operating temperature is ~ 77K.
- An average of 30% increase in QE over the NICMOS bandpass.
- Dark current still at or below the sky background level.
- Readout noise is unchanged.
- Instrument point-spread function is unchanged.
- Mechanical conditions inside the instrument appear unchanged.
- In a typical faint object (mAB=22 mag, 1 arcsec2) at 1.6 um observed in NICMOS channel 2 (NIC2) for a typical time (1/2 orbit), the post-NCS data will have 30% more signal-to-noise than the pre-NCS data.
**The proof is in the pudding.**
- The ERO images confirm these expectations.

## NICMOS Operating Parameters

| Parameter | Pre-NCS | Post-NCS | Units | Comments |
| --- | --- | --- | --- | --- |
| Readout Noise | ~30 | ~30 | e-/readout | Unchanged. |
| Dark Current | 0.1 | ~0.15 | e-/pix/sec |  |
| QE (F110W) | 0.2 | 0.32 | QE = quantum efficiency.
F110W is short wavelength end (1.1 um) for NICMOS, F222M is long wavelength  (2.2 um) end. |  |
| QE (F160W) | 0.3 | 0.42 |  |  |
| QE (F222M) | 0.6 | 0.72 |  |  |
| Focus | See next chart. |  |  | Unchanged. |

## NICMOS Focus is Better Than Ever

**1.1 um (NIC1)**

**1.6 um (NIC2)**

**The restored NICMOS has a point spread function that demonstrates diffraction-limiting imaging.  The image on the left is taken with the highest resolution channel (NIC1) at 1.1 um.  The image on the right is with the medium resolution channel (NIC2) at 1.6 um.  Both images clearly show the sharp central core of a star and the first diffraction ring.**

## Conclusion

**All components installed in March 2002 during Servicing Mission 3B are now fully operational.**
- 100% servicing success.
- 100% deployment success.
**Hubble now enjoys twice the electrical power for science compared with pre-SM3B.**
- A combination of the new Solar Arrays and Power Control Unit.
**Hubble users have a powerful new visible camera (ACS).**
**Hubble users have a restored and improved near-infrared capability (NCS/NICMOS).**
**The outlook for new discoveries is better than ever.**

## To Follow Hubble’s Continuing Story ...

_**[http://hubble.nasa.gov/project-news/press-kits.html](http://hubble.nasa.gov/project-news/press-kits.html)**_
- This information package is available in PowerPoint or PDF using this link.
**http://hubble.nasa.gov**
- General information about the Hubble Space Telescope.
- Up-to-the-minute information during Servicing Missions.
- Live web cameras in HST clean rooms and control areas.
- Q&A for the HST Team during Servicing Missions.
- Extensive mission coverage during Servicing Missions.
**http://www.stsci.edu**
- All the Hubble pretty pictures are available here.
- This is the general scientific observation support site for the international scientific community.