Goddard Ground Calibrations

1. Scope

While ACS is at Goddard Space Flight Center (GSFC) during its first visit, we will have several opportunities to obtain vital calibration data. These include :

• Calibration time during the Thermal Vacuum (TV) test.
• Alignment tests bracketting the TV test.
• Designated calibration time before and after the TV tests.

The calibrations planned for the TV run have been planned in detail. In the following, we outline our plans for the remaining ground-calibration time at GSFC.

The alignment and calibration data will be obtained in the GSFC clean room. ACS will be housed in a dark box which will be purged with dry N₂(at least for portions of the tests). For the alignment portion RAS/CAL will be the stimulus. For the remaining designated calibration time, STUFF and RAS/CAL will be the stimuli. RAS/CAL will be fed by a variety of sources, including a HeNe Laser, a D₂ lamp, and (if we are lucky) a monochromator. The detectors that will be tested are the High Resolution Camera (HRC#2), the Solar Blind Channel (SBC), and the Wide Field Camera (WFC#2). The last of these will not be available until January 1999.

2. Goals

The goals of the tests include :

1. Obtain pre- and post-TV data to compare with data taken during TV.
2. Shake down the equipment and procedures we will use in the TV campaign.
3. Run CCD tests requiring a UV source.
4. Run SBC tests requiring a point source.
5. Run non-detector specific WFC & HRC tests.
6. Channel throughput vs. for SBC and HRC.
7. Other tests, especially those requiring RAS/CAL.

In general flat-fielding will not be the emphasis of these tests, although we will be testing the capabilities of STUFF for obtaining uniform flatfield illumination. This is because, problems with the knife-edge mask in front of the HRC and WFC detectors render pointless the task of obtaining final ground flats with these detectors. High S/N flats will be obtained for the SBC during the TV campaign.

Because of the ever-present threat (and opportunity) of schedule changes, we have planned the calibration tests to be modular, and prioritized to insure that the most important tests are the ones that get done if the duration is cut. The above goals are listed roughly in order of priority.

3. Calibration Items

The following is a list of specific calibration items that will be addressed with these tests. They are arranged in rough priority order.

ID	Title	Channels	Stimulus	Source	Purge	Goals	Notes
A	STUFF shakedown	SBC (HRC?)	STUFF	PtNe1,2, Xe, Kr	Yes	2	lamp functionality; uniform illumination; PMT cal (HRC); pinhole splat location; background light leak check
B	Image quality; focus, tip/tilt	SBC, HRC, WFC	RAS/CAL	D2(SBC)HeNe	SBC	1,4	RH procedures: 1h, 2h GC procedures: 21s, 22s
C	TV calibration SMS dryruns	HRC, WFC	Internal	Tungsten	No	1	TV procedures: 1h, 2h, 3h, 6wh, 1w, 2w, 3w
D	CCD Quantum efficiency hysterises	HRC, WFC	RAS/CAL (Alt -STUFF)	D2, QTH	No	1,3	procedure: 23h
E	CCD Overfull well test	HRC, WFC	RAS/CAL (Alt -STUFF)	D2, QTH	No	1,3	procedure: 24h
F	SBC out of band rejection	SBC, HRC	RAS/CAL	Monochromator	No	4
G	Ramp-filter throughput vs.	HRC, WFC	RAS/CAL	Monochromator	No	5,6	If no monochromator, determine filter offset spacing to use in later tests.
H	Throughput vs. (most filters)	HRC, SBC, WFC	RAS/CAL	Monochromator	SBC	4,6	Red leak of blue filters if no monochromator
I	Scattered light test Ghost image search	HRC, WFC	RAS/CAL	D2	SBC	3,4,7
J	Illumination angle test	HRC, SBC	STUFF	PtNe	SBC	7	TV procedure: 8s
K	Prism/Grism dispersion	SBC, HRC, WFC	RAS/CAL	Monochromator	SBC	4
L	Polarimetry calibration	HRC	RAS/CAL	Monochromator + polarizing prism	No	7
M	Shutter shading, linearity	HRC, WFC	STUFF	PtNe	No	1,5,7
N	CCD Fringing	HRC, WFC	RAS/CAL	Monochromator	No	7

4. Calibration Campaigns

Campaign : Pre-TV (December 1998)

ACS location : GSFC clean room - dark box

Stimuli : RAS/CAL, STUFF, RAS/CAL + Monochromator

Timeline :

Seq.	Item	Title	Det.	Duration(approx)	Notes	Status
1	B	Image quality; focus tip/tilt	HRC	4hr
2	B	Image quality; focus tip/tilt	SBC	6hr
3	C	TV calibration SMS dry runs	HRC,WFC	9hr	Spare time filler
4	D	CCD Quantum efficiency hysterises	HRC	7hr
5	F	SBC out-of-band rejection	SBC, HRC	3hr
6	I	Scattered light test / Ghost image search	HRC	2hr
7	A	STUFF shakedown	HRC,SBC	3 days
8	D	CCD Quantum efficiency hysterises	HRC	7hr	If needed (I.e. not done with RAS/CAL)
9	J	Illumination angle test	HRC (SBC)	2hr (2 days)	SBC test contingent on HRC results
10	M	Shutter shading, linearity	HRC	3hr	Spare time filler
11	B	Image quality; focus tip/tilt	HRC	4hr	Alignment repeatability
12	G	Ramp-filter throughput vs.	HRC	5hr
13	H	Throughput vs. (most filters)	HRC (SBC)	2 days

Marks in the status column above indicate :

• : Task attempted and completed.
• : Task attempted, but either not completed, or requires further work.
• No marks : task not attempted.

Campaign : Pre-TV (January/February 1999)

ACS location : GSFC clean room - dark box

Stimuli : RAS/CAL, internal lamps

Timeline : Plan ? What plan ? Basically we are doing alignment work, some noise debugs and dry running SMS's.

Campaign : Post-TV (March 1999)

ACS location : GSFC clean room - dark box

Stimuli : RAS/CAL

Timeline :

This page was written by G. Meurer. It is incomplete and to some extent, outdated.