Venus observations hst program 12433
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Venus Observations HST Program 12433. Objectives. Explain Venus observing strategy. Review areas of special concern with Venus observations and explain how these concerns are being addressed. Determine if the implementation is correct and complete. Why Is Venus Special?.

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Venus Observations HST Program 12433

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Venus observations hst program 12433

Venus ObservationsHST Program 12433


Objectives

Objectives

  • Explain Venus observing strategy.

  • Review areas of special concern with Venus observations and explain how these concerns are being addressed.

  • Determine if the implementation is correct and complete.


Why is venus special

Why Is Venus Special?

  • At its farthest, Venus gets to be about 47 degrees from the Sun.

  • HST is normally not permitted to point within 50 degrees of the Sun.


Venus observing program history

Venus Observing Program History

  • In 1995, HST observed Venus with GHRS and WFPC2 (GO 4518 and GO 5783).

  • In 1996, two GO Venus proposals (6607 and 6771) were approved by the TAC; and there was one GTO/WF2 program (6851) to observe Venus. All of these were cancelled by the STScI Director shortly after phase 2 submission.

  • In 1997, there was a GTO/STIS program (7581) to observe Venus. Much implementation work was done, but the program was then withdrawn by the PI.


Venus observing program history1

Venus Observing Program History

  • In 2003, HST observed Venus with STIS (GO 8659).

  • NASA program 12433 is now planned for:

    • December 27-28, 2010 (2010.361-362)

    • January 22, 2011

    • January 27, 2011


Scientific goals

Scientific Goals

  • Coordinated observing with ESA’s Venus Express mission.

  • Map variations in SO2, SO, S2, and other UV absorbers.

  • Constrain models of Venus atmosphere and climate evolution


Observing strategy

Observing Strategy

  • Observe while Venus is near maximum elongation

  • Observe while HST is in Earth’s shadow

    • A window of 9-14 minutes per orbit

  • Three visits of 2 orbits each.


Observing strategy details

Observing Strategy Details

Target Visibility

Target Visibility

Target Visibility

Shadow

Shadow

GS Pair Acq

at Venus+5D

Slew to

Venus

Slew to

Venus

Observe

Venus

Observe

Venus

Slew to

Venus+5D

Slew to

Venus+5D

GS Pair

Acqat

Venus+5D

Single GS

Acqat Venus

Single GS

Acq

at Venus

GS Pair

Acqat

Venus+5D

  • Initial GS Acq at Venus+5D

    • A pointing 5.5 degrees from Venus and 51.6 degrees from the Sun.

    • Minimizes slew distance to Venus

    • Precautionary measure to protect against large pointing error after slew


Observing strategy details1

Observing Strategy Details

Target Visibility

Target Visibility

Target Visibility

Shadow

Shadow

GS Pair Acq

at Venus+5D

Slew to

Venus

Slew to

Venus

Observe

Venus

Observe

Venus

Slew to

Venus+5D

Slew to

Venus+5D

GS Pair

Acqat

Venus+5D

Single GS

Acqat Venus

Single GS

Acq

at Venus

GS Pair

Acqat

Venus+5D

  • Single GS Acq at Venus

    • Saves about a minute versus pair acquisition

  • Venus science observation

    • Visit 01: two 153s exposures, Visit 02: two 58s exposures, Visit 03:116sand 2.5s exposures

    • STIS auto wave cal disabled


Venus appearance at observation

Venus Appearance at Observation

  • Apparent magnitude: -4.1 +/- 0.2

  • Surface brightness: +1.5 (average for 1 square arcsecond of illuminated portion of disk)

  • Apparent diameter

    • Visit 01: 28.5 arcseconds

    • Visit 02: 21.4 arcseconds

    • Visit 03: 20.4 arcseconds

  • Phase angle

    • Visit 01: 97.3 degrees

    • Visit 02: 89.9 degrees

    • Visit 03: 79.4 degrees


Vital statistics

Vital Statistics


Areas of concern

Areas of Concern

  • Guide star acquisition failure

  • Spacecraft or instrument problem shortly before scheduled observing time

  • FGS exposure to Venus

  • HST being exposed to sunlight while pointed within the Solar Avoidance Zone (SAZ)

  • HST safing while pointed within the SAZ


Guide star acquisition failure

Guide Star Acquisition Failure

  • Concern

    • If attitude error is greater than the search radius, the guide star acquisition could fail resulting in the loss of the science.

  • Precautions

    • The chances are minimized by the short 5 degree slew to Venus.

    • Too late to perform guide star acquisition test. Stars are in solar avoidance zone.

    • Science exposures will proceed even if GS acquisition fails.

      • Special commanding specified to ignore “take data” flag.

      • AQEXPIRE timer adjusted via SMS edit.


Problem shortly before observation

Problem Shortly Before Observation

  • Concern

    • An unrelated problem may threaten the Venus observing window.

    • In 1995, the Venus observation was originally lost due to an unrelated safing; but it was quickly replanned and executed successfully.

    • The 2003 Venus observations were delayed from 2001 due to the failure of the STIS side 1 electronics.


Problem shortly before observation1

Problem Shortly Before Observation

  • Remedy

    • Visit 01: Second choice coordination opportunity with Venus Express on January 23, 2011

    • Visit 02: ???

    • Visit 03: ???


Fgs exposure to venus

FGS Exposure To Venus

  • Concern

    • If the attitude error is large enough (> 300 arcseconds), an FGS could possibly see Venus and cause potential bright light exposure to the FGS photo-multiplier tubes.

  • Precautions

    • Choose a guide star that is as far as possible from Venus.

    • The chosen guide star is:

      • Visit 01: magnitude 12.4 and 15.5 arcminutesfrom Venus.

      • Visit 02: magnitude 11.7 and 16.8 arcminutes from Venus.

      • Visit 03

        • Orbit 1: magnitude 11.2 and 13.8 arcminutes from Venus

        • Orbit 2: magnitude 11.5 and 12.5 arcminutes from Venus


Hst fov visit 01

HST FOV – Visit 01


Hst fov visit 02

HST FOV – Visit 02


Hst fov visit 03 orbit 1

HST FOV – Visit 03 Orbit 1


Hst fov visit 03 orbit 2

HST FOV – Visit 03 Orbit 2


Hst in the sun

HST in the Sun

  • Concern

    • While slewing away from Venus, HST will be exposed to sunlight and pointed inside the SAZ for up to 3m 32s.

    • HST’s maximum previous exposure to sunlight while pointed inside the SAZ was 2m 30s (2003 observation).

    • Pointing inside the SAZ while HST is in sunlight can be tolerated for at least 15 minutes before the temperature of the paint inside the OTA would become a contamination issue. (EM-MOSES-1267 and EM-MOSES-1268)


Hst in the sun1

HST in the Sun

  • Precautions

    • Guide star search radius was reduced in order to save 10-30 seconds of acquisition time.


Hst safing

HST Safing

  • Concern

    • HST must not enter inertial hold safe mode while pointed within the SAZ.

  • Precautions

    • Disable inertial hold safe mode such that any condition that would normally lead to inertial hold leads to software sun point safe mode instead.

    • This was done in both prior HST observations of Venus.


Hst safing1

HST Safing

  • Concern

    • If there is an anomaly with the 486 flight computer, software sun point safe mode might not be achieved.

  • Precaution

    • Be ready to command HST into hardware sun point safe mode.


Additional information

Additional Information


Observing strategy details2

Observing Strategy Details

Observe

Venus+5D

Target

Visibility

Target

Visibility

Target

Visibility

Display as seen from HST

Shadow

Shadow

GS Pair Acq

at Venus+5D

Slew to

Venus

Slew to

Venus

Observe

Venus

Observe

Venus

Slew to

Venus+5D

Slew to

Venus+5D

Observe

Venus+5D

Single GS

Acq

at Venus

Single GS

Acq

at Venus

GS Pair

Acqat

Venus+5D

GS Pair

Acqat

Venus+5D


Hst s view of venus t 0

Earth

Venus+5D

Sun

Venus

HST’s View of Venus (t = 0)

Venus is in Earth occultation. The Sun is not. HST would be pointed at Venus+5D at this time.


Hst s view of venus t 5 min

HST’s View of Venus (t = 5 min)

The Sun is moving toward setting.


Hst s view of venus t 10 min

HST’s View of Venus (t = 10 min)

The Sun is moving toward setting. The terminator becomes visible on the Earth.


Hst s view of venus t 15 min

HST’s View of Venus (t = 15 min)

The Sun is very close to setting.


Hst s view of venus t 20 min

HST’s View of Venus (t = 20 min)

The Sun has set. HST is now in the Earth’s shadow.


Hst s view of venus t 25 min

HST’s View of Venus (t = 25 min)

Venus is very close to rising. At about this time, HST will begin its slew from Venus+5D to Venus


Hst s view of venus t 30 min

HST’s view of Venus (t = 30 min)

Venus has risen. At about this time, HST will complete its slew to Venus; and the guide star acquisition will begin.


Hst s view of venus t 35 min

HST’s View of Venus (t = 35 min)

At about this time, the guide star acquisition will finish; and the science observation will begin.


Hst s view of venus t 40 min

HST’s View of Venus (t = 40 min)

At about this time, the science observation will finish; and the slew to Venus+5D will begin.


Hst s view of venus t 45 min

HST’s View of Venus (t = 45 min)

The Sun is very close to rising.


Hst s view of venus t 50 min

HST’s View of Venus (t = 50 min)

The Sun has risen. HST is now out of the Earth’s shadow. The slew to Venus+5D finishes a couple of minutes after sunrise.


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