Документ взят из кэша поисковой машины. Адрес оригинального документа : http://www.stsci.edu/ops/swat/safing/95008/93-4.txt Дата изменения: Wed Jan 11 19:28:06 1995 Дата индексирования: Sun Mar 2 00:58:15 2014 Кодировка: Поисковые слова: shadow

Date: Fri, 28 May 93 13:15:13 EDT
From: Glenn Miller
To: sponsler, krueger, lucks, giuliano, gerb, bose, rdouglas, jackson, durkin,
vick, mrose, asson
Subject: Re: [DOXSEY@avion.stsci.edu: Refinements (eg complications) to Solar Array operational rules]

We'll need 1 spike person to come. Trans and Pep optional
Glenn

Date: 28 May 1993 09:26:15 -0400 (EDT)
From: DOXSEY@avion.stsci.edu
Subject: Refinements (eg complications) to Solar Array operational rules
To: mcgrath@stsci.edu, johnston@stsci.edu, miller@stsci.edu


John Isaacs has been working with the GSFC and PASS staff
to define more complete requirements on the ground system given the
SADE-1 failure. The new, and hopefully final, requirements will
provide some additional scheduling flexibility, some additional
restrictions, and are more complicated than the current rules.
The attached note from John summarizes the situation. I would
like to have a meeting on Thursday June 3 from 12:30 - 2:00
in N310 to discuss implementation and operational plans for
responding to these requirements.

Rodger



From: STOSC::ISAACS "John" 27-MAY-1993 18:17:42.46
To: DOXSEY,DUFFORD
CC: ISAACS
Subj: Discussion of issues pertaining to SADE-1 failure accomodation.

SADE-1 FAILURE ACCOMODATION:
---------------------------

As a result of the SADE-1 failure, normal commanding of the solar arrays
has been disabled in PASS. The purpose of this memo is to describe
the recently proposed restrictions imposed as a result of the SADE-1
failure and to discuss the implications of these restrictions on science
operations. Following distribution and review of this memo, a meeting of
operations, development and engineering will be held to discuss operational
procedures and possible software enhancements.

OVERVIEW:
--------

The SADE-1 may be replaced by the servicing mission in December, 1993.
Until after the servicing mission, solar array orientation will be limited
and solar array slewing will be minimized. Solar array orientation will be
limited such that the solar array normal is between 90 and 120 degrees from
the +V1 axis (beginning with the 172 SMS) until September 1993. Beginning
in September 1993 the maximum angle will be increased to 125 degrees.
Solar array slewing will be minimized nominally by limiting the number of
solar array slews to three per week, although a greater frequency will be
allowed if necessary for science operations. In addition, vehicle
orientations which result in shadowing of the solar arrays by the high gain
antennas or by the vehicle body will not be permitted.

Because of the limitations on solar array orientation and slew frequency,
the solar arrays will generally not be at optimal orientation (i.e. with
the solar array normal pointed at the sun). As is the case when the
vehicle is at an non-optimal roll orientation, limits will be imposed on
the magnitude of the sun to solar array normal angle (sun incidence angle)
and the duration of operations at orientations which result in large sun
incidence angles. The new restrictions provide for unlimited operations at
sun incidence angles of less than 30 degrees. Limited operations at
angles between 30 and 40 degrees which are dependent on the minutes of sun
per orbit will be permitted after type #28 command management is resumed by
PASS.

These restrictions limit observation of targets near the ecliptic and
observations which require non-optimal roll angles. Observation of targets
near the ecliptic is restricted because of limits on the maximum sun to +V1
axis (the sum of the maximum solar array orientation and maximum sun
incidence angle). Under current operations, the maximum sun to +V1 axis
angle is 145 degrees. Beginning with the 172 SMS, the maximum solar array
orientation angle will increase to 120 degrees, and the maximum sun to +V1
axis angle will increase to 150 degrees. After PASS resumes type #28 command
management, the maximum solar sun to +V1 axis angle will increase to 160
degrees. Finally, beginning in September the maximum sun to +V1 axis angle
will be 165 degrees. Thus, targets near the ecliptic will not be
observable at certain times of the year. Observations which require
non-optimal roll angles are further restricted, as the maximum sun to +V1
axis angle is reduced to satisfy limits on the maximum sun incidence angle,
and by limits on roll angles to avoid solar array shadowing.

There are three primary concerns which need to be addressed:

1. There is no software support to limit solar array slew frequency,
determine when solar array slews are necessary, and ensure that a solar array
slew can be executed in parallel with the corresponding vehicle slew.
Although SPIKE and SPSS currently have software in operation which enforces
restrictions based upon limitations in solar array orientation, significant
manual processing of calendars is required.

2. The restriction to avoid solar array shadowing will significantly reduce
allowable roll angles. To implement this restriction, the solar array
shadow tables will specify for a given sun to +V1 axis angle the maximum
roll angle at which the solar arrays are not shadowed for any allowable
solar array orientation. The imminent change to the maximum sun incidence
angle (from 30 to 40 degrees), and the eventual change to the
maximum solar array orientation angle (from 120 to 125 degrees) will
further reduce allowable roll angles by about 5 degrees for sun to +V1 axis
angles of 90 to 130 degrees. The decision to implement these changes
should be based upon the relative importance of large off-nominal roll
angles vs. large sun to +V1 axis angles.

3. Neither SPSS nor PASS can implement the new restrictions limiting the
duration of operations at sun incidence angles between 30 and 40 degrees
without software changes. The software change required for SPSS is
minimal. However, the ability of PASS to implement the new restrictions is
severely handicapped by the changes PASS implemented in response to CCR
3291, which removed the capability to limit operations at large sun
incidence angles based upon minutes of sun per orbit. Setting conservative
values for the existing PASS implementation will eliminate the flexibility
provided by the new restrictions, while setting liberal values places some
of the responsibility for enforcing the restrictions on SPSS.

RESTRICTIONS:

The following restrictions will apply:

1. Solar array orientation will be limited such that the solar array normal
is between 90 and 120 degrees from the +V1 axis until September 1, 1993.
After September 1, 1993, the solar array orientation will be limited such
that the solar array normal is between 90 and 125 degrees from the +V1
axis.

Several factors contributed to the formulation of this restriction.

a. The maximum sun incidence angle which will support S/W safemode is
30 degrees based upon the solar array output in July, 1993. The last
significant minimum in solar array output is in August. After this
time, the S/W safemode will be supportable with a sun incidence angle
of 35 degrees until the servicing mission in December. The solar
array output at this angle will support a "modified software
sunpoint" load comprising the average hardware load, the DF-224,
the GHRS LVPS, WFPC TECs and the SI C&DH.

b. The maximum sun to solar array normal angle which will support
H/W safemode between now and the servicing mission is 45 degrees.

c. The worst-case solar array orientation error is 3 degrees from the
commanded orientation.

d. The worst-case solar array braking distance is currently estimated
to be 36 degrees. This is the angle through which the solar arrays
could rotate before excessive array rotation is detected and halted
by the solar array rotation safing check. It is based upon a solar
array rotation safing check angle of 14 degrees.

e. The solar array rotation safing check angle will be 8 degrees. The
current value is 14 degrees, but it is planned to install the new
limit soon after the DF-224 Version 9.0 installation.

f. The maximum orientation error due to coarse sun sensor accuracy is 3
degrees.

In the normal safemode orientation, the +V3 axis is pointed to the sun.
To support S/W safemode, the solar array orientation will be limited to +/-
30 degrees from the +V3 axis (maximum sun incidence angle which will
support S/W safemode), or 60 to 120 degrees from the +V1 axis.

If the solar array orientation due to solar array runaway is more
than 45 degrees from the +V3 axis, the solar array orientation cannot
support H/W safemode at a +V3 sunpoint attitude. If the solar array normal
is more than 45 degrees from the +V3 axis in the -V1 axis direction, then
it may be possible to execute a real-time command to slew the vehicle to a
-V1 sunpoint attitude. Thus, the risk of a solar array runaway in the -V1
direction which results in a solar array normal to +V3 axis angle greater
than 45 degrees is considered acceptable. On the other hand, the risk of a
solar array runaway in the +V1 direction which results in a solar array
normal to +V3 axis angle greater than 45 degrees is considered
unacceptable.

The solar array orientation will be limited to ensure that a solar
array runaway, in the event of a SADE-2 failure during a solar array
slew, will not result in a solar array angle less than 45 degrees.
The limit on solar array orientation of 90 degrees is based upon a
34 degree runaway, 8 degree safing check angle, and 3 degree uncertainty
in solar array position.

2. Vehicle orientation will normally be limited such that the sun to solar
array normal angle is less than 30 degrees. The angle may be between 30
and 40 degrees for limited periods of time, and will require a
corresponding recovery period at angles less than 30 degrees. The
recovery period will be shorter if the incidence angles during the
recovery period are less than 15 degrees. The maximum duration
at incidence angles greater than 30 degrees increases, and the
corresponding recovery period decreases, with increasing minutes of
sun per orbit.

This represents a significant change to the previous version of this
restriction, which normally limited the incidence angle to less
than 15 degrees and permitted incidence angles between 15 and 30 degrees
for limited periods of time with corresponding recovery periods.

The following table specifies the current values of the maximum duration
and recovery times as a function of minutes of sun per orbit which are
proposed for the new restrictions.

Minutes of Max Duration
sun/orbit at >30 degrees Recovery Time (orbits)
(orbits) at <15 Deg at <30 Deg


60 4 4 21
62 6 3 7
64 15 2 4
66 33 2 3
68 unlimited 0 0

3. Vehicle orientation will be limited such that the solar arrays are not
shadowed by the High Gain Antenna or by the vehicle body. This restriction
limits vehicle roll (deviation from optimal orientation which places the
sun in the V1-V3 plane) as a function of sun to +V1 axis angle and solar
array orientation angle.

The following table specifies the maximum roll angles at various sun to +V1
axis angles which avoid solar array shadowing for various solar array
restrictions. These restrictions are limited solar array orientation
(either 90-120 or 90-130 degrees) and maximum sun incidence angle (either
30 degrees or 40 degrees). Due to solar array position uncertainty, the
solar array shadowing restriction will be applied for solar array
orientations from 87-123 and 87-128 degrees, but we have not computed
values for these ranges at this time.

Included in the table are the maximum roll angles based upon optimal
solar array orientation, which formed the basis of the solar array
shadowing restriction prior to the SADE-1 failure.

Sun to +V1 Axis Angle
SA restriction:
90 95 100 105 110 115 120 125 130 135 140+
------------------------------------------------------------

Optimal SA 25 25 26 27 28 29 28 27 26 26 27

SA 90-120
sun-SAN <=30 24 24 22 23 24 25 27 28 30 30 30

SA 90-120
sun-SAN <=40 22 22 22 23 23 23 23 25 27 30 30

SA 90-130
sun-SAN <=30 24 24 20 18 19 20 22 24 26 28 30

SA 90-130
sun-SAN <=40 19 18 17 18 19 20 22 24 26 28 30

When the limit on solar array orientation is relaxed from 120 degrees to
125 degrees, the roll angles which do not result in shadowing at any
allowable solar array orientation will be reduced by as much as 5 degrees.
Thus, changing the solar array orientation restriction to permit
observation of targets at sun to +V1 axis angles of 170 degrees requires
changing the solar array shadowing restriction to reduce allowable roll
angles by up to 5 degrees on other targets (particularly those at sun to
+V1 axis angles of 100-105 degrees).

IMPLEMENTATION:
---------------

The new restrictions have several implications on ground system software
and operations.

1. Restrictions on solar array orientation.

This restriction will be implemented in PASS by modifying existing PDB
fields.

This restriction was implemented in SPIKE and SPSS. The implementation
requires specification of a range of solar array orientations which are
permitted over a specified time interval.

2. Restrictions on when certain targets may be observed due to maximum
sun to +V1 axis angles.

This restriction will be implemented in PASS upon approval of a CCR which
is currently in process.

This restriction was implemented in SPIKE and SPSS, by changing the
computation of sun incidence angles to include solar array orientation.
Thus, all targets are now subject to the "off-nominal roll" restriction.

3. Restrictions on off-nominal roll now that sun to solar array normal
incidence angle is not just a function of sun to +V1 axis angle but also
non-optimal solar array orientation.

The restriction includes dependencies on minutes of sun per orbit. This
dependency was previously included in CARD restriction 3.1.5.11 but was
recently removed by CCR 3192. SPSS did not implement software changes in
response to this CCR, but PASS removed the capability to specify
dependencies based upon minutes of sun per orbit when CCR 3192 was
implemented.

This new restriction differs from the previous restriction. The maximum
durations and recovery times are now also dependent upon minutes of sun per
orbit, and the recovery times do not depend upon the actual durations.

4. Restrictions to avoid solar array shadowing, which may occur at
significantly smaller roll angles than before due to non-optimal solar array
orientation.

This restriction will be implemented in SPSS and PASS to avoid shadowing at
all possible solar array orientations by changing PDB values.

This restriction will require a PASS implementation to check for solar
array shadowing when sun incidence angles are within "normal" limits.
This may not be a problem if "normal" is defined as sun incidence angles
less than 15 degrees, with unrestricted durations for sun incidence angles
of up to 30 degrees.

5. Restrictions on solar array slew frequency.

This restriction will be enforced in PASS by providing an SMS statement
(nominally in the merge SMS) which identifies the desired solar array
orientation at a specified time.

This restriction will be enforced in SPIKE and SPSS by specifying the
desired solar array orientations and corresponding time intervals.


CURRENTLY PROPOSED PASS IMPLEMENTATIONS:
----------------------------------------

Currently, DF-224 power system safemode tests and corresponding PASS
management of the safemode tests via type #28 commanding have been
disabled, as well as PASS commanding of the solar arrays. PASS cannot
accurately predict HGA blockage by the solar arrays, compute sun
incidence angles for constraint checks and issuance of the type #28
command, or perform other power management constraint checks.

A CCR is in process to modify PASS software to:

1) process an SMS statement that will allow PASS to command SAs to optimal
orientation within a specified SA angle range

2) compute sun incidence angles as a function of deviation from optimal
roll and solar array orientation

3) issue type #28 command when the solar arrays are shadowed or when the
sun to solar array normal incidence angle exceeds a data base specified
limit.

PASS removed the software that implemented the previous version of
CARD restriction 3.1.5.11, which included dependencies on minutes of sun
per orbit.


RECOMMENDATIONS:
---------------

1. Modify SPSS to permit implementation of the restriction on sun to solar
array incidence angles with dependencies on minutes of sun per orbit.
Recommend that PASS software be modified accordingly, but otherwise
establish the PASS data base parameters to support a nominal value of
minutes of sun per orbit (e.g. 64 minutes) and rely upon SPSS
implementation to satisfy restrictions for smaller values. At the least,
the SPSS change might be to simply remove the dependency of the recovery
time on the actual duration of the off-nominal operations.

2. Develop a tool which analyzes schedules in SPSS to identify required
solar array orientations and slews, and calculates solar array slew times.

3. Modify SPSS to at least permit specification of a minimum slew time to
ensure that slews which require parallel solar array slews are of
sufficient duration. Otherwise, modify SPSS to identify required solar
array slews from the solar array orientations already specified and
calculate the solar array slew duration as part of the slew calculation.

4. Determine whether it is possible to implement a solar array shadow table
based upon a maximum solar array orientation of 120 degrees, and nominally
limit solar array orientations to the range 90-120 degrees, and override
the maximum sun incidence angle from 40 to 50 degrees for observations
which require sun to +V1 axis angles greater than 160 degrees.

Because the SADE-1 may be replaced by the servicing mission, significant
software modifications are neither warranted nor feasible (development
efforts could easily extend beyond the servicing mission time-frame).
Thus, certain enhancements such as solar array shadow tables which
are indexed to solar array orientation should not be considered unless it
is apparent that the SADE-1 will not be replaced.