Modelling and Constraints Assumptions

Modelling Assumptions

The assumptions described hereunder apply to the latest detailed scenario exercise (either current or carried out recently) and have been inherited from the Europa Flyby 7E1 detailed scenario exercise [7E1].

To obtain the assumptions applicable to a specific scenario please use the appropriate version of this document directly applicable to the scenario o interest.

Resources Assumptions

The combined Data Volume of all the instruments of one instrument type:

  • Geophysics: RIME, GALA, 3GM

  • In Situ: PEPLo, PEPHi, RPWI, J-MAG

  • Remote Sensing: SWI, UVS, MAJIS, JANUS

Need to be within the envelope provided by the segmentation. The share amongst instruments needs to be agreed during the Observation Timeline Harmonisation process.

The instrument type accumulated data volume envelopes are present in the repository, i.e: for ORB17: JUICE_PREOPS/PLANNING/SCENARIOS/S008_01_ORB17_321219_330108/ENVIRONMENT/SEGMENTATION, these envelopes are then evaluated with the appropriate Python Notebooks.

Spacecraft Modelling Assumptions

The assumptions described hereunder are applicable to the detailed scenario exercise and have been inherited from the Europa Flyby 7E1 detailed scenario exercise [7E1] and the PJ12 detailed scenario exercise [PJ12].

On-Board Data Storage

The following assumptions will be applied to the On-Board Data Storage:

  • No limitations for the payload generated data volume will be considered.

  • The SSMM is considered to be empty at the beginning of the scenario.

  • Data latency or SSMM status at the end of the scenario are not considered.

  • Selective downlink is not considered.

  • NAVCAM images and RADEM Data Volume are counted as part of the science budget.

Communication

The following assumptions will be applied to the S/C-Ground communications:

  • The MGA is still and parked in safe position out of the MGA downlink blocks.

  • MGA science downlink starts after 2 hours of contact.

  • For MGA downlinks, if the MGA Mask is not respected, the communication will be considered interrupted. The link will be considered immediately resumed when the MGA pointing is withing the “free envelope” again. In such cases the MGA minimum duration shall be observed.

  • All ground contacts during Jovian moon flybys will be conducted using the MGA.

  • For power computations, Solar Arrays shall be assumed to be in power optimized position at any time except if a phasing is requested.

Power

The power budget for this scenario has been estimated using the battery model as provided by Project [TOURN]. The platform power consumption, taken from [PWRRP] and corresponding to the Europa flyby for crema_3_1 was translated to be centered at PJ12 for the crema_5_0 trajectory. It includes the power needed by the following subsystems:

  • CPS: RCT + ME + PT

  • EPS: PCDU + UPCONV + SADA

  • Attitude and Orbit Control Subsystem: RW + STR + IMU

  • CDMS: CDMU + RIU

  • RADEM and NAVCAM

  • X and Ka band links

A conservative assumption considers the battery fully charged at the start of the scenario and a maximum allowed discharge of 60%.

The battery capacity is set to 90% BoL (4946 Wh) [SPWM], and the solar cells efficiency to 0.334 [SPWM]. A Maximum battery discharge capacity of 1982.92W has been considered [PWRASS].

Spacecraft Dynamics

TODO: Update with latest MPAD values especially if 4RW have been implemented.

The pointing analysis (spacecraft attitude during observations and slew computations between different pointings) is performed using the Attitude Generation Module (AGM) library which is used by OSVE (Pointing Tool, Pointing Tool Wrapper) and MAPPS.

A realistic wheel momentum management simulation, based on industry simulation, has been implemented [SPWM], where the constraints to validate the pointing in use are:

  • Maximum wheel momentum: 60.0 NM/s

  • Maximum wheel torque: 0.14 NM

Detailed values used for the dynamics such as the Spacecraft Inertia Matrix, Reaction Wheel orientations or Natural Bodies gravity constants are available at the AGM XML configuration file: PLANNING/SCENARIOS/S007_01_PJ12_320922_320926/CONFIG/AGM/CFG_AGM_S007_01.xml These values are derived from [SCIPR].

The assumptions for the tranquilisation time to be taken into account for pointing design are the ones concluded in [JANE] based on the requirement of 5 arcsec half-cone ACE:

Raster Scans: - there is a (conservative) tranquilisation period of 60s no matter the mean slew rate between 0.0043 and

0.0144 deg/s. Any additional stare time should correspond to the required measurement time.

  • for slew rates below 0.0024 deg/s, it is not necessary to wait for the 60s tranquilisation.

Continuous Scans: - For scan rates between 0.0017 and 0.0155 deg/s, there is a tranquilisation period of 200s for the

first scan line. The suggested approach is to add 200 sec to the 1st line, starting it further away (the spatial overhead computed according to the scan rate) from the nominal scan coverage so that the S/C arrives stabilised at the nominal scan start point, as illustrated in the Figure below.

Continuous scan design to take into account the dead zone corresponding to the tranquilisation time of the first line [JANE]_.

Continuous scan design to take into account the dead zone corresponding to the tranquilisation time of the first line [JANE].

SPICE Kernels in use

The SPICE Kernel data set used will be the subset provided by the latest version of the applicable Crema meta-kernel (MK) at any time: the MK will always be assumed to be the last version. The underlying reason of this is because during the detailed scenario process, the meta-kernel will be updated with the MTP science planning SPICE kernels that will be generated during the exercise for S/C attitude and Solar Arrays (SA) and Medium Gain Antenna (MGA) pointing.

Given that different meta-kernels will be applicable during the exercise, the MK_IDENTIFIER parameter defined in the MK will be used to identify the applicable version of the MK at a given meeting/milestone of the exercise. This will be appropriately recorded in the minutes of meeting if needed.

Instructions on how to setup the SPICE kernels are provided in SPICE Kernels Setup.

The other SPICE Kernels are subject to updates, including frames kernels (FK), instrument kernels (IK), attitude kernels (CK), etc.

Detailed Scenario Planning Rules

What is described in this section is a set of rules or guidelines that SOC takes into account during the Detailed Scenario process. These are not actual flight rules or constraints but the planning assumptions agreed between the MOC and the SOC.

The applicable operational constraints for the detailed scenarios are described in detail in the MPAD document [MPAD]. The MPAD also refers to the JUICE Spacecraft operational constraints document from Airbus [AIRB] for certain constraints. In addition the Flight Dynamics Database (FDDB) [FDDB] is always applicable.

Details of the rules broken down into categories are provided in the next sub-sections. A table summarizing the rules is provided hereunder:

SOC Planning Rules for the Detailed Scenario

Reference

Description

RUL-OTH-COM-001

HGA minimum contact duration is 3 hours (4-hour segments including slews) [MPAD].

RUL-OTH-COM-002

MGA minimum contact duration is 4 hours (excluding MGA-mask interruptions) [MPAD].

RUL-OTH-COM-003

X+Ka MGA and HGA contacts maximum duration is 8 hours [MPAD].

RUL-OTH-COM-004

Communication pointing blocks with HGA Earth pointing have phasing freedom with limitations.

RUL-ITH-COM-001

During X+Ka MGA and HGA telemetry transmission, instruments must be in a defined set of observations and/or modes as described in 30_modelling_and_constraints:Power limitation during downlink [DREC].

RUL-PTH-COM-001

The MGA setup for navigation during flybys is tracking mode from -6 to +6 hours around CA.

RUL-PTH-COM-002

MGA will not transmit (be in contact) when masked [FDDB].

RUL-OTH-POW-001

During battery-recovery segments, instruments need to be in a defined set of observations and/or modes as described in Battery Recovery Segments.

Battery Recovery Segments

Similarly to Downlink segments, the Battery Recovery Segments have a limited number of allowed instrument observations and/or modes in order to maximise the battery recovery time. The combination is as follows (from [DREC]):

  • PEP: Any observation with a Power less than 41 W

  • JANUS: JAN_IDLE

  • MAJIS: MAJ_SAFE

  • RPWI: Off

  • SWI: SWI_SAFE

  • 3GM: Standby

  • JMAG: Any of MAG_DL_* or MAG_CONTINOP_FIB_FOB_LIGHT_ONLY

  • RIME, UVS, and GALA off.

Note that these observations can be replaced by a combination that provides the same power envelope.

  • RUL-OTH-POW-001: During Battery Recovery segments instruments need to be in a defined set of modes.

Detailed Scenario Constraints

What is described in this section is a set of constraints that SOC takes into account during the detailed scenario process. These are not actual flight rules or constraints but the assumptions agreed with the PI teams, the MOC and the SOC.

The applicable operational constraints for the detailed scenarios are described in detail in the MPAD document [MPAD]. The MPAD also refers to the JUICE Spacecraft operational constraints document from Airbus [AIRB] for certain constraints. In addition the Flight Dynamics Database (FDDB) [FDDB] is always applicable.

The constraints that have been implemented and used during the exercise are provided in the table below and have a reference or identifier e.g. SOC-SPC-001

Implemented SOC Constraints for the Detailed Scenario

Reference

Description

Severity

Implemented

SOC-SPC-001

+X Panel Sun Exclusion: S/C +X shall not be illuminated at any time (MAJIS and SWI radiators) [AIRB].

Error

AGM

SOC-SPC-002

The calculated Battery state of charge shall not drop below 40% (or DoD higher than 60%) [MPAD].

Error

EPS

SOC-SPC-003

Minimum block durations for observations or slews of 2 minutes shall be observed [MPAD].

Error

AGM

SOC-JAN-001

The JANUS Cover Mechanism must be closed during thruster events

Error

EPS

The description of the rules implemented by the SOC and of [otential rules that either require clarifications or that are under discussion to be implemented, and are not included in the MPAD, are provided in the subsections below.

Spacecraft

SOC-SPC-001 +X Panel Sun Exclusion

S/C +X shall not be illuminated at any time (MAJIS and SWI radiators).

SOC-SCP-002 Maximum Battery Discharge

The calculated Battery state of charge shall not drop below 40% (or DoD higher than 60%) [MPAD].

SOC-SCP-003 Minimum Pointing Block Duration

Minimum block durations for observations or slews of 2 minutes shall be observed [MPAD].

Star Tracker Blinding

Star Tracker Blindings need to be avoided. The AIRBUS approach to consider STR blinding is by calculating the angle between the STR boresight direction and the S/C-Body direction. If this angle is smaller than the exclusion angle the blinding status is set to True. The applicable exclusion angles are summarized in the table below:

STR Blindings definition

Body

Exclusion Angle (deg) at Europa

Exclusion Angle (deg) other

Jupiter

15.5

13.5

Europa

19.0

17.0

Sun

26.0

26.0

Ganymede

N/A

15.5

Callisto

N/A

14.0

SWI

JANUS

SOC-JAN-001 JANUS Cover Mechanism must be closed during thruster operations

Warning

The modelling is not yet mature enough to know the status of the cover mechanism. However the constraint is implemented.

The JANUS Cover Mechanism must be closed during WOLs and TCMs

GALA

MGA motor impact on GALA operations

MGA Motors speed above 0.1 deg/s might impact GALA operations.

Observation Compatibilities

These observations compatibilities are checked during the Pointing Timeline Harmonisation.

The observation compatibilities are only checked when an observation is PRIME within a given PTR block. These incompatibilities are described in the following subsections.

The compatibility rules that are implemented in PTWrapper and the Pointing Tool are also listed in the table below and have a reference value e.g. OBS-PEH-001. The ones that are not implemented do not have a reference value.

Observation Incompatibilities implemented in the Pointing Tool/PTWrapper

Reference

Description

Severity

OBS-SWI-001

The SWI observation block minimum duration is 28 minutes.

Warning

OBS-SWI-002

SWI Pointing out of AT/CT range

Warning

OBS-SWI-003

SWI Drift along AT/CT out of range.

Warning

OBS-PEH-001

JENI target and sun concurrence avoidance.

Info/Warning/Error

Note that the boundary between Observation Compatibilities and constraints is not set in stone and can evolve in the future.

SWI

OBS-SWI-001 Minimum observation duration

The SWI observation block minimum duration is 28 minutes. If a PTR block that has a PRIME SWI observation is shorter than the threshold a WARNING is provided.

OBS-SWI-002 Pointing Mechanism within range

The target of the SWI observation needs to be within the range of the SWI pointing mechanism. This range is currently defined as:

  • AT along track mechanism (@ Jupiter phase)

  • CT cross track mechanism (@ Jupiter phase)

The half ranges are are AT = 72.057295, CT = 4.357295 [deg]. However, we use for now values from [SWI]: AT = 71.8965 and CT = 4.318 [deg]. The final decision on these values will be made based on data from NECP and PCWs.

the SWI boresight direction has been determined from NECP data to be offset by 39 and 58 steps in AT and CT respectively, which translates to:

  • AT0 = 39*29.92/3600 = 0.324 [deg]

  • CT0 = 58*8.67/3600  = 0.140 [deg] -> Updated to CT0 = 0.188 (Feb 5 2025)

This correction assumes JUICE +Z axis to be pointing exactly at coordinates (0,0) in the S/C frame. We lump every misalignment on S/C as well as SWI own mechanism offset into this single number for AT and CT.

OBS-SWI-003 Pointing Stability

In general, SWI requires pointing stability in order to be able to use their pointing mechanism for their observations. The S/C pointing as a rule is not stable to the degree expected (due to slews and S/C pointing requested by other instruments).

The target of the SWI observations needs not to drift too fast, this is known as pointing stability. This drift is currently defined as: The drift rate of AT and CT constraint is estimated from wind requirement as 1/10 of 600 GHz beam per 30 min, 6e-6 deg/sec. This was routinely met during NECP.

SWI plans to provide ranges specific to certain observations to enable more tailored checks.

PEPLo

NIM FOV Obstruction

When NIM is operating in neutral mode as defined by the PEPLo PEL_JUPITER_IN_SITU_IMAGING_NOMINAL_3 observation the Solar Array Angle (SADM) must be lower than 74 degrees in order to avoid the neutral gas inflow (i.e. sectors 1 and 4) blockage from the Solar Arrays.

A detailed description of the NIM FOV Obstruction is provided hereunder along with the NIM FOV obstruction as a function of the SADM angle.

PEP NIM Obstruction as a function of SADM angle

PEP NIM Obstruction as a function of SADM angle

  • Sector 1 Only the right-side panel is causing the obstruction of the FoV, entering the FoV of the instrument for angles between ~17 deg and ~163 deg.

  • Sector 2 This sector is mostly obstructed by some sort of pin located next to PEP NIM, obstructing a total amount of ~60 deg.

  • Sector 3 Still, the pin enters in the FoV of this sector, but few more parts can be appreciated. Two of the eight newton thrusters appear at the right side of the image, on its left, it is seen the bottom part of one of the RPWI LP 1, and finally next to the pin, the farthest side of the RIME (towards the HGA side) it is seen.

  • Sector 4 As the first sector, this one is obstructed by the left-side Solar Panel for angles between ~17 deg and ~163 deg.

  • Sector 5 At the left of the image, a small part of the Bus enters in the FoV from below, followed by the RPWI LP 4 and finally the furthest part of the RIME (side opposite to HGA)

  • Sector 6 Again, the top part of two of the newton Thrusters is seen, followed by the RPWI LP 2.

A schematic view of the NIM combined sectors FOV blocked by the S/C elements is provided in the figure below.

PEP NIM Sectors Obstruction

PEP NIM Sectors Obstruction

NIM RAM direction

When NIM is observing as per the PEPLo observation PEL_JUPITER_IN_SITU_IMAGING_NOMINAL_3, that in general can be defined as a interval of interest when the S/C-Moon altitude is less than 1000km or more generally +/- 10 minutes around CA, the +Z axis of the JUICE_CALLISTO_RAM SPICE frame should be within 5 deg of the direction the NIM sector directions: JUICE_PEP_NIM_NEUION_S* where *: 0, 1, 3, 4, 5 (Sector 2 is blocked).

RAM pointing stands for a pointing whose primary axis is the velocity direction; the RAM side of the S/C is the side that points in the direction of the satellite’s motion. It is called the RAM side because it is the side impacting/ramming into the fluid that the satellite moves through -such as the ionosphere-. The RAM vector is calculated by adding the JUICE S/C velocity to the orbital velocity of the Moon (in a Jupiter-centered frame). Alternatively, it is the JUICE velocity vector in a Moon-centered frame.

This requirement indicates that the NIM neutral mode FoV (disk-like shaped, parallel to the S/C x/y plane) should contain the JUICE-Moon RAM velocity vector, i.e. the velocity that JUICE rams into the exosphere of the moon, excluding the Sector 2.

PEPHi

OBS-PEH-001 JENI target and sun concurrence avoidance

For any time when JENI has a pointing requirement (is PRIME), the target and the Sun cannot be in the same FOV. Two FOV or rather field-of-regard (FOR) are considered: JUICE_PEP_JENI_FOR_PY and JUICE_PEP_JENI_FOR_MY with the following options:

  • Sun outside of FOR: Target is in PY FOR, Sun is completely outside JENI’s FOR (PY or MY). Ideal situation indicated by an INFO message.

  • Sun in the other FOR: Target is in PY (or MY) FOR, Sun is in MY (or PY) FOR:. Situation in which quality of observation is degraded indicated by a WARNING message.

  • Sun in the same FOR: Target and Sun are in PY (or MY) FOV. Full incompatibility indicated by an ERROR message.

3GM

MGA outages and interruptions impacting 3GM

The MGA outages and or interruptions due to the S/C masking need to be taken into consideration and communicated to 3GM.