ATHENA mission operations concept with a special ... - Cosmos - ESA

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schedule updates and on-board software maintenance. The facilities will ... Checking, reformatting, scheduling of command requests for payload activities.
ATHENA mission operations concept with a special view on ToO M.G.F. Kirsch, K. Symonds European Space Agency, European Space Operations Centre, Darmstadt, Germany

XMM

ESA UNCLASSIFIED - For Official Use

Standard ESA ground segment

ATHENA specialities Spacecraft (S/C)

km

Athena

Ground Station Network (GS) km

km

Figure Figure 2-2 : Example off a large amp plitude quas si-halo orbit1 t about the Sun-Earth S Liibration Poin nt 2 left: XMM-Newton and Athena

The chief advantagees of orbits about SEL L2 are (I) a constant thermal t en nvironmen nt, since right: Example if a large amplitude quasi they can be b designed d to be ecliipse free, and a (II) a liimited com mmunicatio on distancee. Anot around L2and advantagee for astron nomy misssions ishalo tha atorbit the Sun, Earth d Moon are all located d in one hemispheere as seen from the SC. S Such an o orbit can bee reached via v a so called ‘free’ trransfer traj ajectory, no ot requiring g any q  Launch 2028 (Ariane-64 from Kourou) determiniistic orbit insertion i m manoeuvre after Earth h departurre. The SC travels on the so called stab ble manifo old toward its operatiional orbit about SEL L2. A typica al transfer traject q  5 +1 year science mission on the staable manifo old of the target t orbitt is depicteed in Figuree 2-3. The full stable manif of the targ get orbit orbit is shown. of o the man nifold interrsect with the t near-Ea arth q  Orbit: a large amplitude quasi-halo aboutSoome theparts co-linear Sun-Earth environm ment (the Ea arth is at th he origin), where thee launcher can place the t SC on the t stab Libration Point 2 (SEL2) manifold of the targ get orbit.

Control Centre S/C

G/S Flight Control System

Flight Dynamics System

Simulator

Data Distribution System

Mission Planning System

q  Communications link: X-band q  science data volume: compatible with 4h/day science pass (downlink rate: 8 Mbit/s) q  Off-line monitoring and control approach: the spacecraft will be operated offline by following a pre-scheduled timeline (planned sequences of operations for 7 days) stored on board, and uploaded by the ground at regular intervals. Monitoring will also be off-line, due to the non-continuous contact with the ground q  Autonomous slews according to target quaternions, swap of instruments, instrument initialisation and thermal control settings. q  Exchange of files between space and ground shall follow the CFDP protocol

Onboard Software Maintenance

Figure 2-3: Stable man nifold and fr ree transfer option o to an n SEL examp ple orbit. The e free transffer trajectory iis the single blue line pa assing throug gh the inner r libration po oint orbit re egion

q  Spacecraft autonomy design is safe with ground reaction times larger than 7 days during nominal operations phase à spacecraft continues mission Page 11/39 product generation for a minimum of 3ns Document days without ground contact ATHENAperiod Misssion Assumption

Mission Archive

Issue Date 14/02/2015 Ref DHSO-MGT-MA AD-1001-HSO-O OSA

from users

to users

q  Targets of Opportunity (ToO) response requirement within 4 h from detection

Note: Nominal control centre availability - 8 h / day manning - 24 h / day automated processes

ATHENA ground segment baseline

ATHENA Target of Opportunity (ToO) trade offs

q  Ground segment preparations starts 5 years prior to launch q  One 35m ground station for nominal operations (New Norcia, Australia). LEOP and selected transfer phases supported by Malargüe and Cebreros 35m stations q  All telecommanding and telemetry are via X-band during ground station passes q  Achievable downlink data rate of ~8.7 Mbit/s has been assumed, with a High Gain Antenna. 10 % overhead for packet headers and housekeeping data (equivalent to a science data rate of 8 Mbit/s). The maximum achievable data rate for X-band according to the ECSS standard is slightly higher, albeit still limited by a maximum bandwidth requirement of 10 MHz). q  Ranging compatible with high data rate downlink is assumed to be enabled for full duration of the downlink pass q  Computer configuration used in the MOC will be derived from existing systems q  Flight Control System will be based on infrastructure development (common core replacing the current SCOS 2000 control system), using a distributed architecture for all spacecraft monitoring and control activities, including the following facilities: §  Telemetry reception facilities for acquisition, quality checking, filing and distribution. §  Telemetry analysis facilities for status/limit checking, trend evaluation §  Telecommand processing facilities for the generation of commands for control, master schedule updates and on-board software maintenance. The facilities will provide also uplink and verification capabilities. §  Monitoring of instrument housekeeping telemetry for certain parameters that affect spacecraft safety , command acceptance and execution verification. §  Checking, reformatting, scheduling of command requests for payload activities. §  Operations automation tools as required §  Offline spacecraft and payload housekeeping analysis for trend analysis and trouble shooting §  Use of CCSDS file delivery services protocol (+ updates as required for file management)

Figure 2: Ground Station Visibility example no visibility (red) visibility above 10deg inclination (green) visibility above 5 deg inclination (yellow)

q  XMM-Newton has been operating for 15 years a very successful and efficient ToO system (>400 ToO in the last 15 years) We took this system as baseline and tailored it for the ATHENA case q  ATHENA has stringent Target of Opportunity requirements: for 80% of instances there shall be a maximum of 4 h between an external alarm and the start of observations. In order to satisfy the 80% requirement it is considered sufficient to perform the ToO operations on a best effort basis, i.e. not as a guaranteed service. This reduces the effort for the communications (i.e. small station redundancy and maintenance concept) and the operations (on call concept). Concept for ToO: q  Prerequisite: high level of spacecraft autonomy à perform operations without Flight Dynamics support. q  HGA always pointed to Earth and configured for TC reception à use of small ground stations for ToO communications. q  Small ground stations are located at sites distributed over the world to enable for 24 h or close to 24 h access to the spacecraft for all seasons. Because of the large north-south excursions of the halo orbit the declination, and thus the coverage, varies strongly with the orbital period (~1/2 year) and the Earth year. At least one 4.5 m class small station (NNO-2) will be used (priority for LEOPs but would otherwise be available for ATHENA). An additional small ground station of EQUA-LEOP class (2.5 m) complements the baseline network. These small ground stations will be operated by ESOC. It is possible to satisfy an 80 % availability requirement with the combination of the baseline station (4 h/day pass), NNO-2 and an EQUA-LEOP type station at Cebreros (or Malindi). In order to achieve full 24 h coverage an additional external station in or at the northern Pacific Ocean is required (e.g. at Japan, Hawaii, or Kiritimati) to be provided on a non exchange of funds basis by an external agency. Note: It is possible to satisfy 24h coverage with only 3 stations, but this puts strong restrictions on the station locations (e.g. 3 equatorial sites: Kourou – Malindi – Kiritimati or 3 distributed sites: Malargüe – Malindi – Usuda). q  ToO operation steps: §  Early warning from SOC (alerts MOC team while accepting that some of those alerts may be premature) §  Small ground stations are pointed to the spacecraft by ECC based on SOC early warning (Note: This will be done based on the early warning, whether stations will be used or not, to avoid ground stations being on the critical path). §  ToO operations at MOC by SPACON. SPACONs are cross trained for astronomy family of missions. §  This requires simple spacecraft operations §  SPACONs from other missions are assumed to be available for nominal working hours and for 50 % of the time outside nominal working hours. To guarantee 24 h service for the rest of the time there is the option of SPACONS on call (=> 2 h possible delay) or the ATHENA project pays for the respective permanent SPACON availability (=> cost impact) §  Downlink of HK (real time and stored events) to check the spacecraft status prior to manoeuvre TC (HK compression is applied if required due to limitation of link budget) §  ToO planning input is received from the SOC (or cancellation in case SOC decided against this ToO). An intelligent (with constraints checks and optimization) planning concept is applied to plan ToO operations. (Technically ideal solution: MOC and SOC use same tool to identify operations constraints => planning in one step) §  Check and uplink of ToO timeline §  Suspension of nominal timeline. Continuation of nominal timeline after ToO to either be planned next working day, or return slew and continuation of nominal timeline activities to be automated as part of ToO planning. §  Slew of spacecraft to new target, new instrument setup (and possibly switch of instruments) during slew §  Start of ToO observations

- Exploring the Hot and Energetic Universe: The first scientific conference dedicated to the Athena X-ray observatory September 8 - 10, 2015, European Space Astronomy Centre, Madrid, Spain

Contact: [email protected], [email protected]