Yahsat s Approach to GEO Collision Avoidance A Case Stduy with STTW-4

Transcription

1 Yahsat s Approach to GEO Collision Avoidance A Case Stduy with STTW-4 John Baker Senior Manager - Flight Dynamics Yahsat

2 Agenda Objective Collision Risk Know your enemy Situational Awareness Yahsat Stationkeeping CDMs Encounter Threat Levels Plan avoidance STTW-4 Encounter 11/9/2016 Key Points from the process 2

3 Objective Yahsat has a simple yet very effective approach to collision avoidance in geostationary orbit, one which could be adopted by a number of smaller satellite operators who do not have the resources to perform precise orbit determination and/or complicated analysis. As the CDM process and interaction between JSpOC and Operators evolves, there are fundamental ideas that should be retained, such as: early notification of encounters; and performing simple zero mission cost avoidance manoeuvres. These techniques guarantee satellite safety in an operationally efficient manner. 3

4 Collision Risk There are three types of objects that need to be avoided: Controlled satellites: Separate deadbands If necessary, inter-operator Coordination or SDA Contribute to many False Positive CDMs Non-geosynchronous debris: The hidden enemy Difficult to predict well in advance TLEs too inaccurate Rely on JSpOC to notify us with CDMs We have seen a growing number of Briz-M/Block-DM CDMs Usually a single encounter Geosynchronous debris: The real enemy The rest of this presentation 4

5 Know your Enemy Geosynchronous debris Majority of Objects with Inc<5 are either controlled or recently de-orbited Majority of debris has Inc>5 At Inc=5, debris passes within ±0.1 of the equator in <10 minutes at a speed of about 15km/min The debris passes through a station-kept satellite deadband at most twice per day collision then depends on the altitude at the debris orbit nodes Relative velocity in North- South direction is so fast that Latitude separation at 5 encounter is almost irrelevant

6 Situational Awareness TLEs cannot be used for Encounter Analysis But they are great for Situational Awareness Yahsat knows of potential encounters in most cases over two weeks in advance: Downloading TLE catalogue for Geostationary objects regularly Filtering TLEs according to orbital criteria using simple Yahsat TLE processor tool Recall threatening encounters have a small radial separation Assessing the consistency of TLE encounters 6

7 TLEs for Advance Warning of Encounters 7

8 Yahsat Stationkeeping Yahsat operates two Eurostar 3000 Geostationary satellites Our SK cycle is 14 days SK Cycle starts with one chemical EWSK manoeuvre SK cycle continues with 7-9 pairs of electric NSSK manoeuvres Each electric NSSK manoeuvre has a large radial ΔV, which causes both a large eccentricity change and, more importantly for collision avoidance, a large mean longitude shift 8

9 SpaceTrack CDMs The evolved JSpOC process now allows us to upload to SpaceTrack on a regular basis, Yahsat s Operational ephemeris, which is screened against the SP catalogue Yahsat normally only generates three Operational ephemerides every two weeks. Debris orbits are updated more frequently, every 1 to 2 days Due to our frequent manoeuvres, the Yahsat SP orbit quickly becomes inaccurate and it is relevant to continue to screen updated debris orbits against Yahsat s Operational orbit 9

10 SpaceTrack CDMs Encounter CDMs are provided up to 10 days in advance, but Yahsat s SK cycle is 14 days For an encounter in the first half of the SK cycle, we can usually plan the SK cycle manoeuvres to avoid the encounter this is obviously the preferred option For an encounter later in the cycle, we might need to perform avoidance manoeuvres Yahsat would prefer a longer warning period for CDMs say 20 days. The inaccuracy of the prediction is not an issue knowing there could be a problem is more important. Yahsat proposes not to use a spherical volume criteria for CDM generation, but to have different criteria for different encounter separation components: <20km Total separation, where Radial & Normal separation are both <10km 10

11 False Positive Encounters JSpOC often send us CDMs for an encounter with an object not using our ephemeris; but the predicted encounter is a False Positive, because our manoeuvres are not taken into account. These CDMs can be used to give further information about the true encounters 11

12 Encounter Threat Levels Yahsat takes a conservative approach to ensure we avoid the debris rather than performing a detailed analysis to determine the exact separation. With significant advance notice of an encounter, avoidance manoeuvres are costless, so don t waste time deciding whether to do them or not, just do it! If 6km total & 3km radial separation criteria is breached then plan avoidance manoeuvres to reduce threat level back to Important. 12

13 Plan Avoidance Maneuvers If avoidance manoeuvres are necessary: First choice is simply to add or remove electric NSSKs to the cycle to change the encounter parameters - radial component of Electric North-South manoeuvres changes longitude significantly Can also change chemical EWSK parameters or dates, if first choice insufficient, but so far a two-part EWSK has never been necessary Note that if necessary, manoeuvres already uploaded to the satellite can also be removed No propellant is wasted because: ΔV corresponding to removed NSSKs can be added to subsequent SK cycles. ΔV corresponding to added NSSKs can be removed from future SK cycles. The avoidance strategy Special ephemeris is uploaded to the SpaceTrack website, for confirmation that the encounter parameters are now acceptable. Once verified by JSpOC, the avoidance strategy becomes the nominal strategy. 13

14 STTW-4 Encounter with Y1A September 2016 Initial Encounter - 5.3km 3.9km More CDMs 4.4km 3.7km 4.6km 3.7km 3.9km 3.2km 3.6km 3.4km 4.7km 3.6km 4.3km 3.3km Y1A ½ cycle cal - 6.2km 3.4km Consider last electric NSSK pair removal 10.4km 3.2km Decision CDM - 5.4km 3.5km 9.5km 3.2km Last electric NSSK pair removed Further CDM More CDMs km 3.3km 10.1km 3.4km 9.6km 3.2km 9.6km 3.2km 9.5km 3.2km 9.7km 3.2km 9.4km 3.2km Version Y1A cycle cal km 3.3km

15 Cosmos-1897 Example Avoidance Maneuvers Advance warning of the encounter due to a False Positive CDM meant that Yahsat could plan avoidance manoeuvres as part of the SK cycle planning on 26/10/2014, almost two weeks before the last encounter 15

16 Key points from Yahsat process Be aware that JSpOC independently produced CDMs may have False Positive encounters, but that does not necessarily mean no encounter! Be aware of the encounter long enough in advance to plan avoidance manoeuvres as part of the normal SK cycle which are then easy and free Repeated encounter predictions give more confidence in the knowledge of the encounter parameters Avoiding the encounter by a large separation removes the need for highly accurate knowledge of the encounter parameters 16

17 Request for JSpOC from Yahsat Please for future GEO ephemeris screening CDMs: Propagation and prediction of encounters up to 20 days in advance Prediction of encounters with different Radial, In-Track & Cross-Track criteria, not using a 20km spherical volume, Yahsat s suggested values are: Radial < 10km In-Track < 20km Cross-Track < 10km Use of Operator Operational ephemeris on a regular basis not just once. 17

18 Al Yah Satellite Communications Company Yahsat Yahsat, a UAE-based satellite operator, wholly owned by the Mubadala Development Company, provides multipurpose satellite solutions for broadband, broadcast, government, and communications use to 140 countries across the Middle East, Africa, Europe, Central and South West Asia. Yahsat is the first company in the Middle East and Africa to offer multi-purpose satellite services, which include : YahClick High-speed Broadband satellite internet for home and business YahService Providing tailored managed solutions & Government capacity YahLink Providing IP trunking, corporate networking & backhauling capacity Yahlive a joint venture between Yahsat & SES, providing premium services to broadcasters and a select choice of TV channels Since being incorporated in 2007, Yahsat has successfully launched two satellites, Y1A in April 2011, and Y1B in April 2012, and is currently manufacturing its third satellite, Al Yah 3, due for launch Q an all Ka-band satellite, extending Yahsat s commercial Ka-band to additional markets in Africa, and for the first time in Brazil, where it will cover over 95% of the Brazilian population. After only 6 years in operation, Yahsat is already in the world s top ten largest satellite 18 operators in terms of revenue.

19 Questions? 19