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Phoenix
Peter Schmitz, Olivier Reboud, Thomas Ormston & Mattia Mercolino Mission Operations Department, ESA Directorate of Operations and Infrastructure, ESOC, Darmstadt, Germany
ith the landing of the US Phoenix spacecraft scheduled for 25 May, W NASA has requested the assistance of ESA’s Mars Express, in orbit around Mars since December 2003, as one of three orbiters used to monitor the dramatic arrival at the Red Planet.
Landing on Mars is one of the most difficult tasks any spacecraft can undertake. In the past, efforts to explain failed landings have sometimes been hampered by a lack of data from the atmospheric entry, descent and landing phase. Since the summer of 2007, specialists at ESA’s European Space Operations Centre (ESOC) have been designing and testing a new communications mode that will allow Mars Express to support the Phoenix mission. Under the new ESA/NASA 'Network and Operations Cross-support Agree- ment’, NASA requested support from the European Space Operations Centre (ESOC) for its first Mars Scout Mission, Phoenix. This mission was launched on 4 August 2007 and is expected to land on the Red Planet on 25 May 2008.
esa bulletin 134 - may 2008 21 phoenix_134.qxd 6/5/08 1:05 PM Page 20
Phoenix
Peter Schmitz, Olivier Reboud, Thomas Ormston & Mattia Mercolino Mission Operations Department, ESA Directorate of Operations and Infrastructure, ESOC, Darmstadt, Germany
ith the landing of the US Phoenix spacecraft scheduled for 25 May, W NASA has requested the assistance of ESA’s Mars Express, in orbit around Mars since December 2003, as one of three orbiters used to monitor the dramatic arrival at the Red Planet.
Landing on Mars is one of the most difficult tasks any spacecraft can undertake. In the past, efforts to explain failed landings have sometimes been hampered by a lack of data from the atmospheric entry, descent and landing phase. Since the summer of 2007, specialists at ESA’s European Space Operations Centre (ESOC) have been designing and testing a new communications mode that will allow Mars Express to support the Phoenix mission. Under the new ESA/NASA 'Network and Operations Cross-support Agree- ment’, NASA requested support from the European Space Operations Centre (ESOC) for its first Mars Scout Mission, Phoenix. This mission was launched on 4 August 2007 and is expected to land on the Red Planet on 25 May 2008.
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Operations and Infrastructure Phoenix
‘Delta-DOR’ taken on the baseline New Norcia – Delta-DOR as a tool for the navigation of interplanetary Robledo has been foreseen. The first spacecraft is based on a simple but quite effective operational attempt to have a fully concept. It uses two widely separated antennas (whose interoperable delta-DOR measurement connecting line is known as the baseline) for between two agencies has two objectives: simultaneous tracking of a transmitting probe in order to validating the interagency delta-DOR measure the delay in the signal arrival time between the capabilities in an operational environ- two stations. The measurement of this time delay is ment and cross-checking results obtained named Differential One-way Range (DOR). with ESA antennas only. This represents a huge improvement in the ability of both Theoretically, the obtained delay value depends only on agencies to support deep-space missions. the geometry of the system, that is, on the position of the A total of five test passes (plus the one two antennas and of the source being tracked. However, carried out on 1 December 2007) are in real cases, this delay will be affected by several error foreseen for this option. The data, sources. Delta-DOR corrects these errors using a quasar as a calibration source. This is possible since the quasar’s collected either at ESA or at DSN position (its direction) is extremely accurately known, stations, are transferred to ESOC to be typically to better than 1 nanoradian. processed by the ESA delta-DOR correlator. Reduced data are then A delta-DOR measurement is directly related to the converted into CCSDS standard format component of the angular separation between the and transferred to JPL for orbit spacecraft and quasar, parallel to the baseline between MELACOM 70° footprints (pink) pass over the Phoenix lander during Mars Express (yellow line) nadir over-flight determination purposes. the two antennas. As two angles are required to define a direction, full exploitation of delta-DOR calls for Phoenix Support by Mars Express measurements from two different baseline orientations – Delta-DOR tracking of a deep-space probe and of a nearby quasar from DSA-1 (New Norcia, Rosetta’s flyby of Mars in early 2007. – support from a mixed ESA-DSN In 2007, NASA requested the use of the closer to orthogonal the better. Australia) and DSA-2 (Cebreros, Spain). The effects of common error sources between The technique demonstrated high-level baseline. Mars Express to support the Phoenix spacecraft and quasar observations are cancelled by the quasar tracking. performance, meeting requirements that The support from the ESA-only lander during two critical phases, the For Phoenix navigation with delta-DOR, NASA’s Deep were based on a 1 nanosecond baseline is made of 19 delta-DOR passes Entry, Descent and Landing (EDL) and Space Network (DSN) uses the baseline between the measurement accuracy (corresponding – plus a test pass carried out on subsequent on-surface characterisation Goldstone and Canberra complexes. Since the ESA baseline and can be used to improve navigational baseline (New Norcia to Cebreros 35 m deep space accuracy. Analysis carried out beforehand by JPL to a spacecraft position uncertainty of 1 December 2007 – starting on phase. During EDL, Mars Express will antennas) is almost perfectly orthogonal to the DSN one, it demonstrated that use of the ESA baseline would improve 4.5 km at 1 astronomical unit). 25 January 2008 and occurring with record RF signals emitted by the probe in complements angular results obtained using the DSN-only the uncertainty in Phoenix orbit determination by 15%. After these successful operational increasing frequency as the Phoenix open loop (‘Canister mode’), which will campaigns, ESA has developed a Entry Descent and Landing (EDL) phase provide NASA with valuable information software data translator that is capable approaches. The last ESA-only delta- on Phoenix’s behaviour while it descends of processing not only data coming DOR is foreseen on 23 May 2008, one through the Martian atmosphere. Throughout the journey to Mars, gap’ in spacecraft communications solution accuracy. In order to achieve from its stations, but also from NASA day before the last Trajectory Correction Once Phoenix has landed on Mars it ESOC has provided support for critical between US tracking stations in Madrid the desired level of precision, a heavy DSN or other astronomical institutions, Manoeuvre and two before EDL. will undergo a 10 Sol (Sol = Martian day) Phoenix mission phases, such as ground and Goldstone. use of a technique known as ‘delta- thus enabling the possibility of delta- Together with the ESA-only baseline characterisation phase, when Mars station tracking support during the DOR’ is foreseen. Delta-DOR has DOR interoperability with other space support, a limited number of passes to be Express will act as a communications launch and early orbit phase, delta- Phoenix Delta-DOR Navigation Support already been used operationally by ESA agencies such as NASA or JAXA and DOR (Differential One-way Range) Phoenix navigation has very stringent to support Venus Express before Venus extending the number of possible Mars Express MELACOM antenna spot-pointing footprints over the Phoenix lander during the nominal mission ranging support during Mars approach, requirements in terms of orbital orbit insertion in 2006 and before baselines to be used. communications support during entry, The new system has been validated descent and landing and post-landing with NASA by using Venus Express data relay support through Mars ESA Delta-DOR interoperability concept using software data translator to ensure data compatibility among different agencies orbiter as a target that was tracked Express. simultaneously by one ESA and one DSN antenna on several occasions Phoenix Launch Support during June–July and September– After the successful launch of Phoenix October 2007. on 4 August 2007, the ESA Kourou Thanks to the new data translation ground station provided tracking capability, ESA can now exercise a full support to the NASA project. Kourou is interoperable delta DOR with NASA. the only station able to guarantee The delta-DOR support to NASA 24-hour coverage during this critical foresees two scenarios: mission phase by bridging the ‘Atlantic – support from ESA baseline only;
22 esa bulletin 134 - may 2008 www.esa.int www.esa.int esa bulletin 134 - may 2008 23 phoenix_134.qxd 6/5/08 1:05 PM Page 22
Operations and Infrastructure Phoenix
‘Delta-DOR’ taken on the baseline New Norcia – Delta-DOR as a tool for the navigation of interplanetary Robledo has been foreseen. The first spacecraft is based on a simple but quite effective operational attempt to have a fully concept. It uses two widely separated antennas (whose interoperable delta-DOR measurement connecting line is known as the baseline) for between two agencies has two objectives: simultaneous tracking of a transmitting probe in order to validating the interagency delta-DOR measure the delay in the signal arrival time between the capabilities in an operational environ- two stations. The measurement of this time delay is ment and cross-checking results obtained named Differential One-way Range (DOR). with ESA antennas only. This represents a huge improvement in the ability of both Theoretically, the obtained delay value depends only on agencies to support deep-space missions. the geometry of the system, that is, on the position of the A total of five test passes (plus the one two antennas and of the source being tracked. However, carried out on 1 December 2007) are in real cases, this delay will be affected by several error foreseen for this option. The data, sources. Delta-DOR corrects these errors using a quasar as a calibration source. This is possible since the quasar’s collected either at ESA or at DSN position (its direction) is extremely accurately known, stations, are transferred to ESOC to be typically to better than 1 nanoradian. processed by the ESA delta-DOR correlator. Reduced data are then A delta-DOR measurement is directly related to the converted into CCSDS standard format component of the angular separation between the and transferred to JPL for orbit spacecraft and quasar, parallel to the baseline between MELACOM 70° footprints (pink) pass over the Phoenix lander during Mars Express (yellow line) nadir over-flight determination purposes. the two antennas. As two angles are required to define a direction, full exploitation of delta-DOR calls for Phoenix Support by Mars Express measurements from two different baseline orientations – Delta-DOR tracking of a deep-space probe and of a nearby quasar from DSA-1 (New Norcia, Rosetta’s flyby of Mars in early 2007. – support from a mixed ESA-DSN In 2007, NASA requested the use of the closer to orthogonal the better. Australia) and DSA-2 (Cebreros, Spain). The effects of common error sources between The technique demonstrated high-level baseline. Mars Express to support the Phoenix spacecraft and quasar observations are cancelled by the quasar tracking. performance, meeting requirements that The support from the ESA-only lander during two critical phases, the For Phoenix navigation with delta-DOR, NASA’s Deep were based on a 1 nanosecond baseline is made of 19 delta-DOR passes Entry, Descent and Landing (EDL) and Space Network (DSN) uses the baseline between the measurement accuracy (corresponding – plus a test pass carried out on subsequent on-surface characterisation Goldstone and Canberra complexes. Since the ESA baseline and can be used to improve navigational baseline (New Norcia to Cebreros 35 m deep space accuracy. Analysis carried out beforehand by JPL to a spacecraft position uncertainty of 1 December 2007 – starting on phase. During EDL, Mars Express will antennas) is almost perfectly orthogonal to the DSN one, it demonstrated that use of the ESA baseline would improve 4.5 km at 1 astronomical unit). 25 January 2008 and occurring with record RF signals emitted by the probe in complements angular results obtained using the DSN-only the uncertainty in Phoenix orbit determination by 15%. After these successful operational increasing frequency as the Phoenix open loop (‘Canister mode’), which will campaigns, ESA has developed a Entry Descent and Landing (EDL) phase provide NASA with valuable information software data translator that is capable approaches. The last ESA-only delta- on Phoenix’s behaviour while it descends of processing not only data coming DOR is foreseen on 23 May 2008, one through the Martian atmosphere. Throughout the journey to Mars, gap’ in spacecraft communications solution accuracy. In order to achieve from its stations, but also from NASA day before the last Trajectory Correction Once Phoenix has landed on Mars it ESOC has provided support for critical between US tracking stations in Madrid the desired level of precision, a heavy DSN or other astronomical institutions, Manoeuvre and two before EDL. will undergo a 10 Sol (Sol = Martian day) Phoenix mission phases, such as ground and Goldstone. use of a technique known as ‘delta- thus enabling the possibility of delta- Together with the ESA-only baseline characterisation phase, when Mars station tracking support during the DOR’ is foreseen. Delta-DOR has DOR interoperability with other space support, a limited number of passes to be Express will act as a communications launch and early orbit phase, delta- Phoenix Delta-DOR Navigation Support already been used operationally by ESA agencies such as NASA or JAXA and DOR (Differential One-way Range) Phoenix navigation has very stringent to support Venus Express before Venus extending the number of possible Mars Express MELACOM antenna spot-pointing footprints over the Phoenix lander during the nominal mission ranging support during Mars approach, requirements in terms of orbital orbit insertion in 2006 and before baselines to be used. communications support during entry, The new system has been validated descent and landing and post-landing with NASA by using Venus Express data relay support through Mars ESA Delta-DOR interoperability concept using software data translator to ensure data compatibility among different agencies orbiter as a target that was tracked Express. simultaneously by one ESA and one DSN antenna on several occasions Phoenix Launch Support during June–July and September– After the successful launch of Phoenix October 2007. on 4 August 2007, the ESA Kourou Thanks to the new data translation ground station provided tracking capability, ESA can now exercise a full support to the NASA project. Kourou is interoperable delta DOR with NASA. the only station able to guarantee The delta-DOR support to NASA 24-hour coverage during this critical foresees two scenarios: mission phase by bridging the ‘Atlantic – support from ESA baseline only;
22 esa bulletin 134 - may 2008 www.esa.int www.esa.int esa bulletin 134 - may 2008 23 phoenix_134.qxd 6/5/08 1:05 PM Page 24
Operations and Infrastructure Phoenix
relay between the lander and Earth. The will be used for communications to Phoenix EDL event, the MER objective of this on-surface support is to command the lander and/or relay transmitted a sequence of RF tones that assist NASA in determining Phoenix’s science data to Earth. simulated the RF signature of Phoenix health and to demonstrate Mars Express during the descent and were recorded in relay capabilities should they be needed In-flight Tests and Preparation MELACOM ‘Canister’ mode. later in the mission. In this respect, Mars The principle of a test campaign On board Mars Express, ‘standalone’ Express could complement the between Mars Express and the Mars tests (without the rovers) were also communications coverage of Phoenix, Exploration Rovers (MER) Spirit and conducted to determine whether other which is nominally supplied by the Opportunity was decided in April 2007. Mars Express instruments interfere with NASA orbiters Mars Reconnaissance This was to provide operational the frequency spectrum of the Orbiter (MRO) and Mars Odyssey confidence for Mars Express–Phoenix MELACOM receiver channel. (ODY). Thanks to its elliptical orbit, communications because the rovers both Dedicated interference tests were Mars Express can, in some mission carry the same CE505 model of UHF conducted to verify that neither AOCS phases, provide longer periods of contact radio transponder as Phoenix. (Attitude and Orbit Control System) with Phoenix than MRO or ODY. The beginning of the test campaign units nor payloads like the HRSC (High was hindered by a severe dust storm on Resolution Stereo Camera) or SPICAM Bringing the Two Missions Closer Mars between mid-July and mid-August (Spectroscopy for Investigation of One of the key issues to meet NASA’s 2007, leading to the cancellation at short Characteristics of the Atmosphere of request was a proper phasing of the Mars notice of three tests due to excessive Mars), which are planned to operate Express orbit, allowing the ESA atmospheric dust levels affecting the during the EDL event, would generate spacecraft to track the descent module power situation of the rovers. Fortun- adverse effects on the RF spectrum with an optimised visibility. By taking ately, the weather at Mars improved, while MELACOM is scanning in advantage of the Mars Express orbit allowing a series of 12 tests with both ‘Canister mode’. change to an 18/5 resonance orbit rovers. A total of 900 commands were Those interference tests have shown, (planned for scientific reasons), the phase sent and 145 Mb of lander communi- for instance, that the MARSIS (Mars Artist’s impression of Phoenix on the surface of Mars of the orbit has also been changed with cation data were successfully relayed to Advanced Radar for Subsurface and minimum additional fuel consumption. Earth via Mars Express during duplex Ionosphere Sounding) instrument can If needed, the phase may have to undergo links utilising the CCSDS Proximity-1 operate together with MELACOM, but ASPERA (Analyser of Space Plasmas – transfer to ESOC for final checks and Phoenix and the ability to meet the Mars last-minute tuning one week before Mars protocol. In addition, to prepare for the that severe interference is generated by and Energetic Atoms), resulting in an uplink in the next available ground lander’s requirements will provide arrival, when the final entry trajectory exclusion rule for science planning which station pass; excellent proof that Mars Express can, parameters of Phoenix are known. prevents both instruments from – execution on board Mars Express, i.e. in addition to being an excellent science During EDL, the recorded data will Waterfall diagram processed by ESOC: MELACOM recording in ‘Canister’ mode of mock Phoenix EDL tones transmitted by Opportunity operating together. forwarding of rover telecommands orbiter, also act as a Martian be secured by a copy stored on board MER-B (28 August 2007) The main objectives of this intensive and reception and recording of rover communications relay and support Mars Express in a dedicated area of its test campaign in 2007 were successfully telemetry during the over-flight; future Mars surface missions such as Solid State Mass Memory, and then achieved: – transfer of the recorded data to NASA’s Mars Science Laboratory or dumped three times to Earth to avoid – health check of the MELACOM ground in the next available ground ESA’s ExoMars. any data gap caused by potential ground transponder which had not been station pass; In any case, the intensive test station problems, bad weather switched on for 20 months; – retrieval of the telemetry data from campaign with the Mars Exploration conditions or network issues. The EDL – definition and set-up of operational the ESOC archive by JPL for analysis. Rovers and the support to Phoenix was data would be of highest importance in interfaces between JPL and ESOC, a great opportunity to involve several a contingency situation when Phoenix being able to cope with different Following the Mars Express/MER test agencies and mobilise various would not have landed as expected, planning cycles between Mars campaign in 2007, seven follow-on tests competences within ESA that were making the analysis of the sequence of Express and Phoenix; were carried out between Mars Express required to work together, such as radio tones transmitted by Phoenix – insertion of the MELACOM and the Opportunity rover in early 2008. Flight Dynamics, Mars Express Flight during EDL critical for investigations. pointing requirements and resource The objectives were to test the RF link Control, Mission Planning and Project In the seven days after the EDL, allocation into the medium-term performance while Mars Express was Scientist teams, the RF and Signal ESOC has booked each over-flight of planning cycle by ESOC, three performing a dedicated ‘lander pointing’, Processing team, Mission Control the Phoenix landing site above 10° months before start of activity; targeting the MELACOM antenna System Software support, ground elevation, so that the Mars Express – generation of the MELACOM towards the rover during the over-flight station and navigation teams. It also Lander Communications (MELACOM) operations request by ESOC one in order to optimise the RF link budget established a fruitful partnership with system will be ready to support any month before start of activity; and improving the return link efficiency. our NASA JPL colleagues from the contingency plan decided at any time – generation of the MELACOM MER and Phoenix projects. We thank during this week. Assuming Phoenix command files by JPL up to two days Phoenix and Beyond all of these groups, and hope it is just lands nominally, some of these passes before onboard execution; Success in the Mars Express support to the beginning. e
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Operations and Infrastructure Phoenix
relay between the lander and Earth. The will be used for communications to Phoenix EDL event, the MER objective of this on-surface support is to command the lander and/or relay transmitted a sequence of RF tones that assist NASA in determining Phoenix’s science data to Earth. simulated the RF signature of Phoenix health and to demonstrate Mars Express during the descent and were recorded in relay capabilities should they be needed In-flight Tests and Preparation MELACOM ‘Canister’ mode. later in the mission. In this respect, Mars The principle of a test campaign On board Mars Express, ‘standalone’ Express could complement the between Mars Express and the Mars tests (without the rovers) were also communications coverage of Phoenix, Exploration Rovers (MER) Spirit and conducted to determine whether other which is nominally supplied by the Opportunity was decided in April 2007. Mars Express instruments interfere with NASA orbiters Mars Reconnaissance This was to provide operational the frequency spectrum of the Orbiter (MRO) and Mars Odyssey confidence for Mars Express–Phoenix MELACOM receiver channel. (ODY). Thanks to its elliptical orbit, communications because the rovers both Dedicated interference tests were Mars Express can, in some mission carry the same CE505 model of UHF conducted to verify that neither AOCS phases, provide longer periods of contact radio transponder as Phoenix. (Attitude and Orbit Control System) with Phoenix than MRO or ODY. The beginning of the test campaign units nor payloads like the HRSC (High was hindered by a severe dust storm on Resolution Stereo Camera) or SPICAM Bringing the Two Missions Closer Mars between mid-July and mid-August (Spectroscopy for Investigation of One of the key issues to meet NASA’s 2007, leading to the cancellation at short Characteristics of the Atmosphere of request was a proper phasing of the Mars notice of three tests due to excessive Mars), which are planned to operate Express orbit, allowing the ESA atmospheric dust levels affecting the during the EDL event, would generate spacecraft to track the descent module power situation of the rovers. Fortun- adverse effects on the RF spectrum with an optimised visibility. By taking ately, the weather at Mars improved, while MELACOM is scanning in advantage of the Mars Express orbit allowing a series of 12 tests with both ‘Canister mode’. change to an 18/5 resonance orbit rovers. A total of 900 commands were Those interference tests have shown, (planned for scientific reasons), the phase sent and 145 Mb of lander communi- for instance, that the MARSIS (Mars Artist’s impression of Phoenix on the surface of Mars of the orbit has also been changed with cation data were successfully relayed to Advanced Radar for Subsurface and minimum additional fuel consumption. Earth via Mars Express during duplex Ionosphere Sounding) instrument can If needed, the phase may have to undergo links utilising the CCSDS Proximity-1 operate together with MELACOM, but ASPERA (Analyser of Space Plasmas – transfer to ESOC for final checks and Phoenix and the ability to meet the Mars last-minute tuning one week before Mars protocol. In addition, to prepare for the that severe interference is generated by and Energetic Atoms), resulting in an uplink in the next available ground lander’s requirements will provide arrival, when the final entry trajectory exclusion rule for science planning which station pass; excellent proof that Mars Express can, parameters of Phoenix are known. prevents both instruments from – execution on board Mars Express, i.e. in addition to being an excellent science During EDL, the recorded data will Waterfall diagram processed by ESOC: MELACOM recording in ‘Canister’ mode of mock Phoenix EDL tones transmitted by Opportunity operating together. forwarding of rover telecommands orbiter, also act as a Martian be secured by a copy stored on board MER-B (28 August 2007) The main objectives of this intensive and reception and recording of rover communications relay and support Mars Express in a dedicated area of its test campaign in 2007 were successfully telemetry during the over-flight; future Mars surface missions such as Solid State Mass Memory, and then achieved: – transfer of the recorded data to NASA’s Mars Science Laboratory or dumped three times to Earth to avoid – health check of the MELACOM ground in the next available ground ESA’s ExoMars. any data gap caused by potential ground transponder which had not been station pass; In any case, the intensive test station problems, bad weather switched on for 20 months; – retrieval of the telemetry data from campaign with the Mars Exploration conditions or network issues. The EDL – definition and set-up of operational the ESOC archive by JPL for analysis. Rovers and the support to Phoenix was data would be of highest importance in interfaces between JPL and ESOC, a great opportunity to involve several a contingency situation when Phoenix being able to cope with different Following the Mars Express/MER test agencies and mobilise various would not have landed as expected, planning cycles between Mars campaign in 2007, seven follow-on tests competences within ESA that were making the analysis of the sequence of Express and Phoenix; were carried out between Mars Express required to work together, such as radio tones transmitted by Phoenix – insertion of the MELACOM and the Opportunity rover in early 2008. Flight Dynamics, Mars Express Flight during EDL critical for investigations. pointing requirements and resource The objectives were to test the RF link Control, Mission Planning and Project In the seven days after the EDL, allocation into the medium-term performance while Mars Express was Scientist teams, the RF and Signal ESOC has booked each over-flight of planning cycle by ESOC, three performing a dedicated ‘lander pointing’, Processing team, Mission Control the Phoenix landing site above 10° months before start of activity; targeting the MELACOM antenna System Software support, ground elevation, so that the Mars Express – generation of the MELACOM towards the rover during the over-flight station and navigation teams. It also Lander Communications (MELACOM) operations request by ESOC one in order to optimise the RF link budget established a fruitful partnership with system will be ready to support any month before start of activity; and improving the return link efficiency. our NASA JPL colleagues from the contingency plan decided at any time – generation of the MELACOM MER and Phoenix projects. We thank during this week. Assuming Phoenix command files by JPL up to two days Phoenix and Beyond all of these groups, and hope it is just lands nominally, some of these passes before onboard execution; Success in the Mars Express support to the beginning. e
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