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. 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. esa bulletin 134 - may 2008 21 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 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.