No abstract

The Da wn missio n, part of N A SA 's Di sco very Pro gra m, has as it s goal the scienti fic explo ratio n of the t wo mo st massive mai n-belt a ster oid s, V esta and Ce res.The Da wn spacecraft wa s launched fro m Cape Cana veral Air Fo rce Stati on o n Septe mber 2 7, 20 07 o n a Delta -II 792 5H-9. 5 (Delta-II Hea vy) rocket that placed the 1 218 k g spacecraft int o an Ea rth-e scape t rajector y. Onboard the spacecra ft is an io n pro pul sion sy stem (I P S) devel oped at the Jet Pr opul sio n Lab orato ry w hich will p rovi de mo st of t he ΔV n eeded fo r helioce ntric t ransfer t o Ve sta, o rbit capture at Ve sta, t ran sfer a mon g Vesta scie nc e orbit s, depart ure a nd e scape fr o m Vesta, heliocentric tran sfer t o Ce res, or bit capt ure at Ce res, a nd t ran sfer a mon g Ce res scie nce o rbit s. The f ir st 80 da ys af ter launc h were dedicated to t h e initial checkout of the spacecra ft w hich wa s follo wed b y about ten mont hs of f ull-p owe r th rusti ng leadi ng to a Mar s g ravity a ssist i n Febr uary 2009 t hat pr ovide d 1 k m/ s o f helioce ntr ic energy i ncrea se and i s the o nly pa rt of t he mi ssi on foll owin g la unch in whic h a needed vel ocity cha nge is not acco mpli she d b y t he I P S. Deter mini stic thr usti ng fo r heliocent ric tran sfe r to Vesta re su med in June 20 09 and was conclude d with o rbit capt ure at Ve sta in July 2 01 1. IP S wa s ope rated fo r appr oxi mately 2 3,40 0 hour s, c on su med a ppr oxi mately 25 0 k g o f xe non, and pro vided a delta -V of app roxi matel y 6. 7 km/ s to achieve or bit captu re at Vesta. IP S per f or mance characteri stic s are very clo se to the expected perf or mance c haracteri stic s base d o n an alysi s perfo r med pre-la unch. A fter a bout thre e week s of su rvey ope ration s IP S will be u sed to maneu ver the spacec raft as neede d for scie nce operatio ns i ncludi ng o rbit t ran sfer s. After appr oxi mately o ne year of science o peratio ns I P S will the n be use d f or e scape fro m Ve sta an d be gi n thr usti ng for crui se t o Cere s with a plan ned arrival date at Ce res in Febr uary 201 5. Thi s pa per p rovide s a n ove rvie w o f Da wn 's mi ssio n objective s and the results o f Daw n IP S mi ssion op eration s thro ugh or bit capture and the start o f science ope ration s at Vesta. I. I NTR ODUC TI ONThe number of missions using electric propulsion is increasing. Deep Space 1 (DS1), launched in 1998, operated its single thruster ion propulsion system for over 16,000 hours before successfully completing its mission [1]. A PPS-1350 Hall thruster was used for primary propulsion on board the European Space Agency's SMART-1 probe, with more flights planned [2]. European and U.S.-launched communications satellites have been launched with SPT-100 -based propulsion modules for attitude control and orbit boosting. The Hayabusa spacecraft returned to Earth after exploring asteroid Itokawa [3] and employed ion engines for primary propulsion. Several communications satellites based on the Boeing 702 b...

The first 80 days after launch of the Dawn mission were dedicated to the checkout of the spacecraft with a major emphasis on the ion propulsion system. All three ion thrusters, all three thruster-gimbal assemblies, both power processor units, both digital interface & control units, and the entire xenon feed system were completely checked out and every component was found to be in good health. Direct thrust measurements agreed well with preflight expected values for all three thrusters over the entire throttle range. Measurements of the thruster-produced roll-torque verified that each thruster produces less than the maximum allowed value of 60 µNm at full power. Thruster electrical operating parameters and power processor units efficiencies also agreed well with preflight expected values based on acceptance test data. Two of the three ion thrusters were fully checked out within 30 days after launch. Checkout of all three thrusters was completed 64 days after launch. Deterministic thrusting with the IPS began on December 17, 2007 I.

The Dawn mission, part of NASA's Discovery Program, has as its goal the scientific exploration of the two most massive main-belt asteroids, 4 Vesta, and the dwarf planet 1 Ceres. The Dawn spacecraft was launched from the Cape Canaveral Air Force Station on September 27, 2007 on a Delta-II 7925H-9.5 rocket that placed the 1218-kg spacecraft into an Earth-escape trajectory. On-board the spacecraft is an ion propulsion system (IPS) developed at the Jet Propulsion Laboratory which will provide a total delta-V of approximately 11 km/s for the heliocentric transfer to Vesta, orbit capture at Vesta, transfer between Vesta science orbits, departure and escape from Vesta, heliocentric transfer to Ceres, orbit capture at Ceres, transfer between Ceres science orbits, and orbit maintenance maneuvers for all Vesta and Ceres science orbits. Full-power thrusting from December 2007 through October 2008 was used to successfully target a Mars gravity assist flyby in February 2009 that provided an additional delta-V of 2.6 km/s. Deterministic thrusting for the heliocentric transfer to Vesta resumed in June 2009 and concluded with orbit capture at Vesta on July 16, 2011. An additional 231 hours of IPS thrusting was used to enter the first Vesta science orbit, called Survey orbit, on August 3, 2011 at an altitude of about 2,735 km. The IPS was then used over the next year to transfer the spacecraft to the other science orbits: a high altitude mapping orbit (HAMO-1) in September 2011 at an altitude of approximately 673 km, a low altitude mapping orbit (LAMO) at approximately 210 km altitude, and a second high altitude mapping orbit (HAMO-2) at approximately 673 km altitude. To date the IPS has been operated for approximately 24,327 hours, consumed approximately 260 kg of xenon, and provided a delta-V of approximately 7 km/s. IPS performance characteristics are very close to the expected performance based on analysis and testing performed pre-launch. Thrusting for escape from Vesta and cruise to Ceres is planned to start in late July 2012 with a planned arrival date at Ceres in February 2015. This paper provides an overview of Dawn's mission objectives and the results of Dawn IPS mission operations through preparations for departure from Vesta.

No abstract

No abstract

This paper presents a state-variable bandpass filter with wide frequency range coverage and wide Q tuning range. The state-variable filter was chosen because it can be easily extended to a universal biquad filter structure [1]. A digital tuning technique with a novel Q-tuning algorithm was implemented in Verilog-A, and a real-time tuning of center frequency f c and Q was demonstrated. The technique is accurate as long as there is no phase error in the system. In the presence of phase error and for high Q filter requirements, tuning algorithm based on magnitude detection was demonstrated. A bandpass filter was simulated in 45nm CMOS technology using RF components for more accurate modeling of the fets. Filter simulation results showed frequency range coverage from 520MHz to 2.2GHz, and Q range from 2 to 400. For a filter with Q=33, simulation results showed a dynamic range of 55dB over a 3dB bandwidth at f c =1.5GHz. The current consumption of the designed filter is 75mA at 1.2V.