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New Horizons will visit Pluto and its moons.
New Horizons is a NASA unmanned mission to fly by Pluto and its moons. NASA may also approve flybys of one or more other Kuiper Belt Objects. New Horizons was built primarily by Southwest Research Institute (SwRI) and the Johns Hopkins Applied Physics Laboratory (APL). The mission's principal investigator is S. Alan Stern of the Southwest Research Institute. New Horizons was successfully launched on January 19, 2006. New Horizons is expected to arrive at Pluto in 2015.
The New Horizons spacecraft was launched directly into an Earth- and solar-escape trajectory. It had an Earth-relative velocity of about 16.21 km/s (36,300 mph) just after its last engine shut down, making it the fastest spacecraft launch ever.
New Horizons is the first mission in NASA's New Frontiers mission category, larger and more expensive than Discovery missions but smaller than "flagship" programs.
Mission profile of New Horizons.
An Atlas V 551 rocket launched the spacecraft, with a Boeing Star 48B third stage added to increase the heliocentric (escape) speed. The launch of New Horizons was scheduled for January 11, 2006, but was delayed until January 17 to allow for borescope inspections of the Atlas's kerosene tank. Further delays related to high winds and technical difficulties unrelated to the rocket itself prevented launch until 14:00 EST on January 19.
KinetX is the lead on the New Horizons' navigation team and is responsible for planning trajectory adjustments as the spacecraft speeds toward the outer solar system.
Jupiter gravity assist for New Horizons.
New Horizons is now proceeding to a Jupiter gravity assist in February 2007. It will pass through the Jupiter system at 21 km/s (47,000 mph), with closest approach to Jupiter occurring at approximately 06:00 UTC February 28, 2007. New Horizons was the first probe launched directly towards Jupiter since the Ulysses probe in 1990. Although there were backup launch opportunities in February 2006 and February 2007, only the first 23 days of the 2006 window permitted the Jupiter flyby. Any launch outside that period would have forced the spacecraft to fly a slower trajectory directly to Pluto, delaying its encounter by 2-4 years.
The flyby will increase New Horizons' speed away from the Sun by nearly 4 km/s (9,000 mph), putting the spacecraft on a faster trajectory to Pluto, about 2.5 degrees out of the plane of the solar system (the "ecliptic").
New Horizons Pluto approach.
It is planned for New Horizons to fly within 10,000 km (6,213.7 mi) of Pluto. New Horizons will have a relative velocity of 13.78 km/s at closest approach, and will come as close as 27,000 km (16,800 mi) to Charon, although these parameters may be changed during flight.
Kuiper Belt mission for New Horizons.
After passing by Pluto, New Horizons will continue further into the Kuiper Belt. Mission planners are now searching for one or more Kuiper Belt Objects (KBOs) on the order of 50-100 km (30-60 mi) in diameter for flybys similar to the spacecraft's Plutonian encounter. As maneuvering capability is limited, this phase of the mission is contingent on finding suitable KBOs close to New Horizons' flight path, ruling out any possibility for a planned flyby of Eris, a Trans-Neptunian object larger than Pluto. The available region, being fairly close to the plane of the Milky Way and thus difficult to survey for dim objects, is one that has not been well-covered by previous KBO search efforts.
Current status of New Horizons.
Overall control, after separation from the launch vehicle, is performed at Mission Operations Center (MOC) at APL. The science instruments are operated at the Clyde Tombaugh Science Operations Center (T-SOC) in Boulder, Colorado. Navigation is not realtime, and performed at various contractor facilities.
The New Horizons probe and its Atlas V launcher lifted off from Pad 41 at Cape Canaveral Air Force Station, Florida, directly south of Space Shuttle Launch Complex 39, at 2:00 p.m. EST (1900 UTC) on January 19, 2006. The launch time was slightly delayed due to low cloud ceiling conditions downrange. The Centaur second stage reignited at 2:30 p.m. EST (1930 UTC), successfully sending the probe out of Earth orbit. New Horizons passed Lunar orbit before midnight EST on the same day, and is scheduled to reach Jupiter in February 2007.
On January 28 and January 30, mission controllers guided the probe through its first trajectory correction maneuver (TCM), which was divided into two parts called TCM-1A and TCM-1B. The total velocity change of these two corrections was about 18 meters per second. TCM-1 was accurate enough to permit the cancellation of TCM-2, the second of three originally scheduled corrections.
During the week of February 20, controllers conducted initial in-flight tests of three onboard scientific instruments, the Alice ultraviolet imaging spectrometer, the PEPSSI plasma-sensor, and the LORRI long-range visible-spectrum camera. No scientific measurements or images were taken, but instrument electronics (and in the case of Alice, some electromechanical systems) were shown to be functioning correctly.
On March 9 at 1700 UTC, controllers performed TCM-3, the last of three scheduled course corrections. The engines burned for 76 seconds, adjusting the spacecraft's velocity by about 1.16 meters per second.
On April 7 at about 1000 UTC, the spacecraft passed the orbit of Mars, moving at roughly 21 km/s away from the Sun at a solar distance of 243 million kilometers.
On June 10, June 11, and June 12, the spacecraft successfully tracked the asteroid 2002 JF56. The flyby allowed the mission team to test the spacecraft's ability to track rapidly moving objects. Images were obtained through the Ralph telescope.
On September 4, New Horizons' LORRI imager took its first photographs of Jupiter. The spacecraft will further study the Jovian system beginning in December.
Key mission dates for New Horizons.
Spacecraft subsystems of New Horizons.
The spacecraft is comparable in size and general shape to a grand piano and has been compared to a "piano glued to a sports-bar-sized satellite dish". Its simplicity in design mimics that of the design of the Pioneer 10 and Pioneer 11 probes of the early 1970s, but it benefits from 30+ years of technology refinements and low-power electronics. Many subsystems and components have flight heritage from APL's CONTOUR spacecraft, which in turn had heritage from APL's TIMED spacecraft.
Structural overview of New Horizons.
The spacecraft's body forms a triangle, almost 2.5 feet (0.75 m) thick. (The Pioneers had hexagonal [6-sided] bodies, while the Voyagers, Galileo, and Cassini-Huygens had decagonal [10-sided], hollow bodies.) An aluminum-7075 tube forms the main structural column, between the launch vehicle adapter ring at the "rear," and the 2.1 m radio dish antenna affixed to the "front" flat side. The titanium fuel tank is in this tube. The RTG attaches with a 4-sided titanium mount resembling a gray pyramid or stepstool. Titanium provides strength and thermal isolation. The rest of the triangle is primarily sandwich panels of thin aluminum facesheet (less than 1/64" or 0.4 mm) bonded to aluminum honeycomb core.
The structure is larger than strictly necessary, with empty space inside. The structure is designed to act as shielding, reducing electronics errors caused by radiation from the RTG. Also, the mass distribution required for a spinning spacecraft demands a wider triangle.
Propulsion/Attitude Control of New Horizons.
The spacecraft has both spin-stabilized (cruise) and three-axis stabilized (science) modes, controlled entirely with Hydrazine monopropellant. Seventy-seven kilograms of hydrazine provides a delta-v capability of over 290 m/s after launch. Nitrogen is used as a pressurant, with a tank membrane assisting expulsion. The spacecraft's on-orbit mass including fuel will be over 470 kg for a Jupiter flyby trajectory, but would have been only 445 kg for a direct flight to Pluto. This would have meant less fuel for later Kuiper Belt operations and is caused by the launch vehicle performance limitations for a direct-to-Pluto flight.
There are 16 thrusters, in large (1 lbf or 4.4 N) and small (0.18 lbf or 0.8 N) thruster circuits, with two redundant fuel routings. The large thrusters are primarily for course corrections, the small ones (previously used on Cassini) are primarily for attitude. Two star cameras (from Galileo Avionica) are used for fine attitude control. They are mounted on the face of the spacecraft and provide attitude information while in spinning or in 3-axis mode. Between star camera readings, knowledge is provided by dual redundant Miniature Inertial Measurement Unit (MIMU) from Honeywell. Each unit contains three solid-state gyros and three accelerometers. Two Adcole Sun sensors provide coarse attitude control. One detects angle to the Sun, one measures spin rate and clocking.
Power of New Horizons.
A cylindrical radioisotope thermoelectric generator (RTG) protrudes from one vertex in the plane of the triangle. The RTG will provide about 240 W, 30 V DC at launch, decaying to 200 W at encounter in 2015. The RTG, model "GPHS-RTG," was originally a spare from the Cassini mission. The RTG contains 24 pounds (11 kg) of plutonium-238 oxide pellets. Each pellet is clad in iridium, then encased in a graphite shell.
It was developed by the Department of Energy at the Materials and Fuels Complex (formerly Argonne West), a part of the Idaho National Laboratory north of Idaho Falls, Idaho, near Arco, Idaho. The plutonium was produced at Los Alamos National Laboratory in New Mexico. Less than the original design goal was produced, due to delays at the Department of Energy, including security activities, which held up production. The mission parameters and observation sequence had to be modified for the reduced wattage; still, not all instruments can operate simultaneously. The Department of Energy transferred the space battery program from Ohio to Argonne in 2002 because of security concerns.
There are no onboard batteries. RTG output is relatively predictable; load transients are handled by a capacitor bank and fast circuit breakers.
Thermal lining of New Horizons.
Internally, the structure is painted black. This equalizes temperature by radiative heat transfer.
Overall, the spacecraft is thoroughly blanketed to retain heat. Unlike the Pioneers and Voyagers, the radio dish is also enclosed in blankets which extend to the body. The heat from the RTG also adds warmth to the spacecraft in the outer solar system. In the inner solar system, the spacecraft must prevent overheating. Electronic activity is limited, power is diverted to shunts with attached radiators, and louvers are opened to radiate excess heat. Then, when the spacecraft is cruising inactively in the cold outer solar system, the louvers are closed, and the shunt regulator reroutes power to electric heaters.
Telecommunications of New Horizons.
Communication will be via X band, at a rate of 768 bit/s from Pluto's distance (38 kbit/s at Jupiter) to a 70 m Deep Space Network (DSN) dish. The spacecraft uses dual redundant transmitters and receivers, and either right- or left-hand circular Polarization. The downlink signal is amplified by dual redundant 12-watt TWTAs (travelling wave tube amplifiers) mounted on the body under the dish. The receivers are new, low-power designs.
In addition to the high-gain antenna, there are two low-gain antennas and a medium-gain dish. The high-gain dish has a Cassegrain layout, composite construction, and a 2.1 meter diameter (providing well over 40 dB of gain, and a half-power beam width of about a degree). The prime-focus, medium-gain antenna, with a 0.3 meter aperture and 10-degree half-power beamwidth, is mounted to the back of the high-gain antenna's secondary reflector. The forward low-gain antenna is stacked atop the feed of the medium-gain antenna. The aft low-gain antenna is mounted within the launch adapter at the rear of the spacecraft. This antenna was only used for early mission phases near Earth, just after launch and for emergencies if the spacecraft had lost attitude control.
To save mission costs, the spacecraft will be in "hibernation" between Jupiter and Pluto. It will awaken once per year, for 50 days, for equipment checkout and trajectory tracking. The rest of the time, the spacecraft will be in a slow spin, sending a beacon tone once per week. Depending on frequency, the beacon indicates normal operation, or one of seven fault modes. New Horizons is the first mission to use the DSN's beacon tone system operationally, the system having been flight-tested by the DS1 mission.
Data handling of New Horizons.
New Horizons will record scientific instrument data to its solid-state buffer at each encounter, then transmit the data to Earth. Data storage is done on two low-power solid-state recorders (one primary, one backup) holding up to 8 gigabytes (64 gigabits) each. Because of the extreme distance from Pluto and the Kuiper Belt, only one buffer load at those encounters can be saved. This is due to the fact that New Horizons will have exited the vicinity of Pluto (or future target object) by the time it takes to transmit the buffer load back to Earth.
Part of the reason that there will be a delay between the gathering and transmission of data is because all of the New Horizons instrumentation is body-mounted. In order for the cameras to record data, the entire probe must turn, and the high-gain antenna may not be pointing toward Earth. Previous spacecraft, such as the Voyager program probes, had a rotatable instrumentation platform that could take measurements from virtually any angle without losing radio contact with Earth. New Horizons' elimination of excess mechanisms was implemented to save weight, schedule, and to achieve a 15+ year lifetime.
(The Voyager 2 spacecraft experienced platform jamming at Saturn; the demands of long time exposures at Uranus led to modifications of the probe to rotate the entire probe instead to achieve the time exposure photos at Uranus and Neptune, similar to how New Horizons will rotate.)
Flight computer on New Horizons.
The spacecraft carries two computer systems, the Command and Data Handling system and the Guidance and Control processor. Each of the two systems is duplicated for redundancy, making for a total of four computers. The processor used is the Mongoose-V, a 12 MHz radiation-hardened version of the MIPS R3000 CPU. Multiple clocks and timing routines are implemented in hardware and software to help prevent faults and downtime.
To conserve heat and mass, spacecraft and instrument electronics are housed together in IEMs (Integrated Electronics Modules). There are two redundant IEMs. Including other functions such as instrument and radio electronics, each IEM contains 9 boards.
Mission Science of New Horizons: Instrument suite.
The spacecraft carries seven scientific instruments. Total mass is 31 kg; rated power is 21 watts (though not all instruments operate simultaneously).
Science Objectives and Observation Plan of New Horizons: Jupiter Observations.
The flyby will come within about 32 Jovian radii (3 Gm) of Jupiter and will be the center of a 4-month intensive observation campaign. Jupiter is an interesting, ever-changing target, observed intermittently since the end of the Galileo mission. New Horizons also has instruments built using the latest technology, especially in the area of cameras. They are much improved over Galileo's cameras, which were evolved versions of Voyager cameras which, in turn, were evolved Mariner cameras. The Jupiter encounter will also serve as a shakedown and dress rehearsal. Because of the much shorter distance from Jupiter to Earth, the communications link can transmit multiple loadings of the memory buffer. The mission will actually return more data from Jupiter than Pluto. Imaging of Jupiter began on September 4, 2006.
Primary encounter goals will include Jovian cloud dynamics, which were greatly reduced from the Galileo observation program, and particle readings from the magnetotail of the Jovian magnetosphere. The spacecraft trajectory coincidentally flies down the magnetotail for months. New Horizons will also examine the Jovian nightside for aurorae and lightning.
New Horizons: Jovian moons.
The major (Galilean) moons will be in poor position. The aim point of the gravity-assist maneuver means the spacecraft will pass millions of kilometers from any of the Galilean moons. Still, the New Horizons instruments were intended for small, dim targets, so they will be scientifically useful on large, distant moons. LORRI will search for volcanoes and plumes on Io. The infrared capabilities of LEISA will search for chemical compositions (including Europa ice dopants), and nightside temperatures (including hotspots on Io). The ultraviolet resolution of Alice will search for aurorae and atmospheres, including the Io torus.
Minor moons such as Amalthea will have their orbit solutions refined. The cameras will determine their position, acting as 'reverse optical navigation.'
Pluto Flyby of New Horizons.
Observations of Pluto, with LORRI plus Ralph, will begin about 6 months prior to closest approach. The targets will be only a few pixels across. This should detect any rings or any additional moons (eventually down to 2 kilometers diameter), for avoidance and targeting maneuvers, and observation scheduling. 70 days out, resolution will exceed the Hubble Space Telescope's resolution, lasting another two weeks after the flyby. Long-range imaging will include 40 km (25 mi) mapping of Pluto and Charon 3.2 days out. This is half the rotation period of Pluto-Charon and will allow imaging of the side of both bodies that will be facing away from the spacecraft at closest approach. Coverage will repeat twice per day, to search for changes due to snows or cryovolcanism. Still, due to Pluto's tilt and rotation, a portion of the north pole will be in shadow at all times. At some point REX will perform radiometry of the dayside, from which temperatures will be derived.
During the flyby, LORRI should be able to obtain select images with resolution as high as 50 m/px (if closest distance is around 10,000 km), and MVIC should obtain 4-color global dayside maps at 1.6 km resolution. LORRI and MVIC will attempt to overlap their respective coverage areas to form stereo pairs. LEISA will obtain hyperspectral near-infrared maps at 7 km/px globally and 0.6 km/pixel for selected areas. Meanwhile, Alice will characterize the atmosphere, both by emissions of atmospheric molecules (airglow), and by dimming of background stars as they pass behind Pluto (occultation).
During and after closest approach, SWAP and PEPSSI will sample the high atmosphere and its effects on the solar wind. VBSDC will search for dust, inferring meteoroid collision rates and any invisible rings. REX will perform active and passive radio science. Ground stations on Earth will transmit a powerful radio signal as New Horizons passes behind Pluto's disk, then emerges on the other side. The communications dish will measure the disappearance and reappearance of the signal. The results will resolve Pluto's diameter (by their timing) and atmospheric density and composition (by their weakening and strengthening pattern). (Alice can perform similar occultations, using sunlight instead of radio beacons.) Previous missions had the spacecraft transmit through the atmosphere, to Earth ("downlink"). Low power and extreme distance means New Horizons will be the first such "uplink" mission. Pluto's mass and mass distribution will be evaluated by their tug on the spacecraft. As the spacecraft speeds up and slows down, the radio signal will experience a Doppler shift. The Doppler shift will be measured by comparison with the ultrastable oscillator in the communications electronics.
Reflected sunlight from Charon will allow some imaging observations of the nightside. Backlighting by the Sun will highlight any rings or atmospheric hazes. At some point, REX will perform radiometry of the nightside.
Initial, highly-compressed images will be transmitted within days. The science team will select the best images for public release. Uncompressed images will take about nine months to transmit, depending on Deep Space Network traffic. It may turn out, however, that fewer months will be needed. The spacecraft link is proving stronger than expected, and it is possible that both downlink channels may be ganged together to boost performance even further.
Primary objectives (required).
Loss of any of these objectives will constitute a failure of the mission.
Secondary objectives (expected)
It is expected, but not demanded, that most of these objectives will be met.
Tertiary objectives (desired)
These objectives may be attempted, though they may be skipped in favor of the above objectives. An objective to measure any magnetic field of Pluto was dropped. A magnetometer instrument could not be implemented within a reasonable mass budget and schedule, and SWAP and PEPPSI could do an indirect job detecting some magnetic field around Pluto.
New Horizons: Asteroid Belt.
Because of the need to conserve fuel for possible encounters with Kuiper-belt objects subsequent to the Pluto fly-by, intentional encounters with objects in the asteroid belt were not planned. Subsequent to launch, the New Horizons team scanned the spacecraft's trajectory to determine if any asteroids would, by chance, be close enough for observation. In May 2006 it was discovered that New Horizons would pass close to the tiny asteroid 2002 JF56 on June 13, 2006. Closest approach occurred at 4:05 UTC at a distance of 101,867 kilometers. The asteroid was imaged by Ralph (use of LORRI at that time was not possible), which gave the team a chance to exercise Ralph's capabilities, and make observations of the asteroid's composition as well as light and phase curves. The asteroid's size was estimated to be 2.5 kilometers in diameter.
New Horizons: Neptune Trojans.
New Horizons' trajectory to Pluto passes near Neptune's trailing Lagrange point ("L5"). A number of "Trojan asteroids" have been discovered in these regions recently, although it is not yet known if New Horizons will pass close to any. If any asteroids are found to be close enough to be studied, observations will be planned. Unfortunately, the Lagrange point comes shortly before the Pluto encounter. Depending on where the asteroid is along the spacecraft trajectory, New Horizons may not have significant downlink bandwidth, and thus free memory, for Trojan data.
New Horizons: Kuiper-Belt objects.
New Horizons will fly past one or more Kuiper-belt objects after passing Pluto. Because the flight path is determined by the Pluto flyby, with only minimal hydrazine remaining, objects must be found along that path- a cone, extending from Pluto, of less than a degree's width, within 55 AU. Past 55 AU, the communications link becomes too weak, and the RTG wattage will have decayed too far to perform much science. Desirable KBOs will be well over 50 km in diameter, neutral in color (to compare with the reddish Pluto), and if possible, with a moon. Because the population of KBOs appears quite large, multiple objects may qualify. Large ground telescopes will find suitable objects up until the Pluto flyby; the Pluto aim point, plus some thruster firing, will then determine the subsequent trajectory. KBO flyby observations will be similar to those at Pluto, but reduced due to lower light, power, and bandwidth.
New Horizons: Hurricane Wilma.
The Lockheed Martin Atlas V rocket that was being prepared to carry New Horizons into space was slightly damaged when Hurricane Wilma swept across Florida on October 24, 2005. One of the solid rocket boosters was hit by a door. Julie Andrews, spokeswoman for the Lockheed Martin Corp., stated, "We're pretty confident this isn't going to be a reason to hold up the launch". The booster was replaced with an identical unit, versus inspecting and requalifying the original.
Cost of New Horizons.
The cost of the mission (including spacecraft and instrument development, launch vehicle, mission operations, data analysis, and education/public outreach) is approximately $650 million over 15 years (from 2001 to 2016).
Trivia about New Horizons.
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