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How the New Horizons Spacecraft Was Developed
Missions are notoriously difficult to get approved by NASA, but it is even harder for them to actually reach completion. Too many people want their mission to be selected and sadly not enough money can be spread around to meet everyone’s goals. But fortunately, despite decades of waiting and working, one man finally got a mission to go to one of the least understood objects in the solar system: Pluto.
When the Voyager probes were out investigating the gas giants on their Grand Tour, not much attention was given to Pluto. It was just an icy ball out on the edge of the solar system. In fact, Voyager 1 had the chance to go visit Pluto, but it would have meant giving up an opportunity to have a close fly-by of Titan. However, because Titan was close and Pluto far away it was deemed that the Titan fly-by was the better option. At the time, no one knew about Pluto’s other moons nor about the Kuiper Belt, so Titan was also considered the better science payout (Stern 3).
It is therefore ironic that Voyager 2 may have gotten the ball rolling on a mission to Pluto. When it flew by Triton, a moon of Neptune, in August of 1989 scientists were amazed that what should have been a cold and barren world showed signs of geological activity. Now Pluto could be just as interesting also despite its distance and relative lack of features (3).
Starting in 1989, a study into a potential Pluto mission commenced. Called Pluto-350, it was headed by the Discovery Program Science Working Group. It was to explore the Pluto - Charon system with a 350 kilogram probe that would have a camera, a UV spectrometer, some radio equipment, and also an instrument to study plasma. It would have been half the weight of the Voyager probes, but it never gained support because of the big risk for what was seen as little reward. The mission needed to cover a lot of ground and thus more would be required because of that (3).
Another study was that investigated was using a Cassini-class Mariner Mark II probe. Yes, this is the same type of probe that has gone on to a successful mission at Saturn. But this Mark II would have a second spacecraft attached to it where the Huygens probe would normally me. This secondary probe would detach and fly by Pluto. Even though this mission was considered by many to be cheaper, safer, and less risky than 350, a committee looked into both options and by early 1992 felt 350 was “the more pragmatic choice” (3, 4)
Pluto Fast Flyby
Dr. Alan Stern was one of those people who found Pluto to be enticing and was also a member of 350. He knew from what little knowledge existed on Pluto that it had an atmosphere but that was slowly being lost to space. This atmosphere appears and vanished for several reasons. It sublimates from the frozen material on the surface of the planet and is loosely held by the weak gravity. Only when Pluto is near the sun can it receive enough heat to have the gases escape. But as Pluto moves away from the sun it gets colder and thus will lose that atmosphere. It is for this reason that Stern felt Pluto was more a comet than a planet. He had no idea what was about to be found that would lead some credence to that idea (Guterl 53).
In 1992, David Jewitt and Jane Luu found 1992 QB1, the first object discovered beyond Neptune since Pluto and Charon. Essentially a small planet, it was one of the first Kuiper Belt objects found, extending more than 19 million miles beyond Pluto. Its existence had been postulated for years but now it was proven to be reality. Suddenly a dead area of space now was full of intrigue, and scientists wanted to learn more about it. Stern and his associates form the Pluto Underground in an effort to increase support and develop a base of actions (53-4).
Now that the Kuiper Belt region had been revealed, any mission that was to be sent out there needed to have the right tools. By late 1992, Stern joins a new plan for Pluto that was revealed: the Pluto Fast Flyby, or PFF. Considered an improvement over the Mark II Mission, it would have been a 35-50 kilogram with 7 kilograms of instruments and would have cost less than $500 million. Work on the 350 and Mark II was halted as the PFF gained momentum in the science community. Further plans called for Titan IV Centaur rockets to be used and a travel time of 7-8 years, a vast improvement of 12-15 years for the Mark II. Another benefit of the PFF would have been needing just a single gravity boost from Jupiter, as opposed to the several Earth and Venus boosts that 350 and Mark II would have required (Stern 4).
Of course, as it is with any mission, PFF had some problems. Though it had been designed to be light weight, it quickly grew to 140 kilograms. Also, the costs of the rockets would have been $800 million, which when you take the additional weight into account would have driven PFF to over a billion dollars. Finally, NASA lost the Mars Observer in 1993. This made plans for a deep space mission more complicated as confidence was lowered. NASA decided to look for some help from Europe and Russia. If a Russian Proton rocket were to be used, it would save about $400 million. In exchange, Russia would get to carry their Drop Zond probe which would fly by Pluto and then crash into it. But in 1995 Russia decides it wants us to pay for the launch, so we went to Germany for help but that too did not pan out. Despite these setbacks, PFF was not canceled but it wasn’t developed any further either (4).
As the 1990’s progressed, more objects were found in the Kuiper Belt and interest increased. The PFF team was asked to reevaluate the project and start anew. Now called the Pluto-Kuiper Express (PKE), it was to be a 175 kilogram craft with 9 kilograms of science instruments and a launch date between 2001 and 2006. Unfortunately, PKE was cancelled in 1996 due to cutbacks in NASA’s budget but in 1999 is ready to try again and requests that PKE’s instruments be ready to make by March 2000. Again, in September of 2000 PKE was cancelled after the team found the costs would exceed $1 billion. Stern, whose initial vision of two probes to cover both sides of Pluto was never considered, leaves the team despite Pluto Underground and public outcry for a mission to be done (Stern 5, Guterl 54).
New Horizons is Born
In 2001, NASA reopens the idea of a Pluto-Kuiper Belt mission and asks for ideas. Out of all the petitions for a mission, 5 make it as serious contenders. And by June of 2001 only 2 are left to claim the prize: The Pluto Outer Solar System Explorer (POSSE) and New Horizons. Stern is recruited for the New Horizons team which along with POSSE is given half a million dollars to further develop their concept with regards to engineering costs and a timetable. This game plan was due at the end of September. On November 29, 2001, NASA selects New Horizons as the finalist. Finally, Stern’s 12-year vision was about to get the green light (Stern 1, 5, 7; Guterl 55; Stern "NASA" 24).
However, setbacks still had to be overcome. Not enough money was available to get New Horizons to full development. Also, to make sure that the probe would have enough fuel to make it to Pluto and beyond it needed to use nuclear power. A special type of rocket would be needed to ensure that such a spacecraft could be sent into space safely. Also, the launch was pushed back from December of 2004 to January of 2006, causing a delay of arrival from mid-2012 to mid-2014. However, because of the hard work of the team they were able to create a budget, find an appropriate rocket, and use methods that would allow New Horizons to make it by mid-2015 (Stern 8).
Stern knew that when the probe arrived was critical and the sooner it reached Pluto the better. When he got the idea for the mission in 1989, Pluto was at perihelion (the point in its orbit when it is closest to the Sun) and as Pluto moves away, any atmosphere it happens to possess will freeze. New Horizons had to get there to see if anything was left to study. By ensuring that the launch was in January, Stern was able to find a way to use Jupiter’s gravity as a slingshot, increasing New Horizons velocity to 13 miles a second. If he missed that launch even by a month, it would have meant missing Jupiter and increasing the travel time (Guterl 54, Stern "NASA" 24).
Mission Objectives, Cargo, and Equipment
Now that New Horizons, the first of the New Frontier medium-class missions from NASA, was good-to-go it was time to create her. She is about 1054 pounds, is around the size of a piano, and was built by John Hopkins University Applied Physics Laboratory in Maryland (who were also responsible for NEAR-Shoemaker and MESSENGER). They will also operate the craft during its encounters while the Southwest Research Institute will be in charge of "mission management, payload development, and operating mission science planning, science data reductions, and analysis" (Stern "NASA" 24).
In 2003, in the Planetary Science Decadal Survey of the National Academy of Sciences, the Hopkins team announced their formal mission plan. The craft has three goals that went into its design and execution:
- Study Jupiter during the gravity assist
- Examine Pluto and Charon up close (mapping their surfaces, compositions, pressure, temperatures, and escape rate of atmosphere)
- Investigate other Kuiper-Belt Objects.
Now, that second target has sub-targets which are as follows:
1. Group 1 Targets
- Making composition maps of the surfaces
- Making geological maps of the surfaces
- Collecting data on the atmosphere
2. Group 2 Targets
- Search for atmosphere on Charon
- Make thermal maps of the dwarf planet
- Make stereo images of all objects
3. Group 3 Targets
- See if magnetic fields exist
- See if new moons are in the Pluto system
- Resolve mass/orbital data on the Pluto system
New Horizons will work through these targets in order, with the Group 1 data sent home first followed by Group 2 and then Group 3. At the rate of 1 data link per month, a total of 16 months is required for full transmission of the flyby data (Stern "How Will" 19).
To accomplish this, New Horizons made use of
ALICE: will look at atmosphere with resolution of 32,000 pixels
LORRI: a camera for pictures of what is being visited
RALPH: produces color maps based off temperature with resolution of 65,000 pixels
PEPSII: will look at atmosphere molecules
SWAP: examines solar winds and their interaction with Pluto
REX: looks at radio waves and their interaction with Pluto
Student Dust Counter: will measure how tiny particles impact New Horizons
As mentioned earlier, New Horizons needed its own power source because only 1/1000 the solar energy we have gets to Pluto. Thus, a radioisotope thermoelectric generator (left over from the Galileo and Cassini programs) running on 78 Plutonium-238 allows New Horizons to run on 200 watts. When all 7 instruments are weighed together, it is less than the camera on Cassini and use only 30 Watts. These scientists did their homework (Stern 2, Guterl 55, Fountain 1, Dunbar “NASA," Stern "NASA" 24-5).
New Horizons also carried with it 78 kilograms of traditional fuel for course corrections and accelerations. And since Pluto was the 9th planet at the time of its launch, New Horizons also carries with it 9 small items: 2 U.S. flags, a Maryland and Florida state quarter, a piece of SpaceShipOne, a CD containing 100,000 names, a 1990 stamp with the caption “Pluto: Not Yet Explored,” a separate CD with pictures of New Horizons and the people involved, and finally a small container of Clyde Tombaugh’s ashes. He of course was the discoverer of Pluto in 1930 (Stern 10).
Dunbar, Brian. "NASA's Pluto Mission Launched Toward New Horizons." NASA. NASA, 19 Jan. 2006. Web. 07 Aug. 2014.
Fountain, Glen H., David Y. Kusnierkiewicz, Christopher B. Hersman, Timothy S. Herder, Coughlin, Thomas B., William T. Gibson, Deborah A. Clancy, Christopher C. DeBoy, T. Adrian Hill, James D. Kinnison, Douglas S. Mehoke, Geffrey K. Ottman, Gabe D. Rogers, S. Alan Stern, James M. Stratton, Steven R. Vernon, Stephen P. Williams. “The New Horizons Spacecraft.” arXiv:astro-phys/07094288.
Guterl, Fred. “Journey to the Outer Limits.” Discover: March 2006: 53-5. Print.
Stern, Alan. "How WIll the New Horizons Team Gather Data From the Pluto Flyby?" Astronomy Aug. 2015: 19. Print.
---. "NASA Sets Its Sights on Pluto." Astronomy: Feb. 2015: 24-5. Print.
---. "The New Horizons Pluto Kuiper Belt Mission: An Overview with Historical Context." Space Science Reviews 140.1-4 (2008): 3-21. Web. 07 Aug 2014.
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© 2014 Leonard Kelley